FIELD OF THE INVENTION:
The present invention relates to a vehicle diagnostic system which monitors one or more conditions of the vehicle, more specifically vehicle brake and provides an indication of one or more conditions of the brake, more specifically the brake pad to the driver of the vehicle.

The present invention relates to a wear sensor for brake lining wear indication in a drum brake system in a vehicle.

BACK GROUND OF THE INVENTION.
The driver of a vehicle should always be aware of the good condition of the vehicle more specifically the vehicle brake to ensure safe operation of the vehicle. To achieve this there are many prior art which assures the driver that the vehicle brake is in good condition. It is found necessary that the driver not only needs to know whether the vehicle brake is in good condition or not but it is preferable that he be informed that the vehicle brake lining is at least within safe conditions and poses no immediate danger to the driver and/or passengers of the vehicle. This gives sufficient time for the driver to take the corrective action. So, it is necessary to keep a check on whether there is sufficient amount of brake pad life which means that the brake has sufficient brake lining thickness at all the brake pads for the safe driving until replacement is effected.

Commonly, the vehicle brakes are either drum type or disc type. Each wheel in a vehicle will have one brake and are actuated simultaneously while braking the vehicle.

In drum type brake, a cylindrical brake drum is attached to the rotating wheel. Brake actuation system consisting of brake shoes with friction lining riveted on its outer surface is mounted rigidly to the axle beam as shown in figure 5. While braking, the brake shoes expand and grip or brake the drum and hence the wheel. Brake lining is made of friction material and is prone to wear. The brake drum is predominantly made of cast iron and has high wear resistance. Every time the brake is applied, enormous friction is developed between the drum and lining; the kinetic energy is converted into heat energy. This heat and friction wears out the brake lining of the brake pad. An automatic slack adjuster used in the brake system compensates for this lining wear. As the brake lining wears, the automatic slack adjuster fitted on the brake cam shaft keep on adjusting the shoes/lining for effective braking. The slack adjuster functionally links the brake chamber and the brake camshaft in a conventional system.

Since the brakes are actuated through 'Automatic slack adjuster', the vehicle operator would not know when the lining life is over and is due for replacement. The Automatic slack adjuster will keep on adjusting the shoes/lining to compensate for the wear and at a point of time lining material would have been consumed fully and the rivets are exposed which can potentially damage the drum.

Hence, there is a need to indicate / alert the vehicle operator when the linings are due for replacement.

Various types of brake lining wear monitoring devices have been utilized in the automobile brake system. There are many devices, ranging from simple lever type mechanical indicator to complicated electronic gadgets, which are being used for indicating lining wear in S-cam actuated drum brakes. Some wear alerting devices have complicated electronic circuits for monitoring the lining wear continuously.

As such in the known prior art, the brake pads tend to have some type of brake wear sensors. The most commonly known brake wear sensors are the built in wear sensors that produce scrapping or squealing noise when the pads worn out.

D1 US 20090084638:- In this patent as is known in an existing conventional pad the known method of using a visual indicator is to dispose brightly coloured visual indicator dye or dyes. As the friction material keeps wearing away by the contact with the rotor the thickness of the friction material keeps reducing until eventually the visual indicator becomes exposed. Since this visual dye indicator is disposed at a predetermined depth of the friction material, the identification level of the wear can be designed from case to case.

