GB2176608A

GB2176608A - Vehicle road speed sensor

Info

Publication number: GB2176608A
Application number: GB08614450A
Authority: GB
Inventors: Andrew Stephen Todd; Ian Garth Ashdown Rooker; David Wiley
Original assignee: Lucas Electrical Electronics and Systems Ltd
Current assignee: Lucas Electrical Electronics and Systems Ltd
Priority date: 1985-06-13
Filing date: 1986-06-13
Publication date: 1986-12-31
Also published as: GB8515017D0; DE3619600A1; FR2583520B1; FR2583520A1; GB2176608B; GB8614450D0

Abstract

A Vehicle Road Speed Sensor includes means (W) (a washer) arranged to prevent rotation of the spindle (SM; SA) relative to the body of the sensor by forces tending to cause rotation, below a predetermined value so that spurious output signals are not produced when the vehicle is stationary and the engine is idle. <IMAGE>

Description

SPECIFICATION Vehicle road speed sensor The invention relates to a vehicle road speed sensor.

European exhaust emission regulations require that the fuel supply of a vehicle is adjusted when the vehicle is at rest and the engine of the vehicle is at idle.

Vehicles are often fitted with a road speed sensor driven by the vehicle, for example from the gear box thereof, and operative to provide an output signal dependent upon the vehicle's road speed, which output signal is used to control, among other things, a fuel supply control unit which serves to adjust the fuel supply to suit the vehicle's road speed.

A known vehicle road speed sensor comprises a body, a spindle mounted in the body for rotation relative thereto about its longitudinal axis, and a transducer carried by the body in fixed relationship to the spindle, the arrangement being such that rotation of the spindle relative to the body and the transducer produces an output pulse signal from the transducer, the spindle being rotated during use of the sensor on a vehicle at a speed dependent upon the vehicle road speed.

A difficulty which arises with such a sensor is that when the fuel supply of a vehicle to which the sensor is fitted is being adjusted with the vehicle stationary and its engine at idle, at which time there should be no output signal from the sensor, it can happen that vibrations in the vehicle cause rotation of the spindle of the sensor relative to the body thereof, thus causing a spurious output signal to be supplied to the vehicle's fuel supply control unit thereby causing incorrect adjustment of the fuel supply to be effected.

According to this invention a vehicle road speed sensor as set out above is characterised by means acting to prevent rotation of the spindle relative to the body by forces tending to cause such rotation, below a predetermined value.

Preferably said rotation preventing means comprises means providing a frictional force acting between the body and the spindle.

The spindle can carry a multi-headed member arranged such that during rotation of the spindle the heads of the member successively pass the transducer, said rotation preventing means comprising a friction-providing washer acting between said member and the body.

The multi-headed member can be a multipole magnet, the transducer then being constituted by means responsive to magnetic influence, for example a Hall effect device. Otherwise the multi-headed member can be a ferromagnetic material member, the transducer then comprising a magnet.

The spindle can be arranged to be rotated, in use of the sensor, by a drive member carried by the body and driven by the vehicle, the spindle being coupled to the drive member by means of a lost-motion coupling allowing a predetermined amount of rotation of the drive member before there is corresponding rotation of the spindle.

Preferably the lost-motion coupling allows at least 3 degrees of lost motion.

This invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a sectional view of a sensor according to the invention in a vehicle with a manual gear box; and Figure 2 is a sectional view of a sensor according to the invention in a vehicle with an automatic gear box; and Figures 3 and 4 show details of the sensor of Fig. 2.

The same reference numerals are used whenever possible for corresponding parts throughout the drawings.

The sensor of Fig. 1 comprises a housing H formed of a lower steel body 1 secured as by plastics or ultrasonic welding to an upper plastics material cap. The body 1 contains a vertical bore 3 which receives part of a spindle SM which comprises a series of portions of different diameter. The lowermost portion S1 of the spindle is formed with flats F which engage a drive gear D formed of Nylon or the like. The portion S1 of the spindle is received in the gear D as a loose fit and is retained therein in the vertical direction by means of a generally U shaped clip C. A wider diameter portion S2 which extends from the portion S1 is received with clearance in the bore 3, and leads to a reduced diameter portion S3 there being an intervening shoulder 4.The portion S3 is received in a bronze bush 5 received in fixed manner in the bore 3 such that the spindle SM can rotate in the bush 5 relative to the housing H. A bowed spring steel washer 10 acts between the shoulder 4 and the adjacent end of the bush 5 to urge the spindle downwardly, as seen in the drawing, relative to the body 1.

Above the bush 5 is a washer W formed of a material adapted to provide static friction, and above the washer W is a multi-pole magnet M, having say 16 poles. The upper end portion S4 of the spindle extends through the washer W and the magnet M and the upper end of the spindle is held to the magnet by a clip 6. A printed circuit board P incorporating a Hall effect transducer 8 and other required electrical components, is present within the cap 2 and is electrically connected to a fuel control unit, not shown. In use of the sensor the gear D is engaged with a vehicle's gear box, and with the vehicle moving and the gears in motion, the spindle is rotated by the drive gear D. The rotating magnet M then causes the Hall effect transducer 8 to generate an output pulse control signal which is supplied to the vehicle's fuel control unit.

