Machine element or mechanism – Gearing – Nonplanetary gearing differential type
Patent
1995-06-14
1996-09-24
Wright, Dirk
Machine element or mechanism
Gearing
Nonplanetary gearing differential type
F16H 3504
Patent
active
055579868
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a differential mechanism particularly but not exclusively for use in motor vehicles.
Differential mechanisms commonly used on vehicles are of the sun and planet gear type and have a well known disadvantage that when one wheel is on a slippery surface such as mud or ice and the other wheel is on a firm surface capable of providing traction, the first wheel will simply spin as it receives all the available power transmitted to the differential.
Limited slip differential mechanisms have been proposed in an attempt to overcome this problem which restrict the extent to which one wheel can spin relative to the other but such differentials are more complex and, therefore, most costly to produce.
In the Applicant's European patent application EP-A-0326289 there is proposed an alternative differential mechanism comprising two output cam members rotatable about an axis, each said member having a single frustoconical cam surface thereon of undulating form comprising pairs of mutually inclined surfaces, one of said cam members having a different number of said pairs of inclined surfaces thereon than the other of said cam members, and a plurality of cam followers having end surfaces engaging the cam surfaces of the output cam members, the arrangements being such that relative contra rotation of said output cam members causes the cam followers to slide axially, and an input member which slidably supports the followers and moves the followers circumferentially relative to the output cam members.
A problem associated with the above differential is that because of the different numbers of inclined faces on the two cam members the differential has different torque ratios when cornering in one direction as compared with cornering in the other direction.
According to the present invention there is provided a differential mechanism comprising two output cam members rotatable about an axis each said member having a single annular cam surface thereon of undulating wave form comprising pairs of mutually inclined surfaces, an equal number of said pairs of inclined surfaces, a plurality of cam followers having end surfaces engaging the cam surfaces of the output cam members, the arrangement being such that relative contra rotation of said output cam members causes the cam followers to slide axially, and an input member which slidably supports the followers and moves the followers circumferentially relative to the output cam members, characterised in that the cam members have equal numbers of pairs of inclined surfaces thereon and there are at least two different types of cam followers and the number of cam followers is a multiple of the number of pairs of inclined surfaces, where the multiple is an integral greater than one.
Preferably the integer is two and the number of cam followers is a multiple of four, the or each group of four cam followers comprising two different pairs of cam followers, and the two cam followers in each pair are adjacent each other.
When there are more than two different types of cam followers, the followers of each pair may be interspaced with the other types of follower in such a way that followers of the same type are contacting different relative positions on the respective cam surfaces. This is achieved by having an even number of other followers in between the members of each pair of followers. For example with three or five types of followers these may be assembled sequentially, rather than in pairs. The total number of followers is then a multiple of twice the number of different types of follower.
Preferably, where there are two different types of followers, the mutually inclined surfaces which constitute each pair of surfaces are symmetrically arranged, and the cam follower of one pair of cam followers are a mirror image in plan view of the cam followers of the other pair of cam followers.
Alternatively the mutually inclined surfaces which constitute each pair of surfaces are asymmetrically arranged, and the cam followers of one pair of cam followers are in plan view an i
REFERENCES:
patent: 1886837 (1932-11-01), Robbins
patent: 2034318 (1936-03-01), Wales
patent: 2790334 (1967-04-01), Wildhaber
patent: 2873619 (1959-02-01), Wildhaber
patent: 5461941 (1995-10-01), Young
"Automobile Engineering", No. 6, Jun. 1993, pp.27-30, A New Type of Limited Slip Differential.
Chippendale John P.
Spooner John
Young Alastair J.
Automotive Products plc
Germain Lee A.
Milliken Paul E.
Wright Dirk
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