GB2249175A

GB2249175A - Determining tension in a drive belt

Info

Publication number: GB2249175A
Application number: GB9120130A
Authority: GB
Inventors: Armin Schlereth
Original assignee: SKF GmbH
Current assignee: SKF GmbH
Priority date: 1990-10-24
Filing date: 1991-09-20
Publication date: 1992-04-29
Anticipated expiration: 2011-09-20
Also published as: GB9120130D0; DE4033778C2; DE4033778A1; GB2249175B

Abstract

In order to improve the accuracy and reproducibility of the measured results when ascertaining the tensioned force in drive belts, particularly on internal combustion engines or the like, it is envisaged to provide for measurements by the inherent frequency method both on the loaded 3 and also on the idling 4 strands of the belt transmission and to calculate the mean value thereof. <IMAGE>

Description

2249175 A METHOD OF DETERMINING THE TENSION IN DRIVE BELTS The invention

relates to a method of determining the tension in drive belts.

Due to H. Peeken, F. Fischer "Vorspannungsmessverfahren fur Riementriebe und ihre Genauigkeit" / 11Pre- tension measuring methods for belt transmissions and their accuracy". Antriebstechnik 28 (1989) No. 9, it is already known to measure the belt tension by measuring the inherent frequency of vibration a relevant belt strand. A belt strand disposed between an input and a drive output is thereby energised to produce transverse oscillations. As a function of its free length, its stiffness and mass, tension etc., so the belt strand continues to oscillate at its inherent frequency for a short period after its has been energised. Taking into account the above-mentioned relationships, the inherent frequency is a measure of the belt tension. The accuracy achieved thereby is good if there are no other influencing factors.

If, for example, the output already exhibits, while stationary, torque in respect of the drive or if adhesive forces occur in the mountings or at the contact surfaces of the belt, both belt portions exhibit different tensions even when stationary, the loaded strand and the idling strand being transmitted to the working condition. This condition is provided for example between the crank shaft and the cam shaft in the case of an internal combustion engine. The valve springs impart a static torque to the cam shaft when it is stationary and this assumes different values according to its position. Furthermore, adhesive friction moments falsify the results of measurement, such moments occurring preferably at the contact surfaces in the case of toothed belts and V-belts, although such moments also occur in the mountings. In practice, it has been demonstrated that for these reasons and in the case of the applications mentioned, results of measurements occur which fluctuate by up to 50%. However, these inaccuracies have nothing to do with the basic measurement method but are due solely to the object being measured.

The object on which the invention is based is that of improving the application of the known measurement method and to provide increased reproducibility of the results of measurement.

This problem is resolved by measuring the tension on the idling strand, measuring the tensioni of the loaded strand and calculating the mean value from both measurements. The method according to the invention increases the accuracy of measurement if it is adopted as a premise that in relation to the idling strand the loaded strand has a different tension even when stationary. For example, in the case of the internal combustion engine, it can be taken as a premise that both the crank shaft and also the cam shaft can have inter alia relatively high friction moments. Calculation of the mean value from both measurements produces an outstanding accuracy even with sharply fluctuating individual values such as always arise after the internal combustion engine has been running for a short time. Therefore, reproducibility is excellent.

A method according to the invention will now be described with reference to the accompanying drawing which shows schematically an apparatus for carrying out the method.

The example illustrated in the single drawing represents the simplified form of a belt transmission between a crank shaft 1 and a cam shaft 2.

1 As the result of inner friction forces and due to the influence of the valve springs, tremendous differences occur in the tension Fa, Fb of a loaded strand 3 and an idling strand 4 of the drive belt, even after the internal combustion engine has been shut down.

Both on the loaded strand 3 and also on the idling strand 4, the tensions Fa, Fb are ascertained by the known method of inherent frequency measurement and the mean value is calculated therefrom arithmetically or via an electronic computer stage 5.

Claims

1. A method of determining the tension in a drive belt. comprising the steps of: measuring the inherent frequency of vibration of an idling strand, measuring the inherent frequency of vibration of a loaded strand, and calculating the mean value of the tensions derived from respect measurements.

2. A method according to Claim 1, characterised by simultaneous measurements on the loaded and idling strands.

3. A method of determining the tension in a drive belt, the method being substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.