Cruise Control Servo: Description and Operation

Cruise Control Actuator:

ACTUATOR
The actuator has a diaphragm whose movement is controlled using vacuum and atmospheric pressure.

The vacuum is controlled by the vacuum valve and the atmospheric pressure is controlled by the vent valve. The diaphragm is connected to the throttle valve through the cruise control cable and linkage so that the throttle valve opens to closes as the diaphragm moves.

With the cruise control turned OFF (system deactivated), no diaphragm operation occurs as the atmospheric pressure is prevailing inside the actuator.

How the valves operate in response to signals from the control module:

VALVE OPERATIONS
When the cruise control is out of operation, the safety valve and vent valve are open, while the vacuum valve is closed. In this condition, the inside of the actuator is exposed only to the atmospheric pressure, so that the diaphragm does not move.

During constant-speed driving with the main switch on, the safety valve closes and the vacuum valve and vent valve individually open and close to adjust the vacuum in the actuator. According to the vacuum thus adjusted, the diaphragm moves to a certain position, enabling the throttle cam linked with it to keep the corresponding vehicle speed.

The vacuum valve opens to introduce vacuum when it is energized and closes when it is not energized.

The vent valve closes when it is energized to shut off atmospheric pressure and retain the vacuum in the vacuum chamber. When the vent valve is not energized, it opens, allowing the chamber to be exposed to the atmospheric pressure.

The safety valve closes when it is not energized to block the atmospheric pressure from acting on the vacuum chamber. It opens when it is energized.

When cruise control is canceled or when the vehicle is decelerated, the vent valve also opens to quicken deceleration by opening the vacuum chamber to the atmospheric pressure.