U.S. patent application number 11/682017 was filed with the patent office on 2007-09-13 for acceleration estimation device and vehicle.
This patent application is currently assigned to YAMAHA HATSUDOKI KABUSHIKI KAISHA. Invention is credited to Yoshinobu NISHIIKE, Yoshitaka NISHIIKE, Hiroto WATANABE.
Application Number | 20070213904 11/682017 |
Document ID | / |
Family ID | 38039196 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070213904 |
Kind Code |
A1 |
WATANABE; Hiroto ; et
al. |
September 13, 2007 |
ACCELERATION ESTIMATION DEVICE AND VEHICLE
Abstract
In an acceleration estimation device for estimating acceleration
of a vehicle, a Karman filter for a constant speed estimates
x-direction acceleration offset and z-direction acceleration offset
when a motorcycle is stopped and is traveling at constant speed. An
offset storage stores an x-direction acceleration offset estimated
value and a z-direction acceleration offset estimated value. An
offset corrector corrects an x-direction acceleration and a
z-direction acceleration on the basis of the x-direction
acceleration offset estimated value and the z-direction
acceleration offset estimated value when the motorcycle is
accelerated and decelerated. A Karman filter for
acceleration/deceleration estimates the pitch angle of a vehicle
body when the motorcycle is accelerated and decelerated. An
acceleration corrector obtains an X-direction acceleration and a
Z-direction acceleration on the basis of the estimated pitch angle.
A vehicle speed operation unit integrates over time the X-direction
acceleration to calculate an X-direction speed.
Inventors: |
WATANABE; Hiroto; (Shizuoka,
JP) ; NISHIIKE; Yoshinobu; (Shizuoka, JP) ;
NISHIIKE; Yoshitaka; (Kyoto, JP) |
Correspondence
Address: |
YAMAHA HATSUDOKI KABUSHIKI KAISHA;C/O KEATING & BENNETT, LLP
8180 GREENSBORO DRIVE, SUITE 850
MCLEAN
VA
22102
US
|
Assignee: |
YAMAHA HATSUDOKI KABUSHIKI
KAISHA
Iwata-shi
JP
|
Family ID: |
38039196 |
Appl. No.: |
11/682017 |
Filed: |
March 5, 2007 |
Current U.S.
Class: |
701/45 |
Current CPC
Class: |
G01P 15/08 20130101;
B60T 8/1706 20130101; B60T 2250/06 20130101; B60T 8/172 20130101;
B60W 40/107 20130101; B60W 2520/105 20130101; B60W 2720/16
20130101; B60T 2270/411 20130101; G01P 21/00 20130101; G01P 15/18
20130101; B60W 2050/0013 20130101; B60W 10/184 20130101 |
Class at
Publication: |
701/45 |
International
Class: |
B60R 22/00 20060101
B60R022/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2006 |
JP |
2006-062979 |
Claims
1. An acceleration estimation device for estimating acceleration of
a vehicle, comprising: a first acceleration sensor arranged to
detect an acceleration in a forward-and-backward direction of the
vehicle; a second acceleration sensor arranged to detect an
acceleration in an up-and-down direction of the vehicle; a wheel
speed detector arranged to detect a wheel speed of the vehicle; an
offset estimator arranged to estimate offset in the first
acceleration sensor and offset in the second acceleration sensor
using a relationship among a detected value in the first
acceleration sensor, a detected value in the second acceleration
sensor, and a detected value in the wheel speed detector when the
vehicle is at a substantially constant speed; and a corrector
arranged to correct the detected value in the first acceleration
sensor and the detected value in the second acceleration sensor on
the basis of an estimated value of the offset in the first
acceleration sensor and an estimated value of the offset in the
second acceleration sensor that are obtained by the offset
estimator when the vehicle is accelerated or decelerated.
2. The acceleration estimation device according to claim 1, wherein
the offset estimator includes: a first Karman filter arranged to
estimate the offset in the first acceleration sensor and the offset
in the second acceleration sensor using a relationship among the
acceleration in a traveling direction of the vehicle that is
substantially perpendicular to a direction of gravity, the
acceleration in a vertical direction parallel to the direction of
gravity, the detected value in the first acceleration sensor, the
detected value in the second acceleration sensor, a speed in the
traveling direction, a speed in the vertical direction, the speed
of the vehicle obtained from the detected value in the wheel speed
detector, and a pitch angle of the vehicle.
3. The acceleration estimation device according to claim 1, further
comprising: a pitch angle estimator arranged to estimate a pitch
angle of the vehicle when the vehicle is accelerated or
decelerated; and an acceleration calculator arranged to calculate
an acceleration in a traveling direction of the vehicle that is
perpendicular to the direction of gravity, and an acceleration in
the vertical direction parallel to the direction of gravity on the
basis of the detected value in the first acceleration sensor and
the detected value in the second acceleration sensor that are
corrected by the corrector and the pitch angle estimated by the
pitch angle estimator.
4. The acceleration estimation device according to claim 3, further
comprising a speed calculator arranged to integrate a calculated
value of the acceleration in the traveling direction obtained by
the acceleration calculator to calculate a speed in the traveling
direction.
5. The acceleration estimation device according to claim 3, wherein
the pitch angle estimator includes: a second Karman filter arranged
to estimate the pitch angle of the vehicle using a relationship
among the detected value in the first acceleration sensor and the
detected value in the second acceleration sensor that are corrected
by the corrector, the acceleration in the traveling direction, the
acceleration in the vertical direction, and the pitch angle of the
vehicle.
6. The acceleration estimation device according to claim 1, wherein
the offset estimator is arranged to determine that the vehicle is
in a substantially constant speed state when a rate of change in
the wheel speed detected by the wheel speed detector is not more
than a predetermined threshold value.
7. A vehicle comprising: a vehicle body; a wheel provided on the
vehicle body; an acceleration estimation device arranged on the
vehicle body; and a controller; wherein the acceleration estimation
device includes: a first acceleration sensor on the vehicle and
arranged to detect an acceleration in a forward-and-backward
direction of the vehicle, a second acceleration sensor on the
vehicle and arranged to detect an acceleration in an up-and-down
direction of the vehicle; a wheel speed detector arranged to detect
a wheel speed of the vehicle; an offset estimator arranged to
estimate offset in the first acceleration sensor and offset in the
second acceleration sensor using a relationship among a detected
value in the first acceleration sensor, a detected value in the
second acceleration sensor, and a detected value in the wheel speed
detector when the vehicle is at a substantially constant speed; and
a corrector arranged to correct the detected value in the first
acceleration sensor and the detected value in the second
acceleration sensor on the basis of an estimated value of the
offset in the first acceleration sensor and an estimated value of
the offset in the second acceleration sensor that are obtained by
the offset estimator when the vehicle is accelerated or
decelerated; and the controller controls the rotation of the wheel
on the basis of at least one of the detected value in the first
acceleration sensor and the detected value in the second
acceleration sensor that are corrected by the acceleration
estimation device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an acceleration estimation
device that estimates vehicle accelerations, and a vehicle
including the same.
[0003] 2. Description of the Related Art
[0004] The traveling speeds of vehicles can be calculated on the
basis of the rotational speeds of its wheels. When the vehicle is
rapidly accelerated, however, the wheels may be rotated while
sliding against a road surface. When the vehicle is rapidly
decelerated (braked), the wheels may be caused to slide against the
road surface. In such a case, the speed of the vehicle that can be
calculated from the rotational speed of the wheels does not
coincide with the actual traveling speed of the vehicle.
[0005] Therefore, the acceleration of the vehicle is detected using
an acceleration sensor, and the detected acceleration is integrated
to calculate the speed of the vehicle.
[0006] The acceleration sensor outputs the acceleration as a
voltage. Generally, offset exists in the acceleration sensor. Here,
the offset in the acceleration sensor refers to a value obtained by
expressing a difference between a nominal value of the output
voltage of the acceleration sensor at an acceleration of 0
m/s.sup.2 and a value of the actual output voltage of the
acceleration sensor in terms of units of (m/s.sup.2) of
acceleration.
[0007] The offset varies for each acceleration sensor. JP 10-104259
A discloses a vehicle longitudinal acceleration estimating device
that removes an unnecessary component of an acceleration sensor for
detecting a longitudinal acceleration to calculate an estimated
value of the longitudinal acceleration.
[0008] In the longitudinal acceleration estimating device disclosed
in JP 10-104259 A, the change in an output voltage of the
acceleration sensor is frequency-analyzed and is classified into
changes due to DC offset, changes due to temperature drift, changes
due to road conditions, changes due to acceleration/deceleration of
a vehicle, and changes due to pitching of a vehicle body. A Karman
filter is used to extract only a variation component having a
higher frequency than a particular frequency from a detected value
of the longitudinal acceleration by the acceleration sensor.
[0009] This causes a variation component due to DC offset and a
variation component due to temperature drift respectively having
low frequencies to be removed from the detected value of the
longitudinal acceleration. As a result, the estimated value of the
longitudinal acceleration is not affected by changes with time and
changes in temperature.
[0010] When the vehicle is rapidly accelerated or decelerated,
however, the vehicle body is inclined by pitching. That is, the
front of the vehicle body rises at the time of rapid acceleration,
and lowers at the time of rapid deceleration. Even when the vehicle
is traveling at constant speed, the vehicle body is slightly
pitched. This causes a component of a gravitational force to be
exerted on the acceleration sensor for detecting the longitudinal
acceleration. As a result, the detected value in the acceleration
sensor includes an offset and is affected by the component of the
gravitational force.
[0011] In the longitudinal acceleration estimating device disclosed
in JP10-104259A, an unnecessary component in a particular frequency
band can be removed from the detected value in the acceleration
sensor. However, the effect of the component of force of gravity
due to pitching in a frequency band other than the particular
frequency band cannot be removed. Therefore, the longitudinal
acceleration of the vehicle cannot be accurately estimated.
