GB2541953A - A gap measuring tool - Google Patents

Abstract

A gap measuring tool 300 for measuring the size of a gap (fig 6, 640) comprising a body 110 with a first surface 112 and a second surface (fig 3B, 114) and a piezoelectric material 120, a first electrical contact 130 to the piezoelectric material and a second electrical contact (fig 3B, 140) to the piezoelectric material, wherein a voltage is induced between the first electrical contact and the second electrical contact by a compressive force (fig 1C, Fc) applied to the body of the gap measuring tool via the first surface and second surface of the gap measuring tool. The compressive force induces a voltage between the first and second electrical contacts that are connected to a measuring unit 310 via a first electrical coupling 330 and second electrical coupling (fig 3B, 340) respectively, to display the measurement on the display 312. The measuring unit also has a target gap indicator 314 and a user input interface 316. This tool can be used to measure the gap of the valve clearance between the valve rocker arm (fig 6, 610) and valve bridge (fig 6, 620) of an internal combustion engine.

Description

A GAP MEASURING TOOL

TECHNICAL FIELD

The present disclosure relates to a gap measuring tool for measuring the size of a gap. BACKGROUND

Internal combustion engines (for example, diesel or petrol engines) comprise valves for controlling the introduction of fuel into engine cylinders (fuel valves) and/or the introduction of air into engine cylinders (air intake valves) and/or the exhaust of combustion products from engine cylinders (exhaust valves). The opening and closing of a valve may be controlled by a valve mechanism comprising a valve rocker arm and a valve bridge (which is the top of the valve stem).

The valve clearance, which is the clearance between the valve rocker arm and the valve bridge, may be adjusted using an adjustment screw. If the clearance is too large (i.e., a loose clearance), parts of the valve mechanism may ‘hammer’ together when the internal combustion engine is operating. This may cause damage to the valve mechanism and/or the internal combustion engine and may create a knocking or rattling sound. If the clearance is too small (i.e., a tight clearance), the valve may not close or seat properly, which may lead to premature valve failure, heat damage and/or loss of power from the internal combustion engine. A gap measuring tool, such as a feeler gauge, may be used to measure and set the valve clearance. In particular, a gap measuring tool of a particular thickness corresponding to the desired valve clearance may be inserted into the gap between the valve rocker arm and the valve bridge. The adjustment screw may then be adjusted until the valve rocker arm and the valve bridge engage the gap measuring tool, indicating that the desired valve clearance has been reached.

However, it may be difficult for the operator to tell how tightly the valve rocker arm and valve bridge are engaging the gap measuring tool, and therefore whether or not the desired clearance has actually been reached. For example, if the valve rocker arm and valve bridge very lightly engage the gap measuring tool, the clearance may still be too large, but if they very tightly engage the gap measuring tool, the clearance may be too small.

To help determine how tightly the valve rocker arm and valve bridge engage the gap measuring tool, the operator may perform a drag measurement. This involves the operator inserting the gap measuring tool into the gap between the valve rocker arm and the valve bridge and then dragging it through the gap. The operator will feel a resistance to their dragging being exerted by the valve rocker arm and the valve bridge (a greater resistance indicting a tighter engagement and a lower resistance indicating a lighter engagement). When the operator feels the level of resistance that they deem to be correct, the desired valve clearance will be considered to have been reached.

However, this process is inexact and different operators will estimate the level of resistance differently. This may result in variability in the setting process and inconsistent valve clearance setting between different engines, potentially causing differential performance between internal combustion engines.

Figure 6 shows a cross-sectional view of a valve assembly of an internal combustion engine. The valve assembly comprises a valve rocker arm 610, a valve bridge 620 and an adjustment screw 630 The gap 640 between the valve rocker arm 610 and valve bridge 620, into which a feeler gauge may be inserted during valve clearance setting, can clearly be seen. US4967485A describes an electronic feeler gauge for measuring the dimension of a gap. The electronic feeler gauge comprises a flexible base in a general shape of a shoe-horn. A strain gauge is mounted on the lower portion of the concave curve of the flexible base to measure the strain across the width of the flexible base. As the flexible base is inserted into a gap, it partially flattens and the reading of strain gauge indicates the extent of the flattening, and therefore the dimension of the gap.

