GB2236857A

GB2236857A - Velocity change sensor

Info

Publication number: GB2236857A
Application number: GB9021698A
Authority: GB
Inventors: Allen K Breed; Ted Thuen
Original assignee: Breed Automotive Technology Inc
Current assignee: Breed Automotive Technology Inc
Priority date: 1989-10-06
Filing date: 1990-10-05
Publication date: 1991-04-17
Also published as: IT1241712B; JPH03134927A; SE9001951L; GB9021698D0; CA2026921A1; IT9067750A0; DE4031329A1; FR2652906A1; SE9001951D0; IT9067750A1

Abstract

A sensor 10 for activating a passenger restraint system 140 in a motor vehicle includes a housing 12 with a passage 14 for defining a path of movement, and an inertial element 18 moving in that path. A mechanical member 18 (or a magnetic member 134) is used to bias the inertial element 16 (or 118) toward a preset position. The preset position is defined by a presetting member 22 which is adjustable so that the accelerometer is responsive to crashes with a tolerance of +/- 0.5 m/s. As the inertial element moves away from the preset position in a crash, it closes an electrical contact 18 and 20 for deploying the passenger restraint system. <IMAGE>

Description

:2 2 E5 E5 -7 "Improvements in and relating to velocity change sensorst'

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 close an electrical contact.

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 balloon, 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 vexy 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.

The accuracy of the sensor described in U.S. Patent No. 4,329,549 depends on the proper alignment of the two electrical contact blades. The sensitivity, that is to say, the minimum deceleration that sets off the sensor, is determined by the strength of the magnet and the initial position of the ball. It has been found that, because of variations in dimensions of the sensor during the manufacturing process, the sensor has a tolerance of about 2 mph (1 m/s). In practice this tolerance is not acceptable in the industry because if the sensor triggers at a deceleration which is too low, a restraint bag may be triggered when the car is not involved in a crash (for example, at 8 MPH (3.5 m/s), causing the driver to lose control over the motor vehicle. If the bag is set to trigger only when the vehicle experiences a very high deceleration, corresponding to a crash at above, say, 12 MPH (5 m/s), it may not go off on actual crash, and would fail in its function of protecting the passengers.

- The invention provides an accelerometer for sensing velocity changes, comprising: a housing defining within it a path of movement; an inertial element disposed within the housing and movable along the said path; biasing means for biasing the inertial element towards a first position; and preset means adjustable for changing the said first position of the inertial element.

It is possible to construct a restraint system according to the present invention, in which the sensitivity time, that is to say, the deceleration at which the bag restraint system is deployed, can be preset to an accurate value.

It is also possible to provide a restraint system with a velocity sensor in which a moving element has a presettable initial position for a reduced tolerance.

It is further possible to provide a sensor that is easy and inexpensive to manufacture, and in which critical elements need not be made with high precision because the sensitivity of the sensor can be adjusted for each unit after assembly.

An accelerometer constructed in accordance with the invention may include a housing with contact blades and a contacting element which provides an electrical path between the blades when a deceleration above a threshold level is sensed. An adjusting means may also be provided for presetting the position of the element. This presetting adjusting means is adjusted after the assembly of the sensor to compensate for diminished variations of its components as well as for variations in the field strength of the magnet, if any. With this feature, it has been found that sensors can be made which can be adjusted to trigger a section of the bag system in response to a crash of a given velocity, when said sensor may be preset at an accuracy of + 1 mph (0.5m/s).

Various forms of accelerometer constructed in accordance with the present 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 a first form of accelerometer disposed in a case; Figure 2 is a fragmentary side cross-sectional view of a modified form of the accelerometer shown in Figure 1; and Figure 3 is a cross-sectional view of a second form of accelerometer.

Referring to the accompanying drawings, and initially to Figure 1, one form of sensor 10 constructed F in accordance with the invention is similar to the sensor described in more detail in our co-pending patent application no. Grft902- I'7U.1 (case no. 1247-48) and it consists of a housing 12 with an interior chamber 14 holding a ball 16. The chamber 14 defines a movement path for the ball 16 between a first end wall 24 and a second end wall 26 of the chamber, and a spring blade 18 is used to bias the ball and hold it in abutment with the first end wall 24, as shown in Figure 1. The sensor is positioned in a motor vehicle so that if the vehicle crashes at or above a preselected minimum speed the ball, under the influence of the deceleration resulting from the crash, overcomes the biasing force of the spring blade 18 and starts moving along the path defined by the chamber 14 toward the opposite end wall 26. As the ball moves along its path, it pivots the spring blade 18. When the spring blade 18 hits a second blade 20, an electrical contact is made which is used to generate an electrical signal to a control means for triggering a passenger restraint system such as an air bag (not shown).

An important feature of the sensor 10 is the provision of a preset screw 22 threaded into and extending through the first end wall 24, with its head 28 disposed outside the housing 12, and with its tip 30 being in contact with the ball 16 in the rest position of the ball,, as shown in Figure 1.

