WO2000058133A1

WO2000058133A1 - Vehicle roll-over sensing system

Info

Publication number: WO2000058133A1
Application number: PCT/US2000/008502
Authority: WO
Inventors: Alan J. Riggs; Dennis E. Palmer; William D. Merrick; David A. D'alimonte
Original assignee: Automotive Systems Laboratory, Inc.
Priority date: 1999-03-30
Filing date: 2000-03-30
Publication date: 2000-10-05

Abstract

A rollover sensing apparatus (10) and method for predicting a rollover condition for a vehicle (10) having a passenger restraint system (60) comprises first and second orthogonally aligned accelerometers (20 and 30) for measuring lateral and vertical acceleration of the vehicle (12) and a roll rate sensor (40) for measuring the rate of change of the angle of the vehicle (12) with respect to a horizontal axis over time, each having an output signal. A digital controller (50) calculates a steady-state roll angle of the vehicle (12) based on the sensed lateral and vertical acceleration thereof. The controller (50) also calculates a rollover threshold line by plotting roll rate versus roll angle based on the physical dimensions of the specific vehicle. The controller (50) compares the sensed roll rate and calculated roll angle with the threshold line, and provides an output (52) to initiate the passenger restraint system when an imminent vehicle (12) rollover is determined.

Description

VEHICLE ROLL-OVER SENSING SYSTEM

BACKGROUND OF THE INVENTION

Automotive manufacturers and NHTSA have been attempting to develop

methods to deploy airbags and supplemental passenger restraint systems to

prevent injury in the event of vehicle rollover. However, discerning a rollover

scenario from a hard cornering scenario, or travel over uneven pavement

surfaces, has proven difficult. The presence of spurious vertical and lateral

accelerations of a vehicle due to variations in road surface, rapid lane changes

etc., are problematic for known-in-the-art sensor systems to distinguish from

rollover scenarios.

Prior art techniques for the detection of vehicle roll-over include

monitoring the position of a gas bubble within a liquid-filled chamber or

sensing the position of an articulated pendulum mass using conventional

transducer technology. Bubble-level and pendulous mass position detection

both suffer from severe bandwidth limitations and often provide chaotic

outputs when subjected to highly dynamic environments. Attempts to filter

and damp such systems result in unacceptably low system response.

Prior art tilt-detection systems relying on conventional accelerometers or

analogous transducers cannot predict imminent vehicle roll-over quickly

enough to successfully deploy passenger restraint systems. Additionally,

these systems are easily confused by dynamic driving events such as rough-

roads and high-load cornering. SUMMARY OF THE INVENTION

The instant invention overcomes the aforementioned problems by

providing a system for detection of vehicle "tilt" or rollover and production of a

deployment signal to a vehicle passenger restraint system that utilizes high-

bandwidth, electronically filterable sensors and a unique processing algorithm

to calculate steady-state and near steady-state vehicle roll angle.

The sensor elements utilized in the instant invention are preferably

micro-machined solid state sensors having high bandwidth and filterable signal

outputs that are readily processed in either the analog or digital domain.

Vehicle state information encompassing both position and rate of roll are

provided as inputs to a controller where a decision-making algorithm

determines whether a rollover situation exists. When a determination is made

that vehicle rollover is imminent, the controller provides an output to a vehicle

passenger restraint system indicating the need for immediate deployment

thereof.

Deployment of supplemental restraint devices to reduce or eliminate

injuries resulting from vehicle rollover requires a system able to sense both the

static and dynamic positional state of a vehicle and determine whether a

rollover event is imminent. A rollover event, is where a vehicle reaches a

positional state wherein rotation about the vehicle longitudinal axis

(conventionally the x-axis) results in the vehicle center-of-gravity being

positioned directly over the center of the low-side tire patch or patches. This critical angle is dependent upon particular vehicle dimensions such as the

height of the center of gravity of the vehicle, weight, and vehicle track width.

