GB2198199A

GB2198199A - A device for monitoring the lining wear in shoe brakes

Info

Publication number: GB2198199A
Application number: GB08727696A
Authority: GB
Inventors: Herbert Braun; Gerhard Hammerle
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1986-11-29
Filing date: 1987-11-26
Publication date: 1988-06-08
Anticipated expiration: 2007-11-26
Also published as: GB8727696D0; SE8704597D0; SE500655C2; DE3640888C2; FR2607567A1; GB2198199B; IT1223083B; IT8722556A0; SE8704597L; DE3640888A1; FR2607567B1

Abstract

A device for monitoring the lining wear in shoe brakes, comprises a sensor (42) made of insulating material which contains an electrical conductor (48) connectable to a warning device and which has a sensor stem (46), which in use is arranged in an opening (40) passing through the lining support (18) of a brake shoe (20, 22), and a sensor finger (58) which is arranged at right angles to the stem which can be inserted into a bore (60) in brake lining. The sensor stem is securable in the opening by means of a separate retaining element (44) which can be locked together with the sensor stem upon insertion into the opening, and in the locked together condition, the sensor stem and the retaining element frictionally engage the opening. <IMAGE>

Description

A Device for monitoring the Lining Wear in Shoe Brakes The invention relates to a device for monitoring the lining wear in shoe brakes, in which an electrical sensor connected to a warning device is mounted, with a sensor, in an opening passing through the brake lining support.

A monitoring device of this type in known from German Patent Specification 28 13 244. In this embodiment the retaining element comprises a hollow rivet introduced into a bore in a lining support of a partially lined disc brake. The sensor, which is made of insulating material and contains an electrical conductor, is inserted with a sensor stem into the front end of the hollow rivet which is situated on the lining support on the side of the brake lining which is carried by this support. At the same time reliable mounting of the sensor stem in the hollow rivet is achieved because the sensor engages, with a laterally projecting sensor finger, in an end inserted bore in the brake lining to be checked.

For production engineering reasons this design calls for easy accessibility to the attachment point of the hollow rivet and sensor on both sides of the relevant lining support. In addition, fitting is impossible without special auxiliary equipment or tools because of the necessity for reshaping the hollow rivet. At the same time this type is only suitable for plate-shaped lining supports of partial lined disc brakes in which the attachment point is provided on a section of the support projecting laterally over the brake lining, and is easily accessible from both sides thereof.

Finally, this design makes it impossible to vary the position of the sensor relative to the lining support in the axial direction of the opening in the lining support in order that the sensor finger may engage bores in the lining, the distance between which bores and the lining friction surface which can engage with a rotating part of the brake is variable.

The present invention seeks to provide a brake linig wear monitoring device of the type described generally above in such a manner that it can be fitted without auxiliary tools or by hand and can be used to equal advantage both for disc brakes with partial lining and for drum brakes, while, at the same time enables different fitting depths for the sensor finger in brake linings and assembly only on that side of the lining support remote from the brake lining.

According to the invention, there is provided a device for monitoring the lining wear in shoe brakes, comprising a sensor made of insulating material which is connectable to a warning device and contains an electrical conductor and which has a sensor stem, which is to be arranged in an opening passing through the lining support of a brake shoe, the stem also comprising a sensor finger which is arranged at right angles to the stem and is electrically connected thereto and which can be inserted into a bore in a brake lining, said bore being arranged at a distance from the friction surface of the sensor finger and extending at a right angle to the axis of the opening, the sensor stem being securable therein bv means of a retaining element which can be inserted by frictional connection in the opening of the lining support, wherein the sensor stem and sensor finger are in one piece, and the retaining element is separated from the sensor stem and can be locked together with the sensor stem upon insertion into the opening.

In one embodiment of the invention, the sensor stem can be arranged against a wall section of the opening and the retaining element can be inserted between another wall section of the opening and the sensor stem.

According to another embodiment of the inventioin, the retaining element and sensor stem engage with one another via a T-shaped slot-like connection so as to be slidable relative to one another.

In a further embodiment of the invention, the retaining element has, on the side of the sensor stem that is to be secured, two guide arms which extend in the longitudinal direction thereof, are parallel to and spaced from one another and form the T-shaped slot-like recess and which can engage with lateral longitudinal slots, of the sensor stem, and at least one of the guide arms has, on its longitudinal side opposite the other guide arm, a recess or an elevated part which can be brought into positive engagement with an elevated part or recess provided in the longitudinal slot of the sensor stem for receiving this guide arm.

In yet another embodiment of the invention, the retaining element has, at its end which is accessible after insertion into the opening in the lining support, a projection which extends obliquely in the direction of the sensor stem and which, with the sensor secured, engages a recess in the sensor stem.

A monitoring device constructed in accordance with the invention enables the sensor and retaining element to be fitted on the same side of the lining support. In this case the retaining element comprises a clamping body with the aid of which the sensor stem extending through the opening of the lining support may be firmly clamped in this opening.

The fitting of the sensor finger in the bore in the relevant brake lining at the same time proves to be problem-free since the sensor stem can be inserted through the opening in the lining support and then the sensor finger which projects therefrom can be inserted into the relevant bore in the lining.

