Transfer Case - Project 8: Operation: Notes

The Transfer Case Control Module (TCCM) is electrically connected to the High Speed (HS) Controller Area Network (CAN) chassis systems bus.

The TCCM contains the Intelligent Driveline Dynamics (IDD) software. The IDD system monitors the vehicle behavior, driver input and road surface conditions every 10 milliseconds. The IDD system optimizes torque distribution to deliver maximum traction performance, stability and yaw control.

The IDD system comprises a torque distribution controller based on driver demanded torque, lateral acceleration and vehicle speed. The IDD system is configured to give the desired on-power handling balance. A traction controller responds to slip between the front and rear differentials for maximum traction performance. The system also has an intelligent yaw controller which continuously monitors the yaw behavior of the vehicle. The IDD system responds to on-power oversteer conditions by transferring torque from the rear differential to the front differential to stabilize the vehicle.

The TCCM also features a reactive feedback loop to increase torque to the front differential if traction is lost and slip occurs. The TCCM works in conjunction with the Anti-lock Brake System (ABS) control module.

Torque on demand benefits:

• Full traction capability when required.
• Supports a wide range of vehicle handling characteristics.

For additional information, Refer to: VEHICLE DYNAMIC SUSPENSION - PROJECT 8

Schematic Diagram - Electric Hydraulic Actuation 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The electric hydraulic control provides the Intelligent Driveline Dynamics (IDD) system with pre-emptive and response within 165 milliseconds. The electric hydraulic pump is of the swash plate pump type with centrifugal pressure control and eliminates the need for an accumulator and solenoid valve.

The electric hydraulic pump is powered by an electric motor and consists of:

• A barrel with pistons.
• A pump lid with suction and discharge ports.
• A swash plate and pressure regulating valves.

The rotary motion of the electric motor is converted to linear motion by the angular swash plate. As the barrel rotates, the pistons reciprocate inside the barrel. Hence the transmission fluid from the suction port is delivered to the discharge port, creating transmission fluid flow. As the transmission fluid flow to the multiplate clutch piston increases, the pressure in the multiplate clutch increases.

The transmission fluid pressure from the electric hydraulic pump, is controlled by pressure regulating valves. The pressure regulating valves are located on the circumference of the barrel. The transmission fluid pressure is regulated because of the force balance between the centrifugal force from the arms and the transmission fluid pressure acting on the ball. When the transmission fluid pressure is more than the centrifugal force the valves will open to reduce the transmission fluid pressure. Once the transmission fluid pressure is less than the centrifugal force the valves will close, allowing the transmission fluid pressure to increase. This will be repeated to regulate the transmission fluid pressure from the electric hydraulic pump.

The electric hydraulic pump is controlled by the Transfer Case Control Module (TCCM) and the transmission fluid pressure is regulated by the current to the electric hydraulic pump motor. The transmission fluid pressure output by the electric hydraulic pump depends on the required torque. For example, High Pressure (HP) transmission fluid is delivered under high traction or high slip conditions. While Low Pressure (LP) transmission fluid is provided when making tight curves, for example, to park the vehicle or when driving at high speed.

The TTCM controls the multiplate clutch for optimum All Wheel Drive (AWD) performance, with pre-emptive clutch actuation.

The Pressure Relief Valve (PRV) releases excess transmission fluid pressure by releasing transmission fluid back to the lower transmission fluid reservoir.

All Wheel Drive 

The All Wheel Drive (AWD) operation is as follows:

• The electric hydraulic pump is on.
• The multiplate clutch piston:
  • The transmission fluid pressure from the electric hydraulic pump fills the piston and compresses the multiplate clutch, enabling the transfer of torque from the vehicle's rear differential to the front differential.
  • The transmission fluid pressure is varied by the Transfer Case Control Module (TCCM) to control the amount of torque which is transferred to the front differential.
  • Output to the front differential is via the chain.
• Output to the rear differential is via the output flange rear driveshaft.

Rear Wheel Drive 

The Rear Wheel Drive (RWD) operation is as follows:

• The electric hydraulic pump is OFF.
• The multiplate clutch application piston:
  • No transmission fluid pressure from the electric hydraulic pump and no transmission fluid pressure applied to the multiplate clutch piston.
  • The multiplate clutch is in open state and no torque transfer to the front differential.
  • Vehicle operates in RWD only.
• Output to the rear differential is via the output flange rear driveshaft.