OF AUTOMOTIVE DISC BRAKE ROTORS

Field of the Inventio

[0001] This invention relates to a vernier calliper which can be used for measuring the thickness of automotive disc brake rotors.

Background of the Invention

[0602] As a result of the cessation of the use of asbestos in automotive disc brake pads there has been a significant change in the pattern of wear in disc brakes. The use of new non-asbestos materials has required a change in the hardness of the steel used on the disc rotor and. this has resulted in increased wear of the disc rotor ("disc") itself. The need to replace disc brakes and the frequency of replacement has become a more commo element of vehicle maintenance and a significant cost centre. The practice of machining discs has become uncommon as the discs tend to wear quickly to a thickness outside of the manufacturers specification hence replacement is required. The vast majority of brakes are steel, although there are a small number of ceramic or carbon fibre discs these tend to be for racin or belong to exotic marques.

[0003] Most cars have some form of sensing that indicates wear in the disc pad, usually in the form of a sensor that is attached to the pad and become exposed when the friction material is worn past a certain point. In contrast currently there is no simple means of measuring the thickness of the disc without the removal of the wheel in order to access the disc.

[0004] The object of the present invention is to provide a device and method which can be used to conveniently measure the thickness of a disc brake rotor insitu on a stationary vehicle, As will be described in more detail below, the most convenient implementation of the invention can be carried out by modifying known forms of digital vernier devices. Digital vernier devices are readily available and these devices typically have a pair of jaws at one end referred to for convenience as the proximal end and a slider body located adjacent to the jaws. Sometimes a probe is located at the distal end for measurement of the depth of a bore. [0005] A device of conventional construction cannot conveniently be used to measure the thicknes of a disc brake rotor without first removing the road wheel of the vehicle because it would be difficult to position the jaws so that they could engage opposite sides of the disc brake. Also.,, many vehicles have a dust cover mwardly adjacent to the rotor which could also interfere wit positioning of jaws of a known ferm of calliper. Further,, when disc brakes wear, they tend to form a H at the outer periphery of the rotor which is not engaged by the disc brake pad and therefore does not wear. In a normal vernier calliper, the jaws are straight and the jaws would tend to engage the lip rather than the operating surfaces of the disc rotor so that an accurate reading of the wear on the disc brake could not be obtained.

Summary of the invention

[0006] According to the present invention there is provided a vernier calliper for measuring the thickness of a disc brake rotor fitted to a vehicle, the vernier calliper including:

(i) first and second members which are mounted for sliding movement relative to one another along an axis?

(ii) first and second abutments located on the first and second members respectively and being adapted, in use, to engage first and second sides of a disc brake rotor, the first abutment including an abutment surface; and

(iii) retaining means for retaining the calliper in a operative position in which:

(iv) the first abutment surface engages the first side of the disc and is parallel thereof;

(v) the second abutment engages the second side of the disc; and

(vi) said axis is orthogonal to said first and second sides of the disc.

[0007] The invention also provides a digital vernier calliper including:

a display;

a. first arm;

a slider body which slidably mounted on the first arm, the slider body including a digital display;

a second arm extendin in a distal direction from the slider body and bein movabie therewith;

the second aim having an abutment member at its distal end;

measurement circuitry in the slider body responsive to the relative positions of the first and second arms and coupled to provide distance measurement signals to the digital display;

the first arm includin a magnet at its distal end; and

wherein the arrangement is such that, in use, the magnet can be magnetically coupled to the outer face of a disc of a disc brake and the slider moved in a proximal direction so that the abutment member engages an inner face of the disc and so that, in use, the display displays a distance value indicative of the distance between the inner and outer faces of the disc,

[0008) The invention also provides a digital vernier calliper including;

a first arm;

a slider body which slidabl mounted on the first arm, the slider body including a digital display;

a second arm extending in a distal direction from the slide body and being movable therewith;

characterised in that the slider body is located at the proximal end of the second arm; and

first and second abutment elements are mounted at the distal ends of the first and second arms respectively.

