Diagnostic brake system warning circuit

A warning circuit for a vehicle with a brake system and with an engine which may be actuated by first switch, the brake system having primary and auxiliary sources of brake actuation fluid pressure, sensor means for sensing the operation of the primary source and relay means operatively connected to the sensor means, to the auxiliary source and to a second switch actuated by an operator brake application, said relay means energizing the auxiliary source in response to the actuation of at least one of said first and second switches unless the primary source is operating, the warning circuit comprising:

• a first gate having inputs coupling with said first switch and second switch, the first gate generating an output signal when the switch means are in selected states;
• a bistable device with a set input coupled to the output of the first gate and with a reset input coupled to the output of the first gate and coupled with a terminal common to the relay means and the auxiliary source, the bistable device having an output with a first state triggered by the output signal of the first gate and with a second state triggered by a state of the auxiliary source;
• and
• a second gate having a first input coupled to the output of the bistable device and having a second input for coupling with the terminal, the second gate generating a warning signal at an output thereof when the output of the bistable device and the auxiliary source are in selected states.

A diagnostic and control circuit for a brake system of an engine-driven vehicle including at least one pressure actuated brake, a primary source of brake actuation pressure, and an auxiliary source of brake actuation pressure, said circuit comprising:

• means for sensing the actuation of the brake and for generating a brake actuation signal indicative thereof;
• means for sensing the operation of the engine and for generating an engine operating signal indicative thereof;
• means for sensing the operational state of the primary source and for generating a primary source signal;
• means, responsive to said primary source signal, said engine-operating signal, and said brake actuation signal, for actuating said secondary source whenever said brake actuation signal indicates said brake has been actuated, or whenever said engine-operating signal indicates operation of the engine, and said primary source signal indicates said primary source is not actuated;
• and
• means, responsive to the actuation of the secondary source, for indicating said secondary source has been actuated.

A warning circuit for a vehicle with an engine and a brake system, the vehicle having first switch means for actuating the engine, the brake system having primary and auxiliary sources of brake actuation pressure, sensor means for sensing the operation of the primary source, relay means operatively connected to the sensor means and to the auxiliary source for energizing the auxiliary source, and second switch means for actuating the relay means in response to an operator brake application, the warning circuit comprising:

• means for actuating the relay means to energize the auxiliary source in response to actuation of either one of the switch means upon failure of the primary source;
• the actuating means includes an OR gate with a first input for coupling with the first switch means and with a second input for coupling with the second switch means, the OR gate having output means for coupling with the relay means and for actuating the relay means when either of the switch means is actuated;
• means for coupling a first terminal of the relay means with the output means of the OR gate;
• and
• means for coupling a second terminal of the relay means with a ground potential through the sensor means, the sensor means being capable of uncoupling the second terminal from the ground potential to prevent actuation of the relay means upon operation of the primary source.

A warning circuit for a vehicle with a brake system and with an engine which may be actuated by first switch means, the brake system having an engine driven primary source and an auxiliary source of brake actuation pressure, sensor means for sensing the operation of the primary source, second switch means responsive to an operator brake application, and relay means operatively connected to the sensor means, to the auxiliary source and to the second switch means for energizing the auxiliary source in response to the actuation of either one of the switch means unless the primary source is operating, the warning circuit comprising:

• means for actuating a first warning device in response to selected states of said first and second switch means and of the primary and auxiliary sources;
• means for actuating a second warning device in response to predetermined states of said first and second switch means and of the primary and auxiliary source, at least one of the selected states being distinct from the predetermined states;
• and
• wherein one of the warning devices comprises a first terminal connected with one of the switch means and a second terminal for coupling with the warning circuit;
• and wherein the warning circuit comprises means for coupling the second terminal with a ground potential through the sensor means, the sensor means coupling the second terminal with the ground potential in response to operation of the primary source so that the one warning device may be actuated when the one switch means is actuated.