Vehicle condition dependent supplemental parking brake system with protection against an unwanted application

1. A brake system for a vehicle comprising:

at least one source of pressurized air for pressurizing the vehicle brake system;

a brake actuator configured to receive air from the source of pressurized air;

a control operatively associated with the source of pressurized air for selective application of the brake actuator; and

a supplemental parking brake control system in communication with the control and the brake actuator, the control system:

including a plurality of inputs, individual inputs indicative of a predetermined vehicle condition, the vehicle conditions including (i) a parking condition of the vehicle, (ii) a gradient of a road on which the vehicle is to be held stationary, (iii) a speed of the vehicle and (iv) a state of a vehicle ignition;

responsive to data indicative of gradient and speed vehicle conditions;

configured to send a signal to the brake actuator to allow gradient and speed dependent supplemental parking; and

configured to prevent application of the brake actuator.

2. The brake system of claim 1 , wherein the plurality of inputs includes a parking indicator switch in communication with the control and responsive to data indicative of the control being actuated for a vehicle park condition.

3. The brake system of claim 2 , wherein the parking indicator switch is selectively actuated when a pressure of the brake system is reduced to a predetermined trip brake system pressure.

4. The brake system of claim 1 , wherein the plurality of inputs includes an incline indicator switch responsive to data indicative of gradient, the incline indicator switch being selectively actuated on gradients greater than about 20%.

5. The brake system of claim 4 , wherein the plurality of inputs includes an override switch configured to override the incline indicator switch for verification of brake actuator operation.

6. The brake system of claim 1 , wherein the plurality of inputs includes a speed enable switch responsive to data indicative of vehicle speed, the speed enable switch selectively actuated at vehicle speeds less than about 3 mph.

7. The brake system of claim 1 , wherein the plurality of inputs includes a vehicle ignition switch responsive to data indicative of a state of the vehicle ignition, the vehicle ignition switch being actuated when the vehicle ignition is on.

8. The brake system of claim 1 , further including a solenoid valve operatively associated with the control system, the solenoid valve being responsive to the signal from the control system to prevent actuation of the brake actuator by the control if all vehicle conditions are not met.

9. The brake system of claim 1 , wherein the brake actuator is one of a spring brake actuator and a dual diaphragm lock actuator.

10. The brake system of claim 9 , further including at least one inversion valve for monitoring brake system pressure and delivering a pneumatic brake signal to the dual diaphragm lock actuator.

11. A supplemental brake system for a front pneumatic brake circuit of a vehicle, the front pneumatic brake circuit including a source of pressurized air for pressurizing the brake circuit, a front pneumatic brake actuator configured to receive air from the source of pressurized air, and a control in communication with the source of pressurized air and configured to send a pneumatic signal to the front pneumatic brake actuator to exhaust pressurized air to atmosphere to actuate the front pneumatic brake actuator, the brake control system comprising:

a valve in communication with the control and the front pneumatic brake actuator, the valve having a normally open state for preventing actuation of the front pneumatic brake actuator and a closed state to actuate the front pneumatic brake actuator; and

a plurality of switches in communication with the control and the valve, individual switches responsive to data indicative of a vehicle condition, wherein the vehicle conditions include (i) a parking condition of the vehicle, (ii) a gradient of a road on which the vehicle is to be held stationary, (iii) a speed of the vehicle and (iv) a state of a vehicle ignitions each switch being actuated once its respective vehicle condition is met,

wherein the valve is in the open state and the front pneumatic brake actuator remains released when all switches are not actuated and all vehicle conditions are not met, wherein actuation of each switch sends a signal to the valve to move to the closed state and actuate the front pneumatic brake actuator.

12. The brake system of claim 11 , wherein the plurality of switches includes: a parking indicator switch selectively actuated by a vehicle park condition; an incline indicator switch selectively actuated on gradients greater than a threshold gradient; a speed enable switch selectively actuated at vehicle speeds less than threshold vehicle speed; and a vehicle ignition switch selectively actuated by a state of the vehicle ignition.

13. The brake system of claim 12 , wherein the threshold gradient is greater than about 20% and the threshold vehicle speed is less than about 3 mph.

14. The brake system of claim 12 , wherein the plurality of switches further includes a momentary override switch configured to override the incline indicator switch for verification of front pneumatic brake actuator operation.

15. A method of providing supplemental front parking for a vehicle, the method comprising the steps of: providing air pressure to a front parking brake actuator; activating the front parking brake actuator as a function of vehicle gradient and vehicle speed conditions; and activating the front parking brake actuator if the gradient is greater than about 20% and the vehicle speed is less than about 3 mph.

16. The method of claim 15 , further comprising activating the front parking brake actuator if the vehicle ignition is on and a vehicle park condition is met.

17. The method of claim 16 , further comprising providing a valve in communication with the front parking brake actuator, and selectively actuating the valve to activate the front parking brake actuator if all vehicle conditions are met.