The instant invention determines imminent rollover by acquiring and

subsequently processing roll angle and roll rate information. Roll angle is

measured statically, and in brief roll rate intervals by employing a pair

accelerometers located near the vehicle longitudinal axis. The accelerometers

have their sensing axes arranged orthogonally to the vehicle longitudinal axis,

both transversely (conventionally the y-axis) and vertically (conventionally the

z-axis). Each orthogonally oriented accelerometer is provided with an output

operatively connected to an input of a controller. The controller has a plurality

of analog and digital inputs and outputs, as is well known to one of ordinary

skill in the art, for purposes explained hereinbelow. This arrangement of

accelerometers, in conjunction with processing of information from a roll rate

sensor, allows the vehicle roll angle to be computed by the controller in both

steady-state and near steady-state conditions.

The results of the aforementioned roll angle and rate calculated by the

controller provide clear indication of non-steady-state conditions such as high

lateral acceleration cornering on both flat and banked curves and horizontal

and vertical accelerations caused by rough road conditions. During such

intervals, the controller of the instant invention conditionally determines the

validity of the roll-angle calculations and appropriately weights or ignores the

results based on physics and inherent vehicle parameters such as mass, center

of gravity height from ground, etc. For example, a determination may be rapidly made by the controller that the critical angle has been reached, but the

orthogonally arranged accelerometers indicate that the vehicle is traversing a

banked section of pavement thereby obviating the need for passenger restraint

deployment.

Additionally, vehicle roll angle rate of change is sensed by an angular

rate sensor such as a gyroscope, or other known-in-the-art roll-rate sensor

having an output operatively connected to an input of the controller. During

highly dynamic time intervals the controller maps the roll-angle rate sensor

information in a roll angle rate versus roll angle plane. The abscissa of this

plane is comprised of calculated roll angle from the accelerometer pair

previously described as an initial condition, plus the time-integrated roll angle

rate of change information to produce an instantaneous roll angle value.

Given vehicle parameters such as track width, center-of-gravity height,

mass, and roll-axis moment-of-inertia, an energy balance between rotational

kinetic energy and potential energy is calculated by the controller. A

calculation is then made by the processor whether there exists sufficient

rotational kinetic energy (again based on the physical parameters of the

vehicle) to continue the rotational motion such that the roll-over definition

previously described is met or exceeded. In this way a determination of

imminent vehicle roll-over can be made well before the vehicle roll-angle

reaches the unstable equilibrium point in cases of high roll-angle rates. This

condition occurs frequently, and the disclosed technique allows the deployment of supplemental restraint devices early enough for their potential

benefits to be employed to maximum advantage.

Therefore, one object of the instant invention is a vehicle rollover

sensing system that accurately predicts imminent vehicle rollover.

Another object of the instant invention is a vehicle rollover sensing

system that predicts vehicle rollover based on the rotational energy of a

vehicle.

Another object of the instant invention is a vehicle rollover sensing

system and method that is tailored to the physical dimension of the vehicle in

which it is deployed.

Yet another object of the instant invention is a vehicle rollover sensing

system and method that provides a signal to deploy occupant restraint

systems rapidly enough to provide maximum benefit to an occupant in the

event of a vehicle rollover.

Other objects, features, and advantages of the instant invention will

become evident after reading the following detailed description of the preferred

embodiment with reference to the accompanying drawing figures

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagrammatical representation of the system of the instant

invention.

Fig. 2 is a free body diagram of a vehicle in accordance with the instant

invention. Fig. 3 is a free body diagram of a vehicle in accordance with the instant

invention.

Fig. 4 is an exemplary plot of a rollover threshold line in accordance with the

instant invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Fig. 1 , and in accordance with a preferred embodiment of

the instant invention, a system 1 0 and method for detecting imminent rollover

in a vehicle 1 2 comprises a first accelerometer 20 having a longitudinally

aligned axis for measuring lateral acceleration of the vehicle 1 2, having an

output signal 22 indicative of said acceleration, and a second accelerometer

30 having a vertically aligned axis for measuring vertical acceleration also

having an output signal 32 indicative thereof.

