Engine torque truncation method for a four-wheel drive vehicle

A method for regulating driving torque transfer through a friction clutch in a torque transfer case for a powertrain for a four-wheel drive vehicle;

• the powertrain including an engine, a geared transmission between the engine and the torque transfer case;
• an engine controller and a powertrain controller;
• a primary axle driveshaft connected driveably to torque output elements of the torque transfer case and a secondary axle driveshaft connected to torque output elements at the torque transfer case through the friction clutch;
• the method comprising:
• engaging the friction clutch to effect power transfer from the engine to the secondary axle driveshaft as engine power is delivered to the primary axle driveshaft;
• determining whether driving friction elements of the friction clutch are slipping;
• and
• reducing engine torque until slipping of the driving friction elements of the friction clutch is eliminated;
• the step of reducing engine torque comprising requesting the engine controller to command an initial incremental engine torque reduction;
• determining whether the driving friction elements are slipping following the incremental torque reduction;
• operating the vehicle with reduced engine power when friction element slipping is eliminated;
• and
• requesting the engine controller to command an increased engine torque following the incremental torque reduction when friction element slipping is not present.

A method for regulating driving torque transfer through a friction clutch in a torque transfer case for a powertrain for a four-wheel drive vehicle;

• the powertrain including an engine, a geared transmission between the engine and the torque transfer case;
• an engine controller and a powertrain controller;
• a primary axle driveshaft connected driveably to torque output elements of the torque transfer case and a secondary axle driveshaft connected to torque output elements of the torque transfer case through the friction clutch;
• the method comprising:
• engaging the friction clutch to effect power transfer from the engine to the secondary axle driveshaft as engine power is delivered to the primary axle driveshaft;
• determining whether driving friction elements of the friction clutch are slipping;
• and
• reducing engine torque until slipping of the diving friction elements of the friction clutch is eliminated;
• the step of determining whether the driving friction elements are slipping comprising sensing the speed of the secondary axle driveshaft, sensing the speed of the primary axle driveshaft and comparing the secondary axle driveshaft speed and the primary axle driveshaft speed.