U.S. patent application number 11/239017 was filed with the patent office on 2006-05-18 for abnormality detecting apparatus for wheel speed sensors and automobile incorporating the same.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Mitsuru Ohba.
Application Number | 20060106513 11/239017 |
Document ID | / |
Family ID | 36313982 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060106513 |
Kind Code |
A1 |
Ohba; Mitsuru |
May 18, 2006 |
ABNORMALITY DETECTING APPARATUS FOR WHEEL SPEED SENSORS AND
AUTOMOBILE INCORPORATING THE SAME
Abstract
Wheel speed sensors arranged at each of driving wheels and idler
wheels detect rotational speeds of corresponding wheels. ECU
includes a wheel speed calculating portion calculating wheel speeds
of the driving wheels and the idler wheels based on the detected
rotational speeds, and an abnormality detecting portion detecting
abnormality of the wheel speed sensors based on the calculated
wheel speeds. The abnormality detecting portion detects the
abnormality of the wheel speed sensors based on: a first wheel
speed that is at least one of the wheel speeds of the driving
wheels and the idler wheels being substantially zero; at least one
of the wheel speeds except for the first wheel speed being greater
than a prescribed threshold value; and an average wheel speed of
the idler wheels being greater than an average wheel speed of the
driving wheels.
Inventors: |
Ohba; Mitsuru; (Anjo-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
36313982 |
Appl. No.: |
11/239017 |
Filed: |
September 30, 2005 |
Current U.S.
Class: |
701/29.2 ;
701/63 |
Current CPC
Class: |
B60T 8/885 20130101;
B60T 2270/416 20130101 |
Class at
Publication: |
701/034 ;
701/063 |
International
Class: |
G06F 17/00 20060101
G06F017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 2004 |
JP |
2004-328974 |
Claims
1. An abnormality detecting apparatus for wheel speed sensors
detecting abnormality of wheel speed sensors arranged at each of
driving wheels and idler wheels of a vehicle, wherein said wheel
speed sensors detect rotational speeds of corresponding said
driving wheels and said idler wheels, said abnormality detecting
apparatus for wheel speed sensors comprises: a wheel speed
calculating portion calculating wheel speeds of said driving wheels
and wheel speeds of said idler wheels based on the detected
rotational speeds of said driving wheels and the detected
rotational speeds of said idler wheels, respectively; and an
abnormality detecting portion detecting abnormality of said wheel
speed sensors based on the calculated wheel speeds, wherein said
abnormality detecting portion detects the abnormality of said wheel
speed sensors based on: a first wheel speed that is at least one of
the wheel speeds of said driving wheels and said idler wheels being
substantially zero; at least one of the wheel speeds except for
said first wheel speed being greater than a prescribed threshold
value; and an average wheel speed of left and right said idler
wheels being greater than an average wheel speed of left and right
said driving wheels.
2. The abnormality detecting apparatus for wheel speed sensors
according to claim 1, wherein said vehicle includes a power
transmission transmitting motive power to said idler wheels, and
said abnormality detecting portion stops a motive power
transmission operation of said power transmission when abnormality
of said wheel speed sensors is detected.
3. The abnormality detecting apparatus for wheel speed sensors
according to claim 2, wherein said power transmission transmits to
said idler wheels motive power commensurate to a relative rotation
number between said driving wheels and said idler wheels.
4. The abnormality detecting apparatus for wheel speed sensors
according to claim 1, wherein said prescribed threshold value is a
detection value of said wheel speeds that can be detected by said
wheel speed sensors when said vehicle travels normally, and it is a
value greater than a maximum value of said wheel speeds detected
when said vehicle makes a turn.
5. An automobile, comprising: a motive power source; driving wheels
that receive motive power transmitted from said motive power source
and drive; idler wheels; wheel speed sensors arranged at each of
said driving wheels and said idler wheels for detecting rotational
speeds of corresponding said driving wheels and said idler wheels;
and the abnormality detecting apparatus for wheel speed sensors
detecting abnormality of said wheel speed sensors according to any
of claims 1-4.
Description
[0001] This nonprovisional application is based on Japanese Patent
Application No. 2004-328974 filed with the Japan Patent Office on
Nov. 12, 2004, the entire contents of which are hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an abnormality detecting
apparatus for wheel speed sensors and an automobile incorporating
the same. More specifically, it relates to an abnormality detecting
apparatus for wheel speed sensors with detection performance of
high accuracy and an automobile incorporating the same.
