GB2385425A

GB2385425A - A method of monitoring a load on a gearbox

Info

Publication number: GB2385425A
Application number: GB0204264A
Authority: GB
Inventors: Peter Flamang
Original assignee: Hansen Transmissions International NV
Current assignee: ZF Wind Power Antwerpen NV
Priority date: 2001-10-03
Filing date: 2002-02-22
Publication date: 2003-08-20
Anticipated expiration: 2022-02-22
Also published as: GB0123776D0; GB2385425B; GB0204264D0

Abstract

A method of determining the torque within an intermediate shaft 4 of a gearbox 1 comprising measuring by non-contacting means 7, 8 the angular windup of the intermediate shaft 4, and determining the mechanical torsional stiffness of the intermediate shaft 4 and then calculating the torque by multiplying the angular windup by the torsional stiffness of intermediate shaft 4. The angular windup may be determined by comparison of the instantaneous angular deviation between two spaced apart regions of the torque flow path of the intermediate shaft 4 when under load with the instantaneous angular deviation between the same two regions when the intermediate shaft 4 is rotating in a zero torque transmitting state.

Description

MONITORING OF LOAD IN A GEAR UNIT

The present invention relates to the monitoring of load in a torque transmitter of a gear unit such as a rotary shaft and particularly but not exclusively i to determining the torque existing in one or more components of a gearbox, such as intermediate shafts.

In recent years, the capabilities for monitoring of machines have developed drastically, including complicated algorithms to predict failing components based on the measurement of a number of variables. Also remote monitoring of large industrial equipment over the Internet is now possible.

Amongst measured and monitored variables often are found vibration, temperature, speed and power.

One of the variables of particular importance for rotating machinery is the mechanical torque going through the machine, because this relates directly to instantaneous mechanical stresses. This is particularly true for gear units with their primary function as a torque transformer.

Measuring and monitoring the power of an electrical motor driving a machine, or a generator being driven by a machine, often is insufficient fully to understand and determine mechanical loads because frequently inertia loads are responsible for large shock loads in heavy machinery, and mechanical inertia loads can not be captured by the electrical system.

So far, most torque measurement technology is based on strain gauge technology. Strain gauges have a varying resistance as a function of their elongation. The changing resistance can be measured by measuring voltage and current changes in a bridge set up. If the strain gauges are applied to a torque carrying rotating element and because the technology is basically electrical, an electrical signal has to be transmitted from a rotating to a static part. Various ways

exist to achieve this goat including some non-contacting methods. However most of those are cumbersome and relatively sensitive in their application. The setting up of strain gauge technology for this purpose is also typically relatively sensitive to errors, as well as relatively fragile and not very stable over time. It is therefore often restricted to laboratory conditions and has not found its way into general use in industrial gear units.

Accordingly it is an object of the present invention to provide improved means for monitoring the torque existing in a torque transmitter of a gear unit which mitigates the above mentioned problems.

In accordance with one aspect of the present inventions there is provided a method of determining the torque within a torque transmitter of a gear unit comprising measuring by non-contacting means the angular windup of the torque transmitter, determining the mechanical torsional stiffness of the torque transmitter and then calculating the torque by multiplying the angular windup by the torsional stiffness of the torque transmitter.

Typically the torque transmitter may be a generally cylindrical component, e.g. a shaft of a gear unit, but the invention may be employed also in relation to a torque transmitter comprising a pair of shafts and a pair of gears, or any other combination of torque transmitter components. Preferably the torque transmitter comprises an intermediate shaft.

Further aspects of the invention will become apparent from the following description of embodiments of the invention in conjunction with the following

schematic diagrams in which: Figure 1 shows a cross-sectional view of a gear unit utilising the method of the invention to monitor the torque state of an intermediate shaft; Figure 2 shows an alternative for the shaft angular deviation sensing means; and

Figure 3 shows another alternative arrangement of sensing means.

Figure 1 shows the sectional view of a gearbox 1 having high and low speed shafts 2 and 3 respectively and an intermediate shaft 4 This intermediate shaft 4 is generally cylindrical in shape, having large and small diameter gear wheels fixed to its curved surface between plane shaft ends 5 and 6.

At each of the shaft ends 5 and 6 there is provided non-contacting angular positions sensing means comprising elements 7, 8 fixed on a region of the shaft end, which in this embodiment is spaced apart from the rotational axis C, and a combined source / detector 9, 10 positioned inside the housing on each of the shaft end covers 11 and 12 respectively. Various angular position sensing means can be used to apply the invention. A simple embodiment is achieved by providing a signal comprising a single pulse when the element fixed to the shaft end passes the detector. Further detail of this embodiment is shown in Figure 2.

(As an alternative to the embodiment shown in Figure 1, the sensor arrangement 7, 9 could be installed on the low speed shaft 3 or on the high speed shaft 2 and / or the sensor arrangement 8, 10 could be installed on shaft 2 or shaft 3.) Figure 2A shows further details of the intermediate gearbox shaft for Figure 1. Each of the two shaft ends is provided with an element El, E2 fixed to a point on the shaft end surface remote from the longitudinal rotational axis C. Figure 2B shows a view of one of the shaft ends taken in the direction of arrow F in Figure 2A and shows the position of element E1 with regard to the rotational axis C. Once per revolution of the shaft the passage of elements E1 and E2 past nearby source / detectors, S/D1 shown in Figure 2B and a similar arrangement at the other end of the shaft, produces a single signal pulse.

