GB2238391A

GB2238391A - Method of detecting an acceleration of a vehicle

Info

Publication number: GB2238391A
Application number: GB9025090A
Authority: GB
Inventors: Tsuneo Chikaraishi; Tetsuo Tsuji
Original assignee: Takata Corp
Current assignee: Takata Corp
Priority date: 1989-11-24
Filing date: 1990-11-19
Publication date: 1991-05-29
Also published as: KR910010191A; DE4037328A1; CA2029587A1; GB9025090D0; JPH03165266A; FR2655152A1

Abstract

A method of detecting an acceleration of a vehicle uses a clock pulse signal and vehicle velocity pulses generated with revolutions of an axle and computes a variation in the vehicle velocity on the basis of a difference between the number of clock pulses (N1) counted within a first pulse (P1) of the vehicle velocity pulses and the number of clock pulses (N2) counted within a second vehicle pulse (P2) subsequent to the first pulse (P1). Alternatively, the method comprises computing a variation in the vehicle velocity on the basis of a difference between the number of vehicle velocity pulses counted within a first pulse of the clock pulses and the number of vehicle velocity pulses counted within a second clock pulse subsequent to the first clock pulse. The axle may be one of a driving wheel axle, floating wheel axle, propeller shaft, transmission shaft and axle of a differential gear. <IMAGE>

Description

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METHOD OF DETECTING AN ACCELERATION OF A VEHICLE. The present invention is directed generally to a method of detecting an acceleration of a vehicle, and more particularly, to the method applied to an operation starting device of a vehicle occupant protection apparatus. In this specification, the term "acceleration" also includes "deceleration".

There has been widely employed an apparatus for protecting a vehicle occupant by quickly expanding an air bag or locking a retractor of a seat belt in the event of an emergency such as in a collision of the vehicle.

An acceleration detecting device for starting the operation of the vehicle occupant protection apparatus by detecting the collision of the vehicle has hitherto involved the use of a distortion type gauge or piezo type accelerometer. A known mechanical collision detecting device is of a roller weight type, a viscosity damping type and the like (Automobile Technology p.1351, Vol 42, No. 10, 1988).

In the accelerometer given above, an operating signal is outputted only when the acceleration reaches a level large enough to operate the protection apparatus. An actual acceleration could not be accurately detected. Additionally, the prior art accelerometer suffers from the problem that it senses accelerations in directions other than the -1advancing direction of the vehicle. OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method capable of highly accurately detecting an acceleration in a traveling direction of a vehicle.

According to the present invention, there is provided a first method of detecting an acceleration of a vehicle by a clock pulse signal and vehicle velocity pulses generated with revolutions of an axle, the method comprising the steps of counting the number of clock pulses within a first pulse of the vehicle velocity pulses; counting the number of clock pulses within a second pulse subsequent to the first pulse; computing a variation in the vehicle velocity during a period from the first pulse to the second pulse on the basis of a difference between the former pulse number and the latter pulse number; and detecting the acceleration of the vehicle.

According to the present invention, there is provided a second method of detecting an acceleration of a vehicle by a clock-pulse signal and vehicle velocity pulses generated with revolutions of an axle, the method comprising the steps of: counting the number of vehicle velocity pulses within a first pulse of the clock pulses; counting the number of vehicle velocity pulses within a second pulse subsequent to the first pulse; computing a variation in the vehicle 2 1 1 velocity during a period from the first pulse to the second pulse on the basis of a difference between the former pulse number and the latter pulse number; and detecting an acceleration of the vehicle.

Based on the first method, when causing a variation in the vehicle velocity, the clock pulse number counted within the second pulse changes from the clock pulse number counted within the first pulse. The variation in the number counted is proportional to a magnitude (acceleration) of the variation in the vehicle velocity. Hence, the acceleration of the vehicle can be computed on the basis of the variation in the number counted.

