CAMLESS ENGINE
A SEMINAR REPORT
Submitted by
PIYUSH VYAS in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY
in
MECHANICAL ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
SIR PADAMPAT SINGHANIA UNIVERSITY, UDAIPUR APRIL 2013
Camless Engine
ACKNOWLEDGEMENT I would like to thank everyone who helped to see this seminar to completion. In particular, I would like to thank my seminar coordinators Mr. Kalyan Chakravarthi and Mr. Pawan
Gupta fo r t he i r mo ra l su pp or t an d guid guidan ance ce to comp comple lete te my semi semina narr on on time time.. I would like to take this opportunity to thank Mr. Naveen Kumar , H e a d o f t h e department Mechanical Engineering for his support and encouragement. I express my gratitude to all my friends and the classmates for their support and help on this seminar.
PIYUSH VYAS
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BONAFIDE CERTIFICATE Certified that this project report CAMLESS ENGINE is the bonafide work “
”
of PIYUSH VYAS who carried out the seminar work under my supervision.
(Prof. Naveen Kumar) HEAD
Mechanical Engineering Department Sir PadampatSinghania University Udaipur
(Prof. Kalyan Chakravarthi) SUPERVISOR
Assistant Professor Mechanical Engineering Department Sir PadampatSinghaniaUniversity Udaipur
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ABSTRACT The cam has been an integral part of the IC engine from its invention. The cam controls t he breathing channels of the IC engines, that is, the valves through which the fuel air mixture (in SI engines) or air (in CI engines) is supplied and exhaust driven out. Beside by demands for better fuel economy, more power, and less pollution, engineers around the world are pursuing a radical camless design that promises to deliver the internal-combustion engines biggest efficiency improvement in years. Camless engine technology is soon to be a reality for commercial vehicles. In the camless valve train, the valve motion is controlled directly by a valve actuator - there’s no camshaft or connecting mechanisms. Precise electronic circuit controls the operation of the mechanism, thus bringing in more flexibility and accuracy in opening and closing the valves. The seminar looks at the working of the electronically controlled camless engine with electromechanical valve actuator, its general features and benefits over conventional engine. Camless VVT allows an engine to experience maxi mum engine performance and fuel efficiency at each and every engine speed while following the same principles of the VTEC. Instead of using multiple cam profiles with synchronizing pins, camless VVT is electronically operated by a microcontroller which will control electro-mechanical rotary solenoid actuators. The objective of the seminar is to study about the working, literature review, and conceptual development a device that proved the concept of a CLE. More specifically, it is an electro/hydraulic device capable of producing engine valve displacement at typical automotive demands.
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TABLE OF CONTENTS Acknowledgement
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Abstract
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List of figures
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Definitions and Abbreviations
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1. Introduction 1.1 Pushrod Engine
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1.2 Crankshaft 1.3 Camshaft
3 4 4
2. Introduction to camshaft technology
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3. Working of camless engine 3.1 Camless valve train
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3.1.1 Electromechanical poppet valves 3.1.2 Electromechanical ball valves
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4. Design Consideration
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5. Advantages of Camless Engine
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6. Conclusion
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7. Reference:
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List of Figures Figure 1: Single Cam and Valve Figure 2:Conventional Valve Train Mechanism Figure 3:Typical view of traditional camshaft and valve Figure 4: Typical view of traditional camshaft and valve Figure 5: Basic Block Diagram Of Camless Engine Figure 6: Electromechanical Poppet Valves Closed Figure 7: Electromechanical Poppet Valves Open Figure 8: Electromechanical Poppet Valves Figure 9: Assembly Of Electromechanical Ball Valve Figure 10:Graph of stroke v/s degrees
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Definitions and Abbreviations The following definitions and abbreviations are often encountered in documents associated with internal combustion engines. Since their use is widely accepted, they will be used in this document. ICE – Internal Combustion Engine BDC – Bottom Dead Center TDC – Top Dead Center VCT – Variable Camshaft Timing VVT – Variable Valve Timing CLE – Camless Engine EGR – Exhaust Gas Recirculation ECV – Electrohydraulic Camless Valvetrain IMEP – Indicated Mean Effective Pressure
