Electrical override arrangements, for example for vehicle speed control systems

摘要

A vehicle speed control system is disclosed where the vehicle speed is automatically controlled by an electro-pneumatic actuator subjected to the controlled application of sub-atmospheric pressure. A dump valve is normally held closed by an energized electrical coil but opens when the coil is de-energized and connects the actuator to atmosphere and shuts off the control system. The coil is connected to an electrical power source through a disabling switch which is intended to be opened automatically when the driver operates the vehicle brakes and thus overrides the control system. To ensure that the override is effective even if the disabling switch fails to open, a brake-pedal operated switch connects one end of the coil to the same terminal of the power supply as is connected to the other end of the coil by the disabling switch. Therefore, when the brakes are operated both sides of the coil receive the same potential and the coil is de-energized even if the disabling switch fails to open.