GB2283098A - Accelerometer using inertia mass in a fluid e.g.air - Google Patents
Accelerometer using inertia mass in a fluid e.g.air Download PDFInfo
- Publication number
- GB2283098A GB2283098A GB9321579A GB9321579A GB2283098A GB 2283098 A GB2283098 A GB 2283098A GB 9321579 A GB9321579 A GB 9321579A GB 9321579 A GB9321579 A GB 9321579A GB 2283098 A GB2283098 A GB 2283098A
- Authority
- GB
- United Kingdom
- Prior art keywords
- accelerometer
- accelerometer according
- fluid
- chambers
- diaphragm
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000012530 fluid Substances 0.000 title claims abstract description 33
- 238000005192 partition Methods 0.000 claims abstract description 20
- 230000010355 oscillation Effects 0.000 claims abstract description 9
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 8
- 239000010703 silicon Substances 0.000 claims abstract description 8
- 230000001133 acceleration Effects 0.000 claims abstract description 7
- 229920001971 elastomer Polymers 0.000 claims abstract description 6
- 239000000806 elastomer Substances 0.000 claims abstract description 6
- 238000013016 damping Methods 0.000 claims abstract description 5
- 238000009792 diffusion process Methods 0.000 claims abstract description 5
- 239000011888 foil Substances 0.000 claims abstract description 5
- 239000002184 metal Substances 0.000 claims abstract description 5
- 230000004888 barrier function Effects 0.000 claims abstract description 4
- 238000010438 heat treatment Methods 0.000 claims description 16
- 239000002861 polymer material Substances 0.000 claims description 2
- 229920000642 polymer Polymers 0.000 abstract 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000000151 deposition Methods 0.000 description 1
- 239000002210 silicon-based material Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/09—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up
- G01P15/0922—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up of the bending or flexing mode type
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/12—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by alteration of electrical resistance
- G01P15/123—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by alteration of electrical resistance by piezo-resistive elements, e.g. semiconductor strain gauges
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Air Bags (AREA)
Abstract
An accelerometer comprises a housing (1) defining at least one chamber (2a, 2b) containing a fluid, an inertia mass (4) mounted on a flexible partition and adapted to move in response to acceleration or deceleration, thus causing a change in the volume of at least one of the chambers (22a, 2b), and a pressure sensor (7) in pressure communication with the fluid in each chamber (2a, 2b) and providing an electric output signal (8, 9) which is a continuous function of the acceleration or deceleration acting on the accelerometer. The fluid may be gas or air and the pressure sensor may be a partition between the chambers of silicon with integral piezo-resistive or piezo-capacitive elements. The diaphragm may be an elastomer or polymer and incorporate a metal foil with diffusion barrier characteristics. The resonance of the mass-fluid-diaphragm system may be greater than 400 MHz and the system oscillation may have a damping factor greater than 0.2. The accelerometer may activate a safety device eg an air bag or seat belt pre-tensioner. <IMAGE>
Description
Title "Improvements in or relating to an Accelerometer"
The present invention relates to an accelerometer and more particularly relates to an accelerometer providing a continuous electric output signal.
It is envisaged that a preferred accelerometer in accordance with the invention may find use as part of a crash detection system present in a motor vehicle, such as a motor car, which crash detection system may be adapted to activate a safety device, such as a seat belt pretentioner or an air bag, in the event that an accident or crash is detected.
According to this invention there is provided an accelerometer, said accelerometer comprising a housing defining at least one chamber containing a fluid, an inertia mass adapted to move in response to acceleration or deceleration, movement of the inertia mass causing a change in the volume of the chamber, there being a pressure sensor in pressure communication with the fluid in the chamber, the pressure sensor being adapted to provide an electric output signal which is a continuous function of the acceleration and/or deceleration acting on the accelerometer.
Preferably, the fluid is a gas such as air. The mass may be connected to the housing by means of a deformable diaphragm, and the mass and the diaphragm may be formed as a single integrated unit which may be formed of an elastomer or polymer material. The diaphragm may incorporate a metal foil with diffusion barrier characteristics.