D2 US 6302241:- In another known prior art a dielectric material tab sensor is attached to the backing plate of the brake pad, in which the dielectric material tab wears at the same rate or at some calculated rate as the brake pad. There is always a relationship between the wear of the brake pad and the wear of the dielectric material tab. The circuit is designed to measure the capacitance of the tab when the brake is applied. The capacitance value measured is directly or proportionately changing based on the wear of the dielectric material. The capacitance value is thus utilized to identify and indicate the wear level of the brake pad in this patent.
D3 US 7232103:- In another type of known prior art the brake pad and/or the sensor material may be a material which possesses a feature to change its electrical resistance based on the pressure applied on it. In this principle the sensor material is a composite material at least including an electrically insulating material such as asbestos, fiber glass, etc carrying electrically conductive particles such as metals (brass, copper, etc) therein. The composite material as a whole has the property to change its resistance as a function of the applied pressure on it. When the pressure is applied, the insulating material elastically deforms and the electrically conductive particles are pressed to come into contact with each other. By arranging the conductive particles in wearing manner within the insulating material it is possible to detect a worn brake pad before it becomes unsafe. In this manner wearing of the brake pad due to the change in resistance of the composite material can be identified for generating warning signal. In this prior art a composite material made of electrically insulating and electrically conductive material is used to identify the brake pad thickness based on the changes in the resistance value.
D4 5358075:- In this prior art a displacement sensor having a piston operating in a shaft is used. The movement of the piston within the shaft is relative to the distance the brake's slack adjuster must move to fully activate the brake. When the brake is actuated, the location of the piston in the shaft of the displacement is thereby a determination factor of the level of brake wear. The displacement sensor is sensitive to the position of the piston within the shaft and signals can be generated when it is within safe range or its movement or when it is beyond the safe range. This invention is applicable to non-auto slack adjuster or manual slack adjuster version which needs periodical adjustment and not compatible with Automatic slack adjuster.
D5 20100030490:- In this prior art, it teaches the techniques of embedding of sensor wear material within the brake pad and study its characteristic change to identify the brake wear. In this sensor wear material is embedded within the brake pad to provide an indication of the brake wear. The sensor wear material will change one or more characteristics as brake wear increases, such as it may change its electrical resistance value as brake wear increases. This patent also discloses that the sensor wear material may be embedded in a variety of different methods within the brake i.e. it may be embedded at one point, it may be embedded at many strategic points, it may be spread as surface coating or it may be used to be as part of all of friction material of the brake pad and so also embedded using combination of the above mentioned techniques. Based on the characteristic changes on the sensor wear so embedded within the friction material the brake wear level is identified and indicated to the driver of the vehicle.
D6 20070256901:- This prior art uses a linear transducer as a wear sensor. The wear indicator of this type is mounted on the wear adjuster mechanism itself. This wear adjuster has an axis of rotation and it includes a sleeve rotatable about this axis of rotation. The wear indicator includes a body at one end of the sleeve and a plunger movable relative to the body on the axis of rotation. The plunger is located within the sleeve, thereby the wear adjuster and wear indicator are coaxial. The assembly includes further a bolt screw threaded in the sleeve at the opposite end of the body. The bolt is adapted to be restrained against rotation and has a head engaged by the plunger. In this arrangement the rotation of the sleeve as a consequence of incremental wear adjustment causes incremental axial movement of the bolt due to the screw threaded connection, and hence relative movement of the plunger on the axis. The wear sensor is a linear transducer having an output indicative of this relative extension of the plunger described above. The output is electrical and is adapted to be proportional to the movement of the incremental wear adjuster.
D7 4204190:- This patent discloses embedding a sensor loop in a brake pad, the sensor loop being broken when the brake pad is worn out beyond its working limit.
D8 6384721:- This patent uses a plate type sensors with a pair of electrically conductive plates embedded on a body made of insulating material and mounted on the brake pad, wherein the use of the brake pad causes wear at the braking surface and correspondingly wear at the surface of the plate type sensor which wear includes abrasion of the edges of the plates, so that the wear of the brake pad and sensor body plates cause a change i.e. a reduction of the electrical capacitance between the plates. However, in such designs the wear characteristic of the sensor body and plates should be same as wear characteristics of brake pads i.e. sensor body and plates should wear as if they are part of the brake pad to provide correct indication of the brake wear. This means that in this art the sensor body and the plate wear should be in relation with the brake pad wear.
D9 US 4757300:- Discloses a brake wear signaling device using a set of magnet and magnetically sensitive switch to activate the device for warning.
This patent is about 'brake adjustment monitoring' and uses a magnet which is secured to the brake shaft and a magnetically sensitive switch which is mounted on a rod proximate to the brake shaft at a predetermined distance from the magnet. The switch provides signal to the operator to adjust the brake when it is activated by magnet flux. This invention is applicable to non-auto slack adjuster or manual slack adjuster version which needs periodical adjustment and not compatible with Automatic slack adjuster.
D10 US 3983519:- Discloses better control of the reed switch associated with an innovative electromagnet configuration, instead of using a conventional known combination of reed switch with permanent magnet, which prior art suffers a draw back as the magnetic field from such permanent magnet is not controllable. This patent relates to the basic operational principle of using an electro-magnet and a reed switch to implement a touch free switch. There is no discussion of using a permanent magnet and more importantly does not relate to using this to detect brake lining wear. This invention does not address the automotive application and is thereby not a prior art for the subject invention.
OBJECT OF THE INVENTION:
Most of the owners and drivers are put in a situation by vehicle manufacturers to react to automotive problems rather than anticipating them. This is applicable even for brakes fitted on the vehicle. The brake pad wear sensors are now being used to identify the brake wear. When the wear limit of the brake pad is reached, a signal is generated to warn the driver of the imminent danger even if not immediate. Further, it is preferred that the signal is generally visual though this is not limited and may be extended to audio and/or video.
The main object of the present invention is to provide brake lining wear alerting system for taking corrective measures at the appropriate time.
Another object of the present invention is to provide a sensor for brake lining wear indication in drum brake system.
Yet another object of the present invention is to provide a signal to the display monitor mounted in the dash board of the vehicle and alert the operator when the lining is due for replacement.
Yet another object of the present invention is to utilize simple 'reed switch and magnet' combination coupled with electronic parts for signal conditioning to produce indication to the vehicle operator in the cabin when the brake linings are due for replacement.
