SYSTEM AND METHOD FOR CONTROLLING A POWERTRAIN SYSTEM TO PERFORM EXHAUST BRAKING

1 . A system comprising:

an exhaust braking enabling module that selectively enables exhaust braking based on driver input and independent of an accelerator pedal position;

a driver torque module that selectively determines a driver torque request based on a powertrain braking torque capacity when exhaust braking is enabled; and

an engine actuator control module that controls fuel delivery to cylinders of an engine and a vane position of a turbocharger based on the driver torque request.

2 . The system of claim 1 further comprising a zero pedal torque module that determines a zero pedal torque based on the powertrain braking torque capacity, wherein the driver torque module selectively determines the driver torque request based on the zero pedal torque when the accelerator pedal position is greater than zero.

3 . The system of claim 2 wherein the driver torque module:

determines a pedal torque request based on the accelerator pedal position; and

determines the driver torque request based on the zero pedal torque when the accelerator pedal position is greater than zero and the pedal torque request is less than a first torque required to prevent a decrease in vehicle speed when traveling on a flat grade.

4 . The system of claim 3 wherein the driver torque module sets the driver torque request equal to the pedal torque request when the pedal torque request is greater than or equal to the first torque.

5 . The system of claim 1 further comprising an exhaust braking availability module that determines whether exhaust braking is available based on at least one of a transmission state, a transmission fault, an engine coolant temperature, and an exhaust braking hardware fault, wherein the exhaust braking enabling module does not enable exhaust braking when exhaust braking is not available.

6 . The system of claim 1 further comprising a braking torque capacity module that determines the powertrain braking torque capacity based on an amount of braking torque produced by the engine when fuel delivery to the cylinders of the engine is cutoff and the vane position of the turbocharger is adjusted to yield a predetermined exhaust braking torque.

7 . The system of claim 1 further comprising a transmission control module that adjusts a shift schedule of a transmission when exhaust braking is enabled to increase engine speed and thereby increase a braking torque produced by exhaust braking.

8 . The system of claim 7 wherein the transmission control module downshifts the transmission when fuel delivery to the cylinders of the engine is cutoff, the vane position of the turbocharger is adjusted to yield a predetermined exhaust braking torque, and vehicle speed is at least one of increasing and greater than a cruise control set speed.

9 . The system of claim 8 wherein the transmission control module:

predicts an axle torque capacity after the transmission is upshifted to a higher gear; and

upshifts the transmission to the higher gear when conditions for downshifting the transmission are not satisfied and a present axle torque is within the predicted axle torque capacity.

10 . The system of claim 1 wherein the engine actuator control module stops fuel delivery to the cylinders of the engine when exhaust braking is enabled.

11 . A method comprising:

selectively enabling exhaust braking based on driver input and independent of an accelerator pedal position;

selectively determining a driver torque request based on a powertrain braking torque capacity when exhaust braking is enabled; and

controlling fuel delivery to cylinders of an engine and a vane position of a turbocharger based on the driver torque request.

12 . The method of claim 11 further comprising:

determining a zero pedal torque based on the powertrain braking torque capacity; and

selectively determining the driver torque request based on the zero pedal torque when the accelerator pedal position is greater than zero.

13 . The method of claim 12 further comprising:

determining a pedal torque request based on the accelerator pedal position; and

determining the driver torque request based on the zero pedal torque when the accelerator pedal position is greater than zero and the pedal torque request is less than a first torque required to prevent a decrease in vehicle speed when traveling on a flat grade.

14 . The method of claim 13 further comprising setting the driver torque request equal to the pedal torque request when the pedal torque request is greater than or equal to the first torque.

15 . The method of claim 11 further comprising:

determining whether exhaust braking is available based on at least one of a transmission state, a transmission fault, an engine coolant temperature, and an exhaust braking hardware fault; and

not enabling exhaust braking when exhaust braking is not available.

16 . The method of claim 11 further comprising determining the powertrain braking torque capacity based on an amount of braking torque produced by the engine when fuel delivery to the cylinders of the engine is cutoff and the vane position of the turbocharger is adjusted to yield a predetermined exhaust braking torque.

17 . The method of claim 11 further comprising adjusting a shift schedule of a transmission when exhaust braking is enabled to increase engine speed and thereby increase a braking torque produced by exhaust braking.

18 . The method of claim 17 further comprising downshifting the transmission when fuel delivery to the cylinders of the engine is cutoff, the vane position of the turbocharger is adjusted to yield a predetermined exhaust braking torque, and vehicle speed is at least one of increasing and greater than a cruise control set speed.

19 . The method of claim 18 further comprising:

predicting an axle torque capacity after the transmission is upshifted to a higher gear; and

upshifting the transmission to the higher gear when conditions for downshifting the transmission are not satisfied and a present axle torque is within the predicted axle torque capacity.

20 . The method of claim 11 further comprising stopping fuel delivery to the cylinders of the engine when exhaust braking is enabled.