Abstract: In accordance with one aspect of the present invention, an apparatus is provided for a vehicle equipped with a drive system and a controller for regulating the operating speed of the drive system. The apparatus includes at least one sensor for sensing a vehicle parameter and producing a parameter signal in response to the sensed parameter. A diagnostic device is provided for receiving the parameter signal, processing the parameter signal to detect the presence of an undesirable operating condition; determining the severity of the undesirable operating condition in accordance with a preselected strategy and responsively producing a severity level signal. The controller receives the severity level signal and limits the maximum speed of the vehicle in response to the severity level signal, whereby the maximum allowable vehicle speed decreases as the severity level signal increases.

Abstract: A signal valve (38) is connected to a supply conduit (16) connecting a pump (11) with a control valve (14) for transmitting an artificial load signal to a load signal chamber (34) of a pressure compensated unloader valve (27) when the control valve is at an operating position and the pressure in the supply conduit (16) is below a preselected value. This moves a valve member (31) of the unloader valve (27) to a blocking position causing essentially full pump flow to be directed to the hydraulic jack for decreasing the response time in situations wherein the hydraulic jack has cavitated and no positive load pressure signal is present.