The pressure sensor means may be contained within the housing or may be located within a separate unit.
Preferably, the diaphragm serves to separate two chambers defined by the housing, the pressure sensor being responsive to the differential pressure between the two chambers.
Conveniently, the pressure sensor incorporates a thin partition, fluid from the two chambers being present on opposed respective sides of the partition, the partition being adapted to be deformed in response to the differential pressure between the two chambers.
Advantageously, the partition is made of silicon with one or more piezo resistive or piezo capacitive elements formed integrally with the partition, said elements being connected to the electric output.
Conveniently, the two chambers are connected to the pressure sensor means by separate respective conduits. The two chambers are preferably of substantial equal volume and may be substantially mirror symmetric.
Advantageously, the resonance frequency of the moving system constituted by the inertia mass, the diaphragm and the fluid within the two chambers is greater than 400 Hz.
Conveniently, the oscillation of the moving system comprising the inertia mass, the diaphragm and the fluid within the two chambers is dampened by damping factor greater than 0.2.
Conveniently, at least one stopper means is provided to damp and limit oscillation of the said mass, and the position of the stopper may be adjustable. The stopper may be in the form of the threaded screw and two stoppers may be provided, one located on either side of the diaphragm.
Preferably, at least one heating element is provided for heating the fluid within the chamber and where there are two chambers, preferably two heating elements are provided for heating the fluid, one heating element being located in each of the said chambers. The or each heating element may be in the form of an electric resistor.
In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which:
Fig. 1 is a diagrammatic sectional view of one embodiment of the invention; and
Fig. 2 is a diagrammatic cross-sectional view of a second embodiment of the invention.
In the drawings like reference numerals apply to like parts.
Referring initially to Fig 1, an accelerometer in accordance with the present invention comprises a housing 1 which defines a cavity 2 which is divided into separate chambers 2a,2b by means of a transversely extending flexible or resilient diaphragm 3. The diaphragm may be formed of an elastomer or of some other polymeric or plastic material. Gas may be able to diffuse through a diaphragm of this type. Thus the diaphragm may incorporate a thin metal foil having diffusion barrier characteristics.
The metal foil may be bonded to the elastomer or polymeric material, or may be deposited on that material. Formed integrally with the diaphragm, or mounted on the diaphragm, is a mass 4. Thus, in one embodiment, the mass and the diaphragm together form a single integrated unit made principally of an elastomer or polymeric material.
The mass 4, as will become clear from the following description, is intended to act as an inertia mass, the mass moving, under its own inertia, when a vehicle in which the accelerometer is mounted decelerates. The described accelerometer will, of course, be mounted in the motor vehicle so that when the vehicle decelerates the mass 4 will move transversely of the diaphragm 3, thus tending either to reduce the volume of chamber 2a or tending to reduce the volume of chamber 2b.
The chambers 2a and 2b are each provided with a respective outlet conduit 5,6. Each outlet conduit is connected to a pressure sensor unit 7, which is separated from the housing 1, and which incorporates pressure sensing means adapted to sense the pressure differential between the pressure within the conduit 5 and the pressure within the conduit 6, or to sense the actual pressure in one or both of the conduits. The pressure sensor unit 7 is provided with two electric output leads 8,9. The pressure sensing means within the pressure sensor unit 7 may be any appropriate means, and may, for example, comprise two separate piezo electric transducers or may comprise some other arrangement. The pressure sensor unit 7 provides a continuous electric output which is related to the instantaneous oscillation of the vehicle.
Each chamber 2a,2b is filled with an appropriate fluid medium. The fluid medium may comprise air or may comprise a hydraulic fluid medium.
In the illustrated embodiment, each chamber 2a,2b, is provided with an electric resistance heating element 10,11 through which electric current may be passed to heat the fluid medium within the respective cavity.
