optimization of freevalve´s fully variable valve control
TRANSCRIPT
Optimization of FreeValve´s fully variable valve
control system for a four-cylinder engine
Robin Hamberg
Master of Science Thesis
Stockholm, Sweden 2017
Optimization of FreeValve´s fully variable valve
control system for a four-cylinder engine
Robin Hamberg
Master of Science Thesis MMK 2017:36 MFM 168
KTH Industrial Engineering and Management
Machine Design
SE-100 44 STOCKHOLM
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Examensarbete MMK 2017:36 MFM 168
Optimering av FreeValves fullt variabla
ventilstyrningssystem för en fyrcylindrig motor
Robin Hamberg
Godkänt
2017-05-16
Examinator
Anders Hultqvist
Handledare
Andreas Cronhjort
Uppdragsgivare
FreeValve AB
Kontaktperson
Urban Carlson
Sammanfattning
Bilindustrins avgaskrav är striktare än någonsin och tillverkare spenderar allt större resurser på
att sänka bränsleförbrukning och avgasutsläpp från sina bilar. Något de flesta inte provar är att
ändra en av grundprinciperna i förbränningsmotorn. Kamaxlar används för att styra ventilerna
i gasväxlingsprocessen och har trots många variationer sett mer eller mindre likadana ut det
senaste århundradet. Den största nackdelen med kamaxeln är att den optimala
gasväxlingsprocessen varierar med motorvarvtal och last, men det gör inte kamaxeln. Variabel
ventilstyrning som många tillverkare använder sig av minskar problemen men för att få ut mesta
möjliga prestanda krävs en fullt variabel ventilstyrning. FreeValve AB är ett litet svenskt företag
som utvecklar ett sådant system som använder en Pneumatisk Hydraulisk Elektrisk Aktuator
för att styra varje ventil.
Syftet med examensarbetet var att designa om FreeValves elektriska ventilstyrsystem för att
passa nya krav på att styra en fyrcylindrig motor i en bil. Designprocessen av kretslösningarna
presenteras tillsammans med en litteraturstudie som identifierar designaspekter till en
kommande prototyp av ventilstyrsystemet som ska användas i ett motorrums krävande miljö.
En kravspecifikation sammanställdes och det verifierades att delarna av systemet som rymdes
i projektets omfång var designade och fungerande enligt ställda krav och enligt
litteraturstudiens förslag, med huvudsyfte att styra aktuatorerna med lämplig strömprofil.
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Master of Science Thesis MMK 2017:36 MFM 168
Optimization of FreeValve´s fully variable valve
control system for a four-cylinder engine
Robin Hamberg
Approved
2017-05-16
Examiner
Anders Hultqvist
Supervisor
Andreas Cronhjort
Commissioner
FreeValve AB
Contact person
Urban Carlson
Abstract
Automotive exhaust legislation is stricter than ever and manufacturers are spending increasing
amounts of resources on reducing fuel consumption and emissions from their vehicles. What
most do not try is to change one of the most fundamental concepts of the internal combustion
engine. The camshaft is used to control the poppet valves in the gas exchange process and has,
despite many variations, stayed more or less the same the last century. The largest disadvantage
with the camshaft is that the optimum gas exchange process is dynamic with engine speed and
load, where the camshaft is not. Variable valve timing as many manufacturers explored reduces
the problem but in order to get the real advantages a fully variable valve timing system is
needed. FreeValve AB is a small Swedish company that develop such system which is based on
a Pneumatic Hydraulic Electric Actuator to operate each valve.
The aim of this Master’s thesis was to re-design the FreeValve electric valve control system to
suit new and updated requirements of running a four-cylinder engine in a car. The circuit design
process of the system is presented along with a literature study to identify design considerations
for a future valve control system prototype to operate in the demanding environment of an
engine compartment. A requirement specification was established and it was verified that the
parts of the system within the scope of the project were successfully designed according to the
literature review and specification, with the main task to deliver the correct current profile to
the valve actuators.
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FOREWORD
I would like to thank the following persons for making this thesis project possible:
My supervisor Urban Carlson for giving me the opportunity to perform an interesting thesis
project on a hot topic at FreeValve AB and providing help and advice when needed.
Lars Ivarsson for giving me guidance, ideas and advise in all technical aspects.
My academic supervisors Andreas Cronhjort and Anders Christiansen Erlandsson for help with
all administrative practicalities and for keeping the project on track.
My friends and fellow MSc students Goutham and Paul for providing feedback during planning
and closure of the thesis to improve the work.
At last thank you to all the others that contributed in different ways, you know who you are.
Robin Hamberg
Solna, September 2016
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NOMENCLATURE
Abbreviations
A-D Conversion Analog-Digital Conversion
BGA Ball Grid Array
BOM Bill Of Materials
CAN Controller Area Network
CTE Coefficient of Thermal Expansion
DEP Divided Exhaust Port
DTM Dynamic Thermal Management
DVFS Dynamic Voltage and Frequency Scaling
ECU Engine Control Unit
EMC Electromagnetic Compatibility
EMI Electromagnetic Interference
ESD Electro Static Discharge
FEM Finite Element Methods
FVVT Fully Variable Valve Train
ICE Internal Combustion Engine
IGBT Insulated-Gate Bipolar Transistor
IMS Insulated Metallic Substrates
MOSFET Metal Oxide Semiconductor Field Effect Transistor
NEDC New European Driving Cycle
PCB Printed Circuit Board
PHEA Pneumatic Hydraulic Electric Actuator
PQFP Plastic Quad Flat Pack
PTH Plated Through Hole
VCS Valve Control System
WLTC Worldwide harmonized Light duty driving Test Cycle
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TABLE OF CONTENTS
Sammanfattning ..................................................................................................................... 3
Abstract .................................................................................................................................. 5
FOREWORD ................................................................................................................................. 7
NOMENCLATURE ........................................................................................................................ 9
TABLE OF CONTENTS ................................................................................................................ 11
1 INTRODUCTION ..................................................................................................................... 13
1.1 Background ..................................................................................................................... 13
1.2 Purpose ........................................................................................................................... 13
1.3 Delimitations .................................................................................................................. 14
1.4 Method ........................................................................................................................... 14
2 FRAME OF REFERENCE .......................................................................................................... 15
2.1 FreeValve´s PHEA ............................................................................................................ 15
2.2 Electronics integration in cylinder head ......................................................................... 18
2.2.1 Elevated temperatures ............................................................................................ 18
2.2.2 Thermal cycling ........................................................................................................ 19
2.2.3 Vibrations ................................................................................................................ 20
2.2.4 Sealing ..................................................................................................................... 21
2.2.5 Lubrication oil .......................................................................................................... 21
2.2.6 Surface treatment ................................................................................................... 21
2.2.7 EMC design .............................................................................................................. 22
2.2.8 Expected lifetime ..................................................................................................... 23
2.3 Previous valve control system ........................................................................................ 23
2.4 Valve timing concepts ..................................................................................................... 24
3 IMPLEMENTATION ................................................................................................................. 25
3.1 Requirement specification ............................................................................................. 25
3.2 Prototype design ............................................................................................................ 26
3.2.1 Boost voltage controller .......................................................................................... 26
3.2.2 Actuator controller .................................................................................................. 29
3.2.3 Diagnostics .............................................................................................................. 32
3.2.4 Power input protection ........................................................................................... 32
3.2.5 Fuel injectors and ignition coils ............................................................................... 33
3.2.6 Microcontroller ........................................................................................................ 34
3.2.7 New microcontroller................................................................................................ 34
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4 RESULTS ................................................................................................................................. 35
4.1 Literature study .............................................................................................................. 35
4.2 Prototype ........................................................................................................................ 36
4.2.1 Boost power supply ................................................................................................. 37
4.3 Validation ........................................................................................................................ 38
5 DISCUSSION ........................................................................................................................... 43
5.1 Valve control system ....................................................................................................... 43
5.2 Boost supply ................................................................................................................... 43
5.3 Ethics .............................................................................................................................. 44
5.4 Scope of thesis ................................................................................................................ 44
6 Conclusions ............................................................................................................................ 45
7 FUTURE WORK ....................................................................................................................... 47
8 REFERENCES .......................................................................................................................... 49
List of references .............................................................................................................. 49
List of data sheets and application notes ......................................................................... 50
APPENDIX: SUPPLEMENTARY INFORMATION........................................................................... 53
Appendix A ........................................................................................................................... 53
.............................................................................................................................................. 56
.............................................................................................................................................. 57
.............................................................................................................................................. 58
Appendix B ........................................................................................................................... 61
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1 INTRODUCTION
This chapter will describe the background and motivation of the project. The purpose of the
project will be presented along with the method that was followed and the delimitations.