SUMMARY OF THE INVENTION
[0012] In order to overcome the problems described above, preferred
embodiments of the present invention provide an acceleration
estimation device that can estimate vehicle accelerations with high
accuracy and a vehicle including the same.
[0013] According to a preferred embodiment of the present
invention, an acceleration estimation device that estimates
accelerations of a vehicle includes a first acceleration sensor
that is provided in the vehicle and detects the acceleration in the
forward-and-backward direction of the vehicle; a second
acceleration sensor that is provided in the vehicle and detects the
acceleration in the up-and-down direction of the vehicle; a wheel
speed detector that detects a wheel speed of the vehicle; an offset
estimator that estimates offset in the first acceleration sensor
and offset in the second acceleration sensor using the relationship
among a detected value in the first acceleration sensor, a detected
value in the second acceleration sensor, and a detected value in
the wheel speed detector when the vehicle is at a substantially
constant speed; and a corrector that corrects the detected value in
the first acceleration sensor and the detected value in the second
acceleration sensor on the basis of an estimated value of the
offset in the first acceleration sensor and an estimated value of
the offset in the second acceleration sensor that are obtained by
the offset estimator when the vehicle is accelerated or
decelerated.
[0014] Here, the time when the vehicle is at a substantially
constant speed refers to the time when the vehicle is stopped and
the time when the rate of change in the traveling speed of the
vehicle is not more than a predetermined threshold value. The
threshold value is in a range of about -0.2 m/s.sup.2 to about +0.2
m/s.sup.2, for example.
[0015] In the acceleration estimation device, the first
acceleration sensor and the second acceleration sensor are provided
in the vehicle. The first acceleration sensor detects the
acceleration in the forward-and-backward direction of the vehicle,
and the second acceleration sensor detects the acceleration in the
up-and-down direction of the vehicle. Further, the wheel speed
detector detects the wheel speed of the vehicle.
[0016] The offset estimator estimates the offset in the first
acceleration sensor and the offset in the second acceleration
sensor using the relationship among the detected value in the first
acceleration sensor, the detected value in the second acceleration
sensor, and the detected value in the wheel speed detector when the
vehicle is at a substantially constant speed. Even when a detected
value of the acceleration in the forward-and-backward direction and
a detected value of the acceleration in the up-and-down direction
are affected by gravity due to pitching, the accelerations are
detected using the previously estimated offset when the vehicle is
at a constant speed. This allows the acceleration in a traveling
direction to be accurately detected.
[0017] The offset in the first acceleration sensor and the offset
in the second acceleration sensor preferably are not changed in a
short time period.
[0018] When the vehicle is accelerated or decelerated, the
corrector corrects the detected value in the first acceleration
sensor and the detected value in the second acceleration sensor on
the basis of the estimated value of the offset in the first
acceleration sensor and the estimated value of the offset in the
second acceleration sensor that are obtained when the vehicle is at
a substantially constant speed. This allows the acceleration in the
forward-and-backward direction and the acceleration in the
up-and-down direction of the vehicle to be detected with high
accuracy.
[0019] The offset estimator may include a first Karman filter that
estimates the offset in the first acceleration sensor and the
offset in the second acceleration sensor based on the relationship
among the acceleration in a traveling direction of the vehicle that
is perpendicular or substantially perpendicular to a direction of
gravity; the acceleration in a vertical direction that is parallel
or substantially parallel to the direction of gravity; the detected
value in the first acceleration sensor; the detected value in the
second acceleration sensor; a speed in the traveling direction; a
speed in the vertical direction; the speed of the vehicle obtained
from the detected value in the wheel speed detector; and the pitch
angle of the vehicle.
[0020] In this case, the first Karman filter estimates the offset
in the first acceleration sensor and the offset in the second
acceleration sensor. Even when the detected value of the
acceleration in the forward-and-backward direction and the detected
value of the acceleration in the up-and-down direction are affected
by gravity due to pitching having an arbitrary frequency, it is
possible to more accurately estimate the offset in the first
acceleration sensor and the offset in the second acceleration
sensor.
[0021] An observed disturbance applied to the first acceleration
sensor and the second acceleration sensor is removed in the first
Karman filter. This prevents a control system controlled on the
basis of the acceleration in the forward-and-backward direction and
the acceleration in the up-and-down direction of the vehicle from
being unstable due to the observed disturbance.
[0022] The acceleration estimation device may further include a
pitch angle estimator that estimates the pitch angle of the vehicle
when the vehicle is accelerated or decelerated, and an acceleration
calculator that calculates the acceleration in the traveling
direction of the vehicle that is perpendicular or substantially
perpendicular to the direction of gravity, and the acceleration in
the vertical direction that is parallel or substantially parallel
to the direction of gravity on the basis of the detected value in
the first acceleration sensor and the detected value in the second
acceleration sensor that are corrected by the corrector and the
pitch angle estimated by the pitch angle estimator.
[0023] In this case, the pitch angle estimator estimates the pitch
angle of the vehicle, and the acceleration calculator calculates
the acceleration in the traveling direction that is perpendicular
or substantially perpendicular to the direction of gravity and the
acceleration in the vertical direction that is parallel or
substantially parallel to the direction of gravity on the basis of
the detected value in the first acceleration sensor and the
detected value in the second acceleration sensor that are corrected
and the estimated pitch angle. This allows the acceleration in the
traveling direction of the vehicle to be detected with high
accuracy even when the vehicle is accelerated or decelerated.
[0024] The acceleration estimation device may further include a
speed calculator that integrates a calculated value of the
acceleration in the traveling direction obtained by the
acceleration calculator to calculate a speed in the traveling
direction. In this case, the speed in the traveling direction of
the vehicle can be detected with high accuracy.
[0025] The pitch angle estimator may include a second Karman filter
that estimates the pitch angle of the vehicle using the
relationship among the detected value in the first acceleration
sensor and the detected value in the second acceleration sensor
that are corrected by the corrector, the acceleration in the
traveling direction, the acceleration in the vertical direction,
and the pitch angle of the vehicle.
[0026] In this case, the second Karman filter estimates the pitch
angle of the vehicle. Even when the detected value of the
acceleration in the forward-and-backward direction and the detected
value of the acceleration in the up-and-down direction are affected
by gravity due to pitching having an arbitrary frequency when the
vehicle is accelerated or decelerated, it is possible to more
accurately estimate the pitch angle of the vehicle.
[0027] The offset estimator may determine that the vehicle is in a
substantially constant speed state when the rate of change in the
wheel speed detected by the wheel speed detector is not more than a
predetermined threshold value.
[0028] In this case, it is determined that the vehicle is in the
substantially constant speed state when the rate of change in the
wheel speed is not more than the threshold value. The offset
estimator estimates the offset in the first acceleration sensor and
the offset in the second acceleration sensor. Even when the speed
of the vehicle is slightly changed, the offset in the first
acceleration sensor and the offset in the second acceleration
sensor can be detected with high accuracy.
[0029] According to another preferred embodiment of the present
invention, a vehicle includes a vehicle body, a wheel provided on
the vehicle body, an acceleration estimation device that is
provided on the vehicle body, and a controller, wherein the
acceleration estimation device includes a first acceleration sensor
that is provided on the vehicle and detects the acceleration in the
forward-and-backward direction of the vehicle, a second
acceleration sensor that is provided on the vehicle and detects the
acceleration in the up-and-down direction of the vehicle, a wheel
speed detector that detects a wheel speed of the vehicle, an offset
estimator that estimates offset in the first acceleration sensor
and offset in the second acceleration sensor using the relationship
among a detected value in the first acceleration sensor, a detected
value in the second acceleration sensor, and a detected value in
the wheel speed detector when the vehicle is at a substantially
constant speed, and a corrector that corrects the detected value in
the first acceleration sensor and the detected value in the second
acceleration sensor on the basis of an estimated value of the
offset in the first acceleration sensor and an estimated value of
the offset in the second acceleration sensor that are obtained by
the offset estimator when the vehicle is accelerated or
decelerated, and the controller controls the rotation of the wheel
on the basis of at least one of the detected value in the first
acceleration sensor and the detected value in the second
acceleration sensor that are corrected by the acceleration
estimation device.
[0030] When the vehicle is at a substantially constant speed, the
acceleration estimation device estimates the offset in the first
acceleration sensor and the offset in the second acceleration
sensor. When the vehicle is accelerated or decelerated, the
acceleration estimation device corrects the detected value in the
first acceleration sensor and the detected value in the second
acceleration sensor on the basis of the estimated value of the
offset in the first acceleration sensor and the estimated value of
the offset in the second acceleration sensor that are obtained when
the vehicle is at a substantially constant speed. This allows the
acceleration in the forward-and-backward direction and the
acceleration in the up-and-down direction of the vehicle to be
detected with high accuracy.
[0031] The controller controls the rotation of the wheel on the
basis of at least one of the detected value in the first
acceleration sensor and the detected value in the second
acceleration sensor that are corrected by the acceleration
estimation device.
[0032] According to the preferred embodiments of the present
invention, the offset estimator estimates the offset in the first
acceleration sensor and the offset in the second acceleration
sensor using the relationship among the detected value in the first
acceleration sensor, the detected value in the second acceleration
sensor, and the detected value in the wheel speed detector. Even
when the detected value of the acceleration in the
forward-and-backward direction and the detected value of the
acceleration in the up-and-down direction are affected by gravity
due to pitching, the acceleration is detected using the previously
estimated offset when the vehicle is at a constant speed. This
allows the acceleration in the traveling direction to be accurately
detected.
[0033] When the vehicle is accelerated or decelerated, the
corrector corrects the detected value in the first acceleration
sensor and the detected value in the second acceleration sensor on
the basis of the estimated value of the offset in the first
acceleration sensor and the estimated value of the offset in the
second acceleration sensor that are obtained when the vehicle is at
a substantially constant speed. This allows the acceleration in the
forward-and-backward direction and the acceleration in the
up-and-down direction of the vehicle to be detected with high
accuracy.
