Suspension: Description and Operation

Front wheel suspension
The front suspension is of the McPherson type.

Rear suspension
The rear suspension comprises a multi link rear axle.

Steering
The electrical power steering pump consists of:
- servo pump
- pump motor
- electrical power steering module (EPS).
Servo assistance is determined by the steering gear torsion valve together with the electrical power steering module (EPS).

The torsion valve determines:
- if servo assistance is required
- in which direction servo assistance should go
- how much of the available pump assistance should be used.
The electrical power steering module (EPS) determines the RPM of the pump using:
- the vehicle speed
- the steering wheel angle sensor.
The electric motor provides the pump with the power required to supply the correct hydraulic flow and pressure to the steering gear.

For further information about the electric power steering module (EPS), as well as other electrical components included in the electro-hydraulic power steering system, see Design and Function, electric power steering module (EPS). The adaptive steering column allows a relatively gentle deformation process in the event of a collision (only applies to drivers wearing seat belts, USA/CDN).

Steering shaft
The steering shaft is divided into two parts. The upper part of the steering column is further divided to prevent intrusion into the passenger compartment in event of a collision.

Design
Front wheel suspension





The front suspension is of the McPherson type, which means that the wheels are independently sprung. The suspension on either side consists of: sprint strut (12), control arm (10) and wheel spindle (7). The anti-roll bar (4) is secured in the sub-frame (8) with two clamps (3) and in the spring strut (12). There are a number of anti-roll bar variants.

Spring strut
The upper end of the spring strut is anchored to the wheel arch by way of the upper bearing and the upper mounting (1). The lower end of the spring strut (12) is attached to the wheel spindle (7). The spring strut consists of a pipe into the lower part of which the wheel spindle is pressed and bolted. The wheel spindle is attached to the control arm via the ball joint (11). The ball joint is secured in the lower part of the wheel spindle. The lower spring seat (6) welded to the upper part of the tube.

Shock absorber
The shock absorber is integrated in the spring strut. The shock absorber is located in the pipe and is held in place by a screw in the upper end and a seat in the bottom of the pipe. The shock absorber piston rod is guided by the upper bearing (1). The upper bearing is secured in the upper mount. The bearing consists of a bearing pressed into a plate sleeve which is vulcanized with rubber. Against the upper bearing, the spring provides support via the upper spring seat (1). On the underside of the spring seat there is a buffer and a protective sleeve for the shock absorber piston.

Control arm
The control arm (10) is mounted on the sub-frame (8) using the front bushing (9) and the rear bushing (2). The Toe-in/Toe-out is adjusted using the tie rods.

Sub-frame
The sub-frame (8) is made of two welded plates and a number of smaller plates. The rear bushing (2) is bolted to the sub-frame.

Settings
There are two different settings for shock absorber, spring and anti-roll bar: dynamic setting or comfort setting.

Axle shaft
The drive shaft joint is secured with a locking bolt.

Steering
See: Steering





Rear suspension

Upper control arm
The upper control arm (5) is cast.

Tie rod
The tie rod (6) is produced as a single steel stamp.

Lower control arm
The lower control arm (1) is steel stamped. It is installed between the lateral link (7) and the subframe (2). The Toe-in/Toe-out can be adjusted using the inner mounting on the control arm. The anti-roll bar (3) is mounted in the lower control arm. There are two different mounting variants.

Anti-roll bar
There are a number of anti-roll bar variants (3).

Sub-frame
The sub-frame (2) is made of metal.

Wheel sensor
The wheel sensors (4) are located on the rear wheel bearings. They measure the speed of the vehicle using magnetic discs.

Function





Steering, adaptive steering column

Deformation in the event of a collision
An impact of approximately 2 M is required for the steering column to start to deform.
Deformation takes place in three stages:
1. The upper steering section (3) is pushed into the running bracket (2) equivalent to the remaining potential adjustment in the adjustment mechanism (4)
2. The tear plate (6) is deformed. The running bracket (2) is pushed into the fixed bracket (1). The groove for the running bracket controls the length of deformation
3. The steering shaft (5) with its telescopic design slides together.
The maximum movement (deformation) of the steering column is approximately 95 mm.

Collision process (only USA/CDN)
Driver not wearing seat belt:
The pin (7) engages. This results in the tear plate using its entire structure to absorb energy. The deformation takes place stiffly and slowly. Driver wearing seat belt: The explosive charge (8) is activated and pushes down the pin (7) out of the tear plate (6). The tear plate is weakened and the kinetic energy of the collision is transferred on in the system. This produces a relatively soft deformation process. The collision protection system only works if the driver is wearing a seat belt and the airbag deploys.

Collision process (not USA/CDN)
The steering column does not have an explosive charge. The pin (7) is therefore always engaged. This means that the tear plate (6) uses its entire structure to absorb energy, irrespective of whether or not the driver is wearing a seat belt. The deformation takes place stiffly and slowly.

Electrical steering lock with mechanical locking function
The steering lock (9) is secured in the steering column with two security bolts. The mechanical locking function for the locking mechanism consists of:
- a lug on the steering wheel lock
- a pipe and catch on the steering column
- a pin for locking the lug.

The lug is pushed into the tube with the catch, locking the steering wheel. In the event of damage to the steering lock cover, the pin blocks the lug in the locked position.

Steering, steering gear





The steering gear power steering function is schematically displayed in the above illustration and under Steering, valve section.

The force of oil pressure built up in the power steering pump affects the piston on the steering rack. The oil flow to the right or left-hand side of the piston is regulated in the valve housing. External pipes lead to both sides from the valve housing. The power steering pump pressure hose is connected to the valve housing.

The valve spool has three radial grooves, a small one that is fed by the power steering pump and an upper and a lower groove that are connected with the working cylinders via the outer pipe.

Steering, valve section
Neutral





1. To the right-hand side of the piston
2. To the left-hand side of the piston
3. Outward
4. Fluid return
5. Servo oil, free flow

The valve is open when the vehicles engine is running and there is no steering input. In the open position, none of the ducts to the operating cylinders are blocked. The servo oil circulates freely through the valve.

Steering left





6. Servo oil, low pressure
7. Servo oil, high pressure
When the steering wheel is turned to the left and the wheel resistance is so great that the torsion bar inertia is overcome, the steering gear input shaft moves to the left in relation to the worm screw, within the play between the lugs. With this movement the input shaft stops the free flow through the valve and sends the fluid through the upper feed pipe to the right-hand side of the piston.

As long as the torsion bar is affected by steering input, the oil pressure continues to push the steering rack to the left and servo assistance is obtained. If the steering input reduces, the torsion bar springs back. The valve section then reverts to the center position so that the oil can circulate freely through the valve housing.

Steering right





6. Servo oil, low pressure
7. Servo oil, high pressure
The function when turning right is, in principle, the same as to the left. The only difference is that the steering gear input shaft stops the flow of high pressure oil through the return and down through the groove on the inside of the valve and out through the low pressure pipe to the left-hand side of the piston.

Steering, electrical power steering module (EPS)
The power steering system employs the electrohydraulic principle and is controlled by the electric power steering module (EPS).

Its task is to regulate the power steering affect for the vehicle optimally, using relevant input signals, and always to provide optimum servo assistance, regardless of whether the vehicle is stationary with the engine running or being driven at high speed. The pump is a gear type pump.

The pump motor is controlled by the electric power steering module (EPS).

The pump motor has Hall sensors, which inform the electric power steering module (EPS) about the present pump motor speed. At the same time, information is provided about the relevant hydraulic pressure, which is indirectly dependent on the speed. For further information about the electric power steering module (EPS), see Design and Function, electric power steering module (EPS).