AU637784B2

AU637784B2 - Drive mechanisms

Info

Publication number: AU637784B2
Application number: AU49279/90A
Authority: AU
Inventors: Theodore William Reinhold
Original assignee: Bartlem Pty Ltd
Current assignee: Bartlem Pty Ltd
Priority date: 1989-02-08
Filing date: 1990-02-08
Publication date: 1993-06-10
Anticipated expiration: 2010-02-08
Also published as: AU4927990A

Description

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'IPEa DR11E WI JUli i laM ERE I ITI-IOLBJD so 0 00 0 0 S S (Patent Application No. PJ 2639) COMPLETE SPECIFI( .,ATION FOR THE INVENTION ENTITLED:- I"'DRIVE MECHANISMS" The following statement is full description of this invention, including the best method of performing it know to me/us:- This invention relates to improvements to clutch mechanisms and to actuating means therefor.

In particular, this invention relates to clutch mechanisms for reversible belt drive assemblies of the type illustrated in my earlier Australian Patent Specification No.

402230 in which opposed clutch plates disposed between contra-rotating pulley wheels are selectively engageable with the pulley wheels to reverse the direction of rotation of the shaft on which the pulley wheels and the clutch plates are 10 mounted. Such a drive is illustrated in Fig. 1 herein. Such drives have been incorporated in ride-on mowers to provide a reversible drive to the rear wheels. The clutch plates are actuated by a rocking type pedal in which heel pressure is used to engage one clutch plate for reverse drive and toe 15 pressure is used to engage the opposite clutch for forward drive.

A difficulty associated with such drives is that the power transmission from the clutches to the rear wheels is partly dependent upon the engagement force which may be 20 applied through the clutch actuating means and partly upon the drive belt tension. The engagement force may be insufficient in certain instances to enable the available power to be transmitted.

This difficulty arises because the contra rotating 25 pulley wheels are supported close together in order to minimise the loads on the drive shaft and thus the clutch actuating means has to be supported on a cantilevered bracket which extends between the spaced pulley wheels. In such assemblies the clutch movement is minimal and thus nyv play or deflection of the bracket will limit the engagemern force which can be applied to the clutch plates.

Severe stresses can be imposed on the drive shaft, especially when a user alternates between forward and reverse rotation of the drive shaft with the motor operating at high speed. Such stresses can lead to failure of the drive shaft.

The present invention aims to alleviate one or more of the abovementioned disadvantages and to provide improved clutch mechanisms and actuation means therefor which will be reliable and efficient and useful.

With the forgoing in view, this invention in one aspect resides broadly in actuating means for a forward and reverse drive mechanism of the type having a pair of contra-rotatable pulley wheels rotatably supported on a shaft, a clutch assembly selectively engagable with either one of the pulley wheels to select drive from either the forward or reverse rotating pulley wheel, characterised in that the actuating means includes an operating linkage having limiting means for limiting the engagement pressure between the clutch assembly and at least one of said pulley wheels.

The limiting means may be in the form of a spring which controls the maximum or initial engagement pressure of the respective clutch plate or the limiting means may be in the form of a damper which damps initial engagement of the clutch assembly with the engaged pulley wheel. Alternatively the limiting means may be a spring or the like associated with the foot control pedal and adapted to resist foot pressure so that only a relatively small actuating force is transferred through to the clutch actuating means.

Preferably, the limiting means is incorporated in the 25 actuating linkage interposed between a rocking type foot actuating pedal and the actuating means which engages the clutch assembly and moves the latter between the spaced pulley wheels. Accordingly, the limiting means may be in the form of a bell crank assembly having angularly disposed pivot arms resiliently connected to one another so as to minimize o *9re.

*oe 4 the engagement force which may be applied through the bell crank assembly. Preferably, the limiting means is in a push/pull rod or shaft in the linkage assembly. The push/pull rod may incorporate a collar slidably mounted on the rod and through which reciprocal motion can be transferred from the shaft to a further component of the linkage assembly and an associated buffer or buffers which is/are suitably supported about the shaft and limited for movement therealong whereby movement of the collar in at 10 least one direction results from engagement of the spring 0therewith.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate typical 15 embodiment of the invention and wherein FIG. 1 illustrates a typical embodiment of the invention; FIG. 2 illustrates the spring biased actuating assembly incorporated in FIG. 1; 20 FIG. 3 illustrates another spring biased form of actuating means, and FIG. 4 illustrates a hydraulically damped form of actuating means.

Referring initially to FIGS. 1 and 2 there is illustrated a reversible belt drive assembly 10 having a pair of driven pulley wheels 11 and' 12 supported on a driving shaft 13 and adapted to be driven for contra-rotation via the opposed runs of a V-belt or separate V-belts. A clutch assembly 14 is supported on a square central section 15 of the driving shaft 13 for rotation therewith and incorporates opposed clutch plates 16 and 17 which engage with a side face of a respective pulley wheel 11 or 12. The clutch assembly 14 is reciprocated along the square section 15 by an actuating linkage 18 controlled by a foot pedal 19 whereby the shaft may be selectively driven by one of the contrarotating pulley wheels 11 or 12.

The actuating linkage 19 includes a bell-crank assenmbly and a push/pull rod 21 whereby reciprocal movement of the push/pull actuating rod 21 may be translated into pivotal movement of the bell-crank and subsequent reciprocal movement of the clutch plates 16 and 17 between the pulley wheels 11 and 12.

As illustrated the actuating rod 21 passes through an end stop 22 of a connector assembly 23 which connects the 96:6 10 actuating rod 21 to the bell-crank 20. The actuating rod 21 o also passes through a further guide member 24 provided on the connector assembly 23 so as to maintain alignment between the latter and the actuating rod. The guide member 24 is apertured to enable a sleeve fitted about the rod 21 to pass 15 slidably therethrough. The end of the rod is threaded and a retaining nut 26 is supported thereon to adjust the position of the sleeve along the rod. A further nut or collar 28 is provided on the rod ahead of the end stop 22.

