GB2182402A

GB2182402A - Fluid friction coupling

Info

Publication number: GB2182402A
Application number: GB08622317A
Authority: GB
Inventors: Jurgen Stockmar; Heribert Lanzer
Original assignee: Steyr Daimler Puch AG
Current assignee: Steyr Daimler Puch AG
Priority date: 1985-09-16
Filing date: 1986-09-16
Publication date: 1987-05-13
Also published as: GB8622317D0; DE3630974A1; ATA269385A; DE3630974C2; AT383877B; GB2182402B

Abstract

Two interlocking coaxial sets of clutch elements (12, 13) are arranged in a casing (2) filled with viscous fluid, the elements (12, 13) being relatively movable axially to alter the gap therebetween. In order to vary the coupling characteristics automatically in dependence on the torque transmitted, a further clutch (4-9) is arranged in series with the clutch elements (12, 13). The clutch (4-9) comprises two clutch members (4, 5) with balls 9 in recesses 8 therebetween. One clutch member (5) acts as a pressure plate which moves axially and acts on one set of the elements (12), (13) during 10 relative rotation of the clutch members (4, 5). The member (5) has projections (6) engaging between rubber members (7) inserted in the member (4) and a spring-loaded ball (15) in one projection (6) engages a groove in the member (4) and forms a catch preventing relative rotation of the members (4, 5) until a predetermined torque has been exceeded. <IMAGE>

Description

SPECIFICATION Fluid friction coupling This invention relates to a fluid friction coupling having elements forming two coaxial interlocking sets, enclosed in a casing filled with viscous fluid and axially adjustable for varying the width of the gap between the elements.

In fluid friction clutches of this kind, torque is transmitted via shear stresses in the viscous fluid in the gaps between the clutch elements. The slip or speed of rotation of the driven part of the clutch can be adjusted by varying the width of the gap by moving the clutch elements relative to one another. The drive or transmittable torque is approximately inversely proportional to the gap width.

In a known fluid friction clutch of this kind (US 1 238 447) the two sets of clutch elements are discs having a number of coaxial annular projections, the projections being biconical, i.e. formed with a conical inner and outer peripheral surface, so that both sets are comb-shaped in radial section. The annular projections on the two discs are directed towards one another and radially offset from one another on gaps, so that the annular projections on one disc can penetrate into the annular gap in the other disc during axial displacement of the coupling elements, which are formed by the annular projections. Since these annular projections have conical inner and outer surfaces, the gap width between the interlocking coupling elements and consequently the amount of transmittable torque varies with the depth of penetration.This known fluid friction clutch has a comparatively compiicated construction and is expensive to manufacture, since the interlocking sets of clutch elements, i.e. the discs with annular projections, cannot be manufactured easily and cheaply from sheet metal or the like but need accurate finishing. Furthermore, the active surfaces of the clutch elements need to have a large radial dimension if they have to transmit large torques. It is also advantageous if the areas of the annular projections bounding the gaps vary when the clutch elements are inserted and disengaged. A final important point is that the gap width cannot be altered automatically but has to be done independently.

There is also a known fluid friction clutch (FR 776 210) where one part of the clutch is a casing filled with viscous fluid, into which the other part of the clutch (a shaft) engages.

The casing on the one hand and the shaft on the other hand are non-rotatably connected to interlocking plates which are mounted so as to be axially movable. Thin end spacers are disposed between the plates. In this case, however, the plates are moved and consequently the spacing is changed in dependence on the operating temperature of the viscous fluid, in order to compensate the decrease in the viscosity of the fluid with increasing temperature, which reduces the transmittable torque.

In the case of conventional, non-adjustable fluid friction clutches, the structural viscosity of the fluid used results in a less than proportional increase in torque characteristic with the difference in speed between the two parts of the clutch. The transmitted torque can therefore be doubled only by more than doubling the difference in speed. This results in a disproportionate increase in heat losses per unit time. If these cannot be dissipated via the clutch casing, they result in a decrease in the viscosity of the fluid and consequently in the torque characteristic.Finally it is known (DE 424 788) to compress plates axially, using thrust portions, but the device in question is a conventional disc clutch disposed behind a claw clutch and brake or synchronising device, the plates being compressed by external force when the claw clutch is engaged, so that the problem is quite different.