Thus by monitoring the angular positions of points on either end of the shaft 4 it is possible to determine the change in angular position of one point

relative to the other due to twisting or so called windup of the shaft about its longitudinal axis C due to the transmitted torque. Whilst the invention may be used to monitor the instantaneous angular position of a given point on each of the shaft ends, in the aspect of the invention described by Figure 2 the signals Pi, Pa provided at times tE' and tea by the sensing means are used to determine the time elapsing, td, between the signals P., P next as illustrated in Figure 2C. By measuring the time period between successive signals from one or both of the said sensing means representing the time taken for one complete revolution of the shaft, the angular velocity of the shaft may be determined. Thus knowing the elapsed td time between the signals from both ends the angular separation or deviation between the two fixed points on the shaft ends may be computed. This may then be compared to the angular shift between the points when the shaft is running unloaded so that the changing angular deviation due to torque transmission may be determined.

Thus in all cases, the phase shift between the two signals will reflect the torsional windup of the shaft due to the torque passing through it. Within large boundaries, or degrees of accuracy, the windup of the shaft is linear versus the torque transmitted. The following relationship thus holds Torque (T) - I O,--0o l * stiffness (S) where 9, and 02 are the instantaneous angular positions of the two known points on the shaft ends when the shaft is under load and the 00 is the angular difference between the same two points under no load conditions.

Thus the absolute value of 1 01-02-Oo l represents the angular windup of the shaft due to load transmission.

The torsional stiffness (5) of the shaft may be determined by various means including calculation using well known general engineering formula or by calibration means whereby a known torque is applied to the gearbox unit or the

shaft and the resultant angular deviation determined. Further where the gearbox is to be used in conjunction with a powered motor, stiffness may also be determined by calibration by measuring motor power at a steady running condition. In accordance with the method of the invention the angular variation sensing means may comprise any suitable means such as inductive means or electromechanical means or optical means.

In one aspect of the invention the angular deviation sensing means comprises a reflector such as a mirror fixed on the shaft end to reflect a light source back to an adjacent detector. Means such as these provide a relatively easy and inexpensive means for adding on to existing installations in the field where the

intermediate shaft can be reached by, for instance, removing the bearing covers without the need to extensively dismantle the machine.

In a variant of the present invention rather than using the shaft ends the method may utilise sensing means 30 applied to a shoulder of the shaft or a disc 31 secured to the shaft 32 as shown in Figure 3.

According to the method of the invention the angular windup may be determined by the comparison of the instantaneous angular deviation between two regions at a different positions in the torque flow path of the gear unit / torque transmitter with the instantaneous angular deviation between the same two regions when the gear unit / torque transmitter is rotating in a zero torque transmitting state.

The invention provides also a gear unit comprising at least one torque transmission member which is rotatable relative to a housing of the gear unit and comprises non-contacting means to co-operate with a signal source and signal detector for use in determining the torque within said at least one torque transmission member.

Claims

i CLAIMS

1. A method of determining the torque within a torque transmitter of a gear unit comprising measuring by non-contacting means the angular windup of the torque transmitter, determining the mechanical torsional stiffness of the torque transmitter and then calculating the torque by multiplying the angular windup by the torsional stiffness of said torque transmitter.

2. A method according to claim 1 wherein the angular windup is determined by comparison of the instantaneous angular deviation between two spaced apart regions of the torque flow path of the torque transmitter when under load with the instantaneous angular deviation between the same two regions when the torque transmitter is rotating in a zero torque transmitting state.

3. A method according to claim 2 wherein torque transmitter comprises an elongate member and the angular windup is determined by comparison of the instantaneous angular deviation between two regions of the torque transmitter which are longitudinally spaced apart.

4. A method according to claim 2 or claim 3 wherein the angular deviation between the two regions is determined by providing in each region means for producing a pulse signal whenever a fixed point on a surface of the torque transmitter passes signal detecting means.

5. A method according to claim 4 wherein the pulse signal generating and detecting means comprise electromagnetic means.

6. A method according to claim 4 wherein the pulse signal generating and detection means comprises optical means.

7. A method according to any one of claims 4 to 6 wherein the angular deviation between the two regions is determined by calculating the angular velocity from the time between successive signal pulses from one or both

t regions representing one revolution of the torque transmitter, measuring the time td elapsing between a pulse signal from one region and the next pulse signal from the other region and calculating the angular deviation between the regions by multiplying the angular velocity by the elapsed time td give the angular differential between the two regions.

8. A method according to any one of the preceding claims wherein the torsional stiffness is calculated by determining the angular windup under the condition of an applied torque of known magnitude.

9. A method according to any one of the preceding claims wherein the torque transmitter is the shaft of a gearbox.

10. A method according to claim 9 wherein the shaft is an intermediate shaft interposed between input and output shafts.

11. A method according to any one of claims 1 to 8, wherein the torque transmitter comprises a shaft and gear.

12. A method according to claim 11, wherein said torque transmitter comprises a pair of shafts and a pair of gears disposed to transmit torque between said shafts.

13. A method according to any one of claims 4 to 12 wherein one of the regions is a plane end of a cylindrical component.

14. A method according to any one of claims 4 to 13 wherein both of the regions are the plane ends of a cylindrical component

15. A method according to any one of the preceding claims wherein the means for measuring angular windup is located substantially wholly within the housing of a gearbox.

16. A gear unit substantially as described herein and as shown in Figures 1, 2 and 3.

17. A gear unit comprising at least one torque transmission member which is rotatable relative to a housing of the gear unit and comprises non-

contacting means to co-operate with a signal source and signal detector for use in determining the torque within said at least one torque transmission member.