GB2251951A

GB2251951A - Device for indicating torque overload of a shaft

Info

Publication number: GB2251951A
Application number: GB9201147A
Authority: GB
Inventors: Ernst-Bernhard Arand; Hartmut Zoppke
Original assignee: GKN Cardantec International GmbH
Current assignee: GKN Driveline International GmbH
Priority date: 1991-01-21
Filing date: 1992-01-20
Publication date: 1992-07-22
Anticipated expiration: 2012-01-20
Also published as: GB9201147D0; SE9200048D0; ITMI920035A0; SE9200048L; FR2671874A1; GB2251951B; DE9100654U1; ITMI920035A1; IT1262926B

Abstract

A device for indicating torque overload of a shaft which has a holding element not subject to torque extending coaxially therewith and non-rotatingly connected at one end to the shaft, the device being provided at the other end of the holding element and comprising an indicating means operable by deformation of the shaft relative to the holding element to actuate an electronic switch 33 arranged to give a visual and/or acoustic warning signal in case of overload. <IMAGE>

Description

Title: DEVICE FOR INDICATING TORQUE OVERLOAD OF A SHAFT Description of Invention This invention relates to a device for indicating torque overload of a shaft, the shaft including at least one part having a holding element extending coaxially relative thereto, the holding element not being subject to torque and having one end non-rotatingly connected to the shaft part, the device being provided at the other end of the holding element. The shaft may be a lengthadjustable propeller shaft, e.g. for the drive line of a motor vehicle.

Universally jointed drive shafts are widely used for torque transmission in the drivelines of agricultural or construction machinery, and motor vehicles.

Drive shafts are subject to high torsional and cyclical loads in use, and are safetycritical components, especially in the case of commercial vehicles which incorporate engine or transmission brakes because they have to transmit braking forces To a wheel or wheels of the vehicle.

DE-FS 3 636 167 discloses a propeller shaft which is length-adjustable, comprising shaft parts which are telescopically connected, and wherein a sealing sleeve is provided embracing the cylindrical outer surface of the shaft parts. One end of the sealing sleeve is non-rotatingly connected to one shaft part and the other end of the sealing sleeve is provided with a marking which can be viewed in conjunction with a further marking on the other shaft part, which markings may comprise two scales movable relative to each other. If the torsional deformation of the shaft exceeds the elastic range of deformation, and enters the range of plastic deformation of the shaft, then such plastic deformation will be visible as a permanent displacement between the two scales after the load has been removed from the shaft.If, however, shaft deformation remains within the elastic range, then there is no permanent indication of such deformation and reading of the deformation is only possible when the shaft is subject to torque.

It is broadly the object of the present invention to provide a device for indicating torque overload of a shaft, which is able to provide an indication of deformation due to overload whether such deformation is elastic or plastic.

According to the present invention, it is proposed that the indicating device should comprise an indicating means arranged to cause an electronic switching unit to give a visual and/or acoustic warning signal indicative of a torque causing torsional deformation of the shaft greater than a permissable value.

A device according to the invention can be used to indicate shaft overloads whether such overload results in torsional deformation of the shaft in the elastic or the plastic range. It is conceivable to provide one indicating means to indicate a deformation in the elastic range and another indicating means element to indicate a deformation in the plastic range. The electronic switching unit would provide a signal warning of excessive deformation in either or both ranges. It is possible to store a signal for each case of overloading, and recall information from the store when required to indicate the history of loading of the shaft.

The indicating means may be arranged to break an input circuit of the electronic switching unit. Such breakage may be provided by breaking a wire forming part of the input circuit of the switching unit, in which case the length and arrangement of the wire may be selected to record either a maximum elastic or plastic deformation of the shaft. or possibly both types of deformation could be recorded by two wires.

In a further embodiment, the indicating means may comprise an electrical switch having resilient contact elements associated respectively with a shaft part and the holding element, the switch being operated, e.g. by opening the contacts, when a predetermined torque and consequent torsional deformation in the shaft is exceeded.

