Method and apparatus for controlling a multi-mode powertrain system

1. A method for operating a powertrain system including a multi-mode transmission configured to transfer torque among an engine, torque machine, and a driveline, the method comprising:

controlling operation of the powertrain system in a pseudo-gear range in response to an output torque request including operating the transmission in a variable mode transmission range and controlling a magnitude of torque output to the driveline in response to an output torque request and in proportion to a magnitude of input torque from the engine;

wherein controlling operation in a pseudo-gear range further comprises determining a preferred engine speed and a preferred clutch slip speed for a torque transfer clutch of the transmission in response to the output torque request.

2. The method of claim 1 , wherein determining the preferred engine speed and the preferred clutch slip speed for a torque transfer clutch of the transmission comprises:

for each of a plurality of candidate engine speeds and candidate clutch slip speeds, employing a system torque determination scheme for operating the powertrain system in the pseudo-gear range in response to the output torque request, and employing a cost model to calculate a respective candidate cost; and

identifying the preferred engine speed and the preferred clutch slip speed comprising the candidate engine speed and the candidate clutch slip speed associated with a minimum of the candidate costs.

3. The method of claim 2 , wherein employing the system torque determination scheme for operating the powertrain system in the pseudo-gear range comprises determining a preferred powertrain operating point including motor torque commands for the torque machines to achieve the output torque request in response to the candidate engine speed and the candidate clutch slip speed when operating in the pseudo-gear range based upon powertrain system operating parameters.

4. The method of claim 3 , wherein employing the cost model to calculate the respective candidate cost comprises:

employing the system torque determination scheme for operating the powertrain system in the pseudo-gear range in response to the output torque request to determine an optimized candidate powertrain operating point; and

employing a power cost function to determine a candidate cost for operating the powertrain at the optimized candidate powertrain operating point.