WO1990010301A1

WO1990010301A1 - Short-travel mechanical crash sensor

Info

Publication number: WO1990010301A1
Application number: PCT/US1990/000892
Authority: WO
Inventors: David S. Breed
Original assignee: Automotive Technologies International, Inc.
Priority date: 1989-02-21
Filing date: 1990-02-21
Publication date: 1990-09-07

Abstract

This invention relates to a new class of the design of mechanical crash-detecting sensors. A sensing mass (65, 14, 84) is biased by a spring (63), a diaphragm (13) or one or more cantilever beams (81) with a relatively high biasing force. Air damping is provided by inertial or viscous flow caused by the travel of the sensing mass. The travel of the sensing mass to trigger in this invention is typically 0.05 inch, which is much shorter than those of conventional mechanical crush-zone sensors. This invention also provides a new to increase the duration of contact closure once a sensor (10) has triggered. These improvements can enhance the effectiveness of mechanical sensors, and thus provide a simple reliable sensing device for activating occupant restraint systems.

Description

SHORT-TRAVEL MECHANICAL CRASH SENSOR

BACKGROUND OF THE INVENTION

Sensors or crash detectors used in inflatable restraint systems can be separated into mechanical or electronic types according to the integration method of a crash pulse. Mechanical sensors usually involve the motion of a sensing mass. For example, in conventional ball-in-tube crash sensors, a ball inside a cylinder is kept in its initial position by a biasing force until the deceleration experienced in a crash is greater than the bias. If deceleration is of enough magnitude and duration, the ball will travel towards a designed position and close a circuit or- initiate a mechanism to operate an air bag system. In electronic sensors, the deceleration sensed by an accelerometer 'is transformed into an electrical signal and then integrated by an electronic circuit. Since the integration of a pulse in electronic sensors requires only a very short travel of a sensing mass, electronic sensors respond consistently faster than mechanical sensors. in electronic sensors, a sensing element typically moves only 0.005 inch, while in mechanical sensors a sensing mass usually moves 0.1 inch or more. In cases of vigorous pulses, this can add five to ten milliseconds to sensor triggering time, and thus delay the air bag deployment by five to ten milliseconds. Therefore, it is desirable to minimize the travel distance of the sensing mass for a mechanical sensor.

Current crush zone sensors, either air-damped sensors or spring- mass type sensors, have a common problem of maintaining a long duration of closure once the sensors are triggered. This creates an unreliable situation if simultaneous closure or overlapping of more than one sensor is required to operate the inflatable system in an accident when an air bag deployment is needed. Typically, this can happen when the sensing mass in a crush-zone sensor bounces off the closed position after an early closure while a safing sensor in the non-crush-zone does not close until later in a crash. If the crush-zone sensor does not close again while the safing sensor remains closed, there will be no air bag deployment and no protection for the occupant. If the crush-zone seiisor does close again later in the crash, however, the air bag deployment may be too late and thus cause injuries to out-of-position occupants. It is necessary, therefore, to solve the aforementioned problem by increasing the duration of closure especially for crush-zone sensors.

Ball-in-tube crash sensors utilize air, flowing through a diametrical clearance between a ball and a cylinder, to provide damping to the motion of the ball (sensing mass) . However, due to the existence of this diametrical clearance, under certain excitations the ball not only rolls longitudinally along the cylinder but also orbits and spins inside the cylinder. The whirling and spinning cross-axis motions are likely to happen when vertical and lateral accelerations have comparable magnitudes with the longitudinal pulse, especially in the crush-zone of a vehicle. These cross-axis motions sometimes increase the time needed for the ball to travel longitudinally to trigger, or sometimes prevent the ball from travelling long enough to trigger. These phenomena are verified by recent studies and crash tests. Consequently, these cross-axis problems result in late-fire or even a no-fire condition in crashes where there should have been an in-time deployment of an air bag to protect the occupant.

