ARRANGEMENT FOR AN OPTICAL SPEED INDICATOR

Abstract: Arrangement for an optical speed indicator intended to form part of the system for the anti-lock braking of a vehicle wheel. The speed indicator has a rotationally symmetrical device (1) operatively connected with the wheel, said device being executed with equidistant openings (4) or the like, a light source (2) positioned on one side of said device (1) and so arranged as to illuminate said openings (4), and a detector (3) positioned on the other side of said device (1) and so arranged as to generate a signal pulse each time it is struck via an opening (4) by light from the light source (2). A characteristic feature of the invention is that the arrangement includes a nozzle (8) communicating with the brake cylinder (7) of the vehicle wheel in such a way that the quantity of air discharged from the cylinder (7) via the nozzle (8) during braking produces a jet of air so arranged as to prevent the speed indicator from becoming contaminated with dirt.

Description: Arrangement for an optical speed indicator The present invention relates to an arrangement for an optical speed indicator intended to form part of a system for the anti-lock braking of a vehicle wheel having a rotationally symmetrical device opera- tively connected wi th the wheel , sai d device bei ng executed with equidi stant openi ngs or the l ike, a l ight source posi tioned on one side of said device and so arranged as to ill uminate said openings, and a detector posi tioned on the other si de of sai d device and so arranged " as to generate a signal pul se each time it is struck via an opening by l ight from the l ight source. Speed indicators of thi s kind are often positioned in an environment such that the ri sk of contamination, by dirt and of resul ting mal ¬ function is remarkably high. The object of the present invention is by simple means to el iminate or at l east to reduce by a considerabl e amount any mal functions resul ting from contamination by di rt, which is permissible in accor¬ dance with the invention through the arrangement incl uding a nozzle communicating with the brake cyl inder of the vehicl e wheel in such a way that the quanti ty of ai r di scharged from the cyl i nder via the nozzle during braking produces a jet of air so arranged as to prevent the speed indicator from becoming contaminated by dirt. The invention permi ts effective bl owi ng cl ean, and wi thout the need for speci al equipment for the control of that function. In accordance with one particular characteristic feature of the invention, the level of contamination by dirt is reduced further by the rotationally symmetrical device being executed in a previously disclosed fashion with tongues arranged adjacent to the openings, and by the tongues being positioned in such a way that a flow of air which interacts with the jet of air from the nozzle is obtained from them. The invention is described in greater detail below with reference to the accompanying drawings, of which Fig.1 illustrates diagra atical- ly and in perspective view an illustrative embodiment of an arrangement in accordance with the invention. Fig.2 illustrates a plan view from the side, and Fig. 3 illustrates a plan view from above of the arrangement in accordance with Fig. 1. The arrangement in accordance with the invention comprises a rota¬ tionally symmetrical device 1, consisting in the design illustrated in the drawing of an annular part of the outer surface of a cylinder, and of a light source 2 and a photocell 3 positioned to either side of the ring 1. The ring 1 is operatively connected to a vehicle wheel, the rotational speed of which is to be measured. Neither the aforementioned vehicle wheel nor the operative connection are shown in the drawing. The ring 1 is executed with equidistant openings 4 which are illuminated by the light source 2. When these pass by the photocell 3 as the ring 1 rotates, a series of electrical impulses is produced in a previously disclosed fashion, the frequency of hich provides an indication of the speed of rotation of the wheel. The series of impulses is processed in a manner appropriate for the purpose by means of a computer device 5 connected to the photocell 3. A nozzle 8 communicating with the brake cylinder 7 of the vehicle wheel is present in accordance with the invention in order to prevent the contamination by dirt of the component parts of the speed indicator. In the design illustrated in the drawing, this nozzle is arranged between the light source 2 and the photocell 3 and is so arranged as to produce a jet of air by means of which the optical surfaces of the light source 2 and the photocell 3 are primarily kept free from dirt. The jet of air is produced each time braking by means of the handbrake ,or the footbrake ceases. This is also the case for the electronically controlled pulsed braking provided by the anti- lock braking system. The first-mentioned case is especially advan¬ tageous because dirt may have collected on the detector devices after the vehicle has remained stationary for a certain time. The accumu¬ lated dirt is thus blown away with the help of a jet of air which is produced in conjunction with the release of the handbrake. In a particularly advantageous embodiment of the invention, project¬ ing tongues 6 are arranged in a previously disclosed fashion adjacent to the openings 4. In the embodiment illustrated in the drawing, these tongues project in the manner of fan blades radially outwards from the ring 1, which thus acts simultaneously as a centrifugal fan as it rotates, producing an air flow which additionally prevents contamination of the speed indicator by dirt. It is obvious that the fan blades 6 can be angled in different ways within the scope of the idea of invention in order to produce the greatest possible dirt-preventing effect, having regard for the relative positions of the light source 2, the photocell 3 and the nozzle 8.

Claims: Patent Claims 1. Arrangement for an optical speed indicator intended to form part of a system for the anti-lock braking of a vehicle wheel having a rotationally symmetrical device (1) operatively connected with the wheel, said device being executed with equidistant openings (4) or the like, a light source (2) positioned on one side of said device (1) and so arranged as to illuminate said openings (4), and a detector (3) positioned on the other side of said device and so arranged as to generate a signal pulse each time it is struck via an opening (4) by light from the light source (2), c h a r a c t e r i z e d in that the arrangement includes a nozzle (8) communicating with the brake cylinder (7) of the vehicle wheel in such a way that the quantity of air discharged from the cylinder (7) during braking produces a jet of a*ir so arranged as to prevent the speed indicator from becoming contaminated by dirt. 2. Arrangement according to Patent Claim 1, in which the rotational¬ ly symmetrical device (1) is executed in a previously disclosed fashion with tongues (6) arranged adjacent to the openings (4), c h a r a c t e i z e d in that the tongues (6) are positioned in such a way that a flow of air which interacts with the jet of air from the nozzle (8) is obtained from them.

Inventors: SWIDEN LENNART, SWIDEN, LENNART
Applicants: BYGG VESTA AB, BYGG-VESTA AB
Application year: 1985
Main classification: G01P3
IPC codes: B60T8, G01P3