[0034] Other features, elements, steps, characteristics, and
advantages of the present invention will become more apparent from
the following description of preferred embodiments of the present
invention with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a diagram showing the relationship of
accelerations received by an acceleration sensor at the time of
deceleration.
[0036] FIG. 2 is a diagram showing the schematic configuration of
the overall motorcycle according to a preferred embodiment of the
present invention.
[0037] FIG. 3 is a schematic view showing a hydraulic system and an
electrical system of an ABS.
[0038] FIG. 4 is a block diagram showing the configuration of a
vehicle speed estimator.
[0039] FIG. 5 is a diagram for explaining the relationship between
an operation of estimating x-direction acceleration offset and
z-direction acceleration offset in the vehicle speed estimator and
the change in wheel speed.
[0040] FIG. 6 is a flowchart showing the operations of the vehicle
speed estimator.
[0041] FIG. 7 is a block diagram showing the configuration of an
ABS signal processor.
[0042] FIG. 8 is a diagram showing the relationship between an
acceleration offset true value and an acceleration offset estimated
error.
[0043] FIG. 9 is a diagram showing the change with time of an
acceleration offset estimated value in the process of estimating
acceleration offset.
[0044] FIG. 10 is a diagram showing the results of estimation of
X-direction acceleration.
[0045] FIG. 11 is a diagram showing the results of estimation of a
vehicle speed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] In the following preferred embodiments, description is made
of an example in which an acceleration estimation device according
to the present invention is applied to a motorcycle.
(1) Basic Idea of the Present Preferred Embodiment
[0047] First, the relationship of accelerations at the time of
deceleration of a motorcycle comprising an acceleration detection
device according to the present preferred embodiment will be
described.
[0048] FIG. 1 is a diagram showing the relationship of
accelerations received by an acceleration sensor at the time of
deceleration.
[0049] As shown in FIG. 1, when a motorcycle 100 is decelerated by
a front-wheel brake, a front suspension contracts, and a rear
suspension expands. Therefore, the motorcycle 100 is inclined
forward in its traveling direction.
[0050] A coordinate system fixed to the ground below the motorcycle
100 is taken as a ground coordinate system, and a coordinate system
fixed to the acceleration sensor attached to the motorcycle 100 is
taken as a sensor coordinate system.
[0051] On the ground coordinate system, a traveling direction of
the motorcycle 100 (a direction perpendicular or substantially
perpendicular to gravity) on a horizontal ground surface 600 is
defined as an X-direction, and a vertical direction (a direction of
gravity) is defined as a Z-direction. Consequently, the X-direction
and the Z-direction on the ground coordinate system are not changed
irrespective of the posture of the motorcycle 100.
[0052] On the sensor coordinate system, a direction of the
horizontal axis of the motorcycle 100 (a forward-and-backward
direction of a vehicle body 1) in a case where the motorcycle 100
is in a horizontal state is defined as an x-direction, and a
direction perpendicular or substantially perpendicular to the
horizontal axis of the motorcycle 100 (an up-and-down direction of
the vehicle body 1) is defined as a z-direction. Consequently, the
x-direction and the z-direction on the sensor coordinate system are
inclined to the X-direction and the Z-direction on the ground
coordinate system by the posture of the motorcycle 100.
[0053] Hereinafter, the X-direction on the ground coordinate system
is merely referred to as an X-direction or a traveling direction,
and the Z-direction on the ground coordinate system is referred to
as a Z-direction or a vertical direction.
[0054] From FIG. 1, an acceleration G.sub.x in the x-direction and
an acceleration G.sub.z in the z-direction on the sensor coordinate
system are respectively expressed by the following equations using
an acceleration a.sub.X in the X-direction and an acceleration
a.sub.Z in the Z-direction on the ground coordinate system:
G.sub.x=a.sub.x cos .theta..sub.p-a.sub.z sin .theta..sub.p (1)
G.sub.z=a.sub.x sin .theta..sub.p+a.sub.z cos .theta..sub.p (2)
[0055] In the foregoing equations (1) and (2), .theta..sub.p
denotes the pitch angle of the vehicle body 1.
[0056] The motorcycle 100 in the present preferred embodiment is
provided with an x-direction acceleration sensor for detecting the
acceleration G.sub.x in the x-direction of the vehicle body 1 and a
z-direction acceleration sensor for detecting the acceleration
G.sub.z in the z-direction.
[0057] The acceleration a.sub.X in the X-direction and the
acceleration a.sub.Z in the Z-direction on the ground coordinate
system of the motorcycle 100 can be measured by detecting the
acceleration G.sub.x in the x-direction using the x-direction
acceleration sensor, detecting the acceleration G.sub.z in the
z-direction using the z-direction acceleration sensor, and
determining the pitch angle .theta..sub.P.
[0058] Generally, offset exists in the acceleration sensor. Here,
the offset in the acceleration sensor refers to a value obtained by
expressing a difference between a nominal value of an output
voltage of the acceleration sensor at an acceleration of 0
m/s.sup.2 and a value of an actual output voltage of the
acceleration sensor in terms of unit of acceleration
(m/s.sup.2).
[0059] Hereinafter, offset in the x-direction acceleration sensor
is referred to as x-direction acceleration offset, and offset in
the z-direction acceleration sensor is referred to as z-direction
acceleration offset.
[0060] In the present preferred embodiment, the x-direction
acceleration offset and the z-direction acceleration offset are
estimated using an extended Karman filter, described later, when
the motorcycle 100 is at a substantially constant speed.
[0061] Here, the time when the motorcycle 100 is at a substantially
constant speed includes the time when the motorcycle 100 is stopped
and the time when the rate of change in the traveling speed of the
motorcycle 100 is not more than a predetermined threshold value. In
the following description, the time when the motorcycle 100 is
traveling at a constant speed and the time when the rate of change
in the traveling speed is not more than a threshold value are
merely referred to as the time when the motorcycle 100 is traveling
at a constant speed.
[0062] When the motorcycle 100 is accelerated and decelerated, the
acceleration G.sub.X in the x-direction and the acceleration
G.sub.Z in the z-direction are corrected on the basis of respective
estimated values of the x-direction acceleration offset and the
z-direction acceleration offset, and the pitch angle .theta..sub.P
of the vehicle body 1 is estimated on the basis of respective
corrected values of the acceleration G.sub.x in the x-direction and
the acceleration G.sub.z in the z-direction. Further, the
acceleration in the X-direction and the acceleration in the
Z-direction of the motorcycle 100 are calculated using an estimated
value of the pitch angle .theta..sub.P. Further, the acceleration
in the X-direction is integrated to calculate the speed in the
X-direction of the motorcycle 100.
(2) Configuration of the Motorcycle
[0063] FIG. 2 is a diagram showing the schematic configuration of
the motorcycle 100 according to the present preferred embodiment.
An ABS (Anti-Lock Brake System), described later, is preferably
included in the motorcycle 100.
[0064] As shown in FIG. 2, a front wheel 2 is attached to the front
of the vehicle body 1 of the motorcycle 100, and a rear wheel 3 is
attached to the rear of the vehicle body 1.
[0065] A sensor rotor 4 that rotates with the front wheel 2 is
provided at the center of the front wheel 2. A front-wheel speed
sensor 5 for detecting the rotational speed of the front wheel 2 is
attached to the sensor rotor 4. Further, there is provided a front
brake caliper 6 that is brought into contact with a brake disk of
the front wheel 2 for braking the front wheel 2.
[0066] A sensor rotor 7 that rotates with the rear wheel 3 is
provided at the center of the rear wheel 3. A rear-wheel speed
sensor 8 for detecting the rotational speed of the rear wheel 3 is
attached to the sensor rotor 7. Further, there is provided a rear
brake caliper 9 that is brought into contact with a brake disk of
the rear wheel 3 for braking the rear wheel 3.
[0067] A handle 11 is arranged so as to be swingable right and left
at the top on the front side of the vehicle body 1. The handle 11
is provided with a front brake lever 12 and a warning lamp 13.
[0068] A hydraulic unit 10 is provided at the center of the vehicle
body 1. A rear brake pedal 14 is provided below the center of the
vehicle body 1. An x-direction acceleration sensor 21 and a
z-direction acceleration sensor 22 are attached to a position at
the center of gravity of the vehicle body 1. As the x-direction
acceleration sensor 21 and the z-direction acceleration sensor 22,
a two-axis acceleration sensor or a three-axis acceleration sensor
for use in detection of inclination, an impact of air bags, a drop
of hard disks, etc. can be used.
[0069] An electronic control unit (hereinafter abbreviated as ECU)
30 and a fail-safe relay 31 are provided at the rear of the vehicle
body 1.
(3) Configuration of the ABS
[0070] FIG. 3 is a schematic view showing a hydraulic system and an
electrical system of the ABS.
[0071] As shown in FIG. 3, a master cylinder 15 is connected to the
front brake lever 12, and the master cylinder 15 is connected to
the hydraulic unit 10. The master cylinder 15 is provided with a
brake switch 17. A master cylinder 16 is connected to the rear
brake pedal 14, and the master cylinder 16 is connected to the
hydraulic unit 10. The master cylinder 16 is provided with a brake
switch 18.
[0072] When a driver operates the front brake lever 12, the master
cylinder 15 raises the pressure of hydraulic fluid supplied to the
front brake caliper 6 from the hydraulic unit 10. This causes the
front brake caliper 6 to be driven to brake the front wheel 2. At
this time, the brake switch 17 is turned on so that a front-wheel
brake signal Bf is fed to the ECU 30.
[0073] When the driver operates the rear brake lever 14, the master
cylinder 16 raises the pressure of hydraulic fluid supplied to the
rear brake caliper 9 from the hydraulic unit 10. This causes the
rear brake caliper 9 to be driven to brake the rear wheel 3. At
this time, the brake switch 18 is turned on so that a rear-wheel
brake signal Br is fed to the ECU 30.
