![Possibilities of Valve Varition
[mm]
e
lift
Valv
Copyright: Prof. Dr.-Ing. Wilhelm Hannibal, Fachhochschule Südwestfalen, University of Applied Science, Iserlohn, Germany, hannibal@fh-swf.de
Fig. 20
Crank angle [°CA]](https://image.slidesharecdn.com/chapter1variablevalvetimingandliftingsystem-241209021058-a224eb36/85/Chapter-1-Variable-Valve-Timing-and-Lifting-system-pdf-54-320.jpg)
![Range for Cam Phasing Variation
[mm]
e
lift
Valve
outlet
valve lift
inlet
valve lift
Crank angle [°CA]
Copyright: Prof. Dr.-Ing. Wilhelm Hannibal, Fachhochschule Südwestfalen, University of Applied Science, Iserlohn, Germany, hannibal@fh-swf.de
Fig. 21](https://image.slidesharecdn.com/chapter1variablevalvetimingandliftingsystem-241209021058-a224eb36/85/Chapter-1-Variable-Valve-Timing-and-Lifting-system-pdf-55-320.jpg)
Chapter 1 Variable Valve Timing and Lifting system.pdf
- 1. AUTOMOTIVE ENGINE 2 AUTO 2104D ENGKU AMIRUL RASHIDIN B. ENGKU ARIFF MECHANICAL & AUTOMOTIF ENGINEERING, FEST INFRASTRUCTURE UNIVERSITY KUALA LUMPUR CHAPTER 1
- 2. 1. Identify the component and operation of variable valve timing and lifting systems. 2. Explain the advantages and disadvantages of various types of variable valve timing and lifting systems. At the end of this course, students will be able to:
- 3. VVT-i (Variable Valve Timing-intelligent) Description Camshaft position sensor VVT-I controller Crankshaft position sensor Camshaft timing oil control valve Water temp. sensor Engine ECU Throttle position sensor Air flow meter Crankshaft position sensor Air flow meter Throttle position sensor Water temp. sensor Camshaft position sensor Vehicle speed signal Target valve timing Engine ECU Camshaft timing oil control valve Feedback Correction Actual valve timing Duty control
- 4. Description Full load performance During low and medium speed at high load Engine load During low temperature, during low speed at light load, or during light load Engine speed During high speed at high load During medium load : Valve timing is advanced. : Valve timing is retarded. VVT-i (Variable Valve Timing-intelligent)
- 5. Description Full load performance During low and medium speed at high load Engine load During low temperature, during low speed at light load, or during light load Engine speed During high speed at high load During medium load : Valve timing is advanced. : Valve timing is retarded. VVT-i (Variable Valve Timing-intelligent)
- 6. Description Full load performance During low and medium speed at high load Engine load During low temperature, during low speed at light load, or during light load Engine speed During high speed at high load During medium load : Valve timing is advanced. : Valve timing is retarded. VVT-i (Variable Valve Timing-intelligent)
- 7. Construction VTT-i controller Lock pin Vane (fixed on Intake camshaft) Intake camshaft Housing Oil pressure at a Stop in Operation Lock pin Camshaft timing oil control valve Spring Oil pressure Drain Drain Spool valve (Advance side) (Retard side) Coil Plunger 1.VVT-i controller/ 2.Camshaft timing oil control valve VVT-i (Variable Valve Timing-intelligent)
- 8. Operation Vane Rotating direction Oil pressure Drain Camshaft timing oil control valve Engine ECU VVT-i controller 1. Advance VVT-i (Variable Valve Timing-intelligent)
- 9. Operation Vane Rotating direction Oil pressure Drain Camshaft timing oil control valve Engine ECU VVT-i controller 1. Advance VVT-i (Variable Valve Timing-intelligent)
- 10. Operation Vane 2. Retard Rotating direction Drain Oil pressure Engine ECU VVT-i (Variable Valve Timing-intelligent)
- 11. Operation Engine ECU 3. Hold Oil pressure VVT-i (Variable Valve Timing-intelligent)
- 12. Description Oil pressure switch Oil control valve (for VVTL) Camshaft position sensor Throttle position sensor Vehicle speed signal Air flow meter Water temp. sensor Oil control valve (for VVT) Crankshaft position sensor Engine ECU High-speed cam Low-and medium-speed cam Hydraulic circuit Oil control valve (for VVTL) VVTL VVT from Oil main hole Oil filter VVT-i (Variable Valve Timing-intelligent)
- 13. Construction Oil pressure switch Camshaft position sensor Oil control valve (for VVTL) to Cam changeover mechanism Drain Oil pressure Spool valve Water temperature sensor Oil control valve (for VVT) Crankshaft position sensor High-speed cam Low-and medium-speed cam Rocker arm Oil hole Lock pin Pad Roller 1.Oil control valve for VVTL/ 2.Camshafts and rocker arms VVT-i (Variable Valve Timing-intelligent)
- 14. Operation Rocker shaft Rocker arm Oil pressure switch “OFF” Oil control valve “OFF” Oil pressure Drain High-speed cam Low-and medium-speed cam Pad Lock pin Moves freely Roller Engine ECU 1.Low- and medium-speed (engine speed: below 6000 rpm) Cam changeover mechanism VVT-i (Variable Valve Timing-intelligent)
- 15. Operation Rocker shaft Rocker arm Oil pressure switch “OFF” Oil control valve “OFF” Oil pressure High-speed cam Low-and medium-speed cam Pad Oil pressure Lock state Roller Engine ECU 2.High-speed (engine speed: over 6,000 rpm/coolant temp.: higher than 60 °C) Cam changeover mechanism VVT-i (Variable Valve Timing-intelligent)
- 16. What is a Valve? • In Internal Combustion Engine, valves are used to control the flow of the intake and exhaust gases into and out of the combustion chamber. • The timing, duration and lift of these valve events has a significant impact on engine performance. • Valves allow the engine to breathe.