[0004] 2. Description of the Background Art
[0005] Conventionally, wheel speed sensors for detecting the wheel
speed of each wheel are incorporated in an ABS (Antilock Brake
System) apparatus that prevents wheels from locking during braking,
or in an automatic braking apparatus that generates braking force
for preventing slip or generating yaw moment to stabilize the
attitude of the vehicle that is becoming unstable. As normal
control of those apparatuses is lost if there is abnormality with
the wheel speed sensors, abnormality detection of the wheel speed
sensors is frequently conducted.
[0006] As means for detecting abnormality of wheel speed sensors,
for example, Japanese Patent Laying-Open No. 11-291886 discloses an
abnormality detecting apparatus for wheel speed sensors, of which
object is to improve detection accuracy.
[0007] FIG. 4 is a control block diagram of the abnormality
detecting apparatus for wheel speed sensors described in Japanese
Patent Laying-Open No. 11-291886.
[0008] Referring to FIG. 4, the abnormality detecting apparatus for
wheel speed sensors includes wheel speed sensors 70a outputting
signals respectively responsive to rotational speeds of wheels FL,
FR, RL, and RR (not shown), wheel speed calculating means 70b for
calculating wheel speeds based on the signals from respective wheel
speed sensors 70a, wheel acceleration calculating means 70c for
calculating wheel acceleration, wheel speed sensor abnormality
determining means 70d for determining abnormality of wheel speed
sensors 70a based on a result of the calculation by wheel speed
calculating means 70b, and wheelspin determining means 70e for
determining wheelspin of driving wheels based on a result of the
calculation by wheel accelerations calculating means.
[0009] In this configuration, wheel speed sensor abnormality
determining means 70d involves, as to the result of calculation of
the wheel speeds, an abnormality determination condition as
follows: while the rotational speed of at least one wheel is at
least a prescribed speed, the rotational speed of other wheel is 0
km/h. Specifically, wheel speed sensor abnormality determining
means 70d obtains an assumed vehicle speed based on signals from
respective wheel speed sensors 70a, and compares the assumed
vehicle speed and detected wheel speeds detected by respective
wheel speed sensors 70a. In response to a difference between them
exceeding a prescribed value being continued for at least a
prescribed period, wheel speed sensor abnormality determining means
70d determines that wheel speed sensors 70a are abnormal. Here,
wheel speed sensor abnormality determining means 70d determines
that a wheel speed sensor 70a corresponding to a wheel having a
rotational speed of 0 km/h is abnormal.
[0010] However, on a road surface with a low friction coefficient
(hereinafter also referred to as low .mu.) such as of a
snow-covered road, if a state where a vehicle hardly moves while
the driving wheels are slipping (the wheelspin state) is continued,
wheel speed sensors 70a of the driving wheels show detection values
of high speeds, whereas wheel speed sensors 70a of idler wheel show
detection values of substantially 0 km/h. When this wheelspin state
is continued for a prescribed period, wheel speed sensor
abnormality determining means 70d determines that wheel speed
sensors 70a, which are actually normal, are abnormal.
[0011] Accordingly, the abnormality detecting apparatus for wheel
speed sensors shown in FIG. 4 is configured such that, when
wheelspin determining means 70e determines wheelspin, a
determination operation of wheel speed sensor abnormality
determining means 70d is suspended. Specifically, wheelspin
determining means 70e determines that wheelspin has occurred when
wheel acceleration of the driving wheels has exceeded the wheel
acceleration that would be possible during normal road-gripping
driving. Wheelspin determining means 70e has a wheelspin timer (not
shown) for measuring a predetermined time, and while the wheelspin
timer is measuring the predetermined time, an abnormality
determination operation by wheel speed sensor abnormality
determining means 70d is suspended.
[0012] With such a configuration, the abnormality detecting
apparatus for wheel speed sensors can prevent erroneous abnormality
determination due to wheelspin of the driving wheels.
[0013] As above, the conventional abnormality detecting apparatus
for wheel speed sensors is characterized in that a result of the
determination by wheelspin determining means 70e is considered as a
condition for establishing an abnormality determination operation
at wheel speed sensor abnormality determining means 70d in order to
improve the detection accuracy.
