GB2236621A

GB2236621A - Velocity change sensors

Info

Publication number: GB2236621A
Application number: GB9021740A
Authority: GB
Inventors: Allen K Breed; Ted Thuen; Carl T Grossi
Original assignee: Breed Automotive Technology Inc
Current assignee: Breed Automotive Technology Inc
Priority date: 1989-10-06
Filing date: 1990-10-05
Publication date: 1991-04-10
Anticipated expiration: 2010-10-05
Also published as: GB2236621B; FR2653590A1; DE4031327A1; FR2653590B1; GB9021740D0

Abstract

An accelerometer for sensing velocity changes particularly suited for passenger restraint systems in a motor vehicle for the deployment of an air bag includes a housing 22 containing first 50, 52 and second 48, 46 contact blades and a magnetically biased sensing element 34. The sensing element 34 is arranged to move toward the contact blades when a deceleration exceeding a threshold level is sensed to cause direct contact between the first and second contact blades, thereby deploying the restraint system. One of the contact blades has an insulating coating 62, 64 for insulating it from the sensing element 34. Two contact sets 46, 52 and 48, 50 may be operated by the sensing element 34. <IMAGE>

Description

nImprovements in and relating to velocity change sensors" The invention

relates to a velocity change sensor or accelerometer, and especially to such a sensor used in motor vehicles for detecting sudden changes in velocity and for activating in response a passenger restraining device such as an air bag, which device includes an element that moves to a preset position in response to a sudden deceleration to touch a pair of contact blades.

Studies have been made which indicate that injuries in motor vehicle accidents, especially at high speeds, can be substantially reduced or eliminated by the use of passenger restraint systems. The term "passenger" denotes any person carried by the vehicle, and thus includes the driver. These systems include an inflatable balloonp usually termed an air bag, which is normally stored away in the instrument panel or the steering wheel. When the motor vehicle is subjected to a sudden deceleration, the air bag is inflated and is deployed automatically in a position which cushions the passengers, restrains their movement and prevents contact between them and parts of the automobile interior such as the windscreen, the steering wheel, the instrument panel, and so on. of course, a crucial element of all such systems is the velocity change sensor or accelerometer which initiates the inflation and deployment of the air bags. The motion of the motor vehicle must be carefully and precisely monitored so that the air bags can be deployed very fast, 2 before the passengers suffer any substantial injury.

A velocity change sensor is disclosed in our U.S. Patent No. 4,329,549. That sensor comprises a tubular housing surrounding a metallic shell, a metal ball and a magnet biasing the ball toward a first end of the shell. At the second end of the shell there are a pair of electrical contact blades. The sensor is positioned in the motor vehicle in an orientation such that when the motor vehicle experiences a deceleration which exceeds a preset level, the ball moves from the first toward the second end, making contact with the two blades. Because the blades and the ball are made of an electrically conducting material, when the ball contacts the blades an electrical path is established between the two blades. This electrical path is used to initiate a signal for the deployment of the air bags.

One problem with the device shown in US 4,329,549 is that the electrical contact is made through the ball, and since the contact points are indeterminate the whole surface of the ball must be treated to produce a low resistance electrical path. For example, the ball is often coated with a thin layer of gold or similarly highly conductive material. However, this process is expensive and time consuming. Furthermore, the conductive layer may wear off as the ball moves along its path.

The invention provides an accelerometer comprising: a housing; first and second contact means disposed within the 3 housing; and contact-closing means arranged to cause direct electrical contact between the first and second contact means when the accelerometer is subjected to an acceleration exceeding a threshold level.

The contact means may comprise a pair of contact blades disposed at one end of the housing, and the contactclosing means a sensing element biased towards the other end of the housing. The sensing element, which is advantageously a ball, is then arranged to move towards the contact blades when the accelerometer is subjected to an acceleration that overcomes the bias, and then advantageously comes into contact with one contact blade and deflects it into contact with the other. The said one contact blade is preferably provided with insulation to prevent any electrical path's being established through the ball, and the accelerometer may then include two pairs of contact blades that are brought into contact by a single sensing ball.

