Automatic retarder control system

Claim 1

A retarder system for a vehicular drive train including a transmission gear ratio means having a power input shaft coupled with a prime mover and a power output means for driving the vehicle, comprising a retarder of maximum power absorption capacity having a rotor means coupled for rotation with the power input shaft, the retarder also having an inlet conduit and an outlet conduit, a bypass conduit communicating the retarder inlet and outlet conduits, a heat exchanger in the bypass conduit and including a relief valve for selectively communicating the heat exchangeR with a fluid sump, speed sensing means associated with a rotating part in the drive train, a valve coupled for response to the speed sensing means, the valve being responsive to the speed sensing means for movement to a first power absorption position for communicating the source with the retarder inlet conduit, fluid from the source flowing through the retarder, the heat exchanger and the relief valve included therein, and for movement to another position for communicating the source with the retarder outlet conduit and also for communicating the retarder inlet conduit with a fluid sump in order to substantially bypass the retarder while directing fluid through the heat exchanger and maintaining reduced fluid flow through the retarder for cooling and lubrication, and signal means operatively coupled with the retarder to indicate when its maximum capacity is being employed.