Vehicle creep control in a hybrid electric vehicle

In a vehicle powertrain, an engine including a crankshaft, a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and electric generator, a transmission including an input clutch driveably connected to the crankshaft and an output driveably connected to a first set of wheels, a second machine able to operate as an electric motor and driveably connected to a second set of wheels, and an electric storage battery having a variable state of charge and electrically connected to the first machine and second machines, a method for controlling vehicle creep, comprising the steps of:

• (a) using the second machine to produce torque and drive the second set of wheels after vehicle creep control begins;
• (b) adjusting a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during a vehicle creep condition;
• (c) determining a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed;
• (d) using the magnitude of input clutch torque capacity and the desired change in torque produced by the first machine to determine a desired magnitude first machine torque;
• and
• (e) decreasing torque produced by the second machine and using the first machine to produce said desired magnitude of first machine torque and the engine to drive the first set of wheels during the vehicle creep condition.

A system for controlling a powertrain during a vehicle creep condition comprising:

• wheels for driving the vehicle;
• an engine including a crankshaft;
• a machine driveably connected to the crankshaft and able to operate alternately as an electric motor and an electric generator;
• a transmission including an input clutch driveably connected to the crankshaft, and an output driveably connected to the wheels;
• an electric storage battery having a variable state of charge and electrically connected to the machine;
• and
• a controller configured to use a crankshaft speed error to determine a change in electric machine torque that would produce a desired crankshaft idle speed, to use a desired magnitude of input clutch torque capacity and said change in electric machine torque to determine a desired magnitude of electric machine torque, and to cause the desired electric machine torque to drive the vehicle.

A system for controlling a powertrain during a vehicle creep condition comprising:

• first and second sets of wheels for driving the vehicle;
• an engine including a crankshaft;
• a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and an electric generator;
• a transmission including an input clutch driveably connected to the crankshaft, and an output driveably connected to the first set of wheels;
• a second machine able to operate as an electric motor and driveably connected to the second set of wheels;
• an electric storage battery having a variable state of charge and electrically connected to the machines;
• and
• a controller configured to use the second machine to produce torque and drive the second set of wheels after vehicle creep condition begins;
• to adjust a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during the a vehicle creep condition;
• to determine a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed;
• to use the magnitude of input clutch torque capacity and the desired change in torque produced by the machine to determine a desired magnitude machine torque;
• to decrease torque produced by the second machine, and to use the first machine to produce said desired magnitude of first machine torque and the engine to drive the first set of wheels during the vehicle creep condition.

In a vehicle powertrain, an engine including a crankshaft, a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and electric generator, a transmission including an input clutch driveably connected to the crankshaft and an output driveably connected to a first set of wheels, a second machine able to operate as an electric motor and driveably connected to a second set of wheels, and an electric storage battery having a variable state of charge and electrically connected to the first machine, a method for controlling vehicle creep, comprising the steps of:

• (a) using the second machine to produce torque and drive the second set of wheels after vehicle creep control begins;
• (b) adjusting a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during a vehicle creep condition;
• (c) determining a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed;
• (d) using the magnitude of input clutch torque capacity and the desired change in torque produced by the first machine to determine a desired magnitude first machine torque;
• and
• (e) decreasing the torque capacity of the input clutch, decreasing the torque produced by the first machine, and increasing torque produced by the second machine to drive the vehicle wheels during the vehicle creep condition.