Engine torque estimation systems and methods

1. An engine control system for a vehicle, comprising:

a coefficients determination module that determines first and second torque estimation coefficients that are set based on a braking torque versus air per cylinder (APC) line, and that determines third, fourth, and fifth torque estimation coefficients that are set based on a maximum braking torque (MBT) spark timing versus APC line; and

a braking torque estimation module that estimates a braking torque of an engine based on APC, spark timing, and the first, second, third, fourth, and fifth torque estimation coefficients.

2. The engine control system of claim 1 wherein the braking torque estimation module estimates the braking torque using the equation:

T=a 1 +( a 2 +a 3 *θ+a 4 *θ 2 )*β+ a 5 *θ*β 2 ,

where T is the braking torque, θ corresponds to the spark timing, β corresponds to the APC, a 1 is the first torque estimation coefficient, a 2 is the second torque estimation coefficient, a 3 is the third torque estimation coefficient, a 4 is the fourth torque estimation coefficient, and a 5 is the fifth torque estimation coefficient.

3. The engine control system of claim 2 wherein the first torque estimation coefficient corresponds to a zero intercept of the braking torque versus APC line with a torque axis,

wherein the second torque estimation coefficient corresponds to a slope of the braking torque versus APC line,

wherein the third and fourth torque estimation coefficients are determined based on an intercept of the MBT spark timing versus APC line with an MBT spark timing axis, and

wherein the fourth and fifth torque estimation coefficients are determined based on a slope of the MBT spark timing versus APC line.

4. A torque estimation coefficients calibration system comprising:

the engine control system of claim 1 ; and

a coefficients setting module that sets the first torque estimation coefficient based on an intercept of a braking torque versus APC line with a torque axis, that sets the second torque estimation coefficient based on a slope of a braking torque versus APC line, that sets the third and fourth torque estimation coefficients based on an intercept of a maximum braking torque (MBT) versus APC line with an MBT axis, and that sets the fourth and fifth torque estimation coefficients based on a slope of the MBT versus APC line.

5. An engine control system for a vehicle, comprising:

a coefficients determination module that determines first, second, third, fourth, and fifth torque estimation coefficients; and

a braking torque estimation module that estimates a braking torque of an engine based on air per cylinder (APC), spark timing, and only the first, second, third, fourth, and fifth torque estimation coefficients.

6. The engine control system of claim 5 wherein the braking torque estimation module estimates the braking torque using the equation:

T=a 1 +( a 2 +a 3 *θ+a 4 *θ 2 )*β+ a 5 *θ*β 2 ,

where T is the braking torque, θ corresponds to the spark timing, β corresponds to the APC, a 1 is the first torque estimation coefficient, a 2 is the second torque estimation coefficient, a 3 is the third torque estimation coefficient, a 4 is the fourth torque estimation coefficient, and a 5 is the fifth torque estimation coefficient.

7. The engine control system of claim 5 further comprising an actuation module that controls at least one engine actuator based on the braking torque.

8. The engine control system of claim 5 wherein the first torque estimation coefficient is determined based on a zero intercept of a braking torque versus APC line with a torque axis.

9. The engine control system of claim 5 wherein the second torque estimation coefficient is determined based on a slope of an intercept of a braking torque versus APC line.

10. The engine control system of claim 5 wherein the third and fourth torque estimation coefficients are determined based on a zero intercept of a maximum braking torque (MBT) spark timing versus APC line with an MBT spark timing axis.

11. The engine control system of claim 5 wherein the fourth and fifth torque estimation coefficients are determined based on a slope of a maximum braking torque (MBT) spark timing versus APC line.

12. The engine control system of claim 5 wherein the coefficients determination module determines the first, second, third, fourth, and fifth torque estimation coefficients based on engine speed and intake and exhaust camshaft angles.

13. The engine control system of claim 12 wherein the coefficients determination module determines the first, second, third, fourth, and fifth torque estimation coefficients based only on the engine speed when the engine speed is greater than a predetermined speed.

14. An engine control method comprising:

determining first and second torque estimation coefficients that are set based on a braking torque versus air per cylinder (APC) line;

determining third, fourth, and fifth torque estimation coefficients that are set based on a maximum braking torque (MBT) spark timing versus APC line;

estimating a braking torque of an engine based on APC, spark timing, and the first, second, third, fourth, and fifth torque estimation coefficients; and

controlling at least one engine actuator based on the braking torque.

15. The engine control method of claim 14 further comprising estimating the braking torque using the equation:

T=a 1 +( a 2 +a 3 *θ+a 4 *θ 2 )*β +a 5 *θ*β 2 ,

where T is the braking torque, θ corresponds to the spark timing, β corresponds to the APC, a 1 is the first torque estimation coefficient, a 2 is the second torque estimation coefficient, a 3 is the third torque estimation coefficient, a 4 is the fourth torque estimation coefficient, and a 5 is the fifth torque estimation coefficient.

16. The engine control method of claim 15 further comprising:

setting the first torque estimation coefficient based on a zero intercept of the braking torque versus APC line with a torque axis;

setting the second torque estimation coefficient based on a slope of the braking torque versus APC line;

setting the third and fourth torque estimation coefficients based on an intercept of the MBT spark timing versus APC line with an MBT spark timing axis; and

setting the fourth and fifth torque estimation coefficients based on a slope of the MBT spark timing versus APC line.

17. The engine control method of claim 14 further comprising setting the first, second, third, fourth, and fifth torque estimation coefficients further based on engine speed and intake and exhaust camshaft angles.

18. The engine control method of claim 17 further comprising setting the first, second, third, fourth, and fifth torque estimation coefficients based only on the engine speed when the engine speed is greater than a predetermined speed.