[0009 J The in vention also provides a method of measuring the thickness of a disc brake for a vehicle using a digital vernier having first and second movable members having a first abutoent surface and a second abutment respectively and digital display means, the method including the steps of;

(i) engaging the first abutment surface with a first side of the disc, with the abutment surface being parallel to said first side of the disc;

(ii) engaging the second abutment with a second side of the disc;

(iii) performing a zeroing function on said digital display;

(iv) disengaging the first abutment surface and the second abutment from the disc; (v) returning the first and second members to an initial position in which the first abutment surface engages or substantially engages said second abutment; and

(vi) determining the thickness of the disc brake by reference to a reading of the digital display after steps (i) to (v) have been carried ou

Brief Description of the Drawings

[0010] The invention will now be further described with reference to the accompanyin drawings, in which:

Figure 1 is a side view of a vernier calliper constructed in accordance with the invention;

Figure 2 is a plan view of the calliper;

Figure 3 is a longitudinal cross-section through the calliper with the distal ends of the arms separated;

Figure 4 is an exploded view of the calliper;

Figure 5 is a side view of a first arm of the calliper;

Figure 6 is a view of the other side of the first ami;

Figure 7 is a plan view of the first arm;

Figure 8 is a cross-sectional view along the line 8-8;

Figure 9 is a cross-sectional view along the line 9-9;

Figure 10 is a cross-sectional view along the line 10-10;

Figure 11 is a cross-sectional view along the line 11-11;

Figure 12 is an enlarged end view of the first arm;

Figure 13 is a side view of the second arm;

Figure 14 is a plan view of the second arm;

Figure 15 is an end view of the second arm;

Figure 16 is a side view of a reinforcing aim;

Figure 17 is a plan view of the reinforcing arm;

Figure 18 schematically illustrates the use of the calliper measuring the thickness of a disc brake rotor;

Figure 19 is a schematic plan view of the calliper in use; and Figure 20 is a schematic side view of a modified vernier calliper of the invention.

Detailed Description

[0011] Figures 1 to 4 diagrammaticaliy illustrate a vernier calliper 2 constructed in accordance with the invention. The calliper 2 includes a first arm 4 which for convenience will be referred to as a stationary arm and a second arm 6 which for convenience will be referred to as a movable arm. As will be explained in more detail below, the second arm 6 is slidably mounted relative to the first arm 4. The vernier calliper 2 includes a slider body 8 which is coupled to the second arm 6 and is movable therewith. The first arm 4 is formed with a stop body 10 to limit movement of the slider body 8 to the left as seen in Figures 1 to 4. This direction will be referred to for convenience as the proximal end of the device and the opposite end of the first and second arms 4 and 6 for convenience will be referred to as the distal ends. The vernier calliper 2 includes a tension spring 12 which acts between the stop bod 10 and the slider body 8 and serves to resiliently bias the slider body 8 into contact with the stop body 10. In the illustrated arrangement, the first arm 4 includes a spring mounting post 13 to which the proximal end of the spring 12 is connected and the slider body 8 includes an internal spring mounting post 15 to which the distal end of the spring 12 is connected.

[0012] Figure 3 is a schematic side view of the vernier calliper 2 showing the slider body 3 and second arm 6 extended towards the right against the action of the spring 12. The second arm 6 includes an elongate shaft 14 having a lateral arm 16 located at. its distal end. The aim 16 terminates in a proximally directed engagement tip 18. The elongate shaft 14 is mounted for sliding movement along its axis 21 in an elongate groove 20 formed in the first arm 4. The distal end of the first arm 4 includes a distal flange 24 which includes a recess 26 in which a permanent magnet 28 is mounted. The end flange 24 includes an opening 30 through which the elongate shaft 14 extends, as best seen in Figure 3. Typicall the magnet 28 is a rare earth, magnet cylindrical in shape having a diameter of 12mm and a thickness of 3mm, The arrangement is such that the engagement ti 18 is offset from the axis 21 and is generally aligned with a centreline 23 of the magnet 28, as shown in Figure 3. The distance between the axis 21 and centreline 23 is preferably in the range from 12mm to 20mm and most preferably 15mm. It will also be seen that the engagement tip 18 extends in a proximal direction relative to the lateral arm and its tip is offset by a distance D as shown in Figure 3. Preferably the distance D is in the range from 5mm to 10mm and preferably 8mm. The offset distance D together with the offset between the centreline 23 and axis 21 enable the vernier calliper 2 of the invention to be conveniently used to measure wear in disc brake rotors, as will be described in more detail below,