An advantageous arrangement of the sensor on brake pads of disc brakes with partial linings (spot-type disc brakes) is obtained at the same time if the opening in the lining support which receives the sensor stem is located laterally of a lining face and the bore which receives the sensor finger is introduced into this lining face.

The invention makes it equally possible for the sensor to be arranged on a lining support and concealed by a brake lining. In this case the axis of the opening of the lining support for receiving the sensor stem is to be provided in the plane of two adjacent faces of brake linings, and in this connection, corresponding recesses for receiving the sensor head are to be introduced into both faces and a bore for receiving the sensor finger is to be introduced into one of these recesses. A sensor arrangement of this type is particularly suitable for brake shoes of drum brakes.

The clamping connection for the sensor stem as proposed in accordance with the invention makes it possible for the sensor finger to be arranged within a specific range at an desired distance relative to the surface of lining supports for receiving the brake lining or linings in order that the same distance between the lining bore which receives the sensor finger and the friction surface of the relevant brake lining may always be maintained in the case of brake linings having different thicknesses.

The sensor stem can, in this case, pass through the retaining element which has for example a multiple arm design and the arms of which are pressed by frictional contact against the sensor stem when the retaining element is introduced into the opening in the lining support.

An arrangement in which the sensor stem lies against one wall portion of the opening and the retaining element is inserted between the stem and another wall portion, enables ar arm-free design of the retaining element. In this case a secure keying fit of the retaining element in the opening in the lining support is ensured by the use of the T-shaped, slot-like connection, in which the retaining element, when in its fitted position, is locked together with the secured sensor stem. If the fit of the retaining element in the opening should loosen due to, for example, the influence of vibrations in the brake, the engagement of the sensor finger with the bore in the brake lining ensures firstly that the retaining element cannot become detached from the opening in the lining support and secondly that the sensor finger cannot become detached from the bore in the lining.

An embodiment of the invention, together with a brake shoe of a drum brake, will now be described by way of example and with reference to the accompanying drawings, in which: Figure. 1 shows a partial longitudinal section through a brake shoe of the drum brake which is equipped with a monitoring device; Figure. 2 shows a view of the brake shoe of Figure. 1, seen in the direction of arrow A in that drawing; Figure. 3 shows a cross-section of the brake shoe along the line III-III in Figure. 2, in a state detached from the brake drum, Figure. 4 shows a partial section along the line IV-IV in Figure. 1, on a larger scale to that of Figure. 1, Fig.5 shows a partial section along the line V-V in Figure. 1, Figure. 6 shows a plan view of the sensor, and Figure. 7 shows a view of the retaining element, seen in the direction of arrow B in Figure. 2.

In the drawing reference numeral 10 designates generally a brake shoe of a drum brake 12. Two brake linings 20, 22, for example, are riveted to its segmental brake band 18, which has on its inner side for example two welded-on webs 14, 16 laterally spaced from one another, by means of hollow rivets 24 in such a manner that the adjacent faces 26 and 28 of the linings define a gap 30. The frictional surface 32 of the two brake linings 20, 22 can be applied against the inner circumference 34 of an encircling brake drum 36 which receives the brake shoe 10.

The brake shoe 10 is equipped with a monitoring deice, generally designated by reference number 38, for determining a critical state of wear on the brake linings 20, 22. This device sits inside an opening 40 which extends through the brake band 18 in a radial direction to the brake drum 36 and is in the form of a cylindrical bore. It comprises a sensor 42 and a retaining element 44 for securing the sensor 42 in the opening 40. The sensor 42 passes through the opening 40 with a rib-like sensor stem 46 of approximately rectangular cross-section which is made of insulating material and contains an embedded electrical conductor 48 which is provided with an insulation 50 and extends out of the free end of the stem. The electrical conductor 48 is connected to a warning device (not shown) which is installed, for example, in the driver's cab of a commercial vehicle.

As shown in Figure. 3, the electrical conductor 48 is, for this purpose, inserted with the connector 52 into a plug-in coupler 54 which is connected to the warning device and which is in turn attached to, for example, a lateral fixed shield plate 56 of the drum brake 12.

The sensor 42 has a stem end piece which projects approximately perpendicularly from its sensor stem 46 and forms a sensor finger 58. The sensor finger 58 engages in a bore 60 in the brake lining 22, which bore is introduced into the face 28, preferably in the circumferential direction of the brake drum 36. This bore 60 is situated on the bottom 62 of a recess 64 which is produced in the face 28 and is for example semicircular as shown in Figure. 5 and which is associated symmetrically with another recess 66 in the adjacent face 26 of the other brake lining 20. Both recesses 64, 66 are situated preferably in the longitudinal centre plane of the brake linings 20, 22 and create space for the assembly of the components 42 and 44 of the monitoring device 38.

In the present embodiment of the invention, the sensor 42 can be secured on the brake shoe 10 by means of the retaining element 44 forming a clamping body in its assembled position, which is defined by the engagement of the sensor finger 58 in the bore 60. For this purpose the sensor stem 46 is clamped between the retaining element 44 and a wall section 40' of the opening 40.