However, the flexible base may deform over time, resulting in a loss of accuracy. Even small deformations, not visible to the naked eye, may affect the accuracy of the device. Therefore, the electronic feeler gauge may need to be recalibrated regularly and/or replaced regularly, which is inconvenient and costly. Furthermore, the flexible base may not be sufficiently robust for a workshop environment, resulting in regular damage to the device.

SUMMARY

The present disclosure provides a gap measuring tool for measuring the size of a gap, the gap measuring tool comprising: a body comprising: a first surface; a second surface opposing the first surface; and a piezoelectric material, and a first electrical contact to the piezoelectric material; and a second electrical contact to the piezoelectric material, wherein the piezoelectric material, the first electrical contact and the second electrical contact are arranged such that a compressive force applied to the body via the first surface and the second surface induces a voltage between the first electrical contact and the second electrical contact.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are described below, by way of example only, with reference to the following drawings, in which:

Figures 1A, 1B and 1C show representations of a gap measuring tool 100 in accordance with an aspect of the present disclosure;

Figures 2A, 2B and 2C show representations of a gap measuring tool 200 in accordance with a further aspect of the present disclosure;

Figures 3A and 3B show representations of a gap measuring tool 300 comprising a measurement unit 310 in accordance with a further aspect of the present disclosure; Figures 4A and 4B show representations of a gap measuring tool 400 comprising a measurement unit 310 in accordance with a further aspect of the present disclosure;

Figure 5 shows a schematic representation of the measurement unit 310 of Figures 3 and 4; and

Figure 6 shows a representation of a valve mechanism of an internal combustion engine.

It should be noted that the figures are illustrated for simplicity and are not necessarily drawn to scale. Like features are provided with the same reference numerals.

DETAILED DESCRIPTION

The present disclosure relates to a gap measuring tool comprising a piezoelectric material with a first electrical contact and a second electrical contact. The piezoelectric material, first electrical contact and second electrical contact are arranged such that a compressive force applied to the body via a first surface and a second surface of the gap measuring tool induces a voltage between the first electrical contact and the second electrical contact.

The voltage is therefore indicative of the size of a gap into which the gap measuring tool is inserted, wherein the elements defining the gap impose a compressive force on the gap measuring tool.

The gap measuring tool may be a feeler gauge or any other type of tool/gauge that can be inserted into a gap in order to measure the size/width/clearance of the gap.

Figures 1A, 1B and 1C show schematic representations of a gap measuring tool 100, in accordance with an aspect of the present disclosure. The gap measuring tool 100 comprises a body 110, which has a first surface 112, a second surface 114 that opposes the first surface 112, and a piezoelectric material 120. The gap measuring tool 100 also comprises a first electrical contact 130 on the piezoelectric material 120 and a second electrical contact 140 on the piezoelectric material 120.

Figure 1A shows a top-down perspective view of the gap measuring tool 100. Figure 1B shows a cross-sectional cut-through view of the gap measuring tool 100 through line AA (represented in Figure 1A). Figure 1C shows the same cross-sectional cut-through perspective as Figure 1B, but also shows a representation of a compressive force Fc applied to the body 110 via the first surface 112 and the second surface 114.

Figures 2A, 2B and 2C show schematic representations of a gap measuring tool 200 in accordance with a further aspect of the present disclosure. The gap measuring tool 200 comprises a body 210, which has a first surface 212, a second surface 214 that opposes the first surface 212, and a piezoelectric material 220. The gap measuring tool 200 also comprises a first electrical contact 230 on the piezoelectric material 220 and a second electrical contact 240 on the piezoelectric material 220.

Figure 2A shows a top-down perspective view of the gap measuring tool 200. Figure 2B shows a cross-sectional cut-through view of the gap measuring tool 200 through line AA (represented in Figure 2A). Figure 2C shows the same cross-sectional cut-through perspective as Figure 2B, but also shows a representation of a compressive force Fc applied to the body 210 via first surface 212 and the second surface 214.

The body 110, 210 may be made of any suitable material, for example, metal, ceramic, plastic, etc. In one example, the body 110, 210 may be made of steel. The body 110, 210 may be stiff, or rigid, or inflexible, such that it does not flex or bend, or does not appreciably flex or bend, in normal use. For example, it may have a Young’s Modulus of at least 50GPa such as 200GPa. The body 110, 210 may also be strong and/or hard and/or tough.

