GB2155678A

GB2155678A - Method and device for temperature supervision

Info

Publication number: GB2155678A
Application number: GB08505881A
Authority: GB
Inventors: Rune Westergard
Original assignee: Wartsila Oy AB
Current assignee: Wartsila Oy AB
Priority date: 1984-03-08
Filing date: 1985-03-07
Publication date: 1985-09-25
Also published as: DE3508342A1; FI72186C; FI840934A; JPS60208624A; GB8505881D0; FI840934A0; FR2560946A1; FI72186B

Abstract

The invention relates to a method and a device for monitoring the temperature of a moving member (e.g. a bearing) (3), by means of a signal generated when the temperature of the member exceeds a certain limiting control temperature. The signal is conducted to a central supervisory unit supervising the operation of the moving member. In thermal contact with the moving member (3) is located a thermal release device (10-13) which trips when the temperature exceeds the control temperature. Close to the path of motion of the member a sensing means (4) is disposed, this means (4) sensing when the thermal release device (10-13) has tripped and transmits a signal indicating this to the central supervisory unit. The thermal release device may be a bimetal strip or comprise a memory metal, or alternatively it may incorporate solder which melts to release as indicator which is then moved by a spring or small explosive charge. <IMAGE>

Description

SPECI FICATION Method and device for temperature supervision The invention relates to the method and device for monitoring the temperature of a moving member, for example the bearing of a machine.

Temperature supervision in a moving bearing, for example a big-end bearing located between a connecting-rod and the crankshaft of an internal-combustion engine, has been difficult to achieve. Using a thermocouple operating on the thermoelectric principle is not a satisfactory solution because the rapid movements of the bearing makes accurate measurement difficult in several respects.

Attempts to supervise the temperature of a lubricated bearing by measuring the temperature of the lubricating oil which is lubricating it is also inaccurate, because the measuring results provided in this way depend significantly on the flow rate of the oil.

The temperature of a bearing can be monitored inductively by arranging a sensing coil, whose inductance changes with temperature, in thermal contact with the bearing and ensuring that the sensing coil periodically passes between two measuring coils (by means of which the inductance of the sensing coil is assessed). A disadvantage of this proposal, however, is that impurities, for example oil, adhering to the surfaces of the coils have a considerable influence on the measuring result.

The present invention seeks to provide an improved method and device for supervising the temperature of a bearing. The invention does not require there to be any specific measurement of the temperature of the bearing. When the temperature exceeds a certain limiting control temperature it causes a signal to be generated, which, in a manner known per se, is conducted to a central supervisory unit.

What constitutes the invention is defined in the following claims 1 and 6.

One aim of the invention is to provide a method and device which is simple in design and dependable in use. Another aim is to create a method and device, which are based on the principle that too high a temperature causes a change in the physical shape of a thermal release device in thermal contact with the moving member, which shape change can be detected in a simple manner, and which preferably is automatically reversible in order to facilitate the resetting of the supervisory equipment and/or to trigger an alarm or control device.

The tripping of the thermal release device can be detected at the moment when it occurs or when the moving member subsequently reaches that point on its path of motion where the sensing means senses the effect of the shape change of the thermal release device.

In a preferred embodiment of the invention, the thermal release device is automatically reversible when the temperature drops back below the limiting control temperature. The reversibility of a thermal release device can be accomplished by a release device which is made for example of a bimetal or a material like that. Automatic reversibility means here a property of the thermal release device which depends on temperature. The shape change or tripping of the thermal release device can be detected in several different ways known per se, without any mechanical contact be tween the release device and the sensing means. For this purpose, for example, an inductive, or a capacitive, or possibly an opti cal proximity sensing element may be used.

Its sensing range is most suitably between 10 and 20 mm. It is not necessary to use a thermal release device which trips suddenly.

The magnitude and/or direction of the move ment of the release device during its shape change can then be adjusted in such a man ner that any exceeding of the control temperature is reliably detected.

The release device may include a spring element which causes the release device to trip when a change occurs in the physical state of a retainer holding the spring element under stress. The change in physical state may be directly dependent on the temperature. Wax, metal or metal alloy can be a suitable solder or bonding material that melts or softens within a narrow temperature range centred on the limiting control temperature.

The tripping can be effected using other ther mosensitive materials, for example a small powder charge or the like. A release device such as those just described is not automati cally reversible in its operation.

If the release device is formed at a suffici ently high temperature of a so-called memory metal, or a metal or an alloy material like that, the device will re-establish its original natural shape when the temperature exceeds the lim iting control temperature. The reversibility of such a material and the desired temperature control level are, of course, adjusted to each other.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of part of an engine incorporating one embodiment of means according to the invention, and Figure 2 is a sectional view of a detail of the engine part shown in Fig. 1.

