GB2411938A

GB2411938A - Belt drive with integrated generator

Info

Publication number: GB2411938A
Application number: GB0504775A
Authority: GB
Inventors: Ralph Painta; Herbert Graf; Michael Bogner
Original assignee: INA Schaeffler KG
Current assignee: IHO Holding GmbH and Co KG
Priority date: 2004-03-12
Filing date: 2005-03-08
Publication date: 2005-09-14
Anticipated expiration: 2025-03-08
Also published as: GB2411938B; DE102004012140A1; GB0504775D0; FR2867538A1; FR2867538B1

Abstract

Belt drive with an integrated generator, particularly a starter generator, with a belt roller on which roller the belt is guided mounted on a generator shaft and which is movably mounted in order to tension the traction mechanism counter to a restoring force, the mechanical properties of the belt 2 regarding rigidity being selected so that its elasticity allows at least partial reduction of load peaks occurring in the belt 2 itself in the drive 1 while simultaneously ensuring adequate force transmission through the drive 1. Details of the specific rigidity of ribbed V-belts with different numbers of ribs are also disclosed.

Description

241 1 938 - 1 - Belt drive with an integrated generator, particularly a

starter generator Scope of the invention s The invention relates to a belt drive with an integrated generator, particularly a starter generator, having a belt roller on which the belt is guided mounted on a generator shaft and which is movably mounted in order to tension the traction mechanism counter to a restoring force.

Background to the invention

In order to be able to transmit the necessary driving torques of the sub assemblies safely, in traction drives, particularly in belt drives, sufficient prestressing force must be guaranteed in the traction mechanism. At the same time the number and arrangement of the subassemblies must be kept low or compact enough, respectively, to avoid as far as possible unnecessary disturbances (e.g. additional alternating bending of the traction mechanism caused by guide or tension rollers) in the drive. If the ever greater power of the sub-assemblies is coupled with an unfavourable drive layout, e.g. a two disc drive with alternating bending after one or more tensioning devices, it is impossible to achieve an adequate service life with conventional tensioning devices. Because of the limited length of the belt and the resulting frequency of the alternating flexural stresses the belt will age prematurely. If it were possible to reduce the number of alternating bends and ideally even eliminate them altogether, the life of the belt could be extended without any problem.

In order to reduce the number of local reversed bending points it is possible to use the generator integrated in the drive itself as the tensioning device for the traction mechanism. In other words, the generator has a double function, on the one hand its primary function as a generator and on the other hand its function as a tensioning device. This removes the need for one or even more tensioning devices which would otherwise have to be additionally integrated in the drive and would lead to reversed bending points. Unfortunately, - 2 - because the generator has a large mass which has to be moved for the tensioning, it is only possible to compensate dynamic effects, i.e. dynamic alternations of load on the drive, to a limited extent, if at all. Thus, if frequently changing load peaks occur in the drive, a corresponding shock absorbing option, generally the integration of a tensioning device, as would be required anyway, has to be used to ensure the damping of the load peaks, but in the last analysis this is counter- productive for the reasons stated above.

Summary of the invention

The problem addressed by the invention is therefore to provide a traction drive, particularly a belt drive, which constitutes an improvement to this.

To solve this problem, the invention provides a belt drive with an integrated generator, particularly a starter generator, with a belt roller on which the belt is guided mounted on a generator shaft and which is movably mounted in order to tension the traction mechanism counter to a restoring force, characterized in that the mechanical properties of the belt regarding rigidity are selected so that its elasticity allows at least partial reduction of load peaks occurring in the belt itself in the drive while simultaneously ensuring adequate force transmission through the drive. The mechanical properties of the belt regarding rigidity are selected so that its elasticity allows at least partial reduction of load peaks occurring in the belt itself during operation while simultaneously ensuring adequate force transmission through the drive.