Such an arrangement of resilient contact elements readily permits an electrical signal to be supplied to the electronic switching unit when a predetermined torque is exceeded and the shaft is torsionally deformed beyond the corresponding permissible value.

Alternatively, a switch may be provided, having an actuating element arranged to be operated by relative movement between the holding element and adjacent shaft part, the actuating element causing the switch to be operated when a predetermined torque is exceeded.

The actuating element may be arranged to operate one or even several switches at a predetermined torque overload. The actuating element may comprise a resilient or spring loaded element, or a lever having a longer lever arm arranged to operate the switch. In an arrangement in which the switch and the lever element are associated with a shaft part or the holding element, and the other of the shaft part and holding element is arranged to move the lever, by selecting a suitable lever configuration it is possible for the longer lever arm to move through a relatively long distance to operate the switch in the case of a slight relative movement between the shaft and the holding element. In this way it is only necessaly to provide a holding element which extends a relatively small proportion of the total length of the shaft.

In a further embodiment of the invention, the indicating means may comprise magnetic elements cooperabie with one another and provided in association with the'shaft part and the holding element. For example, a magnetic tape comprising a coded signal, or a toothed ring, may cooperate with a magnetic sensor which does not require physical contact with the tape or ring.

Alternatively, parts which cooperate optically, e.g. a tape having an at least partially reflective surface, and a light barrier, may be associated with a shaft part and the holding element. In either case a sensor may be arranged to provide a signal proportional to the angle of torsional deformation of the shaft, to be transmitted to the electronic switching unit.

These latter embodiments of the invention provide the additional possibility of measuring the torque load continuously and of storing the maximum value of any overloads, so that subsequent examination of the stored data provides more detailed information on the loads to which the shaft has been subjected. A shaft equipped with the invention may be used in a prototype of the equipment for which it is intended, and the data derived therefrom used for determining optimum shaft design.

The shaft may be a universally jointed shaft incorporating inner and outer parts axially movable relative to one another, in which case the holding element may take the form of a cover tube or an element disposed within one or both parts of the shaft. The shaft may be a torque-transmitting drive shaft and the holding element may be a cover tube.

The electronic switching unit may be arranged to record and store details of repeated overloads, or may indicate only a single case of overloading.

The unit may comprise a destructible element to release a single and permanent visual indication of overload, which destructible element may be a semiconductor, a fuse, or other element.

The incorporation of a destructible element inside the electronic switching unit makes it possible to release a permanent signal which cannot be erased or eliminated by the user. The switching unit may be provided with a housing having a colour marking so that it can be seen immediately if the destroyed element is replaced.

The invention will now be described by way of example with reference to the accompaning drawings, wherein: Figure 1 is a side elevation, partly in section, of a length-adjustable propeller shaft provided with a holding element in the form cf a cover tube; Figure 2 is a view as Figure 1 of a further embodiment of propeller shaft, bring a holding element in the form of a cover tube but covering part only of the shaft; Figure 3 is a view, as Figure 1 and Figure 2, of yet a further embodiment of propeller shaft, incorporating a holding element in the form of an iiidicating shaft extending 'vi+hin part only of the shaft;; Figure 4 is a view, as Figures 1 to 3, of yet a further embodiment of propeller shaft, having a holding element in the form of an indicating shaft extending within both the relatively movable parts of the shaft; Figures SA and 5B are perspective views of a cover tube, respectively in the closed condition fitted to a shaft and in the open condition; Figures 6A and 6B are respectively a longitudinal section through the cover tube assembly of Figure 5 and a section on the line A-B of Figure 6A; Figures 7A and 7B are respectively longitudinal and transverse crosssections through the region "Z" of Figure 1 or Figure 2; Figures SA and 8B are respectively a transverse section through the region "X" in Figure 3 and a section on the line B-B of Figure 8A;; Figures 9A, B and C are respectively a longitudinal, transverse, and horizontal section through the region "Y" in the shaft of Figure 4; Figures 10, 11 and 12 show different embodiments of electronic switching unit for the invention.