- 17. What are the Valve Functions? • INTAKE :- The Intake valve allows the air-fuel mixture from the carburettor to enter into the combustion chamber. • EXHAUST :- The exhaust valve releases the exhaust gases and spent fuel to escape out of the engine cylinder into the atmosphere.
- 18. How does the valves operate? • CAMS :- These provide the force to push the valves open, usually with the help of a rocker arm. • ROCKER ARMS :- These are the links between the cam and the valve. • SPRINGS :- These are used to keep the valves in place and to provide the force required to close the valve.
- 19. What is Valve Timing? • It’s the regulation of the points in the combustion cycle, at which valves are set to open and close. • The design of the valve-operating cam provides for the smooth transition from one position to other. • The cam setting determines the timing of the valve. • In a typical 4-stroke engine, the inlet valve is set to open before TDC (Top Dead Centre), towards the end of the exhaust stroke and close after BDC (Bottom Dead Centre), at the start of the compression stroke.
- 20. Valve Timing…..Continued • Inlet Valve Timing :- Theoretically, the inlet valve should open at TDC. But, its timed to occur a few degrees prior to the arrival of piston at TDC on the exhaust stroke. This is done to induct as much as possible amount of charge into the cylinder before the piston reaches BDC.
- 21. Valve Timing…..Continued • Exhaust Valve Timing :- The exhaust valve is set to open before BDC, towards the end of the power stroke. This is done to prevent the exhaust gases from forming a high-pressure cushion, which would impede the movement of the piston. The valve closes after TDC which ensures that the entire burnt mixture is thoroughly scavenged.
- 22. Valve Timing…..Continued • Valve Overlap :- This refers to the time when both the intake & exhaust valves are open. It ensures that the exhaust gases rushing out of the cylinder create suction. The fresh mixture entering the cylinder pushes out the burnt fuel mixture. • Valve timing of any engine depends on :- The amount of valve overlap. Lag & lead, i.e. the degrees that the crankshaft turns between valve opening and TDC or BDC.
- 23. What is Multi-Valve Technology? A multi-valve engine is one where each cylinder has more than two valves. Adding more valves increases valve area and improves the flow of intake and exhaust gases, thereby enhancing combustion and power output. Multi-valve geometry allows the spark plug to be ideally located within the combustion chamber for optimal flame propagation. Some engines are designed to open each intake valve at a slightly different time, which increases turbulence, improving the mixing of air and fuel at low engine speeds.
- 24. What’s Variable Valve Timing (VVT) and it’s Need? • In internal combustion engines, Variable valve timing is the process of altering the timing of a valve lift event. • It has the task of setting the most advantageous valve timing for the particular engine for different operating modes. • When the engine rev increases, the duration of intake and exhaust stroke decreases so that fresh air becomes not fast enough to enter the combustion chamber, while the exhaust becomes not fast enough to leave the combustion chamber. • The best solution is to open the inlet valves earlier and close the exhaust valves later. Hence, Overlapping between intake period and exhaust period should be increased as rev increases.
- 25. VVT’s necessity….Continued • Without Variable Valve Timing technology, engineers used to choose the best compromise timing. • For example, a van may adopt less overlapping for the benefits of low speed output. • A racing engine may adopt considerable overlapping for high speed power. • An ordinary sedan may adopt valve timing optimize for mid-rev so that both the low speed drivability and high speed output will not be sacrificed too much. • No matter which one, the result is just optimized for a particular speed.