The first surface 112, 212 and the second surface 114, 214 may be planar surfaces. The first surface 112, 212 and the second surface 114, 214 may be parallel to each other. They may be separated by a distance that represents the thickness, t, of the gap measuring tool (see Figures 1B, 1C, 2B, 2C). The thickness t may be of any size or dimension, or example any size between 0.01 mm to 10mm, such as 0.02mm, or 0.05mm, or 0.1 mm, or 0.25mm, or 0.8mm, or 2mm, or 8.3mm, etc, or any size between 0.0001 to 0.5 inches, for example 0.0005 inches, or 0.0020 inches, or 0.0085 inches, or 0.015 inches, or 0.030 inches, or 0.100 inches, or 0.250 inches, etc. Thus, the gap measuring tool may be used to measure a gap, or set a gap size (for example the valve clearance described in the ‘Background’ section), approximately equal to the thickness t. A piezoelectric material 120, 220 is a material that accumulates electric charge in response to mechanical stress. The piezoelectric material 120, 220 may be any form of piezoelectric material, for example a piezoelectric crystal or a piezoelectric ceramic, such as Lead Zirconate Titanate (PZT). The piezoelectric material 120, 220 may be of a ‘hard’ type to withstand high levels of electrical and mechanical stress, or of a ‘soft’ type. The piezoelectric material 120, 220 may be formed in any suitable way, for example, pressing, extruding, casting, etc.

The piezoelectric material 120, 220 is positioned such that a compressive force Fc applied to the body 110, 210 via first surface 112, 212 and the second surface 114, 214 induces accumulated electric charge in the piezoelectric material 120, 220. The first electrical contact 130, 230 and the second electrical contact 140, 240 are positioned on the first surface 112, 212 and the second surface 114, 214 such that the accumulated electric charge in the piezoelectric material 120, 220 results in an electrical potential at the first electrical contact 130, 230 being different to an electrical potential at the second electrical contact 140, 240. In this way, a potential difference, or voltage V, between the first electrical contact 130, 230 and the second electrical contact 140, 240 is induced. Thus, the piezoelectric material 120, 220, the first electrical contact 130, 230 and the second electrical contact 140, 240, are arranged such that the compressive force Fc applied to the body 110,210 via first surface 112,212 and the second surface 114, 214 induces a voltage V between the first electrical contact 130, 230 and the second electrical contact 140, 240.

Whilst Figures 1A, 1B and 1C show the first electrical contact 130 on the first surface 112 of the body 110 and the second electrical contact 140 on the second surface 114 of the body, it will be appreciated that they may be located anywhere on or in the piezoelectric material 120, provided the compressive force Fc induces a voltage V between the first electrical contact 130 and the second electrical contact 140. For example, they may both be on the first surface 112, or both on the second surface 114, or at least one of them may be within the piezoelectric material 120 with a conductive coupling connected to the electrical contact to provide an electrical connection point to the electrical contact outside the piezoelectric material 120, 220. Furthermore, they may both be located in-line with each other (for example, vertically in-line with each other in the perspective view shown in Figures 1B and 1C) or off-set from each other (which is the configuration shown in Figures 1B and 1C).

Figures 2B and 2C show the first electrical contact 230 and the second electrical contact 240 being on the two opposing surfaces of the piezoelectric material 220, and within the body 210. Flowever, again, it will be appreciated that they may be located anywhere on or in the piezoelectric material 120, provided the compressive force Fc induces a voltage V between the first electrical contact 130 and the second electrical contact 140. Furthermore, conductive coupling connecting the first electrical contact 130 and the second electrical contact 140 to points outside of the body 110 (for example, points on the surface of the body 210 or away from the body 210), may be provided such that electrical connections to the electrical contacts may be made outside of the body.

In Figures 1A, 1B and 1C, part of the piezoelectric material 120 is exposed on the first surface 112 and part of the piezoelectric material 120 is exposed on the second surface 114. In Figures 2A, 2B and 2C, the piezoelectric material 220 is completely buried within the body 210. In alternative implementations, at least part of the piezoelectric material may be exposed on the first surface 112, 212, and/or the second surface 114, 214, and/or on any other part of the body 110,210.

