The device and principle of operation of EGUR Servotronic

Servotronic electro-hydraulic power steering is an element of the vehicle's steering that creates additional force when the driver turns the steering wheel. In fact, the electrohydraulic power steering (EGUR) is an advanced power steering. The electrohydraulic booster has an improved design, as well as a higher level of comfort when driving at any speed. Consider the principle of operation, the main components, as well as the advantages of this steering element.

The principle of operation of EGUR Servotronic

The principle of operation of the electrohydraulic power steering is similar to that of the hydraulic power steering. The main difference is that the power steering pump is driven by an electric motor, not an internal combustion engine.

If the car moves straight ahead (the steering wheel does not turn), then the fluid in the system simply circulates from the power steering pump to the reservoir and vice versa. When the driver turns the steering wheel, the circulation of the working fluid stops. Depending on the direction of rotation of the steering wheel, it fills a certain cavity of the power cylinder. Liquid from the opposite cavity enters the tank. After that, the working fluid begins to press on the steering rack with the help of the piston, then the force is transferred to the steering rods, and the wheels turn.

Hydraulic power steering works best at low speed (cornering in tight spaces, parking). At this moment, the electric motor rotates faster, and the power steering pump works more efficiently. In this case, the driver does not need to apply special effort when turning the steering wheel. The higher the speed of the car, the slower the motor runs.

Device and main components

EGUR Servotronic has three main components: an electronic control system, a pump unit and a hydraulic control unit.

The pumping unit of the electro-hydraulic booster consists of a reservoir for the working fluid, a hydraulic pump and an electric motor for it. An electronic control unit (ECU) is placed on this component. Note that the electric pump is of two types: gear and vane. The first type of pump is distinguished by its simplicity and reliability.

The hydraulic control unit includes a power cylinder with a piston and a torsion bar (torsion rod) with a distribution sleeve and a spool. This component is integrated with the steering gear. The hydraulic unit is an actuator for the amplifier.

Servotronic electronic control system:

• Input sensors - speed sensor, steering wheel torque sensor. If the vehicle is equipped with ESP, the steering angle sensor is used. The system also analyzes the engine speed data.
• Electronic control unit. The ECU processes the signals from the sensors, and after analyzing them, sends a command to the executive device.
• Executive device. Depending on the type of electro-hydraulic amplifier, the actuator can be a pump electric motor or a solenoid valve in the hydraulic system. If an electric motor is installed, the performance of the amplifier depends on the power of the motor. If a solenoid valve is installed, then the performance of the system depends on the size of the flow area.

Differences from other types of amplifiers

As noted earlier, unlike a conventional power steering, EGUR Servotronic includes an electric motor that drives a pump (or another actuator - a solenoid valve), as well as an electronic control system. These design differences allow the electro-hydraulic booster to adjust the force depending on the speed of the machine. This ensures comfortable and safe driving at any speed.

Separately, we note the ease of maneuvering at low speeds, which is inaccessible to conventional power steering. At high speeds, the gain is reduced, allowing the driver to control the vehicle more precisely.

Advantages and disadvantages

First, about the advantages of EGUR:

• compact design;
• driving comfort;
• functioning when the engine is off / not running;
• ease of maneuvering at low speeds;
• precise control at high speeds;
• efficiency, reduced fuel consumption (turns on at the right time).

Disadvantages:

• the risk of EGUR failure due to the delay of the wheels in the extreme position for a long time (overheating of the oil);
• reduced steering wheel information content at high speeds;
• higher cost.

Servotronic is a trademark of AM General Corp. EGUR Servotronic can be found on cars of such companies as: BMW, Audi, Volkswagen, Volvo, Seat, Porsche. Servotronic electro-hydraulic power steering undoubtedly makes life easier for the driver, making driving more comfortable and safe.