It is to be observed that the chambers 2a and 2b are substantially equal volume, and the illustrated embodiment is symmetric about a substantially vertical line of symmetry A/A.
It is preferred that the resonance frequency of the moving system comprised by the inertia mass 4, the diaphragm 3 and the fluid within the chambers 2 and 2b should be greater than 400 Hz, and preferably the oscillation of the moving system is damped by a damping factor greater than 0.2.
As the vehicle in which an accelerometer as described above with reference to Fig. 1 is mounted accelerates or decelerates, the inertia mass 4 will either move towards the right or the left in Fig. 1 thus tending to increase the pressure within chamber 2a, whilst decreasing the pressure within chamber 2b or vice-a-versa, that is say increasing the pressure within chamber 2b whilst decreasing the pressure within chamber 2a. The changes in pressure are caused by the inertia mass moving the diaphragm which effectively changes the volume of each of the chambers. The pressure sensor unit is adapted to sense the changes in pressure and provide an appropriate continuous electric output signal on the electric leads 8 and 9. The output signal can be analyzed by appropriate circuitry, that circuitry being adapted to activate a safety device, such as a seat belt pre-tensioner or an air bag, should the output signal from the sensor unit have predetermined characteristics.
The heating elements 10 and 11 will raise the temperature of the fluid within the chambers 2a and 2b, thus enabling the pressure sensor to be tested and also enabling checks to be carried out to ensure that there is no leakage of fluid from within the cavities. By altering the power supplied to the two heating elements an oscillation of the mass 4 could be initiated, thus simulating a variable acceleration.
In many instances it may be preferable for the fluid within the chambers to be gas, such as air. Such a fluid has a very low mass and should the fluid leak no pollution problems will arise.
Fig. 2 illustrates a second embodiment of the invention in which the pressure sensor arrangement is not a separate unit but is contained integrally with the inertia mass within a single housing. Thus, in the embodiment of Fig. 2, the housing 1 defines two chambers 2a, 2b which are separated by a diaphragm 3 of the type described with reference to Fig. 1 which again is formed integrally with or carries an inertia mass 4.
The housing defines conduits 5,6 which lead to a pressure sensor arrangement 7 provided in the lower part of the housing 1. As can be seen from Fig. 2, the lower part of the housing 1 defines two lower cavities 12a,12b, the lower cavity 12a being a communication within the conduit 5 and the lower cavity 12b being in communication with the conduit 6. The lower cavities 12a,12b are separated by a dividing wall 13 having an aperture 14 formed therein. A bridging element 15 incorporating a silicon sensor element is provide within the lower cavity 12a extending across the aperture 14. Part of the bridging element 15 is defined by a flexible thin partition 16 formed of silicon. One side of the partition is thus exposed to the pressure present in the chamber 2a, and the other side of the partition is exposed to the pressure present in the chamber 2b. The partition is deformed by a differential pressure across the partition. A piezo-resistive or piezo-capacitive element 17 is formed integrally with the silicon partition 16, preferably in a region which the silicon partition is of reduced thickness. The piezo-resistive or piezo-capacitive element may be formed within the silicon material by known diffusion and deposition techniques. The operative terminals of the piezo-resistive or piezo-capacitive element 17 are connected to electric output leads 8,9.
Each chamber 2a,2b is asociated with a stop element 18,19 in the form of a grub screw passing through the wall of the housing 1 defining the respective chamber. Each stop element 18,19 may thus be selectively positioned. The stop members 18 and 19 are positioned to damp and limit the oscillating movement of the inertia mass 4. This can therefore prevent excessive oscillations of the mass 4, which could damage the silicon partition 16, and which could also damage the diaphragm 3.
It is to be observed that as in the embodiment of
Fig. 1 electrically resistive heating elements 10 and 11 are provided within the chambers 2a and 2b. Again the resonance frequency of the moving system comprising the inertia mass, the elastic diaphragm and the fluid within the chambers should lie above 400 Hz, and the system should be damped by a damping factor greater than 0.2.