The voltage V may be read by attaching a voltmeter across the first electrical contact 130, 230 and the second electrical contact 140, 240, or by other means (for example, those that are described in more detail later).

The gap measuring tool 100 may further comprise a conductive coupling from the first electrical contact 130, 230 and/or a conductive coupling from the second electrical contact 140, 240, such that an electrical connection point to the first electrical contact 130, 230 and/or the second electrical contact 140, 240 may be available away from the piezoelectric material 120, 220 (for example, towards the distal end of the body 110, 210 away from the piezoelectric material 120, 220). In this way, an operator may more conveniently connect a voltmeter across the first electrical contact 130, 230 and second electrical contact 140, 240.

When the gap measuring tool 100, 200 is inserted into a gap between two elements (for example, the gap between the valve rocker arm and the valve bridge of a valve mechanism in an internal combustion engine) and the two elements impose a compressive force Fc on the body 110, 210 via the first surface 112, 212 and the second surface 114, 214, the voltage V provides a measure of the mechanical stress applied by the compressive force Fc. A voltage V of 0V may imply that the size of the gap is greater than or equal to t. A voltage V with magnitude greater than 0V may imply that the size of the gap is less than t, wherein the greater the magnitude of voltage V, the smaller the size of the gap. By performing a calibration process by inserting the gap measuring tool 100, 200 into gaps of known size, a correlation may be identified between the voltage V and the size of the gap. Thus, the voltage V may provide an accurate indication of the size of the gap in which the gap measuring tool 100, 200 has been inserted.

Consequently, when setting the size of a gap, for example the valve clearance for a valve mechanism in an internal combustion engine, the gap measuring tool 100, 200 may be inserted into the gap and the size of the gap gradually decreased until the voltage V has reaches a predetermined threshold value. At that predetermined threshold value, the gap may have been accurately set to the desired size and the gap measuring tool 100, 200 may be removed.

Figures 3A and 3B show schematic representations of a gap measuring tool 300 in accordance with an aspect of the present disclosure. The gap measuring tool 300 comprises a body 110, which has a first surface 112, a second surface 114 that opposes the first surface 112, and a piezoelectric material 120, as described earlier with reference to Figures 1A, 1B and 1C. The gap measuring tool 300 also comprises a first electrical contact 130 on the piezoelectric material 120 and a second electrical contact 140 on the piezoelectric material 120, as described earlier with reference to Figures 1A, 1B and 1C. The gap measuring tool 300 may also comprise: a measurement unit 310, which comprises a display 312, a target gap indicator 314 and a user input 316; a first electrical coupling 330, which electrically couples the first electrical contact 130 to the measurement unit 310; and a second electrical coupling 340, which electrically couples the second electrical contact 140 to the measurement unit 310.

Figure 3A shows a top-down perspective view of the gap measuring tool 300. Figure 3B shows a cross-sectional cut-through view of the gap measuring tool 300 through line AA (represented in Figure 3A).

Figures 4A and 4B show schematic representations of a gap measuring tool 400 in accordance with a further aspect of the present disclosure. The gap measuring tool 400 comprises a body 210, which has a first surface 212, a second surface 214 that opposes the first surface 212, and a piezoelectric material 220, as described earlier with reference for Figures 2A, 2B and 2C. The gap measuring tool 400 also comprises a first electrical contact 230 on the piezoelectric material 220 and a second electrical contact 240 on the piezoelectric material 220, as described earlier with reference to Figures 2A, 2B and 2C. The gap measuring tool 400 may also comprise the measurement unit 310, a first electrical coupling 430, which electrically couples the first electrical contact 230 to the measurement unit 310, and a second electrical coupling 440, which electrically couples the second electrical contact 240 to the measurement unit 310.

Figure 4A shows a top-down perspective view of the gap measuring tool 400. Figure 4B shows a cross-sectional cut-through view of the gap measuring tool 400 through line AA (represented in Figure 4A).

The first electrical coupling 330, 430 and second electrical coupling 340, 440 may be any form of electrically conductive coupling, for example a metal wire or track. Where the body 110, 210, is made of an electrically conductive material, such as a metal, first electrical coupling 330, 430 and second electrical coupling 340, 440 may be insulated from the body 110, 210 by any suitable means, for example with insulative sheathes.