[0013] The first arm 4 is preferably injection moulded from plastics material such as nylon or polycarbonate. The material could be reinforced with glass or carbon fibres. In order to improve or impart additional rigidity to the first arm A, it includes a reinforcing arm 32 which is located in a second elongate groove 34 which is parallel to the groove 20. The reinforcing arm 32 includes a lateral arm 36 located in a lateral groove 38 formed in the distal flange 24. The reinforcing arm 32 is retained in the grooves 34 and 38 by interference fit and/or by the use of an adhesive. Alternatively, it would be possible to make the first, arm 4 from metallic material such as forged stainless steel or aluminium and in that case the reinforcing arm 32 would not be required.

10014] In the preferred form of the invention, the second arm 6 and the reinforcing arm 32 are made from stainless steel rod of square section and the sides are 4mm wide. In the preferred form of the invention, the second arm 6 is about 212mm long although this can be varied. The shapes of the second arm 6 and reinforcing arm 32 are shown in more detail in Figures 13 to 17.

10015] In the illustrated arrangement, the slider body 8 is formed with a front panel 40 and back plate 42, the front panel and back plate being connected together by means of four screws 44 as shown in Figure 4, The back plate 42 includes upper and lower cam formations 46 and 47 which are slidably movable along the upper and lower edges respectively of the first arm 4, as best seen in Figures 3 and 4 to assist in guiding linear movement of the slider body 8 along the first arm 4. Movement of the slider body S is limited in the distal direction by the distal end 50 of the cam formation 46 engaging a web 52 formed near the distal end of the third groove 48 ,

[0016] The slider body 8 is connected to the second arm 6 by means of mounting screws 49 which pass through bores in the back plate 42 and are received within tlireaded bores 51 formed near the proximal end of the second arm 6, as shown in Figure 4.

[00171 f & ^e fro ¹³ * anel 40 includes an LED display 54, includes an ON/OFF button 56, zero button 58 and unit button 60 for changing the display to read from metric or imperial units. A circuit board 62 is located within the slider body 8 between the front panel 40 and back plate 42. The circuit board 62 includes components for producing signals for the LED displa 54. The device includes a printed or etched array 64 of conductive bars which is mounted in a recess 66 formed in the first arm 4, The circuit board 62 includes other etched or printed conductive bars (not shown), which are capacitively coupled to those in the array 64 and the circuitry is arranged to produce positional signals when the slider body 8 is moved relative to the array 64, The technique for producing signals in this way and displaying measurements is very well known and does not need to be described. The circuitry could, for instance, be the same or similar to that in known callipers made by Shenzhen Shenliang Precision Measuring Co., Ltd., of China,

[0018] In the assembled calliper 2 the slider body 8 is resiliently engaged against the stop body 10 by means of the spring 12. If the zero button 58 is pressed in this position and the slider body is then moved so that an object (not shown) can be placed between the gap 70, between the magnet 28 and engagement tip 18, the LED display will indicate the l ength of the gap 70 or the thickness or length of the obj ect

