GB2155589A

GB2155589A - Transmission shaft

Info

Publication number: GB2155589A
Application number: GB08503645A
Authority: GB
Inventors: Hans Heinrich Welschof
Original assignee: Loehr and Bromkamp GmbH
Current assignee: GKN Driveline Deutschland GmbH
Priority date: 1984-03-12
Filing date: 1985-02-13
Publication date: 1985-09-25
Also published as: GB8503645D0; BR8500697A; IT1186260B; JPH0114051B2; JPS60193722A; IT8506913V0; IT8505111A0; GB2155589B; IT8505111A1; FR2560831A1; DE3408940C2; DE3408940A1; FR2560831B1

Abstract

A propeller shaft for a motor vehicle, comprising two parts each of which comprises at least one tubular element 4, 5, interfitting telescopically to define an annular space 6 therebetween containing a viscous medium such as a silicone oil. Torque is transmitted between the shaft parts by shearing of the medium therebetween, permitting torsional and possibly axial shock absorption. <IMAGE>

Description

SPECIFICATION Transmission shaft This invention relates to a transmission shaft suitable for use in a motor vehicle. The shaft has at each end a connecting member which either forms part of or is adapted to be connected to a torque transmitting universal joint, either a Hookes joint or a constant velocity ratio joint, and such a shaft is commonly termed the propeller shaft when it is installed to extend generaily longitudinally of the vehicle, to connect, for example, a forwardly mounted engine and gearbox with a rear axle in a conventional rear wheel drive vehicie, or a transfer box with a front or a rear axle in the case of a four wheel drive vehicle.

It is usual to provide such a transmission shaft with means which permits adjustment of the length of the shaft, for convenience in assembly and/or to accommodate length changes due to suspension movement in service. Such length adjustment is usually provided by incorporating a splined joint in the shaft. It is also known to provide transmission shafts with a torsionally resilient property, for example by arranging for torque to be transmitted through a layer of a flexible material such as rubber. This provides for attenuation of shock torque loadings, and acts as a damper to prevent natural frequencies of vibration of the drive line from reaching dangerous ranges of resonance.It is also known to incorporate a multi-plate clutch running in oil in a transmission shaft, for similar purposes, but this has a penalty in that the clutch assembly increases the weight of the shaft and requires increased space for its instalation.

it is the object of the present invention to provide a transmission shaft which can provide for length adjustment, and has the above properties of torsional damping and attenuation of shock torque loads. It is desirable that such objects are achieved without requiring any additional space for the shaft, and it is further desirable that the shaft length should be capable of being- fixed or allowed to vary slightly under axial forces.

According to the invention, we provide a transmission shaft for motor vehicles, comprising two interfitting shaft parts having connecting members at their free ends, wherein each of said shaft parts comprises at least one tubular element, said tubular elements interfitting telescopicaily to define at least one annular space therebetween containing a viscous medium, there being provided sealing means at the outermost tubular element for retaining said viscous medium therein.

In such a shaft, torque is transmitted by way of the viscous medium in the annular space or spaces between the tubular elements, the viscous medium being subjected to a shear stress. The width of the annular space or spaces, the viscosity of the medium and the dimensions of the opposed surfaces of the tubular elements are preferably chosen such that torque is transmitted in use without there being a substantial speed differential between the tubular elements. Consequently, one usually finds small annular spaces of a typical width less than 1 mm, high viscosity medium, and large shear faces. To provide the latter, each of the shaft parts preferably comprises two concentric tubular elements, to define three annular spaces.The design of the shear faces and the selection of viscous medium may be such that at small speed differences only a small torque, and at greater speed differences a high torque, can be transmitted.

By use of such a shaft, it may be possible to replace the central (inter-axle) differential in a four wheel drive vehicle, the shaft taking over the function of a limited slip differential gear.