In Figures 3A and 3B, the first electrical coupling 330 and second electrical coupling 340 are both on the surfaces of the body 110. The second electrical coupling 340 is shown running along the second surface 114 and then passing through the body 110 to the measurement unit 310. However, it will be appreciated that the second electrical coupling 340 may alternatively go from the second surface 114 to the measurement unit 310 in any other way, for example by passing around an outer edge of the body 110. Furthermore, at least one of the first electrical coupling 330 and second electrical coupling 340 may be formed at least in part within the body 110, away from the surfaces of the body 110.

Likewise, in Figures 4A and 4B, the first electrical coupling 430 and second electrical coupling 440 are both within the body 210, away from the surfaces of the body. However, it will be appreciated that at least one of the first electrical coupling 430 and second electrical coupling 440 may be formed at least in part on the first surface 212 or second surface 214 of the body 210.

Figure 5 shows a schematic representation of the measurement unit 310. The measurement unit 310 may comprise the display 312, the target gap indicator 314, the user input 316, a processor 510, a memory 520 and a communications interface 530.

The display 312 may be any suitable type of display for displaying to an operator of the gap measuring tool 300, 400, a measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 (as explained later). For example, it may be an LED display, an OLED display, an LCD display, a TFT display, etc. The target gap indicator 314 may be any suitable type of indicator to output an indication of when the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 is between a first threshold value and a second threshold value (as explained later). For example, it may comprise at least one of: an optical element, for example an LED, an OLED, a LCD element, a TFT display element; and/or an audio element, such as a buzzer, and/or a tactile element, such as a vibration motor. In one aspect, the target gap indicator 314 may form part of the display 312. The user input 316 may be any formed of input device that enables an operator of the gap measuring tool 300, 400 to input data, for example during calibration. In the example shown in Figures 3A and 4A, it is a 12 key keypad (for example, a button keypad, or a touchscreen, etc), although it may alternatively comprise any number of keys, for example only two keys, one to increase the first threshold value and/or second threshold value and a second to decrease the first threshold value and/or second threshold value, etc.

The processor 510 may comprise at least one microprocessor, or programmable logic, or any other suitable type of computer processor(s), etc. The memory 520 may be any suitable type of memory, for example volatile or non-volatile memory. The communications interface 530 may be any type of communications interface suitable for enabling wired or wireless communication between the measurement unit 310 and an electronic device (for example, a desktop or laptop computer, or a tablet computer, or a smart phone, etc). For example, the communications interface 530 may comprise at least one of a Bluetooth communications chip and aerial, a Near Field Communication (NFC) chip and aerial, a WiFi chip and aerial, and mobile telecommunications chip and aerial (for example, GPRS, EDGE, GSM, UTMS, LTE, etc), a LAN interface chip and connection port so that a wired connection may be made to an electronic device, etc.

In one aspect of the present disclosure, the processor 510 may determine the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 using at least the signals from the first electrical coupling 330, 430 and the second electrical coupling 340, 440. It may then output the voltage measurement on the display 312.

Alternatively, the processor 510 may be configured to determine the distance between the first surface 112, 212 and the second surface 114, 214 using at least the determined voltage, and thus determine the dimension, or size, of the gap. It may then output the dimension (which may be in any suitable units, for example micrometres, millimetres, centimetres, thousandths of inches, hundredths of inches, tenths of inches, etc) to the display 312 as the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240. The processor 510 may determine the dimension using calibration data that it may have stored in memory 520 from an earlier calibration process.

In a calibration process, an operator may put the gap measuring tool 300, 400 in at least one gap of known size and input to the measurement unit 310 the size of the gap(s) (for example, using the user input 316 or via an electronic device coupled to the measurement unit 310 via the communications interface 530). The processor 510 may then store in memory 520 the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 for each gap size. During subsequent use, the processor 510 determine the dimension, or size, of a gap from the voltage V by utilising the stored data (for example, by determining a correlation between the voltages and the gap sizes in the calibration results and then using that correlation to determine the gap size from a measured voltage V).