[0074] A front-wheel speed signal Rf representing the rotational
speed of the front wheel 2 is fed to the ECU 30 from the
front-wheel speed sensor 5 provided in the sensor rotor 4 in the
front wheel 2. A rear-wheel speed signal Rr representing the
rotational speed of the rear wheel 3 is fed to the ECU 30 from the
rear-wheel speed sensor 8 provided in the sensor rotor 7 in the
rear wheel 3. Hereinafter, the rotational speed of the front wheel
2 is referred to as a front wheel speed, and the rotational speed
of the rear wheel 3 is referred to as a rear wheel speed.
[0075] An x-direction acceleration signal Ax representing
x-direction acceleration is fed to the ECU 30 from the x-direction
acceleration sensor 21. A z-direction acceleration signal Az
representing z-direction acceleration is fed to the ECU 30 from the
z-direction acceleration sensor 22.
[0076] The ECU 30 outputs a motor driving signal MD for driving a
motor for a hydraulic pump within the hydraulic unit 10 to the
hydraulic unit 10 through the fail-safe relay 31 in response to the
front-wheel brake signal Bf or the rear-wheel brake signal Br.
[0077] The ECU 30 outputs a reduced pressure signal FP for the
front wheels and a reduced pressure signal RP for the rear wheels
to the hydraulic unit 10 through the fail-safe relay 31 on the
basis of the front-wheel speed signal Rf, the rear-wheel speed
signal Rr, the x-direction acceleration signal Ax, and the
z-direction acceleration signal Az.
[0078] The hydraulic unit 10 reduces the pressure of hydraulic
fluid supplied to the front brake caliper 6 in response to the
reduced pressure signal FP. This causes the braking of the front
wheel 2 by the front brake caliper 6 to be released. Further, the
motorcycle 100 reduces the pressure of hydraulic fluid supplied to
the rear brake caliper 9 in response to the reduced pressure signal
RP. This causes the braking of the rear wheel 3 by the rear brake
caliper 9 to be released.
[0079] The fail-safe relay 31 switches the operation of the ABS in
the hydraulic unit 10 into a normal braking operation when the ABS
fails. When the ABS fails, the warning lamp 13 lights up.
(4) Configuration of the Vehicle Speed Estimator
[0080] FIG. 4 is a block diagram showing the configuration of a
vehicle speed estimator.
[0081] The acceleration estimation device according to the present
preferred embodiment is preferably used for a vehicle speed
estimator 300 shown in FIG. 4. The vehicle speed estimator 300
includes a speed selector 310, a filter selector 320, a Karman
filter 330 for constant speed, a Karman filter 340 for
acceleration/deceleration, an offset storage 350, an offset
corrector 360, an acceleration corrector 370, and a vehicle speed
operation unit 380. Each of the constituent elements within the
vehicle speed estimator 300 is preferably provided in the ECU 30
shown in FIGS. 2 and 3 with an associated program function.
[0082] The front-wheel speed signal Rf and the rear-wheel speed
signal Rr are respectively fed to the speed selector 310 from the
front-wheel speed sensor 5 and the rear-wheel speed sensor 8, and
the x-direction acceleration signal Ax is fed thereto from the
x-direction acceleration sensor 21.
[0083] The speed selector 310 selects the front-wheel speed signal
Rf as a vehicle speed when the motorcycle 100 is at a substantially
constant speed (is stopped and is traveling at constant speed).
When the motorcycle 100 is accelerated and decelerated, the front
wheel speed and the rear wheel speed are compared with each other
on the basis of the front-wheel speed signal Rf and the rear-wheel
speed signal Rr, to select the smaller one of the front wheel speed
and the rear wheel speed as a vehicle speed at the time of the
acceleration, while selecting the larger one of the front wheel
speed and the rear wheel speed as a vehicle speed at the time of
the deceleration. Note that a substantially constant speed state or
an accelerated/decelerated state is determined on the basis of the
rate of change in the vehicle speed selected at the time of the
determination. The vehicle speed selected by the speed selector 310
is outputted to the vehicle speed operation unit 380.
[0084] The vehicle speed is provided to the Karman filter 330 from
the speed selector 310, and the x-direction acceleration signal Ax
and the z-direction acceleration signal Az are respectively fed
from the x-direction acceleration sensor 21 and the z-direction
acceleration sensor 22. The Karman filter 330 estimates the
x-direction acceleration offset and the z-direction acceleration
offset in a method, described later, when the motorcycle 100 is at
a substantially constant speed (is stopped and is traveling at a
constant speed), to obtain an x-direction acceleration offset
estimated value and a z-direction acceleration offset estimated
value.
[0085] The offset storage 350 stores the x-direction acceleration
offset estimated value and the z-direction acceleration offset
estimated value that are obtained by the Karman filter 330.
[0086] The x-direction acceleration signal Ax and the z-direction
acceleration signal Az are respectively fed to the offset corrector
360 from the x-direction acceleration sensor 21 and the z-direction
acceleration sensor 22, and the x-direction acceleration offset
estimated value and the z-direction acceleration offset estimated
value are fed thereto from the offset storage 350. The offset
corrector 360 corrects the x-direction acceleration and the
z-direction acceleration on the basis of the x-direction
acceleration offset estimated value, the z-direction acceleration
offset estimated value, the x-direction acceleration signal Ax, and
the z-direction acceleration signal Az when the motorcycle 100 is
accelerated and decelerated.
[0087] The Karman filter 340 estimates the pitch angle of the
vehicle body 1 on the basis of the wheel speed given from the speed
selector 310 and the x-direction acceleration and the z-direction
acceleration that are corrected by the offset corrector 360 when
the motorcycle 100 is accelerated and decelerated, to obtain a
pitch angle estimated value.
[0088] Information representing the results of the determination of
the substantially constant speed state or the
accelerated/decelerated state is given to the filter selector 320
from the speed selector 310. Based on the information representing
the results of the determination, the filter selector 320 operates
the Karman filter 330 in the substantially constant speed state or
operates the Karman filter 340 as well as the vehicle speed
operation unit 380 in the accelerated/decelerated state.
[0089] The acceleration corrector 370 corrects the x-direction
acceleration and the z-direction acceleration that are corrected by
the offset corrector 360 on the basis of the pitch angle estimated
value obtained by the Karman filter 340 to obtain an X-direction
acceleration and a Z-direction acceleration.
[0090] The vehicle speed operation unit 380 integrates overtime the
X-direction acceleration obtained by the acceleration corrector 370
using the vehicle speed obtained from the speed selector 310 as an
initial value immediately before the operation to calculate an
X-direction speed (vehicle speed) and output a vehicle speed signal
VX representing the vehicle speed.
(5) Operation of the Vehicle Speed Estimator
[0091] FIG. 5 is a diagram for explaining the relationship between
an operation of estimating the x-direction acceleration offset and
the z-direction acceleration offset in the vehicle speed estimator
300 and the change in the wheel speed. In FIG. 5, the vertical axis
represents offset and wheel speed, and the horizontal axis
represents time. A thick solid line indicates the change in the
wheel speed, and a thin solid line indicates the respective changes
in the x-direction acceleration offset estimated value and the
z-direction acceleration offset estimated value.
[0092] The operation of estimating the x-direction acceleration
offset and the z-direction acceleration offset is performed in the
Karman filter 330 for a constant speed when the motorcycle 100 is
stopped and is traveling at a constant speed, while the x-direction
acceleration offset estimated value and the z-direction
acceleration offset estimated value are held when the motorcycle
100 is accelerated and decelerated.
[0093] FIG. 6 is a flow chart showing the operations of the vehicle
speed estimator 300.
[0094] The filter selector 320 in the vehicle speed estimator 300
determines whether or not the rate of change in a wheel speed
selected by the speed selector 310 is larger than a predetermined
threshold value (step S1). Here, the threshold value is about -0.2
m/s.sup.2 to about +0.2 m/s.sup.2, for example.
[0095] When it is determined in the step S1 that the rate of change
in the wheel speed is not more than the predetermined threshold
value, the filter selector 320 considers that the motorcycle 100 is
stopped or is traveling at a constant speed to calculate a vehicle
speed from the wheel speed (step S2). Here, the vehicle speed
corresponds to an X-direction speed observed value, described
later.
[0096] The Karman filter 330 then respectively estimates offset in
the x-direction acceleration sensor 21 (x-direction acceleration
offset) and offset in the z-direction acceleration sensor 22
(z-direction acceleration offset) by a method, described later, to
obtain an x-direction acceleration offset estimated value and a
z-direction acceleration offset estimated value (step S3). In this
case, a Z-direction speed observed value, described later, is taken
as zero, for example. Thereafter, the procedure is returned to the
step S1.
[0097] When it is determined in the step S1 that the rate of change
in the wheel speed is more than the predetermined threshold value,
the filter selector 320 considers that the motorcycle 100 is
accelerated or decelerated, and the offset storage 350 stores
previous respective values of the x-direction acceleration offset
estimated value and the z-direction acceleration offset estimated
value (values estimated in the step S3) (step S4).
[0098] The offset corrector 360 then respectively corrects a
detected value in the x-direction acceleration sensor 21 and a
detected value in the z-direction acceleration sensor 22 by a
method, described later, on the basis of the x-direction
acceleration offset estimated value and the z-direction
acceleration offset estimated value that are stored in the offset
storage 350 (step S5).
[0099] The Karman filter 340 for acceleration/deceleration then
estimates the pitch angle of the vehicle body 1 by a method,
described later, on the basis of the detected value in the
x-direction acceleration sensor 21 and the detected value in the
z-direction acceleration sensor 22 that are corrected by the offset
corrector 360 to obtain a pitch angle estimated value (step
S6).
[0100] The acceleration corrector 370 then corrects an x-direction
acceleration and a z-direction acceleration by a method, described
later, using the detected value in the x-direction acceleration
sensor 21 and the detected value in the z-direction acceleration
sensor 22 that are corrected by the offset corrector 360 and the
pitch angle estimated value to calculate an X-direction
acceleration and a Y-direction acceleration (step S7).