The selection of the properties of the shaft may be such that a difference in speed between the parts is achieved in the case of unevenness in the torque transmitted, or shock torque loadings. In such cases, the shearing of the viscous medium occurs and torque variations are damped or shocks attenuated. Similarly, the shaft has a damping effect in the case of axial impacts. In order to obtain a quasi rigid coupling between the parts of the shaft, appropriate dimensioning of the annular spaces and lengths of the tubular elements is required.

A shaft in accordance with the invention requires a small amount of radial space, i.e.

the diameter of the shaft need be no greater than that of a conventional shaft. The weight and cost of the shaft are lower than employing a conventional shaft and additional equipment such as a multi-plate clutch.

In one preferred embodiment of the invention, the interior of the inner tubular element is at least partially filled with the viscous medium. The annular spaces between the tubular elements are connected to the interior, so that the viscous medium can flow into and out of such interior if this is necessary due to changes in length of the shaft.

In one embodiment, a medium-containing part of the interior of the inner tubular element is separated by a pressure resistant wall from a part of the interior not containing the medium. This provides that the volume of medium in the interior of the inner tubular element is kept constant, so that change in length of the shaft, which would cause displacement of the viscous medium to or from the annular space or spaces, is resisted. The free end of the outer tubular element may be attached mechanically to a connecting member for a universal joint, and if changes in length of the shaft are required, a plunging constant velocity ratio universal joint must be utilized.

The connecting member which is adjacent the medium-containing part of the interior of the shaft may include a channel leading to the outside of the shaft, and including an excess pressure relief valve. Then, while the length of the shaft is basically determined by the amount of medium containing therein, the pressure relief valve may allow medium to escape if the pressure thereof increases beyond a pre-determined, possibly adjustable, value. When the pressure relief valve is opened, the shaft length is adjustable.

In cases where conventional propeller shafts are used, high axial forces may be caused if the vehicle is in a collision. In such a case, not only the front part of a vehicle may be damaged but the impact is transmitted by way of the propeller shaft to the rear thereof, thereby deforming the rear axle and possibly the entire rear part of the vehicle. With a shaft according to the invention, however, the shaft can yield axially under the impact, in a manner which provides an appreciable axial damping effect. This can be beneficial in such a collision. As an alternative to providing the channel containing the excess pressure relief valve through the connecting member to the exterior of the shaft, it would of course be possible to lead it through the pressure resistant wall to a part of the shaft interior not filled with the viscous medium.

In another embodiment of the invention, a medium-containing part of the shaft interior may be separated from a part of the interior not containing the medium by a wall yieldable to the pressure-of the medium. Then, the length of the shaft may change to the extent that the wall yields to the pressure of the medium. In one embodiment, such wall may be a piston movable in the inner tubular element, which piston is loaded by the pressure of the medium on one side and, if axial forces are sufficiently high, may move within the inner tubular element. A further possibility is that the yieldable wall is a membrane which ruptures when the pressure of the viscous medium exceeds a pre-determined value.As in the case where an excess pressure relief valve is provided, the medium may flow into the otherwise air-filled interior of the inner tubular element, whereupon the shaft length is no longer fixed. Preferably, the part of the shaft interior not containing the viscous medium is connected with the outside air by way of a channel extending through the associated connecting member. This ensures that the airfilled part of the interior is always at atmospheric pressure.

Spring means may be provided, operative between abutment means associated with said tubular elements, to bias said tubular elements to a pre-determined axial position relative to one another. Such springs provide a restoring force if the shaft is compressed or extended.

At least one connecting member may form part of or be adapted for connection to a plunging constant velocity ratio universal joint. Dynamic changes in shaft length in service are then accommodated in the plunging joint, whereas only the relatively greaterchanges in length, e.g. during instalation, are accommodated by the shaft itself. Otherwise the universal joints may be of conventional design.

The tubular elements of the shaft may be provided with uneven surfaces, holes or slots.

This enables a larger quantity of viscous medium to be carried, and the shear effect is increased. The viscous medium may be a silicone oil, which is available in a range of different viscosities.

