rack and pinion steering gear with a shift movement is used not only on small and medium-sized passenger cars, but also on heavier and faster vehicles, such as the Audi A8 and Mercedes E and S Class, plus almost all new light van designs with independent front wheel suspension. The advantages over manual recirculating ball steering systems are :
- simple construction;
- economical and uncomplicated to manufacture;
- easy to operate due to good degree of efficiency;
- contact between steering rack and pinion is free of play and even internal damping is maintained
- tie rods can be joined directly to the steering rack;
- minimal steering elasticity compliance;
- compact (the reason why this type of steering is fitted in all European and Japanese front-wheel-drive vehicles);
- the idler arm (including bearing) and the intermediate rod are no longer needed;
- easy to limit steering rack travel and therefore the steering angle.
The main disadvantages are:
- greater sensitivity to impacts;
- greater stress in the case of tie rod angular forces;
- disturbance of the steering wheel is easier to feel (particularly in front-wheel drivers);
- tie rod length sometimes too short where it is connected at the ends of the rack (side take-off design;
- size of the steering angle dependent on steering rack travel;
- this sometimes requires short steering arms 3 resulting in higher forces in the entire steering system;
- decrease in steering ratio over the steer angle associated with heavy steering during parking if the vehicle does not have power-assisted steering;
- cannot be used on rigid axles.
There are four different configurations of this type of steering gear :
- Type 1 Pinion gear located outside the vehicle centre (on the left on left-hand drive and on the right on right-hand drive) and tie rod joints screwed into the sides of the steering rack (side take-off).
- Type 2 Pinion gear in vehicle centre and tie rods taken off at the sides.
- Type 3 Pinion gear to the side and centre take-off, i.e. the tie rods are fixed in the vehicle centre to the steering rack.
- Type 4 ‘Short steering’ with off-centre pinion gear and both tie rods fixed to one side of the steering rack.
- Types 1 and 3 are the solutions generally used, whereas Type 2 was found in some Porsche vehicles, and Type 4 used to be preferred by Audi and VW.