- 26. Types of Variable Valve Timing System:- 1. Cam-Changing VVT • It uses different cam profiles to lift the valves depending on engine load and speed (RPM). • One common system uses two rocker arms for normal operation on its two intake valves, with a third, higher profile, rocker arm between the other two arms. • At engine speeds above 5000-6000 rpm, the engine ECU activates an oil pressure controlled pin that locks the three rocker arms together. • The centre rocker arm follows a larger and more aggressive profile, transferring its movement to the intake valves which now open further and for a longer period. • When engine speed fall below the threshold speed, oil pressure is removed from the pin and a spring deactivates the pin.
- 27. Cam-Changing VVT Applications Honda’s latest 3-stage VTEC (Valve Timing Electronic Control) has been applied in CIVIC SOHC engine in Japan. The mechanism has 3 cams with different timing and lift profile. • Stage 1 (Low Speed) :- The 3 pieces of rocker arms move independently. Both cams' timing is relatively slow compare with the middle cam, which actuates no valve now. • Stage 2 (Medium Speed) :- Hydraulic pressure connects the left and right rocker arms together, driven by the right cam. As a result, both inlet valves obtain slow timing but medium lift. • Stage 3 (High Speed) :- Hydraulic pressure connects all the 3 rocker arms together. Since, middle cam is largest, both inlet valves are actually driven by that cam. Therefore, fast timing and high lift are obtained in both valves.
- 28. Types of VVT….Continued 2. Cam-Phasing VVT • It is the simplest, cheapest and most commonly used mechanism at this moment. • It varies the valve timing by shifting the phase angle by shifting the phase angle of camshafts. • At high speed, the inlet camshaft will be rotated in advance by 30 degrees so to enable earlier intake. This movement is controlled by engine management system according to need, and actuated by hydraulic valve gears. • It cannot vary the duration of valve opening. It just allows earlier or later valve opening. Earlier open results in earlier close. It also cannot vary the valve lift, unlike cam-changing VVT.
- 29. Cam-Phasing VVT Applications • Toyota's VVT-I (Variable Valve Timing - Intelligent) has been spreading to more and more of its models, from the tiny Yaris (Vitz) to the Supra. Its mechanism is based on the working of Cam-Phasing VVT, it is also a continuously variable design. • However, the word "Intelligent" emphasize the clever control program. Not only varies timing according to engine speed, it also consider other conditions such as acceleration, going up hill or down hill.
- 30. Types of VVT….Continued 3. Cam-Changing + Cam-Phasing VVT • Combining cam-changing VVT and cam-phasing VVT. • It could satisfy the requirement of both top- end power and flexibility throughout the whole rev range, but it is inevitably more complex. • At the time of writing, only Toyota and Porsche have such designs.
- 31. Benefits of Variable Valve Timing(VVT) • EGR (Exhaust gas recirculation) is a commonly adopted technique to reduce emission and improve fuel efficiency. However, it is VVT that really exploits the full potential of EGR. • Variable valve timing systems can provide better torque for an engine. • With more precise handling of engine valves, automakers have shown that VVT can produce better fuel economy for vehicles. • Reduced nitrogen oxide and Hydrocarbon emissions .
- 32. Present Development in VVT Systems Koenigsegg’s FreeValve Technology :- The FreeValve technology is equipped with pneumatic spring and position sensor so that the valve can reciprocate in & out of the engine cylinder. It provides full control of gas exchange, variable valve lift and accurate valve opening and closing time. The FreeValve technology is connected to the ECU of the engine which feeds the system with the timing and amount of valve lift required. FreeValve’s primary goal is to reduce emissions and fuel consumption. Secondary goals are downsizing, torque and power increases.
- 33. Conclusion • Variable valve timing technology has grown as technological availability increases. The need for ever more efficient, clean, powerful engines has pushed the bar higher within production automotive engines. • The trend toward computer controls is rapidly approaching a limit within the cam engine world and the jump into camless designs is something of the future that holds much promise. • The problem of transition time has been virtually solved and the seating speed will soon be under control. • Despite the problems, the camless engine is the future. The level of control (lift, duration, phase) is practically unheard of in mechanical systems.