Current crash sensors are sensitive to temperature changes. For example, the clearance in ball-in-tube sensors varies with temperature changes. This variation, coupled with the change of air viscosity, gives a sensor a different sensitivity level according to the ambient temperature. If a sensor can perform more uniformly in a prescribed range of temperature, it can make the design of a sensing system easier and more reliable. With this new invention, since the travel of the sensing mass is shortened, the temperature effect can be reduced by adjusting the travel distance to compensate variations in viscosity and other dimensions.

Air-damped, low-bias ball-in-tube sensors are generally known to have a "flat" response curve with respect to pulse duration, which means that a sensor is triggered by an approximately same velocity change of pulses for short or long duration. This creates a potential problem in some crashes, in which the prescribed velocity change occurs late in a crash so that an occupant has moved forward into the way of a deploying air bag. The deploying air bag in this case may cause unexpected injuries to the out-of-position occupant, while the occupant may not be injured as much in the accident without an air bag. For these marginal crashes, it is important for a sensor to discriminate the pulses and not to trigger to avoid unexpected injuries.

It is the purpose of this invention to design a mechanical sensor to overcome the above limitations of mechanical crash detectors.

SUMMARY OP THE INVENTION

A principal object of this invention is to provide an effective mechanical crash sensor with a short travel distance of the sensing mass.

Another object of this invention is to provide a long duration of closure of a sensor to improve the performance of a sensing system.

A further object of this invention is to provide a new design of crash sensor without the cross-axis problems of conventional mechanical sensors. An additional object of this invention is to avoid late-firing of sensors in marginal crashes where a out-of-position occupant will be injured by a deploying air bag.

Another object of this invention is to provide a temperature compensation method to make mechanical sensors less sensitive to temperature variations.

A further object of this invention is to provide a new sensor design, which is inexpensive and easy to manufacture.

Other objects and advantages of this invention will become apparent from descriptions of the preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross sectional view of a diaphragm sensor.

Figure 2 illustrates an annular diaphragm used in a sensor.

Figure 3 shows the assembly of a sensing mass, a flapper valve, and a diaphragm in their separated position.

Figure 4 is another embodiment of a crash sensor, consisting of a diaphragm with slots, thin films for sealing the diaphragm, a sensing mass, a flapper valve, and orifices on the sensing mass.

Figure 5 shows the flapper valve and orifices of a sensor depicted in FIG. 4.

Figure 6 is a side cross section view of a crash sensor with a sharp edge disk, which is supported by multiple cantilever beams.

Figure 7 is the back view of the disk and cantilever beams of the sensor in FIG. 6.

Figure 8 is another embodiment of a sensor with a sharp edge disk using a spring for biasing.

Figure 9 shows a sensor similar to Figure 8, with the sharp edge disk replaced by a disk with arc-edge.

Figure 10 is another invention of a crash sensor, consisting of a sharp-edge disk supported by a single cantilever beam, a sensing mass, and dual contacts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, sensor 10 is fixed to a vehicle with its axis 101 parallel to a prescribed direction. For example, to detect a frontal impact, axis 101 can be aligned with the longitudinal direction of a vehicle, and arrow A points to the front of the vehicle. Sensor 10 is assembled by joining a left casing 11 and a right casing 12 by any methods such as gluing, ultrasonic welding, heat sealing, etc.. The outside shape of sensor 10 is a short cylinder, about 2 inches in diameter and 0.7 inch in thickness. An inner chamber is formed by a bore 111 inside casings 11 and 12. A diaphragm 13, with its periphery clamped between elements 11 and 12, holds a sensing mass 14 and a flapper valve 15 in its center. Sensing mass 14 is constructed of two tightly-fit pieces 16 and 17. These two pieces and flapper valve 15 are coupled with diaphragm 13 by pushing 16 and 17 into each other through a center hole in diaphragm 13. If sensing mass 14 travels a prescribed distance to the left, contact 18 with one end attached to the left casing 11 is pushed to close an electrical circuit with contact 19. Contact 19 is electrically insulated from casing 11 by a thin plate 20 made of insulating materials, such as plastic, film board or others.