[0014] However, the conventional abnormality detecting apparatus
for wheel speed sensors involves the following problem as to the
determination accuracy of wheelspin determining means 70e
itself.
[0015] In general, wheel acceleration can be obtained from the
following equation expressing driving force exerted on the driving
wheels: Id.omega.=T-.mu.WR (1)
[0016] where, I: wheel inertia (kg/m.sup.2), d.omega.: wheel
acceleration (m/s.sup.2), T: input torque (Nm), .mu.: road surface
frictional coefficient, W: weight on the ground (N), R: wheel
radius (m).
[0017] As apparent from equation (1), wheel acceleration dot
largely changes depending on input torque T (proportional to
acceleration pedal depression), road surface frictional coefficient
.mu., and weight on the ground W. On the other hand, actually it is
difficult to accurately detect road surface frictional coefficient
.mu. and weight on the ground W, and it is not easy to accurately
determine wheel acceleration d.omega.. Therefore, in the
conventional abnormality detecting apparatus for wheel speed
sensors, wheelspin determining means 70e that is based on wheel
acceleration d.omega. yields varied determination result, and the
abnormality detection accuracy is not always high.
[0018] Meanwhile, among four-wheel-drive (4WD) vehicles, what is
called standby 4WD is known, which normally travels employing
either front wheels or rear wheels as driving wheels and, when
relative rotation occurs between the front and rear wheels due to
slip or the like, motive power is transmitted to the other rear or
front wheels to achieve four-wheel driving.
[0019] Specifically, with standby 4WD, rotational speeds of the
driving wheels and rotational speeds of the idler wheels are
detected, and based on the difference between them, a relative
rotation number between the driving wheels and the idler wheels is
detected. Further, transmission torque (differential limiting
torque) in accordance with the detected relative rotation number is
transmitted to the idler wheels via a power transmission, whereby
the idler wheels are driven.
[0020] In such a configuration, the rotational speeds of the
driving wheels and that of the idler wheels are respectively
detected by wheel speed sensors arranged at respective wheels.
Accordingly, with standby 4WD, it is critical that the wheel speed
sensors are normal in order to correctly control switching between
two-wheel drive (2WD) and four-wheel drive. When the wheel speed
sensors are abnormal, actuation of four-wheel drive is prohibited,
since correct control cannot be continued. Specifically, with
standby 4WD, based on abnormality detection information on the
wheel speed sensors, prohibition/permission of actuation of
four-wheel drive is determined. Here, if the abnormality detection
accuracy of the abnormality detecting apparatus for wheel speed
sensors is low, the wheel speed sensors that are actually normal
are erroneously determined to be abnormal, whereby actuation of
four-wheel drive is prohibited and the drivability may be
decreased. Accordingly, particularly high detection accuracy is
required for the abnormality detecting apparatus for wheel speed
sensors incorporated in a vehicle employing standby 4WD scheme.
[0021] However, as described above, the conventional abnormality
detecting apparatus for wheel speed sensors cannot yet guarantee
full detection accuracy, as the wheelspin determination is
difficult.
SUMMARY OF THE INVENTION
[0022] An object of the present invention is to provide an
abnormality detecting apparatus for wheel speed sensors with high
detection accuracy.
[0023] Another object of the present invention is to provide a
vehicle incorporating an abnormality detecting apparatus for wheel
speed sensors with high accuracy.
[0024] According to the present invention, an abnormality detecting
apparatus for wheel speed sensors detecting abnormality of wheel
speed sensors arranged at each of driving wheels and idler wheels
of a vehicle is provided, wherein the wheel speed sensors detect
rotational speeds of corresponding driving wheels and idler wheels.
The abnormality detecting apparatus for wheel speed sensors
includes a wheel speed calculating portion calculating wheel speeds
of the driving wheels and wheel speeds of the idler wheels based on
the detected rotational speeds of the driving wheels and the
detected rotational speeds of the idler wheels, respectively, and
an abnormality detecting portion detecting abnormality of the wheel
speed sensors based on the calculated wheel speeds. The abnormality
detecting portion detects the abnormality of the wheel speed
sensors based on: a first wheel speed that is at least one of the
wheel speeds of the driving wheels and the idler wheels being
substantially zero; at least one of the wheel speeds except for the
first wheel speed being greater than a prescribed threshold value;
and an average wheel speed of left and right idler wheels being
greater than an average wheel speed of left and right driving
wheels.