Referring firstly to Figure 1 of the drawings, the shaft there illustrated and indicated generally by the reference numeral 1 is a length-adjustable propeller shaft for the drive line of, e.g., a motor vehicle, the shaft comprising a first shaft part 2 and a second shaft part 3 which are connected to one another by length-adjusting 'means. The first shaft part 2 is provided with a journal or spigot 4 which fits within, and has an external profile which cooperates with, an internally profiled sleeve 5 connected to the second shaft part 3. At their ends remote from one another, the first and second shaft parts are provided respectively with Hookes universal joint yokes 6, 7 which are connected, by cross members S as is conventional in Hookes universal joints, with further joint yokes provided with connecting flanges 9.

A holding element in the form of a cover tube 11 is connected to the first shaft part 2 by a non-rotating connection 10. As illustrated, in the condition where the spigot 4 is fully inserted in the sleeve 5 so that the overall length of the shaft is at a minimum, the other, free, end of the cover tube lilies adjacent the joint yoke 7 of the shaft. At its free end 13, the cover tube 11 is provided with a radially inwardly extending support 14 which is in the form of a seal engaging the external surface 12 of the second shaft part 3, for holding the cover tube at a uniform distance from the surface 12 and for preventing ingress of dirt to the space inside the cover tube and to the length-adjusting means 4, 5 when the length of the shaft changes.

Figure 2 shows a shaft which is similar to the shaft of Figure 1 in respect of the shaft parts 2, 3, and parts corresponding to parts of the shaft shown in Figure 1 are identified by the same reference numerals as used in Figure 1.

In this embodiment, however, the cover tube ii extends over the second shaft part 3 only, having a non-rotating connection thereto at 10a, adjacent the connection of the shaft part 3 to the sleeve 5. It will be appreciated, therefore, that when the length of the shaft changes by relative movement between the shaft parts 2 and 3, the position of the free end 13 of the cover tube 11 relative to the shaft part 3 does not change. Because the cover tube 11 does not cover the length-adjusting means 4, 5, a separate protective tube 15 is provided for this purpose, being connected to the shaft part 2 at a connection 16 and having a seal 17 engaging the external surface of the sleeve 5.

Figure 3 shows a shaft which is again similar to the shaft of Figures 1 and 2, with corresponding parts being identified by the same reference numerals.

In this embodiment, however, the holding element is provided by an indicating shaft 19 disposed within the shaft part 3, the indicating shaft being non-rotatingly connected to the shaft part 3 at a connection lOb. The other, free, end 13 of the indicating shaft 19 is provided with a radially extending indicating element 18.

To support the indicating shaft 19 when the propeller shaft 1 is rotating at high speed, at least one radially inwardly extending support element 20 is provided.

Figure 4 shows yet a further embodiment of shaft which, as in the embodiment of Figure 3, the holding element comprises an internally disposed indicating shaft 19. In this case, the indicating shaft 19 is non-rotatingly connected to the first shaft part 2 adjacent the joint yoke 6, by a connection 10c.

The other end of the indicating shaft is supported within the joint yoke 7, and adjacent such other end the indicating shaft has a radially outwardly extending pin 42 which extends through an aperture 43 which is of elongated configuration in the direction circumferentially of the yoke. The arrangement of the aperture 43 and pin 42 fixes the adjacent end of the indicating shaft axially relative to the shaft part 3, and the non-rotating connection 10c of the indicating shaft comprises a squared head on the indicating shaft fitted within a square aperture in the yoke 6 so that relative axial movement between these parts is possible. Alternatively, however, it would be possible to provide the necessary relative axial movement between the indicating shaft and an adjacent part of torque transmitting shaft at the end of the former at which the pin 42 is provided.To increase the critical rotational speed of the shaft, the indicating shaft 19 is supported between its ends by at least one support element 20.