FIG. 2 shows diaphragm 13 and valve 15 separated from the other elements of the sensor in a horizontal position. The diaphragm 13 is about two inches in diameter with a circular hole 131 in the center. Eight slit openings 132 are cut from the inner hole 131 and extended to about 0.05 inch inside the outside perimeter 133. Valve 15 has eight extended wings 151 covering half-distance of opening slits 132.

Diameter of the inner hole of valve 15 is the same as that of hole 131.

In FIG. 3, sensing mass element 16 has an extended short shaft 161, which is machined to fit tightly within a bore 171 of sensing mass element 17. In assembly, flapper valve 15 is arranged so that its wings 151 are aligned with opening slits 132 of diaphragm 13. These four components are coupled together by pushing shaft 161 into bore 171 through the center hole 131 of diaphragm 13. Notice that in a complete assembly of the sensor 10 shown in FIG. 1, flapper valve 15 is located on the right side of diaphragm 13, while contact 18 is located on the other side of diaphragm 13.

In an initial, non-operating position of sensor 10 in FIG. 1, diaphragm 13 is in its equilibrium position and element 17 of sensing mass 14 rests on the inner surface 121 of right casing 12. When a crash pulse occurs, sensing mass 14 tends to travel to the left in FIG. 1. Due to the opening slits of diaphragm 13, sensing mass 14 is allowed to travel a significant distance without causing material yield of diaphragm 13. As diaphragm 13 is deformed, pressure in front of diaphragm 13 becomes higher than the other side of diaphragm 13, so air flows from the left side of diaphragm 13 to the right side through slit openings on diaphragm 13 and provides damping effects on the motion of sensing mass 14. ings 151 of flapper valve 15, which is made of flexible material such as thin plastic, gradually opens and enlarges the opening area of slits 132 as sensing mass 14 moves further to the left^* and deforms diaphragm 13 more. The opening of flapper valve 15 is mainly caused by the air flow from the left side of diaphragm 13 to the right side. If the crash pulse is of enough magnitude and duration, sensing mass travels a distance of approximately 0.05 inch and closes contacts 18 and 19.

If the motion of sensing mass starts to reverse in the other direction, the air flow also reverses its direction and thus forces the flapper valve 15 to close on the diaphragm 13. This will result in the reduction of opening area by half. The damping effect or the resistance caused by air flow consequently increases. If sensing mass 14 is in a position that closes contacts 18 and 19, this increase in damping can slow down the reverse motion and produces a longer duration of contact closure or dwell.

In the above preferred embodiment, the sensing mass is made of stainless steel. The travel distance of the sensing mass is 0.05 inch. The diaphragm is made of beryllium-copper and is [0.004] in thickness. The diaphragm exerts an average biasing force of 8 G's on the sensing mass. The flapper valve is made of Acetate and is 0.003 inch thick. The sensor is about 2 inches in diameter and 0.7 inch in thickness.

Another embodiment of this invention is shown in FIG. 4. The openings on a diaphragm 30 are covered by flexible thin films 31 on both sides so that air is not allowed to flow through diaphragm 30. Instead, orifices 32 are located on the sensing mass 33 to let air flow through. FIG. 5 illustrates a view from the back side of diaphragm 30 shown in FIG. 4. Part of the orifice area is covered by a flapper valve 41 with wings 42, which opens when sensing mass 33 moves to trigger but closes when sensing mass 33 moves in the opposite direction. These orifices can be replaced by a porous plug, an annular orifice, multiple orifices, or a viscous restrictor constructed by multiple fine tubes to achieve the same damping effect. The opening area and the damping effect can be adjusted by a similar flapper valve or any other types of one-directional valves.

Another embodiment of a short-travel mechanical sensor is shown in FIG. 6. A disk-shaped sensing mass 50 is supported by four cantilever beams 51. Disk 50 is guided to travel insile a tube 52. A clearance 53 between disk 50 and tube 52 allows air to flow through when disk 50 senses a crash and travels to push contact 54 into contact 55 and close an electrical circuit. The cantilever beams are arranged out-of-line from each other as shown in FIG. 7 to prevent disk 50 from rotating besides moving longitudinally along tube 52. The movable ends 56 of the beams 51 can slide in the grooves 57 on disk 50 so that the beams 51 can allow disk 50 to travel the full range without exceeding the yield limit of material of beams 50. The slidable design also allows the use of shorter cantilever beams and thus reduces the size of a sensor. Because of the sharp edge of disk 50, the air flow through clearance 53 is dominated by inertial effect, while the viscous effect is negligible. Therefore, the damping function provided by air flow is not affected by temperature variations, as long as the sensor is sealed and thus the density of the gas remains constant.