[0025] Preferably, the vehicle includes a power transmission
transmitting motive power to the idler wheels. The abnormality
detecting portion stops a motive power transmission operation of
the power transmission when abnormality of the wheel speed sensors
is detected.
[0026] Preferably, the power transmission transmits to the idler
wheels motive power commensurate to a relative rotation number
between the driving wheels and the idler wheels.
[0027] Preferably, the prescribed threshold value is a detection
value of the wheel speeds that can be detected by the wheel speed
sensors when the vehicle travels normally, and it is a value
greater than a maximum value of the wheel speeds detected when the
vehicle makes a turn.
[0028] According to the present invention, an automobile is
provided. The automobile includes: a motive power source; driving
wheels that receive motive power transmitted from the motive power
source and drive; idler wheels; wheel speed sensors arranged at
each of the driving wheels and the idler wheels for detecting
rotational speeds of corresponding the driving wheels and the idler
wheels; and the abnormality detecting apparatus for wheel speed
sensors detecting abnormality of the wheel speed sensors according
to any of claims 1-4.
[0029] According to the present invention, with a simple apparatus
configuration, an abnormality detecting apparatus for wheel speed
sensors with high detection accuracy can be implemented.
[0030] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic view showing a vehicle incorporating
an abnormality detecting apparatus for wheel speed sensors
according to an embodiment of the present invention.
[0032] FIG. 2 is a control block diagram for describing an ECU
shown in FIG. 1.
[0033] FIG. 3 is a flow chart for describing an abnormality
detection operation of wheel speed sensors according to the present
embodiment.
[0034] FIG. 4 is a control block diagram of the abnormality
detecting apparatus for wheel speed sensors described in Japanese
Patent Laying-Open No. 11-291886.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In the following, an embodiment of the present invention
will be described in detail referring to the drawings. Throughout
the drawings, identical reference characters denote identical or
corresponding parts.
[0036] FIG. 1 is a schematic view showing a vehicle incorporating
an abnormality detecting apparatus for wheel speed sensors
according to the embodiment of the present invention. It is noted
that, in the following description, it is assumed that the vehicle
employs what is called front-wheel based standby 4WD scheme, where
front wheels FL and FR are driving wheels and rear wheels RL and RR
are idler wheels.
[0037] Referring to FIG. 1, the vehicle includes an engine 10, a
front differential 12, axles 16, 18, 32, and 34, front wheels FL
and FR, rear wheels RL and RR, a propeller shaft 20, a power
transmission 30, a linear solenoid valve 60, a rear differential
26, an ECU (Electrical Control Unit) 40, and wheel speed sensors
50a-50d.
[0038] An output of engine 10 is split from front differential 12
to left and right axles 16 and 18, and transmitted to left and
right front wheels FL and FR, which are the driving wheels.
[0039] Front differential 12 includes an input rotary member 14.
Input rotary member 14 is coupled to propeller shaft 20 via a bevel
gear.
[0040] Propeller shaft 20 is divided into a front shaft 22 coupled
to input rotary member 14 and a rear shaft 24 coupled to rear
differential 26 via a bevel gear, between which power transmission
30 is arranged. It is noted that front shaft 22 and rear shaft 24
can relatively rotate with a rotational speed difference that is
commensurate to a rotational speed difference between front wheels
FL and FR and rear wheels RL and RR.
[0041] Power transmission 30 is constituted by a viscous coupling
that utilizes the shearing resistance force of a viscous fluid of
high viscosity such as silicon oil, for example.
[0042] Power transmission 30 has: a shaft 301 that is rotated
axially and integrally with front shaft 22; a case 302 that is
arranged at the outer periphery of shaft 301 to be capable of
relatively rotating with shaft 301, and that forms a coupling
chamber between an outer surface of shaft 301; and a coupling 303
that is arranged in the coupling chamber. Power transmission 30
transmits motive power that is commensurate to the relative
rotation number between case 302 and shaft 301.
