LIMITED SLIP DIFFERENTIAL

Abstract: A "limited slip" differential (10) employing transfer gears (23, 24) drivingly connected to output gears (18, 19) such that upon relative rotation of the output gears (18, 19) the transfer gears (23, 24) pump a hydraulic fluid through a circuit to inhibit relative rotation between the output gears (18, 19).

Description: "LIMITED SLIP DIFFERENTIAL' The present invention relates to the relative proportioning of rotary power applied to at least two rotary driven elements by a common rotary drive inlet, and more particularly but not exclusively to "limited slip" differentials for vehicles such as earth moving equipment, motor vehicles especially motor lorries and "off highway" vehicles. BACKGROUND ART Traditionally "limited slip" differentials have employed friction clutches or hydraulic pumps to limit the relative speeds of rotation of the axles extending from the differential. These known devices have many disadvantages including wear of the frictional surfaces and the requirement for additional pumps of the transfer of torque between the axles, which pumps are not included within the major differential assembly. It is the object of the present invention to overcome or substantially ameliorate the above disadvantages. DISCLOSURE OF INVENTION There is disclosed herein a differential assembly including a pinion, a crown gear rotatable about a fixed axis and meshingly engaged with the pinion, a carrier fixed to said crown gear so as to rotate therewith about said axis, a pair of output gears mounted within said differential so as to rotate about said fixed axis, power transfer gear means driven by said output gears, said transfer gear means being rotatably supported by said carrier, and wherein said transfer gear means co-operate to pump hydraulic fluid between a pair of chambers when relative notation between said output gears, and said differential includes duct means extending between said two chambers so that the pumping of hydraulic fluid between said two chambers inhibits relative rotation between said output gears. BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 is a schematic perspective view of a differential having a limited slip capability; Fig. 2 is a schematic end elevation of three separate carriers which may be employed in the differential of Fig. l.- Fig. 3 is a schematic part section side elevation of the differential depicted in Fig. 4 sectioned along the line A-A; and Fig. 4 is a schematic end elevation of the differential of Fig. 3 sectioned along the line B-B. BEST MODE OF CARRYING OUT THE INVENTION AND INDUSTRIAL APPLICABILITY In Fig. 1 there is schematically depicted a differential 10, which in a conventional manner includes a pinion.12 driven by a shaft 13, which pinion 12 meshingly engages a crown wheel 14 rotatably supported in the differential housing so as to be rotatable about the axis 15. Extending from the differential 10 are two driven shafts 16 and 17 which are splined to output gears 18 and 19 rotatably supported within a carrier 27 (Fig. 2). Rotatably supported by the carrier 27 is a drive transfer gear assembly 20. The gear transfer assembly 20 includes a first pair of gears 21 and 22 meshingly engaged with the gears 18 and 19, and a second pair of gears 23 and 24 which are meshingly engaged the gear 23 is fixed to the gear 21, and the gear 24 fixed to the gear 22. The gears 21 and 23 are rotatably supported on a shaft 25, which in turn is rotatably supported in the carrier 27, while the gears 22 and 24 are rotatably supported on the shaft 26 also supported by the carrier 27. Turning now to Figs. 3 and 4 wherein the differential assembly 10 is more fully depicted. However it should be appreciated that in this particular embodiment described with reference to Figs. 3 and 4, there are three drive transfer assemblies 20 as best seen in Fig. 4. Each transfer assembly is substantially identical to the drive transfer assembly 20 of Fig. 1. More particularly, the drive transfer assemblies 20 are mounted in a carrier 27 fixed to the crown wheel 14. As best seen in Fig. 4, the carrier 27 generally surrounds each drive transfer assembly 20 so that in co-operation with each drive transfer assembly 20 a pair of chambers 28 and 29 are provided. There is further provided by the carrier 27 reservoirs 30 located at angularly spaced locations between the drive transfer assemblies 20. There is further provided passages 31 which each extend in a clockwise direction from a particular chamber 28 to the next adjacent clockwise reservoir 30. Still further, there is provided passages 32 which extend in an anticlockwise direction from a particular chamber 29 to the next adjacent reservoir 30. The reservoirs 30, passages 31 and 32, and the chambers 28 and 29 are filled with hydraulic fluid. In operation of the abovedescribed differential 10, co-operating pairs of gears 23 and 24 pump fluid between the chambers 28 and 29 (depending on the direction of rotation of the shaft 13) so that hydraulic fluid is caused to circulate between the various reservoirs 30 via the passages 31 and 32. However it should particularly be noted that the passages 31 and 32 would provide resistance to the flow of hydraulic fluid through the circuit thereby providing a resistance to the rotation of the gears 23 and 24. Thus if shafts 16 and 17 have the same angular velocity, then there will be no hydraulic fluid caused to circulate through the carrier 27. However, as the relative rotational speed of the shafts 16 and 17 increases, the flow rate of the hydraulic fluid circulating in the carrier 27 will increase. However inhibiting this flow is the resistance provided by the passages 31 and 32. Accordingly, as the flow rate increases, the resistance to the rotation of the gears 23 and 24 will also increase thereby inhibiting any further increase in the relative speed of the shafts 16 and 17. Thus, the pumping action of the gears 23 and 24 provides the differential 10 with a "limited slip" differential function. Turning now to Fig. 12 wherein various configurations of the carrier 27 are depicted. In Fig. 2A, the carrier 27 is provided with two transfer assemblies 20, in Fig. 2B, the carrier 27 is provided with four drive transfer assemblies 20, while in Fig. 2C there is provided five transfer assemblies 20. If so desired the circuit through which the hydraulic fluid psses could be sealed in order to retain the hydraulic fluid within the carrier 27. However as an alternative the fluid could be circulated throughout the overall differential housing to aid in cooling of the fluid. The abovedescribed preferred embodiment has many advantages over conventional limited slip differential assemblies. Of these advantages the following are prominent: (1) the drive transfer assemblies 20 are totally located within the differential assembly; (2) the forces generated within the carrier 27 are purely radial and have no substantial axial component since bevel gears are not used to transfer motion between the gears 18 and 19; (3) the differential function is performed hydraulically therefore eliminating the inherent wear factors of friction drive assemblies; and (4) the differential function performed hydraulically may be tailored to the particular situation in which the differential 10 is to be employed by varying the resistance to the flow of hydraulic fluid around the carrier 27. More particularly this may be accomplished by varying the resistance to the flow of hydraulic fluid through the passages 31 and 32.

