GB2327723A - Limited slip differential - Google Patents

Abstract

A bevel gear limited slip differential has a pinion carrier 18 supporting a pair of planet pinions 32,34 each containing a mating conical insert 78,80. The planet pinions are displaced outward when the carrier 18 is subjected to drive torque to bring them into frictional braking engagement with the carrier. The controlled outward displacement is obtained using an outward component of the rotating carrier drive torque force as it is transmitted to the said planet pinions from their contained conical inserts at the sloping interface between them. An adjustable preload on the pinions is provided by springs 54 and a sleeve assembly 52.

Description

IMPROVED DIFFERENTIAL MECHANISM This invention relates to differential mechanisms as used in the drive transmissions of land vehicles and is more specifically concerned with limited slip mechanisms incorporating provisions for automatically inhibiting the differential action if conditions arise in which there is substantial inequality of effective driving torque at the two driven output shafts or other driven outputs of the mechanism for example when wheel spin would otherwise tend to occur.

Numerous proposals have been put forward for meeting this requirement but have not always been too successful in operation or economically viable.

The object of the invention is to provide a differential mechanism simple in construction, durable and reliable in use. It is closely associated with the device described in GB 2253662 and U.S. 5,183,446. It presents an alternate method of inhibiting differential action using a > .

predetirmined component fraction of the transmitted driving force.

According to the invention there is provided a/ limited slip differential mechanism including a casing, a carrier journalled in said formation for operatively driven rotation about a first axis, a pair of driven output elements each journalled for independent rotation about a first axis, and at least one planet pinion with a mating conical insert journalled in the carrier for rotation about a second axis normal to the first axis said planet pinion being meshed with both output elements to transmit drive thereto in common from the carrier while permitting differential motion of the output elements to each other characterised in that said planet pinion can shift relative to the carrier by outward displacement with respect to its mating conical insert between between a neutral position at which the planet pinion can rotate freely in providing said rotational motion and an inhibiting position at which rotation of said planet pinion is resisted or prevented by direct or indirect coaction between the planet gear and a braking or stop formation of or on the carrier and or said planet pinion whereby the differential motion is inhibited automatically as a function of the driving force transmitted through the said carrier.

Preferably there will be a pair of said planet pinions with conical inserts disposed to mesh with diametrically opposite sides of both output elements so that they rotate in opposite directions under the differential motion the said planet pinions will be displaceable as referred to above between neutral and inhibiting positions.Conveniently the planet pinion inserts will be carried on a common planet pinion shaft located in the carrier.

The assembly will include provision for adjustable preloading of the planet pinions to provide predetirmined resistance to their rotation about the second axis at the inhibiting position and simultaneously prevent the planet pinions inserts shifting inwards as said planet pinions are urged outwards in the said inhibiting position.

Preferably differential action inhibition is accomplished by a braking effect produced with frictional engagement of said coacting formation without locking the planet pinions solid which would cause excessive stressing and consequent damage to components of the mechanism. It is desirable that the planet pinions are resiliently preloaded as aforesaid.

Examples of the invention are more particularly described with reference to the accompanying drawings, wherein- Figure 1 is a cross section of a vehicle final drive unit incorporating the differential mechanism of the invention.

Figure 2 is a detail on an enlarged scale showing the location of the planet pinions and their respective conical inserts of said mechanism.

Figure 3 is a component force diagram illustrating the derived upward component of transmitted driving force produced as said driving force is transmitted from the rotating carrier via the planet pinion shaft to the planet pinion through a mating conical insert along the sloping conical insert - planetary pinion interface.

Referring to Figure 1 the final drive unit 10 shown by way of example is a land vehicle axle unit of generally conventional layout having an axle casing 12 (part only shown) locating a pair of half shafts 14,16 on a common first axis which will drive near and offside road wheels (not shown) in the usual way.

The inner ends of shafts 14,16 are received in a coaxially rotating carrier 18 journalled on bearings 20 in casing 12. The carrier mounts a crown wheel 22 meshing with main drive input pinion 24 also journalled in casing 12 so that the carrier is operatively rotatably driven about the first axis.

Differential mechanism indicated generally as 26 acts between half shafts 14,16 within and carried by the carrier 18. The inner end of each said half shaft mounts a respective drive output pinion 28,30. these output pinions are spaced axially apart in facing relationship and are located against axial outward thrust by bearing surfaces of carrier 18. The shafts 14,16 having splined engagement with them.

Meshing with the output pinions 28,30 at diametrically opposite positions are a pair of planet pinions 32,34 located and rotatable on a second axis normal to the first axis of rotation of said output pinions and carrier 18 in the form of planet pinion insert shaft 36 which is in turn located in said carrier.

As thus far described the planet pinions act in a conventional manner to permit differential relative motion of the output pinions and their associated road wheels when the vehicle is cornering fnr example.