1.1 Background
One of the largest challenges for the automotive industry is to meet current and future exhaust
legislation. The transportation sector accounts for a large part of the global greenhouse gas
emissions and of which a major part is from the internal combustion engines. Even though
electric propulsion is growing fast among passenger transportation the energy density of the
liquid fuels, short refueling time and well established infrastructure for an ICE (Internal
Combustion Engine) is still far ahead of alternative technologies. The development of the ICE
has made small progress the last century and is still relying on old principles with different
modern variations and add-ons. The ICE is basically an air pump and by adding fuel with an
often stoichiometric mixing ratio, power can be extracted. The important gas exchange process
is controlled by the camshafts and poppet valves inside the engine. A well designed camshaft
together with efficient flow paths for the air is necessary for good overall engine efficiency. A
major drawback with the camshaft is that there is no one design that fulfills all needs (Trajkovic,
2010). The optimum cam profile differs with intended use, engine load and engine speed. There
are several systems to alter the cam profile and timing, for example BMWs Vanos or Hondas
V-TEC, but there is still the dependence on the camshaft and full flexibility is not possible. One
solution to get full flexibility is to remove the camshaft and actuate all the valves individually.
FreeValve is a small Swedish company that is developing a valve control system (VCS) for
valve actuation in internal combustion engines without the use of a traditional camshaft. Each
valve is controlled by an PHEA (Pneumatic Hydraulic Electric Actuator) and the valve actuators
are housed in two rails in the cylinder head, where the camshafts normally sits. As a sister
company to Koenigsegg the development at FreeValve has progressed for more than a decade
to change one of the most basic principles of combustion engines. The FreeValve technology
offers a Fully Variable Valve Train actuation (FVVT) which opens new possibilities for higher
fuel efficiency, higher power and lower emissions.
1.2 Purpose
The aim of this thesis is to convert the electrical part of an existing valve control system (VCS)
from modular laboratory use to a prototype to use in a car on road. The current VCS is a
development friendly modular system and has been tested thoroughly, with the next step being
to adapt it for use on a four-cylinder engine in a car. The VCS is to be optimized to control 8
valve actuators, read 8 valve position sensors and control 4 coils, either fuel injectors or ignition
coils. The VCS should handle up to 10 000 rpm engine speed. The deliverable of this thesis is
a circuit design of the VCS that connects between the engine ECU (Engine Control Unit) and
the actuator rail.
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The possibility to integrate the VCS circuits in the cylinder head will be investigated in a
literature review and the prototype VCS circuits should be adapted for this already now to as
large extent as possible.
1.3 Delimitations
The deliverable in this thesis is based on an existing system, which means the solutions will not
be developed from scratch. The system will within the time frame be re-designed to support
operation in a car, but will not be put into series production. The system will be fully designed
except for physical PCB (Printed Circuit Board) design and manufacturing.
The implementation of the VCS electronics inside the actuator rails will be investigated in a
literature review. No such prototype will be built but design considerations obtained during the
literature review will be used in the development of the deliverable where applicable to shorten
the lead time in future rail integration.
1.4 Method
The thesis will follow a common product development methodology starting with establishing
a requirements specification of what requirements the deliverable must satisfy. Quantitative
requirements will be given an interval that prototype validation measurements should operate
within. A literature review of related work will be conducted to identify design considerations
as well as the current state of the art within the company and in the industry. Later the existing
circuits will be broken down into suitable size parts prior to the re-design phase. The completed
parts will be put together and form the hardware for the prototype. At last the prototype will be
validated against the product requirements.
Following these steps ensure that the prototype is designed with the latest technology and
knowledge in the field.
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2 FRAME OF REFERENCE
In this chapter, the state of the art within the company and in the industry, will be presented as
a foundation to the system design.
2.1 FreeValve´s PHEA
The FreeValve system consists of a number of valve actuators as depicted on the cover page
which are mounted on a rail, one actuator for each valve as seen in Figure 1.
The abbreviation PHEA stands for Pneumatic Hydraulic Electric Actuator. Pneumatic which is
the acting force when a valve is actuated. Hydraulics act as a dampener to the pneumatic force
and to lock the actuator in open position. Electrics control the pneumatics and hydraulics and
do also monitor the movement of the valve. The symbiosis of those three techniques results in
a system that is reliable, fast, quiet, compact, light and reasonably cheap. All of which necessary
in a production car.
A typical peak efficiency for a conventional gasoline engine is 37,6%. However, since the
engine is not optimized to run on part load, when it’s rather throttled to lower power output the
efficiency drops to about 20% on part load (FreeValve 1, 2016). The PHEA enable the engine
to be optimized for different loads and to run closer to peak efficiency for a larger part of the
driving cycle. This can be done in a number of ways, among others by removing the throttle for
higher volumetric efficiency, deactivate cylinders to reduce part load losses, deactivate valves
to alter the charge flow in the cylinder, and utilize different residual gas scavenging techniques
to prevent knock and reduce exhaust emissions. An over expanded combustion cycle called the
Miller cycle, with longer expansion than compression stroke, can be utilized to decrease the
engine power density and thermal efficiency in order to reduce the pumping losses. A trade off
which can increase the overall efficiency and reduce fuel consumption at low load conditions
Figure 1: FreeValve rail with actuators and valves (www.FreeValve.com)
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(Wan and Du, 2013). With a fully variable valve train (FVVT) it is easy to alter the effective
compression ratio, hence the engine can be built with a higher compression ratio, admitting a
higher peak efficiency (Trajkovic, 2010).
The power consumption of the PHEA is roughly 2% of the engine power output and around
10% lower than a conventional valve train during normal driving (FreeValve 2, 2016). During
higher engine speeds, the PHEA will experience higher losses than a conventional system, but
the average driving cycle on lower average engine speed will still benefit from the FreeValve
system. An estimation on an engine currently in development is an improvement in part load
efficiency by around 5% and a fuel consumption reduction by 12-17% compared to an
equivalent cam shaft engine (FreeValve 3,2016).
The FreeValve system offer the valve lift profiles in Figure 2, where normal camshafts engines
are stuck with the regular cam lift profile with heavily rounded corners as depicted in Figure 3,
with some variation. The FreeValve lift profiles offer the possibility to change height and
change width from cycle to cycle which allow great responsiveness and high engine
performance for any operating condition.
Figure 2: FreeValve valve lift profile
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The larger area under the FreeValve profile compared to a regular cam profile means that more
air-fuel mixture will pass with each valve opening. The benefits of this combined with throttle
less operation and other improvements possible to implement is shown in Figure 4.
Another benefit of the individual valve actuation compared to a camshaft engine is higher fault
tolerance, despite the higher complexity. The FreeValve engine can operate when one or a few
valves are defective, with reduced output power but without damaging the engine. Up to 75%
of the actuators can fail before the engine can no longer provide limp home operation, but with
an otherwise undamaged engine. This is when a broken timing belt normally has catastrophic
consequences in damaged parts and large costs.
