System constraints method of controlling operation of an electro-mechanical transmission with two external input torque ranges

1. A method for controlling an electro-mechanical transmission operatively coupled to first and second electric machines to transmit power to an output member, the method comprising:

determining motor torque constraints for the first and second electric machines;

determining battery power constraints for an electrical energy storage device electrically connected to the first and second electric machines;

determining a range for a first torque input to the electro-mechanical transmission;

determining a range for a second torque input to the electro-mechanical transmission;

determining a preferred output torque to the output member of the electro-mechanical transmission that is achievable within the motor torque constraints, is achievable within the range for the first torque input, is achievable within the range for the second torque input, and is based upon the battery power constraints; and

controlling operation of the electro-mechanical transmission and the first and second electric machines to achieve the preferred output torque to the output member of the electro-mechanical transmission;

wherein determining the preferred output torque comprises:

formulating mathematical equations representing the motor torque constraints comprising maximum and minimum motor torque constraints for the first and second electric machines;

formulating mathematical equations representing maximum and minimum battery power constraints;

formulating a mathematical equation representing the output torque;

formulating mathematical equations representing the range for the first torque input;

formulating mathematical equations representing the range for the second torque input;

transforming the mathematical equations representing the maximum and minimum battery power constraints to equations of concentric circles having respective radii;

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

transforming the mathematical equations representing the range for the first torque input to equations comprising lines;

transforming the mathematical equations representing the range for the second torque input to equations comprising lines;

transforming the mathematical equation representing the output torque to an equation comprising a line;

determining at least one transformed achievable output torque based upon the transformed mathematical equations representing the maximum and minimum motor torque constraints for the first and second electric machines, the maximum and minimum battery power constraints, the range for the first torque input and the range for the second torque input;

determining a transformed achievable maximum output torque corresponding to the at least one transformed achievable output torque; and

retransforming the transformed achievable maximum output torque as the preferred output torque to the output member.

2. The method of claim 1 , wherein the preferred output torque comprises a maximum tractive torque to the output member.

3. The method of claim 1 , wherein the preferred output torque comprises a maximum braking torque to the output member.

4. The method of claim 1 , wherein the first torque input comprises an engine input torque.

5. The method of claim 4 , wherein the second torque input comprises a torque for an applied clutch.

6. The method of claim 1 , wherein controlling operation of the electro-mechanical transmission and the first and second electric machines to achieve the preferred output torque to the output member of the electro-mechanical transmission comprises controlling operation of the electro-mechanical transmission and the first and second electric machines to achieve the preferred output torque at the output member that is achievable within the motor torque constraints, is achievable within the range for the first torque input, is achievable within the range for the second torque input, and is based upon the battery power constraints.

7. The method of claim 1 , wherein the preferred output torque comprises a commanded output torque to the output member to achieve an operator torque request.

8. The method of claim 1 , wherein the battery power constraint comprises a maximum battery discharging power and a maximum battery charging power.

9. The method of claim 1 , further comprising:

determining an initially achievable first torque point achievable within the motor torque constraints, achievable within the range for the first torque input, and based upon the battery power constraints;

determining an initially achievable second torque point achievable within the motor torque constraints, achievable within the range for the second torque input, and based upon the battery power constraints; and

selecting the preferred output torque to the output member based upon the initially achievable first torque point and the initially achievable second torque point.

10. The method of claim 1 , further comprising:

using the transformed achievable maximum output torque to determine preferred motor torques for the first and second electric machines.

11. The method of claim 1 , wherein determining the transformed achievable maximum output torque corresponding to the at least one transformed achievable output torque comprises calculating at least one intersection of the transformed mathematical equations representing the maximum and minimum battery power constraints, the transformed mathematical equations representing the maximum and minimum motor torque constraints for the first and second electric machines, the transformed mathematical equation representing the first and second torque inputs, and the transformed mathematical equation representing the output torque.

12. A method for controlling an electro-mechanical transmission operatively coupled to first and second electric machines to transmit mechanical power to an output member, the method comprising:

determining motor torque constraints for the first and second electric machines;

determining battery power constraints for an electrical energy storage device electrically connected to the first and second electric machines;

determining a range for a first torque input to the electro-mechanical transmission;

determining a range for a second torque input to the electro-mechanical transmission;

formulating mathematical equations representing the motor torque constraints for the first and second electric machines, the battery power constraints, the output torque, the range for the first torque input, and the range for the second torque input;

transforming the mathematical equations representing the battery power constraints to equations of concentric circles having respective radii and transforming the mathematical equations representing the motor torque constraints for the first and second electric machines, the output torque, the range for the first torque input, and the range for the second torque input to equations comprising lines;

simultaneously solving the said transformed mathematical equations to determine at least one transformed achievable output torque; and

retransforming the transformed achievable output torque to determine a preferred output torque to the output member of the electro-mechanical transmission that is achievable within the motor torque constraints, is achievable within the range for the first torque input, is achievable within the range for the second torque input, and is based upon the battery power constraints.