Additionally, or alternatively, the processor 510 may store the measurement (i.e., the voltage V and/or the dimension of the gap) in memory 520. If the gap measuring tool 300, 400 is being used to measure a range of gaps (for example, valve clearances for multiple valves of an internal combustion engine and/or valve clearances for multiple different internal combustion engines) the operator may also input a gap ID (for example, using the user input 316 or via an electronic device coupled to the measurement unit 310 via the communications interface 530) such that the measurement may be stored with an association to the gap ID. In this way, a record of the exact valve clearance set for each valve of an internal combustion engine and/or each valve of each vehicle in a fleet of vehicles, may be kept.

Additionally, or alternatively, the measurement unit 310 may output the measurement derived at least in part from the voltage V between the first electrical contact 130, 230 and the second electrical contact 140, 240 (for example, the measured voltage V and/or the dimension of the gap) to an external electronic device using the communications interface 530. In this way, the external electronic device may display the measurement to an operator and/or keep a record of the measurement (analogously to storage of the measurements in memory 520). In this aspect, the operator may input the gap ID to the measurement unit 310 using the user input 316, or using a user interface on the external electronic device, or alternatively, may input the gap ID directly into the external electronic device.

The processor 510 may determine when the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 is between a first threshold value and a second threshold value. The first threshold value and second threshold value may be in the same units (for example, volts, or millimetres, or inches, etc) as the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240.

The first threshold value may represent a minimum allowable gap size (for example, 0.05mm) and the second threshold value may represent a maximum allowable gap size (for example, 0.09mm). The measurement unit 310 may be configured such that at least one of the first threshold value and/or the second threshold value is a fixed value (for example, fixed during calibration). Additionally, or alternatively, the measurement unit 310 may be configured such that at least one of the first threshold value and/or the second threshold value is variable, in which case the measurement unit 310 may be configured to receive a setting for at least one of the firs threshold value and/or the second threshold value (for example, via the user input 316 and/or the communications interface 530).

When it is determined that the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 is between a first threshold value and a second threshold value, an indication may be output by the measurement unit 310. The indication may be output via the target gap indicator 314, for example by turning on a light (such as an LED), and/or by changing the colour of a light (for example, from red to green), and/or by sounding a buzzer, and/or by turning on a vibration motor. Additionally or alternatively, the indication may be output via the communications interface 530 to an external electronic device, for example as data indicating that the measurement is between the first and second threshold values. Thus, an operator may have a clear indication of when a gap is between allowable limits (for example, when setting a valve clearance) without necessarily knowing exactly what the dimension of the gap is.

The measurement unit 310 may be configured to output just the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240, or just the indication that the measurement is between the first threshold value and the second threshold, or both.

Optionally, the measurement unit 310 may not comprise any of the display 312, the target gap indicator 314 or the user input 316, and may instead only output the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240, and/or the indication that the measurement is between the first threshold value and the second threshold value, using the communications interface 530. Any data that might be input to the measurement unit 310 (for example, during calibration or in setting of thresholds) may be input via the communications interface 530.

In a further alternative, the measurement unit 310 may not comprise the communications interface 530. It may comprise at least one of the display 312 and/or target gap indicator and may be configured to output the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 and/or the indication that the measurement is between the first threshold value and the second threshold value using the display 312 and/or target gap indicator 314. Optionally, it may also comprise the user input 316, for use if the measurement unit 310 is configured to receive data from an operator.

In a further alternative, the measurement unit 310 may comprise any one or more of the display 312, the target gap indicator 314, and/or the communications interface 530 and may be configured to output the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 and/or the indication that the measurement is between the first threshold value and the second threshold value via whichever means are available.

In a further alternative, the measurement unit 310 may be configured not to receive any data via a user input 316 or communications interface 530 (for example, calibration may not be necessary because the measurement unit 310 is configured to output only the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240, or it may be configured to receive all calibration data during initial set-up and programming) in which case the measurement unit 310 may not have a user input 316 and optionally also not have a communications interface 530.

Furthermore, the measurement unit 310 may not have memory 520, for example where no calibration settings need to be stored in memory.

Thus, according to the aspects of the present disclosure, an operator of the gap measuring tool 300, 400 may obtain an accurate measurement indicative of the size of a gap and/or have an accurate indicator of when the dimension of a gap is within allowable limits.