In all the above described embodiments of shaft, it will be appreciated that when torque is being transmitted some relative angular movement about the rotational axis of the shaft takes place between the free end of the holding element, remote from its non-rotating connection to a shaft part, and the adjacent part of the shaft, because the holding element does not partake in torque transmission. The position of any point at the free end of the holding element changes relative to the adjacent shaft part. Torsional deformation of the torque transmitting shaft may take place within the range of elastic or plastic deformation behaviour of the shaft, in the former of which cases no permanent deformation remains while in the latter there is some permanent deformation.

The embodiments of indicating means described hereafter permit an indication to be given even in the case of elastic deformation of the shaft.

Figures 5A and SB show a holding element in the form of a cover tube which is relatively short, and is in the form of a unitary moulding of plastics material. It comprises two halves 20, 21 connected to one another by an integral hinge formation 22. The ends of the element have radially inwardly extending reinforcing flange formations 23 so that therebetween the cover tube is spaced from the surface of a shaft to which it is applied, and the flange formations 23 of one half of the element have bores 24 while those of the opposite half have pins 25 which engage in the bores 24 for securing the two halves of the coupling element together on a shaft. The flange formation 23 at one end of the holding element is provided with a bore 26 for receiving a pin 26a extending outwardly from the shaft, to provide a non-rotating connection between the shaft and that end of the holding element.

Referring now also to Figures 6A and 6B, an actuating lever 28 is disposed within the part of the cover tube 11 which is spaced from the surface of the shaft. The actuating lever 28 comprises a relatively short arm 29 and a relatively long arm 30, the short arm 29 ending in an integral hinge formation at the adjacent flange formation 23 of the holding element. The opposite end of the lever, at the free end of its long arm 30, lies between two switches 31 spaced from one another in the direction circumferentially of the shaft and secured to the cover tube 11. A bearing pin 27 extends radially outwardly from the shaft and engages in an aperture in the lever 28 between its short and long arms.It will be appreciated that when the shaft is subject to torque, the length of the part 3 thereof between the pin 26a and the pin 27 will undergo a small torsional deformation so that the pin 27 moves circumferentially relative to the adjacent part of the cover tube 11. Even a small circumferential movement here will produce a relatively large movement ai the free end of the long arm 30 of lever 28, to operate a switch 31. The switches 31 are so arranged as to switch when the overload limit of the shaft is reached, and by an electronic switch it causes the overload to be indicated. If required, an electronic switching unit can be arranged to ensure that after the switch has been operated once upon occurrence of a single overload, the switched condition is maintained. The switch signal is used to give an electrically operated visual and/or acoustic signal.

Figures 7A and 7B show an arrangement of a switch, indicated generally in these figures by reference numeral 31, which comprises contacts associated respectively with a shaft part 3 and a cover tube 11. The inner face 32 of the cover tube 11 is provided with an insulating layer 33 of plastics, and with a contact element 31a which is a generally U-section component of sheet metal.

Between the parallel limbs of the U-section contact element 31a, there is disposed a second contact element 31b which is secured to the external surface of the shaft part 3 with an interposed insulating layer 33. Torque in the shaft part 3 leads to relative circumferential movement between the contact elements 31a, 31b so that contact is established therebetween when a certain torsional deformation caused by the torque is reached. As described above, such contact can be used to cause a visual and/or acoustic signal to be given by an electronic switching unit.

Referring now to Figures 8A and 8B of the drawings, these show in detail the arrangeinent which may be provided within the portion "X" of Figure 3. A pin 42 projecting radially at the free end of the indicating shaft 19 extends to a position adjacent the internal wall of the cylindrical recess provided in the joint yoke 7. Within the recess in the joint yoke there is provided an insulating housing 49 whose internal configuration includes a recess 143 into which the end of the pin 42 extends. The recess 143 contains electrical switch contacts which comprise a pair of spaced contact elements 47a and a contact element 47b therebetween, the contact elements 47a being biased by springs 48 into engagement with the contact element 47b, or being resilient so as to engage the contact element 47b.In the case of torque overload and excessive torsional deformation of the shaft part 3, the pin 42 engages one or other of the contact elements 47a and breaks the contact thereof with the contact 47b. This enables an electronic switching unit to be operated, to provide a signal to warn of such torque overload.

