System and method for using a pneumatic line as a backup communication channel for first and second park brake controllers

1 . A park brake system comprising:

a first park brake controller; and

a second park brake controller;

wherein the first park brake controller is configured to selectively alter air pressure in an air line of a vehicle to pneumatically communicate a message to the second park brake controller after a loss of electronic communication with the second park brake controller.

2 . The park brake system of claim 1 , further comprising:

at least one pressure sensor coupled with the second park brake controller and configured to detect air pressure in the air line;

wherein the second park brake controller is configured to recognize changes in detected air pressure in the air line as the message.

3 . The park brake system of claim 1 , further comprising:

at least one pressure sensor coupled with the first park brake controller and configured to detect air pressure in the air line;

wherein:

the second park brake controller is configured to selectively alter air pressure in the air line to pneumatically communicate a second message to the first park brake controller; and

the first park brake controller is configured to recognize changes in detected air pressure in the air line as the second message.

4 . The park brake system of claim 1 , wherein:

the second park brake controller is configured to attempt to park the vehicle in response to the second park brake controller detecting the loss of electronic communication; and

the first park brake controller is further configured to pneumatically communicate the message in response to the second park brake controller not being able to park the vehicle after an amount of time after the first park brake controller detects the loss of electronic communication.

5 . The park brake system of claim 4 , wherein the amount of time is based on a speed of the vehicle.

6 . The park brake system of claim 5 , wherein the amount of time is also based on a time constant.

7 . The park brake system of claim 4 , wherein the first park brake controller is further configured to park the vehicle in response to the vehicle not being parked after a second amount of time after the first park brake controller pneumatically communicates the message.

8 . The park brake system of claim 1 , wherein:

the first park brake controller is configured to control a first valve configured to control a supply of air to a park brake of the vehicle; and

the second park brake controller is configured to control a second valve configured to control a supply of air to the first valve.

9 . The park brake system of claim 1 , further comprising:

a first set of pressure sensors coupled with the first park brake controller; and

a second set of pressure sensors coupled with the second park brake controller;

wherein the first and second sets of pressure sensors are along an air flow to one of a tractor park brake and a trailer park brake.

10 . The park brake system of claim 9 , further comprising an additional set of pressure sensors along an air flow to the other one of the tractor park brake and the trailer park brake.

11 . The park brake system of claim 1 , wherein the first and second park brake controllers are in a single brake circuit.

12 . The park brake system of claim 1 , further comprising:

a controller area network (CAN) configured to facilitate electrical communication between the first and second park brake controllers.

13 . The park brake system of claim 1 , wherein the vehicle is controlled by an automated driving system.

14 . A method comprising:

performing in a park brake system of a vehicle comprising first and second park brake controllers:

with the second park brake controller, attempting to park the vehicle in response to detecting of a loss of electronic communication between the first and second park brake controllers; and

with the first park brake controller:

determining whether the second park brake controller was successful in parking the vehicle prior to a first countdown timer elapsing; and

in response to determining that the second park brake controller was not successful in parking the vehicle prior to the first countdown timer elapsing, pneumatically communicating a message to the second park brake controller to indicate that a second countdown timer has started.

15 . The method of claim 14 , further comprising:

with the first park brake controller:

determining whether the second park brake controller was successful in parking the vehicle prior to the second countdown timer elapsing; and

in response to determining that second park brake controller was not successful in parking the vehicle prior to the second countdown timer elapsing, executing a first park brake controller exhaust control strategy.

16 . The method of claim 14 , wherein the message is pneumatically communicated by selectively altering air pressure in an air line comprising a pressure sensor coupled with the second park brake controller.

17 . The method of claim 14 , wherein the first countdown timer is based on a speed of the vehicle.

18 . The method of claim 17 , wherein the first countdown timer is also based on a time constant.

19 . The method of claim 14 , further comprising:

detecting the loss of electronic communication by detecting a lack of messages received over a controller area network (CAN).

20 . A park brake system comprising:

a first park brake controller;

a second park brake controller; and

means for selectively altering air pressure in an air line of a vehicle to pneumatically communicate a message to the second park brake controller after a loss of electronic communication with the second park brake controller.