GB2416017A

GB2416017A - An engine belt drive system

Info

Publication number: GB2416017A
Application number: GB0410576A
Authority: GB
Inventors: Keith Gordon Hall; Nathan James Roulson; Martin James Raper; Ian Robinson
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-05-12
Filing date: 2004-05-12
Publication date: 2006-01-11
Anticipated expiration: 2024-05-12
Also published as: GB2416017B; GB0410576D0

Abstract

There is provided an idler pulley assembly 20 for use in a belt drive system (10, fig 1) on an internal combustion engine and which comprises an idler pulley 13 rotatably mounted on a spindle 21 which in turn is fixedly mounted on a support 22 capable of rotation about an axis off-set from the spindle axis. There is also provided a method of fitting a drive belt to a drive belt system including the idler pulley assembly. In said method, the drive belt is located around other pulleys, the support 22 is moved to a first rotational position which minimises the distance between pulleys and enables the drive belt to be located on the idler pulley 13, the belt then being tensioned by rotation of the support 22.

Description

An Engine Belt Drive System

Field

This invention relates to a belt drive system of the type which are utilised on internal combustion engines for driving accessory equipment, and in particular to belt drive systems which are used in relation to motor vehicle engines.

Background of the Invention

Some belt drive systems for transferring rotary drive from an engine crankshaft pulley to one or more accessory equipment pulleys have to have sufficient tension in the belt to avoid unnecessary belt slippage. The belts may be tightened manually, often using an adjustable position idler pulley within the belt run, spring tensioned and more recently self tensioned, that is by using elastic drive belts formed from a rubber and textile cord composite. Removal of the belt requires the belt to be cut and special belt fitting tools are required when fitting a drive belt to the system. These tools are expensive, need to be supplied with each replacement belt, and generally lack robustness.

Self tensioning belts are fitted using a guide ramp on the side of the most suitable pulley.

The ramp guide may be temporary and may be removed after the belt is in position, or may be an integral part of the pulley. The belt is stretched over the pulley flange by rotating the pulley whilst the belt is laterally constrained so that the ramp guide stretches the belt over the pulley flange and into position.

It is beneficial to also provide a means of statically adjusting the drive centre distance in order to optimise the belt tension and negate the effects of manufacturing tolerances in both the engine components and the belts.

A drive belt system is shown in US 20040009837-A1 which describes a pulley having a spindle mounted eccentrically on a pin and which is adjustable to alter the length of the belt run.

The present invention provides an alternative method of fitting an elastic belt to a drive belt system, and an idler pulley assembly which facilitates the fitting of such belts.

Statements of Invention

According to a first aspect of the invention there is provided a pulley assembly for use in a belt drive system on an internal combustion engine and having a pulley rotatably mounted on a spindle which in turn is fixedly mounted on a support capable of rotation about an axis off-set from the spindle axis.

The support may be rotatably mounted on a body by means of an integrally formed shaft, and the body in use may be secured directly or indirectly to the vehicle engine, eg the cylinder head or cylinder block.

The support may be in the form of a crank arm with the pulley spindle located at one end of a crank arm, the other end of which is rotatably mounted to the body by the shaft which is rotatably mounted in the body.

The body has an abutment formed thereon which limits the rotation of the support relative to the block, preferably in both rotational directions i. e. clockwise and anti-clockwise.

The abutment comprises an inclined straight abutment surface off-set to one side of the axis of rotation of shaft and which allows for 180 degrees of movement between an unloaded condition (the pulley being able to receive a belt) and loaded condition (the position of the pulley in use). The abutment may be formed on an adjustable position stop.

The angle of inclination of the abutment shown is about 35 of arc from the vertical and the over-centre angle, that is the angle between a line passing through the axis of rotation of the pulley spindle and said offset axis and the line of force of the belt load in use which also passes through the pulley spindle. The over centre angle is preferably about 5- 1 0 of arc.

The invention further provides an internal combustion engine having a belt drive system including a drive pulley, typically the crankshaft pulley, at least one auxiliary system driven pulley and an idler pulley assembly according to the present invention, the support being moveable to a first position to receive a belt which is then tensioned by rotation of the support about said off-set axis to another rotational position.