Based on the second method, similarly when causing the variation in the vehicle velocity, the vehicle velocity pulse number counted within the second pulse changes from the vehicle velocity pulse number counted within the first pulse. The acceleration of the vehicle can be computed on the basis of the variation in the number counted. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of this invention will become apparent during the following discussion taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a time chart of assistance in explaining a method in one embodiment of the invention; FIG. 2 is a block diagram; and 3 - FIG. 3 is a ime chart of assistance in explaining a method in another embodiment. DESCRIPTION OF THR PREFERRED ENBODIMENTS

Embodiments of this invention will hereinafter be described with reference to the accompanying drawings.

As illustrated in FIG. 2, a vehicle velocity pulse generator 2 is mounted on an axle (such as a propeller shaft, a rotary"shaft of a transmission and a rotary shaft of a differential gear in addition to a driving wheel axle and a floating wheel axle) of a vehicle. Outputs of the vehicle velocity pulse generator 2 are inputted to a counter 4. The vehicle velocity pulse generator 2 involves the use of, e.g., a rotary encoder which generates several tens through several thousands of pulses while the vehicle travels 1m.

Inputted to the counter 4 are clock pulses from a clock pulse generator 3. Output signals of the counter 4 are inputted to an operator 5. The operator 5 outputs signals to a load controller 6. The load controller 6 supplies an operating current to, e.g., a lock unit of a retractor of a seat belt device.

The following is a specific description of the method claimed in claim 1, referring to FIG. 1.

As depicted in FIG. 1, clock pulse signals (hereinafter referred to as clock signals) of a v predetermined cycle are accurately inputted from the clock pulse generator 3 to the counter 4. Vehicle velocity pulse signals corresponding to traveling velocities of the vehicle are inputted from the vehicle velocity pulse generators 2. Pulse widths of the clock signal and of the vehicle velocity pulse signal are selected so that a multiplicity of clock pulses are counted within 1 pulse of the vehicle velocity pulse signal even when the vehicle reaches a prescribed maximum velocity (e.g., 20Okm/h).

When the vehicle travels, the clock pulses for N1 are inputted to the counter 4 during a first pulse Pl. The clock pulses for N2 are inputted to the counter 4 during a second pulse P2. In this case, the operator 5 computes an acceleration of the vehicle during a period from the first pulse P, to the second pulse P2 in the following manner.

Note that in the following formulae, the symbols c and denote as follows:

c... the pulse width (sec) of the clock signal j... the distance (m) which the vehicle travels during 1 pulse of the vehicle velocity pulses.

1 A velocity v, of the vehicle during the first pulse P, (timings 0 - tl) is given such as v, = 11/tl. tl is c-Ni (sec), and eventually V1 = lc-NJ.

- A velocity v2 Of the vehicle during the second pulse P2 (timings tl t2) is similarly expressed such as:

v2 '= 21 (t2 - tl) = J2/c.N2 An acceleration a during a tl-t2 period is given by a (v2 - vl) / (t2 - tl)- t2 - tl is CN2.

and eventually -2/c'N2 - Alc-N1 a = -... (1) c-N2 In this formula (1), A and c are known. For example, is calculated by dividing a wheel outer peripheral length by the number of vehicle velocity pulses generated per revolution of the wheel. The pulse width c is calculated as an inverse number of a clock frequency.

In conformity with such an arithmetic formula, the operator 5 calculates the acceleration a on the basis of the counted numbers NI and N2 of the counter 4. In this arithmetic result, when the acceleration a is greater than, e.g., 0.7G (G is a gravity acceleration of 9.79m/sec2), the signal is inputted to the load controller 6. The retractor of the seat belt is thereby locked.

The operation of an embodiment, shown in FIG. 3, of claim 2 is also the same. Referring to FIG. 3, the vehicle velocity pulse signals for NI are counted during the first pulse (timings 0 - tl) of the clock signal. The vehicle velocity pulse signals for N2 are counted during the second pulse (timings t1"t2). As in the previous case, the symbol c designates the pulse width of the clock signal, and S- denotes the distance at which the vehicle travels during 1 pulse of the vehicle velocity pulses.