It is possible in accordance with the present invention to provide a restraint system in which, in response to a crash, an electrical path is completed which does not pass through the inertial or moving element of the sensor.

It is also possible to provide a restraint system with a velocity sensor in which an inertial moving element causes a contact between two electrical contact blades substantially simultaneously.

one form of accelerometer constructed in accordance with the invention includes a housing with at least one pair of contact blades; and an element moving in a predetermined path in response to a change in velocity of the motor vehicle. The two contact blades are disposed in the path of the moving element in such a manner that a direct electrical path is established as a result of the contact by the ball. The contact is arranged so that the electrical path does not pass through the movirg element itself, thereby reducing costs.

One form of accelerometer constructed in accordance with the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a side elevation view of an accelerometer; Figure 2 is a cross-section taken along the line 2-2 of Figure 1, to a larger scale than Figure 1; Figure 3 is a cross-section taken along the line 3-3 of Figure 2; and Figure 4 is a side view similar to part of Figure 2, with electrical contact blades in a closed position.

Referring to the drawings, one form of accelerometer or velocity change sensor, indicated generally by the reference number 10. according to the invention is usually mounted on a motor vehicle (not shown). The sensor 10 is connected by a cable 14, including at least two conductors 16 and 18, to a control device for the deployment of one or more air bags.

The sensor 10 has a tubular body 20 disposed in a housing 22 and having at one end a portion 24 of reduced diameter terminating in an end wall 26. An extension 28 projects outwardly from the end wall 26 as shown, to hold an annular permanent magnet 30. The reduced portion 24 contains a metal ball 34 which is slidably disposed within a metallic sleeve 32, at one end of a passageway 40 that extends along the centre of the body 20.

The body 20 is terminated, at the other end from the extension 28, with an axially disposed cap 44. The cap 44 may be attached to the body 20 by any well known means, such as with an adhesive, or by sonic welding. Mounted on the cap 44 there are four blades 46, 48, 50 and 52. For the sake of convenience, blades 46 and 48 shall be referred to as the lower blades while blades 50 and 52 shall be referred to as the upper blades. Each of these blades is secured to the cap 44 by a pin 56 or other similar means known in the art, and is made of a relatively thin and flat piece of conductive material such as copper. The blades are formed into U- shapes as shown in Figure 2, with a curved portion near the outside of the body 20 and a free end portion extending radially inwards between the metal ball 34 and the cap 44. The lower blades 46 and 48 are terminated at their upper portions with respective curved sections 58 and 60 convex towards the upper blades 50 and 52, as shown in Figure 2. The upper blades 50 and 52 extend further radially inward into the passageway 40 and their tips are preferably coated with an insulating material 62 6 and 64, such as a plastics material. Disposed within the body 20, there is a plurality of ribs 66, 68, 70, 72 for biasing the blades to the positions shown in Figure 2.

Preferably, each of the blades is split into two parallel sections for the sake of redundancy. For exampler in Figure 3 the blade 50 is shown with two parallel sections 501 and 5011 each terminating with an insulating material 64. The blade 52 is similarly split into parallel sections 52t and 5299.

A space 74 is provided between the body 20 and the housing 22, outside the cap 44, for holding other electronic parts mounted, for example, on a printed circuit board 76.

The sensor 10 operates in the following manner. The permanent magnet 30 generates a magnetic field, and the sleeve 32 and the ball 34 are made of a magnetically permeable material. The sleeve is arranged and constructed to bias the ball against the end wall 26, as shown in Figure 2. The sensor is positioned within a motor vehicle (for example, in the engine compartment or the passenger compartment) in such an orientation that, if the vehicle experiences a declaration, the ball 34 is urged relative to the housing 22 in the direction indicated by arrow A in Figure 2. away from the end wall 26 and towards the cap 44. If the deceleration is greater than a preselected threshold level (defined, for example, by the dimensions of the sensor and the strength of the field generated by the

