Lotus Active Valve Train Research System
Download PDF
The Lotus AVT system is a powerful tool for research into advanced combustion techniques including:
- Low Temperature Combustion,
- CAI (Controlled Auto Ignition)
- HCCI (Homogeneous Charge Compression Ignition)
Such is the capability of Lotus AVT system that it is used on single cylinder engines in the research departments of vehicle manufacturers and universities around the world.
Using electronically controlled, hydraulically operated engine valve lift, it allows rapid testing and development of engines and combustion without the need to change engine hardware. It can also be used for simulating camshaft designs without physical changes to the engine. What used to take many hours can now be achieved in a matter of minutes this is the power and advantage of the Lotus developed AVT system.
It is capable of producing a wide range of valve lift profiles including trapezoidal, conventional camshaft polynomial form as well as multiple lift and events during two/four/six/eight stroke engine cycles.
- Low Temperature Combustion,
- CAI (Controlled Auto Ignition)
- HCCI (Homogeneous Charge Compression Ignition)
Such is the capability of Lotus AVT system that it is used on single cylinder engines in the research departments of vehicle manufacturers and universities around the world.
Using electronically controlled, hydraulically operated engine valve lift, it allows rapid testing and development of engines and combustion without the need to change engine hardware. It can also be used for simulating camshaft designs without physical changes to the engine. What used to take many hours can now be achieved in a matter of minutes this is the power and advantage of the Lotus developed AVT system.
It is capable of producing a wide range of valve lift profiles including trapezoidal, conventional camshaft polynomial form as well as multiple lift and events during two/four/six/eight stroke engine cycles.
The AVT- System Description
The Lotus AVT system is an electronically controlled, hydraulically operated system that allows the control of individual valve lift profiles by a digital signal processor based controller. AVT allows the user, via a PC to specify the desired valve lift profile per valve. The user can edit and save pre-defined valve-lift profiles from a selection of profiles stored on hard disk, or generate, edit and save user defined profiles. Thus, it provides a flexible research and development tool with which to control the lift and timing of the valves, whilst still allowing conventional valve acceleration and velocity characteristics to be obtained.
Conventional camshafts are replaced with hydraulically operated actuators and proportional electro-hydraulic servo valves. A double-acting hydraulic actuator is fixed to the cylinder head and co-axially aligned with the engine valve. The actuators hydraulic piston is directly attached to the engine valve and a displacement transducer is connected to the top of the piston enabling the position of the valve to be accurately monitored.
A hydraulic power pack supplies pressurised hydraulic fluid to the electro-hydraulic servo valves which proportionally control the flow of hydraulic fluid to either the top or bottom of the actuator piston. This enables control of the velocity, timing and lift displacement of the engine valves for each individual crankshaft degree of rotation.
The control parameters of the system are accessed via a graphical user interface program on a PC which communicates with the AVT Controller.
The system employs a phase advanced P/D controller to detect and correct automatically the actual measured displacement towards achieving the desired displacement. The system operation is continuously monitored to identify potential malfunctions such as hydraulic pressure loss, crank or valve position signal loss, and potential valve to piston or valve to valve clash scenarios. A desired valve lift profile can be defined via the Lotus Engine Valve Profile Generator software (EVPG) which is communicated to the AVT Controller via a PC based user interface. It is possible to vary the opening and closing points of a profile individually in one-degree increments, and the maximum lift is adjustable to any valid figure between 0.01mm and the maximum travel of the actuator. Each engine valve is controlled individually. A library of many thousands of user specified lift profiles can be established by the user for use in their engine
test programs. From this library the user can select up to 256 lift profiles, that can be applied to any engine valve, for use in any given engine test session and each of these profiles can also be phase advanced or retarded +/- 128 degrees. If required, whilst the engine is running, a lift profile may be changed or modified every engine cycle and can contain as many lift events as are physically possible to implement. For example an engine can be configured to swap between two and four stroke combustion on alternate cycles if required. This allows the user to change a profile quickly and to observe its effects on exhaust emissions and engine performance, using standard test cell monitoring equipment. For a four stroke cycle a lift demand is specified as 720 lift points. ie. one lift increment for every degree of crankshaft rotation.
A crankshaft encoder provides the crank position and LVDTs provide the individual engine valve displacements to the AVT controller, these signals are compared to the demanded profile, approximately every 100 microseconds, as part of the feedback control loop and actuator demand signals are sent to the servo valve.
The Lotus AVT system is an electronically controlled, hydraulically operated system that allows the control of individual valve lift profiles by a digital signal processor based controller. AVT allows the user, via a PC to specify the desired valve lift profile per valve. The user can edit and save pre-defined valve-lift profiles from a selection of profiles stored on hard disk, or generate, edit and save user defined profiles. Thus, it provides a flexible research and development tool with which to control the lift and timing of the valves, whilst still allowing conventional valve acceleration and velocity characteristics to be obtained.
Conventional camshafts are replaced with hydraulically operated actuators and proportional electro-hydraulic servo valves. A double-acting hydraulic actuator is fixed to the cylinder head and co-axially aligned with the engine valve. The actuators hydraulic piston is directly attached to the engine valve and a displacement transducer is connected to the top of the piston enabling the position of the valve to be accurately monitored.
A hydraulic power pack supplies pressurised hydraulic fluid to the electro-hydraulic servo valves which proportionally control the flow of hydraulic fluid to either the top or bottom of the actuator piston. This enables control of the velocity, timing and lift displacement of the engine valves for each individual crankshaft degree of rotation.
The control parameters of the system are accessed via a graphical user interface program on a PC which communicates with the AVT Controller.
The system employs a phase advanced P/D controller to detect and correct automatically the actual measured displacement towards achieving the desired displacement. The system operation is continuously monitored to identify potential malfunctions such as hydraulic pressure loss, crank or valve position signal loss, and potential valve to piston or valve to valve clash scenarios. A desired valve lift profile can be defined via the Lotus Engine Valve Profile Generator software (EVPG) which is communicated to the AVT Controller via a PC based user interface. It is possible to vary the opening and closing points of a profile individually in one-degree increments, and the maximum lift is adjustable to any valid figure between 0.01mm and the maximum travel of the actuator. Each engine valve is controlled individually. A library of many thousands of user specified lift profiles can be established by the user for use in their engine
test programs. From this library the user can select up to 256 lift profiles, that can be applied to any engine valve, for use in any given engine test session and each of these profiles can also be phase advanced or retarded +/- 128 degrees. If required, whilst the engine is running, a lift profile may be changed or modified every engine cycle and can contain as many lift events as are physically possible to implement. For example an engine can be configured to swap between two and four stroke combustion on alternate cycles if required. This allows the user to change a profile quickly and to observe its effects on exhaust emissions and engine performance, using standard test cell monitoring equipment. For a four stroke cycle a lift demand is specified as 720 lift points. ie. one lift increment for every degree of crankshaft rotation.
A crankshaft encoder provides the crank position and LVDTs provide the individual engine valve displacements to the AVT controller, these signals are compared to the demanded profile, approximately every 100 microseconds, as part of the feedback control loop and actuator demand signals are sent to the servo valve.