Additionally, the instant invention comprises a roll rate sensor 40, often

referred to as a gyroscope or an angular rate sensor, for measuring the rate of

change of the angle of said vehicle 1 2 with respect to a horizontal axis over

time, having an output signal 42 indicative thereof. The roll rate sensor 40

and the first and second accelerometers 20 and 30 respectively, are preferably

mounted at a point proximate the center of gravity 14 of the vehicle 1 2.

The present invention further comprises a controller 50 or

microprocessor for receiving the output signals from each of said sensors,

preferably secured in a protected location in the vehicle 1 2. While a

conventional digital controller 50 is employed in the instant invention, one of ordinary skill in the art will appreciate that various other analog and digital

controllers may be employed herein without departing from the scope of the

claims appended hereto.

Referring now to Figs. 2 and 3, the controller 50 receives the outputs

from the first and second accelerometers 20 and 30 and the roll rate sensor

40 to determine whether a rollover event is imminent. A rollover, for purposes

of the instant invention, is defined as the vehicle 1 2 attaining a position

whereby rotation about the longitudinal axis thereof has progressed to the

point where the vehicle center of gravity 14 is positioned directly over the

center of the low side tire patches, as depicted in Fig. 3. When the vehicle is

at this point, the angle between a vertical line originating at the point of

rotation B (the trip point) of the vehicle 1 2 and the horizontal plane is called

the critical angle or stability limit. If the vehicle 1 2 has a roll rate that is

positive while in this position, rollover is imminent.

To determine imminent vehicle rollover, the controller 50 receives the

outputs from the first and second orthogonally aligned accelerometers 20 and

30 indicative of vertical and lateral acceleration, and calculates a steady state

roll angle θ therefrom. The controller 50 next calculates a rollover threshold

line TH, readily plotted in a plane of angular velocity versus roll rate, that is

dependent upon the physical dimensions of each particular vehicle. The

vehicle roll rate ω is readily mathematically described using the vehicle track

width T, the distance from the trip point B to the vehicle center of gravity L,

the angle between the trip point B and the vehicle center of gravity α, the vehicle roll angle θ, the mass moment of inertia around the trip point l_b, and

the weight of the vehicle mg, according to the following formula:

Fig. 4 depicts the threshold line TH plotted in the angular velocity

versus roll angle plane for positive roll angles and roll rates. A rollover

condition for the given vehicle 1 2 obtains when the point described by

intersection of the calculated roll angle and the sensed roll rate (angular

velocity) is above and to the right of the rollover threshold line TH on the plot,

indicating that there exists sufficient rotational kinetic energy to rotate the

vehicle 1 2 past its stability limit or critical angle.

In order to accurately calculate the roll angle in highly dynamic

conditions, a dynamic roll angle θ_d may be calculated by the controller 50 by

summing the steady state calculated roll angle θ with the instantaneous roll

rate from the roll rate sensor integrated over time to produce an instantaneous

roll-angle value θ, Stated another way, the dynamic roll angle θ_d is the sum of

the steady state roll angle θ and the instantaneous roll angle θj.

The controller 50 has an output signal 52 operatively coupled to the

vehicle passenger restraint system 60 that initiates operation of a passenger

restraint system 60 including deployment of airbags and actuation of seatbelt

pretensioners if an imminent rollover is detected. The orthogonally aligned first and second accelerometers 20 and 30 of

