Vehicle and method for controlling engine start in a vehicle

A method for starting an engine in a hybrid vehicle being driven by an electric machine, the vehicle having a first clutch located between the engine and the starter motor and at least one other clutch disposed between the electric machine and vehicle drive wheels, the at least one other clutch being selectively engageable for facilitating torque transfer between the electric machine and the vehicle drive wheels, the method comprising:

• requesting an engine start when the engine is shutdown and a first clutch connecting the engine to the electric machine is open;
• initiating operation of the starter motor such that torque is transferred from the starter motor to the engine;
• raising the pressure in a first level to a first level, while operating the starter motor, to cause the first clutch to slip such that less than an engine turnover torque is transferred from the electric machine to the engine;
• stopping the starter motor upon detecting engine start;
• fully engaging the first clutch;
• controlling oncoming and offgoing transmission clutches during a downshift according to a predetermined shift schedule, thereby effecting slip between the electric machine and the vehicle drive wheels;
• determining an amount of slip between the electric machine and the vehicle drive wheels;
• continuing to control the on-going and offgoing clutches according to the predetermined shift schedule if the determined slip is above a target slip;
• and
• controlling the on-going and offgoing clutches through a closed loop control around the target slip if the determined slip is not above the target slip.

A hybrid vehicle comprising:

• an engine;
• a starter motor for rotating the engine to facilitate an engine start;
• an electric machine operable to propel the vehicle and to rotate the engine;
• a first clutch disposed between the engine and the electric machine for selectively connecting the engine to the electric machine;
• and
• a control system including at least one controller, the control system being configured to:
• request an engine start when the engine is shutdown and the first clutch is open;
• operate the electric machine;
• initiate operation of the starter motor such that torque is transferred from the starter motor to the engine;
• reduce the pressure of the first clutch to a second level while the starter motor is operating;
• fuel the engine, thereby facilitating torque production by the engine;
• detect engine start;
• stop the starter motor;
• engage the first clutch;
• wherein the control system is further configured to:
• control oncoming and offgoing transmission clutches during a downshift according to a predetermined shift schedule to effect slip between the electric machine and the vehicle drive wheels;
• determine an amount of slip between the electric machine and the vehicle drive wheels;
• continue to control the on-going and offgoing clutches according to the predetermined shift schedule if the determined slip is above a target slip;
• and
• control the on-going and offgoing clutches through a closed loop control around the target slip if the determined slip is not above the target slip.