Yet another aspect of the present invention provides a method of fitting a drive belt to a drive belt system including a drive pulley, a driven pulley and at least one idler pulley with the belt run around said pulleys being substantially planar, wherein in said method with the drive belt located around said other pulleys, the idler pulley is fixedly mounted on a rotatable support whose axis of rotation is offset from the pulley spindle enabling the drive belt to be located on the pulley with the support in a first rotational position which minimises the distance between pulleys, the belt then being tensioned by rotation of the support through a position of maximum distance between the pulleys to a second rotational position with a lesser distance between the pulleys. s

In this way, the support is rotated through a position which generates maximum tension within the belt to the second rotational position in which the tension in the belt is less than said maximum, that is the idle pulley goes "over centre" during the rotation of the axle and preferably the support comes to rest against an abutment when in the second position.

The tension in the belt prevents the idler pulley from moving away from the second position.

Description of the Drawings

The invention will be described by way of Example and with reference to the accompanying drawings in which: Fig. 1 is a schematic front view of belt drive system according to the present invention showing the idler pulley in the different conditions, Fig. 2 is a schematic front view of a pulley assembly according to the present invention and which is used for the idler pulley assembly in Fig. 1 and is shown with the belt in a nontensioned condition, Fig 3 is a schematic front view of a pulley assembly shown in Fig.2 with the belt in the tensioned condition in use, and Fig. 4 is a cross-section through a pulley assembly according to the present invention taken on the line IV-IV of Fig 3.

Detailed Description of the Invention.

With reference to Fig. 1 there is shown a drive belt system 10 comprising a drive pulley I l, at least one engine auxiliary system driven pulley 12 and an idler pulley 13 and a belt 14. The drive pulley I 1 is typically a crankshaft pulley and examples of typical accessory system pulley 12 are an alternator pulley, a water pump pulley, air conditioning compressor pulley. The belt 14 is an elastic belt typically having a plurality of parallel V shaped teeth extending around the inner surface of the belt and which in use engage like V shaped grooves on the pulleys 1 1-13.

With reference to Fig.2, the idler pulley 13 forms part of an idler pulley assembly 20 in which the idler pulley 13 is mounted for rotation on a spindle 21 which in turn is mounted at one end of a support 22. The support 22 is generally in the form of a crank arm and is fixed to a shaft 23 that is rotatably mounted to a body or bracket 24. The axis of rotation A of the shaft 23 is off-set from the axis B of spindle 21 by a distance D, that is the throw of the crank arm, suitable to achieve the necessary tensioning in the belt 14. In use the body 24 is used for mounting the idle pulley assembly 20 in a suitable location on a vehicle engine, or engine or engine component.

The body 24 is provided with an abutment surface 25 in the form of a straight elongate shoulder, which is inclined at an angle a from a vertical passing through the axis A of rotation of the support 23. The angle a is typically between 30-40 , and typically about 35 of arc. The shoulder 25 provides an abutment which limits rotation of the crank arm 22 in both the clockwise and anti-clockwise directions of rotation and allows for rotational movement of about 180 of arc. This is illustrated by the different positions of the arm 22 as shown in Figs. 2 & 3.

Fig. 2 shows the pulley support 22 at the limit of its anti-clockwise movement and in abutment with the lower portion of the shoulder 25. Fig. 1 A shows the drive belt system with the pulley 13 located in the position shown in Fig 2, the system is set for minimum belt length, i.e. minimum distance between pulley centres, allowing for belt fitting over the pulley 13.

Support 22 is then rotated clock-wise by means of a suitable tool to a position as shown in Fig.3. During the rotation of the support the pulley passes through the position for maximum belt length, that is maximum distance between pulley centres, as shown in Fig I B in which maximum tension is induced within the belt 14. The further rotation of the support 22 to the limit of its maximum clockwise movement, as shown in Fig. 3, moves the spindle 21 over-centre slightly decreasing the distance between the pulleys and decreasing the tension within the belt 14. This is shown in Fig. 1C. The tension within the belt 14 holds the support 22 against the shoulder 25. The line of force L for the tension load in the belt may be considered as passing through the axis of rotation B of the pulley spindle 21 when the support is located in the over-centre position and forms an over centre angle defined by the angle between a line passing through the axis B of rotation of the pulley spindle 21 and the axis of rotation A of the support shaft 23 and the line of force L. This is preferably between 5-10 of arc.