Referring now to Figures 9A, B and C, these show in detail the arrangement within the portion "Y" of Figure 4. An insulating housing 49 is secured to the exterior of the joint yoke 7, and contains two contact elements 44a which are biased towards one another by a spring 46 and which rest against abutment edges 45 of the housing 49. A further U-shaped contact element 44b is disposed within the housing 49, being separated from the contact elements 44a by an insulated layer 44c. The free end of the pin 42 extending radially outwardly from the indicating shaft 19 through circumferentially elongated aperture 43 in the yoke 7 lies between the contact elements 44a, to engage one or other of the contact elements 44a and push it into contact with the contact element 44b when the torsional deflection in the shaft parts 2 and 3 exceeds a permissible limit.

Because the contact elements 44a are held against surfaces 45 by spring 46, the switch is prevented from being actuated by shaft vibrations.

Figure 10 shows a relatively simple switching assembly which comprises a thyristor 34, a light emitting diode 35, and two resistors 36, 37. The resistor 37, thyristor 34 and light emitting diode 35 are connected in series with one another to a power supply, whilst the resistor 36 is connected in series with the switch 31 to the thyristor in an arrangement such that when the switch 31 is open the thyristor is in the non-conducting state but when the switch 31 is closed the application of voltage to the control electrode of the thyristor 34 causes it to become conductive. The light emitting diode 34 is thus caused to light and give a signal of closing of the switch 31.The circuit of Figure 10 may thus give a visual warning of shaft overload if the arrangement of the switch 31 in relation to the shaft is such that the switch is closed when overload occurs. As an alternative to a light emitting diode 35, an acoustic warning device could be provided, e.g. a piezo crystal device.

Figure 11 shows a further switching circuit which comprises a switch 31 and resistor 36, connected in parallel with a light emitting diode 35 and further resistor 37. The power supply to these components is by way of a further diode 38 whose capacity is such that it is able to carry the current taken by the light emitting diode 35 through the resistor 37, but is not able to carry the additional current through resistor 36 when the switch 31 is closed. This circuit operates such that when the shaft is carrying acceptable torque and the switch 31 is open, the light emitting diode 35 is lit to provide a pilot light signal that torque is acceptable, but if an overload causes the switch 31 to be closed, the diode 38 is destroyed by the excess current through it and the light emitting diode 35 is extinguished.Resumption of normal operation of the circuit requires external measures to be taken, namely the replacement of the diode 38.

Figure 12 shows a switching assembly incorporating a light emitting diode 35, a switching transistor 41, and resistors 39 and 40 which are arranged as a voltage divider, the base of the transistor 41 being connected therebetween.

Light emitting diode 35 is connected at the positive line of the power supply to the collector of the transmitter 41, while the emitter of the transmitter 41 is connected by a resistor 37 to the negative line of the power supply. Switch 31 is connected in parallel with the two resistors 39, 40, both the switch and these resistors being connected to the negative line of the power supply by way of a diode 38 whose current-carrying capacity is limited. Under normal operating conditions, with switch 31 open, the transistor 40 is in the non-conductive state, but when switch 31 is closed causing the diode 38 to be destroyed, the transistor has a voltage applied to its base by way of resistor 39 so that it becomes conductive and the light emitting diode 35 lights up. External measures, i.e.

replacement of the diode 38, is required to restore the previous condition of the circuit. Instead of the diode 38, it would be possible to use a fusible element or the like.

In each of the embodiments described above, the electronic switching assembly as well as the power supply for it could be installed in the drive shaft and could work independently of the power supply of the vehicle. When maintenance of the vehicle is carried Out the shaft could be inspected to find whether it has been overloaded.