In Fig. 1 part of an internal-combustion engine is shown, the engine comprising a piston 2 which is slidably located in a cylinder 1, a connecting-rod 8 and an associated bot tom bearing cap 7 linking a crank 6 of a crankshaft to the piston 2. In the connecting rod 8 an opening 9 is provided, which extends through to the crankshaft bearing shell 3. Within the opening 9 a thermal release device 10-13 (see Fig. 2) is located, which is temperature sensitive and thus capable of responding to the temperature of the bearing 3. A proximity sensing means 4 for the release device 10-13 is attached to a frame 5 of the engine and is used to indicate when the thermal release device 10-13 located in the opening 9 is tripped by an excessive temperature rise.The crankshaft rotates in the direction of the arrow 15, and the mid-point of the crankshaft main bearing is indicated at 1 6.

When the thermal release device 10-13 is at its position of closest approach to the sensing means 4, the separation is in the range 10 to 20 mm.

Fig. 2 is an enlarged sectional view of the thermal release device and sensing means 4 of Fig. 1. In a wider outer part of the bore of the opening 9 a body element 11 of the thermal release device 10-13 is threadedly secured in place. The element 11 includes a temperature sensing body 1 3 which is directly affected by the temperature of the bearing 3.

As shown in Fig. 2, the sensing element 1 3 is attached at its inner end either to the bearing 3 or to the connecting-rod 8 by means of a thermosensitive solder 1 2 which is selected to melt when its temperature exceeds a pre-set control temperature. The body element 11 houses a spring (not shown) which is capable of moving a movable indicator 10 radially outwards with respect to the bearing 3. The position, or the change of the position, of the indicator 10 is detected by the sensing means 4, from which a sensing signal is conducted by a conductor 14 to engine supervisory equipment (not shown). In place of a solder 12, the sensing element 1 3 can be made of a so-called memory metal which has the property of changing shape when its temperature exceeds a critical temperature.Below the critical temperature the element 1 3 has an artificial compressed state but on reaching the critical temperature, the sensing element 1 3 returns to its original expanded state (for example by stretching longitudinally) and thus affects the position of the indicator 10. The sensing element 1 3 can also be made as a bimetal which changes length as its temperature changes, in which case sufficient space needs to be provided inside the body element 11 to allow the stretching-shrinking movement of the sensing element 1 3 to occur. The operation of the thermal release device 10-13 thus, in its various embodiments corresponds in principle to the operation of an automatic or a heat coil fuse known in electrical engineering.

A modification of the invention uses, as a part of the thermal release device 10-13, a small explosive charge which is ignited at a given temperature by thermal energy conducted to it from the bearing 3 through the sensing element 1 3. In this modification it may be necessary to arrange a suitable catching element between the indicator 10 and the body element 11 so that the indicator 10 will be arrested in its outermost position when the charge is fired.

The invention is not limited to the embodiments shown, since several modifications thereof are feasible within the scope of the following claims.

Claims

1. A method of monitoring the temperature of a moving member which comprises locating a thermal release device in thermal contact with the member, which device trips when the temperature of the member exceeds a certain limiting control temperature, and arranging a sensing means adjacent to the member, which sensing means is adapted to detect said tripping of the thermal release device, and to send a signal indicating this to a central supervisory unit.

2. A method according to claim 1, in which a reversible thermal release device is used which device returns to its normal shape when the temperature drops below the control temperature.

3. A method according to claim 1 or 2, in which the sensing means is an observation device which senses the tripping without any mechanical contact with the thermal release device.

4. A method according to claim 3, in which the sensing means is an inductive or capacitive proximity sensing means.

5. A method of monitoring the temperature of a moving member substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

6. A device for applying the method as claimed in any preceding claims to a moving bearing which comprises a thermal release device in thermal contact with the bearing, which device trips when the temperature exceeds said limiting control temperature, and a sensing means close to the path of motion of the bearing, which sensing means is arranged to detect the tripping of the thermal release device and to send a signal indicating this has occurred to a central supervisory unit.

7. A device according to claim 6, in which the thermal release device automatically reverts to its original shape when the temperature drops below the limiting control temperature.

8. A device according to claim 6 or 7, in which the operation of the thermal release device is based on the properties of a bimetal, or other metal or alloy, which reacts to tem perature change.

9. A device according to claim 6, in which the thermal release device is formed of memory metal deformed from a natural shape, which memory metal returns to its natural shape when its temperature exceeds the limiting control temperature.

1 0. A device according to claim 6, in which the thermal release device includes a solder connection, the melting or softening of which causes the tripping of the thermal release device.

11. A device according to claim 10, in which the thermal release device includes a spring-loaded part, which part is moved by the spring to change the shape of the device when the temperature exceeds the limiting control temperature.

1 2. A device for monitoring an excessive temperature rise in a bearing substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.