[0101] Furthermore, the vehicle speed operation unit 380 integrates
over time the X-direction acceleration, to calculate a vehicle
speed (step S8). Thereafter, the procedure is returned to the step
S1.
(6) Configuration and Operation of the Abs Signal Processor
[0102] FIG. 7 is a block diagram showing the configuration of an
ABS signal processor.
[0103] The ABS signal processor shown in FIG. 7 includes the
vehicle speed estimator 300, a first signal generator 400, and a
second signal generator 500. The ABS signal processor shown in FIG.
7 is provided in the ECU 30 shown in FIGS. 2 and 3 with an
associated program function.
[0104] The first signal generator 400 includes an acceleration
operation unit 410, a slip determination unit 420, an acceleration
determination unit 430, and a reduced pressure signal generator
440. The second signal generator 500 includes an acceleration
operation unit 510, a slip determination unit 520, an acceleration
determination unit 530, and a reduced pressure signal generator
540.
[0105] The front-wheel speed signal Rf is fed to the slip
determination unit 420 in the first signal generator 400 from the
front-wheel speed sensor 5, and the vehicle speed signal VX is fed
thereto from the vehicle speed estimator 300. The front-wheel speed
signal Rf is fed to the acceleration operation unit 410 from the
front-wheel speed sensor 5.
[0106] The slip determination unit 420 determines whether or not
the front wheel 2 is slipping depending on whether or not the
difference between the vehicle speed calculated on the basis of the
front-wheel speed signal Rf and the vehicle speed represented by
the vehicle speed signal VX is larger than a predetermined
reference value.
[0107] The acceleration operation unit 410 calculates the
acceleration of the front wheel 2 on the basis of the front-wheel
speed signal Rf. The acceleration determination unit 430 determines
whether or not the front wheel 2 is returned from a slipping state
depending on whether or not the acceleration calculated by the
acceleration operation unit 410 is changed from negative to
positive.
[0108] The reduced pressure signal generator 440 feeds a reduced
pressure signal FP to the hydraulic unit 10 shown in FIG. 3 when
the slip determination unit 420 determines that the front wheel 2
is slipping while releasing the reduced pressure signal FP when the
acceleration determination unit 430 determines that the front wheel
2 is returned from a slipping state.
[0109] The rear-wheel speed signal Rr is fed to the slip
determination unit 520 in the second signal generator 500 from the
rear-wheel speed sensor 8, and the vehicle speed signal VX is fed
thereto from the vehicle speed estimator 300. The rear-wheel speed
signal Rr is fed to the acceleration operation unit 510 from the
rear-wheel speed sensor 8.
[0110] The slip determination unit 520 determines whether or not
the rear wheel 3 is slipping depending on whether or not the
difference between the vehicle speed calculated on the basis of the
rear-wheel speed signal Rr and the vehicle speed represented by the
vehicle speed signal VX is larger than a predetermined reference
value.
[0111] The acceleration operation unit 510 calculates the
acceleration of the rear wheel 3 on the basis of the rear-wheel
speed signal Rr. The acceleration determination unit 530 determines
whether or not the rear wheel 3 is returned from a slipping state
depending on whether or not the acceleration calculated by the
acceleration operation unit 510 is changed from negative to
positive.
[0112] The reduced pressure signal generator 540 feeds a reduced
pressure signal RP to the hydraulic unit 10 shown in FIG. 3 when
the slip determination unit 520 determines that the rear wheel 3 is
slipping while releasing the reduced pressure signal RP when the
acceleration determination unit 530 determines that the rear wheel
3 is returned from a slipping state.
(7) Estimation of offset by Karman Filter 330 for Constant
Speed
[0113] A method of estimating x-direction acceleration offset and
z-direction acceleration offset by the Karman filter 330 will now
be described.
[0114] Considering x-direction acceleration offset, z-direction
acceleration offset, observed noise, and process noise, the
following equation of a state is obtained (k is a step in discrete
time).
Equation 3 [ V x ( k + 1 ) a x ( k + 1 ) offx z ( k + 1 ) V z ( k +
1 ) a z ( k + 1 ) offz ( k + 1 ) ] = [ 1 T 0 0 0 0 0 1 0 0 0 0 0 0
1 0 0 0 0 0 0 1 T 0 0 0 0 0 1 0 0 0 0 0 0 1 ] [ V x ( k ) a npx ( k
) offx ( k ) V npz ( k ) a npz ( k ) offz ( k ) ] + [ V npx ( k ) a
npx ( k ) npoffx ( k ) V npz ( k ) a npz ( k ) npoffz ( k ) ] + [ 0
0 0 - 9.8 T 0 0 ] ( 3 ) ##EQU00001##
[0115] An observation equation is expressed by the following
equation:
Equation 4 [ V obx ( k ) G obx ( k ) V obz ( k ) G obz ( k ) ] = [
1 0 0 0 0 0 0 cos .theta. p ( k ) 1 0 - sin .theta. p ( k ) 0 0 0 0
1 0 0 0 sin .theta. p ( k ) 0 0 cos .theta. p ( k ) 1 ] [ v x ( k )
a x ( k ) offx ( k ) v z ( k ) a z ( k ) offz ( k ) ] + [ V nobx (
k ) G nobx ( k ) V nobz ( k ) G offz ( k ) ] ( 4 ) ##EQU00002##
[0116] Elements of the matrix in the foregoing equations (3) and
(4) are shown in Table 1.
TABLE-US-00001 TABLE 1 V.sub.x (k) X-direction Speed [m/s] Ground
Coordinate System V.sub.z (k) Z-direction Speed [m/s] Ground
Coordinate System V.sub.obx (k) X-direction Speed Observed Ground
Value [m/s] Coordinate System V.sub.obz (k) Z-direction Speed
Observed Ground Value [m/s] Coordinate System a.sub.x (k)
X-direction Acceleration [m/s.sup.2] Ground Coordinate System
a.sub.z (k) Z-direction Acceleration [m/s.sup.2] Ground Coordinate
System G.sub.obx (k) x-direction Acceleration Sensor Observed Value
[m/s.sup.2] Coordinate System G.sub.obz (k) z-direction
Acceleration Sensor Observed Value [m/s.sup.2] Coordinate System
.di-elect cons..sub.offx (k) x-direction Acceleration Sensor Offset
[m/s.sup.2 ] Coordinate System .di-elect cons..sub.offz (k)
z-direction Acceleration Sensor Offset [m/S.sup.2] Coordinate
System .theta..sub.p (k) Pitch Angle of Sensor Coordinate System to
Ground Coordinate System [rad] V.sub.nobx (k) Observed Noise at
Ground X-direction Speed [m/s] Coordinate System V.sub.nobz (k)
Observed Noise at Ground Z-direction Speed [m/s] Coordinate System
G.sub.nobx (k) Observed Noise at Sensor x-direction Acceleration
[m/s.sup.2] Coordinate System G.sub.nobz (k) Observed Noise at
Sensor z-direction Acceleration [m/s.sup.2] Coordinate System
V.sub.npx (k) Process Noise at Ground X-direction Speed [m/s]
Coordinate System V.sub.npz (k) Process Noise at Ground Z-direction
Speed [m/s] Coordinate System a.sub.npx (k) Process Noise at Ground
X-direction Acceleration [m/s.sup.2] Coordinate System a.sub.npz
(k) Process Noise at Ground Z-direction Acceleration [m/s.sup.2]
Coordinate System .di-elect cons..sub.npoffx (k) Process Noise in
X-direction Ground Acceleration Offset [m/s.sup.2] Coordinate
System .di-elect cons..sub.npoffz (k) Process Noise in Z-direction
Ground Acceleration Offset [m/s.sup.2] Coordinate System T Sampling
Period [s]
[0117] An X-direction speed observed value V.sub.obx (k) in the
foregoing equation (4) is obtained by the front-wheel speed signal
Rf fed from the front-wheel speed sensor 5 shown in FIG. 4. A
Z-direction speed observed value V.sub.obz (k) is herein set to 0.0
m/s because it is considered to be almost zero when the motorcycle
100 is stopped and is traveling at a constant speed.
[0118] An x-direction acceleration observed value G.sub.obx (k) is
obtained by the x-direction acceleration signal Ax from the
x-direction acceleration sensor 21, and a z-direction acceleration
observed value G.sub.obz (k) is obtained by the z-direction
acceleration signal Az from the z-direction acceleration sensor
22.
[0119] Values that are actually and empirically valid are
respectively set as the observed noise and the process noise. The
observed noise and the process noise are adjusted by simulation on
the basis of the values.