Figure 4: Engine torque improvement example with FreeValve system.
Figure 3: Camshaft generical valve lift profile
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2.2 Electronics integration in cylinder head
The current VCS is located in an external box in the engine compartment of the car and is
communicating with the engine ECU to control the actuators inside the rails in the cylinder
head. Four wires to each actuator implies that a lot of wires have to be routed from the 16
actuators through the engine compartment to the VCS. To reduce the wire harnessing and get
better communication with less disturbances it is favorable to move the VCS inside the actuator
rails. This will reduce wiring cost and complexity and will simplify assembly.
Housing electronics in the harsh environment inside the engine compartment that should
comply with requirements on longevity and reliability is a difficult task, and to integrate
electronics inside the engine itself pose an even bigger task. Higher levels of temperatures and
vibration, exposure to oil and high pressure are the downside of having a system this highly
integrated.
This section will identify design considerations that apply to the future rail integration in
particular, but also to some extent for the prototype of this theses. To design according to these
considerations is important in order to meet the requirements for this prototype and to save
development time in future rail integration.
2.2.1 Elevated temperatures
The operating temperature of the electronics depend on the mounting location in the vehicle. A
possible temperature range according to (Wayne Johnson et al, 2004) is -40ºC to +175ºC for
electronics mounted on the engine, but can reach 200ºC depending on location and operating
point. Figure 5 show a FreeValve rail operating on an engine under load and 25ºC ambient
temperature. The rail is shielded from the glowing turbo and exhaust manifold to the left and
has a surface temperature close to 80ºC where the electronics would be located.
Figure 5: FreeValve rail in engine test.
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Even in this cold environment the headroom to the maximum temperature limit of the
electronics have shrunk significantly and the system will have to be carefully designed for
sufficient thermal management. Too high operating temperature reduces the operating life,
reliability and efficiency in an electronic system. Moreover, a power device operating at its
maximum rated temperature can sink zero power without violation of its temperature rating due
to the internal heating. This gives very small headroom for devices operating in the engine
compartment with temperatures close to their maximum rating. Higher power density and the
tendency to mount electronics on hotter locations require efficient thermal paths to maintain the
operating temperature within specified range. Adding a traditional heat sink on components to
reduce operating temperature is well proven but add a costly step in assembly (Lall et al, 2006).
One alternative is to use plated connection vias through the PCB to transport heat to other heat
conducting layers, for example thick copper layers. Worth noting is that only filled vias can be
used underneath components to prevent solder soaking and faulty solder joints. Heat can
effectively be dissipated in a PCB metal backing, called IMS (Insulated Metallic Substrates).
Metal backed PCBs provide excellent thermal dissipation and mechanical stability against
vibrations, but due to higher CTE (coefficient of thermal expansion) than traditional PCBs the
mechanical strain on components is higher and the solder joint reliability is lowered. A thermal
cycling experiment conducted by (Lall et al, 2006) showed a solder joint crack propagation rate
1,7 times higher for a BGA (Ball Grid Array) package mounted on a IMS board compared to a
standard board. Hence a tradeoff has to be made between thermal dissipation and reliability.
The impact of mechanical strain can be reduced using BGA underfill, but this adds cost and
steps in assembly.
The estimated power dissipation from the electrical components will have to be calculated and
suitable thermal paths will have to be designed. The system can either be cooled actively by the
pressurized air, oil and cooling fans, or cooled passively by a heat sink to ambient air. The active
cooling need a cooler for the cooling medium and a guarantee that the temperature will not rise
to unaccepted levels when the engine is stopped. For example, with a delayed stop of the active
cooling. A passive cooler will have to be properly located and be large enough to dissipate
enough heat in worst possible operating condition.
2.2.2 Thermal cycling
Any component mounted on an ICE will be subject to thermal cycling and thermal shocks.
Some of which spanning through the entire specified temperature range in a short time, during
a cold start in winter for example.
Different CTE for different components will cause strain in the joints when heat is applied (Li,
2004). In electronics, the solder joint between components and the PCB is subject to this strain
and hence fatigues during thermal cycling. By selecting components and PCB assemblies with
matching CTE the strain on joints are reduced, otherwise the stiffness in the solder joint must
be low enough to meet the lifetime requirements. Leaded components are less sensitive to
thermal cycling than leadless components due to the compliance in the gull wing leads (Li,
2004). Experiments also showed that the BGA ball fatigue performance differed with type of
packaging, PCB material and layout. (Li, 2004) showed that in a BGA package the inner rows
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solder joints are more prone to crack than the corner joints since the thermal stresses are
amplified by the rigid silicon die. The opposite was shown when (Lall et al, 2006) performed
thermal cycling on a IMS PCB and showed that the corner BGA solder balls experienced the
highest deformation. This concludes that several factors play a role in the solder joint fatigue
and it’s difficult to predict where the largest stresses are occurring. Thermal shock experiments
by (Pippola et al, 2014) showed that a common type of PCB failure was so called barrel crack
failures in plated through hole vias due to the difference in CTE of the PCB material FR-4 and
the PTH (Plated Through Hole). This can be limited by matching the PTH with the PCB
properties.
An electronic unit mounted on the engine is directly impacted by the engine temperature and
its variations with different driving conditions. For example, city driving will have intermittent
changes in air speed and engine load. Apart from ensuring high thermal conductivity to the
ambient to avoid overheating DTM (dynamic thermal management) can be applied to the
electronics (Park et al, 2011). DVFS (dynamic voltage and frequency scaling) is a popular
method to limit the power dissipation, where operating voltage and frequency of an integrated
circuit changes with operating condition to reduce power loss. The engine temperature
measurements by the ECU and the engines thermal capacity between the heat source and the
electronics can be used to estimate the temperature in the electronic unit to ensure maximum
performance without overheating, and still not using any extra temperature sensors.
2.2.3 Vibrations
Despite the use of different engine concepts and balance shafts the engine will still be a major
source of vibration, which everything mounted on it will have to endure. Vibrations will cause
the PCB to bend and cause component and solder joint fatigue.
Experiments by (Li, 2004) showed that for BGA packages there was no solder joint failures for
packages located close to the PCB mounting location. PQFP (plastic quad flat pack) packages
showed a 5-10 times longer fatigue life when mounted close to the PCB mounting location
opposed to the board center. The PQFP package broke off the leads close to the package corners
rather than crack the solder joint. Similarly, the highest ball stresses for the BGA package was
near the package corners. FEM (Finite Element Methods) analysis confirmed that the bending
of the PCB due to vibrations is the dominant cause of joint failure. This low cycle vibrations
with large amplitudes and plastic deformation on the solder joints should be limited. A stiffer
PCB with better clamping will instead yield high cycle vibrations with lower amplitudes where
the deformation in the joints remain elastic.
To prepare the electrical system for vibration several precautions can be made. Properly secure
and damp the PCB to avoid large deflection. Screws that might loosen can be secured with
thread lock, securing any loose wires, secure tall or heavy components to the PCB with adhesive
underfill or filling along edges. Alternatively, is potting a way to completely encapsulate the
components for high mechanical reliability (Parsa et al, 2013).
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2.2.4 Sealing
A proper sealing of the system will prevent any of the oil or the pressurized air to escape the
system or let any moisture or ambient matter in. A conductive EMI-sealing gasket
(Electromagnetic Interference) will help in reduce EMI escaping or intruding the system by
forming a continuously electrically conducting housing environment. If the system varies
between under- and over pressure in relation to ambient, air will try to pump through all the
seals with possible moisture ingression as a result. The sealing must be designed for the
necessary over pressure but also some under pressure inside the system. Any moisture inside
the system will condense after engine operation on all contacting surfaces. Sensitive surfaces
like electronics will need some sort of surface treatment to avoid damage and ensure good
reliability.
