GB2358899A

GB2358899A - Unidirectional worm drive unit

Info

Publication number: GB2358899A
Application number: GB0002439A
Authority: GB
Inventors: David Robert Shearing
Original assignee: Trico Products Corp
Current assignee: Trico Products Corp
Priority date: 2000-02-04
Filing date: 2000-02-04
Publication date: 2001-08-08
Anticipated expiration: 2020-02-04
Also published as: GB2358899B; GB0002439D0

Abstract

A drive unit 1 for a windscreen wiper assembly, comprising a worm 101, the thread of the worm 101 engaging the teeth 111 of the gear wheel 110 which is connected to a pivot shaft 120, wherein the pivot shaft 120 and/or gear wheel 110 is/are provided with means, such as a roller clutch 5 or resilient means (fig 4), only allowing rotation thereof in a single direction.

Description

1 2358899 DRIVE UNIT DESCRIXTION This invention relates to a drive unit

and, more specifically, a drive unit which may be used for automobile windscreen wipers.

Electric motors are used to drive members or elements in a variety of situations. Conventionally, such motors drive automobile windscreen wipers.

In most circumstances, the electric motor drives a shaft which, in turn, drives a worm. The worm engages the teeth of a gear wheel which is drivingly connected to an output shaft. The output shaft drives a crank, which is drivingly connected to the proximal end of a windscreen wiper arm, and causes reciprocal pivotal motion thereof, thereby ensuring that the windscreen wiper blade traverses the windscreen to effect its cleaning and clearing of rain or debris.

In order to guarantee smooth, quiet running of such a -systern the components may be machined to within small tolerances to ensure their mutual compatibility. However, in order to reduce frictional losses the thread of the worm and teeth of the gear wheel are not perfectly matched. The worm drives against one side of the teeth of the gear wheel only, to mitigate, or at least substantially reduce, these frictional losses. If, for example, the two sets of teeth were perfectly mated, not only are the manufacturing costs greatly increased but also the thread "pinches" the engaged teeth of the gear, which increases the friction between the components and consequently the wear.

Thus, in practically all cases, these two components are not machined to be absolutely compatible and there is some so-called "play" in the system.

This play results in what is known as "backlasW, which is to say that when the worm stops driving the gear, the gear travels in an opposite direction to the direction in which it has been driven and knocks against the thread of the worm. This backlashing causes wear of the components and noise.

As the wear of the components increases, the backlashing becomes worse and consequently the noise increases. As the wear and noise becomes progressively worse the performance of the windscreen wiper assembly can deteriorate. Indeed, excess wear can cause blade flutter, which affects the efficacy of the wiper system.

It is therefore desirable to substantially reduce backlashing in such a system. BOSCR in their patent WO 99/00278, have suggested a possible solution. They describe an assembly wherein the drive or output shaft is mounted in an eccentric bushing which can be rotated to alter the distance between the output shaft and worm. By altering the relative position of the two components backlash, and the problems associated therewith, can be reduced.

It has been found, however, that BOSCH does not provide an effective reduction of backlash in all circumstances and, furthermore, it requires machining to relatively small tolerances.

Accordingly, it is an object of the present invention to provide a drive unit in which backlash is significantly reduced and which can provide a relatively inexpensive and yet resilient solution to the problem.

According to a first aspect of the invention there is provided a drive unit for an automobile windscreen wiper assembly comprising a worm driveable by a drive motor, the thread of the worm engaging the teeth of a gear wheel via which a connected pivot shaft is driveable, wherein the pivot shaft and/or gear wheel are provided with means to allow rotation thereof in the 30 driven direction only.

In a preferred embodiment the means is disposed about the pivot shaft.

Preferably the means comprises at least one needle roller clutch and, more preferably, two needle roller clutches each of which may be disposed about opposed ends of the pivot shaft.

Alternatively or additionally, the gear wheel comprises the means to allow rotation in the driven direction only.