[0120] The left side of the foregoing equation (3) is a state
vector x.sub.k+1 in a step k+1. The state vector x.sub.k+1 is
expressed by the following equation:
Equation 5 x k + 1 = [ V x ( k + 1 ) a x ( k + 1 ) offx ( k + 1 ) V
z ( k + 1 ) a z ( k + 1 ) offz ( k + 1 ) ] ( 5 ) ##EQU00003##
[0121] The first term on the right side of the foregoing equation
(3) is the product of a coefficient vector A and a state vector
x.sub.k in a step k. The coefficient vector A and the state vector
x.sub.k are expressed by the following equations:
Equation 6 A = [ 1 T 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 T 0 0
0 0 0 1 0 0 0 0 0 0 1 ] ( 6 ) ##EQU00004##
Equation 7 x k = [ V x ( k ) a x ( k ) offx ( k ) V z ( k ) a z ( k
) offz ( k ) ] ( 7 ) ##EQU00005##
[0122] The second term on the right side of the foregoing equation
(3) is a process noise vector w.sub.k in the step k. The process
noise vector w.sub.k is expressed by the following equation:
Equation 8 w k = [ V npx ( k ) a npx ( k ) npoffx ( k ) V npz ( k )
a npz ( k ) npoffz ( k ) ] ( 8 ) ##EQU00006##
[0123] The third term on the right side of the foregoing equation
(3) is an external force vector u.sub.k in the step k. The external
force vector u.sub.k is expressed by the following equation:
Equation 9 u k = [ 0 0 0 - 9.8 T 0 0 ] ( 9 ) ##EQU00007##
[0124] The left side of the foregoing equation (4) is an
observation vector y.sub.k in the step k. The observation vector
y.sub.k is expressed by the following equation:
Equation 10 y k = [ V obx ( k ) G obx ( k ) V obz ( k ) G obz ( k )
] ( 10 ) ##EQU00008##
[0125] The first term on the right side of the foregoing equation
(4) is the product of a coefficient vector B and the state vector
x.sub.k in the step k. The coefficient vector B is expressed by the
following equation:
Equation 11 B = [ 1 0 0 0 0 0 0 cos .theta. p ( k ) 1 0 - sin
.theta. p ( k ) 0 0 0 0 1 0 0 0 sin .theta. p ( k ) 0 0 cos .theta.
p ( k ) 1 ] ( 11 ) ##EQU00009##
[0126] The second term on the right side of the foregoing equation
(4) is an observed noise vector v.sub.k in the step k. The observed
noise vector v.sub.k is expressed by the following equation:
Equation 12 v k = [ V nobx ( k ) G nobx ( k ) V nobx ( k ) G nobx (
k ) ] ( 12 ) ##EQU00010##
[0127] From the foregoing equations (5) to (9), the foregoing
equation (3) is expressed by the following equation:
Equation 3a
[0128] x.sub.k=1=Ax.sub.k+w.sub.k+u.sub.k (3a)
[0129] From the foregoing equations (10) to (12) and (7), the
foregoing equation (4) is expressed by the following equation:
Equation 4a
[0130] y.sub.k=Bx.sub.k+v.sub.k (4a)
[0131] Here, the x-direction acceleration offset and the
z-direction acceleration offset are estimated by sequential
calculation using an extended Karman filter in the following manner
with a pitch angle .theta..sub.P included in quantities of state
(elements of a state vector).
[0132] A state vector z.sub.k in the step k, including the pitch
angle .theta..sub.P, is expressed by the following equation:
Equation 13
[0133]
z.sub.k=[x.sub.k.sup.T.theta..sub.p(k)].sup.T=[V.sub.x(k)a.sub.x(k-
).epsilon..sub.offx(k)V.sub.z(k)a.sub.z(k).epsilon..sub.offz(k)|.theta..su-
b.p(k)].sup.T (13)
[0134] A subscript T denotes a transported matrix. Further, a
function f.sub.k(z.sub.k) is expressed by the following
equation:
Equation 14
[0135] f.sub.k(z.sub.k)=F.sub.kz.sub.k+[000-9.8T00|0].sup.T
(14)
[0136] In the foregoing equation (14), a coefficient vector F.sub.k
is expressed by the following equation:
Equation 15 F k = [ 1 T 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0
1 T 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 A ax 0 0 0 0 A .theta. p ] (
15 ) ##EQU00011##
[0137] where, 0.ltoreq.A.sub.zx<1,
0<A.sub..theta.p.ltoreq.1
[0138] A constant A.sub.ax is zero, for example, and a constant
A.sub..theta.P is 1, for example. Here, letting Z.sub.Ek|k be an
estimated value of the state vector z.sub.k in the step k, letting
Z.sub.Ek|k-1 be an estimated value of a state vector z.sub.k in a
step k-1, and letting Z.sub.Ek+1|k be an estimated value of a state
vector z.sub.k+1 in a step k, a filter equation is expressed by the
following equations:
Equation 16
[0139]
z.sub.Ek|k=z.sub.Ek|k-1+K.sub.k(y.sub.k-h.sub.k(z.sub.Ek|k-1))
(16)
Equation 17
[0140] z.sub.Ek+1|k=f.sub.k(z.sub.Ek|k) (17)
[0141] In the foregoing equation (16), K.sub.k denotes a Karman
gain, and the observation vector y.sub.k is expressed by the
foregoing equation (10). A function h.sub.k(z.sub.Ek|k-1) will be
described later.
[0142] The Karman gain K.sub.k is expressed by the following
equation:
Equation 18
[0143]
K.sub.k=.SIGMA..sub.k|k-1H.sub.k.sup.T(H.sub.k.SIGMA..sub.k|k-1H.s-
ub.k.sup.T+.SIGMA..sub.vk).sup.-1 (18)
[0144] In the foregoing equation (18), .SIGMA..sub.k|k-1 denotes a
covariance matrix of an estimated error in the state vector z.sub.k
in the step k-1, and .SIGMA..sub.vk denotes a covariance matrix in
the observed noise vector v.sub.k. A matrix H.sub.k will be
described later.
[0145] A covariance matrix .SIGMA..sub.k|k of an estimated error in
the state vector z.sub.k is expressed by the following
equation:
Equation 19
[0146]
.SIGMA..sub.k|k=.SIGMA..sub.k|k-1-K.sub.kH.sub.k.SIGMA..sub.k|k-1
(19)
[0147] A covariance matrix equation of the error is expressed by
the following equation:
Equation 20
[0148]
.SIGMA..sub.k+1|k=F.sub.k.SIGMA..sub.k|kF.sub.k.sup.T+G.sub.k.SIGM-
A..sub.wkG.sub.k.sup.T (20)
[0149] A matrix G.sub.k will be described later. The matrix H.sub.k
in the foregoing equations (18) and (19) is expressed by the
following equation:
Equation 21 H k = [ 1 0 0 0 0 0 0 0 cos .theta. p ( k ) 1 0 - sin
.theta. p ( k ) 0 - a x sin .theta. p ( k ) - a z cos .theta. p ( k
) 0 0 0 1 0 0 0 0 sin .theta. p ( k ) 0 0 cos .theta. p ( k ) 1 a x
sin .theta. p ( k ) - a z cos .theta. p ( k ) ] ( 21 )
##EQU00012##
[0150] The function h.sub.k(z.sub.Ek|k-1) in the foregoing equation
(16) is expressed by the following equation:
Equation 22
[0151]
h.sub.k(z.sub.Ek|k-1)=C.sub.k(.theta..sub.pEk|k-1).times..sub.Ek|k-
-1 (22)
[0152] In the foregoing equation (22), x.sub.Ek|k-1 denotes an
estimated value of the state vector x.sub.k in the step k-1.
.theta..sub.pEk|k-1 denotes an estimated value of a pitch angle
.theta..sub.P (k) in the step k-1. A matrix C.sub.k is expressed by
the following equation:
Equation 23 C k = [ 1 0 0 0 0 0 0 cos .theta. p ( k ) 1 0 - sin
.theta. p ( k ) 0 0 0 0 1 0 0 0 sin .theta. p ( k ) 0 0 cos .theta.
p ( k ) 1 ] ( 23 ) ##EQU00013##
[0153] A matrix G.sub.k in the foregoing equation (20) is expressed
by the following equation:
Equation 24 G k = [ I 0 ] ( 24 ) ##EQU00014##
In the foregoing equation (24), I denotes a unit matrix.
[0154] The extended Karman filter allows the pitch angle
.theta..sub.P (k), together with x-direction acceleration offset
.epsilon..sub.offx (k) and z-direction acceleration offset
.epsilon..sub.offz (k) at the time when the motorcycle 100 is
stopped and is traveling at a constant speed, to be estimated.
(8) Simulation of Karman Filter 330 for Constant Speed
[0155] Here, the Karman filter 330 was simulated to estimate the
x-direction acceleration offset and the z-direction acceleration
offset.
[0156] FIG. 8 is a diagram showing the relationship between an
acceleration offset true value and an acceleration offset estimated
error.
[0157] In FIG. 8, the horizontal axis represents respective true
values of the x-direction acceleration offset and the z-direction
acceleration offset, and the vertical axis represents an estimated
error of the acceleration offset. The estimated error of the
acceleration offset is a difference between an estimated value of
the x-direction acceleration offset and the true value of the
x-direction acceleration offset and a difference between an
estimated value of the z-direction acceleration offset and the true
value of the z-direction acceleration offset.
[0158] In FIG. 8, the estimated error of the z-direction
acceleration offset is indicated by a white circle, and the
estimated error of the x-direction acceleration offset is indicated
by a black triangle. As shown in FIG. 8, the estimated error of the
x-direction acceleration offset is within about 0.06 m/s.sup.2, and
the estimated error of the z-direction acceleration offset is
within about 0.001 m/s.sup.2.
[0159] FIG. 9 is a diagram showing the change with time of an
acceleration offset estimated value in the process of estimating
the acceleration offset.
[0160] In FIG. 9, the horizontal axis represents time, and the
vertical axis represents acceleration offset. In FIG. 9, the true
value of the z-direction acceleration offset is indicated by a thin
solid line, the estimated value of the z-direction acceleration
offset is indicated by a thick solid line, the true value of the
x-direction acceleration offset is indicated by a thin dotted line,
and the estimated value of the x-direction acceleration offset is
indicated by a thick dotted line.
[0161] As shown in FIG. 9, both the estimated value of the
x-direction acceleration offset and the estimated value of the
z-direction acceleration offset are completely converged in two
seconds. This allows the x-direction acceleration offset and the
z-direction acceleration offset to be estimated if a constant speed
state for two or more seconds exists.
(9) Estimation of Pitch Angle by Karman Filter 340 for
Acceleration/Deceleration
[0162] A method of estimating a pitch angle by the Karman filter
340 will now be described.
[0163] Considering observed noise and process noise, the following
equation of state is obtained (k is a step in discrete time).
Equation 25 [ a x ( k + 1 ) a z ( k + 1 ) ] = [ 1 0 0 1 ] [ a x ( k
) a z ( k ) ] + [ a npx ( k ) a npz ( k ) ] ( 25 ) ##EQU00015##
[0164] An observation equation is expressed by the following
equation.