FIG. 8 is a side cross-section view of a crash sensor 60 made of a circular disk 61 and a cylinder 62. Instead of supporting a disk by one or more cantilevers, a spring 63 is used to provide the biasing force needed for the sensor. Sensing mass 65 is located in the center of disk 61, which rests on support 64 at its initial position. The height of support 64 can be used to control the volume of air behind disk 61. FIG. 9 shows another sensor 70. In FIG. 9, the sharp-edge disk 61 in FIG. 8 is replaced by a thicker disk 71 with an arc-shaped edge 72. The disk is similar to a slice of a sphere cut from the central portion of a ball. Bias is provided by a spring 73. At its initial position, disk 71 rests on support 74. Both embodiments of FIG. 8 and FIG. 9 have the advantage of reducing cross-axis problems because the momentum in the cross-axis directions will be insignificant when compared to the ball-in-tube sensors. Contacts or switches are not shown in FIG. 8 and 9, but contacts similar to those shown in FIG. 1 or 4 can be applied to the invention of FIG. 8 and 9.

FIG. 10 depicts another embodiment of a disk-type sensor 80, the disk is supported by a bendable cantilever beam 81. Disk 82 initially rests on a surface 83 inclined from the vertical position by 10 degrees. When the sensor is subjected to a pulse, the mass 84 located at the center of disk 81 begins to swing forward if the acceleration is greater than the initial biasing force, which is provided by contacts 85. If the pulse is of enough magnitude and duration, the mass will move and press contacts 85 into second contacts 86 to close electrical circuits and provide two separate triggering signals.

When a disk swings in a cylinder as explained above, the disk eventually touches the inner surface of the cylinder and stops. The maximum distance the disk can travel is a function of the disk radius and the clearance between the cylinder and the disk. For example, by a geometric analysis, if disk radius is equal to 0.75", radius clearance equal to 0.005", and if the disk is concentric with the inner circle of the cylinder at the neutral vertical position, then the disk can swing back and forth from the neutral position for 13.1 degrees before it touches the inner surface of the cylinder. This allows the mass at the center of the disk to travel for a maximum distance of 0.3" from its initial inclined position. Generally, the travel of the mass to trigger the sensor should be kept at a minimum to -accommodate a long contact overtravel, which is the allowable travel after the contacts are closed. In this embodiment, there are two pairs of contacts to provide two separate triggering signals. This dual-contact sensor design is especially useful for safing sensors to provide separate signals for driver-side and passenger-side air bag systems.

An alternate implementation of the invention in FIG. 10 is shown in FIG. 11. The left side of the cylinder 91 and the disk 92 are molded in a single plastic piece, while the disk is connected to the cylinder by a plastic hinge 93. The needed sensing mass is provided by the weight of the disk. There is no need for another piece for the sensing mass or the cantilever beam as shown in FIG. 10. Since the disk, the hinge, and the cylinder are molded in a single piece, the alignment of the disk and the cylinder can be controlled very precisely. The first contacts 94, which provide the biasing force, and second contacts 95 are inserted to the right side of the cylinder 96. The sensor 90 can be easily assembled by combining the two parts of the cylinder.

If hysteresis is desired for the sensor in FIG. 10 and 11, one or more thin-film flappers can be attached to the left-side edge of the disk to obtain a long dwell for the sensor in a way explained in previous embodiments of FIG. 1 and 4.

The sensors of this invention are designed to minimize the cross- axis problems of conventional mechanical crash sensors. Because of the flapper valve design, this sensor can have a longer and more reliable duration of contact closure than conventional spring-mass or ball-in-tube sensors. A high bias disclosed in this invention for crush zone sensors also prevents undesirable late triggering in marginal crashes as stated in the background of this invention. These improvements are verified by a study of sensor analysis on a complete car crash library with comparison of responses of this new sensor and other crash sensors.