The skilled person will readily appreciate that a number of alterations and/or alternatives to the aspects described above may be used and fall within the scope of the present disclosure.

For example, whilst all of the gap measuring tools 100, 200, 300 and 400 represented in the drawings are ‘parallel’ gap measuring tools (i.e., the body 110, 210, has parallel edges when viewed from the top-down - see Figures 1 A, 2A, 3A and 4A), it will be appreciated that the gap measuring tools 100, 200, 300 and 400 may alternatively have a tapered shape, such that the edges of the body 110, 210 as viewed from the top-down (see Figures 1 A, 2A, 3A and 4A) are tapered at at least one distal end of the gap measuring tool 100, 200, 300 and 400. It will be understood that a tapered gap measuring tool may nevertheless have a consistent thickness t along the length of the gap measuring tool 100, 200, 300 and 400.

Whilst the gap measuring tools 100, 200, 300 and 400 each comprise a body 110, 210 comprising a material that is different to the piezoelectric material 120, 220, in an alternative aspect the entire body 110, 210 may comprise only piezoelectric material 120, 220, such that the piezoelectric material 120, 220 defines the body 110,210. In a further alternative, the body 110, 210 may comprise piezoelectric material 120, 220 and at least one other material (such as metal, plastic, ceramic, etc), and the piezoelectric material 120, 220 may be of any size or shape, for example the piezoelectric material 120, 220 may make up the majority of the volume of the body 110, 210.

The measurement unit 310 may be further configured to display at least one of the upper threshold value and/or the lower threshold value, such that an operator may determine that the measurement derived at least in part from the voltage between the first electrical contact 130, 230 and the second electrical contact 140, 240 is between a first threshold value and a second threshold value.

Any one of the gap measuring tools 100, 200, 300 and 400 may form at least part of a gap measuring tool set comprising at least two gap measuring tools. At least one of the gap measuring tools within the gap measuring tool set may be of the type described above with reference to any of Figures 1,2, 3 and 4.

The measurement unit 310 may be located on the first surface 112,212, or on the second surface 114, 214, or anywhere else (for example, it may be located off the body 110, 210 altogether, but still coupled to the first electrical contact 130, 230 and the second electrical contact 140, 240 via conductive couplings)

The voltage V between the first electrical contact 130, 230 and the second electrical contact 140, 240 may be a positive or a negative voltage. It is the magnitude of the voltage V that is an indicator of the size of a gap.

Whilst use of the gap measuring tool 100, 200, 300, 400 has been described in relation to the setting of a valve clearance for a valve assembly of an internal combustion engine, it will be appreciated that the gap measuring tool 100, 200, 300, 400 may be used for determining the size of any sort of gap. For example, the size of a gap between two elements (for example, the size of a slit in a piece of metal) may be determined when the gap measuring tool 100, 200, 300, 400 is inserted into the gap and the size of the gap is such that the two elements exert a compressive force on the body 110,210 via the first surface 112, 212 and the second surface 114, 214, of the gap measuring tool 100, 200, 300, 400.

In Figures 1C and 2C, the compressive force Fc applied to the body 110, 210 via the first surface 112, 212 and the second surface 114, 214 is shown to be applied perpendicular to the first surface 112, 212 and the second surface 114, 214. Flowever, it will be appreciated that the compressive force Fc may be any force, applied to any part of the first surface 112, 212 and the second surface 114, 214 and in any direction, that results in at least some compression of the piezoelectric material 120, 220 in a direction perpendicular (or normal) to the first surface 112, 212 and the second surface 114, 214. Optionally, the force may also result in compression of the piezoelectric material 120, 220 in some other direction(s) as well, but provided at least part of the compression of the piezoelectric material 120, 220 is in a direction perpendicular (or normal) to the first surface 112, 212 and the second surface 114, 214, it is still a compressive force applied to the body 110, 210 via the first surface 112, 212 and the second surface 114, 214 within the meaning of this disclosure.