Figure 2 shows in more detail the essential unique design features allowing automatic differential action inhibition when required Planet pinions 32,34 each contain and can freely rotate on thP;r respective conical inserts 78.80. These inserts are freely rotatable on the planet pinion insert shaft 36 which is in turn located in carrier 18 by cross pin 40.

The friction means 50 between the planet pinions and carrier generally consist of a cnnventional clutch assemblv For example a friction plate mounted on each planet pinion outer face 42,44 opposed to a mating friction plate mounted on the mating inner facts 46.48 of the carrier using sturdy mounting means and allowing renlanoment when required.

The planet pinions can be urged outwardly from their respective conical inverts themselves able to axially shift and rotate on the planet pinion insert shaft. Said conical inserts are preloadeF axially outwards of each other by an adjustable. resilient sleeve assembly 52.

Said sleeve assembly is located on said shaft between the axially inner end faces of said conical pinion inserts comprising of a stark of resilient spring washers 54. a spacer sleeve 56 having inner and outer parts in screw threaded engagement for selective adjustment of its effective axial length, secured by a lock nut against displacement once adjusted, and annular inner washers 60,61 which bear respectively against the inner end faces of the planet pinions inserts in opposite directions.

Said sleeve assembly 52 is adjusted to provide a predetirmined preloading of the planet pinions common frictional means 50 with respect to the carrier 18.

Any axial adjustment of the output pinions 28,20 needed to ensure correct meshing with the planet pinions 32,34 can be achieved by inserting spacer shims between the axially outer faces of the said output pinions and carrier.

The driving torque force applied from the rotating carrier is transmitted by pinion insert shaft to the inserts and hence to the planet pinions along their mutual sloping interface. Figure 3 illustrates directionally the outward force component generated at the said interface. The said outward force component is a calculable predetirmined fraction of the said transmitted driving torque force and urges both planet pinions outwards with respect to their contained conical inserts, effectively inhibiting planet pinion rotation with respect to the carrier by engaging their common friction means 50 which inhibits differential movement of the output pinions 28,30 and their contained half shafts 14,16. Note that the component outward force fraction is a quantitative function of the said mutual sloping interface angle with respect to planet pinion insert shaft 36.

On turning normal differential action is restored by the faster outside wheel while major driving force is applied to the inside wheel ensuring stability during turns.

Under poor traction conditions the wheel with better traction receives most driving force.

Claims (12)

1. A limited slip differential mechanism including a supporting formation, a carrier journalled on or in said formation for operatively driven rotation about a first axis, a pair of driven output elements each journalled for independent rotation about said first axis, and at least one planet pinion with a mating conical insert journalled in the carrier for rotation therewith being rotatable about a second axis normal to the first axis, said planet pinion being meshed with both output elements to transmit drive thereto in common from the carrier while permitting differential motion of the output elements relative to each other; characterised in that said planet pinion can shift relative to the carrier outwardly from its contained conical insert along said second axis between a neutral position at which the planet pinion can rotate freely in providing said differential motion and an inhibiting position at which rotation of said pinion is resisted or prevented by restrictive formation or formations located between said pinion and carrier whereby the differential motion is inhibited automatically as a calculated quantitative function of the transmitted driving force

2. A mechanism as in Claim 1 including a pair of said planet pinions disposed to mesh with diametrically opposite sides of both output elements so that they rotate in opposite directions under the differential motion.

3. A mechanism as in Claim 2 wherein each said planet pinion is displaceable between neutral and inhibiting positions.

4. A mechanism as in Claim 3 wherein the planet pinions both contain conical inserts carried on a common shaft located in the carrier, the pinions being displaceable from their respective inserts between neutral and inhibiting positions.

5. A mechanism as in any preceding claim including provision for adjustable preloading of the planet pinion or pinions to provide predetirmined resistance to its or their rotation about the second axis at the inhibiting position.

6. A mechanism as in Claim 5 wherein said preloading is resilient.

7. A mechanism as in Claim 5 or 6 so far as dependent on Claim 4 wherein the planet pinions are displaceable relative to each other along the second axis, said preloading being effected by a preloading assembly located on the planet pinion shaft to urge said pinions conical inserts and hence the planet pinions themselves apart from each other.

8. A mechanism as in claim 7 wherein the preloading assembly includes spring means, a compression sleeve selectively adjustable in effective length with intermediate washers acting on the planet pinions respective conical inserts.

9. A mechanism as in any preceding claim in which said inhibition of differential motion is progressively effected by frictional braking engagement of said restrictive formations located between the planet pinions and carrier.

10. A mechanism as in Claim 9 wherein said breaking formations consists of opposing mating high friction braking material clutch plates located respectively on the carrier inner surface and the planet pinion upper surface

11. A mechanism as in claim 9 or 10 wherein outward displacement of planet pinions is limited to prevent them becoming completely locked.

12. A limited slip differential mechanism substantially as hereinbefore described with reference to and as shown in Figures 1 and 2.