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CHAPTER1: INTRODUCTION Automobile manufacturers have recognized the compromises associated with engines that are governed by the rotation of a camshaft. This rotation, the speed of which is proportional to the engine speed, determines the timing of the engine valves. For this reason, automotive engineers must make a decision early in the design process that dictates the performance of the automobile. The engine will either have powerful performance or increased fuel economy, but with the existing technology it is difficult to achieve both simultaneously. In response to the needs of improved engines, some manufacturers have designed mechanical devices to achieve some variable valve timing. These devices are essentially camshafts with multiple cam lobes or engines with multiple camshafts. For example, the Honda VTEC uses three lobes, low, mid, and high to create a broader power band. This does represent an increased level of sophistication, but still limits the engine timing to a few discrete changes. The concept of variable valve timing has existed for some time. Unfortunately, the ability to achieve truly variable valve timing has eluded automotive manufacturers. Most variable timing mechanisms were created as tools for the automotive engineer. Their use was limited to the laboratory as a means of testing multiple, “virtual” cam profiles. These early Camless engines allowed for the designers to choose the best cams for the engine under scrutiny, but were less than energy efficient. Furthermore, they were one laboratory machines and were not capable of being mass produced or utilized in an automobile but with the change of the growing world the concept of VVT has taken a new shape as Camless engine and now it’s making its wings spread in this broad area of automobile. The basic requirement of tradition engine is pushrod, crankshaft and camshaft.
1.1PushRod Engine Pushrod engines have been installed in cars since the dawn of the horseless carriage. A pushrod is exactly what its name implies. It is a rod that goes from the camshaft to the top of the cylinder head which push open the valves for the passage of fuel air mixture and exhaust gases. Each cylinder of a pushrod engine has one arm (rocker arm) that operates the valves tobring the fuel air mixture and another arm to control the valve that lets exhaust gas escape after the engine fires. There are several valve train arrangements for a pushrod. 3
Camless Engine
1.2 Crankshaft Crankshaft is the engine component from which the power is taken. It receives the power from the connecting rods in the designated sequence for onward transmission to the clutch and subsequently to the wheels. The crankshaft assembly includes the crankshaft and bearings, the flywheel, vibration damper, sprocket or gear to drive camshaft and oil seals at the front and rear.
1.3 Camshaft The camshaft provides a means of actuating the opening and controlling the period before closing, both for the inlet as well as the exhaust valves, it also provides a drive for the ignition distributor and the mechanical fuel pump. The camshaft consists of a number of cams at suitable angular positions for operating the valves at approximate timings relative to the piston movement and in the sequence according to the selected firing order. There are two lobes on the camshaft for each cylinder of the engine; one to operate the intake valve and the other to operate the exhaust valve
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CHAPTER2 : INTRODUCTION TO CAMSHAFT TECHNOLOGY Since the initiation of the automobile, the internal combustion engine has evolved considerably. However, one constant has remained throughout the decades of ICE development. The camshaft has been the primary means of controlling the valve actuation and timing, and therefore, influencing the overall performance of the vehicle. The camshaft is attached to the crankshaft of an ICE and rotates relative to the rotation of the crankshaft. Therefore, as the vehicle increases is velocity, the crankshaft must turn more quickly, and ultimately the camshaft rotates faster. This dependence on the rotational velocity of the crankshaft provides the primary limitation on the use of camshafts. As the camshaft rotates, cam lobes, attached to the camshaft, interface with the engine’s valves. This interface may take place via a mechanical linkage, but the result is, as the cam rotates it forces the valve open. The spring return closes the valve when the cam is no longer supplying the opening force. Figure 1 shows a schematic of a single valve and cam on a camshaft and figure 2 shows the conventional value train mechanism.
Figure 1: Single Cam and ValveFig ur e 2: Co nv en ti on al Va lv e Tr ai n Mechanism
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Since the timing of the engine is dependent on the shape of the cam lobes and the rotational velocity of the camshaft, engineers must make decisions early in the automobile development process that affect the engine’s performance. The resulting design repr esents a compromise between fuel efficiency and engine power. Since maximum efficiency and maximum power require unique timing characteristics, the cam design must compromise between the two extremes. This compromise is a prime consideration when consumers purchase automobiles. Some individuals value power and lean toward the purchase of a high performance sports car or towing capable trucks, while others value fuel economy and vehicles that will provide more kms per liter. Recognizing this compromise, automobile manufacturers have been attempting to provide vehicles capable of cylinder deactivation, variable valve timing (VVT), or variable camshaft timing (VCT). These new designs are mostly mechanical in nature. Although they do provide an increased level of sophistication, most are still limited to discrete valve timing changes over a limited range. Regardless of the VVT technology differences among the leading automotive manufacturers, the prime similarity of a camshaft remains. Therefore, limitations continue, since the timing is still a function of engine speed. These limitations have initiated research into Camless engine technology.