Since the pulley 13 has gone over-centre during the belt fitting and tensioning, any anti clockwise movement of the support 22 results in an increase in belt load and this effectively clamps the support in position preventing the idler pulley from moving away from the shoulder 25. The belt 14 is released by application of a tool to the support which allows sufficient load to be applied to the support to rotate the pulley assembly anti clockwise through the maximum belt length condition.

With reference to Fig. 4, there is shown a section through the pulley assembly 20 in the belt tensioned condition shown in Fig.3. The pulley 13 mounted to the support 22 for rotation around a spindle 21 comprising a bearing 31 and bolt 32. The support 22 is in the form of a crank arm formed with an integral shaft or pin 23 which is rotatably mounted in an aperture 33 in the body 24. The shaft 23 is an interference fit in aperture to minimise radial mix-alignment of the pulley. The crank arm 22 is in abutment with the shoulder 25.

In a modification to the present embodiment (not shown) the fixed abutment 25 may be formed as an adjustable position stop mounted on the body 24 to compensate for belt/drive length variation. The shaft 23 may be held in rotational position relative to the body 24 by a clamp which must be released prior to rotation of the support 22.

Claims

Claims 1. A pulley assembly for use in a belt drive system on an internal

combustion engine and which comprises a pulley rotatably mounted on a spindle which in turn is fixedly mounted on a support capable of rotation about an axis off-set from the spindle axis.
2. A pulley assembly as claimed in Claim 1, wherein the support is rotatably mounted on a body by means of an integral shaft and the body in use may be secured to the engine.
3. A pulley assembly as claimed in Claim 1 or 2, wherein the support comprises a crank arm with the pulley spindle located at one end of a crank arm, the other end of which is rotatably mounted to the body.
4. A pulley assembly as claimed in any one of Claims I to 3, wherein the body has an abutment formed thereon which limits the rotation of the support relative to the body.
5. A pulley assembly as claimed in Claim 4, wherein the abutment limits the rotation of the support in both clockwise and anti-clockwise directions.
6. A pulley assembly as claimed in Claim 5, wherein the abutment comprises an inclined straight abutment surface off-set to one side of the axis of rotation of shaft and which allows for 180 degrees of movement.
7. A pulley assembly as claimed in Claim 6, wherein the angle of inclination of the abutment is about 35 of arc from the vertical.
8. A pulley assembly as claimed in any one of Claims 4 to 7, wherein the abutment is an adjustable position stop mounted on the body.
9. An internal combustion engine having a belt drive system including a drive pulley, typically the crankshaft pulley, at least one accessory system driven pulley and an idler pulley assembly having a pulley assembly as claimed in any one of Claims 1 to 8 mounted to the engine, the idler pulley being movable to a first position to receive a belt which is then tensioned in use by rotational movement of the support about said off-set axis to another rotational position in which the pulley spindle is held in position by the tension in the belt.
10. An engine as claimed in Claim 9, wherein the idler pulley spindle is held in position against an abutment by the tension in the belt, and said tension in use increases when the pulley spindle moves away from the abutment. ]5
11. A belt drive system substantially as described herein and as illustrated in the accompanying drawings.
12. A method of fitting a drive belt to a drive belt system including a drive pulley, a driven pulley and at least one idler pulley with the belt run around said pulleys being substantially planar, the idler pulley having a spindle fixedly mounted on a rotatable support whose axis of rotation is offset from the idler pulley spindle, wherein in said method with the drive belt located around the other pulleys, the support is moved to a first rotational position which minimises the distance between pulleys and enables the drive belt to be located on the idler pulley, the belt then being tensioned by rotation of the support through a position of maximum distance between the pulleys to a second rotational position with a lesser distance between the pulleys.
13. A method as claimed in Claim 12, wherein the support is biased against an abutment when in the second position by the tension in the belt.
14. A method as claimed in Claim 12 or 13, wherein when the support is located in the second rotational position the pulley spindle is in an over-centre condition forming an over-centre angle defined by the angle between a line passing through the axis of rotation of the pulley spindle and the axis of rotation of the support and the line of force of the belt load which also passes through the pulley spindle
15. A method as claimed in Claim 14, wherein the over centre angle is between 5-10 of arc.