GB2174154A - Flexible drives - Google Patents

Abstract

A bushing (20) to cover the portion of a mechanical drive cable entering a motor or gear assembly is composed essentially of urethane and has the shape of an elongated cylinder with a longitudinal axial opening (28) running its entire length. Each end of the opening is countersunk having its edges (30, 32) at about a 15 DEG angle to the longitudinal axis of the bushing. The diameter of the opening is about one-half of the outside diameter of the bushing. <IMAGE>

Description

SPECIFICATION Flexible drives The present invention relates to flexible drives and in particular to flexible drive cables as are used, for example, in the power-operated seat-adjusting mechanism of an automotive vehicle.

In such mechanisms it is necessary to transmit the mechanical torque that is produced by electric motors to a drive shaft. The drive shaft usually comprises a threaded shaft that, by its rotation, moves a seat drive mechanism having a threaded opening receiving the shaft. Due to the physical arrangement of the seat drive mechanism, it is usually not possible to have the motor output shafts aligned with the gear mechanism driving the shaft. Further, as a multiple adjustable seat has multiple adjustment directions, there are frequently three or more motor drive shafts to provide the desired adjustment. Such motors are usually combined into a single housing from which the three or more drive shafts protrude. Accordingly, the mechanical drive cables from the motor shafts must be flexible to connect with the different gear mechanisms to drive the various shafts.Such flexibility provides a degree of design adaptability for the power seat mechanism in that a single three shaft motor unit can be connected to gear mechanisms in slightly differing locations by a simple selection of the correct length of flexible mechanical drive cable.

However, it is aiso desirable to have the motor drive mechanism as quiet as possible.

A special concern is the degree of joint looseness that occurs in particular seat-adjusting joints. For example, when a tilt adjuster mechanism of a power seat is actuated from one position to another, the joint looseness must be taken up before the tilt mechanism begins to move. As a result the electric motor driving the tilt mechanism will run at a very high no-load speed until the joint looseness is taken up. During this short interval the sound level produced by the mechanical flexible drive cables running and actually whipping about at high speed will be objectionable.

One method of reducing such cable noise is to house a portion of the flexible cable in a sheath filled with viscous grease. This forces the cable to shear through the grease upon whipping or lateral motion and thus to increase the load on the motor. Accordingly the drive speed and noise produced by the cable are reduced. This method is undesirable when a relatively short length of cable is used as assembly time and effort become impractical.

Another method of quietening such drive cables is th sheath a portion of the cable in rubber. Usually the portion of the cable covered is the portion entering the motor or the gear assembly. Various types of rubbers with various properties have been tried. The usual result is that the rubber does not absorb the cable whip energy and instead elastically intensifies the whip energy and resulting noise.

Other materials have been tried including nylon, polyethylene and polypropylene, all without success.

One particular problem with many of the sleeve materials is the abrasion resistance of the material to the metal cable rotary motion.

Certain materials of a relatively low durometer hardness have been found to provide adequate sound attenuation for an initial period of operation. However, after a certain number of operations, the drive cable is likely to cut through or channel into the interior wall of the sleeve. This permits the cable to whip about and produce objectionable levels of noise.

Such abrasion usually occurs near the ends of the sleeves especially when the cable ends are laterally offset in their connection from the motor to the gear mechanism.

According to the invention in its broadest aspect there is provided a bushing for a flexible drive cable comprising an elongated, cylindrical body having a longitudinal axial opening extending there-through from either end of the body, each end of the opening being countersunk.

The material from which the bushing is made is essentially urethane, with a durometer hardness number of about 38. The urethane material has shown excellent abrasion-resistance characteristics together with the desirable degree of noise attenuation. The desired tensile strength is about 4000 psi and elongation about 550%. The diameter of the opening is about one half the diameter of the outside of the bushing. Accordingly, the bushing can be appropriately sized to accept various diameter drive cables.

At either end of the bushing, where the axial opening begins, the lip of the opening is countersunk to provide a chamfer in the end of the opening. The angle of such chamfer is about 15 from a longitudinal with the opening axis. The chamfer is uniform about the bushing end, and extends inwardly to a depth of about one quarter the outer diameter of the bushing. Such a chamfer angle will permit the bushing to accommodate a cable connecting a motor to a gear mechanism when the two are horizontally offset from each other.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a top view in partial cross section of a portion of a power-operated seatadjusting mechanism utilising the bushing of the present invention, and Figure 2 is a longitudinal sectional view of the bushing of the present invention.

Referring now to Fig. 1, a power-operated seat-adjusting mechanism includes a motor unit 10 having flexible drive shafts 11, 12 and 14 extending therefrom. Motor unit 10 is mounted on a portion of the seat frame 16. A drive shaft 11 terminates at a gear assembly 21 and has its end surrounded by a partial sleeve or bushing 19. Drive shaft 12 terminates at a gear assembly 24. The end of shaft 12 entering gear assembly 24 is surrounded by a bushing 20. A portion of bushing 20 is cut away to show the opening therethrough. Shaft 14 enters gear assembly 26 and has its end surrounded by bushing 22.

Bushings 19., 20 and 22 are essentially comprised of urethane.

Referring now to Fig. 2 a detailed crosssectional view of bushing 20 is shown. Bushings 19 and 22 are of identical configuration.

Bushing 20 is an elongated cylinder having a longitudinal axial cylindrical opening 28 therethrough. Each end of opening 28 has a chamfered or countersunk configuration, with edges 30 and 32 extending uniformly inwardly to a depth of about one-fourth the outer diameter of the bushing. Edge 32 (and similarly edge 30) form an angle a at about 15" to the longitudinal axis of opening 28. Of course, this angle could be varied depending on the length of bushing 20 and the relative offset between the motor output shaft and gear assembly 24.

It should be noted that flat end portions 33, 35 perpendicular to the axis of bushing 22 are present at both ends of opening 28.

Claims (10)

1. A bushing for a flexible drive cable comprising an elongated, cylindrical body having a longitudinal axial opening extending therethrough from either end of the body, each end of the opening being countersunk.

2. A bushing as claimed in claim 1 which is composed essentially of urethane.

3. A bushing as claimed in claim 1 or 2, wherein the countersunk opening sides are at an angle of about 15 to the longitudinal axis of the bushing.

4. A bushing as claimed in any preceding claim wherein the diameter of the opening in the bushing is about one-half the outside diameter of the bushing.

5. A bushing as claimed in claim 2, 3 or 4, wherein the urethane material has a durometer hardness of about 38.

6. A bushing as claimed in any preceding claim, wherein the countersunk opening at the end of the bushing has a depth equal to about one quarter the outer diameter of the bushing.

7. A power-operated seat-adjusting mechanism for an automotive vehicle comprising one or more flexible drive cables passing through respective bushings according to any preceding claim.

8. A power-operated seat-adjusting mechanism as claimed in claim 7 wherein the diameter of the longitudinal axial opening in the or each bushing is approximately equal to the diameter of the cable passing therethrough plus about 0.04 inches (0.1 cm).

9. A bushing for a flexible drive cable substantially as described with reference to the accompanying drawings.

10. A power-operated seat-adjusting mechanism for an automotive vehicle substantially as described with reference to the accompanying drawings.