Whilst the invention has been described with reference to specific embodiments in which the inertia mass is mounted on a diaphragm which separates two chambers, it is to be appreciated that in another embodiment of the invention there may be means defining a single chamber, an inertia mass being provided for movement relative to that chamber to apply pressure to a fluid medium within the chamber. Thus, the mass could be mounted on a diaphragm which is provided at one end of the chamber, the diaphragm effectively separating the interior of the chamber from the exterior of the chamber, or, alternatively, the mass could comprise a piston element located within a cylinder which defines the chamber.
In either event, pressure sensor means would be provided to sense the pressure of the fluid within the chamber, the pressure sensor having an electric output signal which is a function of the pressure acting on the pressure sensor.
The provision of the diaphragm does enable the described embodiments to operate by measuring differential pressure, thus avoiding any problems that might arise due to changes in absolute pressure, for example if the vehicle ascends to a significant height in a mountainous region.
Claims (26)
1. An accelerometer, said accelerometer comprising a housing defining at least one chamber containing a fluid, an inertia mass adapted to move in response to acceleration or deceleration, movement of the inertia mass causing a change in the volume of the chamber, there being a pressure sensor in pressure communication with the fluid in the chamber, the pressure sensor being adapted to provide an electric output signal which is a continuous function of the acceleration and/or deceleration acting on the accelerometer.
2. An accelerometer according to Claim 1, wherein the fluid is a gas.
3. An accelerometer according to Claim 2 wherein the gas is air.
4. An accelerometer according to any one of the preceding claims wherein the mass is connected to the housing by means of a deformable diaphragm.
5. An accelerometer according to Claim 4, wherein the mass and the diaphragm are formed as a single integrated unit.
6. An accelerometer according to Claim 5, wherein the mass and the diaphragm are formed of an elastomer or polymer material.
7. An accelerometer according to Claim 4, wherein the diaphragm incorporates a metal foil with diffusion barrier characteristics.
8. An accelerometer according to any one of the preceding claims wherein the pressure sensor means are contained within the said housing.
9. An accelerometer according to any of Claims 1 to 10, wherein the pressure sensor means are located within a separate unit.
10. An accelerometer according to any one of the preceding claims wherein the diaphragm serves to separate two chambers defined by the housing, the pressure sensor being responsive to the differential pressure between the two chambers.
11. An accelerometer according to Claim 10, wherein the pressure sensor incorporates a thin partition, fluid from the two chambers being present on opposed respective sides of the partition, the partition being adapted to be deformed in response to the differential pressure between the two chambers.
12. An accelerometer according to Claim 11, wherein the partition is made of silicon with one or more piezo resistive or piezo capacitive elements formed integrally with the partition, said elements being connected to the electric output.
13. An accelerometer according to any one of Claims 8 to 12, wherein the two chambers are connected to the pressure sensor means by separate respective conduits.
14. An accelerometer according to any one of Claims 8 to 13, wherein the two chambers are of substantially equal volume.
15. An accelerometer according to Claim 14, wherein the two chambers are substantially mirror symmetric.
16. An accelerometer according to any one of Claims 8 to 15 wherein the resonance frequency of the moving system constituted by the inertia mass, the diaphragm and the fluid within the two chambers is greater than 400 Hz.
17. An accelerometer according to any one of Claims 8 to 16, wherein the oscillation of the moving system comprising the inertia mass, the diaphragm and the fluid within the two chambers is dampened by damping factor greater than 0.2.
18. An accelerometer according to any one of Claims 8 to 17, wherein at least one stopper means is provided to damp and limit oscillation of the said mass.
19. An accelerometer according to Claim 18, wherein the position of the stopper is adjustable.
20. An accelerometer according to Claim 19, wherein the stopper is in the form of a threaded screw.
21. An accelerometer according to any one of Claims 18 to 20, wherein two stoppers are provided, one located on either side of the diaphragm.