[0043] Linear solenoid valve 60 controls the pressure of a
hydraulic fluid used in engagement and disengagement of coupling
303 of power transmission 30. Specifically, the pressure of the
hydraulic fluid used in controlling the engagement force of
coupling 303 is adjusted based on a line pressure from a not-shown
oil pump. As the hydraulic fluid is supplied from the oil pump to a
control valve (not shown), the control valve adjusts the pressure
of the hydraulic fluid to a desired line pressure based on the
control pressure from linear solenoid valve 60.
[0044] Linear solenoid valve 60 is controlled by a control current
Itr from ECU 40, as shown in FIG. 1. As will be described later,
control current Itr is calculated at ECU 40 based on an engagement
force of coupling 303 required for transmitting desired motive
power. Linear solenoid valve 60 generates a control pressure that
increases in accordance with an increase in control current Itr,
and exerts the generated control pressure to the not-shown control
valve. It is noted that, when control current Itr is 0, no control
pressure is generated and therefore, coupling 303 is disengaged and
does not transmit motive power.
[0045] Rear differential 26 is coupled to left and right rear
wheels RL and RR via left and right axles 32 and 34.
[0046] Wheel speed sensors 50a-50d detect the rotational speeds of
respective corresponding wheels FL, FR, RL, and RR, and output the
detected rotational speeds to ECU 40.
[0047] ECU 40 receives pulse signals from wheel speed sensors
50a-50d commensurate to rotational speeds of respective
corresponding wheels FL, FR, RL, and RR. ECU 40 calculates a
relative rotation number .DELTA.N between front and rear wheels
based on the rotational speeds of wheels FL, FR, RL, and RR. ECU 40
calculates control current Itr based on an engagement force of
coupling 303 required for transmitting transmission torque Tr that
is commensurate to the magnitude of the obtained relative rotation
number .DELTA.N, and outputs the calculated control current Itr to
linear solenoid valve 60.
[0048] Further, ECU 40 calculates wheel speeds of wheels FL, FR,
RL, and RR from the rotational speeds received from wheel speed
sensors 50a-50d. Based on the obtained wheel speeds, ECU 40
conducts an abnormality detecting operation on wheel speed sensors
50a-50d by means of a method described later.
[0049] With the configuration described above, power transmission
30 is employed as coupling means of a standby 4WD. Specifically,
when relative rotation number .DELTA.N between front wheels FL and
FR and rear wheels RL and RR is substantially 0, that is, when the
rotational speed difference between front shaft 22 and rear shaft
24 is substantially 0, power transmission 30 does not transmit
motive power as transmission torque Tr is 0 (control current Itr
also corresponds to 0). Here, rear wheels RL and RR are the idler
wheels that are rotated in accordance with the traveling of the
vehicle.
[0050] Meanwhile, when a relative rotation has occurred between
front wheels FL and FR and rear wheels RL and RR due to front
wheels FL and FR being slipping or being ditched, linear solenoid
valve 60 receives from ECU 40 control current Itr calculated based
on transmission torque Tr that is commensurate to relative rotation
number AN between front wheels FL and FR and rear wheels RL and RR.
Then, power transmission 30, under the pressure control of linear
solenoid valve 60, transmits motive power commensurate to
transmission torque Tr to rear differential 26 through rear shaft
24. Thus, rear wheels RL and RR are rotary driven by engine 10.
[0051] FIG. 2 is a control block diagram for describing ECU 40
shown in FIG. 1.
[0052] Referring to FIG. 2, ECU 40 includes a wheel speed
calculating portion 42, a wheel speed sensor abnormality detecting
portion 44, and power transmission controlling portion 46.
[0053] Wheel speed calculating portion 42 receives rotational
speeds of wheels FL, FR, RL, and RR from wheel speed sensors
50a-50e. Based on the rotational speeds, wheel speed calculating
portion 42 calculates wheels speeds VFR, VFL, VRL, VLL of wheels
FL, FR, RL, and RR, respectively, and outputs the calculated wheel
speeds VFR, VFL, VRL, and VLL to wheel speed sensor abnormality
detecting portion 44. Wheel speed calculating portion 42 further
determines relative rotation number .DELTA.N between front wheels
FL and FR and rear wheels RL and RR based on the rotational speeds
of wheels FL, FR, RL, and RR, and transmits the obtained relative
rotation number .DELTA.N to power transmission controlling portion
46.
