BELT TENSIONING DEVICE

Abstract: A device for tensioning a belt (40) on an engine has a roller (13) rotatably mounted on one end of an arm (11) pivotally mounted intermediate its ends on a pin (12) on a base plate (10), a tension spring (14) connected between a pin (16) the other end of the arm and a pin (15) on the base plate, and a setting screw (17) mounted on the base plate and adjustable into abutting engagement with the arm. The base plate has an aperture for a clamp screw (20) and an arcuate slot (21) for another clamp screw (22), the slot (21) being centered on the aperture so that the base plate, when attached by the screws (20, 22) to the casing of an engine, can be pivoted about the screw (20) to engage the roller against the belt. Before mount­ ing the device on the engine casing, the arm (11) is pivoted by the setting screw (17) so as to tension the spring (14). The base plate is then clamped to the casing of the engine with the roller (13) engaged against the belt (40) to take up excess slack, and the setting screw (17) unscrewed out of engage­ ment with the arm so that the roller is urged by the spring against the belt.

Description: BELT TENSIONING DEVICE This invention relates to a device for tightening an endless belt on a machine. The term 'endless belt" is used herein for convenience to denote any form of endless elongated strip member suitable for transmitting power, and includes endless bands and chains. The object of the invention is to provide an improved construction of belt tightening device suitable for applying to an endless belt a load which is approximately equal to a predetermined load. According to the invention there is provided a device for tightening an endless belt on a machine, the device comprising a base, a member adapted for rolling or sliding engagement with the belt, the member being mounted on the base by means permitting movement of the member along a path fixed relative to the base, spring means resisting movement of the member in one direction along said path, setting means operable to move the member in said one direction along the path and thereby stress the spring means, and means for securing the base on the machine with the member engaged against the belt to take up the slack thereof and the belt intersecting said path, whereby, when the device is secured on the machine with the spring means stressed by the setting means and the member engaged against the belt to take up the slack thereof, release of the setting means causes the spring means to urge the member along said path and against the belt. The device of the invention is a self-contained unit in which the spring means can be stressed to a predetermined load prior to the fitting of the device on the machine. The load on the spring means can thus be set at a value which will ensure that the device will not exert on the belt a load in excess of the design load for the belt or the design load for the components driven by the belt. In the belt tightening device of the invention, the member adapted for rolling or sliding engagement with the belt can conveniently be mounted on an arm pivotably mounted on the base. Preferably, the arm is pivotably mounted intermediate its ends on the base, the member is mounted on one end portion of the arm, the spring means are connected between the other end portion of the arm and an anchorage on the base, and the setting means are operable to pivot the arm in a direction to stress the spring means. The setting means may comprise a screw mounted in a screw threaded aperture in a part of the base and arranged to engage against the arm, and the base may be provided with indicia which is aligned with the arm when the arm is in a position in which the spring means is stressed to a predetermined load. The construction of the member adapted for rolling or sliding engagement with the belt will of course depend on the type and form of the endless belt. In a device suitable for tensioning a belt having a smooth outer surface the member can conveniently comprise a double-row deep-groove ball bearing fitted with a tyre on the outer bearing ring, and in a device suitable for tensioning a chain the member can conveniently comprise a rotatable sprocket. Alternatively, the member may comprise a shoe adapted to make sliding contact with the chain. The device of the invention, when in use for tightening an endless belt on a machine, can readily be disengaged from the belt when the device is to be removed from the machine by operating the setting means so as to take up the stress on the spring means and thereby permit the member to be moved along its fixed path away from the belt. The device of the invention also has the advantage that it can be mechanically controlled