Variable CAM Control
Continuously Variable Valve Timing (VVT)
Cam control, otherwise known as VVT, CVVT, VVTi, VANOS and various other names is a technique used by manufacturers to modify an engines valve timing while the engine is running. Unlike older systems where the valve timing could be switched between one of two settings (eg early VTEC and MIVEC), VVT allows valve timing to be adjusted anywhere within a fixed range. Link Engine Management gives the expert "tuner" full control of these cams.
Advantages of VVT:
- Improved power over the entire operating range
- Improved fuel economy
- Improved emissions
- More flexibility for engine tuners
What is involved
VVT requires sophisticated control algorithms to precisely position valve timing. Valve timing is adjusted by varying camshaft position with relation to crankshaft position (in other words by advancing or retarding camshaft position). Cam shaft position is usually controlled by a special electronic valve that alters the flow of engine oil into the camshafts position regulator (which usually resides inside the cam belt pulley). Cam position is measured using dedicated cam position sensors and fed back to the ECU. Link ECU's use a user adjustable PID control algorithm that continuously compares the actual cam position to the tuners desired cam position and automatically acts to reduce the difference between the two. This results in fast precise and stable control of cam position.
Features of Link Engine Management VVT Control
- Up to four independent control channels.
- Share settings between channels (eg share settings for both inlet cams and both exhaust cams).
- Fully tunable high speed closed loop PID control algorithm.
- Preset configurations for popular engines (means the user does not have to know how tune tune control algorithms!).
- RPM and Temperature lockouts to disable VVT control if required.
Setting up VVT Control
To use VVT control on a Link ECU two things must be present for each cam who's position is to be controlled:
- A position sensor must be wired to a Digital Input
- A control valve must be wired to an Auxiliary Output (of course this is not necessary on a plug-in ECU).
After wiring VVT control solenoids and configuring the appropriate inputs/outputs in PCLink the ECU will have capability to measure and control camshaft position. After this the control algorithm must be tuned to optimise the response of the position control algorithm. This can be done by either selecting one of the pre-configured options or manually (requires experience). VVT Control is then is simple as entering the desired camshaft position for any particular load/RPM combination in a 3D table.
Other Points:
- An after-market ECU with VVT control is required for any engine that has continuously variable valve timing.
- Significant midrange power gains can be made by optimising cam position for power rather than emissions (as done by most manufacturers). "Click" on the dyno sheet to see these dramatic changes.
PCLink displaying Link VVT control
Select the image below to view cam control mapping (larger image) on PCLink.
Photo and drawing credits
Vanos pics from BMW technology website
www.mazda6tech.com/images/engine_tech/enginetech_vvt.gif
www.mikuni.com/oem_components/variable_valve_timing.jpg