Connectors must be properly sealed to prevent any leakage and rated for the expected
temperature and vibration levels. No cables can be routed directly from the rail since
pressurized air can escape through them, between the strands and the insulation. The rail must
be sealed off with a connector.
2.2.5 Lubrication oil
The electronic unit will be exposed to lubrication oil which can cause complications. The oil
needs to be dielectric enough to not cause any short circuits in the electronics. At the same time,
it has to be conductive enough to not build up electrostatic charge. A phenomenon known as
tribocharging is known to occur in flowing oil when the contact between the oil and a solid
surface is sheared, generating free electrostatic charges (Harvey et al, 2002). The charge builds
up is influenced by the base oil, additives, age of oil and occurrence of moisture, contaminates
and oxidation among other things. An ESD (Electro Static Discharge) can seriously damage the
electronics or burn the lubrication oil, forming sludge. The conductivity should be higher than
400 pS/m to keep charge build up at a reasonable level (Ölchecker, 2012). The same source
state that charge build up can be reduced by using proper sized earthed oil piping, have moderate
flow speeds, avoid dissolved air and use low friction filter elements.
Lubrication oil might as well be corrosive or carry conductive debris like metal wear particles
to the electronics. Good filtering and PCB coating will prevent corrosion and short circuits.
2.2.6 Surface treatment
Surface treatment can be used to protect the electronics from the harsh environments inside the
actuator rail. Different kinds of polymer coatings or moldings can protect against particles,
corrosive oil, pollutants and humidity along with reducing thermal and mechanical stress
(Pippola et al, 2014). Such polymer moldings and coatings can be epoxy, polyurethane, silicone,
acryl or polyamide, all with different properties. When choosing suitable surface treatment
properties like CTE, elastic modulus, resistivity to chemicals, moisture absorption, adhesion
and thermal and electric conductivity should be considered. Some parameters reduce the
reliability of the systems and have to be carefully balanced to the benefits of the surface
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treatment. For instance (Pippola et al, 2014) identified several threats to reliability caused by
conformal coating and moulding material. Potential thermal shock failures included
delamination and cracked solder joints under polyurethane moulding caused by the rigidity and
different CTE of the moulding in relation to the PCB and component interconnections. Results
by (Goth et al, 2012) and (Pippola et al, 2014) showed that silicone based moulding material is
well suited for thermal cycling due to the low elastic modulus is not putting strain on component
interconnections. The silicone moulding did also decrease the heating rate of the PCB and
caused a more constant heat distribution in ambient temperature cycles. How this affects the
internally heated components is not discussed, but it can be assumed to change the heat
dissipation to air so the thermal conductivity of the moulding must be considered for sufficient
cooling.
One observation made by (Pippola et al, 2014) was that the conformal coating not only was
protecting the components, but in some cases penetrated into the component and put excess
strain on internal copper wires causing them to fail. A different risk with conformal coating is
potential ingression of water or other corrosives in case of a coating defect which will damage
the electronics (Goth et al, 2012). A more expensive conformal coating is parylene with
excellent dielectric, thermal, flexibility and penetration properties. But the application process
is complicated and not very suited for large volumes.
A good method to protect a circuit where serviceability is not of concern is potting
encapsulation where the PCB is embedded in potting material. This gives excellent protection
against mechanical shocks and vibrations. Depending on the thermal conductivity of the potting
material good thermal properties can be achieved which improves reliability in thermal cycling
(Goth et al, 2012). The distribution of heat in the potting material helps in reducing hotspots
and the impact of differences in CTE. By choosing a potting material resistant to oil all the
issues in the earlier oil section will be of no concern.
2.2.7 EMC design
The VCS will be enclosed inside the cylinder head which will act as an EMI shield if sealed
properly according to the sealing section. Hence the largest considerations for EMC
(Electromagnetic Compatibility) will be the internal radiated EMI between different parts of
the PCB and also the EMI transmitted though the cabling. To keep the sourcing of EMI low the
first step is a proper and robust design of the PCB and cabling. For example, by keeping current
paths and current return paths close to each other and to keep current return paths separated
between power and signals. Also use proper shielding on cables to reduce stray inductance
(Williams, 2007). The influence of radiated EMI can be reduced by separating sources and
victims of EMI on the PCB. For example, separate the sensitive current measuring circuits from
the boost voltage supply and other switching components.
An effective approach to reducing EMI is to electrically lower the noise transmitted by using
well designed conduction paths, filters close to switching components and decoupling
capacitors close to components that emit electrical noise.
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2.2.8 Expected lifetime
The expected lifetime of an electronic unit depends on the environment it will be subjected to.
Often a combination of the discussion in the sections above. Adding to that is the lifetime of
single components like capacitors expressed in hours or cycles and is dependent on operating
conditions. Power cycling models can be used to estimate the lifetime of an electronic system
(de Brito et al, 2015). The power cycling includes the Joule effects internal heating due to
internal resistance of the components and may give a more accurate estimation on lifetime, but
is difficult to model. Simulations of the PCB lifetime including solder joints and such can be
done with software, for example with Sherlock Automated Design Analysis™ provided by DfR
Solutions or with The Anand Viscoplasticity model in ANSYS. Component and PCB
specifications is used with profiles for the environment the system will operate in. Such profiles
include information of for example expected lifetime and operating temperatures depending on
on-time schedules (Hu and Garfinkel, 1998). One of such profile is the NEDC (New European
Driving Cycle) that is used in Europe to assess the fuel consumption and exhaust emission
certification. Despite the name the cycle is old and is due to slow transients and long idling
periods difficult for a consumer to mimic. A newer profile is the Worldwide harmonized Light
duty driving Test Cycle (WLTC) which better reflect an average driving cycle (Tutuianu et al,
2013). A guess from such a driving cycle, where speed profiles and average speeds are given,
is that the average engine speed is around 2500 rpm. The total number of lifetime cycles for
each component depends on the application, for example a capacitor in a switching circuit at
250 kHz will endure more cycles than a valve actuator at less than 100 Hz during a driving
cycle.
During its lifetime, the rail and VCS have to be possible to remove from the engine for
maintenance. The rail must be robust enough to not break during handling, including accidental
mechanical shocks. If the rail would break down it’s favorable to be able to disassemble it to
change the broken parts. If the PCB or an electrical component fails the safest thing is to replace
the entire PCB to preserve an intact surface treatment.
2.3 Previous valve control system
The previous VCS is a modular system with add on cards controlling 4 actuators each. New
add on cards can be added to extend the VCS capability up to 24 actuators, corresponding to a
six-cylinder engine. The system is easy to use with different engine configurations and is well
suited for measurements and development of the VCS. The system includes all functionality
necessary including actuator control, ECU communication through CAN (Controller Area
Network), programming port to a computer and diagnostics. Due to the number of add on ports
some of them are left unused when operating a four-cylinder engine. This leads to an
unnecessary bulky and costly system for further testing in an engine compartment of a car. The
add on cards and connectors also have a doubtful robustness since they are not designed to
operate in the harsh environments of the car.
24
2.4 Valve timing concepts
In order to design a Fully Variable Valve Timing system care has to be taken to not design any
unintended limitations in either hardware or software. Here follow some valve timing concepts
to keep in mind during the design process.
Regular four-stroke operation is the simplest operation in the sense that the timing and ignition
order of a regular camshaft can be duplicated. The only difference is the possibility of longer
valve opening due to the quick opening and closing time of the valve. This requires that the
valves can be operated in pairs. The next step is different timing for the two intake valves in
one cylinder to enable precise control of air charge mixing, tumble and swirl. Different exhaust
valve timings are also useful for DEP (Divided Exhaust Port) with several benefits among low
exhaust back pressure and quick catalyst warm up. This operation requires that all the valves
can be operated individually.
