Schematic Diagram - Electric Hydraulic Actuation
| ITEM | DESCRIPTION |
|---|---|
| A | Working pressure |
| B | Atmospheric pressure |
| 1 | Multiplate clutch |
| 2 | Pressure Relief Valve (PRV) |
| 3 | Pressure regulating valves closed in the electric hydraulic pump |
| 4 | Electric hydraulic pump |
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.