- 34. VARIABLEVALVETIMING (VVT) In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions.There are many ways in which this can be achieved, ranging from mechanical devices to Cam Phasing, Cam Switching, electro-hydraulic and camless systems. • Early variable valve timing systems used discrete (stepped) adjustment. • For example, one timing would be used below 3500 rpm and another used above 3500 rpm. Discrete • Infinite adjustment of the valve timing. • Timing can be optimized to suit all engine speeds and conditions. Continuous T Y P E S
- 35. CAM SWITCHING • Uses two cam profiles, with an actuator to swap between the profiles (usually at a specific engine speed). • Cam switching can also provide variable valve lift and variable duration, however the adjustment is discrete rather than continuous. • Different companies have different methods of switching between cam profiles. • The first production use of this system was Honda'sVTEC system that will be discussed in later slides.
- 36. CAM PHASING • The simplest and cheapest form ofVVT. • Phase angle of the camshaft is rotated forwards or backwards relative to the crankshaft. For example, at high speed, the inlet camshaft will be rotated in advance by 30°. • This movement is controlled by engine management system • The valves open and close earlier or later. • The camshaft lift and duration cannot be altered with a cam-phasing system. • AudiV8 inlet, BMW DoubleVanos inlet, Ferrari 360 Modena exhaust
- 37. Typical effect of timing adjustments Late intake valve closing Early intake valve closing Early intake valve opening Early/late exhaust valve closing
- 38. Late intake valve closing • The piston pushes air out of the cylinder and back into the intake manifold during the compression stroke. • The air which is expelled fills the manifold with higher pressure, and on subsequent intake strokes the air which is taken in is at a higher pressure. • Reduce pumping losses by 40% during partial load conditions, and to decrease nitric oxide (NOx) emissions by 24%. • Peak engine torque showed only a 1% decline, and hydrocarbon emissions were unchanged.
- 39. Early intake valve closing • Closing the intake valve midway through the intake stroke. • Air/fuel demands are so low at low-load conditions and the work required to fill the cylinder is relatively high, so Early intake valve closing greatly reduces pumping losses. • Studies have shown early intake valve closing reduces pumping losses by 40%, and increases fuel economy by 7%. It also reduced nitric oxide emissions by 24% at partial load conditions. • A possible downside to early intake valve closing is that it significantly lowers the temperature of the combustion chamber, which can increase hydrocarbon emissions.
- 40. Early intake valve opening • In a traditional engine, a process called valve overlap is used to aid in controlling the cylinder temperature. • By opening the intake valve early, some of the inert/combusted exhaust gas will back flow out of the cylinder, via the intake valve, where it cools momentarily in the intake manifold.This inert gas then fills the cylinder in the subsequent intake stroke, which aids in controlling the temperature of the cylinder and nitric oxide emissions. • It improves volumetric efficiency, because there is less exhaust gas to be expelled on the exhaust stroke.
- 41. Early/late exhaust valve closing • Traditionally, the exhaust valve opens, and exhaust gas is pushed out of the cylinder and into the exhaust manifold by the piston as it travels upward. By manipulating the timing of the exhaust valve, engineers can control how much exhaust gas is left in the cylinder. • By holding the exhaust valve open slightly longer, the cylinder is emptied more and ready to be filled with a bigger air/fuel charge on the intake stroke.This results in more power. • By closing the valve slightly early, more exhaust gas remains in the cylinder which increases fuel efficiency and reduces NOx emissions.This allows for more efficient operation under all conditions.
- 42. VARIABLEVALVE LIFT (VVT) • VVL is mainly used to enhance performance. AVVL engine has two cam profiles: low-lift and high-lift. • Under regular conditions, the engine will use the low-lift cam to operate the valves • Under higher load, a solenoid switches the engine over to the to the high-lift cam (or cams), increasing valve travel and therefore, performance.
- 43. VARIABLEVALVETIMING & LIFT ELECTRONIC CONTROL(VTEC) • Developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. • TheVTEC system uses two (or occasionally three) camshaft profiles and hydraulically selects between profiles. • It is distinctly different from standardVVT systems which change only the valve timings and do not change the camshaft profile or valve lift in any way.
- 44. VTEC-E VARIABLETIMING CONTROL (VTC) • Mechanism used at the intake camshaft and it is essentially cam phasing. • It allows intake camshaft to be continuously variable overlap b/w intake & exhaust cam. • Can be infinitely adjustable during rev range. • Gives better results when used at input • Not Designed for power but for fuel efficiency. • Variation of Single Overhead Camshaft (SOHC)VTEC. • Turns 16 valve four cylinder engine into 12 valve four cylinder engine by not allowing one of the intake valves to fully open.
- 45. HONDA i-VTEC • i-VTEC is a system that combinesVTEC and VTC into one unit. • Results in an incredibly efficient and powerful engine. • TheVTEC part of the system has two different camshaft profiles, one for low rpms, and one for high rpm. • TheVTC part of the system allows valve overlap to be adjusted at any moment, resulting in much greater efficiency and slightly better performance.
