GB2266005A - Levelling system - Google Patents

Abstract

In an apparatus and method for checking a vehicle head lamp levelling system, a laser 15 is mounted in place of a headlamp bulb and used to illuminate a scale or scales. The deviation of the beam resulting from operation of the levelling system is used to monitor the angular movement of the headlamp unit 1 and the hysteresis of the associated servomotor system. <IMAGE>

Description

LEVELLING SYSTEM The present invention relates to an apparatus and method for checking a headlamp levelling system of a vehicle.

Vehicle headlamp levelling systems are becoming more common and may eventually be mandatory under the laws of many countries. They allow a driver to adjust the angle of a headlamp beam by eg. operating a multi-position switch. If, for example, a heavy load is placed in the rear of a vehicle, the vehicle body is caused to tilt so that the angle which the headlamp dipped beam makes with respect to the road is reduced. By operating the switch, the driver can compensate for this deviation.

A conventional headlamp levelling system comprises a servo-motor arrangement which causes the headlamp assembly to tilt according to the position to which the switch is set. During the design and manufacture of headlamp levelling systems, it is important to ensure that the correct beam adjustment can be made for various vehicle loads.

As with most control systems, there is inevitably some hysteresis of servo-motor response to the input (switch position). It is important to establish that this hysteresis follows a predictable path and is within permitted tolerances. This means that it is necessary to test operation of the headlamp levelling system on an actual vehicle.

Up to now, testing has been done by placing the vehicle in a ce 10 metre darkened room. One headlamp is switched on and the centre (hot spot) of the beam is located by moving a light meter across its path and finding the point of maximum intensity. When the levelling system is operated to compensate for a given load, this procedure is repeated to find the new position of maximum beam intensity. By measuring the deviation of this point from the original position, operation of the levelling system can be determined.

Obviously, only one lamp can be tested at one time.

It will be evident that this coventional procedure is neither reliable nor accurate. Not only is it dependent on the skill of the person operating the light meter but it is also confounded by the large amount of scatter of the beam when it passes through the headlamp lens.

The applicants have now devised a system which overcomes these problems. Thus, according to the present invention there is provided a method of checking a headlamp levelling system of a vehicle, the method comprising mounting a diode laser in place of a headlamp bulb, illuminating a scale with a beam from the laser to establish a datum position, operating the levelling system and measuring the deviation of the beam from the datum position.

The aforementioned method of the present invention is effected using an apparatus according to the present invention for checking a headlamp levelling system of a vehicle, the apparatus comprising a laser and an adaptor for mounting the laser in the place of a headlamp bulb.

Preferably, the apparatus also comprises a beam spreader which is mounted in front of the laser. Most preferably, the beam spreader is a line generator. If the beam is spread-out in a flat fan-shape, the position where it impinges on the scale can be determined more easily. This is particularly advantageous when the scale comprises a rule or a pair of rules arranged vertically in front of the beam.

However, instead of a rule, photodetector means, preferably provided with an appropriate focussing arrangement, may be used to measure movement of the beam. Such photodetector means may comprise an array of discrete photodetector elements such as photodiodes or it may comprise a camera such as a CCD camera.

Such photodetector means would first be calibrated by moving the laser beam a certain amount using the servomotor and measuring the distance traversed across the detector surface using a manual rule. This value could be input to a microcomputer connected via appropriate interface circuitry to the photodetector mear After calibration, the microcomputer would then be able to determine the angular variation in the laser beam as the levelling system is operated, according to the distance the beam moves across the photodetector surface.

It will be appreciated that when such photodetector means are used, it is not necessary to provide a beam spreader if the field of view of the detector is chosen appropriately.

The method and apparatus according to the present invention provides a number of advantages to the previously used system.

Since the laser is compact and is used in place of the standard bulb, the test involves all parts of the actual vehicle levelling system other than the bulb itself.

If the laser can operate at or below the normal headlamp voltage, it is not necessary to employ high voltages which are needed for certain types of laser. These would be dangerous as the test procedure usually takes place on a metal surface plate.

The apparatus is relatively inexpensive and is more accurate than the known system. By mounting relatively inexpensive lasers in both headlamps, these can be chec > -eF simultaneously whilst the vehicle is loaded-and unloaded.

Since the laser output can be varied easily, it is possible to select the minimum beam intensity necessary to carry out the test whilst maximising safety. In this respect, it should be noted that whilst a laser such as a semiconductor diode laser may have a relatively high power output, the intensity at a given point of the beam is reduced if a beam spreader such as a line generator is placed in front of it.

Since the laser is mounted in the actual headlamp socket in place of the headlamp bulb, movement of the laser during test is restricted in the same way as for the real bulbs of the headlamp system.

It is not necessary to use a darkened room, nor to use a test-bed of ca, 10 metres. A scale or scales may be placed in a few metres, typically 2-3 metres of the headlamp in order to obtain excellent accuracy.