The traveling distance of the vehicle during a 0-tj period is I -Nj. Hence, a mean velocity vj during c second from 0 to tj is expressed such as:

v, = I - N, / tj = I - N, / c The traveling distance of the vehicle during the tjrt2 period is I- N2. Therefore, the velocity v2 during the tj,,ot2 period is given by:

v2 = k - N2 / (t2 - tl) = - N2 /C Hence, the acceleration a during the tl,t2 period is expressed such as:

a (v2 - vl) / (t2 - tl) J - (N2 - NO / c2... (2) In accordance with this formula (2), as in the formula (1), and c are known. The acceleration a is therefore calculated on the basis of the counted numbers N, and N2 Of the counter 4.

The vehicle travels at a lower limit speed (e.g., a speed per hour is 10 km/h) requiring the operation of an occupant protecting apparatus in the event of a collision.

7 - f Based on the method of FIG. 3, even in such circumstances, the pulse width is selected so that a multiplicity of vehicle velocity pulses are counted during 1 pulse of the clock signal.

The method of the present invention is suitably applied to the control of a tensionless state cancelling device of a seat belt in addition to the above described lock device thereof.

For application to the lock device, if the vehicle acceleration, as explained above, exceeds the predetermined value (e.g. 0.7G), a mechanism for locking the belt retractor may be adopted. In this case, the operating noise is less than in the conventional mechanical acceleration detecting mechanism (lock mechanism).

For application to the tensionless state cancelling device, if the vehicle acceleration exceeds the predetermined value, a tension is given to the seat belt which is tensionless (in a so-called slackened state). The device positively operates to tightly restrain the occupant. The device for carrying out the method of the invention incorporates a travelling speed detecting circuit of the vehicle. When the vehicle speed increases, and even if the acceleration is smaller than the predetermined value, the seat belt tensionless state is cancelled to tighten up the seat belt.

z Although the illustrative embodiments of the present invention have been described in detail with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those embodiments. Various changes or modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

3

Claims

What is claimed is:

(1) A method of detecting an acceleration of a vehicle by a clock pulse signal and vehicle velocity pulses generated with revolutions of an axle, said method comprising the steps of: counting the number of clock pulses within a first pulse of said vehicle velocity pulses; counting the number of clock pulses within a second pulse subsequent to said first pulse; computing a variation in said vehicle velocity during a period from said first pulse to said second pulse on the basis of a difference between said former pulse number and said latter pulse number; and detecting said acceleration of said vehicle.

(2) A method of detecting an acceleration of a vehicle by a clock pulse signal and vehicle velocity pulses generated with revolutions of an axle, said method comprising the steps of:

counting the number of vehicle velocity pulses within first pulse of said clock pulses; counting the number of vehicle velocity pulses within second pulse subsequent to said first pulse; computing a variation in said vehicle velocity during period from said first pulse to said second pulse on the basis of a difference between said former pulse number and - 10 p said latter pulse number; and detecting said acceleration of said vehicle.

(3) The method as set forth in Claim 1, said acceleration a is computed as follows:

-91 cN2 - S/ c-N1 where c: the pulse width of a clock signal -: the distance at which the vehicle travels during 1 Nj:

pulse of vehicle velocity pulses the number of clock pulses counted within the first pulse, and N2: the number of clock pulses counted within the second pulse.

(4) The method as set forth in Claim 2, wherein said acceleration a is computed in conformity with the following formula:

a= - (N2 - N1) / C2 (5) The method as set forth in Claim 3, wherein k is obtained by dividing a wheel outer periph-eral length by the nuber of vehicle velocity pulses generated per revolution of a wheel.

(6) The method as set forth in Claim 4, wherein k i obtained by dividing a wheel outer peripheral length by the number of vehicle velocity pulses generated per 11 1 1 revolution of a wheel.

(7) The method as set forth in Claim 3, wherein an axle is one of a driving wheel axle of said vehicle, a floating wheel axle, a propeller shaft, a rotary shaft of axle of a differential gear. set forth in Claim 4, wherein an axle is one of a driving wheel axle of said vehicle, a floating wheel axle, a propeller shaft, a rotary shaft of a transmission and an axle of a differential gear.

Q a transmission and an (8) The method aE - 12 Published 1991 at The Patent Office. State House. 66/71 High Holborn. London WCIR47?. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmifelinfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. Kent-