Equation 26 [ G Aobx ( k ) G Aobz ( k ) ] = [ cos .theta. p ( k ) -
sin .theta. p ( k ) sin .theta. p ( k ) cos .theta. p ( k ) ] [ a x
( k ) a z ( k ) ] + [ G nobx ( k ) G nobz ( k ) ] ( 26 )
##EQU00016##
[0165] Elements of the matrix in the foregoing equations (25) and
(26) are shown in Table 2.
TABLE-US-00002 TABLE 2 a.sub.x (k) X-direction Acceleration
[m/s.sup.2] Ground Coordinate System a.sub.z (k) Z-direction
Acceleration [m/s.sup.2] Ground Coordinate System G.sub.Aobx (k)
x-direction Acceleration Sensor Corrected Value [m/s.sup.2]
Coordinate System G.sub.Aobz (k) z-direction Acceleration Sensor
Corrected Value [m/s.sup.2] Coordinate System .theta..sub.p (k)
Pitch Angle of Sensor Coordinate System to Ground Coordinate System
[rad] G.sub.nobx (k) Observed Noise at Sensor x-direction
Acceleration [m/s.sup.2] Coordinate System G.sub.nobz (k) Observed
Noise at Sensor z-direction Acceleration [m/s.sup.2] Coordinate
System a.sub.npx (k) Process Noise at X-direction Ground
Acceleration [m/s.sup.2] Coordinate System a.sub.npz (k) Process
Noise at Z-direction Ground Acceleration [m/s.sup.2] Coordinate
System
[0166] Here, an x-direction acceleration corrected value
G.sub.Aobx(k) is an x-direction acceleration corrected by the
offset corrector 360 shown in FIG. 4, and is a value obtained by
subtracting the x-direction acceleration offset
.epsilon..sub.offx(k) from the x-direction acceleration observed
value G.sub.obx(k). Further, a z-direction acceleration corrected
value G.sub.Aobz(k) is a z-direction acceleration corrected by the
offset corrector 360 shown in FIG. 4, and is a value obtained by
subtracting the z-direction acceleration offset
.epsilon..sub.offz(k) from the z-direction acceleration observed
value G.sub.obz(k).
[0167] Values that are actually and empirically valid are
respectively set as the observed noise and the process noise. The
observed noise and the process noise are adjusted by simulation on
the basis of the values.
[0168] The left side of the foregoing equation (25) is a state
vector x.sub.k+1 in a step k+1. The state vector x.sub.k+1 is
expressed by the following equation:
Equation 27 x k + 1 = [ a x ( k + 1 ) a z ( k + 1 ) ] ( 27 )
##EQU00017##
[0169] The first term on the right side of the foregoing equation
(25) is the product of a coefficient vector A and a state vector
x.sub.k in a step k. The coefficient vector A and the state vector
x.sub.k are expressed by the following equations:
Equation 28 A = [ 1 0 0 1 ] ( 28 ) Equation 29 x k = [ a x ( k ) a
z ( k ) ] ( 29 ) ##EQU00018##
[0170] The second term on the right side of the foregoing equation
(25) is a process noise vector w.sub.k in the step k. The process
noise vector w.sub.k is expressed by the following equation:
Equation 30 w k = [ a npx ( k ) a npz ( k ) ] ( 30 )
##EQU00019##
[0171] The left side of the foregoing equation (26) is an
observation vector y.sub.k in the step k. The observation vector
y.sub.k is expressed by the following equation:
Equation 31 y k = [ G Aobx ( k ) G Aobz ( k ) ] ( 31 )
##EQU00020##
[0172] The first term on the right side of the foregoing equation
(26) is the product of a coefficient vector B and the state vector
x.sub.k in the step k. The coefficient vector B is expressed by the
following equation:
Equation 32 B = [ cos .theta. p ( k ) - sin .theta. p ( k ) sin
.theta. p ( k ) cos .theta. p ( k ) ] ( 32 ) ##EQU00021##
[0173] The second term on the right side of the foregoing equation
(26) is an observed noise vector v.sub.k in the step k. The
observed noise vector v.sub.k is expressed by the following
equation:
Equation 33 v k = [ G nobx ( k ) G nobz ( k ) ] ( 33 )
##EQU00022##
[0174] From the foregoing equations (27) to (30), the foregoing
equation (25) is expressed by the following equation:
Equation 25a
[0175] x.sub.k+1=Ax.sub.k+w.sub.k (25a)
[0176] From the foregoing equations (31) to (33) and (29), the
foregoing equation (26) is expressed by the following equation:
Equation 26a
[0177] y.sub.k=Bx.sub.k+v.sub.k (26a)
[0178] Here, a pitch angle .theta..sub.P is estimated using an
extended Karman filter in the following manner with the pitch angle
.theta..sub.P included in quantities of state (elements of a state
vector).
[0179] A state vector z.sub.k in the step k, including the pitch
angle .theta..sub.P, is expressed by the following equation:
Equation 34
[0180]
z.sub.k=[x.sub.k.sup.T.theta..sub.p(k)].sup.T=[a.sub.x(k)a.sub.z(k-
)|.theta..sub.p(k)].sup.T (34)
[0181] A subscript T denotes a transported matrix. Further, a
function f.sub.k(z.sub.k) is expressed by the following
equation:
Equation 35
[0182] f.sub.k(z.sub.k)=F.sub.kz.sub.k (35)
[0183] In the foregoing equation (35), a coefficient vector F.sub.k
is expressed by the following equation:
Equation 36 F k = [ 1 0 0 0 1 0 A ax 0 A .theta. p ] where , 0
.ltoreq. A ax < 1 , 0 < A .theta. p .ltoreq. 1 ( 36 )
##EQU00023##
[0184] A constant A.sub.ax is zero, for example, and a constant
A.sub..theta.P is 1, for example. Here, letting z.sub.Ek|k be an
estimated value of the state vector z.sub.k in the step k, letting
z.sub.Ek|k-1 be an estimated value of a state vector z.sub.k in a
step k-1, and letting z.sub.Ek+1|k be an estimated value of a state
vector z.sub.k+1 in a step k, a filter equation is expressed by the
following equations:
Equation 37
[0185] z.sub.Ek|k=z.sub.Ek|k-1+K.sub.k(y.sub.k-h.sub.k(z.sub.Ek|k))
(37)
Equation 38
[0186] z.sub.Ek+1|k=f.sub.k(z.sub.Ek|k) (38)
[0187] In the foregoing equation (37), K.sub.k denotes a Karman
gain, and the observation vector y.sub.k is expressed by the
foregoing equation (31). A function h.sub.k(z.sub.Ek|k-1) will be
described later.
[0188] The Karman gain K.sub.k is expressed by the following
equation.
Equation 39
[0189]
K.sub.k=.SIGMA..sub.k|k-1H.sub.k.sup.T(H.sub.k.SIGMA..sub.k|k-1H.s-
ub.k.sup.T+.SIGMA..sub.vk).sup.-1 (39)
[0190] In the foregoing equation (39), .SIGMA..sub.k|k-1 denotes a
covariance matrix of an estimated error in the state vector z.sub.k
in the step k-1, and .SIGMA..sub.vk denotes a covariance matrix in
the observed noise vector v.sub.k. A matrix H.sub.k will be
described later.
[0191] A covariance matrix .SIGMA..sub.k|k of the estimated error
in the state vector z.sub.k is expressed by the following
equation:
Equation 40
[0192]
.SIGMA..sub.k|k=.SIGMA..sub.k|k-1-K.sub.kH.sub.k.SIGMA..sub.k|k-1
(40)
[0193] A covariance matrix equation of the error is expressed by
the following equation:
Equation 41
[0194]
.SIGMA..sub.k+1|k=F.sub.k.SIGMA..sub.k|kF.sub.k.sup.T+G.sub.k.SIGM-
A..sub.wkG.sub.k.sup.T (41)
[0195] A matrix G.sub.k will be described later. The matrix H.sub.k
is expressed by the following equation:
Equation 42 H k = [ cos .theta. p ( k ) - sin .theta. p ( k ) - a x
sin .theta. p ( k ) - a z cos .theta. p ( k ) sin .theta. p ( k )
cos .theta. p ( k ) a x cos .theta. p ( k ) - a z sin .theta. p ( k
) ] ( 42 ) ##EQU00024##
[0196] The function h.sub.k(z.sub.Ek|k-1) in the foregoing equation
(37) is expressed by the following equation:
Equation 43
[0197]
h.sub.k(z.sub.Ek|k-1)=C.sub.k(.theta..sub.pEk|k-1).times..sub.Ek|k-
-1 (43)
[0198] In the foregoing equation (43), x.sub.Ek|k-1 denotes an
estimated value of the state vector x.sub.k in the step k-1.
.theta..sub.pEk|k-1 denotes an estimated value of a pitch angle
.theta..sub.P(k) in the step k-1. A matrix C.sub.k is expressed by
the following equation:
Equation 44 C k [ cos .theta. p ( k ) - sin .theta. p ( k ) sin
.theta. p ( k ) cos .theta. p ( k ) ] ( 44 ) ##EQU00025##
[0199] The matrix G.sub.k in the foregoing equation (41) is
expressed by the following equation:
Equation 45 G k = [ I 0 ] ( 45 ) ##EQU00026##
In the foregoing equation (45), I denotes a unit matrix.
[0200] The extended Karman filter allows the pitch angle
.theta..sub.P(k) at the time when the motorcycle 100 is accelerated
and decelerated to be estimated.
(10) Correction of Acceleration by Acceleration Corrector 370
[0201] The acceleration corrector 370 corrects the x-direction
acceleration and the z-direction acceleration by the following
equation using a pitch angle estimated value obtained by the Karman
filter 340 for acceleration/deceleration. Thus, an X-direction
acceleration estimated value and a Z-direction acceleration
estimated value are obtained.