As a rule, relatively rigid belts which therefore have only limited elasticity are used for belt drives, in order to be able to transmit the necessary torques for operating the units integrated in the drive. However, it has surprisingly been found that even belts which are significantly more elastic than the belts used hitherto are suitable for transmitting force, to some extent, but their elasticity also confers the additional particular advantage that any dynamic load peaks which may occur can be broken down at least partially, i.e. they are negated in the belt itself, which stretches or contracts elastically. In other words, the - 3 - relatively high frequency load peaks which occur in the belt drives known hitherto with a tensioning generator and which are usually produced by rotational eccentricities of the crankshaft integrated in the drive and which are transferred to and load the sub-assemblies as a result of the considerable rigidity of the belts used hitherto, can be eliminated by the use of a belt of suitably selected rigidity or elasticity which will still be capable of transmitting the necessary force.

The belt used is expediently a ribbed V-belt with a rigidity of between 40,000 N and 80,000 N for four ribs, between 50,000 N and 100,000 N for five ribs, between 60,000 N and 120,000 N for six ribs, between 70,000 N and 140,000 N for seven ribs and between 80,000 N and 160,000 N for eight ribs.

The ranges specified are within the range for the rigidity values of socalled standard belts as used in the prior art, the rigidity of which is above the upper IS limit stated, and the rigidity values of so-called elastic belts which are not used for belt drives of the type under discussion, as they are much too elastic, and the rigidity values of which are below the lower limit specified. Depending on the number of ribs, different rigidity values are obtained which are determined as a function of the particular modulus of elasticity and the cross-sectional area of the belt in the rigid part of the belt through which cord threads or the like run.

It is particularly expedient if the belt has a rigidity of between 50,000 N and 75,000 N for four ribs, between 60,000 N and 95,000 N for five ribs, between 70,000 N and 115,000 N for six ribs, between 80,000 N and 135,000 N for seven ribs and between 90,000 N and 155,000 N for eight ribs. To define the appropriate rigidity ranges even more precisely, the belt may have a rigidity of between 55,000 N and 70,000 N for four ribs, between 70,000 N and 90,000 N for five ribs, between 80,000 N and 110,000 N for six ribs, between 90,000 N and 130,000 N for seven ribs and between 100,000 N and 150,000 N for eight ribs. Finally, it is particularly preferred if the rigidity is between 60,000 N and 70,000 N for four ribs, between 75,000 N and 90,000 N for five ribs, between 90,000 N and 110,000 N for six ribs, between 100,000 N and 130,000 N for seven ribs and between 110,000 N and 150,000 N for eight ribs, i.e. the tendency is for a somewhat more rigid range of values.

At this point it should be mentioned that according to the invention all the intermediate values or all the values lying between the limits specified as the upper and lower limits are also disclosed. This means that any intermediate range which falls within any one of the ranges specified above is described as being integral to the invention and is hence disclosed for purposes of restriction, even where the specific combination of numbers is not explicitly 1 0 stated.

The invention is generally based on the concept of selecting the belt as a function of the load peaks produced, in order to achieve the necessary damping in the system. The mechanical properties are thus selected as a IS function of the damping of the load peaks produced.

Brief description of the drawing

Figure 1 shows a traction drive according to the invention.

Detailed description of the drawing

The Figure shows a traction drive 1 according to the invention, in this case a belt drive, having a belt 2 which is guided over a plurality of units. Integrated in the belt drive is, firstly, a generator 3, e.g. a starter generator, on which a belt roller 4 over which the belt 2 is guided is arranged on a generator shaft.

The generator 3 is mounted to be pivotable about a pivot point D. A tensioning means 5 in the form of a hydraulic tensioning element, shown purely by way of example, acts thereon, exerting a continuous restoring force on the generator and forcing it in the direction of the arrow A around the pivot point D, thereby tensioning the belt 2. - 5 -

Also integrated in the traction drive 1 in the embodiment shown is a crankshaft 6 which is actively driven by the starter generator 3 when starting up, i.e. in this case the starter generator 3 drives the traction drive 1 itself, and which in turn actively drives the traction drive once the associated internal S combustion engine (not shown here) is running.