[0054] As described above, power transmission controlling portion
46 calculates control current Itr based on the engagement force of
coupling 303 required for transmitting transmission torque Tr
commensurate to the input relative rotation number .DELTA.N, and
outputs the calculated control current Itr to linear solenoid valve
60 shown in FIG. 1.
[0055] When wheel speed sensor abnormality detecting portion 44
receives wheel speeds VFR, VFL, VRL, and RVV of wheels FR, RL, RL,
and RR, respectively, it conducts an abnormality detecting
operation on wheel speed sensors 50a-50d according to a method
described in the following. It is noted that, when wheel speed
sensor abnormality detecting portion 44 detects abnormality of
wheel speed sensors 50a-50d, it outputs a signal AD specifying the
detection result to power transmission controlling portion 46.
Power transmission controlling portion 46 determines that wheel
speed sensors 50a-50d are abnormal based on the input signal AD,
and stops control for four-wheel drive.
[0056] Specifically, when power transmission controlling portion 46
receives signal AD, it sets control current Itr to 0 and outputs to
linear solenoid valve 60. When linear solenoid valve 60 receives
control current Itr at 0, it does not generate a control pressure
and it disengages coupling 303 of power transmission 30 to stop
transmission of motive power. Thus, four-wheel drive control is
stopped, and two-wheel drive is continued or the control shifts to
two-wheel drive.
[0057] FIG. 3 is a flow chart for describing abnormality detection
operation on wheel speed sensors according to the present
embodiment.
[0058] Referring to FIG. 3, first, wheel speed sensor abnormality
detecting portion 44 determines as to whether or not any of the
input wheel speeds VFL, VFR, VRL, and VRR is 0 km/h (step S01).
Here, when it is determined that none of wheel speeds VFR, VFL,
VRL, and VRR are 0 km/h, wheel speed sensor abnormality detecting
portion 44 determines that all of wheel speed sensors 50a-50d are
normal (step S08), and ends the abnormality detecting
operation.
[0059] On the other hand, if it is determined at step S01 that any
of wheel speeds VFR, VFL, VRL, and VRR is 0 km/h, then it is
determined as to whether or not any of wheel speeds VFR, VFL, VRL,
and VRR is greater than a prescribed threshold value V1 (step
S02).
[0060] Here, prescribed threshold value V1 is any wheel speed set
within a prescribed wheel speed range that can be detected by the
wheel speed sensors when the vehicle travels normally (for example,
10 km/h). It should be noted that this wheel speed range does not
include wheel speeds when the vehicle travels at a low speed where
the detection performance of wheel speed sensors 50a-50d is
relatively low. When the vehicle is traveling at a low speed, wheel
speed sensors 50a-50d cannot detect correct wheel speeds, and
detect the wheel speeds to be 0 km/h.
[0061] In the abnormality detecting operation, in order not to
detect a difference in rotation between front and rear wheels due
to a turning radius difference of a vehicle making a turn as
abnormality of wheel speed sensors 50a-50d, prescribed threshold
value V1 is set to a value greater than the maximum value of the
wheel speeds of front wheels FR, FR when making a turn.
Specifically, when the vehicle makes a turn, if the wheel speed of
the innermost rear wheel exhibits 0 km/h and the wheel speed of the
outermost front wheel exhibits a prescribed value (V0 km/h; V0 is a
value greater than 0), prescribed threshold value V1 is set to a
value greater than prescribed value V0.
[0062] At step S02, when it is determined that all of wheel speeds
VFR, VFL, VRL, and VRR are at most at prescribed threshold value
V1, wheel speed sensor abnormality detecting portion 44 determines
that all of wheel speed sensors 50a-50d are normal (step S08), and
ends the abnormality detecting operation.
[0063] On the other hand, if it is determined at step S02 that any
of wheel speeds VFR, VFL, VRL, and VRR exceeds prescribed threshold
value V1, wheel speed sensor abnormality detecting portion 44
compares the magnitude of average wheel speed Vfa of front wheels
FL and FR and that of average wheel speed Vra of rear wheels RL and
RR (step S03). Average wheel speed Vfa of front wheels FL and FR is
an average value of wheel speeds VFL and VFR of left and right
front wheels FL and FR. Average wheel speed Vra of rear wheels RL
and RR is an average value of wheel speeds VRL and VRR of left and
right rear wheels RL and RR. Both of average wheel speeds Vfa and
Vra are calculated at wheel speed sensor abnormality detecting
portion 44.