In use, the rod 21 is moved in directioto engage 20 forward motion. This action causes the stop 28 to abut the end stop 22 and thus provides positive connection of the bell crank assembly 20 to the foot pedal 19. For selecting reverse movement, the rod 21 is moved in direction CB' This moves the stop 28 away from the end stop 22 and places the 25 compression spring 27 into compression between the end stop 22 and the end of the sleeve 25. Accordingly as the bell crank 20 is pivoted to initially engage the respective clutch plate with the respective pulley wheel, the engagement pressure is limited by the compression of the spring which is selected to apply the appropriate small engagement force.

The linkage assembly is so made that the spring 27 cannot be completely closed so that the applied force to the bell crank is a function of the spring force which can be set to achieve the desired result.

In use, normal direct control is provided in the forward direction. However when reverse is selected, the initial engagement force is limited to that which may be transmitted through the compression spring 27. Of course the spring 27 may be a progressive spring so that initial contact pressure between the clutch plate and the pulley is sufficiently low that slippage occurs during normal operation. As the foot pedal is further pivoted the compression force transmitted through the spring may be sufficient to prevent slipping occurring, This arrangement will reduce the shock loadings which may be applied through the clutch to the shaft 13.

The embodiment illustrated in FIG. 3 is similar to FIG.

2, however in this embodiient the bell crank assembly 20 is pivotally connected to a sleeve 29 via a stud 30 projecting from one side thereof. The sleeve 29 is fitted to engage slidably about the end of the actuating rod 33 which is threaded along its end portion 34 and provided with a fixed stop 35 against which the inner end of the sleeve 29 may abut. The outer end of the sleeve 29 is adapted to engage a compression spring 31 supported about the zod 33 and between the outer end and a retaining nut engaged about the threaded end portion 34. Thus a positive pivoting motion of the associated bell-crank 20 may be achieved in one direction while its pivoting movement in the opposite direction is controlled by the compression of the spring 31.

25 Of course if desired compression springs may be arranged at opposite ends of the sleeve 29 so that desired application pressures can be achieved in both directions. The springs could be formed identically but of course they may be of different sizes to provide different operating characteristics in opposite directions. Furthermore, the springs can be adapted to close completely during actuation so as to provide an initial pre-set actuating force until the springs are closed whereupon the actuating force will be proportional to the foot pressure applied to the actuating 35 pedal.

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7 The embodiment 36 illustrated in FIG. 4 is adapted to form limiting means in the push/pull actuating rod 37 which prevents high initial pressures being applied through the linkage from the push rod 37. This is achieved by forming a piston 42 on the rod 37 which is reciprocal within a cylinder 43 from which a stud 44 projects. The latter is adapted to engage with a bell-crank assembly or the like as described previously. The cylinder 43 is provided with end caps 45 and seals 46 to enable oil to be retained in the cylinder as the 10 rod moves through the end caps and the pistons 42 reciprocates there within.

The piston is provided with a longitudinal passage 48 substantially parallel to the rod 37 through which oil may bleed at a predetermined rate to damp the connection between 15 the rod 37 and the member connected to the stud 44. If desired, a valve may be arranged in the passage through the piston 42 such that the resistance of flow of oil there through is greater in one direction than in the other.

•The drive shaft of the reversible drive mechanism may 0000 20 also be reinforced to prevent breakage due to bending loads by substituting a sleeve, threaded at one end and closely fitted about the shaft, for the nut which retains the pulley wheels on the shaft. The sleeve or sleeves may be of such length as to extend fully between the pulley wheel or wheels 25 and the respective support bearing which supports the drive shaft and may be provided with spanner flats.

This arrangement enables the shaft to be reinforced against bending loads applied through the forward reverse drive mechanism. Of course if desired, the drive shaft could terminate with a spigot mounting adapted to engage in a socket mounting of a larger diameter stub shaft and be coupled thereto via suitable drive transfer means.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as 8 would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is defined in the appended claims.

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Claims

1. Actuating means for a forward and reverse drive mechanism of the type having a pair of contra-rotatable pulley wheels rotatably supported on a shaft, a clutch assembly selectively engagable with either one of the pulley wheels to select drive from either the forward or reverse rotating pulley wheel, characterised in that the actuating means includes an operating linkage having limiting means for limiting the engagement pressure between the clutch assembly and at least one of said pulley wheels.

2. Actuating means as claimed in claim 1, wherein said limiting means is incorporated in said operating linkage between a rocking type foot actuating pedal and said clutch assembly. 15

3. Actuating means as claimed in claim 1 or claim 2, wherein said limiting means limits the engagement pressure between the clutch assembly the reverse driving pulley wheel.

4. Actuating means as claimed in any one of the preceding claims, wherein said limiting means includes a two part 20 linkage interconnected by spring means.

5. Actuating means as claimed in claim 4, wherein said parts of said linkage are slidably connected to one another and said spring means limits their relative sliding movement with respect to one another.

6. Actuating means as claimed in claim 4 or claim wherein said spring means is a coil spring supported about one said link and wherein said coil spring limits tension loads which may be transmitted through said linkage.

7. Actuating means as claimed in any one of claims 1 to 3, wherein said limiting means is in the form of a fluid damper.

8. Actuating means substantially as hereinbefore described with reference to the accompanying drawings. DATED THIS TWENTY-FOURTH DAY OF MARCH 1993. THEODORE WILLIAM REINHOLD by PIZZEY. COMPANY PATENT ATTORNEYS S o o