- 46. How Does it Increase Horsepower? • Horsepower is just a measure ofTorque X RPM.To increase torque, you must let more air and fuel into the engine. • If the valves must open further and for longer, the amount of air being sucked into the cylinder can be increased. Since the camshaft spins half as fast as the crankshaft, it cannot be optimized for all RPM ranges. Having multiple camshaft lobes allows you to maximize lift and duration for various RPM ranges. • Since the camshaft is optimized for both high and low rpm ranges, it makes more torque in those ranges. More torque, especially at high RPMs, equals more horsepower.
- 48. AUDIVALVELIFT SYSTEM (AVS) AVS refers to the cam switching mechanism. In general, cam switching is performed by hydraulically controlling a rocker arm such asVTEC or MIVEC, or in a somewhat special case, hydraulically controlling a lifter such as a variable cam lift mechanism such asVariocam Plus or Subaru . In these, the cam is switched by switching the rocker arm under hydraulic control, and the camshaft itself does not change.
- 49. AUDIVALVELIFT SYSTEM (AVS) Cont. In AVS, cam switching is performed by physically moving the camshaft side axially in the axial direction, and the rocker arm side does not change at all. A cam piece having two cam ridges movable in the axial direction is attached to each of the cylinders on the camshaft, and the cam switching is performed by moving the cam piece. A spiral groove is dug at the end of the cam piece, and the pin is inserted into the groove to move the cam piece by the rotation of the camshaft, and the switching is completed during one revolution. Fixing of the cam piece is made by fitting a ball roller (with a spring) inside the shaft into either of two grooves provided in the cam piece. When moving, the ball roller climbs over the ridge between the two grooves and is fixed again by fitting into the other groove. Closer Look of AVS
- 50. AUDI A4 has also got aVVT(Variable Valve Timing) at its intake to match the continuously changing driving conditions and thus, delivering max. efficiency and/or power.
- 51. FIAT Multi Air Engine • MultiAir is a hydraulically- actuated variable valve timing and variable valve lift engine technology enabling "cylinder by cylinder, stroke by stroke" control of intake air directly via a gasoline engine's inlet valves. • Multi air engine is different from other engines because it consists of solenoid valve. • A SolenoidValve is an electromechanical technology used for functioning of valves.
- 52. 5 main different strategies possible are: 1. Full Lift(Fig 1. ) is suitable for high rpm running and provides Max Power. 2. LIVO(Fig 2. ) is suitable for low-load operation. Its late valve opening leads to a partial vacuum in the combustion chamber. In addition to the low valve lift, the intake air stream is greatly speeded up, generating turbulence thus improve air and fuel mixture.This benefits fuel economy and emission. 3. EIVC(Fig 3. ) is suitable for a wide range of part-load operation. Depending on the requirement of power, the amount of air can be controlled by the early closing of intake valves.This eliminates the need of throttle butterfly (like BMW Valvetronic) and reduce pumping loss by up to 10%. 4. Partial Load(Fig 4. ) is designed for enhanced low-rpm acceleration.While it enables more intake air volume compare with Fig 2 & 3, its early valve closure ensures no air flow back into the intake manifolds near the end of the intake stroke. 5. Multi Lift(Fig 5. ) is designed for very low rpm operation. It combines the strategy of Fig 2 & 3 and their benefits - regulated consumption and improved quality of air-fuel mixture.
- 53. ADVANTAGES DISADVANTAGES Reduced 10% of the fuel consumption. Opening and Closing of valves requires some power Reduced emissions – 10% CO2, 60% NOx and 60% particulate. Current solenoids cannot run at high RPMs Increased lower end torque by 15%. Hidden cost of microprocessor and software controls Increased fuel economy by 7-10%. Not perfectly compatible with variable cam phasing Lesser pumping losses(reduced friction) due to lesser moving components since SOHC works like DOHC. Mechanism quite bulky such that difficult to apply to DOHC engines
- 54. Possibilities of Valve Varition [mm] e lift Valv Copyright: Prof. Dr.-Ing. Wilhelm Hannibal, Fachhochschule Südwestfalen, University of Applied Science, Iserlohn, Germany, hannibal@fh-swf.de Fig. 20 Crank angle [°CA]
- 55. Range for Cam Phasing Variation [mm] e lift Valve outlet valve lift inlet valve lift Crank angle [°CA] Copyright: Prof. Dr.-Ing. Wilhelm Hannibal, Fachhochschule Südwestfalen, University of Applied Science, Iserlohn, Germany, hannibal@fh-swf.de Fig. 21