Method of providing brake retardation capability safety check. Method includes generating a signal representing vehicle mass, and combining it with an electric brake feedback signal and a brake cylinder pressure signal to generate a signal representing vehicle deceleration rate. Integrating the signal representing vehicle acceleration rate to generate an output signal representative of a process cycle speed reduction value. Inputting and storing values of process cycle speed reduction output signals to and in, respectively, a summation unit. Adding such values inputted to summation unit to a predetermined number of seconds worth of process cycle speed reduction values and generating output signal representative of braking effort available in terms of speed reduction over such predetermined number of seconds. Inputting brake command signal to brake command jerk limiting unit. Adding a delay value to brake command signal and jerk limiting brake command signal to provide output signal having a value equal to deceleration rate request value. Inputting deceleration rate request output signal to minimum capability level determination unit and generating output signal representative of minimum acceptable braking capability level in terms of speed reduction over predetermined number of seconds and comparing braking effort available to minimum acceptable braking capability level and determine whether minimum required safe braking level has been achieved.

An electronically controlled brake system includes a brake actuator wherein a valve is electrically controlled to maintain the spring chamber in the non-actuated position during normal operation. However, should there be a failure in the electrical system, then the spring chamber is allowed to set the brake actuator. The "failure" could also include a diagnostic system included in the control which identifies a failure in control operation. In this way, should there be an electrical failure, either in the control or power circuits, the truck is stopped.

A brake system for off-road vehicles of the type including an operator seat, a brake pedal and a hydraulic brake responsive to operator actuation on the brake pedal. The brake system includes a tank for hydraulic fluid, an electric pump hydraulically connected to the tank, a pressure modulating valve actuated by the brake pedal and a flow control valve for controlling the flow of pressurized hydraulic fluid between the pump, pressure modulating valve and brake. During normal braking operation, a switch responsive to operator actuation of the brake pedal causes to provide pressurized hydraulic fluid to the brake through the flow control valve. The return flow of pressurized fluid to the tank is modulated by the pressure modulating valve in response to operator actuation of the brake pedal to control the braking pressure. The flow control valve is responsive to the presence of an operator in the operator compartment, and is coupled to a switch. In the event an unoccupied seat condition is sensed, the switch actuates the pump, and the flow control valve is switched to a flow path which routes all the pressurized fluid to the brake. The brake is thereby automatically actuated when an unoccupied seat condition is sensed. The pressure modulating valve also includes a secondary fail-safe chamber which is actuated by the brake pedal to supply hydraulic fluid to the brake during a fail-safe mode when the pump is not operating.

A hydraulic braking system for a towed vehicle provides actuation of the hydraulic pump motor of the towed vehicle responsive to an electrical switch which is closed upon application of the brake pedal of the towing vehicle. However, even after actuation of the hydraulic pump, the towed vehicle brakes are only able to be applied in response to sensed relative movement of the towing and towed vehicle toward each other. A break-away switch sets the trailer brakes in the event of accidental separation of the towed vehicle from the towing vehicle. The control valve may be used in other situations to control a hydraulic pump and associated hydraulic braking system.