Speed limiting comfort enhancement

1. A vehicle, comprising:

a vehicle speed detector detecting a vehicle speed;

a brake system; and

a control system:

implementing a control mode including determining a threshold speed;

monitoring the vehicle speed and implementing a control scheme to derive and output an initial brake torque demand to maintain the vehicle speed below the threshold speed; and

applying a rate-limit operator to the initial brake torque demand to derive a rate-limited brake torque demand for output to the brake system.

2. The vehicle of claim 1 , further comprising a steering system, wherein:

the control mode is a backup mode for reversing a trailer further including controlling the steering system to maintain the trailer along a path.

3. The vehicle of claim 1 , wherein the control system includes:

a first controller coupled with the steering system and implementing the backup mode; and

a second controller coupled with the speed detector and the brake system and implementing the control scheme to derive and output the rate-limited brake torque demand to the brake system to maintain the vehicle speed below the threshold speed.

4. The vehicle of claim 3 , wherein the second controller is a proportional-integral controller implementing the control scheme to derive and output the initial brake torque demand.

5. The vehicle of claim 3 , wherein the control scheme is non-linear and uses a zero integral gain if the vehicle speed is below a reference speed that is less than the threshold speed.

6. The vehicle of claim 1 , wherein the rate-limiting operator reduces a ramp up rate of the rate-limited brake torque demand compared to a ramp up rate of the initial brake torque demand.

7. The vehicle of claim 1 , wherein the control system further adjusts the rate-limiting operator on receipt of a selection of a comfort mode.

8. The vehicle of claim 7 , wherein:

the control scheme is a proportional-integral control scheme; and

the control system further adjusts at least one of a proportional gain and an integral gain of the proportional-integral control scheme based on receipt of the selection of the comfort mode.

9. A backup assist system for a vehicle reversing a trailer, comprising:

a steering module;

a brake module;

a vehicle speed detector detecting a vehicle speed; and

a controller:

implementing a backup mode including providing an output to the steering module to maintain the trailer along a path; and

attempting to maintain the vehicle speed below a threshold speed, derived using a parameter of the backup mode, by selectively outputting a rate-limited brake torque demand to the brake module.

10. The system of claim 9 , wherein the controller:

includes a vehicle speed detector;

receives a vehicle speed signal from the vehicle speed detector; and

derives the rate-limited brake torque demand using:

a proportional-integral control scheme with the threshold speed and the vehicle speed signal as inputs and an initial brake torque as an output; and

a rate limiting operator with the initial brake torque as an input and the rate-limited brake torque as an output.

11. The system of claim 10 , wherein the rate limiting operator reduces a ramp up rate of the initial brake torque demand.

12. The system of claim 10 , wherein the controller further filters the threshold speed into the proportional-integral controller.

13. The system of claim 10 , wherein the controller adjusts the rate limiting operator on receipt of a selection of a comfort mode.

14. A method for assisting reversing of a vehicle with a trailer, comprising:

controlling a steering angle of a vehicle steering system to maintain the trailer along a user-selected reversing curvature path;

monitoring a speed of the vehicle; and

attempting to maintain a vehicle speed below a threshold speed, derived based on a parameter used in controlling the steering angle, by selectively outputting a rate-limited brake torque demand to a brake module of the vehicle.

15. The method of claim 14 , wherein the rate-limited brake torque demand is derived using:

a proportional-integral control scheme with the threshold speed and the vehicle speed as inputs and an initial brake torque as an output; and

a rate limiting operator with the initial brake torque as an input and the rate-limited brake torque as an output.

16. The method of claim 15 , further including adjusting the rate limiting operator on receipt of a selection of a comfort mode.