Yet another object of the present invention is to provide accurate indication of which brake in the vehicle requires lining replacement.
Further object of the present invention is to provide alerting signal to the vehicle operator only at the time when the brake lining is due for replacement.
SUMMARY OF THE INVENTION :
The present invention relates to a lining wear monitoring device which includes a wear sensor applicable to drum type brakes, especially used with automatic slack adjuster which is fitted on the S-cam shaft.
The present invention is about 'brake lining wear monitoring' and uses Reed switch positioned at an angular distance relative to the magnet fixedly connected to the brake cam shaft. The unit provides signal to the vehicle operator by monitoring the brake cam shaft rotation. The Reed switch is stationary and is activated by the magnet which is moving. The invention is compatible with Automatic slack adjuster unlike D4 US5338075 or D9 US4757300.
It is known in the prior art to measure the angular rotation of an S-cam shaft that brings the brake shoes and brake pads into frictional engagement with the brake drum to determine the adjustments of the brakes and also the wear of the brakes. However to employ this method in prior art which have been put forth in previous paragraphs complicated calculations have been performed to convert the angular rotation of the S- cam to an estimated travel distance at the brake shoe center. This calculation in prior art was depending on brake size, brake type and S-cam radius. Such S-cam type
sensors are configured to calculate the brake shoe travel of the particular brake type and size it is monitoring.
When the sensors, many of which have been described in the prior art, may itself fail, the failure of the sensor itself needs to be identified. When the sensor is not in good condition an indicating lamp is preferred to be energized to glow continuously to indicate that the sensor system has failed. Further when the brake pad has worn beyond working limit, the same lamp or an another indicating lamp may be energized which may be blinking light or of a different colour warning the driver of the extraordinary wear of the brake pad.
The wear sensor is designed in such a way that it monitors the brake lining wear of S- cam brake system. The wear sensor use simple 'reed switch and magnet' combination coupled with electronic parts for signal conditioning. It provides a signal to the display monitor which is mounted in the dash board of the vehicle and alert the operator when the lining in any of the various brakes in the vehicle is due for replacement.
DESCRIPTION OF THE DRAWINGS:
PART NAME PART NO
Reed switch R
Magnet M
Wear sensor 1
Automatic slack adjuster 2
Rotor 3
Bottom casing 4
Printed circuit board assembly 5
Top casing 6
Connector pins 7
Lock screw 8
__ -
Circlip 10
Figure 1 illustrates the wear sensor arrangement.
Figure 2 &2A illustrates the general arrangement of wear sensor in the assembled condition with a slack adjuster in a vehicle.
Figure 3 illustrates the exploded view of the wear sensor arrangement. Figure 4 illustrates the wear sensor with reed switch and magnet arrangement. Figure 5 general drum brake assembly. Figure 6 a circuit diagram of the invention.
The part numbers marked in the drawing are as follows :
11 - Air chamber
12 - Rotating cam
13 - Brake drum
14 - Brake lining
15 - Push rod
DESCRIPTION OF THE INVENTION:
The invention relates to a lining wear monitoring system, which comprises of a wear sensor(1), which includes a top casing(6) , a bottom casing(4), a rotor(3), a magnet(M), a reed switch(R), PCB assembly (5), lock screws(8) and nuts(9). The magnet(M) is positioned on the rotor(3). The PCB assembly(5) with reed switch(R) are positioned on the outer casing particularly in top casing(6).
The rotor (3) is mounted within the outer casing. The outer casings (4&6) are fixed to the auto slack adjuster(2) by lock screw(8) and prevented from rotation. The rotor(3) has internal splines and rotates within the outer casing. While the automatic slack adjuster keep on adjusting the shoes/lining to compensate for the wear, at the same
time the wear sensor rotor also rotates with brake cam shaft and monitors the lining wear.
The wear sensor uses simple 'reed switch and magnet' combination coupled with electronic parts for signal conditioning.
The reed switch is activated when the magnet is positioned near the reed switch. The activated reed switch provides signal to the monitor fitted in the dash board of the vehicle and makes the LED to glow warning indication. The wear sensor as shown in Fig. 2 is designed in such a way that it monitors the brake lining wear of S-cam brake system. It provides signal to the display monitor mounted in the dash board of the vehicle and alert the operator. The operator can understand the LED indication in following manner.
The circuit is designed in such a way that, the LED does not glow when the wires are connected, system is live and lining is not worn out. The LED will glow in RED colour, indicating the wires are not connected and the system is not live.
As the brake lining wears out, the cam shaft and hence the rotor is adjusted by automatic slack adjuster. This causes the magnet getting positioned near the reed switch after a gradual rotation, the reed switch is activated by the magnet and makes the LED to glow a warning indication; this indicates to the vehicle operator that the 'linings are due for replacement'.
The sensor has a magnet secured into a rotor which is mounted within an outer casing which inturn is fixedly secured to the existing conventional auto slack adjuster assembly. On the outer stationary casing a reed switch which is a magnetically sensitive switch is mounted at a predetermined distance from the magnet secured on the rotor. This reed switch is electrically connected to a wear signal indicator circuit. This reed switch is operable to open or close by the magnetic flux generated by the magnet, when the camshaft moves corresponding to the brake adjustment affected by the auto slack adjuster. With this arrangement the magnet along with the camshaft rotates or travels the predetermined distance to close the magnetic sensitive switch and energize the circuit for indicating the desired warning signal.
The description has been done with a single magnet, a single reed switch and corresponding electronic circuit. However, the described design and principle will teach the skilled persons in the art and permit mounting of many numbers of magnets on the rotor and each magnet mounted at different predetermined distance from the reed switches. With this arrangement a reed switch is closed to energize one associated circuit of the many circuits of the wear signal and indicate one of the many warning signal desired, which signal may be optical.
The magnet and the reed switch as disposed in the present invention support the object to achieve the desired performance. This arrangement is to achieve a control between the two, of which the magnet is movable in relation to the static reed switch. The control is designed based on the magnet and reed switch taking a position within or beyond a predetermined distance in relation to each other. The selectively controlled magnetic field of the magnet will control the state of the reed switch between open state and close state thereby controlling the indicator circuits.
The working of the invention can be more illustratively explained with figure 6.
In operation when the sensor is in good condition, the transistor Q1 will be non conductive and prevent current flowing through collector and thereby LED lamp is prevented from glowing.
When the magnet has been displaced but is still within a predetermined distance, the transistor Q1 will still be non conductive and preventing the energizing of the lamp and lamp does not glow.
However, when the magnet is displaced beyond the predetermined distance, the reed switch will close and the voltage at resistor R1 will rise and make transistor Q1 conductive and thereby energizing the lamp through the above circuit allowing the lamp to glow giving a warning to the driver. With oscillator U1 provided in the circuit, the LED is made to glow in 'blinking' mode.