The invention- will now be described by way of example with reference to the accompany drawings, of which: Figure 1 is a longitudinal section of one embodiment of shaft according to the invention; Figure 2 is a section on line A-B of Fig. 1; Figure 3 is a longitudinal section through a further embodiment of shaft according to the invention; Figure 4 is a longitudinal section through yet another embodiment of shaft according to the invention; Figure 5 is a longitudinal section through part of yet another embodiment of shaft according to the invention.

Referring firstly to Fig. 1, there is shown a transmission shaft 1 having at one end a plunging constant velocity ratio universal joint 2 at its other end a yoke 3 of a Hookes universal joint. A connecting member 2a which has a splined end portion to engage the joint 2, is welded to two concentric tubular elements 4. A connecting member 3a, which is welded to the Hookes joint yoke 3, is welded to two concentric tubular elements 5.

The tubular elements 4, 5 are dimensioned so that they fit together telescopically, with three annular spaces 6 defined therebetween. The dimensions of the tubular elements are such that the annular spaces each have a width of about 1 mm, and the wall thicknesses of the tubular elements may be of the order of 1.5mm to 2mm. At its end remote from the connecting member 2a, the innermost tubular element 4, at four diagonally opposed regions, is bent outwardly to form supporting brackets 4a. They engage the interior of the innermost tubular element 5. Similarly, the innermost tubular element 5 is bent inwardly to form four brackets 5a. Thus, the tubular elements 4, 5 are centered relative to one another, and are able to move axially relative to one another.

The free end of the outermost tubular element 5 is expanded at 5b, and contains an annular seal 7 which engages the exterior of the outermost tubular element 4. A retaining ring 8 holds the seal 7 in place, even if there is relative movement between the tubular elements 4, 5. The entire interior 9 of the shaft is filled with a viscous silicone fluid, the brackets 4a, 5a permitting communication of such medium between all the annular spaces 6 and the inside of the innermost tubular element 4. Thus, torque is capable of being transmitted between the connecting members 2a, 3a by sheer force in the viscous medium.

Because the entire interior of the shaft assembly is full of the viscous medium, the length of the shaft is fixed.

Referring now to Fig. 3 of the drawing, parts corresponding to those in the embodiment of Figs. 1 and 2 are indicated by like reference numerals. Thus, the shaft comprises tubular elements 4, 5 aligned relative to one another by formations 4a, 5a and defining annular spaces 6 therebetween. In this case, however, the interior of the innermost tubular element 4 contains a piston 10 movable axially therewithin and sealed by an annular seal 1 0a. This piston separates a part 9a of the interior of the shaft filled with the viscous medium from a part 9b not containing such medium.Part 9b of the interior is connected by a passage 11 with the external atmosphere, so that the piston on one side is loaded by atmospheric pressure only, independently of its position, whereas at the other side of the piston the pressure of the viscous medium is applied. In this embodiment, changes in length of the shaft are possible, causing displacement of the piston 10 within the inner tubular element 4.

In the embodiment of Fig. 3, the part 5b of the outermost tubular element 5, which is expanded, is relatively longer than the embodiment of Figs. 1 and 2. The seal 7 and retaining ring 8 are of different form. An abutment ring 4c is attached to the outer tubular element 4, and a helical compression spring 1 2 is disposed between it and the retaining ring 8. The outer tubular element 4 also is provided with an abutment 4b at its free end, and a further helical compression spring 1 3 is disposed between such abutment and the connecting member 3a. The springs 12, 1 3 hold the tubular elements 4, 5 in the central position illustrated, i.e. if the shaft is compressed or extended the springs are effective to return the shaft to its original length.

To effect such length changes in the shaft, the force applied has to overcome the force of the spring 1 2 or 13, the frictional resistance to movement of the piston 10 and the resistance to axial movement cause by shear of the viscous medium contained within the shaft assembly.

Referring now to Fig. 4 of the drawings, the parts 9a, 9b of the shaft interior, respectively containing and not containing the viscous medium, are separated by a pressure resistant wall provided by a plug 14 in the free end of the innermost tubular element 4. The plug 14 has an annular sealing ring 14a. The plug 14 contacts the interior of the innermost tubular element 5 so that the tubular elements are concentrically guided relative to one another.

