Page 264 - Automotive Engineering Powertrain Chassis System and Vehicle Body
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CH AP TER 9 .1       Steering

               detected by a measurement system located in the region  power steering systems have to be designed in such a
               of the input shaft of the steering gear or in the steering  way that a sufficient supply volume is available for fast
               tube, and additional forces or moments are introduced  steering movements even at a low engine speed, supply
               into the system. This follows a characteristic curve  flow limiting valves are required. These limit the supply
               (valve characteristic) or group of curves depending on  flow to about 8 l per minute in order to prevent the
               the height of the steering-wheel torque, if another  hydraulic losses which would otherwise occur at higher
               quantity, e.g. driving speed, is entered as a signal. The  engine speeds. Depending on the driving assembly and
               steering boost is thereby reduced, with the aim of  pump design, the additional consumption of fuel can lie
               achieving better road contact at higher speeds.    between 0.2 and 0.7 l per 100 km.
                                                                    Assemblies which are added to provide auxiliary
                                                                  power are shown in Fig. 9.1-16, taking the example of the
               9.1.4.1 Hydraulic power steering                   rack and pinion steering used by Opel in the Vectra
               systems                                            (1997). The pressure oil required for steering boost is
                                                                  supplied direct to the steering valve 6 located in the
               Hydraulic power steering systems are still the most  pinion housing from vane pump 1 via the high-pressure
               widely used. The method of using oil under pressure  line 2 and the cooling circuit 3. From here, depending on
               to boost the servo is sophisticated and advantageous in  the direction of rotation of the steering wheel and the
               terms of cost, space and weight. Sensitivity to move-  corresponding counterforce on the wheels, distribution
               ments caused by the road surface and hence the effect  to the right or left cylinder line takes place (items 7 and
               of torsional impacts and torsional vibrations passing  8). Both lead to the working cylinder which is integrated
               into the steering wheel is also noticeably reduced,  in the steering-gear housing 5. A disc located on the gear
               particularly with rack and pinion steering. This can be  rack divides the pressure chamber. Differences in pres-
               attributed to the hydraulic self-damping. It might also  sure generate the required additional axial force in the
               be the reason why it is possible to dispense with an  gear rack F Pi via the active areas of the disc:
               additional steering shock absorber in most vehicles
               with hydraulical rack and pinion steering, whereas it is  F Pi ¼ðp hyd;2    p hyd;1  ÞA Pi   (9.1.1)
               required for the same vehicles with manual steering
               (see Section 9.1.6).                               where A Pi is the effective piston surface, here the dif-
                 The oil pump is directly driven by the engine and  ference between the disc and gear rack surfaces, and
               constantly generates hydraulic power. As hydraulic  p hyd,1 or 2 are the pressures acting on the working piston.

























               Fig. 9.1-16 Hydraulic power steering system of the Opel Vectra (1997). The individual components are:
               1  vane pump, driven by V-belts
               2  high-pressure line
               3  cooling circuit
               4  return line, from the steering valve to the pump
               5  steering gear with external drive, attached to the auxiliary frame
               6  steering valve
               7/8 pressure lines to the working cylinder
               9  steering column with intermediate shaft
               10 steering wheel with integrated airbag


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