Instead of a servo pump (bladed), like the previous amplifiers, it uses a gear pump, combined into one unit with an electric motor. The gear pump is not driven by the internal combustion engine of the vehicle, but by its own electric motor. The electric motor only works when the ignition is switched on and the vehicle engine is running. The signals of the angular velocity of the steering wheel, vehicle speed and engine speed are sent to the control unit. This block regulates the speed of the armature of the motor/gear pump and therefore the pump capacity/amount of pumped liquid.
Reclosing protection
The electro-hydraulic booster has protection against restarting in case of a malfunction, after a failure or an accident. To remove the restart protection, switch off the ignition and start the engine again. If the electric pump assembly has overheated, it is necessary to wait approximately 15 minutes for it to cool down. If the protection is not removed, despite the elapsed waiting time and restarting the engine, then this indicates a malfunction in the on-board network or the electric pump unit. In this case, it is necessary to run a self-diagnosis and, if a malfunction is found, replace the motor assembly.
Like a conventional hydraulic booster, the hydraulic control unit has a torsion bar, which is connected on one side to a rotating spool, and on the other to a drive gear and a control sleeve.
Rectilinear motion
In straight motion, the torsion bar holds the rotating spool and control sleeve in the neutral position. According to the power steering sensor, the steering wheel does not deviate from the center position. Almost without pressure, the liquid flows through the hydraulic control unit and through the return line to the reservoir. The grooves of the spool and the control sleeve are in a neutral position relative to each other, so that the liquid enters both cavities of the working cylinder and, accordingly, flows down the reverse grooves of the control sleeve back into the reservoir.
Turn left
Due to the deformation of the torsion bar, the rotating spool rotates relative to the control sleeve. The control grooves of the spool open the way for oil to the right cavity of the working cylinder. Pressurized oil rushes into the slave cylinder and helps turn the steered wheels. At the same time, the spool shuts off the oil supply to the left cavity and opens the drain from it. Under the action of pressure in the right cavity of the working cylinder, oil is squeezed out of the left cavity into the return pipeline. When the steering wheel is turned back to the middle position, the torsion bar returns the spool and control sleeve to the neutral position.
As in the old system, in the new power steering, the auxiliary force creates fluid pressure in the hydraulics. The hydraulic gear pump is driven by an electric motor and is therefore independent of the vehicle engine. In addition, now the degree of reinforcement depends on the angle of rotation of the steering wheel.
Description of the power steering sensor G250 (capacitive sensor)
Between 9 small plate capacitors, a rotor mounted on the steering shaft rotates. The rotation of the rotor causes a change in the capacitance of the capacitors. Based on the change in capacitance, the electronic circuit of the sensor calculates signals (steering angle and speed) and transmits them to the power steering control unit.
Principle: scheme for changing the capacitance of capacitors
Diagram: top view
The electric pump assembly consists of a hydraulic unit with a gear pump and an electric motor; power steering reservoir; electronics to control the electro-hydraulic booster. To check/correct the fluid level, the left headlight must be removed. Do not under any circumstances pinch the pressure and return pipelines of the hydraulic booster! Clamping of pipelines leads to damage to their plastic layer. When tying the pressure and return pipelines, make sure that their bending radius is at least 100 mm.
Used power steering J500
Uses input signals: engine speed from G28; vehicle speed from G68; steering wheel speed from the G250. To control the gear pump drive depending on the steering wheel angle and vehicle speed. Self-diagnosis is carried out via the instrument cluster, address word 17. Communication takes place exclusively via the drive CAN bus. The error message is issued via the instrument cluster control unit.
Pump operation
Ignition | Vehicle engine | Electric pump | Reinforcement in the steering gear |
On | works | works | There is |
Off | not working, vehicle speed = 0 km/h | does not work | No |
Reinforcement in the steering gear
Vehicle speed | Steering wheel speed | Pump performance | Reinforcement in the steering gear |
Low, e.g. when parking | high | high | high ("easy" steering wheel) |
High, for example, on the track | low | low | low ("tight" Steering wheel) |
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