Method for determining constraints on input torque in a hybrid transmission

1. Method for controlling a hybrid transmission including torque machines and an energy storage device connected thereto, the hybrid transmission operative to transfer power between an input member and an output member and the torque machines, wherein a control module performs the following steps comprising:

monitoring operating parameters of the hybrid transmission;

monitoring an operator demand for power;

determining an output torque range to the output member based upon states of the operating parameters of the hybrid transmission;

constraining the output torque range to the output member based upon the operator demand for power;

determining input torque constraints to the input member based upon the constrained output torque range to the output member; and

controlling operation of an engine coupled to the input member based upon the input torque constraints to the input member.

2. The method of claim 1 , further comprising:

determining maximum and minimum power constraints for the energy storage device;

determining maximum and minimum motor torque outputs from the torque machines; and

determining the output torque range to the output member based upon the maximum and minimum power constraints for the energy storage device and the maximum and minimum motor torque outputs from the torque machines.

3. The method of claim 1 , further comprising:

monitor operator inputs to an accelerator pedal and a brake pedal;

determining an immediate accelerator torque request and a net accelerator torque request based upon the operator inputs to the accelerator pedal and the brake pedal; and

constraining the output torque range to the output member based upon the immediate accelerator torque request and a net accelerator torque request.

4. The method of claim 1 , further comprising:

formulating equations representing maximum and minimum motor torque constraints for the first and second torque machines and equations representing maximum and minimum power constraints for the energy storage device;

formulating a parametric equation representing the output torque;

formulating a parametric equation representing a range for a first torque constraint;

formulating a parametric equation representing a range for a second torque constraint;

transforming the equations representing the maximum and minimum power constraints for the energy storage device to equations comprising concentric circles having corresponding radii;

transforming the equations representing the maximum and minimum motor torque constraints for the first and second torque machines to equations comprising lines;

transforming the parametric equation representing the range for the first torque constraint;

transforming the parametric equation representing the range for the second torque constraint;

transforming the parametric equation representing the output torque; and

determining transformed minimum and maximum raw output torques based upon the transformed minimum and maximum motor torque constraints for the first and second torque machines, the transformed maximum and minimum power constraints for the energy storage device, the transformed range for the first torque constraint and the transformed range for the second torque constraint.

5. The method of claim 4 , further comprising simultaneously solving the parametric equations for the transformed minimum and maximum motor torque constraints for the first and second torque machines, the transformed maximum and minimum power constraints for the energy storage device, the transformed range for the first torque constraint and the transformed range for the second torque constraint to determine the transformed minimum and maximum raw output torques.

6. The method of claim 4 , further comprising retransforming the transformed minimum and maximum raw output torques to determine the minimum and maximum raw output torques from the transmission.

7. The method of claim 4 , further comprising:

formulating a first parametric torque equation representing the input torque;

formulating a second parametric torque equation representing the minimum and maximum raw output torques;

formulating a third parametric torque equation representing a range for a second torque constraint;

transforming the first, second, and third parametric equations; and

determining transformed minimum and maximum raw input torques based upon the transformed minimum and maximum motor torque constraints for the first and second torque machines, the transformed maximum and minimum power constraints for the energy storage device, the transformed range for the minimum and maximum raw output torques and the transformed range for the second torque constraint.

8. The method of claim 7 , further comprising

simultaneously solving the parametric equations for the transformed minimum and maximum motor torque constraints for the first and second torque machines, the transformed maximum and minimum power constraints for the energy storage device, the transformed range for the minimum and maximum raw output torques and the transformed range for the second torque constraint to determine the transformed minimum and maximum raw input torques.

9. The method of claim 7 , further comprising retransforming the transformed minimum and maximum raw input torques to determine the minimum and maximum raw input torques.

10. A method for controlling a powertrain including an engine mechanically coupled to a transmission, the transmission operative in an operating range state to transfer power between the engine and first and second electric machines and an output member by selectively applying torque transfer clutches, the first and second electric machines electrically connected to an electrical energy storage device, wherein a control module performs the following steps comprising:

monitoring operating parameters of the hybrid transmission;

monitoring an operator demand for power;

determining an output torque range to the output member based upon states of the operating parameters of the hybrid transmission;

constraining the output torque range to the output member based upon the operator demand for power;

determining input torque constraints to the input member based upon the constrained range of output torque to the output member;

constraining engine torque based upon the input torque constraints to the input member and the operator demand for power; and

controlling operation of the engine based upon the constrained engine torque.

11. The method of claim 10 , further comprising determining available battery power from the electrical energy storage device and determining maximum and minimum motor torques from the first and second electric machines, and determining the output torque range to the output member based thereon.

12. The method of claim 11 , further comprising:

determining maximum and minimum power constraints for the electrical energy storage device;

determining maximum and minimum motor torques from the first and second electric machines; and

determining the output torque range to the output member based upon the maximum and minimum power constraints for the electrical energy storage device and the maximum and minimum motor torques from the first and second electric machines.

13. Method for controlling a hybrid transmission including first and second torque machines and an energy storage device connected thereto, the hybrid transmission operative to transfer power between an input member and an output member and the first and second torque machines, wherein a control module performs the following steps comprising:

monitoring operating parameters of the hybrid transmission;

monitoring an operator demand for power;

determining an output torque range to the output member based upon states of the operating parameters of the hybrid transmission;

constraining the output torque range to the output member based upon the operator demand for power; and

determining input torque constraints to the input member based upon the constrained range of output torque to the output member.