These and other advantageous of the method and apparatus according to the present invention may now be appreciated from the following description of a preferred embodiment and with reference to the accompanying drawings in which: Figure 1 shows a headlamp unit with an associated levelling system; Figure 2 shows a front view of the headlamp unit shown in Figure 1; Figure 3 shows an axial cross section of the headlamp unit shown in Figures 1 and 2, in which is located a laser unit for performance of the present invention; Figure 4 shows a laser unit according to the present invention; Figure 5 shows a side view and Figure 5A shows a front view of a sleeve of the laser unit shown in Figure 4; Figure 6 shows a side view and Figure 6A shows a front view of the bulb base of the laser unit shown in Figure d;; Figure 7 shows a side view and Figure 7A shows a front view of a line generator of the laser unit shown in Figure 4; and Figure 8 shows how the laser unit is used to perform a method according to the present invention.

As shown in Figure 1, a conventional headlamp assembly 1 comprises a reflector mounting 3 over which is situated a lens 5. Electrical connections 7 supply electrical power to the headlamp bulb (not shown). A levelling mechanism 9 is situated behind the reflector.

As seen more clearly from Figure 2, a reflector 11 is located inside the mounting 3. At the centre of the reflector, there is provided a bulb mount socket 13.

Referring next to Figure 3, a laser unit 15 is inserted in the bulb-mount socket in place of the normal headlamp bulb, for use as described in more detail hereinbelow.

In use, the headlamp lens is removed. The overall outward appearance of the laser unit can be seen from Figure 4.

The laser unit 15 comprises a sleeve 17 which houses a laser diode.

The sleeve is an optional feature but is preferably provided to protect the laser and its electrical connections during use and during interchange of the laser unit from one headlamp assembly to another.

The electrical connection to the laser can be made from any suitable low voltage power supply, which power supply can be arranged to power either one or both laser units mounted within the vehicle lamp assemblies. The power supply, preferably is fitted with a key switch for operation together with a suitable visual indicator, such as an LCD, to show clearly when the lasers are being energised.

The structure of the sleeve 17 can be seen in more detail from Figures 5 and 5A. It comprises a body portion 27 and a rear portion 29 of smaller diameter than the body portion. The laser diode is located into the sleeve with electrical connection provided through a gland assembly 31, 33.

The front of the casing has an opening 34 through which the laser light emanates. The front portion of the body is provided with a hole 35 for receiving a grub screw for fixing the laser into the sleeve which in turn is fixed into an adaptor 25.

Details of the adaptor can be seen from Figures 6 and 6A. It comprises a cylindrical portion 37 and circumferential lugs 39, 41, 43. An opening 45 at the rear receives the sleeve 17 which is positioned to project through a front opening 46 of the adaptor and fixed in place by means of a grub screw 47.

A line generator 19 as shown in Figures 7 and 7A is then mounted onto the front end 23 of the sleeve which projects through the front opening 46. It comprises a silica rod 49 diametrically disposed across the opening 51 in a hexagonal nut portion 53. A collar 55 provided with a through-screw 57 is attached to the nut so that the line generator can be attached to the front end 23 of the sleeve 17.

The use of the laser in a method according to the present invention will now be explained with reference to Figure 8.

The laser unit 15 mounted in the headlamp unit 1 of a vehicle 59 produces a flat fan-shaped beam 61 which is used to illuminate a pair of vertical scales 63, 65 respectively arranged at (say) about 2m and 3m from the headlamp but in any event, at a known distance.

When the beam is parallel to the ground, ie. horizontal, the beam will intersect both scales at the same height.

As the vehicle is loaded and unloaded, and the levelling system operated to compensate, if the angle of the beam changes, the deviation of the beam can be read-off the scale(s) and used to calculate the true orientation of the headlamp.

In this way, operation of the levelling system and in particular, hysteresis in the functioning of the servo-motor can be determined.

In the light of this disclosure, modifications of the described embodiment, as well as other embodiments, all within the scope of the present invention as defined by the appended claims, will now be apparent to persons skilled in the art.

Claims (10)

1. An apparatus for checking a headlamp levelling system of a vehicle, the apparatus comprising a laser and an adaptor for mounting the laser in the place of a headlamp bulb.

2. An apparatus according to claim 1, further comprising a beam spreader.

3. An apparatus according to claim 2, wherein the beam spreader is a line generator.

4. An apparatus according to either preceding claim, wherein the laser is a semiconductor diode laser adapted to operate from a voltage not exceeding the normal operational voltage of the headlamp.

5. A system for checking a headlamp levelling system of a vehicle, the system comprising an apparatus according to any preceding claim, and a scale.

6. A method of checking a headlamp levelling system of a vehicle, the method comprising mounting a laser in the place of a headlamp bulb, illuminating a scale with a beam from the laser to establish a datum position, operating the levelling system and measuring the deviation of the beam from the datum position.

7. A method according to claim 6, wherein the measured deviation is used to determine the angle through which the laser beam has been moved as a result of the operation of the levelling system.

8. An apparatus for checking a headlamp levelling system tf a vehicle, the apparatus being substantially as hereinbefore described with reference to any of Figures 3-8 of the accompanying drawings.

9. A system for checking a headlamp levelling system of a vehicle, the checking system being substantially as hereinbefore described with reference to any of Figures 3-8 of the accompanying drawings.

10. A method of checking a headlamp levelling system of a vehicle, the method being substantially as hereinbefore described with reference to any of Figures 3-8 of the accompanying drawings.