[0019] Figures 18 and 19 schematically illustrate the manner in which the vernier calliper 2 can be used to measure the thickness of the rotor 72 of the disc brake (not shown) of a vehicle (not shown). Typically the disc brake includes a dust cover 74 mounted inwardly of the disc brake rotor 72. in the illustrated arrangement, the disc brake rotor 72 has been subject to wear and a lip 76 (of unworn material) is normally formed at the outer peripher of the rotor, as shown in Figure 18. The broken line 78 indicates the initial (unworn) outer or proximal face of the rotor which is spaced from the outer worn face 80 of the rotor, as shown. Figure 19 is a schematic plan view in which the Hp 76 has been omitted for clarity of illustration. It will be seen that the axis 21 of the second arm 6 is also held parallel to the centreline 23 of the magnet by engagement of the flat distal face of the magnet being held orthogonal to the worn face 80 by magnetic attraction. [0020] The preferred manner in which the vernier calliper 2 is applied to the rotor is as follows. First, the user moves the slider body 8 in a distal direction away from the stop body 10 so as to form a gap 70 which is large enough to enable the engagement tip 18 to be moved over the lip of the rotor 72 as shown in Figure 18, After this step, the user can then move the First arm 4 towards the rotor 72 so that the magnet 28 engages the worn face 80 of the rotor 72. The distal face of the magnet 28 is perpendicular to the longitudinal axis 21 of the second arm 6 and is firmly held in position by magnetic attraction. The pull force of the magnet 28 is in the range from 1,5kg to 4kg and preferably 2.6kg. The user can then release the slider body 8 so that it moves i a proximal direction under the influence of the spring 12 so that the engagement tip 18 comes into contact with the inner worn face 82 of the disc brake rotor 72. When in this position, the user can press the zero button 58 so that a zero reading will appear on the LED display 54. The calliper can then be removed from the disc brake rotor. This can be carried out by moving the slider body 8 in a distal direction so that the engagement tip 18 disengages the worn face 82 of the disc brake rotor 72 and the vernier calliper 2 can then be moved away from the disc brake rotor 72. Normally some tilting of the first aim 4 will assist in disengaging the magnet 28 from the worn face 80. Having released the vernier calliper 2 from the disc brake the slider body 8 is moved by the spring 12 back to its position where it engages (or nearly engages) the stop body 10. The reading in this position indicates the thickness of the disc brake rotor 72 _> that is to say the distance between the faces 80 and 82. If the circuitry mounted on the circuit board 62 is identical to those used in normal digital vernier callipers then the reading will be shown as a negative value but this does not affect its accuracy. If necessary, the standard circuitry could be modified so that it shows as a positive value once this measurement procedure has been followed.

[0021] It will also be appreciated from Figure 18 that if a person attempted to use a normal digital vernier calliper having straight edged jaws, if it were possible to place it in a position to engage the rotor 72 it would not produce an accurate reading because the jaws would engage the lip 76. Accordingly, the calliper 2 of the invention provides a substantial advantage in having its jaws located at a distal end of the device rather than the proximal end which is normal.

[0022] Figure 20 illustrates a modified calliper 100 constructed in accordance with the invention. The same reference numerals will be used to denote parts which are the same as or correspond to those of the embodiment of Figures i to 1 . in the calliper 100, the positions of the magnet 28 and the engagement tip 18 are reversed, that is to say the magnet 28 is located on the lateral arm 16 of the second arm 6 and the engagement tip 18 is located on the distal flange 24, The operation of this device is analogous to that described previously.

[0023] Some known digital callipers have the capacity to output data wirelessly or through an outlet port to a lap top or other receiving devices and it will be understood by a person skilled in the art that these capabilities can be incorporated into the calliper of the invention.

[0024] it will be appreciated that the calliper of the invention is a very simple yet effective way of determining wear in disc brake rotors.

LIST OF PARTS

[0025]

vernier calliper 2 distal end 50 first arm 4 threaded bores 51 second arm 6 web 52 slider body 8 LED display 54 stop body 10 ON/OFF button 56 tension spring 12 zero butto 58 spring mounting post 13 unit button 60 elongate shaft 14 circuit board 62 spring mounting post 15 array 64 lateral arm 16 recess 66 engagement tip 18 ga 70 elongate groove 20 disc brake rotor 72 axis 21 dust cover 74 join line 22 lip 76 centreline 23 broken line 78 distal flange 24 outer worn face 80 recess 26 inner worn face 82 magnet 2$ calliper 100 opening 30

reinforcing arm 32

second elongate groove 34

lateral arm 36

lateral groove 38

front panel 40

back plate 42

screws 44

upper and lower cam formations 46, 47

third groove 48

mounting screws 49