Equation 46 [ a Ex a Ez ] = [ cos .theta. Ep sin .theta. Ep - sin
.theta. Ep cos .theta. Ep ] [ G Aobx ( k ) G Aobz ( k ) ] ( 46 )
##EQU00027##
[0202] Elements of the matrix in the forgoing equation (46) are
shown in Table 3.
TABLE-US-00003 TABLE 3 a.sub.Ex (k) X-direction Acceleration Ground
Estimated Value [m/s.sup.2] Coordinate System a.sub.Ez (k)
Z-direction Acceleration Ground Estimated Value [m/s.sup.2]
Coordinate System G.sub.Aobx (k) x-direction Acceleration Sensor
Corrected Value [m/s.sup.2] Coordinate System G.sub.Aobz (k)
z-direction Acceleration Sensor Corrected Value [m/s.sup.2]
Coordinate System .theta..sub.Ep (k) Estimated Value of Pitch Angle
of Sensor Coordinate System to Ground Coordinate System [rad]
[0203] Here, an x-direction acceleration corrected value
G.sub.AObx(k) is an x-direction acceleration corrected by the
offset corrector 360 shown in FIG. 4, and is a value obtained by
subtracting the x-direction acceleration offset
.epsilon..sub.offx(k) from the x-direction acceleration observed
value G.sub.obx(k). Further, a z-direction acceleration corrected
value G.sub.Aobz(k) is a z-direction acceleration corrected by the
offset corrector 360 shown in FIG. 4, and is a value obtained by
subtracting the z-direction acceleration offset
.epsilon..sub.offz(k) from the z-direction acceleration observed
value G.sub.obz(k).
[0204] The foregoing equation (46) allows an x-direction
acceleration estimated value a.sub.Ex and a Z-direction
acceleration estimated value a.sub.Ez at the time when the
motorcycle 100 is accelerated and decelerated to be calculated.
(11) Simulation of Karman Filter 340 for
Acceleration/Deceleration
[0205] Here, the Karman filter 340 and the acceleration corrector
370 were simulated to estimate the X-direction acceleration and the
Z-direction acceleration.
[0206] FIG. 10 is a diagram showing the results of the estimation
of the X-direction acceleration.
[0207] In FIG. 10, the horizontal axis represents time, and the
vertical axis represents acceleration. In FIG. 10, a true value of
the X-direction acceleration is indicated by a dotted line, the
X-direction acceleration estimated value a.sub.Ex obtained by the
acceleration corrector 370 using a pitch angle estimated value
.theta..sub.Ep obtained by the Karman filter 340 is indicated by a
solid line, and an x-direction acceleration corrected value
G.sub.Aobx(k) obtained by the offset corrector 360 is indicated by
a one-dot and dash line. The x-direction acceleration corrected
value G.sub.Aobx(k) is affected by a pitch angle, although the
effect of the x-direction acceleration offset is removed
therefrom.
[0208] As shown in FIG. 10, the X-direction acceleration estimated
value a.sub.Ex is closer to the true value of the X-direction
acceleration, as compared with the x-direction acceleration
corrected value G.sub.Aobx(k).
[0209] Furthermore, the true value of the X-direction acceleration,
the X-direction acceleration estimated value a.sub.Ex, and the
x-direction acceleration corrected value G.sub.AObx(k) were
integrated over time to estimate a vehicle speed.
[0210] FIG. 11 is a diagram showing the results of the estimation
of the vehicle speed. In FIG. 11, the horizontal axis represents
time, and the vertical axis represents a vehicle speed estimated
value.
[0211] In FIG. 11, a vehicle speed calculated using the true value
of the X-direction acceleration (an X-direction vehicle speed true
value) is indicated by a dotted line, an X-direction vehicle speed
estimated value calculated using the X-direction acceleration
estimated value a.sub.Ex is indicated by a solid line, and an
x-direction vehicle speed estimated value calculated using the
x-direction acceleration corrected value G.sub.Aobx(k) is indicated
by a one-dot and dash line.
[0212] As shown in FIG. 11, the X-direction vehicle speed estimated
value calculated using the X-direction acceleration estimated value
a.sub.Ex is closer to the X-direction vehicle speed true value, as
compared with the x-direction vehicle speed estimated value
calculated using the x-direction acceleration corrected value
G.sub.Aobx(k).
(12) Effects of the Preferred Embodiments
[0213] In the motorcycle 100 according to the present preferred
embodiment, the offset in the x-direction acceleration sensor 21
and the offset in the z-direction acceleration sensor 22 are
estimated with high accuracy by the Karman filter 330 for a
constant speed in the vehicle speed estimator 300 when the
motorcycle 100 is stopped and is traveling at a constant speed.
Even when the detected value in the x-direction acceleration sensor
21 and the detected value in the z-direction acceleration sensor 22
are affected by gravity due to pitching having an arbitrary
frequency, it is possible to accurately estimate the offset in the
x-direction acceleration sensor 21 and the offset in the
z-direction acceleration sensor 22.
[0214] An observed disturbance given to the x-direction
acceleration sensor 21 and the z-direction acceleration sensor 22
are removed in the Karman filter 330. This prevents the ABS
controlled by the vehicle speed in the X-direction obtained by the
vehicle speed estimator 300 from being unstable due to the observed
disturbance.
[0215] The estimated value of the offset in the x-direction
acceleration sensor 21 and the estimated value of the offset in the
z-direction acceleration sensor 22 that are obtained when the
motorcycle 100 is stopped or is traveling at a constant speed are
stored in the offset storage 350, while the detected value in the
x-direction acceleration sensor 21 and the detected value in the
z-direction acceleration sensor 22 are corrected by the offset
corrector 360 on the basis of the estimated value of the offset in
the x-direction acceleration sensor 21 and the estimated value of
the offset in the z-direction acceleration sensor 22 that are
stored in the offset storage 350 when the motorcycle 100 is
accelerated or decelerated. This allows the x-direction
acceleration and the z-direction acceleration of the motorcycle 100
to be detected with high accuracy.
[0216] The pitch angle of the vehicle body 1 is estimated by the
Karman filter 340 for acceleration/deceleration when motorcycle 100
is accelerated or decelerated. This allows the pitch angle due to
pitching having an arbitrary frequency to be estimated at low cost
and with high accuracy without using a high-cost gyro sensor.
[0217] Furthermore, the X-direction acceleration and the
Y-direction acceleration of the motorcycle 100 are calculated by
the acceleration corrector 370 on the basis of the estimated value
of the pitch angle, the detected value in the x-direction
acceleration sensor 21, and the detected value in the z-direction
acceleration sensor 22. This allows the X-direction acceleration of
the motorcycle 100 to be detected with high accuracy.
[0218] The vehicle speed operation unit 380 obtains the vehicle
speed in the X-direction from the X-direction acceleration with
high accuracy. When both the front wheel 2 and the rear wheel 3 are
braked, therefore, it is possible to detect the sliding of the
front wheel 2 and the rear wheel 3 as well as to detect the vehicle
speed with high accuracy.
[0219] In cases where both the front wheel 2 and the rear wheel 3
slide, for example, a case where the front wheel 2 is braked during
the driving of the rear wheel 3, the speed at the center of gravity
of the vehicle body 1 cannot be found from the respective wheel
speeds of the front wheel 2 and the rear wheel 3. Even in such a
case, it is possible to detect the sliding of the front wheel 2 and
the rear wheel 3 using the vehicle speed estimator 300 in the
present preferred embodiment as well as to detect the vehicle speed
with high accuracy.
(13) Other Preferred Embodiments
[0220] Although in the preferred embodiments described above,
description was made of a case where the acceleration estimation
device is applied to the ABS, the present invention is not limited
to this. For example, the acceleration estimation device may be
applied to another brake control system, a traction control system,
or a cruise control system. The traction control system refers to a
system for obtaining a driving force most suitable for the time of
turning, the time of starting, or the time of acceleration by
controlling a driving force of a driving wheel or an output of the
engine and a braking force. The cruise control system refers to a
system for automatically controlling a vehicle speed to be constant
in the case of long-distance or long-term traveling.
[0221] The acceleration estimation device is also applicable to
drivability control by an electronic throttle. The drivability
control refers to the control for obtaining a comfortable driving
performance. When the acceleration estimation device is applied to
the drivability control, an error of an acceleration sensor can be
reduced. Therefore, the comfortable driving performance can be
controlled with high accuracy. As a result, it is possible to
provide smooth acceleration characteristics that do not make a
driver feel changes and variations in acceleration.
[0222] Moreover, the acceleration estimation device of the present
invention can be utilized for estimating the acceleration of a
vehicle when a GPS (Global Positioning System) signal cannot be
received in a navigation system.
[0223] Although in the preferred embodiments described above, each
of the constituent elements within the vehicle speed estimator 300
is preferably provided by the ECU 30 and associated program
function, the present invention is not limited to this. For
example, parts or all of the plurality of constituent elements
within the vehicle speed estimator 300 may be provided by hardware
such as an electronic circuit.
[0224] Although in the preferred embodiments described above, the
offset estimator preferably includes the Karman filter 330 for a
constant speed composed of an extended Karman filter, the present
invention is not limited to this. For example, the offset estimator
may be achieved by another adaptive filtering method. For example,
an LMS (Least Mean Square) adaptive filter or H filtering may be
used.
[0225] Although in the preferred embodiments described above, the
pitch angle estimator preferably includes the Karman filter 340 for
acceleration/deceleration composed of an extended Karman filter,
the present invention is not limited to this. For example, the
pitch angle estimator may be achieved by another adaptive filtering
method. For example, an LMS adaptive filter or H filtering may be
used.
[0226] The vehicle speed estimator 300 in the preferred embodiments
described above is not limited to the motorcycle 100. For example,
it can be applied to various types of vehicles such as motorcycles,
four-wheeled vehicles, and three-wheeled vehicles, or any other
suitable vehicle.
[0227] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
* * * * *