Figure 3& 4: Typical view of traditional camshaft and valve
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CHAPTER3: WORKING OF CAMLESS ENGINE To eliminate the cam, camshaft and other connected mechanisms, the Camless engine makes use of three vital components – the sensors, the electronic control unit and the actuator. The basic block diagram of a camless engine is shown in figure 5.
ELECTRONIC
SENSORS
ACTUATORS
CONTROL UNIT Figure 5: Basic Block Diagram Of Camless Engine
Mainly five sensors are present, which senses: 1. Speed of the engine. 2. Load on the engine. 3. Exhaust position sensor. 4. Valve position sensor. 5. Current sensor.
Microprocessors are present in ECU to issue signal and control the actuators The electronic control unit consists of a microprocessor, which is provided with a software algorithm. The microprocessor issues signals to the solid-state circuitry based on this algorithm, which in turn controls the actuator, to function according to the requirements. 7
Camless Engine
3.1 CAMLESS VALVE TRAIN In the past, electro hydraulic camless systems were created primarily as research tools permitting quick simulation of a wide variety of cam profiles. For example, systems with precise modulation of a hydraulic actuator position in order to obtain a desired engine valve lift versus time characteristic, thus simulating the output of different camshafts. In such systems the issue of energy consumption is often unimportant. The system described here has 8
Camless Engine
been conceived for use in production engines. It was, therefore, very important to minimize the hydraulic energy consumption.
The different types of valve trains are as follows: 1. Electro-Mechanical poppet valve 2. Electro-Mechanical ball valve
3.1.1 ELECTRO-MECHANICAL POPPET VALVES Electromechanical actuators are generally made with two solenoids and two springs. As can be seen in Figure 6 the ECM receives input from the crankshaft position sensor to close the valve, which activates Solenoid 1 by taking current from the battery. The current is passed through a pulse width modulator which tunes the amplitude of the current to control the speed of valve seating. The magnetic field created by Solenoid 1 attracts the armature in the upper position. Spring 1 is compressed and thus closes the valve. Solenoid 2 pulls the armature down to open the valve as shown in Figure 7.
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Figure 6: Electromechanical Poppet Valves closed
Figure 7: Electromechanical Poppet Valves Open This type of system uses an armature attached to the valve stem. The outside casing contains a magnetic coil of some sort that can be used to either attract or repel the armature, hence opening or closing the valve. Most early systems employed solenoid and magnetic attraction/repulsion actuating principals using an iron or ferromagnetic armature. These types of armatures limited the performance of the actuator because they resulted in a variable air gap. As the air gap becomes larger (i.e. when the distance between the moving and stationary magnets or electromagnets increases), there is a reduction in the force. To maintain high forces on the armature as the size of the air gap increases, a higher current is 10
Camless Engine
employed in the coils of such devices. This increased current leads to higher energy losses in the system, not to mention non-linear behavior that makes it difficult to obtain adequate performance. The result of this is that most such designs have high seating velocities (i.e. the valves slam open and shut hard!) and the system cannot vary the amount of valve lift.
Figure 8: Electromechanical Poppet Valves The electromechanical valve actuators of the latest poppet valve design eliminate the iron or ferromagnetic armature. Instead it is replaced with a current-carrying armature coil. A magnetic field is generated by a magnetic field generator and is directed across the fixed air gap. An armature having a current-carrying armature coil is exposed to the magnetic field in the air gap. When a current is passed through the armature coil and that current is perpendicular to the magnetic field, a force is exerted on the armature. When a current runs through the armature coil in either direction or perpendicular to the magnetic field, an electromagnetic vector force, known as a Lorentz force, is exerted on the armature coil. The force generated on the armature coil drives the armature coil linearly in the air gap in a direction parallel with the valve stem. Depending on the direction of the current supplied to the armature coil, the valve will be driven toward an open or closed position. These latest electromechanical valve actuators develop higher and better-controlled forces than those designs mentioned previously. These forces are constant along the distance of travel of the armature because the size of the air gap does not change. 11
Camless Engine
The key component of the Siemens-developed infinitely variable electromechanical valve train is an armature-position sensor. This sensor ensures the exact position of the armature is known to the ECU at all times and allows the magnetic coil current to be adjusted to obtain the desired valve motion.