7 magnet) the force needed to decelerate the ball 34 at the same rate as the housing 22 is greater than the force of the magnetic field and the ball 34 is projected. relative to the decelerating housing 22, in the direction A along the passageway 40. As the ball moves through the passageway, it comes into contact (relatively simultaneously) with the tips of the upper blades 50 and 52. Since those tips are insulated, no electrical contact is made at that time. The ball keeps moving in the direction A, bending the blades 50 and 52 in the same direction, until those blades come into contact with the curved sections 58 and 60 of the lower blades 46 and 48. as shown in Figure 4. That contact forms an electrical path between the blades 48 and 50 and another, separate, electrical path between the blades 46 and 52. Those completed electrical paths may be used to. generate an electrical signal which may be sent, for example, on the conductors 14 and 16 to a passenger restraint apparatus 80 such an air bag assembly (not shown) for the deployment of the passenger restraints.

claims:

1. An accelerometer comprising: a housing; first and second contact means disposed within the housing; and contact-closing means arranged to cause direct electrical contact between the first and second contact means when the accelerometer is subjected to an acceleration exceeding a threshold level.

2. An accelerometer as claimed in claim 1, wherein the contact-closing means comprises a sensing element movably disposed in the housing; and biasing means for generating a biasing force on the sensing element urging the sensing element towards a first position, the sensing element being constructed and arranged to move towards a second position away from the said first position in response to a deceleration force exceeding the said biasing force to cause the said direct electrical contact.

3. An accelerometer as claimed in claim 2, wherein in operation the sensing element comes into operative engagement with the contact means only when it has moved away from the first position.

4. An accelerometer as claimed in claim 2 or claim 3, wherein one of the sensing element and the said contact means is provided with an insulating coating to prevent an electrical path through the sensing element.

5. An accelerometer as claimed in any one of claims 2 to 4, wherein the biasing means is magnetic biasing means.

6. An accelerometer as claimed in claim 5, wherein the 9 magnetic biasing means comprises a permanent magnet.

7. An accelerometer as claimed in claim 5 or claim 6. wherein the biasing means comprises a conductive sleeve disposed inside the housing for applying magnetic force to the sensing element.

8. An accelerometer as claimed in any one of claims 2 to 7, wherein the sensing element comprises a ball.

9. An accelerometer as claimed in any one of claims 2 to 8, wherein the first and second contact means comprises contact blades.

10. An accelerometer as claimed in claim 9, wherein each of the said first and second contact means comprises a pair of contact blades.

11. An accelerometer as claimed in claim 10, comprising a first pair of blades disposed in the path of the sensing element and a second pair of blades spaced away from the said first pair, and wherein in operation the first pair of blades are bent by the sensing element to form two electrical paths through the second pair of blades.

12. An accelerometer as claimed in any one of claims 9 to 11, wherein said contact blades have an insulated coating for insulating the blades electrically from the sensing element.

13. An accelerometer as claimed in any one of claims 1 to 12, which comprises two said first contact means and two said second contact means, and wherein the contact-closing means is arranged to cause direct electrical contact between each first contact means and a respective one of the second contact means.

14. An accelerometer as claimed in any one of claims 1 to 13, wherein the housing is cylindrical.

15. An accelerometer as claimed in any one of claims 1 to 14, wherein the housing has a first end and a second end opposite the first end; and the first and second contact means are disposed at the first end of the housing.

16. An accelerometer substantially as hereinbefore described with reference to. and as shown in, the accompanying drawings.

17. A passenger restraint system for a motor vehicle comprising: at least one air bag disposed in the motor vehicle; a control unit for selectively deploying the said air bag in the motor vehicle for protecting a passenger in a crash; and an accelerometer as claimed in any one of claims 1 to 16 for sensing a velocity change of the motor vehicle coupled to the control unit.

18. A passenger restraint system as claimed in claim 17, wherein the housing is arranged in a housing position in which the contact-closing means is urged towards operative engagement with the contact means when the motor vehicle is decelerated from motion forwards.

19. A motor vehicle equipped with at least one passenger restraint system as claimed in claim 17 or claim 18.

Published 1991 at The %tent Office. State House. 66171 High Holborn. London WC] R 4TP. Further copies maybe obtained frorn Sales Branch. Unit 6. Nine Mile Fbint. Cwmfelinfach. Cross Keys. Newport, NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.