It would also be possible for an indicating means to be installed in the vehicle so that die driver could observe any indication of overload. In such a use some means of transmitting a signal frorn the shaft to the adjacent vehicle structure would he provided. For example, slip rings or other devices could be provided.

The features disclosed in the foregoing description, or the following claims, or the accompanyímg drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A device for indicating torque overload of a shaft, the shaft comprising at least one part and a holding element extending coaxially relative thereto, the holding element not being subject to torque and having one end non-rotatingly connected to a shaft part, the device being provided at the other end of the holding element and comprising an indicating means operable by deformation of the shaft relative to the holding element and arranged to cause an electronic switching unit to give a visual and/or acoustic warning signal indicative of a torque causing torsional deformation of the shaft greater than a permissible value.

2. A device according to Claim 1 wherein the indicating means comprises a wire, breakage of which breaks an input circuit of the electronic switching unit.

3. A device according to Claim I wherein the indicating means comprises an electrical switch having contact elements associated respectively with a shaft part and the holding element. the contact elements opening or closing when a predetermined torque is exceeded.

4. A device according to Claim 1 wherein the indicating means comprises a switch having an actuating element arranged to be operated by relative movement between the holding element and adjacent shaft part when a predetermined torque is exceeded.

5. A device according to Claim 4 wherein the actuating element comprises a resilient member on the shaft part or holding element.

6. A device according to Claim 4 wherein the actuating element comprises a lever supported by the holding element, having a longer lever arm arranged to operate the switch.

7. A device according to Claim 1 wherein the indicating means comprises magnetic elements cooperable with one another and provided in association with the shaft part and holding element, including a non-contact sensor providing a signal in accordance with the torsional deformation of the shaft, for transmission to the electronic switching unit.

8. A device according to Claim 1, wherein the indicating means comprises a sensor and a part cooperating optically therewith so that the sensor provides a signal in accordance with the torsional deformation of the shaft, for transmission to the electronic switching unit.

9. A shaft according to any one of the preceding claims wherein the electronic switching unit is adapted to store data relating to repeated overloading of the shaft.

10. A shaft according to any one of the preceding claims wherein the electronic switching unit comprises an element adapted to be destroyed in the case of shaft overload, to provide a single permanent overload signal.

11. A shaft according to Claim 10 wherein the destructible element comprises a semi-conductor or a fusible element.

12. A device according to any one of the preceding claims wherein a visual signal is provided in case of overloading and under normal operating conditions.

13. A device according to any one of the preceding claims wherein an acoustic signal is provided in case of overloading.

14. A device according to Claim 7 or any claim appendant thereto wherein one magnetic element of the indicating means comprises a magnetic tape bearing a coded signal, and the sensor comprises a magnetic head providing a signal dependant on the torsional deformation of the shaft.

15. A device according to Claim 7 or any one of Claims 8 to 13 as appendant thereto wherein one magnetic element of the indicating means comprises a toothed ring, and the sensor comprises a magnetic head providing a signal dependant on the torsional deformation of the shaft.

16. A device according to Claim 8 or any claim appendant thereto wherein the indicating means includes an element having an at least partially reflective surface and a light barrier, associated with the shaft part and the holding element, and an optical sensor arranged to provide a signal dependent on the torsional deformation of the shaft.

17. The combination of a shaft and device according to any one of the preceding claims, wherein the shaft is a universally jointed drive shaft comprising first and second shaft parts movable axially relative to one another, and wherein the holding element extends within or on the outside of at least one of said parts.

18. The combination of a shaft and device according to any one of Claims 1 to 16 wherein the shaft comprises a drive shaft and the holding element comprises a cover tube.

19. The combination according to Claim 15 wherein the cover tube is split longitudinally into two semi-tubular portions.

20. A device for indicating torque overload of a drive shaft, substantially as hereinbefore described with reference to any one of the accompanying drawings.

21. Any novel feature or novel combination of features described herein and/or in the accompanying drawings