The embodiment shown also comprises an integrated water pump 7 and air conditioning compressor 8, which are driven by means of the belt 2, while corresponding rollers over which the belt 2 runs are naturally provided on the units in question. Fig. 1 is merely a diagrammatic representation showing a belt drive, but this may of course be of a completely different design with different units integrated in it.

If the traction drive 1 is driven by the crankshaft, load peaks are induced in IS the system by any eccentricities in the movement of the crankshaft, and these load peaks may have a detrimental effect, particularly with regard to the mounting of the sub-assemblies on which the load peaks primarily act. In particular, load peaks of this kind are generated in the non-driving free length of the belt between the crankshaft and the generator when the belt is being driven by means of the crankshaft, and in the exemplifying embodiment shown the drive pulley of the water pump is disposed in this non-driving free length and acts on the traction mechanism. During brief acceleration of the crankshaft caused by rotational eccentricity the relatively inert generator is also accelerated. The same is true of the two drive pulleys of the water pump and of the air-conditioning compressor. This in itself demonstrates the value of using a sufficiently elastic belt according to the invention, as in this case the higher tensile force caused by the acceleration which would act on the air conditioning compressor pulley is counteracted by the elongation of the belt.

As the speed of rotation of the crankshaft is reduced as a result of fluctuations the very inert generator is also slowed down relatively abruptly, leading to high tensile forces in the non-driving free length. If these forces were not partly eliminated by the more elastic belt which is used according to the invention, they would act fully on the drive pulley of the water pump. \ l - 6

However, they are at least partly cancelled out by the elongation of the belt on the driving side and therefore have less influence on the water pump unit than if conventional very rigid belts were used. Nevertheless, in spite of the dependency of the desired damping or the expected load peaks on the chosen elasticity of the belt there is still sufficient rigidity, ensuring reliable driving of all the units or assemblies connected to the drive. - 7 -

Reference numerals 1 traction drive 2 belt 3 generator 4 belt roller tensioning means 6 crankshaft 7 water pump 8 air-conditioning compressor A arrow D pivot point \ - 8 -

Claims

Patent Claims 1. Belt drive with an integrated generator, particularly a

starter generator, with a belt roller on which the belt is guided mounted on a generator shaft and which is movably mounted in order to tension the traction mechanism counter to a restoring force, characterized in that the mechanical properties of the belt regarding rigidity are selected so that its elasticity allows at least partial reduction of load peaks occurring in the belt itself in the drive while simultaneously ensuring adequate force transmission through the drive.
2. Belt drive according to claim 1, characterized in that the belt is a ribbed V-belt the rigidity of which is selected to be between 40,000 N and 80,000 N for 4 ribs, between 50,000 N and 100,000 N for 5 ribs, between 60,000 N and 120,000 N for 6 ribs, between 70,000 N and 140,000 N for 7 ribs and between 80,000 N and 160,000 N for 8 ribs.
3. Belt drive according to claim 2, characterized in that the rigidity is selected to be between 50,000 N and 75,000 N for 4 ribs, between 60,000 N and 95,000 N for 5 ribs, between 70,000 N and 115,000 N for 6 ribs, between 80,000 N and 135,000 N for 7 ribs and between 90,000 N and 155, 000 N for 8 ribs.
4. Belt drive according to claim 3, characterized in that the rigidity is selected to be between 55,000 N and 70,000 N for 4 ribs, between 70,000 N and 90,000 N for 5 ribs, between 80,000 N and 110,000 N for 6 ribs, between 90,000 N and 130,000 N for 7 ribs and between 100,000 N and 150, 000 N for 8 ribs.
5. Belt drive according to claim 4, characterised in that the rigidity is selected to be S between 60,000 N and 70,000 N for 4 ribs, between 75,000 N and 95,000 N for 5 ribs, between 90,000 N and 110,000 N for 6 ribs, between 100,000 N and 130,000 N for 7 ribs and between 110,000 N and 150, 000 N for 8 ribs.
6. Belt drive substantially as hereinbefore described with reference to the figure.