[0064] Here, as a front-wheel drive base standby 4WD is employed as
the vehicle according to the present embodiment, in either case of
two-wheel drive and four-wheel drive, average wheel speed Vra of
rear wheels RR and RL that are the idler wheels never exceeds
average wheel speed Vfa of front wheels FL and FR that are the
driving wheels.
[0065] Specifically, in two-wheel drive, rear wheels RL and RR are
the idler wheels that are rotated in accordance with the drive by
the front wheels, and therefore the wheel speeds thereof is always
slower than those of front wheels FL and FR.
[0066] In four-wheel drive, in addition to front wheels FL and FR,
rear wheels RL and RR also receive transmission of driving force of
engine 10 and thereby caused to drive. Here, the driving force is
based on torque distribution for suppressing relative rotation
between the front and rear wheels when the rotational speeds of
front wheels FL and FR exceed the rotational speed of rear wheels
RL and RR due to slip or the like. Accordingly, it can be said that
the wheel speeds of rear wheels RL and RR that are the idler wheels
hardly exceed the wheel speeds of front wheels FL and FR that are
the driving wheels, when the wheel speed sensors are normal.
[0067] Therefore, in the present embodiment, at step S03, wheel
speed sensor abnormality detecting portion 44 determines that wheel
speed sensors 50a-50d are abnormal based on detection that average
wheel speed Vra of rear wheels RL and RR that are the idler wheels
has exceeded average wheel speed Vfa of front wheels FL and FR that
are the driving wheels in a front-wheel drive base standby 4WD
(step S04). Thus, the difficult wheelspin determination is not
required as a condition for establishing the abnormality detection
operation, and therefore, the abnormality detection on wheel speed
sensors 50a-50d can be conducted easily and in higher accuracy.
[0068] On the other hand, when average wheel speed Vfa of front
wheels FL and FR exceed average wheel speed Vra of rear wheels RL
and RR, wheel speed sensor abnormality detecting portion 44
determines that wheel speed sensors 50a-50d are normal (step S08),
and ends the abnormality detection operation.
[0069] When the vehicle employs rear-wheel drive base standby 4WD
scheme where rear wheels RL and RR are the driving wheels and front
wheels FL and FR are the idler wheels, at step S03 in FIG. 3, wheel
speed sensor abnormality detecting portion 44 detects that average
wheel speed Vfa of front wheels FL and FR exceeds average wheel
speed Vra of rear wheels RL and RR, and determines that wheel speed
sensors 50a-50d are abnormal.
[0070] Next, at step S04, when wheel speed sensor abnormality
detecting portion 44 detects abnormality of wheel speed sensors
50a-50d (step S04), it generates signal AD specifying the detection
result and output to power transmission controlling portion 46.
[0071] In response to input of signal AD, power transmission
controlling portion 46 determines as to whether or not the current
vehicle driving state is four-wheel drive (step S05). When it is
determined that the vehicle driving state is four wheel drive at
step S05, power transmission controlling portion 46 sets control
current Itr to 0 that is output to linear solenoid valve 60, and
stops four-wheel drive control (step S07). Thus, the vehicle
driving state shifts from four-wheel drive to two-wheel drive.
[0072] On the other hand, if it is determined at step S05 that the
vehicle driving state is not four-wheel drive, that is, it is
two-wheel drive, then power transmission controlling portion 46
sets control current Itr to 0 and prohibits actuation of four-wheel
drive, and continues current two-wheel drive (step S06).
[0073] While the example where the abnormality detecting apparatus
for wheel speed sensors is applied to a standby 4WD vehicle has
been described in the present embodiment, it is also applicable to
two-wheel drive vehicle employing either front wheels or rear
wheels as the driving wheels. Specifically, when the abnormality
detecting apparatus for wheel speed sensors according to the
present invention is applied to a two-wheel drive vehicle, it is
configured such that, in the abnormality detecting operation,
abnormality of wheel speed sensors is detected based on detection
that the average wheel speed of the idler wheels has exceeded the
average wheel speed of the driving wheels.
[0074] As above, according to the embodiment of the present
invention, with a simple apparatus configuration, the detection
accuracy of the abnormality detecting apparatus for wheel speed
sensors can further be improved.
[0075] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
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