GB1585968A

GB1585968A - Belt drive mechanisms

Info

Publication number: GB1585968A
Application number: GB1963177A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-10
Filing date: 1978-05-10
Publication date: 1981-03-11

Description

(54) BELT DRIVE MECHANISMS (71) I, EDWARD APPLEBY, a British subject, of 2A Hill Road, Heath End, Farnham, Surrey GU9 0OJ, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to belt drive mechanisms which find particular, but not exclusive, application as drive transmissions for such light vehicles as electrically-assisted golf trolleys and invalid carriages where the motor drive is intended as a supplement to human propulsion.

In such light traction applications the drive transmission usually has a high stepdown gear ratio and the use of a conventional transmission results in a low inverse efficiency: in other words there is an unacceptably high drag from the transmission when the vehicle is being manually propelled or is free-wheeling. Centrifugal clutches are practicably useful only at higher rotational speeds and must therefore be employed at the input stage of the transmission; however at this stage of the transmission they have the disadvantage that they do not decouple the reduction gearing and hence do not reduce drag to an acceptable degree.

An object of the present invention is to provide a drive mechanism which will offer very little frictional resistance to freewheeling in either direction when disengaged and yet allows the drive to be smoothly taken up and to be very positive when fully engaged.

According to the present invention there is provided a belt drive mechanism comprising a rotary drive member for connection to a rotary power source and a belt, the belt and the drive member each being provided with means for positive mutual engagement, a rotatable driven member with which the belt can be brought into frictional driving engagement and two jockey rollers which are mounted for rotation on a resiliently mounted assembly so as, when the drive member is stationary, to bear inwardly on respective free lengths of the belt between said members to maintain the belt in a non-driving engagement position which allows free rotation of the driven member, the mounting of the jockey rollers also being such that on rotation of the drive member the resultant tension in one of the free lengths of belt will cause an outward displacement of one roller and consequent inward displacement of the other roller to bring the belt into driving engagement with the driven member. It will be appreciated that the effect is cumulative, the initial frictional engagement of the belt with the driven member causing an increase in said tension which in turn results in increased deflection of the other free length of the belt to bring it into greater frictional engagement with the driven member.

To accommodate motion in opposite senses it is clearly preferable for the jockey rollers to form an identical pair, symmetrically mounted. The jockey rollers are conveniently mounted for rotation on a pivotable carrier plate which is spring-biased to cause the belt to assume its non-driving engagement position.

The displacement of the jockey rollers may usefully be fed back to the control system for the source of rotary motion for the driving member An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic elevation of a drive mechanism for a golf trolley; and Figure 2 is a diagrammatic elevation of a modification of the mechanism of Figure 1 linked to a control system for the power input to the mechanism.

In Figure 1 the reference 1 indicates a toothed drive pulley mounted on a countershaft driven by an electric motor (not shown) and the reference 2 a plain pulley solid with the axle of the driving wheels (not shown) of a golf trolley. A toothed belt 3 having unsupported or free lengths 3a and 3b is in permanent positive engagement with the pulley 1 and may be positioned in paths in which it is engaged or disengaged from the pulley 2 by means of the action of a pair of jockey rollers 4 and 5 mounted on a carrier plate 6 which is itself pivotally mounted and resiliently urged towards a central rest position by a spring 7. The purpose of an actuating link 8 will be described with reference to Figure 2.

When the drive pulley 1 is stationary, the jockey rollers 4 and 5 are biased by the spring 7 to the position shown in Figure 2 in which they rest lightly on the belt 3 causing it to assume a path which allows the pulley 2 to rotate freely in either direction to allow the trolley to free-wheel. When the drive pulley 1 is caused to rotate by operation of the motor in the direction shown by the arrow 9, the unsupported length 3a of the belt 3 is brought under tension causing displacement of the roller 4, the associated carrier plate 6 and the roller 5. The displacement of the roller 5 causes inward deflection of the slack length 3b of the belt 3 causing it to assume the path shown in full lines in Figure 1 and wrapping it further round the pulley 2 to cause it to come into frictional driving engagement therewith. This results in increased tension in the belt length 3a and increased frictional engagement of the belt 3 with the pulley 2. The above-described cumulative effect enables a very smooth take-up of the drive to be achieved.

