ERAD, Clutch
| 1 | Solenoid | 4 | Return spring |
| 2 | Journal bearing | 5 | Hall sensor |
| 3 | Measuring disc | 6 | Two toothed clutch halves (not illustrated) |
The clutch between electric motor and gearbox is of the dog clutch type and is directly connected to the differential.
The clutch connects the crown wheel with the differential when it is activated. When the clutch is not activated the differential remains still. Only the differential wheels within the differential rotate with the drive shafts.
Mechanical engagement of ERAD
When the car is being powered by the internal combustion engine and the electric motor is engaged (for electric operation or regeneration), the following takes place:
- The electric motor is accelerated to the correct rotation speed.
- The clutch is activated by the solenoid which compresses the dog clutch. When the clutch is activated the differential housing starts to rotate and the drive force is directed to both the drive shafts.
- For smooth engagement of the electric motor, the rotation speed for the freely rotating drive shafts must correspond with the rotation speed from the electric motor. The deviation must not exceed 30 RPM.
- A hall sensor in the gearbox housing registers the measuring disc's axial movement. By means of knowing the position of the clutch, together with the current through the solenoid, IEM can determine that the clutch is activated. When the clutch is engaged the current is decreased to 1.2 A, which is sufficient to keep the clutch closed.
Information about the current wheel speed is sent directly from the wheel speed sensors to VDDM and onward to the IEM control module via Propulsion CAN. IEM controls the electric motor to the correct rotation speed by sending out a 3-phase alternating current. When the electric motor has reached the correct rotation speed, IEM applies 3.2 A to the clutch solenoid via hard-wired control signal to the current control circuit.
The electric motor is mechanically engaged in the following drive modes and speeds:
- Pure, only electric operation up to 125 km/h
- Pure, with engaged internal combustion engine up to till 65 km/h
- Hybrid, up to 65 km/h
- Save, up to 65 km/h
- Off Road, up to 40 km/h
At speeds higher than those specified above, the electric motor is engaged when:
- The driver requests increased torque, for example, when overtaking.
- The driver releases the accelerator pedal (engine brakes) or during active braking.
In addition, the electric motor is always engaged at speeds of up to 175 km/h in the AWD and Power drive modes. The electric motor is disengaged at higher speeds since it has then reached its highest permitted rotation speed.
Engagement of the electric motor takes 150-350 ms, depending on temperature conditions.
Mechanical disengagement of ERAD
On disengagement of electric operation or regeneration, the following takes place:
- When the solenoid that compressed the clutch is deactivated, the clutch is released by means of a disc-shaped Belleville type spring.
- To avoid locking the clutch the electric motor oscillates for a short period of time.
- The hall sensor registers the movement of the measuring disc, now in the opposite direction.
- The electric motor is switched off.
Disengagement of the electric motor takes approx. 500 ms.
Stage 1
- The car is driven with the internal combustion engine as drive source.
- The left-hand part of the clutch rotates freely at the speed of the drive shafts.
- The right-hand part, which is connected to the crown wheel and the differential, remains still.
Stage 2
- The electric motor has accelerated to the speed that corresponds to the speed of the rotating left-hand part.
- Both parts of the clutch have the same speed.
Step 3
- The clutch is activated and the electric motor drives the rear wheels.
- In this position the differential functions as a "normal" differential and the power is routed from the crown wheel and the differential out to the drive shafts.