Any of the features described specifically relating to one aspect or example may be used in any other aspect by making the appropriate changes

INDUSTRIAL APPLICABILITY

The gap measuring tool of the present disclosure may enable an accurate, consistent and objective measurement of the size of a gap. For example, an operator may insert the gap measuring tool into a gap and obtain an accurate measurement of the extent to which the first and second surfaces have been compressed (for example, by a valve rocker arm and valve bridge during valve clearance setting), which is indicative of the size of the gap, from the voltage induced between the first electrical contact and the second electrical contact. The gap measuring tool may be kept stationary in the gap whilst the measurement is taking place, or may be dragged through the gap whilst the measurement is taking place, without affecting the measurement.

Consequently, when adjusting the size of a gap, for example when setting a valve clearance, the gap may accurately and repeatably be set to a particular size. In the example of setting valve clearances, this may result in valve clearances being consistently set to a specific desired amount, all valves in an internal combustion engine and across all engines in a fleet of vehicles, regardless of operator, thereby achieving optimum, consistent performance of internal combustion engines.

The body of the gap measuring tool may be stiff, and therefore be more resilient to damage and less prone to deformation over time, particularly in workshop environments. The longterm accuracy of the gap measuring tool may thereby be improved.

The gap measuring tool may further comprise a measurement unit configured to output a measurement derived at least in part from the voltage between the first electrical contact and the second electrical contact. This may simplify determination of the size of the gap for the operator.

The measurement unit may be further configured to output an indication when the measurement derived at least in part from the voltage between the first electrical contact and the second electrical contact is between a first threshold value and a second threshold value. An operator may straightforwardly recognise from the indication when the gap (for example, a valve clearance) is within desirable limits. This may be particularly useful when setting gap sizes in awkward, difficult locations such that the operator cannot easily read a display on a screen, etc.

The first threshold value and/or the second threshold value may be variable. Thus, the tolerance of the allowable limits of the gap may be adjusted. For example, for some gaps, a wide range of different gap sizes may be acceptable, such that the first threshold value and second threshold value can be set to be a wide distance apart, whereas for some gaps a very small range of different gap sizes may be acceptable, such that the first threshold value and the second threshold value may be set to be close together.

The measurement unit may keep a record (for example, in memory) of the measurement derived at least in part from the voltage between the first electrical contact and the second electrical contact. Thus, a record may be kept of gap sizes, for example a record of the valve clearance for each valve assembly in an internal combustion engine, which may be useful for fault diagnosis at a later time and/or for recalling the valve clearance that has previously be used when servicing an internal combustion engine.

Claims (12)

1. A gap measuring tool for measuring the size of a gap, the gap measuring tool comprising: a body comprising: a first surface, a second surface opposing the first surface, and a piezoelectric material, a first electrical contact to the piezoelectric material; and a second electrical contact to the piezoelectric material; wherein the piezoelectric material, the first electrical contact and the second electrical contact are arranged such that a compressive force applied to the body via the first surface and the second surface induces a voltage between the first electrical contact and the second electrical contact.

2. The gap measuring tool of claim 1, wherein the first surface is a planar surface and the second surface is a planar surface.

3. The gap measuring tool of any preceding claim, wherein the body is stiff.

4. The gap measuring tool of any preceding claim, wherein the body further comprises a metal material.

5. The gap measuring tool of any preceding claim, wherein the body further comprises a plastic material.

6. The gap measuring tool of any preceding claim, wherein the body further comprises a ceramic material.

7. The gap measuring tool of any preceding claim, further comprising: a measurement unit electrically coupled to the first electrical contact and the second electrical contact, wherein the measurement unit is configured to output a measurement derived at least in part from the voltage between the first electrical contact and the second electrical contact.

8. The gap measuring tool of claim 7, wherein the measurement indicates the distance between the first surface and the second surface.

9. The gap measuring tool of either claim 7 or claim 8, wherein the measurement unit further comprises: a display configured to display the measurement.

10. The gap measuring tool of any of claims 7 to 9, wherein the measurement unit is further configured to output an indication when the measurement is between a first threshold value and a second threshold value.

11. The gap measuring tool of claim 10, wherein: at least one of the first threshold value and the second threshold value are variable; and wherein the measurement unit is configured to receive a setting for at least one of the first threshold value and the second threshold value.

12. The gap measuring tool of any of claims 7 to 11, wherein the measurement unit is further configured to: keep a record of the measurement derived at least in part from the voltage between the first electrical contact and the second electrical contact.