3.1.2 ELECTROMECHANICAL BALL VALVES: An alternative to the conventional poppet valve for use in camless valve trains is a ball valve. This type of electromechanical valve system consists of a ball through which a passage passes. If the ball is rotated such that the passage lines up with other openings in the valve assembly, gas can pass through it. (Exactly like the ball valves many of us use valve is accomplished by electromagnets positioned around its exteriorto control our boost).
Figure 9:Assembly Of Electromechanical Ball Valve
Referring to Figure 10, the valve housing (7) is shown in two pieces. Ball valve (8) has two rigidly attached pivots (12). The disc (10) is permanently attached and indexed to the ball valve and contains permanent magnets around its perimeter. The electromagnets (11) are situated on both sides of the ball valve (8) and they are fixed to the valve housing.The electromagnets are controlled through the ECU. A crank 12
Camless Engine
trigger sensor on the crankshaft provides information about the position of the pistons relative to top dead centre. Thus, at top dead centre of the power stroke, the ECM could be used to fix the polarity of both electromagnets so that they are of opposite polarity to the magnets in the ball valve, rotating the ball valve to the closed position. The substitution of a simple, efficient ball valve and valve housing arrangement in a four stroke reciprocation piston engine eliminates all the independent moving parts in the valve train. This may even be an improvement over the poppet valve camless
system - the ball valve needs only to rotate on its axis to achieve the desired flow conditions, rather than be accelerated up and down in a linear fashion. A partially open ball valve state may also be able to be used to create more turbulence. Electromechanical valve train implementation would not be possible with a normal 12V electrical system. Theautomotive industry has chosen a 42V electrical system as the next automotive standard. Consequently, the energy demand of EMVT can be optimally matched by a crankshaft-mounted starter-generator (KSG - in Siemens speak) operating at 42V; it is integrated in the flywheel and designed for the starting process as well as generator operation.
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CHAPTER 4: DESIGN CONSIDERATION For the purposes of this seminar it was decided that the valve would be run up to speeds of 3000rpm. This is fast enough to be useful in motor vehicles but will require less force then to run at greater speeds (for example up to 6000rpm). Generating theforces required to run the engine at up to 6000rpm was considered beyond the scopeof this seminar report.
The electronic valve actuation design has to take into account the followingconstraints:
Force required by solenoids must be minimized in order to reduce the powerrequired and the heat which must be dissipated by them.
Force provided by solenoids decreases exponentially with the distance theplunger moves from the coil.
At lesser engine speeds the force due to inertia will be nearly zero, so that having very stiff springs will mean that the solenoids will have to overcome these on their own.
The valve is to follow a standard valve profile, as soft landings are required by the valve for the same reason they are used in a traditional camshaft setup. That is, to reduce noise and wear on the valve, ther eby increasing the lifespanof the valve.
Due to these constraints the mechanical design had to be set up in such a way as toreduce the required force from the solenoids, while not being disadvantaged by theforce drop off due to distance. In order to achieve this mechanical design consistingof two springs and two solenoids was chosen. Two solenoids are to be used so thatone can be fixed to pull when opening the valve and the other when closing the valve.
This allows the solenoid to be used at its most effective. That is, when the gap it isacting across is very small. The two-spring design was chosen so that the valve’sresting point (no current applied to either solenoid) could be offset so as to be somedistance between both the closed and shut positions. This was found to greatly reducethe forces required to be generated by the solenoids. 14
Camless Engine
CHAPTER 5 : ADVANTAGES OF CAMLESS ENGINE Electro hydraulic camless valve train offers a continuously variable and independent control of all aspects of valve motion. This is a significant advancement over the conventional mechanical valve train. It brings about a system that allows independent scheduling of valve lift, valve open duration, and placement of the event in the engine cycle, thus creating an engine with a totally uncompromised operation. Additionally, the ECV system is capable of controlling the valve velocity, perform selective valve deactivation, and vary the activation frequency. It also offers advantages in packaging. Freedom to optimize all parameters of valve motion for each engine operating condition without compromise is expected to result in better fuel economy, higher torque and power, improved idle stability, lower exhaust emissions and a number of other benefits and possibiliti es. Camless engines have a number of advantages over conventional engines.