Since the sensors of this invention is designed to- have a relatively small travel, it then becomes possible to render a sensor insensitive to temperature variations by adjusting the travel distance by a temperature-compensation method. However, most of the sensors disclosed in this invention uses inertia! flow type damping, which is insensitive to temperature variations because the flow rate through orifices depends on the density of the gas but not on the viscosity. Viscosity is very sensitive to temperature changes, but density of gas can be kept constant if the sensor is well sealed.

Although several preferred embodiments are illustrated and described above, there are possible combinations of using other materials and different dimensions of components that can perform the same function. Therefore, this invention is not limited to the above embodiment and should be determined by the following claims.

Claims

CLAIMSI claim:

1. A crash sensor comprising:

(a) a diaphragm;

(b) a sensing mass, coupled with said diaphragm and biased by said diaphragm at a first location;

(c) means for closing an electrical circuit when said sensing mass travels a prescribed distance to a second location;

(d) means for providing a damping effect on the motion of said sensing mass;

(e) means for adjusting said damping effect when said sensing mass moves from said second location back to said first location;

2. The invention in accordance with claim 1, wherein said means for closing a circuit comprises a first contact, which is arranged to make contact with a second contact when said sensing mass moves to said second location.

3. The invention in accordance with claim 1, wherein said damping effect is provided by air flow, dominated by high Reynold-number inertial effects, through opening slits on said diaphragm.

4. The invention in accordance with claim 1, wherein said damping effect is provided by air flowing through an orifice on said sensing mass.

5. The invention in accordance with claim 1, wherein said damping effect is provided by air flowing through a plurality of fine tubular passages on said sensing mass.

6. The invention in accordance with claim 1, wherein said damping effect is provided by a porous plug located on said sensing mass. '

7. The invention in accordance with claim 1, wherein said means of adjusting damping is accomplished by an one-directional valve controlling the area of air flow.

8. A crash sensor comprising:

(a) a tubular passage;

(b) a sensing mass, arranged to move in said tubular passage;

(c) a single or a plurality of cantilever beams coupled with said sensing mass, biasing said sensing mass at a first location in said passage;

(d) means for closing an electrical circuit when said sensing mass moves a prescribed distance to a second location;

(e) means for providing a damping effect on the motion of said sensing mass.

9. The invention in accordance with claim 8, wherein said sensing mass is a sharp-edge disk.

10. The invention in accordance with claim 8, wherein said sensing mass is a disk with an arc-shaped edge.

11. The invention in accordance with claim 8, wherein movable ends of said cantilever beams are arranged to slide in grooves located on said sensing mass so that said sensing mass travels in a prescribed path and the travel of said sensing mass does not cause said beams to yield or deform plastically.

12. The invention in accordance with claim 8, wherein said means for closing a circuit comprises a first contact, which is arranged to make contact with a second contact when said sensing mass moves to said second location.

13. The invention in accordance with claim 8, wherein said damping effect is provided by inertial or viscous air flow through a clearance between said sensing mass and said tubular passage.

14. The invention in accordance with claim 8, wherein said sensing mass is a disk, supported by a single cantilever beam, swinging in said tubular passage as said cantilever beam deflects due to the motion of said sensing mass.

15. The invention in accordance with claim 8, wherein said means of closing an electric circuit comprises two pairs of contacts to provide dual signals if the sensor is triggered.

16. A crash sensor comprising:

(a) a tubular passage;

(b) a sensing mass, hinged to and arranged to move in said tubular passage;

(c) a single or a plurality of contact springs, biasing said sensing mass at a first position in said passage;

(e) means for providing a damping effect on the motion of said sensing mass.

17. The invention in accordance with claim 16, wherein said sensing mass is a sharp-edge disk.

18. The invention in accordance with claim 16, wherein said damping effect is provided by inertial or viscous air flow through a clearance between said sensing mass and said tubular passage.