Claims: CLAIMS 1. A differential assembly including a pinion, a crown gear rotatable about a fixed axis and meshingly engaged with the pinion, a carrier fixed to said crown gear so as to rotate therewith about said axis, a pair of output gears mounted within said differential so as to rotate about said fixed axis, power transfer gear means driven by said output gears, said transfer gears means being rotatably supported by said carrier, and wherein said transfer gears co-operate to pump hydraulic fluid between a pair of chambers when relative notation between said output gears, and said differential includes duct means extending between said two chambers so that the pumping of hydraulic fluid between said two chambers inhibits relative rotation between said output gears. 2. The differential of claim 1 wherein said carrier provides said chambers. 3. The differential of claim 2 wherein said transfer gear means includes at least one pair of meshingly engaged first transfer gears each driven by a respective one of the output gears. 4. The differential of claim 3 wherein there is a plurality of pairs of said first transfer gears, with chambers associated therewith, the pairs of transfer gears being equally angularly spaced about said axis. 5. The differential of claim 4 further including a further transfer gear associated with each of the first transfer gears, and wherein each further transfer gear is meshingly engaged with a respective one of the output gears and is drivingly connected with the associated first transfer gear. 6. The differential of claim 5 wherein each first transfer gear and its associated further transfer gear is fixed to a common shaft rotatably supported by said carrier. 7. A differential substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: COOMBS BARRY WALLACE, COOMBS, BARRY, WALLACE
Applicants: COOMBS BARRY WALLACE, COOMBS, BARRY, WALLACE
Application year: 1985
Main classification: F16H1
IPC codes: F16H48