The retaining element 44 is, for this purpose, designed in such a manner that, when sliding along the back of the sensor stem 46, it can be pushed into the opening 40 while at the same time being compressed until there is sufficient frictional contact between the wall of the opening 40, the retaining element 44 and the sensor stem 46. At the same time the retaining element 44 and sensor stem 46 engage positively with one another in such a manner that, when the retaining element 44 is in the final assembled position, it is locked together with the sensor stem 46 thereby ensuring that automatic detachment of the retaining element 44 from the opening 40 due to vibration effects, for example, is impossible since the sensor finger 58 engaging the bore 60 does not allow axial displacement of the sensor stem 46.

As shown in Figure. 4, the transverse dimension of the retaining element 44 is smaller than the opening diameter and the height dimension thereof is adjusted in such a manner that the retaining element is slightly compressed when pushed into the opening 40 in the direction of the sensor stem 46.

In order to further this deformation a pocket-like recess 70, which preferably decreases inwardly in depth and which ensures appropriate elasticity, is formed in the retaining element 44, approximately parallel to the sensor stem 46 and starting from its inner face 44'.

The retaining element 44 rests with a flat lower sliding face 72 on a corresponding rear face 74 of the sensor stem 46 and, with lateral arms 76, 78 of angular cross-sections, engages in lateral longitudinal slots 80 and 82, respectively, in the sensor stem 46.

It can be seen in Figure. 6 that preferably both longitudinal slots 80, 82 have at the bottom 84 of each slot for example, a ledge-like projection 86 which, when the retaining element 44 is in the final assembled position, engages positively with each recess 88 which complements this projection and is formed in each of the arms 76, 78 which are flexible perpendicular to their longitudinal direction. This creates an arrangement of the retaining element 44 in the opening 40 which is self-locking, but which permits detachment thereof from the opening 40.

As shown in Figure. 4, the face 90 of the sensor stem 46 which is adjacent to the wall of the opening 40 has preferably the circumferential curvature of this opening. In order that the specified assembly position of the retaining element 44 in the opening 40 may be discernible, a tongue-like projection 92 extending obliquely in the direction of the sensor stem 46 is formed on the outer face 44" of the retaining element and, when assembled, engages in a corresponding recess 94 at the back of the sensor stem 46.

The sensor 42 and retaining element 44 form moulded bodies made of suitable plastics material.

A prerequisite for the fitting of the monitoring device 38 in riveted-on brake linings 20, 22 is that the diameter of the opening 40 permit introduction of the sensor 42, with its sensor finger 58, into the space formed by the recesses 64, 66 in brake lining 20, 22, and also insertion of the sensor finger into the bore 60. After the sensor has been positioned, the retaining element 44 can be pushed on to the back of the sensor and so far into the opening 40 until the retaining element is locked together with the sensor 42.

The described monitoring device 38 has the essential advantage that, in relation to the centre of the brake drum it is suitable for different radial fitting depths of the sensor finger 58 in brake linings without the necessity for storing different sizes of components 42 and 44 for this purpose.

Claims

1. A device for monitoring the lining wear in shoe brakes, comprising a sensor made of insulating material which is connectable to a warning device and contains an electrical conductor and which has a sensor stem, which is to be arranged in an opening passing through the lining support of a brake shoe, the stem also comprising a sensor finger which is arranged at right angles to the stem and is electrically connected thereto and which can be inserted into a bore in a brake lining, said bore being arranged at a distance from the friction surface of the sensor finger and extending at a right angle to the axis of the opening, the sensor stem being securable therein b means of a retaining element which can be inserted by frictional connection in the opening of the lining support, wherein the sensor stem and sensor finger are in one piece, and the retaining element is separated from the sensor stem and can be locked together with the sensor stem upon insertion into the opening.

2. A monitoring device according to Claim 1, wherein the sensor stem can be arranged against a wall section of the opening and the retaining element can be inserted between another wall section of the opening and the sensor stem.

3. A monitoring device according to Claim 2 or Claim 3, wherein the retaining element and sensor stem engage with one another via a T-shaped slot-like connection so as to be slidable relative to one another.

4. A monitoring device according to Claim 4, wherein the retaining element has, on the side of the sensor stem that is to be secured, two guide arms which extend in the longitudinal direction thereof, are parallel to and spaced from one another and form the T-shaped slot-like recess and which can engage with lateral longitudinal slots, of the sensor stem, and at least one of the guide arms has, on its longitudinal side opposite the other guide arm, a recess or an elevated part which can be brought into positive engagement with an elevated part or recess provided in the longitudinal slot of the sensor stem for receiving this guide arm.

A A monitoring device according to any one of the preceding Claims, wherein the retaining element has, at its end which is accessible after insertion into the opening in the lining support, a projection which extends obliquely in the direction of the sensor stem and which, with the sensor secured, engages a recess in the sensor stem.

6. A device for monitoring the lining wear in shoe brakes, substantially as hereinbefore described and with reference to the accompanying drawings.