The gear wheel may comprise two matched identical gears mounted such that the respective teeth are out of phase and connected by one or more resilient members.

The resilient members may be springs and each gear is arranged to be rotatable in the driven direction only.

The pivot shaft may be received in a bore of a housing which accommodates the gear wheel and the worm.

According to a second aspect of the invention there is provided an automobile windscreen wiper assembly comprising at least one windscreen wiper arm arranged to traverse, in use, a windscreen, the arm being driveable by a pivot shaft which is rotatably driveable about its longitudinal axis by a worm, wherein the pivot shaft is arranged to allow unidirectional rotation 25 thereof only.

Preferably means disposed about the pivot shaft allows said unidirectional rotation thereof The means may comprise at least one, and preferably two, needle roller clutches. Each of the two needle clutches may be 30 disposed about opposed ends of the pivot shaft.

Embodiments of the invention in accordance with the aspects of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a schematic plan view of a conventional worm and gear wheel., the invention; Figure 2 is an isometric "cut-away" view of the first embodiment of Figure 3 is an isometric view of a needle roller clutch; and Figure 4 is an isometric view of a worm and gear wheel according to a second embodiment of the invention.

Referring in the first instance to Figure 1, there is shown a drive assembly generally indicated at 100, comprising a worm 101, a gear wheel 110 and a pivot or output shaft 120.

The worm 10 1 is connected to an armature of a motor (not shown), through which it is arranged to rotate about its longitudinal axis as indicated by arrow A. The thread 102 of the worm 10 1 has a pitch or wavelength P and is engaged with the teeth 111 of the gear wheel 110. The teeth 111 of the gear wheel 110 have a pitch Y.

Rotation of the worm 10 1 about arrow A causes corresponding rotation of the gear wheel 110 about arrow B. The gear wheel 110 has a pivot shaft 120 connected centrally, and extending normally, thereto which consequently rotates about its longitudinal axis in the direction of B. The other end of the shaft 120 may be connected via a crank (not shown), for example, to a proximal end of a windscreen wiper arm (also not shown). Whereby rotation of the worm 10 1 causes rotation of the pivot shaft 120 and corresponding reciprocal motion of the wiper arm across a windscreen to effect cleaning or clearing thereof In operation, the thread 102 of the worm 10 1 drives against one face, for example 115, of the teeth 111 of the gear wheel 110. Once the motor has stopped driving the worm 101 inherent resistance and inertia in the system causes the gear wheel 110 to "backlash" against the worm 10 1, forcing the driven faces 115 of the teeth 111 to drive against the thread 102 of the worm 101.

The effect of this "backlashing" is to create noise and to wear the respective colliding components 102, 115. As previously stated, excessive wear on the components has the effect of affecting the efficiency and efficacy of the wiper system. Such wear may require the components to be replaced.

Referring now to Figure 2, in which similar components have been denoted by the numbers utilised above, there is shown a drive assembly generally indicated at 1, comprising comprising a worm 101, a gear wheel 110 20 and a pivot or output shaft 120.

In a similar fashion to that described above, rotation, in the direction of A, of the worm 10 1 about its longitudinal axis X-X', causes rotation of the shaft 120 in the direction of B about its longitudinal axis Y-Y.

The distal end 121 of the shaft 120 may be connected to a crank (not shown) which may drive a windscreen wiper arm (also not shown).

The shaft 120 and gear wheel 110 are accommodated within a housing 30 10, with the shaft housed in a bore 11 thereof Frictionally retained and positioned within the bore 11 of the housing 10 are two needle roller clutches 5, which are disposed about opposite ends of the shaft 120.

Figure 3 shows a needle roller clutch 5. Each roller clutch 5 is cylindrical with a central bore 6 through which the shaft 120 extends. The internal cylindrical wall 7 of the clutch 5 has a plurality of rotatable cylinders 8 mounted therein. Each of the cylinders 8 is rotatable in the direction denoted by the arrows C only.