In case of wire snap or cut at connectors CP1, CP2 or CP3, the circuit is designed in such a way that LED will glow continuously.

All of the above descriptions, illustrations and drawings are for the purpose of the understanding and are not limited by the disclosed material but are encompassing all of the contents so disclosed as will be understood by the skilled person in the art.

WE CLAIM :

1. A vehicle brake lining wear alerting system having brakes actuated through automatic slack adjuster, comprising of:

(i) a sensor for monitoring the rotation of cam shaft by the automatic slack adjuster whose rotary adjustment of cam shaft happens during brake actuation as the brake lining wears, the said sensor comprising :

a. an outer stationery casing fixedly screwed to the auto slack adjuster,

b. a rotor having splines and mounted within the said outer casing such that the rotor will rotate, and

c. a sensing means attached to the outer casing for sending the relative position of the rotor within the casing with respect to the stationery outer casing to determine the degree of wear of the brake lining,

d. the said sensing means comprising :

i. a magnet attached to the rotor,

ii. a reed switch positioned on the outer casing for operation by the magnet for sensing when the rotor displaced in a rotary direction is beyond a selected range indicating a level of wear demanding attention to the brake lining,

iii. a LED indicator electrically connected to the reed switch with two indicator glowing modes wherein without any glow indicating the state of normal functioning of sensing means, glowing in first mode indicating disruption in the sensing means and adapted to glow in second mode for outputting the signal from the sensing means when the rotor is displaced beyond the selected range,

iv. a power source operably associated with the switch and the indicator, and

v. a control circuit associated with the power source, the reed switch and the LED,

e. the said sensing reed switch being normally open switch connected with the LED and the power source in series through the control circuit,
whereby LED will be illuminated in first mode indicating that the sensor means is disrupted,

f. the said sensing reed switch further changing from open to close status when the rotor magnet is identified by the sensing reed switch whereby LED will be illuminated in second mode through the control circuit indicating that the level of brake lining wear is unsafe,

g. wherein the first mode is preferably steady illumination,

h. wherein the second mode is preferably blinking illumination,

i. wherein the color of LED light is preferably red,