This arrangement provides a resistance to length changes in the shaft, because compression or extension thereof would place the viscous medium under increased or reduced pressure. In addition, the free end of the outermost tubular element 5 has been provided with a fixing ring 1 5 which engages the exterior of the connecting member 2a and is sealed thereto by an annular seal 1 5a. Limited relative axial movement between the tubular elements 4, 5 is possible, constrained by the dimensions of the ring 1 5.

Referring now to Fig. 5 of the drawings, this shows part of a shaft in which the innermost tubular element 4 has a plug 1 4 as in the embodiment of Fig. 4. In this case, there are no additional mechanical axial constraining means such as the fixing ring 1 5. The connecting member 3a, however, is provided with an axially extending passage 16, closed by a ball 1 6a held in contact with a seating by a spring 1 6b. This provides an excess pressure relief valve, providing communication between the part 9a of the interior of the shaft containing the viscous medium and the external atmosphere if the pressure in the viscous medium exceeds a predetermined limit. If this occurs, the ball 1 6a is displaced from its seating against springs 1 6b and allows the viscous medium to escape. The tubular elements 4, 5 are then no longer fixed axially relative to one another and the shaft may be compressed, e.g. in the case of an axial impact, with at least part of the energy of such impact being absorbed by shearing of the viscous medium between the tubular element.

Claims

1. A transmission shaft for motor vehicles comprising two interfitting parts having connecting members at their free ends wherein each of said shaft parts comprises at least one tubular element, said tubular elements interfitting telescopically to define at least one annular space therebetween containing a viscous medium, sealing means being provided at the outermost tubular element for retaining said viscous medium therein.

2. A shaft according to Claim 1, wherein each of said shaft parts comprises two concentric tubular elements to define three annular spaces.

3. A shaft according to Claim 1 or Claim 2, wherein the width of said annular spaces, the viscosity of the medium and the dimensions of the opposed surfaces of said tubular elements are such that torque is transmitted in use without there being a substantial speed differential between the shaft parts.

4. A shaft accocrding to any one of Claims 1 to 3, wherein the interior of the inner tubular element is at least partially filled with said viscous medium.

5. A shaft according to Claim 4, wherein a medium-containing part of the interior of the inner tubular element is separated by a pressure resistant wall from a part of said interior not containing said medium.

6. A shaft according to any of of the preceding claims, wherein the free end of the outer tubular element is attached mechanically to a connecting member for a universal joint.

7. A shaft according to any one of the preceding claims, wherein one of said connecting members, which adjoins a mediumcontaining part of the interior of the inner tubular element, contains a channel leading to the outside and having an excess pressure relief valve.

8. A shaft according to Claim 4, wherein a medium-containing part of the interior is separated from a part of the interior not containing said medium by a wall yieldable to the pressure of the medium.

9. A shaft according to Claim 8, wherein said wall is a piston movable in said inner tubular element.

10. A shaft according to Claim 8, wherein said wall is a membrane which ruptures if the pressure of the medium exceeds a predetermined level.

11. A shaft according to any one of Claims 8 to 10, wherein said part of the interior not containing the viscous medium is connected with the outside air by way of a channel extending through the associated connecting member.

1 2. A shaft according to any one of the preceding claims, wherein spring means is provided, operative between abutment means associated with said tubular elements, to bias said tubular elements to a predetermined axial position relative to one another.

1 3. A shaft according to any one of the preceding claims, wherein at least one connecting member forms part of or is adapted for connection to a constant velocity plunging joint.

1 4. A shaft according to any one of the preceding claims, wherein said tubular elements have been provided with uneven surfaces, holes or slots.

1 5. A shaft according to any one of the preceding claims, wherin the viscous medium is a silicone oil.

1 6. A shaft substantially as hereinbefore described with reference to the accompanying drawings.