The position of the carrier plate 6 and the path of the belt 3 indicated by the broken lines is that assumed when the trolley is being driven in the opposite direction by the motor or is being braked by the motor.

In Figure 2 the references 1 to 9 have the previous significance, 10 denotes a pivoted lever which is manually controlled or is subject to an input derived from loadsensing, and which is arranged in one position to operate a switch 11 controlling forward operation of the motor and in another position to operate a switch 12 controlling reverse operation of the motor.

The lever 10 has a laterally-projecting pin 13 which projects through a slot 14 in the actuating link 8 and is connected to springs 15 and 16 which urge it towards a central position in the slot 14.

Movement of the lever 10 in the forward direction to operate the switch 11 initially causes no movement of the link 8 due to the free movement allowed by the slot 14.

However, consequent operation of the motor and of the drive mechanism causes pivotal movement of the plate 6 in the manner already described which in turn moves the link 8 to hold the lever 10 in a position in which it maintains the switch 11 in a closed position until over-ridden manually or by an input derived from loadsensing. A corresponding sequence of movements is of course performed when the reverse switch 12 is operated. Thus, by a suitable choice of spring rates and mechanical advantages a positive switching action can be achieved by means of the abovedescribed controlled dead-band arrangement. This positive switching action prevents partial and excessively frequent operation of the drive mechanism.

Where electrical control of the motor power output is available the switches 12 and 13 may be replaced by a continuously variable transducer having a central null position. The sense of feedback may then be reversed giving 'negative feedback' and a torque or tractive effort control system achieved.

It will be appreciated that the invention provides a belt drive mechanism which finds a wide range of applications on light vehicles, for example electrically-assisted trolleys used, not only by golfers and invalids, but also by shoppers, air and rail travellers with heavy luggage, and the like.

WHAT WE CLAIM IS: 1 .A belt drive mechanism for a light vehicle, comprising a rotary drive member for connection to a rotary power source, a belt, the belt and the drive member each being provided with means for positive mutual engagement, a rotatable driven member with which the belt can be brought into frictional driving engagement and two jockey rollers which are mounted for rotation on a resiliently mounted assembly so as, when the drive member is stationary, to bear inwardly on respective free lengths of the belt between said members to maintain the belt in non-driving engagement position which allows free rotation of the driven member, the mounting of the jockey rollers also being such that on rotation of the drive member the resultant tension in one of the free lengths of belt will cause an outward displacement of one roller and consequent inward displacement of the other roller to bring the belt into driving engagement with the driven member.

