Steering Overview

Steering

Adaptive steering column, design




The adaptive steering column is one complete unit.
The steering column contains the following parts:





The fixed bracket (1) is mounted against the cowl panel. The steering column is adjustable in height and length. It is equipped with an electric steering lock with mechanical locking function.
The steering shaft is divided into two parts and is equipped with two joints, partly with a joint between the upper and lower steering shaft sections and partly a joint as a connection to the steering gear.

Adaptive steering column, function










Deformations in the event of a collision
It requires an impact of about 2 kN for the steering column to start deforming. The deformation occurs in three steps:
1. The upper steering section (3) slides into the running bracket (2) corresponding to the remaining adjustment on the adjustment mechanism (4).
2. The grater plate (6) deforms. The running bracket (2) slides into the fixed bracket (1). The running bracket's track controls the deformation length.
3. The steering shaft (5) with its telescopically shaped design slides together.
Maximum movement (deformation) of the steering column is about 95 mm.
The adaptive steering column allows for a relatively smooth deformation sequence in the event of a collision (only applies to belted drivers, USA/CDN).

Collision sequence (applies to USA/CDN)
Unbelted driver:
The pin (7) is in operation. This allows the grater plate to use its entire structure to absorb energy. Deformation occurs silently and slowly.
Belted driver:
The pyrotechnic charge (8) is activated and pushes down the pin (7), from the grater plate (6). The grater plate weakens and the collision's kinetic energy is passed on in the system. This provides a relatively smooth deformation sequence. The collision protection only works if the driver is belted and the airbag deploys.

Collision sequence (does not apply to USA/CDN)
The steering column does not have a pyrotechnic charge. The pin (7) is therefore always in operation. This allows the grater plate (6) to use its entire structure to absorb energy regardless whether the driver is belted or not. Deformation occurs silently and slowly.

Electric steering lock with mechanical locking function
The steering lock (9) is secured in the steering column by two security bolts.
The lock mechanism's mechanical locking function consists of:
- a lug on the steering lock
- a tube with locking channels on the steering column
- a pin for locking the lug.
The lug slides into the tube with locking channels, so that the steering wheel locks. When the steering lock's cover is affected, the pin locks the lug in the locked position.

Steering gear, design









The description covers the steering gear in the left-hand drive version. The gear in the right-hand version is a mirror image of the left-hand version. There is also a speed dependent steering gear, for further information, see Design and Function, Central electronic module (CEM).
The steering gear is the rack and pinion type with the mechanical and servo assisted elements combined in one module.
The mechanical element consists of the gear drive (8), steering rack (12) and track rods (14).
The gear drive is carried by a journal bearing (7) and a roller bearing (10) in the steering gear housing.
The steering rack is carried by a journal bearing on the right end and in the housing is guided by the gear drive (8) and the sprung actuation piston (9).
A cylinder pipe (13) is secured to the steering gear housing (11). This pipe operates as the servo element's working cylinder for the hydraulic piston on the steering rack.
Regulation of the oil flow to the hydraulic cylinder occurs in the valve housing, which is integrated into the steering gear housing.

Valve section
The gear drive is driven by the steering gear input shaft (1) which has exterior lugs. There is radial play between the lugs.
A torsion bar (2) which joins the input shaft to the gear drive holds the lugs in a position where the play is equal on each side when there is no steering input on the shaft.
A torsion bar is pressed into the gear drive. The gear drive is fastened to the input shaft with a pressed in lock pin.
A valve spool (5) is located in the valve housing and fixed to the gear drive with a lock pin. The valve operating range is radial between four thin vertical grooves in the valve spool and four cut-outs in the input shaft.
The valve is balanced as a complete unit and cannot be rebalanced.

Steering gear, function









The steering gear's servo function is displayed schematically in the above image and under the heading "Valve section".
The force of oil pressure built up in the power steering pump affects the piston on the steering rack. The valve housing regulates the flow of oil to the left or right sides of the piston. External pipes lead from the valve housing to both sides. Even the power steering pump pressure hose is connected to the valve housing.
The valve spool has three radial grooves, one in the middle 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 pipes.

Valve section

Neutral position




- 1. To right-hand side of piston
- 2. To left-hand side of piston
- 3. Supply
- 4. Return oil
- 5. Servo oil, free flow
The valve is open when the car 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 through the valve freely.

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. If the steering input diminishes the torsion bar springs back. The valve section returns to the centre position so that the oil can circulate freely within 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 spool and out through the low pressure pipe (return oil) to the left-hand side of the piston.