How does hydraulic power steering work and problems that can occur

The steering assist system, electric, hydraulic or electro-hydraulic, greatly reduces the effort required to maneuver the steering wheel. Most modern systems benefit from different degrees of assistance, depending on the speed (higher at low speeds to ease parking/traffic maneuvers, respectively lower at high speeds for increased accuracy).

Most cars made in the last decades have this endowment in standard car equipment, with positive effects, both on comfort and safety.

Destination and parts of hydraulic power steering.

In cars, hydraulic power steering is one of the power steering mechanism options that are used. These steering mechanisms reduce the force required for maneuvering the steering wheel, thus contributing to the ease of driving the car and to the damping of the steering mechanism oscillations.

Depending on the model of the power steering mechanism, there are two types of power steering:

  • The power steering that is performed separately, by the steering mechanism, acting on the transmission parts.
  • The power steering makes one with the steering mechanism.

Power steering consists of

hydraulic power steering components

The main components of the power steering system: steering box, steering semi-box, high-pressure pump, oil reservoir, steering wheel with shaft, connecting pipes, steering rods, and rod ends.

The steering box is composed of the housing, provided on the inside with a cylinder in which the piston moves, which transforms the rotational movement of the steering wheel shaft into a translation movement, transmitting it to the gear sector, on which the steering lever is mounted.

For this, the piston is provided on the outside with a gear, through which it engages the toothed sector, and on the inside with a cylindrical housing, in which the leading screw enters. Inside the piston, there is also the steering nut mounted with the help of the ring nut.

In the housing mounted on the steering box, there is the mechanism of the power steering valves, sealed by the inner cover and the seals. This mechanism is composed of the valve port block, the drive shaft valves, and the torsion bar.

The valve port block makes one with the leading screw and contains, in the transverse plane, two cylinders (upper and lower), corresponding to the two valves.

The valves are of the piston type drawer, the upper one allowing the oil to be sent in the space between the steering box and the right side of the piston, and the lower one allows the oil to be sent in the space between the steering box and the left side of the piston.

It has the role of transmitting the turning moment from the steering wheel shaft to the driving screw, and to restore the pressure of the drawer valves to the neutral position, when the driver no longer exerts a rotational force on the steering wheel.

How does power steering work?

When moving the car in a straight line the draw valves are in a neutral position, and the centers of their radial drive holes are in line with the center of the central hole of the valve port block. In this situation, both the feed holes on the right of the valves are opened, as well as the discharge holes on the left of the drawer valves.

A high-pressure pump sends the oil to the valve block through the pipe. From here, a part passes through the cutting hole, opened by the upper valve, and through the channel enters the steering box, in the right of the piston. Because the oil pressure on both sides of the piston is the same, it remains fixed, and the gear with the toothed sector is in the middle position.

After filling the mentioned spaces, the oil charged by the pump returns to the crankcase directly from the cutting channels, through the holes, the central channel of the valve block and the discharge pipe.

How to maintain power steering

The maintenance of the steering system consists of:

  • measuring the steering wheel play
  • verifying the joint play
  • adjusting the drive mechanism
  • checking and adjusting the position angles of the steering wheels and pivots
  • tightening the steering box fastening screws
  • tightening the spherical joints and lubricating them according to the lubrication scheme.

The main components of the steering system provided with a mechanical safety system, with pinion and rack: steering column, power steering pump, rotary distributor, bolt pinion, piston, and rack.

 The steering wheel play  is checked as follows:

  • – Bring the steering wheel in the position for walking in a straight direction;
  • – Turn the steering wheel to the right and then to the left to the maximum positions in which it is easy to handle without turning the wheels.

The steering wheel play must not exceed 15 degrees, because in this situation the steering becomes insecure.

The causes of this play at the steering wheel can be the wear of the steering mechanism joints or the control mechanism parts.

Adjusting the steering mechanism.

The way of adjusting the steering mechanism differs depending on its construction type. In all cases, however, the adjustment operation will be performed only after this play has been removed from the mechanism joints.

Adjusting the mechanisms of action with the globoid screw and the roller involve the adjustment of the axial play of the steering wheel (of the screw).

Before adjusting the steering lever, the steering rod is disconnected. The adjustment of the axial clearance of the screw is made by unmounting one or two gaskets, after which the lid is reassembled.

Control of wheel alignment.