2. A mechanism as claimed in Claim 1, in which the two jockey rollers form a symmetrically-mounted identical pair.

3. A mechanism as claimed in Claim 1 or 2, in which the jockey rollers are mounted for rotation on a pivotable carrier plate which is spring-biased to cause the belt to assume its non-driving engagement position.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In Figure 1 the reference 1 indicates a toothed drive pulley mounted on a countershaft driven by an electric motor (not shown) and the reference 2 a plain pulley solid with the axle of the driving wheels (not shown) of a golf trolley. A toothed belt 3 having unsupported or free lengths 3a and 3b is in permanent positive engagement with the pulley 1 and may be positioned in paths in which it is engaged or disengaged from the pulley 2 by means of the action of a pair of jockey rollers 4 and 5 mounted on a carrier plate 6 which is itself pivotally mounted and resiliently urged towards a central rest position by a spring 7. The purpose of an actuating link 8 will be described with reference to Figure 2. When the drive pulley 1 is stationary, the jockey rollers 4 and 5 are biased by the spring 7 to the position shown in Figure 2 in which they rest lightly on the belt 3 causing it to assume a path which allows the pulley 2 to rotate freely in either direction to allow the trolley to free-wheel. When the drive pulley 1 is caused to rotate by operation of the motor in the direction shown by the arrow 9, the unsupported length 3a of the belt 3 is brought under tension causing displacement of the roller 4, the associated carrier plate 6 and the roller 5. The displacement of the roller 5 causes inward deflection of the slack length 3b of the belt 3 causing it to assume the path shown in full lines in Figure 1 and wrapping it further round the pulley 2 to cause it to come into frictional driving engagement therewith. This results in increased tension in the belt length 3a and increased frictional engagement of the belt 3 with the pulley 2. The above-described cumulative effect enables a very smooth take-up of the drive to be achieved. The position of the carrier plate 6 and the path of the belt 3 indicated by the broken lines is that assumed when the trolley is being driven in the opposite direction by the motor or is being braked by the motor. In Figure 2 the references 1 to 9 have the previous significance, 10 denotes a pivoted lever which is manually controlled or is subject to an input derived from loadsensing, and which is arranged in one position to operate a switch 11 controlling forward operation of the motor and in another position to operate a switch 12 controlling reverse operation of the motor. The lever 10 has a laterally-projecting pin 13 which projects through a slot 14 in the actuating link 8 and is connected to springs 15 and 16 which urge it towards a central position in the slot 14. Movement of the lever 10 in the forward direction to operate the switch 11 initially causes no movement of the link 8 due to the free movement allowed by the slot 14. However, consequent operation of the motor and of the drive mechanism causes pivotal movement of the plate 6 in the manner already described which in turn moves the link 8 to hold the lever 10 in a position in which it maintains the switch 11 in a closed position until over-ridden manually or by an input derived from loadsensing. A corresponding sequence of movements is of course performed when the reverse switch 12 is operated. Thus, by a suitable choice of spring rates and mechanical advantages a positive switching action can be achieved by means of the abovedescribed controlled dead-band arrangement. This positive switching action prevents partial and excessively frequent operation of the drive mechanism. Where electrical control of the motor power output is available the switches 12 and 13 may be replaced by a continuously variable transducer having a central null position. The sense of feedback may then be reversed giving 'negative feedback' and a torque or tractive effort control system achieved. It will be appreciated that the invention provides a belt drive mechanism which finds a wide range of applications on light vehicles, for example electrically-assisted trolleys used, not only by golfers and invalids, but also by shoppers, air and rail travellers with heavy luggage, and the like. WHAT WE CLAIM IS:

1 .A belt drive mechanism for a light vehicle, comprising a rotary drive member for connection to a rotary power source, a belt, the belt and the drive member each being provided with means for positive mutual engagement, a rotatable driven member with which the belt can be brought into frictional driving engagement and two jockey rollers which are mounted for rotation on a resiliently mounted assembly so as, when the drive member is stationary, to bear inwardly on respective free lengths of the belt between said members to maintain the belt in non-driving engagement position which allows free rotation of the driven member, the mounting of the jockey rollers also being such that on rotation of the drive member the resultant tension in one of the free lengths of belt will cause an outward displacement of one roller and consequent inward displacement of the other roller to bring the belt into driving engagement with the driven member.

4. A mechanism as claimed in any pre

ceding claim, in which the displacement of the jockey rollers is arranged to be fed back to a control system for the source of rotary motion. for the vehicle.

5. A mechanism as claimed in Claim 4, in which the feed back is through a mechanical linkage provided between the pivotal carrier plate and the control system and arranged, when the belt is engaged with the driven member, so as to maintain the rotary power source in operation until over-ridden manually or by an input derived from load-sensing.

6. A mechanism as claimed in Claim 5 as dependent on Claim 3, in which the linkage comprises a connecting member pivoted to said plate and having therein a slot through which projects a control lever for controlling the power source or engagement means associated therewith, the arrangement being such that when the plate is in the non-driving engagement position the slot is positioned to allow free movement of the lever to control the rotary power source, and when the plate is in the belt-engaged position one end of the slot engages the control lever or said means to hold the lever in a position in which the rotary power source is maintained in operation.

7. A belt-drive mechanism substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawing.

8. A vehicle incorporating a mechanism as claimed in any preceding claim.