during dismounting and remounting of the belt without slackening the means securing the base of the device to the machine. Thus, when a belt is to be dismounted, the setting means are operated to stress the spring means and thereby disengage the device from the belt. The belt can then easily be removed and replaced by a new belt, whereupon the setting means are released to cause the spring means to urge the member against the belt. One construction of a belt tightening device according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a front elevation of-the device when in use holding taut a belt for driving auxiliaries of an internal combustion engine, and Figure 2 is a side elevation of the device shown partly in section. The device shown in the drawings comprises an elongated base plate 10, a tension arm 11 pivotally mounted intermediate its ends on a pivot pin 12 on the base plate, a tension roller 13 rotatably mounted on one end of the arm 11, a coil spring 14 having one end anchored on a pin 15 on the base plate and the other end attached to a pin 16 on the other end of the arm 11, and a tension setting screw 17 mounted on a lug 18 on the base plate. The base plate has an aperture at one end thereof for reception of a clamp screw 20, and an arcuate slot 21 adjacent the other end thereof for reception of another clamp screw 22, the arcuate slot 21 having a radius which is centered on the aperture for the clamp screw 20. The pin 15 for anchoring one end of the spring is secured in an aperture in the base plate adjacent the aperture for the clamp screw 20, and the pivot pin 12 is secured in an aperture in the other end of the base plate. The centre portion of the base plate has a rectangular section cut along three sides thereof and folded along the fourth side at right angles to the general plane of the base plate to form the lug 18. The lug has a screw threaded aperture for reception of the screw 17. The tension arm 11 is formed with an aperture intermediate its ends for reception of a bush 23 which receives the pivot pin 12, the bush 23 having a collar 24 between the arm 11 and the base plate, and the tension arm 11 is held in position on the pin 12 by a spring retaining ring 25 engaged in a groove in the pin adjacent the end thereof. The pin 16 for attaching an end of the coil spring to the arm 11 is secured in an aperture in the end of the arm. The end portion of the arm 11 fitted with the roller 13 projects beyond the adjacent end of the base plate and is cranked inwardly so as to lie approximately in the general plane of the base plate. A small abutment plate 26 similar in size to the lug 18 is welded to the part of the arm 11 opposite the lug 18. The lug 18 and the plate 26 are arranged so that they are substantially parallel to one another when the tension arm 11 is in its operative position shown in Figure 1, so that the plate 26 can form an abutment for the tension setting screw 17 on the lug 18. The tension roller 13 comprises an outer bearing ring 30 rotatably mounted on an inner bearing ring 31 by two rows of balls 32 disposed between the two bearing rings and in rolling engagement with grooved tracks on the two bearing rings, and a cylindrical tyre 33 is secured on the outer bearing ring 30. The end of the inner bearing ring adjacent the arm 11 projects out of the outer bearing ring and is formed with an inwardly projecting annular flange 34. The tension roller 13 is mounted on the arm 11 by a shouldered pin 35 which is riveted into a flared aperture in the arm 11, the pin 35 having a head 36 which engages the flange 34 and retains the end of the inner bearing ring against the arm 11. The annular space between the two bearing rings is sealed at the inner end adjacent the arm 11 by an annular seal 37 which is located in a groove in the outer bearing ring and is in sliding engagement with the inner bearing ring. The outer end of the roller 13 is sealed by an end cap (not shown) which is a press fit in a groove 38 in the outer end of the outer bearing ring. Figure 1 shows the belt tightening device mounted on the outer casing of the engine of a motor vehicle and holding taut an endless belt 40 extending around a pulley 41 drivably connected to the crankshaft of the engine, the belt driving a camshaft and water pump (not shown). The base plate 10 of the device is clamped against a flat surface on the engine casing by the clamp screws 20, 22 which are screwed into screw threaded apertures in the engine casing. Before the belt tightening device is attached to the engine casing, the tension setting screw 17 is screwed into the lug 18 and against the abutment plate 26 so as to pivot the tension arm 11 about the pivot pin 12 in the clockwise direction relative to the base plate as