When the vehicle stops but with the engine idling, the spindle SM is constrained from rotation by the static friction between the washer W and the adjacent end of the bush 5 introduced by the positive end thrust provided by the spring washer 10. As a result, the -spindle SM will not rotate until a predetermined level of force is applied, this level not occuring due to vibration of the engine or vehicle, so that no matter where the spindle SM comes to rest relative to the poles of the magnet M when the vehicle stops the sensor will not give an output signal until the vehicle moves again and the drive gear D and with it the spindle SM are positively driven by the vehicle's gear box.

The embodiment of Figs. 2, 3 and 4, is for use with a vehicle with an automatic gear box, not shown. The body 1 is extended to be received within the gear box, and has a lower bore 11 which receives a drive quill O of generally square section and having paddles 9 at its upper end. The head of the quill Q is freely received in a socket 12 at the lower end of the spindle SA. The upper end portion S6 of the spindle SA stands proud of the magnet M and is contacted by a thrust pad T held between depending walls 16 by a spring 14 to the underside of the cap 2. The spring is held in position by barbs 15 struck from the spring 14, see Fig. 4.This arrangement replaces the spring washer 10 of Fig. 1, and provides positive end thrust which serves to urge the magnet M into contact with the washer W, and this in turn with the end of the bush 5, to provide the rotation preventing forces as in the embodiment of Fig. 1.

When the vehicle is in motion the quill O is rotated and the spindle SA rotates therewith.

As shown in Fig. 3, the lower end of the spindle SA is formed with a pair of perpendicular slots 17 in which the paddles 9 or the quill Q are received with clearance, this forming a lost-motion coupling between the quill O and the spindle SA such that there must be at least 3 degrees of rotation of the quill O before there is corresponding rotation of the spindle SA.

The thrust pad T under the action of the spring 14, exerts a downward force to urge the magnet M into engagement with the washer W, and the friction force provided thereby further prevents unwanted rotation of the spindle SA under vibration and rocking of the vehicle when stationary with the engine running and thus prevents the supply of spurious control signals by the transducer 8 to the vehicle's fuel supply control unit.

From the above description it can be seen that in both of the embodiments of sensor described frictional forces provided by the washer W being compressed between the magnet M and the adjacent end of the bush 5 by the spring means provided, ie the spring washer 10 or spring 14, provide a force resisting rotation of the spindle carrying the magnet, which must be overcome before there can be such rotation. Thus, unwanted rotation of the spindle such as might be caused by vibration of the vehicle on which the sensor is used when at rest is prevented, and thus no spurious output signals are supplied to the vehicle's fuel supply control unit.

In the embodiment of Figs. 2, 3 and 4 of the drawings this prevention of the production of spurious output signals is assisted by the lostmotion coupling between the quill 0 and the spindle SA, thus allowing the quill O to vibrate and rotate a small amount without any rotation of the spindle SA, held by the washer W, being caused.

Claims

1. A vehicle road speed sensor comprising a body (1, 2); a spindle (SM; SA) mounted in the body (1, 2) for rotation relative thereto about its longitudinal axis; and a transducer (8) carried by the body (1, 2) in fixed relationship to the spindle (SM;SA), the arrangement being such that rotation of the spindle (SM;SA) relative to the body (1, 2) and the transducer (8) produces an output pulse signal from the transducer (8) the spindle (SM; SA) being rotated during use of the sensor on a vehicle at a speed dependent upon the vehicle road speed, characterised by means (W) acting to prevent rotation of the spindle (SM;SA) relative to the body (1,2) by forces tending to cause such rotation, below a predetermined value.

2. A sensor as claimed in Claim 1, characterised in that said rotation preventing means (W) comprises means providing a frictional force acting between the body (1, 2) and the spindle (SM; SA).

3. A sensor as claimed in Claim 2 characterised in that the spindle (SM;SA) carries a multi-headed member (M) arranged such that during rotation of the spindle (SM;SA) the heads of the member (M) successively pass the transducer (8), the rotation preventing means comprising a friction-providing washer (W) acting between the member (M) and the body (1,2).

4. A sensor as claimed in Claim 3, characterised in that the spindle (SM;SA) is mounted in the body (1,2) in a bush (5), the washer (W) acting between the member (M) and an end face of the bush (5).

5. A sensor as claimed in Claim 3 and Claim 4, characterised by a spring member (10 or 14) acting between the spindle (SM;SA) and the body (1,2) and serving to compress the washer (W) between the member (M) and the body (1,2).

6. A sensor as claimed in Class 3, Claim 4 and Claim 5, characterised in that the multiheaded member (M) is a multi-pole magnet.

7. A sensor as claimed in Claim 3, Claim 4 and Claim 5, characterised in that the multiheaded member is a ferro-magnetic material member, the transducer (8) comprising a magnet.

8. A sensor as claimed in any preceding claim, characterised in that the spindle (SA) is arranged to be rotated, in use of the sensor, by a drive member (Q) carried by the body (1, 2) and driven by the vehicle, the spindle (SA) being coupled to the drive member (0) by means of a lost-motion coupling (17, 19) allowing a predetermined amount of rotation of the drive member (Q) before there is corresponding rotation of the spindle (SA).

9. A sensor as claimed in any preceding claim, characterised in that the body (1) is of metal, the transducer (8) being carried by a non-metal cap (2) secured to the body (1).

10. A sensor as claimed in any preceding claim, characterised in that the spindle (SM; SA) is arranged to be rotated by connection to a vehicle gear box.

11. A vehicle road speed sensor substantially as hereinbefore described with reference to Fig. 1 or Figs. 2, 3 and 4 of the drawings.