Running in two-stroke operation is possible to get a higher torque output. By operating one pair
of valves for each of two cylinders firing in parallel in an actuator rail the torque output can be
increased roughly by 20% in a gasoline engine and 50% in a diesel engine. Since the diesel
engine is not lambda regulated a higher torque is easier to achieve compared to the gasoline
engine. This two-stroke operation require that the VCS manage four valves at the time.
A simple way of increase the efficiency of the engine is to deactivate cylinders to increase the
loading of firing cylinders. Even though the engine is not throttled there is some room for
improvement in thermal efficiency. Cylinder deactivation is possible by simply shutting off the
valves to the cylinders which are to be deactivated. By deactivating the cylinders instead of
only shutting off the fuel no air is pumped through the engine, which ensures proper three-way
catalyst operation (Wilcutts et al, 2013). Instead of one or more designated cylinders to shut off
they can all be running eight-stroke, like a four-stroke engine with every second cycle
deactivated, or in any other similar way. This ensure that all cylinders keep operating
temperature and wear evenly. This operation is no different from regular four-stroke operation
in terms of hardware, just an omitted signal in software.
These concepts lay the foundation to endless variations of valve timings. Although not all valves
can be actuated at the same time most realistic timing concepts will be covered by actuating up
to half of the valves individually and simultaneously.
25
3 IMPLEMENTATION
The implementation describes the design of each part of the system in the following chapter.
3.1 Requirement specification
The valve control system should:
Priority 1
• Control 8 valve actuators
• Read 8 valve position sensors
• Control 4 auxiliary coils, either fuel injectors or ignition coils
• Allow 10 000 rpm engine speed
• Allow -40ºC to +125ºC operation temperature
• Allow 6V-30V battery voltage
• Lifespan of 10 000 hours at an average of 2500 rpm
• Allow full flexibility for valve opening
• Be robust enough to use in a car
• Be possible to diagnose
• Use CAN communication
Priority 2
• Be optimized for low cost
• Be optimized for small packaging dimensions
• Be optimized for low energy consumption
Priority 3
• Be prepared for cylinder head integration
26
3.2 Prototype design
This section will describe the different parts of the valve control system and how they were
developed. The parts are illustrated in Figure 6, with the flow of power to the left and signals
to the right.
3.2.1 Boost voltage controller
A boost voltage controller is a device that is used to amplify a DC voltage to a higher voltage.
A simplified schematic is shown in Figure 7. The basic operation is that the MOSFET (metal
oxide semiconductor field effect transistor) in the middle is closed to build up an
electromagnetic field in the inductor. When the MOSFET is opened the sudden change of
current through the inductor will produce a voltage spike that is harvested through the diode to
the load. The boost controller will operate the MOSFET to achieve desired output voltage.
Figure 6: Valve Control System overview
27
The maximum engine speed in a non-performance engine, around 6 000 rpm will allow enough
time for the actuator to open, but when running at 10 000 rpm all possible delays should be
reduced. To shorten the opening time of the actuator an elevated voltage of 50V is applied to
the actuator during opening. The boost voltage is supplied by a Texas Instruments LM5122
boost controller. It uses peak current mode control to regulate the output voltage to a level
programmed with a simple voltage divider. The LM5122 was chosen because it is a high
efficiency boost controller that allows a wide input voltage and automotive operating
temperature. It also required relatively few external components.
The output voltage is fully adjustable and the controller can be tuned for good stability and high
efficiency at light loads. The external components were calculated and chosen with help of the
LM5122 data sheet to ensure proper operation with good stability and not violating any pin or
controller limitations. The switching frequency was set to 250 kHz to have a good compromise
between the smaller component size of a high frequency and the efficiency of a low frequency.
The efficiency is of special concern at light load operation since the boost controller is designed
to keep up at maximum engine speed but will operate at lower load most of the time. Due to
switching and bias current losses at low load different strategies can be implemented to reduce
the losses. A diode emulation mode of the high side MOSFET is chosen together with pulse
skipping operation that skips pulses, or effectively pauses the boost controller during low load
operation.
The actuator boost current consumption and duration per actuator in the existing system were
measured and were later extrapolated to 5A at 410μs to accommodate headroom for a future
raise in current. The highest mean current is during four-stroke operation at 10 000 rpm. This
will set the continuous output current capability for the boost supply, according to equation 1
and with the result of equation 2.
𝑂𝑝𝑒𝑛𝑖𝑛𝑔𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛
𝑃𝑒𝑟𝑖𝑜𝑑𝑇𝑖𝑚𝑒×
𝑁𝑜𝑂𝑓𝐶𝑦𝑙𝑖𝑛𝑑𝑒𝑟𝑠
𝑅𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠𝑃𝑒𝑟𝑂𝑝𝑒𝑛𝑖𝑛𝑔×𝑁𝑜𝑂𝑓 𝐴𝑐𝑡𝑢𝑎𝑡𝑜𝑟𝑠 𝑐𝑦𝑙⁄ ×𝑐𝑢𝑟𝑟𝑒𝑛𝑡 = 𝐼 (1)
Figure 7: Simplified schematic of a boost converter
28
0,41𝑚𝑠
12𝑚𝑠×4
2×2×5𝐴 = 683𝑚𝐴 (2)
The highest momentary current is during two-stroke operation at 20A for 410μs, according to
equation 3.
𝑐𝑢𝑟𝑟𝑒𝑛𝑡×𝑁𝑜𝑂𝑓 𝐴𝑐𝑡𝑢𝑎𝑡𝑜𝑟𝑠 𝑐𝑦𝑙⁄ ×𝑁𝑜𝑂𝑓𝐶𝑦𝑙𝑖𝑛𝑑𝑒𝑟𝑠𝑃𝑒𝑟𝑃𝑢𝑙𝑠𝑒
= 5𝐴×2×2×2 = 20𝐴 (3)
The two-stroke operation is only used with lower engine speeds and will have a lower mean
current output than four-stroke operation. Hence the four-stroke operation sets the size of the
bulk output capacitors. The boost circuit was built on an experiment card, as seen in Figure 8,
to verify proper operation. After problems with instability caused by long signal paths and
insufficient grounding an evaluation PCB was instead modified with the new components,
Figure 9, with a satisfying result. The schematic for the boost circuit can be found in Appendix
B.
Figure 8: Boost controller circuit on experiment card
29
3.2.2 Actuator controller
Each valve actuator is driven by a current from the actuator controller. The controller is
responsible for sourcing the correct current level to every actuator with the correct timing. An
opening of a valve actuator is requested by the VCS microcontroller to the NXP Semiconductors
MC33816 solenoid controller. The controller receives a signal labeled Startx for each actuator
when to open and will keep it open for the duration of the signal. The profile of the current is
illustrated in Figure 10.
Figure 9: Boost controller circuit on a modified evaluation board
30
Figure 10 illustrates how the boost voltage is applied to the actuator solenoid during the peak
phase to quickly open the actuator with a high current. Later during the hold phase the battery
voltage is used to hold the actuator open with a lower current. The switching between voltages,
the current regulation and all the timing is governed by the actuator controller. The peak phase
time is dependent on the dynamic properties of the actuator with the same duration for all the
openings. The remaining hold phase time is varying with the duration of the Startx signal.
The MC33816 actuator controller is commonly used to control up to six solenoids, connected
in three pairs and has an integrated boost voltage supply. One of the pairs lack the boost voltage
functionality and neither of the solenoids in a pair can be used at the same time since they share
the same current sensing resistor. The current sensing resistor is used by the actuator controller
to source the correct current level to the actuator. In this case it will be necessary to operate all
actuators individually in order to run different valve timing concepts and use different timing
for the valves in one cylinder. The boost voltage will also be necessary for all actuators. To
fulfill these requirements the external MOSFET drivers used to switch the different voltages
were rearranged according to Figure 11 for each actuator to enable independent switching of all
actuators. The boost voltage supply is also built as a separate system to free one extra driver.
