Tham khảo tài liệu 'advanced vehicle technology 2 episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | a Central position. Zero eccentric shaft peg offset. Straight ahead steer kJ 1B0D eccentric shaft peg rotation. Right hand peg offset. Opposite direction steer e 360 eccentric shaft peg rotation. Zero steering peg offset Fig. a-d Principle of rear steering box mechanism the epicyclic gear set does not operate in the fourth quadrant even under full steering lock conditions. Variable-ratio rack and pinion Fig. a-d Variable-ratio rack and pinion can be made to improve both manual and power assisted steering operating characteristics. For a manual rack and pinion steering system it is desirable to have a moderately high steering ratio to provide an almost direct steering response while the steering wheel is in the normally central position for straight ahead driving and for very small steering wheel angular correction movement. Conversely for parking manoeuvres requiring a greater force to turn the steering wheel on either lock a more indirect lower steering ratio is called for to reduce the steering wheel turning effort. However with power assisted steering the situation is different the steering wheel response in the straight ahead driving position still needs to be very slightly indirect with a relatively high steering ratio but with the power assistance provided the off-centre steering response for manoeuvring the vehicle can be made more direct compared with a manual steering with a slightly higher steering ratio. The use of a more direct low steering ratio when the road wheels are being turned on either lock is made possible by the servo action of the hydraulic operated power cylinder and piston which can easily overcome the extra tyre scrub and swivel-pin inclination resisting force. The variable-ratio rack is achieved by having tooth profiles of different inclination along the length of the rack accordingly the pitch of the teeth will also vary over the tooth span. With racks designed for manual steering the centre region of the rack has wide .
