Electronic Cruise Control: Operation
The system uses manifold vacuum to actuate the servo. The amount of vacuum to the servo is controlled by the solenoid valve attached to the servo inline with the vacuum control valve. The solenoid valve constantly modulates vacuum to the servo in response to commands from the electronic control module. The control module receives signals from the engagement and instrument panel switches, electrical brake release switch, and speed sensor. The speed sensor, near the speedometer cable, consists of a light emitting diode and a photo transistor. Power to the diode is supplied when the system is turned on. When the photo transistor is exposed to light from the diode, the transistor generates a signal to the control module. These signals are representative of the cars speed. Input signals received from the sensor by the control module are used to control the solenoid valve which regulates the amount of vacuum supplied to servo. When the brakes are applied, the electrical brake release switch cancels the control module signal to the solenoid valve, thus shutting off the system and venting the vacuum servo. The vacuum brake switch also vents the system vacuum as a second disengagement system.
The control switches operate as follows.- With instrument panel switch set to "CRUISE" and engagement switch fully released, the system is not engaged. Or, if system was previously engaged, the throttle position for the previously desired speed will be maintained. With the engagement switch in the center (detent) position, the solenoid valve regulates the vacuum supplied to the servo to initially set or reset the speed. With the engagement switch fully depressed, the servo is vented to atmosphere. This position is used by the driver when a decrease in speed is desired. If the driver fully depresses the button with no pressure on the accelerator pedal, then releases the button, the car will cruise at the new lower speed. With the instrument panel switch in the "AUTO" position, operation is the same except when the engagement switch is in the center (detent) position. In this position, the driver can engage the system at a given speed. If braking was necessary, partially depressing button will automatically accelerate car, at a controlled rate, until previously set speed is attained. Or, partially depressing the button and holding it will allow an automatically controlled rate of acceleration until the button is released. The car will now cruise at the new speed.