An object of the present invention is to improve the initially-described fluid friction clutch so that the clutch characteristic can be automatically changed in dependence on the amount of torque to be transmitted.

The invention provides a fluid friction coupling as claimed in claim 1.

The angle of relative rotation of the members in the torsionally-resilient clutch varies with the amount of torque to be transmitted.

Since however the relative rotation of the clutch members results in axial displacement of the pressure plate acting on the interlocking sets of clutch elements, the width of the gap between the elements varies with the transmitted torque. Consequently the spacing between the sets of elements is not varied as previously in dependence on the operating temperature or by external forces, but automatically dependent on the torque being transmitted by the coupling. The axial displacement of the clutch member acting as a pressure plate, and consequently of the interlocking sets of clutch elements, also changes the volume of the space in the fluid friction clutch, thus increasing the filling ratio and additionally varying the clutch characteristic by increasing the transmittable torque.

In a preferred embodiment of the invention a spring-mounted catch device is arranged between the clutch members of the torsionallyresilient clutch so as to prevent relative rotation between the clutch members until a given limiting torque has been exceeded. In this manner, the action of the torsionally-resilient clutch, and consequently the change in the gap width between the sets of clutch elements, does not begin until a given torque or a given difference- in speed between the clutch elements has been exceeded, i.e. the characteristic is "soft" in the lower differential speed range.

Preferably, the clutch member acting as a pressure plate of the torsionally-resilient clutch is formed with an inner casing carrying one of the sets of clutch elements.

An embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 shows a fluid friction clutch in axial section; and Figure 2 shows a cross-section taken along the line ll-ll of Fig. 1.

A fluid friction clutch, constructed as a disc clutch, has a casing comprising an outer casing 1 and an inner casing 2 filled with viscous fluid, the outer casing 1 being driven by a shaft 3. A torsionally-resilient clutch is disposed between the outer casing 1 and the inner casing 2 and comprises a disc 4 nonrotatably connected to casing 1 and a disc 5 welded to casing 2. Disc 5 has axially parallel projections 6 engaging in rubber members 7 inserted in disc 4. Discs 4, 5 have V-section recesses 8 tapering inwardly on both sides in the peripheral direction and receiving balls 9.

During relative axial rotation of discs 4, 5, which is permitted by the rubber members 7, the discs are urged axially apart owing to the special shape of the recesses 8. Since the disc 4 is fixed, the axial displacement occurs only for the disc 5 attached to the inner casing 2.

A hollow shaft 10 is rotatably mounted in the inner casing 2 and has a power take-off 11. The casing 2 and the shaft 10 are nonrotatably connected to two interlocking sets of plates 12, 13, respectively, resilient spacers 14 being inserted between the inner plates 13. The disc 5 acts via a thrust bearing on the set of inner plates 13, the other side of which bears, likewise via a thrust bearing, on an end cover of the casing 1.

If an increase in the transmitted torque results in relative rotation of the discs 4, 5 forming the torsionally-resilient clutch, the disc 5 is pushed away from the axially fixed disc 4, as described above, and acts as a pressure plate on the set of elements formed by the inner plates 13, thus reducing the width of the gap between the inner.and outer plates 12 and 13. A spring-loaded ball 15 is mounted in one of the projections 6 of the disc 5 and engages in a shallow groove in the disc 4.

The resulting catch device does not allow relative rotation of the discs 4, 5 until a given limiting torque has been exceeded and presses the ball 15 radially inwards against spring pressure out of the groove in the disc 4.

Claims

1. A fluid friction coupling comprising two axially-aligned sets of interlocking clutch elements arranged in a casing containing viscous fluid, the axial spacing between the clutch elements being adjustable to vary torque transmission, and a torsionally-resilient clutch having two clutch members, one of the clutch members acting as a pressure plate and being axially movable during relative rotation of the clutch members so as to vary the axial spacing between the clutch elements.

2. A coupling as claimed in claim 1, wherein a spring-mounted catch device is arranged between the clutch members of the torsionally-resilient clutch so as to prevent relative rotation between the clutch members until a given limiting torque has been exceeded.

3. A coupling as claimed in claim 1 or 2, wherein the clutch member acting as a pressure plate of the torsionally-resilient clutch is formed with an inner casing carrying one of the sets of clutch elements.

4. A fluid friction coupling as herein described with reference to the accompanying drawings.