Engine carburetor throttle blade positioning control

An engine carburetor throttle valve position control comprising, in combination, a caburetor mounted on an engine and having an induction passage open to atmospheric pressure at one end and adapted to be connected to the engine intake manifold at the opposite end and including a throttle valve rotatably mounted across the passage movable open from an essentially closed throttle engine idle speed position and having a return movement, for controlling flow through the passage, spring means biasing the throttle valve towards the closed position, first vacuum controlled servo means having stop means extending into the path of movement of the throttle valve in a closing direction to predetermine the idle speed position of the throttle valve, passage means connecting a source of vacuum to the servo to vary the position of the stop means and thereby vary the idle speed setting of the throttle valve,

• an exhaust gas recirculation (EGR) passage means connecting engine exhaust gases to the induction passage below the closed position of the throttle valve, a spring closed, vacuum opened EGR flow control valve mounted in the EGR passage means for a variable movement between open and closed positions to control the volume of EGR gas flow, a second vacuum controlled servo means connected to the EGR valve for moving the EGR valve to an open position, means connecting the second servo means to the passage means, and
• control means to control flow of vacuum to the first and second servo means to control opening of the EGR valve and to determine the idle speed setting of the throttle valve, the control means comprising a switching means alternately movable to supply vacuum to the first servo means while cutting off flow of vacuum to the second servo means and vice-versa.