Figure 10: Typical actuator current profile. Source: NXP, Four Injector and Fuel Pump Drive, 2014
31
This enables four actuators to be individually controlled by each MC33816 controller chip,
hence two controllers are needed to run a complete actuator rail. Due to an excess of low side
MOSFET drivers, some of them were used with a small N-channel MOSFET to switch a P-
channel MOSFET to allow high side switching. As a result, no MOSFET driver was left unused.
To test the rearranged design an KIT33816AEEVM evaluation board was rebuilt and extended
with all the new connections and components to fulfill the requirements. The design is shown
in Figure 12 and the schematics can be found in Appendix A.
Figure 12: Actuator controller
Figure 11: Actuator voltage switching
32
The green card is the modified evaluation board with the actuator controller chip and the
remaining components. To the left is the cabling to the microcontroller and to the right is the
connectors to the actuators. The yellow experiment card contains all the components that did
not find room on the evaluation board, such as the boost voltage switches at the top and a few
extra components. After all components were fitted the assembly was tested to verify proper
operation.
3.2.3 Diagnostics
The diagnostics is based on connections of the source pin of the high side MOSFETs and the
drain pin of the low side MOSFETs to the microcontroller. With other words, the two
connections to the load. By measuring the upper and lower voltage and comparing them to the
boost or battery voltage and the ground respectively it can be concluded if each MOSFET is
switching as intended. If not, proper action must be taken, for example shut off the errant
actuator. A small current, too small to trigger the actuator, can be sourced through the load and
depending on the voltage in each measurement it can be concluded if the load is connected
properly without short or open circuits.
3.2.4 Power input protection
To protect the VCS from damage due to over voltage or reverse battery voltage a circuit based
on the Maxim Integrated MAX6496 over voltage limiter controller was implemented. This
device has an adjustable threshold for the input voltage over which it regulates the output
voltage like a simple buck controller to not exceed the threshold. This ensures safe system
functionality in the event of an over voltage transient, for example a load dump when the battery
is disconnected with the generator running. In the event of a reverse battery voltage the load
will be isolated to prevent damage. The input voltage range is expressed in Figure 13 by the
referenced application note by Littelfuse.
The input protection consists of few external parts and the voltage threshold is set by two
voltage divider resistors. The maximum current capacity is set by the two MOSFETs current
Figure 13: Input voltage range
33
capacity at maximum ambient temperature. The evaluation board with the MAX6496 is shown
in Figure 14.
The use of a MOSFET for reverse polarity protection instead of a regular diode admits a lower
voltage drop and better system efficiency. The speed and precision of the active over voltage
protection is superior any passive component.
3.2.5 Fuel injectors and ignition coils
In addition to the valve actuator drivers it would be convenient to house the drivers to the fuel
injectors and ignition coils in the VCS according to the requirement specification. Even though
each system will control either of fuel or ignition, the drivers to both has to be implemented in
order to have identical systems packaging for lower cost and fewer unique parts. The solenoid
in the fuel injector is similar to the solenoid in the valve actuator and is controlled with the same
peak and hold current control and uses the same diagnostics. Hence one actuator controller can
be used for the fuel injectors with minor changes in timing to account for the dynamic properties
of the fuel injector solenoid. This means there will be three MC33816 in the VCS including the
two for the valve actuators.
The ignition system control depends on what kind of ignition coils are used. Either with a built-
in driver or without. In the case of a built-in driver there has to be a small circuit interfacing the
driver with the microcontroller. The other case without built in driver is a bit more complicated
where an IGBT (insulated-gate bipolar transistor) with suitable voltage rating and sufficient
cooling is required for all ignition coils.
Figure 14: Power input protection
34
3.2.6 Microcontroller
The currently used microcontroller NXP MPC5644A communicates with the ECU via CAN
and controls the VCS according to the demands from the ECU. The position of the valve is
constantly monitored by the microcontroller through the valve position sensor. The reading of
the sensor is done digitally without A-D conversion which allows real time monitoring with an
accuracy of 0,1 mm. The processor communicates with the actuator controller via a pin to each
actuator that is pulled high when an actuator opening is requested and pulled low when the
actuator closing is requested. The processor manages the diagnostics for the actuators to detect
short circuits and open circuits and will send a flag to the ECU if any errors occur. The
microcontroller is also flashing the software to the actuator controller upon start up in order to
start the controller properly. The operation of the microcontroller and its peripherals in detail is
not within the scope of this thesis.
3.2.7 New microcontroller
During the project, a new microcontroller NXP MPC5746R was discovered that was similar to
the existing microcontroller but included most of the functionality of the actuator controller.
This results in that the actuator controller can be removed by adding some extra functionality
in the microcontroller, for example the diagnostics of the actuators. This will give a simpler
system without the actuator controller and the separate software associated. Instead the software
functions can be included in the microprocessor software. There will also be room to operate
the fuel injectors and ignition coils directly from the microcontroller. The benefits of using the
new microcontroller were so many that the remainder of the project focused on preparations for
a transition to the new processor. Since the scope of the thesis does not cover the microcontroller
this will instead be of high priority in the future work section.
35
4 RESULTS
In this section, the result of the literature study is presented along with the developed prototype
with the knowledge from the study implemented where applicable. The prototype is also
validated against the requirement specifications.
4.1 Literature study
Design of an electric system intended to operate in the harsh environment of an engine
compartment was as expected a non-trivial task. Luckily a lot of research has been done and
the industry has many solutions to the problems in this type of environment.
Even if all components used allow -40ºC to +125ºC there should be carefully designed heat
flow paths to keep the temperature rise from internal heating low to avoid violation of the
temperature limits. This will allow high engine compartment temperatures. Efficient heat flow
paths are essentially a low thermal resistance path, a combination of high thermal conductivity
and a large conduction area in every transition. Large copper planes, many copper plated vias
between planes, a PCB coating with low thermal resistance and external cooling are elements
to a low and evenly spread circuit temperature. The temperature will differ with different
driving conditions so low thermal resistance is important to reduce hotspots from a sudden
increase in load and power dissipation. When temperature is cycled, sufficient compliance is
needed in component joints to accommodate movement due to different CTE. Too stiff joints
will cause damage on joints or components.
To prevent damage from vibrations a stiff and properly fastened PCB is needed and that any
cabling or large component is properly secured to keep deflection amplitudes small. Large
deflections will shake loose components or crack joints. By mounting large components close
to PCB mounting locations and make use of moulding or potting will help reduce deflection of
the PCB. The system must be properly sealed with an electrically conductive casing in order to
keep moisture and contamination on the outside and to avoid EMC problems. Internal EMC is
already considered when designing the PCB but some shielding is useful in order to not interfere
with external sources or victims outside of the system causing any unwanted behavior. If the
system is properly designed to emit low levels of EMI and robust enough to not be affected by
other EMI sources the conducting layer may be omitted.
The lubrication oil must, from an electric perspective, be slightly electrically conductive. Not
too much to cause any shortcuts but slightly to not build up any electrostatic charge. A discharge
of such can potentially damage the electronic system causing very unpredictable errors that is
hard to diagnose. To protect the circuits from oil, corrosives and other pollutants surface coating
is widely used. Silicone based moulding material, conformal coating or potting encapsulation
would be well suited for the VCS with its flexibility and good thermal cycling properties. It is
easy to apply and also possible to remove in order to change components. If potting of the
system is used only EMC is of larger concern since the potting provides good mechanical and
thermal stability.