the instant invention can be monitored by the controller 50 to determine the

existence of non-steady-state conditions such as high vertical acceleration

cornering on banked curves and spurious horizontal or vertical accelerations

caused by rough road conditions. The controller 50 of the instant invention

conditionally determines the validity of the roll angle calculations and may

determine not to activate the passenger restraint deployment output 52 based

on physics and inherent vehicle 1 2 parameters such as mass, center of

gravity, height from ground, etc. As an example, the controller 50 may

determine the existence of an imminent rollover event based on the calculated

roll angle and roll rate as discussed hereinabove, but the second accelerometer

30 indicates a high vertical acceleration while the first accelerometer 20

indicates minimal lateral acceleration. This state is readily recognizable by the

controller 50 of the instant invention as traversal of a banked section of

pavement or a large bump rather than a rollover condition, thereby obviating

the need for deployment of passenger restraints. The controller 50 may make

an analogous determination where high lateral acceleration is present while

vertical acceleration is minimal.

While specific embodiments of the instant invention have been

described in detail, those with ordinary skill in the art will appreciate that

various modifications and alternatives to those details could be developed in

light of the overall teachings of the disclosure. Accordingly, the particular

arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the

appended claims and any and all equivalents thereof.

Claims

WE CLAIM:

1 . An apparatus for detecting and predicting a rollover condition for

a vehicle having a passenger restraint system comprising:

a first accelerometer for measuring lateral acceleration of said vehicle

having an output signal indicative thereof;

a second accelerometer for measuring vertical acceleration of said

vehicle having an output signal indicative thereof;

a roll rate sensor for measuring the rate of change of the angle of said

vehicle with respect to a horizontal axis over time, having an

output signal indicative thereof; and

a controller for receiving the signals from said first accelerometer, said

second accelerometer, and said roll rate sensor and for calculating

vehicle roll angle based on the signals from said first and second

accelerometers, and for calculating a roll rate versus roll angle

threshold of said vehicle and comparing said threshold to the

measured vehicle roll rate and said calculated roll angle, said

controller having an output for deploying vehicle passenger

restraint measures when said measured roll rate and said

calculated roll angle exceed said roll rate versus roll angle

threshold.

2. An apparatus for detecting and predicting a rollover condition for

a vehicle having a passenger restraint system as claimed in claim 1 wherein said calculated roll angle further comprises an instantaneous roll rate

component.

3. An apparatus for detecting and predicting a rollover condition for

a vehicle having a passenger restraint system as claimed in claim 2 wherein

said instantaneous roll rate comprises the output signal of said roll rate sensor

integrated with respect to time.

4. A method for detecting and predicting a rollover condition for a

vehicle having passenger restraint measures comprising:

a.) sensing the lateral acceleration of said vehicle;

b.) sensing the vertical acceleration of said vehicle;

c.) sensing the roll rate of said vehicle about a horizontal axis;

d.) calculating a roll angle of said vehicle with respect to a horizontal

axis based on the sensed lateral and vertical acceleration thereof;

e.) calculating a rollover threshold line for said vehicle by plotting roll

rate versus roll angle for all positive values thereof;

f.) providing an output signal for actuation of a vehicle passenger

restraint system when said sensed roll rate and calculated roll

angle exceed said rollover threshold.

5. A method for detecting and predicting a rollover condition for a

vehicle having a passenger restraint system comprising:

a.) sensing the lateral acceleration of said vehicle;

b.) sensing the vertical acceleration of said vehicle;

c.) sensing the roll rate of said vehicle about a horizontal axis; d.) calculating a dynamic roll angle of said vehicle with respect to a

horizontal axis based on the sensed lateral and vertical

acceleration thereof summed with an instantaneous roll rate;

e.) calculating a rollover threshold line for said vehicle by plotting roll

rate versus roll angle for all positive values thereof;

f.) providing an output signal for actuation of a vehicle passenger

restraint system when said sensed roll rate and calculated roll

angle exceed said rollover threshold.

6. A method for detecting and predicting a rollover condition for a

vehicle having a passenger restraint system as claimed in claim 5 wherein said

instantaneous roll rate comprises said sensed roll rate integrated with respect

to time.