Motor vehicles – Compensating devices
Patent
1994-01-27
1995-07-04
Focarino, Margaret A.
Motor vehicles
Compensating devices
74422, 74842, 180147, B62D 312
Patent
active
054292026
DESCRIPTION:
BRIEF SUMMARY
This invention relates to anti-roll mechanisms for rack and pinions and has been conceived in connection with a rack and pinion for a vehicle steering mechanism and will primarily be discussed in relation thereto. However, it is to be noted that the invention is applicable to rack and pinions used in other than vehicle steering mechanisms.
A rack and pinion is a widely accepted mechanism for steering motor vehicles and it is recognised that to achieve positive steering, mesh clearance (backlash) between the teeth of the rack and pinion needs to be kept to a minimum. Ideally, zero backlash is required but manufacturing tolerances, however tight, make this virtually impossible without involving extra components and/or machining operations which introduce unacceptable higher manufacturing costs.
It is common to employ a pinion with helical teeth and this gives rise to a force which imparts a rocking motion to the rack. FIG. 1 of the accompany drawings illustrates a known rack and pinion for a steering mechanism in which the rack 1 is supported for axial sliding movement in a support 2, the rack being formed from cylindrical stock and the support being provided with a corresponding part-cylindrical support surface 3. The teeth 4 of the helical pinion 5 mesh with the teeth 6 of the rack 1 and on rotation, the pinion generates an axial force F.sub.AX along its axis of rotation, which force acts at the pitch line P of the rack 1, the distance between the pitch line and the longitudinal axis of the rack 1 representing a moment arm M. The rotational force or torque T acting on the rack 1 is thus: rise to wear and/or damage. Clearly, this is undesirable especially when long term use is essential as in a vehicle steering mechanism.
Attempts have been made to minimise the rocking motion of the rack 1 due to the torque T, one arrangement being to provide inclined faces on the rack to give a general v-shaped cross-section to the rack as illustrated in FIG. 2 of the accompanying drawings. The support 2 for the rack 1 has a corresponding V-shaped mating surface 3 formed therein. In view of the accuracy required, the inclined faces have to be machined and it will be appreciated that it is not a simple matter to effect this machining, relative to the rack teeth 6, without tolerance or error and to produce likewise the mating surface 3 on the support 2. Furthermore, additional errors are likely to be introduced when assembling the anti-roll mechanism in the housing of the steering mechanism. Consequently, not only is this anti-roll mechanism relatively expensive to manufacture, but the cumulative errors or tolerances contribute to a reduction in efficiency of operation of the rack and pinion, particularly the freedom of movement of the rack, which is unacceptable.
The primary object of the present invention is to provide an anti-roll mechanism for a rack and pinion which is relatively inexpensive to manufacture but which is effective without detracting from the efficiency of operation of the rack and pinion.
According to the present invention, there is provided rack and pinion apparatus comprising a toothed rack, the tops of the teeth of which lie in a common plane, the rack and pinion apparatus further comprising an anti-roll mechanism having rack-teeth-engaging means mounted to permit relative movement between the rack and teeth-engaging means and so as to be in contact, at any given instant, with the tops of at least two teeth of the rack.
Inasmuch as it is common practice to provide flat tops to the rack teeth and to ensure that these tops are co-planar, then the present invention makes use of this existing "surface" to provide the means for preventing rolling or rocking motion of the rack, thus dispensing with the relatively expensive machining or manufacturing equipment discussed above.
The teeth-engaging means of the anti-roll mechanism may comprise a hardened pad, preferably supported in a carrier which is provided with means for adjusting the pad relative to the rack teeth in order to accommodate manufacturing toler
REFERENCES:
patent: 2193898 (1940-03-01), Carter et al.
patent: 3157061 (1964-11-01), Parker
patent: 3897845 (1975-08-01), Von Lowis of Menar
patent: 4584893 (1986-04-01), Harding et al.
patent: 4599911 (1986-07-01), Rosell
patent: 4986382 (1991-01-01), Harrison
Chandler Kenneth
Millard Barry J.
Adwest Engineering Limited
Focarino Margaret A.
Hurley Kevin
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