The response of the sensor depends on a number of factors including the weight of the ball 16, the dimensions of the sensor, the spring constant of the blade 18 and so on. By varying these parameters, the sensor can be built to sense and respond to a preset deceleration. For example, the parameters may be selected so that the sensor activates the passenger restraint system when a crash is sensed at a nominal speed of 10 MPH (4.5 m/s). However, because of variations in those parameters which occur during the manufacturing process, the sensor has a characteristic error or tolerance of 2 MPH (1 m/s). As previously mentioned, that tolerance may be unacceptable. However, it has been discovered that in a sensor constructed in accordance with the present invention that tolerance can be reduced considerably. More particularly, the rest position of the ball 16 may be adjusted with the preset screw 22. Advancing the screw causes the ball to move slightly away from the end wall 24. Retracting the screw 22 out of the housing 12 causes the ball 16 to move slightly closer to the wall 24. In that manner the preset velocity of the sensor, that is to say, the velocity at which a crash will cause the sensor to activate a passenger restraint system, may be preset with an accuracy or tolerance of 1 MPH (0.5 m/s).

In the sensor shown in Figure 1, the tip 30 of the preset screw 22 abuts the ball 16 directly. In order to increase the contact area between the screw and the ball, 1 a disk 32 may be attached to the screw tip 30, as shown in Figure 2. In that manner the amount of wear and tear between the screw 22 and the ball 16 is reduced considerably. The disk 32 is even more effective if it is so attached to the screw 22 that the screw can rotate relative to the disk.

A different type of sensor 110 is shown in Figure 3. That sensor, is similar to the sensor described in U.S. Patent No. 4,329,549, and has a housing 112 with an interior shell 114 made of magnetically permeable material. The housing 112 has two opposed end walls 124 and 126. One end wall 126 holds two blades 118 and 120 whicb in this configuration have similar shapes and sizes. A permanent magnet 134 is disposed outside the housing 112. Within the housing 112 there is also a ball 116 having a diameter slightly smaller than the internal diameter of the shell 114. The ball is also made of a magnetically permeable material. The shell 114, the ball 116, and the magnet 134 are constructed and arranged so that the magnetic field generated by the magnet biases the ball to the rest position shown in Figure 3. An adjusting screw 122 is threaded into a bore in the other end wall 124, and the ball 116 in its rest position is held against the tip of the screw 122 by the attraction of the magnet 134. The sensor is disposed in a motor vehicle in such a manner that, in a crash at a speed above a preselected level, the ball 116 moves towards the said one end wall 126. When the ball 116 contacts the blades 118 and 120, an electrical signal is generated by well known means in the art. The signal is sent, for example on wires 136 and 138, to a passenger restraint system 140 for activating it. Again, without the preset screw 122, the sensor would have a toterance of about 2 MPH (I m/s). That tolerance can be reduced to about 1 MPH (0.5 m/s) by adjusting the screw 122 to move the ball 116 either towards or away from the other end wall 124.

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Claims

Claims:

1. An accelerometer for sensing velocity changes, comprising: a housing defining within it a path of movement; an inertial element disposed within the housing and movable along the said path; biasing means for biasing the inertial element towards a first position; and preset means adjustable for changing the first said position of the inertial element.

2. An accelerometer as claimed in claim 1,. wherein the biasing means comprises spring means.

3. An accelerometer as claimed in claim 1, wherein the inertial element is made of magnetically permeable material and the biasing means comprises means for generating a magnetic field.

4. An adcelerometer as claimed in claim 3, wherein the biasing means comprises a permanent magnet arranged and constructed to generate a magnetic field for biasing said ball.

5. An accelerometer as claimed in claim 3 or claim 4, wherein the housing includes a cylindrical sleeve having an internal diameter substantially equal to the diameter of the inertial element, and wherein the sleeve is made of magnetically permeable material.

6. An accelerometer as claimed in any one of claims 1 to 5, wherein the preset means comprises a preset screw extending from the housing into the said path,

7. An accelerometer as claimed in any one of claims - 10 1 to 6, which comprises contact means disposed on the said path at a second position at a predetermined distance from the said first position,, which contact means are arranged to sense when the inertial element has moved to the second position.

8. An accelerometer as claimed in any one of claims 1 to 7, wherein the inertial element comprises a ball.

9. An accelerometer substantially as hereinbefore described with reference to, and as shown in, Figure 1, or Figures 1 and 2, or Figure 3 of the accompanying drawings.

10. A passenger restraint assembly for protecting one or more passengers in a motor vehicle in a crash, comprising a passenger restraint device, and an accelerometer as claimed in any one of claims 1 to 9 arranged in use to activate the passenger restraint device.

11. A vehicle equipped with at least one passenger restraint assembly as claimed in claim 10.

Published 1991 2tfbe Patent Office. State House. 66/71 High Holborn. LondonWCIR47P. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.

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