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Variable valve lift (VVL) is an automotive piston engine technology which varies the height a valve opens in order to improve performance, fuel economy or emissions. There are two main types of VVL: discrete, which employs fixed valve lift amounts, and continuous, which is able to vary the amount of lift.
The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary to achieve the desired result in intake and exhaust efficiency . This has been described ...
Valve lift can be expressed as an actual dimension in decimal inches or mm. It can also be specified as a ratio between a characteristic diameter and the lift L/D. Most often used is the valve head diameter. Normally engines have an L/D ratio from 0 up to a maximum of 0.35. For example, a 1-inch-diameter (25 mm) valve would be lifted a maximum ...
Valve timing and the valve profile are continuously altered according to conditions and engine load. For improved responsiveness on cold starts, VarioCam Plus raises the amount of lift and retards valve timing. At medium revs with minimal loads, the valve lift is lowered and timing advanced to help minimize fuel consumption and emissions.
The solenoid valve regulates the amount of oil pumped by the cam action to either the valve or a bypass reservoir. When pressurized, the hydraulic line behaves like a solid body and transmits the lift schedule imparted by the intake cam directly to the intake valve. When the solenoid is disengaged, a spring takes over valve actuation duties.
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The Valvetronic system is a BMW variable valve lift system [1] which, in combination with VANOS, allows infinite adjustment of the intake valve timing and lift. [2] [3] The system claims to improve fuel economy and emissions, and negates the need for a throttle body in regular use. [4]
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