Wheel alignment measuring and control devices can be mechanical or optical.
The mechanical devices are relatively simple and cheaper than the optical ones, but they have low accuracy. The position angles of the wheels and the pivots must be within the limits provided in the technical book of the respective car.

Deterioration of the wheel alignment can lead to a bad trajectory of the car on the road, additional efforts of the driver in maintaining the direction of the vehicle, rapid wear, premature and uneven tires.

Lubrication of the steering system

The parts of the steering mechanism, which require lubrication are the steering box, the spherical joints, and the pivots. The lubrication of the steering box is usually done with automatic transmission oil, respecting the periodicity prescribed by the factory.

Periodically the level is checked and if necessary, the losses are filled with the same type of oil. If the oil losses are too much, the cause that generates them must be detected and removed to avoid damage.

In the case of hydraulic power steering, once the oil is replaced, the oil filter is changed. Spherical joints and pivots are greased with a consistent type U grease, introduced under pressure through the greases with which they are provided. The lubrication periodicity varies between 1000 and 2000 km traveled.

Symptoms of a bad hydraulic power steering

  • Handling the steering wheel requires more effort.
  • The wheels oscillate at low speeds.
  • The wheels swing at high speeds.
  • Steering pulls on sides.
  • The steering transmits shocks to the steering wheel that comes from the wheels.
  • Abnormal steering noises.

The problem is due to the following causes: high friction in the joints, abnormal friction in the steering box and at the spindles pivots, deformation of the steering wheel as well as some tire defects.

The large joints in the joints occur as a result of incorrect fitting or adjustment, the unsatisfactory lubrication or the penetration of dust between the joints. The problems are solved in the repair shop, by unmounting the respective parts and cleaning and lubricating them.

Abnormal friction in the steering box is due to insufficient lubrication, wear or damage of the screw, worn or incorrectly mounted bearings, and insufficient play between the elements of the cassette or incorrect fixing of the steering box within the car. Faults, except for insufficient lubrication, can only be remedied at an authorized service workshop.

Abnormal friction, at spindles pivots, is due to bad lubrication, an insufficient play between pivots and bearings or bushings or pivot grip. The solution consists of cleaning and lubricating the pivots, the damaged organs are replaced at an authorized workshop.

The tire faults that make wheel steering difficult can be caused by:

  • Insufficient or uneven pressure;
  • Uneven wear or different sizes.
  • The steering wheels oscillate at low speeds.

The steering wheel oscillation, at speeds less than 60 km / h, is due to the following causes:

  • Incorrect tire pressure;
  • Tires of different sizes;
  • Wheels not properly balanced;
  • The steering system bodies are worn;
  • Wheel bearings have a great play;
  • Front axle displaced;
  • The suspended suspension (broken springs, bad shock absorbers);
  • The deformed frame;
  • Wheel alignment incorrectly adjusted.

During the course, the faults related to tire pressure recovery are solved. The rest of the problems are remedied at an authorized workshop.

Causes of the wheels swinging at high speeds.

The causes are similar to those that cause oscillations when running at low speeds, but also, there are:

  • Imbalance or deformation of the rear axle wheels;
  • The engine supports weakened or defective.

At high speeds, the oscillation of the wheels is a dangerous defect, especially when these oscillations resonate with the oscillations of the frame or those of other organs of the steering or suspension system.

Causes that can determine the steering to not have the corresponding trajectory:

  • The front-wheel tires do not have the same pressure or are not identical in size;
  • The brakes are adjusted incorrectly;
  • The frame is deformed;
  • One of the front suspension springs has the main sheet broken.

During the course, the tire pressure is corrected and the brakes are adjusted. The rest of the faults are remedied at an authorized service workshop.

If the front axle tires do not have the same pressure or different dimensions, they will affect the power steering parameters.

The shocks from the interaction of the wheels with the road are transmitted to the steering wheel. The phenomenon appears especially on the road when traveling on uneven roads due to:

  • Too high tire pressure;
  • Wheel unbalance;
  • Defective shock absorbers;
  • Improper use or adjustment of the steering system parts.

The causes that lead to abnormal steering noise can be:

  • Excessive plays in the steering transmission joints;
  • Slackening of the steering column and its support or steering gear;
  • Damage to bearings or incorrect mounting;
  • Abnormal friction due to unsatisfactory lubrication.
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