Thus, and as shown in Figure 2, if a roller clutch 5 is ffictionally fitted around the output shaft 120 it only allows rotation of the output shaft 120 in one direction, the driven direction B. Therefore, and in contrast to the assembly shown in Figure 1, once the worm 101 has stopped driving the shaft 120 in the direction B the or each needle clutch 5 resists any, or at the least most, backlashing motion. The roller clutch 5 is chosen such that it can resist the maximum force exerted in the backlashing motion of the system 1.

Figure 4 shows part of a drive unit, generally indicated at 30, comprising a worm 10 1 drivingly rotateable in the direction A, a gear wheel 60 and an output shaft 120 rotateable in the direction B. The gear wheel 60 comprises two identical gears 61, 62 with matched teeth 71. The gears 61, 62 are mounted such that their respective teeth 71 are slightly out of phase with respect to one another. The gears 61, 62 are connected together by internally mounted springs (not shown) such that if one gear 61 is engaged by the worm 101 the other gear 62 has exerted thereon a force by virtue of the interconnecting spring. The non-driven gear 62 is thereby encouraged to travel in the same direction as the first 61.

The fact that the gears 61, 62 are slightly out of phase means that the effective pitch of the gear wheel 60 is reduced and this affords the assembly less play than would be possible if the gears 61, 62 were in phase. Both gears 61, 62 are only rotateable in the driving direction by virtue of the internally mounted spring mechanism. Thus, the gear wheel 60 resists any backlashing motion once the worm 10 1 has ceased driving it.

Whilst the embodiments show drive units in which either needle roller clutches or anti-backlash gears are provided, it is obviously possible, and in some circumstances desirable, to provide a drive unit comprising both means. In wiper assemblies where high torque is transmitted during backlash, both io means are utilised.

Therefore, both of the embodiments described herein provide a new means to reduce backlashing in drive units. As described they have particular use in windscreen wiper assemblies due to the large forces present and the problems associated with backlash in such systems. However, as described these systems could be used in a variety of situations where backlash is a known and undesirable.

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Claims

A drive unit for an automobile windscreen wiper assembly, comprising a worm drivable by a motor, the thread of the worm engaging the teeth of a gear wheel via which a connected pivot shaft is drivable, wherein the pivot shaft and/or gear wheel is/are provided with rneans to allow rotation thereof in the driven direction only.
2. An assembly according to claim 1, wherein said means is disposed 10 about the pivot shaft.
3. An assembly according to claim 1 or 2, wherein said means comprises at least one needle roller clutch.
4. An assembly according to claim 3, wherein said means comprises two needle roller clutches each of which is disposed about opposed ends of the pivot shaft.
5. An assembly according to any preceding claim, wherein the gear 20 comprises said means to allow rotation in the driven direction only.
6. An assembly according to claim 5, wherein the gear wheel comprises two matched identical gears mounted such that the respective teeth are out of phase and connected by one or more resilient members.
7. An assembly according to claim 6, wherein the or each resilient member in a spring and each gear is arranged to be rotatable in the driven direction only.
8. An assembly according to any preceding claim, wherein the pivot shaft is received in a bore of a housing which accommodates the gear wheel and the worm.
9. An automobile windscreen wiper assembly comprising at least one windscreen wiper arm arranged to traverse, in use, a windscreen, the arm being drivable by a pivot shaft which is rotatably drivable about its longitudinal axis by a worm, wherein the pivot shaft is arranged to allow unidirectional rotation thereof only.
10. An assembly according to claim 9 including means disposed about the pivot shaft to allow said unidirectional rotation thereof
11. An assembly according to claim 10, wherein said means comprises at 15 least one needle roller clutch.
12. An assembly according to claim 10 or 11, wherein said means comprises two needle roller clutches.
13. An assembly according to claim 12, wherein each of the two needle clutches is disposed about a respective opposed end of the pivot shaft.
14. An automobile windscreen wiper assembly substantially as hereinbefore described with reference to the accompanying drawings and in 25 accordance with at least claim 1.