36
The lifetime of the system is equal to the lowest lifetime of either any of the components in the
system or the PCB assembly. The lifetime of components is often stated by the manufacturer
but the assembly should be simulated to ensure that sufficient lifetime can be expected. This
can be done with different simulation methods with different accuracy and level of detail. If the
system would fail preterm the diagnostics must be designed well enough to take early and
accurate actions to limit hazardous consequences. The system should also be possible to remove
for repair or replacement.
4.2 Prototype
The finished prototype is shown in Figure 15.
The parts of the VCS designed within the scope of the thesis is the two actuator controller cards
at the top of the picture that connect to the microcontroller to the left and to the valve actuators
to the right. Four test solenoids were used to verify proper operation of the system. To the
bottom left is the input power protection that supply power to the other parts and to the bottom
right is the boost voltage converter which supply boost voltage to the actuator controller.
The actuator controller is designed to control all the valves individually but in order to keep the
power consumption and stress on components limited the boost power supply is designed to
run a maximum of half the valve actuators simultaneously according to the reasoning in the
Figure 15: The Valve Control System with test actuators connected. microcontroller not shown
37
frame of reference. A software limit in the actuator controller to ensure this is suggested in
future work.
4.2.1 Boost power supply
The benefits of pulse skipping operation can be seen in Figure 16 where the efficiency increase
at low load compared to a typical regulator without it as exemplified in Figure 17.
Figure 16: LM5122 Boost voltage supply efficiency
Figure 17: Typical boost regulator efficiency
38
The output current is proportional to the engine speed and for the design case of an actuator
consuming 5A for 410μs the lowest efficiency of 78% correspond to 1500rpm and the
maximum efficiency is 89% at 940rpm and 5690rpm.
4.3 Validation
The boost power supply regulates the 50V boost voltage in a proper way throughout the input
voltage range as expected according to Figure 18.
Figure 18: Boost supply, 50V red output voltage graph, 6V-30V blue input voltage graph
39
The boost output voltage is properly regulated when the load is changed as seen in Figure 19
Figure 19: Boost supply, 50V blue output voltage graph, 0-0,8A red load current graph [0,2A/div]
During an experiment in room temperature at full load the temperature of the hottest
components on the experiment card is depicted in Figure 20.
The operation of the input voltage protection is seen in Figure 21. The output voltage in red
followed the input voltage in blue within the limits of 0V to 17V. The load got isolated when a
Figure 20: LM5122 Boost voltage supply temperature
40
reverse voltage was applied and an input voltage above the threshold was regulated down to the
threshold voltage.
The actuator controller is verified that the boost and battery voltage is properly switched to the
valve actuators to achieve the correct current profile as described by Figure 10. The actuators
are smoothly following different engine speeds according to signals from the microcontroller.
The current to the actuators is shown in Figure 22.
Figure 21: Input voltage protection, red output voltage, blue input voltage
41
The actuator current without the boost voltage supply connected is shown in Figure 23, for
reference. Notice the lower maximum current and the slower increase in current, in the
beginning, and decrease in current at the end.
Figure 22: Actuator current [100mA/div]
Figure 23: Actuator current without boost voltage applied [100mA/div]
42
Since this system is a prototype and not the final product for operation in a car the requirements
of robustness were not verified. The operating temperature requirement was used for design but
was not verified for practical reasons.
43
5 DISCUSSION
A discussion is presented below which mention the outcome of the thesis, its implementation
and potential hazards involved with the result.
5.1 Valve control system
The parts of the valve control system within the scope of the project were successfully designed.
As stated in the requirement specification the system is with an external microcontroller able to
control 8 valve actuators at a speed corresponding to an engine speed of 10 000 rpm. The
components in the system are chosen to withstand temperatures from -40ºC to +125ºC and a
battery voltage of 6V to 30V including high voltage transients that may occur in the automotive
environment. The design lifetime is at least 10 000h that applies to all components and the
ability to diagnose the system is implemented. The hardware circuits admit full flexibility to
open the valves for all useful operating cycles. The drivers to the auxiliary coils for fuel and
ignition are discussed but only the circuits to the fuel injectors are designed since the type of
ignition coils were not yet decided.
Since the deliverable is still a prototype that is not ready to be put in a car some design
considerations from the frame of reference do not apply yet. For example, considerations of
robustness, surface treatment and sealing. However, those are important to consider early in the
design process to reduce the risk of run into problems later on. Many design considerations do
apply to the prototype and special care has been taken that all components fitted are rated for
the temperatures they might be subject to. The lowest temperature range used is -40ºC to
+125ºC junction temperature. Extra care was shown to the electrolytic capacitors where long
useful life in high temperatures are rare.
5.2 Boost supply
Although the high and low side MOSFET switches are the hottest components in the
configuration of the experiment in Figure 10 the boost controller chip has the smallest headroom
to its maximum junction temperature. In this configuration, this roughly translates to a
maximum engine compartment temperature of 100ºC but a PCB design with more efficient
cooling will allow higher ambient temperatures.
This application puts high demands on the boost power supply with a maximum voltage
amplification of 8 times and a wide output current range. It is unfortunate that the lowest
efficiency, despite the pulse skipping strategy, is in the range of frequent operation but it is
necessary in order to cover the whole operating range. This is in perfect analogy with the cam
shaft issue the FreeValve system is aiming to solve.
44
5.3 Ethics
The required lifetime in this case is 10000 hours. If a system would fail, regardless of within or
beyond the expected lifetime the hazards of a failure must be assessed. For a VCS, there is a
potential risk of lethal consequences if the vehicle behaves unpredictably at high speed. Hence
any failure should be detected by the diagnostics, identified and take a fast and accurate action.
At the same time alert the driver. The main motivation to the FreeValve system is to reduce
emissions and improve performance in cars, but also the redundancy of many individual valve
actuators and the high fault tolerance it yields when simply switching off defective ones without
damaging the engine is possible. The positive long term environmental impact and reliability
will balance the potential risks.
5.4 Scope of thesis
During the planning phase of the thesis there were many uncertainties as to what parts would
need to be included in the system and how long the design of each part would take. The recent
and earlier achievements within the company were studied along with the direction of current
projects in order to formulate a requirement specification for the VCS which was up to date and
heading into the future in the right direction. Since the thesis was part of an ongoing project at
the company some flexibility in the project plan was needed in order to contribute in a
meaningful way. Early in the project it was realized that the scope of the thesis was too wide
for the time available and was narrowed down in discussion with the supervisors according to
the project plan. Since priority 2 and 3 in the requirement specification apply to all parts in the
system rather than being individual deliverables a few tasks were left out from priority 1. The
microcontroller and its peripherals such as ECU communication and valve position sensor
reading circuits were moved outside the scope of the thesis and are subjects for future work.
This also concluded that no final prototype would be built to operate in a car. Later during the
thesis when the new microcontroller was discovered the need for the actuator controller were
changed. The decision was made to finish the rebuilt design in preparation for a smooth
transition to the new microcontroller. No software was written for the old microcontroller,
which anyway would end up unused.
45
6 Conclusions
The parts of the FreeValve valve control system in the scope of this thesis has been designed to
operate under the conditions given in the requirement specifications with the main task to
deliver the correct current profile to the valve actuators. The profile shape and timing varies
with operating condition of the engine and the interspacing of profiles change with the engine
speed. The electrical circuits of the design are well functioning but from the literature study it
is empathized that the hardware design and protection from the automotive environment is of
huge importance for a reliable operation throughout the expected lifetime of the system.
Suggestions are made on design considerations to ensure reliable operation. Of special concern
is the thermal cycling which tend to strain components and solder joints. Efficient thermal paths
in the PCB and protective coating help reduce the problem. The importance of a mechanically
stable PCB and assembly to resist vibration and the internal and external issues of EMC are
also discussed.
