3. What is a Throttle? The throttle controls the amount of air that enters the cylinder It is associated with pumping losses
4. Pumping Losses Pumping losses account for about 15% of the Brake Power. In our vehicle, we found that there is about 35kW of power that is removed from the brake power due to pumping losses. Throttle losses are big factor in pumping losses
5. Methods of Operating Throttless Exhaust Gas Recirculation EGR cannot be used alone in throttleless operation, need other methods that also reduce pumping losses Turbocharging Variable Valve Timing The biggest factor in throttleless operation
6. Exhaust Valve Opening Variable Valve Timing System For High Speeds The timing for the exhaust valve opening should begin before the bottom dead center (50-60 degrees BBDC) This reduces the pumping work done by the piston to expel the combustion products For Low Speeds The timing for the exhaust valve opening should begin just after the bottom dead center
7. Exhaust Valve Closing Timing is critical because at full loads there should be no exhaust gas left in the cylinder However at partial loads it is desirable to have some exhaust gases left in the cylinder i.e. EGR Exhaust valve closing should occur right at top dead center or just after (5-15 degrees ATDC)
8. Intake Valve Opening Timing for the intake valve opening is critical If it is open before top dead center exhaust gases could flow into the intake manifold If it is open too late the air/fuel ratio in the cylinder could be restricted and could cause a drop in pressure as the piston descends Also can reduce the volumetric efficiency Typically 0-10 degrees BTDC
9. Intake Valve Closing Timing for the intake valve closing affects the amount of air/fuel ratio in the cylinder The greatest ratio will result in the largest torque As the engine speed increased the timing moves farther after bottom dead center Typically 50-60 degrees ABDC
10. Methods of Variable Valve Timing (VVT) Phase Changing Systems In order to advance or retard the timing of the engine valves, a phase changing system changes the timing of the camshaft in relation to the crankshaft. If this system is applied to an engine with a single camshaft then all valve events are shifted by the same amount Phase change systems cannot change the duration of the valve events and do not have an effect on the valve peak timing.
11. Methods of VVT Continued Profile Switching Systems Unlike the Phase Changing System, the Profile Switching System has the ability to independently change the valve timing and valve peak lift. This system has two different camshaft profiles and switches between them usually at some specified engine speed. This system can be used on one or both shafts.. By being able to change the valve event, lift, and duration, this system allows for the ability to have a high power output while complying with lower emission legislation.
12. Methods of VVT Continued Variable Event Timing Systems The Variable Event Timing System almost combines the Profile Switching and Phase Change System. It can not only change the phase, but also change the duration of the valve events. The Variable Event Timing System cannot change the peak valve lift. These systems are not only optimized for engine speed, but also optimized for variable loads and can be controlled to any setting between two extremes.
13. Methods of VVT Continued Variable Lift Systems There are two types of Variable Lift Systems that are currently being researched and developed One type “scales” the valve lift such that its opening duration is unchanged The second type of valve lift system “truncates” such that the valve opening duration reduces as lift reduces A major benefit of using this system is the potential of throttling the cylinder by reducing the intake valve lift
14. Methods of VVT Continued Electro-magnetic Valve Actuation Systems The idea is that IVO, IVC, EVO, EVC, and valve lift could all be controlled by an engine management system Electro-magnetic Valve Actuation Systems have the greatest potential to be able to optimize all of the engine valve events
15. VVT System Chosen for the Truck The Ford truck has 3 valves – 2 intake and 1 exhaust. At lower speeds, only one intake valve would be opened. At medium speeds, one intake valve would be opened and the other valve would only be partially opened. This allows for better swirl and thus better combustion. At high speeds, both intake valves would be open to allow for maximum air flow.
16. Throttleless System Chosen for the Truck Camshaft On the camshaft, there will be three lobes. Two for low speed RPM and one for high speed Lobes are connected by a rocker Lobe Switching Mechanism At specified speed stored in the ECU, an electric signal is sent to open a spool valve. The spool directs oil pressure to a mechanical sliding pin. The pin locks the valve actuator to the high speed cam lobe.
18. Throttleless System Chosen for the Truck Since throttle not only controls how much air is being inducted into the cylinder, it also notifies the CPU (in modern cars) of how much fuel is needed based on the throttles position. Thus a modified algorithm will need to be programmed into the CPU to ensure that the proper amount of fuel is being injected into the cylinder. In a normal engine the throttle body setting is dominant and controls the amount of fuel and the valve lift. In the throttleless engine neither the fuel nor the valve lift is dominant over the other and the fuel and valve lift can adjust to each other. The fuel system and variable lift are controlled using parallel signals. This will allow much finer control of the engine and its characteristics
19. ThrottlelessSystem Chosen for the Truck Different spray patterns can be created by increasing the pressure of fuel rail. The duty cycle of the injectors can also be adjusted to give different spray effe. Adjusting the pressure of the injector can also change the amount of atomization and the flow rate of the fuel
20. Conclusions Further development of VVT systems is key for throttleless Fine tuning other components of the engine, such as the fuel injector is also key Decreases the pumping losses