shown in Figure 1, and thereby stress the coil spring 14 to a predetermined tension. The base plate can conveniently be provided with an indicator mark 42 which is uncovered by the arm 11 when the spring is loaded to the required tension. The device is then mounted on the engine casing by the clamp screws 20, 22 which are not fully tightened at this stage. The device is then pivoted manually about the clamp screw 20 to engage the roller 13 against the belt 40 and take up excess slack in the belt. The clamp screws 20, 22 are then fully tightened and the screw 17 unscrewed out of contact with the abutment plate 26 so that the tension roller 13 is urged by the spring 14 against the belt. The belt tightening device can readily be removed from the machine by screwing the tension setting screw 17 against the abutment plate 26 so as to take up the load exerted on the arm by the spring. There will then be little or no load on the belt, and the clamp screws 20, 22 can be loosened to enable the device to be pivoted in the clockwise direction about the clamp screw 20 and thereby swing the roller 13 away from the belt. The belt can readily be removed from the engine without slackening the clamp screws 20, 22 by screwing the tension setting screw 17 against the abutment plate 26 so as to swing the arm 11 clockwise about the pivot pin 12, against the action of the coil spring 14, and thereby swing the roller 13 away from the belt. The belt can then be replaced by a new belt, and the tension setting screw 17 unscrewed out of engagement with the abutment plate 26. If the new belt is slightly different in length from the previous belt, it will be necessary to loosen the clamp screws 20, 22 while the screw 17 is engaged against the abutment plate 26, swing the whole device about the clamp screw 20 to move the roller 13 clear of the belt, re-adjust the tension setting screw 17 to stress the coil spring to the desired load, swing the device back to engage the roller 13 against the belt and take up the excess slack, retighten the clamp screws 20, 22, and finally unscrew the screw 17 out of engagement with the abutment plate 26.

Claims: CLAIMS: 1. A device for tightening an endless belt on a machine, the device comprising a base (10), a member (13) adapted for rolling or sliding engagement with the belt (40), the member (13) being mounted on the base by means (11, 12) permitting movement of the member (13) along a path fixed relative to the base, spring means (14) resisting movement of the member (13) in one direction along said path, setting means (17) operable to move the member (13) in said one direction along the path and thereby stress the spring means (14), and means (20, 22) for securing the base on the machine with the member (13) engaged against the belt to take up the slack thereof and the belt intersecting said path, whereby, when the device is secured on the machine with the spring means (14) stressed by the setting means (17) and the member (13) engaged against the belt to take up the slack thereof, release of the setting means (17) causes the spring means (14) to urge the member (13) along said path and against the belt. 2. A device as claimed in claim 1, wherein the said member (13) adapted for rolling or sliding engagement with the belt is mounted on an arm (11) pivotably mounted on the base. 3. A device as claimed in claim 2, wherein the arm (11) is pivotably mounted intermediate its ends on the base, the said member (13) is mounted on one end portion of the arm, the spring means (14) are connected between the other end portion of the arm and an anchorage (15) on the base, and the setting means (17) are operable to pivot the arm in a direction to stress the spring means (14). 4. A device as claimed in claim 3, wherein the setting means comprises a screw (17) mounted in a screw threaded aperture in a part (18) of the base and arranged to engage against the arm (11). 5. A device as claimed in any of claims 2-4, wherein the base is provided with indicia (42) which is aligned with the arm (11) when the arm is in a position in which the spring means (14) is stressed to a predetermined load. 6. A device as claimed in any of claims 1-5, wherein the means for securing the base on a machine comprises a clamping screw (20) engaged in an aperture in the base and a further clamping screw (22) engaged in an arcuate slot (21) in the base, the arcuate slot (21) having a radius which is centered on said aperture. 7. A device as claimed in any of claims 1-6, wherein said member (13) comprises a double-row deep-groove ball bearing fitted with a tyre (33) on the outer bearing ring (30).

Inventors: CLARK, PAUL STEWART
Applicants: SKF (U.K.) LIMITED
Application year: 1985
Main classification: F16H7
IPC codes: F16H7