46
47
7 FUTURE WORK
Since the scope of this thesis was narrowed down, the first task for future work is to finish the
design of the VCS and manufacture the hardware for installation in a car. The parts that remain
are to move the actuator controller circuits from the old solenoid controller to the new
microcontroller and design of the sensor reading circuits and ignition system interface. The
software has to be written to control all parts of the microcontroller including the valve
actuators, fuel injection and ignition, ECU communication, diagnostics and valve position
sensor reading.
When designing the software to the actuator controllers, care must be taken to not program the
actuation of more than half of the valve actuators simultaneously for any kind of operation.
Preferably a safety function would be implemented to avoid this from happening.
When the VCS is mounted in the car the exciting work begins to tune all engine parameters for
optimum performance, low fuel consumption, low emissions and a smooth and enjoyable
driving experience.
48
49
8 REFERENCES
List of references
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FreeValve AB, “Questions and Answers”, 2016,
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FreeValve AB, “FreeValve Technology”, 2016,
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Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in
Microelectronics and Microsystems, EuroSimE 2013, 2013, pp 1-6
T.J. Harvey, R.J.K. Wood, G. Denuault, H.E.G. Powrie, “Investigation of electrostatic charging
mechanisms in oil lubricated tribo-contacts”, Tribology International, vol 35, no 9, 2002, pp
605-614
50
Ölchecker, “Electrostatic discharges in hydraulic oils and lubricants”, Oelcheck, Spring 2012,
pp. 6-7, 2012
Christian Goth, Jörg Franke, Andreas Reinhardt, Philipp Widemann, “Reliability of Molded
Interconnect Devices (MID) Protected by Encapsulation Methods Overmolding, Potting and
Coating”, 2012 7th International Microsystems, Packaging, Assembly and Circuits Technology
Conference, 2012, pp 137-140
Tim Williams, “EMC for Product Designers”, Elsevier Ltd, ISBN: 978-0-7506-8170-4, chapter
13, pp. 341-374, 2007
Alirio Cavalcanti de Brito, Marcelo Lopes de Oliveira e Souza, “A Discussion on the Methods
of Thermal Cycling and Power Cycling for Reliability Prediction of Solder Joints of Electronic
Components”, SAE International, 2015
Jimmy M. Hu, George A. Garfinkel, “Correlation of Thermal Cycle Tests to Field Usage
Profiles for Solder Joints in Automotive Electronics”, SAE International, 1998
Monica Tutuianu, Alessandro Marotta, Heinz Steven, Eva Ericsson, Takahiro Haniu, Noriyuki
Ichikawa, Hajime Ishii, “Development of a World-wide Worldwide harmonized Light duty
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List of data sheets and application notes
Chipcon Products, “LC filter with improved high-frequency attenuation”, 2003
Diodes Incorporated, “BSS123Q-7 Datasheet”, 2016
EDN Network, “Controlling switch-node ringing in DC/DC converters”, 2016
Freescale Semiconductor, “KIT33816AEEVM Evaluation Board Datasheet”, 2014
Freescale Semiconductor, “MC33816 Datasheet”, 2015
Freescale Semiconductor, “MPC5644A Datasheeet”, 2014
Freescale Semiconductor, “MPC5644A Reference Manual”, 2012
Linear Technology, “PCB Layout Considerations for Non-Isolated Switching Power Supplies”,
2012
Loctite, “Materials for Automotive Electronic Applications”, 2014
51
Loctite Technomelt, “Printed Circuit Board Protection”, 2014
Maxim Integrated, “MAX6495–MAX6499 Datasheet”, 2015
Maxim Integrated, “MAX6496 Evaluation Kit Datasheet”, 2007
NXP Semiconductors, “BUK9230-100B Datasheet”, 2011
NXP, “Four Injector and Fuel Pump Drive”, 2014
ON Semiconductor, “ATP301-TL-H Datasheet”, 2013
Texas Instruments, “Designing Fault Protection Circuits Using Wide VIN LM5121”, 2015
Texas Instruments, “LM5122 Datasheet”, 2015
Texas Instruments, “LM5122EVM-1PH Evaluation Module Datasheet”, 2013
Texas Instruments, “Minimizing Ringing at the Switch Node of a Boost Converter”, 2006
Texas Instruments, “Basic Calculation of a Boost Converter's Power Stage”, 2014
Texas Instruments, “Ringing Reduction Techniques for NexFET High Performance MOSFETs”,
2011
52
53
APPENDIX: SUPPLEMENTARY INFORMATION
Appendix A
Actuator controller schematics
Figure 22: MC33816 Actuator controller with microprocessor connector
54
Actuator controller BOM
Reference designator Description Qty.
IC1 MC33816AE 1
C3, C5, C6, C7, C9 0,1uF 50V 5
C2 0,1uF 63V 1
C4 1uF 25V 1
C8 4,7uF 10V 1
C10 10uF 50V 1
C11 22uF 10V 1
C12 100uF 63V 1
55
Actuator driver schematics
Figure 23: Driver Actuator 1
56
Figure 24: Driver Actuator 2
57
Figure 25: Driver Actuator 3
58
Figure 26: Driver Actuator 4
59
Actuator drivers BOM
Reference designator Description Qty.
C2, C10 330pF 100V 6
C3, C6, C11 1000pF 100V 12
C4, C5 0,33uF 25V 5
C7, C8 4700pF 100V 8
C9 10nF 100V 4
C12 330pF 25V 4
R2 1,8 kΩ 0,1W 4
R3 4,7 kΩ 0,1W 4
R4, R5, R8 10 Ω 0,1W 12
R6 50 mΩ 1,5W Kelvin
connections 4
R7 4,7 Ω 0,1W 4
D2 15V 0,5W zener diode 4
D3 200V 10A Schottky diode 4
D4, D5 100V 2A Schottky diode 8
Q1 BSS123Q-7 4
Q2, Q4 BUK9230-100B 8
Q3 ATP301-TL-H 4
60
61
Appendix B
Boost voltage controller schematics
Figure 27: Boost voltage controller
62
Boost voltage controller BOM
Reference designator Abbreviation Description Qty.
IC2 Boost controller LM5122-Q1 1
C1 Ccs 100pF 5% 50V Ceramic 1
C2, C3, C4, C5 Cvinbulk 3,3uF 10% 50V Ceramic 4
C6 Cuvlo 100pF 5% 50V Ceramic 1
C7 Css 8,7uF 10% 35V Ceramic 1
C8 Cvin 0,47uF 10% 35V Ceramic 1
C9, C10, C11 Cout 220uF 20% 63V Low ESR 3
C12, C13, C14, C15 Coutx 10uF 20% 63V Ceramic 4
C16 Coutxx 1uF 10% 100V Ceramic
C17 Cho 470pF 5% 100V Ceramic 1
C18 Cbst 82nF 10% 35V Ceramic 1
C19 Cvcc 4,7uF 10% 16V Ceramic 1
C20 Cres 4uF 10% 35V Ceramic 1
C21 Chf 470pF 10% 50V Ceramic 1
63
C22 Ccomp 330nF 10% 50V Ceramic 1
R1, R2 Rcsfp, Rcsfn 100Ω 1% 0,1W 2
R3 Rvin 3,3Ω 5% 0,1W 1
R4 Ruv2 49,9kΩ 1% 0,1W 1
R5 Ruv1 15,8kΩ 1% 0,1W 1
R6 Rsense 4mΩ 1% 3W 1
R7 Rrt 36kΩ 1% 0,1W 1
R8 Rho 8,2Ω 5% 0,75W 1
R9 Rslope 172kΩ 1% 0,1W 1
R10 Rfb1 48,7kΩ 1% 0,125W 1
R11 Rfb2 1,2kΩ 1% 0,1W 1
R12 Rcomp 30,7kΩ 1% 0,1W 1
D1 Dbst 60V 1A Schottky diode 1
L1 Lin 39uH 9A 1