In a conventional engine, the camshaft controls intake and exhaust valves. Valve timing, valve lift, and event duration are all fixed values specific to the camshaft design. The cams always open and close the valves at the same precise moment in each cylinder’s constantly repeated cycle of fuel-air intake, compression, combustion, and exhaust. They do so regardless of whether the engine is idling or spinning at maximum rpm. As a result, engine designers can achieve optimum performance at only one speed. Thus, the camshaft limits engine performance in that timing, lift, and duration cannot be varied.
The improvement in the speed of operation valve actuation and control system can be readily appreciated with reference to Figure 10. It shows a comparison between valve speeds of a mechanical camshaft engine and the camless engine valve actuation. The length of the valve stroke in inches versus degrees of rotation of a mechanical camshaft is illustrated.
Figure 10: Graph of stroke v/s degrees 15
Camless Engine
When graphed, the cycle of opening and closing of a valve driven by a mechanical camshaft will display a shape similar to a sine curve. The opening period (as measured in crankshaft degrees) remains constant for any engine load or rpm. However, the cycle of opening and closing of valves driven by the electromechanical valve actuators operates much faster. But in a cam less engine, any engine valve can be opened at anytime to any lift position and held for any duration, optimizing engine performance. The valve timing and lift is controlled 100 percent by a microprocessor, which means lift and duration can be changed almost infinitely to suit changing loads and driving conditions. The promise is less pollution, better fuel economy and performance.
Another potential benefit is the camless engine’s fuel savings. Compared to conventional ones, the camless design can provide a fuel economy of almost 7-10% by proper and efficient controlling of the valve lifting and valve timing.
The implementation of camless design will result in considerable reduction in the engine size and weight. This is achieved by the elimination of conventional camshafts, cams and other mechanical linkages. The elimination of the conventional camshafts, cams and other mechanical linkages in the camless design will result in increased power output.
The better breathing that a camless valve train promotes at low engine speeds can yield 10% to 15% more torque. Camless engines can slash nitrogen oxide, or NO x, pollution by about 30% by trapping some of the exhaust gases in the cylinders before
they can escape. Substantially reduced exhaust gas emissions during cold start and warm-up operation.
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CHAPTER 6 : CONCLUSION 1. The electronic valve actuation is thebasic way to provide an easy method ofinfinitely varying the valve timing in internal combustion engines.
2. The aim camless engine is liberation from a constraint that has handcuffed performance since the birth of the internal-combustion engine. In the camless valve train, the valve motion is controlled directly by a valve actuator – there are no camshaft and hence no connecting mechanisms
3. The benefits expected from a camless engine points to substantial improvements in performance, fuel economy, and emissions over and above what is achievable in engines with camshaft-based valve trains
4. The development of a camless engine with different type of valve train described in this report is only a first step towards a complete engine optimization. Further research and development are needed to take full advantage of this system exceptional flexibility
5. Even though some disadvantages are present, we can expect electrohydraulic& electromechanical valves to replace the conventional camshaft technology.
6. The overall results of a complete Camless engine will provide the consumer with a vehicle that performs to expectations, but facilitates increased fuel economy. This combination is essential, since evidence shows consumers are not prepared to compromise on performance, while at the same time fuel prices continue to rise.
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References
1. Dobson, N. and Muddell, G., 1993, “Active Valve Train System Promises to Eliminate Camshafts,” Automotive Engineer Februar y/March 1993 2. Internal combustion engine by V.Ganesan 3. Ladd, D; Camless Engine is Gaining Momentum. September 13, 1999. 4. Siemens Automotive. July 4, 2000. 5. Thesis by John Steven Brader, Boston Universit y, 1995 6. www.autospeed.com 7. www.google.com 8. www.howstuffworks.com 9. www.machinedesign.com 10. www.scribd.com 11. www.wikipedia.com
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