Vacuum system for engine with variable valve lift
A vacuum system for an engine with variable valve lift includes a controllable vacuum-forming valve at the entrance to the intake manifold and a programmable engine control module (ECM) to increase vacuum as desired within the manifold by modulating the valve as needed to optimize fuel economy. To provide vacuum brake assist, a brake booster diaphragm is connected conventionally to the manifold and a vacuum storage tank and check valve are disposed between the booster diaphragm and the manifold. During periods of vehicle deceleration, when engine load is low, the ECM may switch the VVL-controlled intake valves to a higher lift to increase the pumping capacity of the engine, while simultaneously partially closing the vacuum-forming valve to create vacuum in the intake manifold, the brake booster, and the vacuum storage tank at little or no expense to engine performance.
1. A method for generating vacuum in an intake manifold in a fuel-injected internal combustion engine in a vehicle, the engine having variable valve lift as a primary throttle means for regulating engine load and having an engine control module for controllably varying valve lift, comprising the steps of:
a) providing a pressure sensor disposed in said intake manifold and connected to said engine control module for providing manifold pressure input to said engine control module;
b) providing a secondary throttle means disposed at an inlet to said intake manifold, connected to and controlled by said engine control module;
c) providing a vacuum capacitance tank connected to said intake manifold and an auxiliary vacuum activated system;
d) inputting vehicle deceleration information into said engine control module;
e) during said vehicle deceleration, at least partially closing said secondary throttle means to restrict the flow of air into said manifold and increasing the lift of said valves to pump air from said manifold through said engine, thereby generating manifold vacuum; and
f) recharging said vacuum capacitance tank.
2. A method in accordance with claim 1 further comprising the step of stopping flow of fuel from at least one of the fuel injectors of said fuel-injection engine during said vehicle deceleration.