22. An accelerometer according to any one of the preceding claims comprising at least one heating element for heating the fluid within the chamber.
23. An accelerometer according to any one of Claims 8 to 21, wherein two heating elements are provided for heating the fluid, one heating element being located in each of the said chambers.
24. An accelerometer according to Claim 22 or Claim 23, wherein the or each heating element is in the form of an electric resistor.
24. An accelerometer substantially as herein described with reference to and show in Fig. 1 of the accompanying drawings.
25. An accelerometer substantially as hereinbefore described with reference to and as shown in Fig. 2 of the accompanying drawings.
26. Any novel feature or combination of features disclosed herein.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9321579A GB2283098A (en) | 1993-10-20 | 1993-10-20 | Accelerometer using inertia mass in a fluid e.g.air |
| AU80087/94A AU8008794A (en) | 1993-10-20 | 1994-10-20 | A sensor apparatus |
| PCT/SE1994/000989 WO1995011455A1 (en) | 1993-10-20 | 1994-10-20 | A sensor apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9321579A GB2283098A (en) | 1993-10-20 | 1993-10-20 | Accelerometer using inertia mass in a fluid e.g.air |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9321579D0 GB9321579D0 (en) | 1993-12-08 |
| GB2283098A true GB2283098A (en) | 1995-04-26 |
Family
ID=10743801
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9321579A Withdrawn GB2283098A (en) | 1993-10-20 | 1993-10-20 | Accelerometer using inertia mass in a fluid e.g.air |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2283098A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2343952A (en) * | 1998-11-18 | 2000-05-24 | Breed Automotive Tech | Pendulum mass acceleration sensor |
| WO2007116156A1 (en) * | 2006-04-12 | 2007-10-18 | Commissariat A L'energie Atomique | Inertial micro-electronic device with liquid integrator |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB727034A (en) * | 1952-03-19 | 1955-03-30 | Pyrene Co Ltd | Improvements in devices responsive to rates of change of acceleration |
| US3828294A (en) * | 1971-08-02 | 1974-08-06 | Nissan Motor | Acceleration transducer having semiconductive piezoresistive element |
| GB1496784A (en) * | 1975-02-28 | 1978-01-05 | Bendix Westinghouse Ltd | Rate of change of speed sensors |
| US4138893A (en) * | 1977-12-09 | 1979-02-13 | The United States Of America As Represented By The Secretary Of The Army | Hydrostatic accelerometer |
-
1993
- 1993-10-20 GB GB9321579A patent/GB2283098A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB727034A (en) * | 1952-03-19 | 1955-03-30 | Pyrene Co Ltd | Improvements in devices responsive to rates of change of acceleration |
| US3828294A (en) * | 1971-08-02 | 1974-08-06 | Nissan Motor | Acceleration transducer having semiconductive piezoresistive element |
| GB1496784A (en) * | 1975-02-28 | 1978-01-05 | Bendix Westinghouse Ltd | Rate of change of speed sensors |
| US4138893A (en) * | 1977-12-09 | 1979-02-13 | The United States Of America As Represented By The Secretary Of The Army | Hydrostatic accelerometer |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2343952A (en) * | 1998-11-18 | 2000-05-24 | Breed Automotive Tech | Pendulum mass acceleration sensor |
| GB2343952B (en) * | 1998-11-18 | 2000-11-08 | Breed Automotive Tech | Pendulum mass acceleration sensor |
| US6184764B1 (en) | 1998-11-18 | 2001-02-06 | Breed Automotive Technology, Inc. | Pendulum mass acceleration sensor |
| WO2007116156A1 (en) * | 2006-04-12 | 2007-10-18 | Commissariat A L'energie Atomique | Inertial micro-electronic device with liquid integrator |
| FR2899889A1 (en) * | 2006-04-12 | 2007-10-19 | Commissariat Energie Atomique | INERTIAL MICROELECTRONIC DEVICE WITH LIQUID INTEGRATOR |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9321579D0 (en) | 1993-12-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |