U.S. patent application number 09/865695 was filed with the patent office on 2002-01-17 for device for changing the speeds of the front and rear wheels in a four-wheel-drive vehicle.
Invention is credited to Koga, Hidetaka, Tanaka, Hirohisa.
Application Number | 20020007242 09/865695 |
Document ID | / |
Family ID | 18665990 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020007242 |
Kind Code |
A1 |
Tanaka, Hirohisa ; et
al. |
January 17, 2002 |
Device for changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle
Abstract
A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle, which is equipped with a continuously
variable speed-changing mechanism for the front wheels which
changes the input rotational speed and outputs it to the front
wheel drive shafts and a continuously variable speed-changing
mechanism for the rear wheels which changes the input rotational
speed and outputs it to the rear wheel drive shafts. The device for
changing the speeds of the front and rear wheels comprises a
detector means for detecting the operation conditions of the
vehicle and a controller for variably controlling the speeds of
said continuously variable speed-changing mechanism for the front
wheels and of said continuously variable speed-changing mechanism
for the rear wheels based on the operation conditions of the
vehicle detected by said detector means. The controller calculates
a tire diameter ratio of the front wheels to the rear wheels when
the vehicle travels straight, sets a target speed-changing ratio
obtained based on the vehicle operation conditions detected by the
detector means to be a target speed-changing ratio for the rear
wheels in the continuously variable speed-changing mechanism for
the rear wheels or to be a target speed-changing ratio for the
front wheels in the continuously variable speed-changing mechanism
for the front wheels, and sets a speed-changing ratio obtained by
correcting the target speed-changing ratio based on the tire
diameter ratio to be a target speed-changing ratio for the front
wheels or to be a target speed-changing ratio for the rear
wheels.
Inventors: |
Tanaka, Hirohisa; (Tokyo,
JP) ; Koga, Hidetaka; (Kanagawa, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18665990 |
Appl. No.: |
09/865695 |
Filed: |
May 29, 2001 |
Current U.S.
Class: |
701/69 ;
701/74 |
Current CPC
Class: |
B60W 2530/20 20130101;
B60K 23/0808 20130101; F16H 15/38 20130101; B60K 17/348
20130101 |
Class at
Publication: |
701/69 ;
701/74 |
International
Class: |
G06F 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2000 |
JP |
2000 - 162050 |
Claims
What we claim is:
1. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle, which is equipped with a continuously
variable speed-changing mechanism for the front wheels which
changes the input rotational speed and outputs it to the front
wheel drive shafts, and a continuously variable speed-changing
mechanism for the rear wheels which changes the input rotational
speed and outputs it to the rear wheel drive shafts, so that the
front wheels and the rear wheels can be driven at continuously
variable speeds independently of each other owing to the
continuously variable speed-changing mechanisms, wherein: said
device for changing the speeds of the front and rear wheels
comprises a detector means for detecting the operation conditions
of the vehicle and a controller for variably controlling the speeds
of said continuously variable speed-changing mechanism for the
front wheels and of said continuously variable speed-changing
mechanism for the rear wheels based on the operation conditions of
the vehicle detected by said detector means; and said controller
calculates a tire diameter ratio of the front wheels to the rear
wheels during the vehicle travels straight, sets a target
speed-changing ratio obtained based on the vehicle operation
conditions detected by the detector means to be a target
speed-changing ratio for the rear wheels in the continuously
variable speed-changing mechanism for the rear wheels or to be a
target speed-changing ratio for the front wheels in the
continuously variable speed-changing mechanism for the front
wheels, and sets a speed-changing ratio obtained by correcting the
target speed-changing ratio based on the tire diameter ratio to be
a target speed-changing ratio for the front wheels or to be a
target speed-changing ratio for the rear wheels.
2. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 1, wherein a driving
force disconnection device is provided to disconnect the driving
force transmitted to the front wheels from the continuously
variable speed-changing mechanism for the front wheels or to
disconnect the driving force transmitted to the rear wheels from
the continuously variable speed-changing mechanism for the rear
wheels, and the controller calculates the tire diameter ratio in a
state where the driving force disconnection device is
disconnected.
3. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 1, wherein the
controller calculates said tire diameter ratio from a ratio of the
rotational speed of the front wheel drive shafts to the rotational
speed of the rear wheel drive shafts.
4. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 1, wherein the
controller sets the speed-changing ratio obtained by correcting the
target speed-changing ratio according to a predetermined equation
using the target speed-changing ratio and the tire diameter ratio
as variables to be the target speed-changing ratio for the front
wheels or the target speed-changing ratio for the rear wheels.
5. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 1, wherein the
controller obtains said target speed-changing ratio for the front
wheels or said target speed-changing ratio for the rear wheels by
adding an amount for correcting the speed-changing ratio calculated
based on the tire diameter ratio to the target speed-changing
ratio.
6. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 5, wherein the
controller calculates said amount for correcting the speed-changing
ratio in compliance with a predetermined equation or an approximate
equation using the tire diameter ratio as a variable.
7. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 5, wherein the
controller obtains said amount for correcting the speed-changing
ratio from a map prepared in advance based on the values calculated
or approximated by a predetermined equation or an approximate
equation determined in advance by using the tire diameter ratio as
a variable.
8. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 5, wherein the
controller obtains said approximate amount for correcting the
speed-changing ratio calculated by a predetermined approximate
equation using the tire diameter ratio as a variable, from a map
prepared in advance based on the approximate values which have been
further corrected based on a deviation of the ratio between the
target speed-changing ratio for the front wheels and the target
speed-changing ratio for the rear wheels at said tire diameter
ratio.
9. A device for changing the speeds of the front and rear wheels in
a four-wheel-drive vehicle according to claim 1, wherein each of
the continuously variable speed-changing mechanism for the front
wheels and the continuously variable speed-changing mechanism for
the rear wheels is constituted by a toroidal type continuously
variable speed-changing device comprising an input disk for
receiving a driving force, an output disk that is disposed being
opposed to the input disk and is drive-coupled to the front wheel
drive shafts or to the rear wheel drive shafts, and power rollers
disposed between the input disk and the output disk so as to rotate
in a tilted manner and to change contact points to the input disk
and to the output disk to continuously change the rotational speed
of the input disk and to transmit the rotation to the output
disk.
10. A device for changing the speeds of the front and rear wheels
in a four-wheel-drive vehicle according to claim 9, wherein the
controller sets a target tilting angle of the power rollers for the
front wheels in the continuously variable speed-changing mechanism
for the front wheels and a target tilting angle of the power
rollers for the rear wheels in the continuously variable
speed-changing mechanism for the rear wheels, respectively,
correspondingly to the target speed-changing ratio for the front
wheels and the target speed-changing ratio for the rear wheels, to
control the continuously variable speed-changing mechanism for the
front wheels and the continuously variable speed-changing mechanism
for the rear wheels based on the target tilting angle for the front
wheels and the target tilting angle for the rear wheels.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a continuously variable
speed-changing device and, more particularly, to a device for
changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle, capable of variably driving the front
wheels and the rear wheels independently from each other by using a
toroidal type continuously variable speed-changing device or a
belt-type continuously variable speed-changing device.
DESCRIPTION OF THE PRIOR ART
[0002] There has heretofore been proposed a four-wheel-drive
vehicle equipped with a continuously variable speed-changing
mechanism for the front wheels and with a continuously variable
speed-changing mechanism for the rear wheels in order to variably
drive the front wheel drive shafts and the rear wheel drive shafts
independently from each other via the continuously variable
speed-changing mechanisms, in an attempt to decrease the weight of
the four-wheel-drive mechanisms, to avoid the loss of power and to
improve the fuel efficiency.
[0003] A typical example of the continuously variable
speed-changing device in the four-wheel-drive vehicle can be
typified by a toroidal type continuously variable speed-changing
device disclosed in Japanese Laid-open Patent Publication (Kokai)
No. 157151/1993 (JP-A 5-157151). This continuously variable
speed-changing device includes an input shaft supported by a
casing, and a continuously variable speed-changing mechanism for
the front wheels and a continuously variable speed-changing
mechanism for the rear wheels that are arranged, spaced apart, in
the axial direction of the input shaft. The continuously variable
speed-changing mechanism for the front wheels changes the input
rotational speed of the input shaft and outputs it to the front
wheel drive shafts. The continuously variable speed-changing
mechanism for the rear wheels changes the input rotational speed of
the input shaft and outputs it to the rear wheel drive shafts.
These continuously variable speed-changing mechanisms have been so
constituted as to variably drive the front wheels and the rear
wheels independently from each other.
[0004] The above continuously variable speed-changing mechanism for
the front wheels has substantially the same constitution as that of
the continuously variable speed-changing mechanism for the rear
wheels. Therefore, the constitution of the continuously variable
speed-changing mechanism for the front wheels will now be briefly
described. The continuously variable speed-changing mechanism for
the front wheels includes an input disk which is secured to the
input shaft and has one surface in the axial direction thereof
formed as an input side recessed surface of an arcuate shape in
cross section, and an output disk having one surface in the axial
direction thereof formed as an output side recessed surface of an
arcuate shape in cross section. The output disk is so disposed as
to rotate relative to the input shaft and to surround the outer
peripheral surface of the input shaft and has its output side
recessed surface disposed so as to be opposed to the input side
recessed surface of the input disk in the axial direction. A pair
of power rollers are disposed between the input side recessed
surface of the input disk and the output side recessed surface of
the output disk so as to rotate relative to the input disk and the
output disk. The power rollers are supported by trunnions so as to
rotate. The axes of rotation of the power rollers are arranged at
right angles with the axes of the trunnions that will be described
later.
[0005] The trunnions are so supported as to rotate about their axes
relative to the casing and to move in the axial direction. The axes
of the trunnions extend in parallel with each other in the
tangential direction relative to the input shaft at symmetrical
positions with the input shaft interposed therebetween at an equal
distance. On the cross sections of the input disk and of the output
disk opposed to each other in the axial direction, the center of
arc of the input side recessed surface of the input disk and the
center of arc of the output side recessed surface of the output
disk are arranged on a common center of arc. Further, the axial
centers of the trunnions are arranged to be in agreement with the
centers of the corresponding arcs. The axes of the trunnions define
tilting axes along which the corresponding power rollers rotate.
The power rollers are so constituted as to possess spherically
protruded surfaces in the peripheries thereof, the protruded
surfaces being brought into a pressed contact (point contact) with
the input side recessed surface of the input disk and with the
output side recessed surface of the output disk. The trunnions are
moved in the axial directions but in the opposite directions
relative to each other by the actuators such as hydraulic
cylinders, whereby the power rollers rotate about the axes which
are tilted by an angle corresponding to the amount of motion of the
trunnions and changing of the speed between the input disk and the
output disk is performed. According to the toroidal type
continuously variable speed-changing device as described above, the
rotational forces of the output disks of the continuously variable
speed-changing mechanism for the front wheels and of the
continuously variable speed-changing mechanism for the rear wheels
are output to the front wheels and to the rear wheels independently
from each other, to execute the full-time four-wheel drive.
Constitutions of trunnions of the toroidal type continuously
variable speed-changing device have been disclosed in, for example,
Japanese Utility Model Publication (Kokoku) No. 11425/1994 and
Japanese Laid-open Patent Publication (Kokai) No. 269039/1997 (JP-A
9-269039).
[0006] In the continuously variable speed-changing device, when a
steering angle is given to the front wheels, the tilting angle of
the power rollers of the continuously variable speed-changing
mechanism for the front wheels is differed from the tilting angle
of the power rollers of the continuously variable speed-changing
mechanism for the rear wheels to drive the four wheels with little
loss of power while absorbing the difference in rotational speed
between the front wheels and the rear wheels when the vehicle
turns, without using the center differential.
[0007] Another typical example of the continuously variable
speed-changing device can be represented by a belt-type
continuously variable speed-changing device. This continuously
variable speed-changing device employs a belt-type continuously
variable speed-changing mechanism for the front wheels and a
belt-type continuously variable speed-changing mechanism for the
rear wheels instead of the above-mentioned toroidal type
continuously variable speed-changing mechanism for the front wheels
and the toroidal type continuously variable speed-changing
mechanism for the rear wheels. Each of the belt-type continuously
variable speed-changing mechanism for the front wheels and the
belt-type continuously variable speed-changing mechanism for the
rear wheels comprises a primary pulley having a pulley fixed to the
primary shaft drive-coupled to the output shaft of the engine and a
movable pulley which is opposed to the fixed pulley and can move in
the axial direction, a secondary pulley having a pulley fixed to
the secondary shaft and a movable pulley which is opposed to the
fixed pulley and can move in the axial direction, and a drive belt
wrapped round the primary pulley and the secondary pulley. Upon
changing the gaps of the pulley grooves of the primary pulley and
of the secondary pulley, the belt-wrapping diameters of the pulleys
change and the speed-changing ratio between the primary shaft and
the secondary shaft is continuously adjusted. Even by using the
thus constituted belt-type continuously variable speed-changing
device, the front wheels and the rear wheels can be variably driven
independently from each other by the continuously variable
speed-changing mechanism for the front wheels and by the
continuously variable speed-changing mechanism for the rear wheels
in substantially the same manner as in the above-mentioned toroidal
type continuously variable speed-changing device.
[0008] In the four-wheel-drive vehicle, part of the tire diameters
of the wheels often changes not only when a temporary tire is used
but also when the tire pneumatic pressure is decreased, the tire
pneumatic pressures have not been well adjusted and tread surfaces
are worn out. A change in the tire diameter of either the right
wheel or the left wheel appears as a change in the average tire
diameter of the right and left wheels for the front wheel drive
shafts or for the rear wheel drive shafts, since differentials are
provided for the front wheel drive shafts and for the rear wheel
drive shafts, respectively. When a difference occurs in the tire
diameter between the front wheels and the rear wheels, on the other
hand, there results inconvenience such as loss of power due to a
difference in the rotational speed between the front and rear drive
systems, impairing smooth four-wheel-drive traveling. Therefore,
this inconvenience must be avoided.
[0009] In the case where a difference occurs in the tire diameter
between the front wheels and the rear wheels as described above, if
the speed-changing ratio for the front and rear wheels is so set
that the front wheel drive shafts and the rear wheel drive shafts
run at an equal rotational speed, unequal tire diameters of the
front and rear wheels turn out to be a difference in the peripheral
velocity of the front and rear wheel tires when traveling straight,
causing inconvenience such as loss of power. When the tire
diameters of the front and rear wheels are not the same, therefore,
it is desired to avoid inconvenience such as loss of power ascribed
to unequal tire diameters by changing the speed-changing ratios for
the wheels so that all of the wheels have an equal peripheral
velocity, by utilizing the fact that the speed changing ratios for
the front and rear wheels can be independently controlled. The
conventional toroidal type continuously variable speed-changing
device described earlier is so constructed to allow to carry out
the four-wheel-drive with little loss of power while absorbing the
difference in the peripheral speed between the front wheels and the
rear wheels during turning without using the center differential by
imparting a difference to the speed between the front wheels and
the rear wheels when the vehicle turns. However, no means has yet
been proposed for solving the problem for the case where a
difference exists in the tire diameters between the front wheels
and the rear wheels. Inconvenience such as loss of power due to
unequal tire diameters of the front and rear wheels is possible to
occur not only in the above-mentioned conventional toroidal type
continuously variable speed-changing device but also in the
above-mentioned belt-type continuously variable speed-changing
device. Therefore, it is necessary to provide a means for solving
the problem.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a novel
device for changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle, which prevents the occurrence of
inconvenience such as loss of power caused by a difference in the
tire diameters between the front wheels and the rear wheels and
ensures smooth four-wheel-drive traveling.
[0011] Another object of the present invention is to provide a
novel device for changing the speeds of the front and rear wheels
in a four-wheel-drive vehicle, which avoids the inconvenience such
as loss of power and ensures smooth four-wheel-drive traveling, by
detecting changes in the tire diameters of the front wheels and the
rear wheels during traveling straight and, when differences in the
tire diameters of the front and rear wheels are detected,
separately controlling the speed-changing ratios for the front and
rear wheels according to the differences such that the front and
rear wheels will assume the same peripheral velocity.
[0012] A further object of the present invention is to provide a
novel device for changing the speeds of the front and rear wheels
in a four-wheel-drive vehicle, which avoids inconvenience such as
loss of power caused by a difference in the tire diameters between
the front wheels and the rear wheels and ensures smooth
four-wheel-drive traveling, by effecting a relatively simple
control operation.
[0013] According to the present invention, there is provided a
device for changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle, which is equipped with a continuously
variable speed-changing mechanism for the front wheels which
changes the input rotational speed and outputs it to the front
wheel drive shafts and a continuously variable speed-changing
mechanism for the rear wheels which changes the input rotational
speed and outputs it to the rear wheel drive shafts, so that the
front wheels and the rear wheels can be driven at continuously
variable speeds independently of each other owing to the
continuously variable speed-changing mechanisms, wherein:
[0014] the device for changing the speeds of the front and rear
wheels comprising a detector means for detecting the operation
conditions of the vehicle and a controller for variably controlling
the speeds of said continuously variable speed-changing mechanism
for the front wheels and of said continuously variable
speed-changing mechanism for the rear wheels based on the operation
conditions of the vehicle detected by said detector means; and
[0015] the controller calculates a tire diameter ratio of the front
wheels to the rear wheels during the vehicle travels straight, sets
a target speed-changing ratio obtained based on the vehicle
operation conditions detected by the detector means to be a target
speed-changing ratio for the rear wheels in the continuously
variable speed-changing mechanism for the rear wheels or to be a
target speed-changing ratio for the front wheels in the
continuously variable speed-changing mechanism for the front
wheels, and sets a speed-changing ratio obtained by correcting the
target speed-changing ratio based on the tire diameter ratio to be
a target speed-changing ratio for the front wheels or to be a
target speed-changing ratio for the rear wheels.
[0016] It is desired that a driving force disconnection device is
provided to disconnect the driving force transmitted to the front
wheels from the continuously variable speed-changing mechanism for
the front wheels or to disconnect the driving force transmitted to
the rear wheels from the continuously variable speed-changing
mechanism for the rear wheels, and the controller calculates the
tire diameter ratio in a state where the driving force
disconnection device is disconnected.
[0017] It is desired that the controller calculates the tire
diameter ratio from a ratio of the rotational speed of the front
wheel drive shafts to the rotational speed of the rear wheel drive
shafts.
[0018] It is desired that the controller sets the speed-changing
ratio obtained by correcting the target speed-changing ratio
according to a predetermined equation by using the target
speed-changing ratio and the tire diameter ratio as variables to be
a target speed-changing ratio for the front wheels or a target
speed-changing ratio for the rear wheels.
[0019] It is desired that the controller obtains the target
speed-changing ratio for the front wheels or the target
speed-changing ratio for the rear wheels by adding an amount for
correcting the speed-changing ratio calculated based on the tire
diameter ratio to the target speed-changing ratio.
[0020] It is desired that the controller calculates the amount for
correcting the speed-changing ratio in compliance with a
predetermined equation or an approximate equation using the tire
diameter ratio as a variable.
[0021] It is desired that the controller obtains the amount for
correcting the speed-changing ratio from a map prepared in advance
based on the values calculated or approximated by a predetermined
equation or an approximate equation determined in advance by using
the tire diameter ratio as a variable.
[0022] It is desired that the controller obtains an approximate
amount for correcting the speed-changing ratio calculated by a
predetermined approximate equation using the tire diameter ratio as
a variable, from a map prepared in advance based on the approximate
values which have been further corrected based on a deviation of
the ratio between the target speed-changing ratio for the front
wheels and the target speed-changing ratio for the rear wheels at
said tire diameter ratio.
[0023] It is desired that each of the continuously variable
speed-changing mechanism for the front wheels and the continuously
variable speed-changing mechanism for the rear wheels is
constituted by a toroidal type continuously variable speed-changing
device comprising an input disk for receiving a driving force, an
output disk that is disposed opposite to the input disk and is
drive-coupled to the front wheel drive shafts or to the rear wheel
drive shafts, and power rollers disposed between the input disk and
the output disk so as to rotate in a tilted manner and to change
contact points to the input disk and to the output disk to
continuously change the rotational speed of the input disk and to
transmit the rotation to the output disk.
[0024] It is desired that the controller sets a target tilting
angle of the power rollers for the front wheels in the continuously
variable speed-changing mechanism for the front wheels and a target
tilting angle of the power rollers for the rear wheels in the
continuously variable speed-changing mechanism for the rear wheels,
respectively, correspondingly to the target speed-changing ratio
for the front wheels and the target speed-changing ratio for the
rear wheels, to control the continuously variable speed-changing
mechanism for the front wheels and the continuously variable
speed-changing mechanism for the rear wheels based on the target
tilting angle for the front wheels and the target tilting angle for
the rear wheels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a plan view schematically illustrating a
four-wheel-drive vehicle equipped with a device for changing the
speeds of the front and rear wheels;
[0026] FIG. 2 is a vertical sectional view of the device for
changing the speeds of the front and rear wheels of the
four-wheel-drive vehicle shown in FIG. 1;
[0027] FIG. 3 is a diagram of the constitution of major portions
for illustrating a relationship between the tilting angle .phi. of
the power rollers and the rotational speed N3 of the output disk in
the toroidal type continuously variable speed-changing device;
[0028] FIG. 4 is a graph illustrating a relationship between the
tilting angle .phi.r in the continuously variable speed-changing
mechanism for the rear wheels and the speed-changing ratio in the
continuously variable speed-changing mechanism for the front wheels
and in the continuously variable speed-changing mechanism for the
rear wheels in the device for changing the speeds of the front and
rear wheels with the tire diameter ratio as a reference according
to the present invention; and
[0029] FIG. 5 is a graph illustrating a relationship between the
tilting angle .phi.r in the continuously variable speed-changing
mechanism for the rear wheels and the deviation of the ratio
between the speed-changing ratio in the continuously variable
speed-changing mechanism for the front wheels and the
speed-changing ratio in the continuously variable speed-changing
mechanism for the rear wheels in the device for changing the speeds
of the front and rear wheels on the basis of the tire diameter
ratio as a reference according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Embodiments of the device for changing the speeds of the
front and rear wheels in a four-wheel-drive vehicle according to
the invention will now be described with reference to the
accompanying drawings. Referring to FIG. 1, a four-wheel-drive
vehicle 1 equipped with a device for changing the speeds of the
front and rear wheels according to the present invention is
provided with an engine 2, a torque converter 3 on the output side
of the engine, a clutch unit 4 at the back of the torque converter
3, and a double-cavity toroidal type continuously variable
speed-changing device 6 arranged on the main shaft 5 on the output
side of the clutch unit 4. The continuously variable speed-changing
device 6 will be described later. The clutch unit 4 is constituted
by a planetary gear which can be changed to the forward and
reverse, and is equipped with a ring gear, a carrier and a clutch
capable of being selectively coupled to the casing. Part of the
driving force output from the continuously variable speed-changing
device 6 is transmitted to a propeller shaft 7 for driving the
front wheels, a differential 8 for the front wheels connected to
the propeller shaft 7 for driving the front wheels, right and left
front wheel drive shafts 9,9 on the output side of the differential
8 for the front wheels and the front wheels 10,10 attached to the
front wheel drive shafts 9,9. The remaining driving force output
from the continuously variable speed-changing device 6 is
transmitted to a propeller shaft 11 for driving the rear wheels, a
differential 12 for the rear wheels connected to the propeller
shaft 11 for driving the rear wheels, right and left rear wheel
drive shafts 13,13 on the output side of the differential 12 for
the rear wheels and the rear wheels 14,14 attached to the rear
wheel drive shafts 13,13. The front wheels 10,10 are steered as a
driver turns a steering wheel 15.
[0031] A vehicle speed sensor 16 is disposed on the continuously
variable speed-changing device 6 close to a gear on a power
transmission passage to the rear wheels 14. The vehicle speed
sensor 16 detects the rotational speed of the gear (corresponds to
the vehicle speed V). A steering angle sensor 18 for detecting the
steering angle of the steering wheel 15 detects the steering angle
.zeta. of the front wheels 10,10, and sends an output to the
controller 30.
[0032] The continuously variable speed-changing device 6 is further
provided with a tilting angle sensor 19 for the front wheels to
detect the true tilting angle .phi.af of the power rollers 42 for
front wheels in the continuously variable speed-changing mechanism
6a for the front wheels that will be described later, and with a
tilting angle sensor 20 for rear wheels to detect the true tilting
angle .phi.ar of the power rollers 42 for rear wheels in the
continuously variable speed-changing mechanism 6b for the rear
wheels that will be described later. In order to control the
movement of trunnions 43 of the continuously variable
speed-changing mechanism 6a for the front wheels and of the
continuously variable speed-changing mechanism 6b for the rear
wheels that will be described later, there are arranged a hydraulic
servo circuit 21 for the front wheels and a hydraulic servo circuit
22 for the rear wheels for the hydraulic cylinders (not shown) for
actuating the trunnions 43 corresponding to the continuously
variable speed-changing mechanisms 6a and 6b. As will be described
later, the tilting angles of the power rollers 42 are defined
according to the moving amounts of the trunnions 43. As will be
described later in detail, the target tilting angles of the power
rollers 42 in the continuously variable speed-changing mechanisms
6a and 6b correspond to the target speed-changing ratios of the
continuously variable speed-changing mechanisms 6a and 6b. A
detection signal from the tilting angle sensor 19 for the front
wheels is input to the hydraulic servo circuit 21 for the front
wheels, and a detection signal from the tilting angle sensor 20 for
the rear wheels is input to the hydraulic servo circuit 22 for the
rear wheels.
[0033] The controller 30 is equipped with a predetermined
speed-changing map which comprises the accelerator pedal operation
amount Ac such as an accelerator pedal-pushing amount of the
four-wheel-drive vehicle 1, vehicle speed V and the engine
rotational speed Ne. The accelerator pedal operation amount Ac can
be detected by, for example, a potentiometer (not shown) that
detects the amount of operation of the accelerator pedal. The
vehicle speed can be detected by the vehicle speed sensor 16.
Further, the engine rotational speed Ne can be detected by
detecting the rotational speed of the flywheel of the engine 2 by
using, for example, an engine rotational speed sensor that is not
shown. These potentiometer, vehicle speed sensor 16 and engine
rotational speed sensor constitute detector means for detecting the
operation conditions of the vehicle, and detection signals obtained
by the detector means are input to the controller 30.
[0034] In this embodiment, the controller 30 sets a target
speed-changing ratio obtained based on the operation conditions of
the vehicle detected by the detector means to be a target
speed-changing ratio for the rear wheels (corresponds to a target
tilting angle .phi.cr for rear wheels) in the continuously variable
speed-changing mechanism 6a for the rear wheels (sent the target
speed-changing ratio as a target speed-changing ratio for the rear
wheels to the hydraulic servo circuit 22 for the rear wheels), and
adds an amount for correcting the speed-changing ratio (corresponds
to an amount .DELTA..phi. for correcting the tilting angle) which
is a difference between the target speed-changing ratio and the
target speed-changing ratio for the front wheels (corresponds to
the target tilting .phi.cf for the front wheels) in the
continuously variable speed-changing mechanism 6b for the front
wheels to the target speed-changing ratio to obtain a target
speed-changing ratio for the front wheels (corresponds to the
target tilting angle .phi.cf for the front wheels) which is, then,
set as the target speed-changing ratio for the front wheels (sent
as the target speed-changing ratio for the front wheels to the
hydraulic servo circuit 21 for the front wheels). The amount for
correcting the speed-changing ratio is determined based on a tire
diameter ratio of the front wheels 10 and the rear wheels 14. This
will be described later. The hydraulic servo circuits 21 and 22
receive the target tilting angle .phi.cf for the front wheels and
the target tilting angle .phi.cr for the rear wheels output from
the controller 30, receive the true tilting angle .phi.af for the
front wheels detected by the continuously variable speed-changing
mechanism 6a for the front wheels and receive the true tilting
angle .phi.ar for the rear wheels detected by the continuously
variable speed-changing mechanism 6b for the rear wheels. In
response to these input data, control signals Uf and Ur are output
to the hydraulic servo circuits 21 and 22, thereby to control the
hydraulic pressure of the hydraulic cylinders which are the
actuators of the continuously variable speed-changing mechanism 6a
and 6b, to control the displacement of the trunnions 43 in the
direction of the tilting axis, to control the tilted angle of the
power rollers 42, and to control the change of speed in the
continuously variable speed-changing mechanisms 6a and 6b.
Controlling the tilting angles of the continuously variable
speed-changing mechanisms 6a and 6b by the controller 30 will be
described later in detail.
[0035] When a certain steering angle .zeta. is given by the
operation of the steering wheel 15, an amount of correction
.DELTA..phi.s (see a correction circuit 31 in FIG. 1) calculated by
the correction circuit 31 in response to the steering angle .zeta.
is added to the amount for correcting the speed-changing ratio
based on the tire diameter ratio to cope with a difference between
the loci along which the rear wheels 14 travel and the loci along
which the front wheels 10 travel. When the steering angle is
brought to the opposite side, the graph becomes symmetrical with
respect to the vertical axis of steering angle .zeta.=0 as shown in
the correction circuit 31. Since in this invention, it is based on
the assumption that the vehicle travels straight, the amount
.DELTA..phi. of correcting the tilting angle based on the steering
angle .zeta. is not described in further detail.
[0036] Next, the toroidal type continuously variable speed-changing
device 6 will be described with reference to FIG. 2. In FIG. 2, the
same constituent elements as those shown in FIG. 1 are denoted by
the same reference numerals, and their description is not repeated.
Referring to FIG. 2, the continuously variable speed-changing
device 6 comprises a main shaft 5 supported by a casing 60, and the
continuously variable speed-changing mechanism 6a for the front
wheels and the continuously variable speed-changing mechanism 6b
for the rear wheels 6b arranged, spaced apart, in the axial
direction of the main shaft 5. The output from the engine 2 is
input to the main shaft 5 from the torque converter 3 through the
clutch unit 4. The continuously variable speed-changing mechanism
6a for the front wheels changes the input rotational speed of the
main shaft 5 and outputs it to the front wheel drive shafts 9.
Further, the continuously variable speed-changing mechanism 6b for
the rear wheels changes the input rotational speed of the main
shaft 5 and outputs it to the rear wheel drive shafts 13. The
continuously variable speed-changing mechanisms 6a and 6b are
controlled by the controller 30 so as to continuously vary the
speeds of the front wheels 10, 10 and the rear wheels 14, 14
independently from each other.
[0037] The continuously variable speed-changing mechanism 6a for
the front wheels and the continuously variable speed-changing
mechanism 6b for the rear wheels are constituted substantially in
the same manner. Therefore, the continuously variable
speed-changing mechanism 6a for the front wheels will be briefly
described. The continuously variable speed-changing mechanism 6a
for the front wheels has an input disk 40 secured to the main shaft
5 and having one surface in the axial direction of the main shaft 5
formed as an input side recessed surface of an arcuate shape in
cross section, and an output disk 41 having one surface in the
axial direction of the main shaft 5 formed as an output side
recessed surface of an arcuate shape in cross section. The output
disk 41 is disposed so as to rotate relative to the main shaft 5
and to surround the outer peripheral surface of the main shaft 5,
the output side recessed surface thereof being opposed to the input
side recessed surface of the input disk 40 in the axial direction.
A pair of power rollers 42 are disposed between the input side
recessed surface of the input disk 40 and the output side recessed
surface of the output disk 41 so as to freely rotate relative to
the input disk 40 and the output disk 41. The axes of rotation of
the power rollers 42 are disposed to meet at right angles with the
axes of the trunnions 43 that will be described later. The power
rollers 42 are so constituted as to possess spherical protruded
surfaces along the periphery thereof, and the protruded surfaces
come in pressed contact (point contact) with the input side
recessed surface of the input disk 40 and with the output side
recessed surface of the output disk 41.
[0038] The power rollers 42 are rotatably supported by the
trunnions 43. The trunnions 43 are so supported as to rotate about
the axes (axes in agreement with the tilting axis 55 shown in FIG.
3) relative to the casing 60 and to move in the axial direction.
The axes of the trunnions 43 extend in parallel with each other in
the tangential direction with respect to the main shaft 5
(front-and-back direction in FIG. 2) at symmetrical positions with
the main shaft 5 sandwiched therebetween at an equal distance. The
center of arc (not shown) of the input side recessed surface of the
input disk 40 and the center of arc (not shown) of the output side
recessed surface of the output disk 41 are arranged on a common
center of arc on the cross section (cross section shown in FIG. 2)
of the input disk 40 and the output disk 41 opposed to each other
in the axial direction of the main shaft 5. Further, the axes of
the trunnions 43 are so arranged as to be in agreement with the
centers of the corresponding arcs. Further, the axes of the
trunnions 43 define the tilting axis 55 (see FIG. 3) of the
corresponding power rollers 42. By moving the trunnions 43 in the
axial directions and in the opposite directions by the hydraulic
cylinders (not shown) which are the actuators described earlier,
the power rollers 42 are tilted on the tilting axis 55 by a tilting
angle .phi. (see FIG. 3) corresponding to the moving amount of the
trunnions 43. The contact points are varied between the power
rollers 42 and the two disks 40 and 41 according to the tilted
rotation of the power rollers 42, whereby the rotational speed of
the input disk 40 is continuously varied and is transmitted to the
output disk 41 to change the speed between the input disk 40 and
the output disk 41. The continuously variable speed-changing device
6 including the thus constituted continuously variable
speed-changing mechanism 6a for the front wheels and the
continuously variable speed-changing mechanism 6b for the rear
wheels, works to output the rotational forces of the output disks
41 of the continuously variable speed-changing mechanism 6a for the
front wheels and of the continuously variable speed-changing
mechanism 6b for the rear wheels to the front wheels 10,10 and to
the rear wheels 14,14 independently from each other, to accomplish
the full-time four-wheel drive. As will be obvious from the
foregoing description, the continuously variable speed-changing
mechanism 6a for the front wheels and the continuously variable
speed-changing mechanism 6b for the rear wheels, constitute,
single-cavity toroidal type continuously variable speed-changing
mechanisms, respectively. Therefore, the continuously variable
speed-changing device 6 constitutes a double-cavity toroidal type
continuously variable speed-changing device.
[0039] In the continuously variable speed-changing mechanism 6a for
the front wheels, the rotation of the output disk 41 is transmitted
to the front right and left wheels 10,10 from the propeller shaft 7
for the front wheels through a chain transmission device 47 having
sprockets 44 and 45 and a chain 46 and through a gear mechanism 48
having an idler gear for bringing the rotational direction into
match with the rear wheels 14,14. The front wheel driving force is
distributed to the front right and left wheels 10,10 in compliance
with the rotational speeds that are different for the inner wheel
and for the outer wheel in response to the steering angle .zeta. of
the steering wheel 15 through the differential 8 for the front
wheels coupled to the propeller shaft 7 for the front wheels. In
the continuously variable speed-changing mechanism 6b for the rear
wheels, the rotation of the output disk 41 is transmitted to the
propeller shaft 11 for the rear wheels from a chain transmission
device 52 having sprockets 49, 50 and a chain 51 through a gear 54
on a counter shaft 53 and a gear 55 on the propeller shaft 11 for
the rear wheels arranged in concentric with the main shaft 5. The
rotation of the propeller shaft 11 for the rear wheels is
transmitted to the right and left rear wheels 14,14. The rear wheel
driving force is distributed to the rear right and left wheels
14,14 in compliance with the rotational speeds that are different
for the inner wheel and for the outer wheel through the
differential 12 for the rear wheels coupled to the propeller shaft
11 for the rear wheels.
[0040] Referring to FIG. 1, in order to selectively change the
driving state over to the four-wheel drive and to the two-wheel
drive, the front wheel drive shafts 9 are provided with a clutch 35
for coupling the front right and rear wheels 10,10 together in such
a manner that they can be disconnected. The clutch 35 which is a
driving force disconnection device includes a spline and a sleeve
that slides in a meshing direction relative to the spline to engage
with the spline. A hydraulic cylinder 81 which is an actuator is
disposed to disconnect the clutch 35 by actuating the sleeve. The
hydraulic cylinder 81 is controlled by the controller 30. The
four-wheel-drive vehicle 1 is provided with front wheel rotational
speed sensors 91,91 for detecting the rotational speeds of the
front wheel drive shafts 9,9 (i.e., rotational speeds of the front
wheels 10,10) and rear wheel rotational speed sensors 131,131 for
detecting the rotational speeds of the rear wheel drive shafts
13,13 (i.e., rotational speeds of the rear wheels 14,14). Detection
signals of the front wheel rotational speed sensors 91,91 and of
the rear wheel rotational speed sensors 131,131 are input to the
controller 30 for controlling the speed of the continuously
variable speed-changing device 6. In the four-wheel-drive state,
rotations of the front wheels 10,10 and of the rear wheels 14,14
affect each other. When the vehicle is traveling straight,
therefore, the controller 30 disconnects the clutch 35 so that the
vehicle assumes the two-wheel-drive state, and obtains a ratio of
tire diameters between the front wheels and the rear wheels based
on average values of the values detected by the front wheel
rotational speed sensors 91,91 and on average values of the values
detected by the rear wheel rotational speed sensors 131,131.
[0041] If the rotational speeds of the front wheels and of the rear
wheels are measured to be Nf and Nr while traveling straight in the
two-wheel-drive state in which the tires slip little due to the
driving force (desirably, traveling straight at a constant speed,
but may be traveling straight in an accelerated state), then, the
ratio (in terms of the rotational speed Nr of the rear wheels as a
reference) .alpha. becomes the tire diameter ratio (ratio of the
tire diameter of the front wheels to the tire diameter of the rear
wheels),
.alpha.=Nf/Nr (1)
[0042] Even when the tire diameters are not the same, inconvenience
such as loss of power due to a difference in the rotational speed
between the front wheels and the rear wheels when traveling, can be
avoided provided the front wheels and the rear wheels have an equal
peripheral velocity. Therefore, the four-wheel-drive vehicle 1 is
allowed to travel smoothly if the tilting angles .phi. of the power
rollers 42,42 in the continuously variable speed-changing
mechanisms 6a and 6b are so controlled that the ratio of the
speed-changing ratio ef of the continuously variable speed-changing
mechanism 6a for the front wheels to the speed-changing ratio er of
the continuously variable speed-changing ratio er of the
continuously variable seed-changing mechanism 6b becomes equal to
the rotational speed ratio .alpha. determined by the equation (1),
as expressed by the following equation (2),
ef/er=.alpha. (2)
[0043] In practice, there exists a nonlinear relationship between
the speed-changing ratio and the tilting angle. In the half
toroidal type continuously variable speed-changing device, however,
the adjustment can be easily accomplished as described below.
[0044] The controller 30 sets the target speed-changing ratio
obtained from the speed-changing map, based on the operation
conditions of the vehicle detected by the detector means, to be the
target speed-changing ratio ecr for the rear wheels in the
continuously variable speed-changing mechanism 6b for the rear
wheels. The controller 30 further adds an amount .DELTA.e for
correcting the speed-changing ratio to the target speed-changing
ratio ecr for the rear wheels in the continuously variable
speed-changing mechanism 6b for the rear wheels, and sets the added
result to be a target speed-changing ratio ecf for the front wheels
in the continuously variable speed-changing mechanism 6a for the
front wheels. More specifically, since the target speed-changing
ratios correspond to the tilting angles of the power rollers 42 in
the continuously variable speed-changing mechanisms 6a and 6b, the
controller 30 sends, as an instruction tilting angle for the rear
wheels, a target tilting angle .phi.cr for the rear wheels
corresponding to the target speed-changing ratio ecr for the rear
wheels in the continuously variable speed-changing mechanism 6b for
the rear wheels to the hydraulic servo circuit 22 for the rear
wheels. The hydraulic servo circuit 22 for the rear wheels further
receives the true tilting angle .phi.ar for the rear wheels
detected by the continuously variable speed-changing mechanism 6b
for the rear wheels. In response to these input data, the hydraulic
servo circuit 22 for the rear wheels produces a control signal Ur
to control the hydraulic pressure of the hydraulic cylinder in the
continuously variable speed-changing mechanism 6b for the rear
wheels, controls the displacement of the trunnions 43 in the
direction of tilting axes in the continuously variable
speed-changing mechanism 6b for the rear wheels to control the
tilted angle of the power rollers 42, and brings the tilting angle
of the power rollers 42 to the position of target tilting angle
.phi.cr for the rear wheels. The rear wheels 14,14 are rotatively
driven substantially at the above target speed-changing ratio ecr
for the rear wheels. The controller 30 further adds an amount
.DELTA..phi. for correcting the tilting angle to the target tilting
angle .phi.cr for the rear wheels, as expressed by the following
equation (3), and sets the added result to be the target tilting
angle .phi.cf for the front wheels in the continuously variable
speed-changing device 6a for the front wheels. More specifically,
the controller 30 sends, as an instruction tilting angle for the
front wheels, the target tilting angle .phi.cf corresponding to the
target speed-changing ratio ecf for the front wheels in the
continuously variable speed-changing mechanism 6a for the front
wheels to the hydraulic servo circuit 21 for the front wheels.
[0045] The hydraulic servo circuit 21 for the front wheels further
receives the true tilting angle .phi.af for the front wheels
detected by the continuously variable speed-changing mechanism 6a
for the front wheels. In response to these input data, the
hydraulic servo circuit 21 for the front wheels outputs the control
signal Uf to control the hydraulic pressure of the hydraulic
cylinder in the continuously variable speed-changing mechanism 6a
for the front wheels, controls the displacement of the trunnions 43
in the direction of tilting axes in the continuously variable
speed-changing mechanism 6a for the front wheels to control the
tilted angle of the power rollers 42, and brings the tilting angle
of the power rollers 42 to the position of the target tilting angle
.phi.cf for the front wheels. The front wheels 10,10 are rotatively
driven substantially at the target speed-changing ratio ecf for the
front wheels.
.phi.cf=.phi.cr+.DELTA..phi. (3)
[0046] The amount .DELTA..phi. for correcting the tilting angle is
so determined that the ratio of the speed-changing ratios becomes
ef/er=.alpha. in a state where the speed is most decreased (e.g.,
in a state corresponding to the low gear where the tilting angle
for the rear wheels is .phi.r=20.degree.). Referring, for example,
to FIGS. 3 and 4, in the structure of the toroidal type
continuously variable speed-changing mechanism having a cavity
aspect ratio k.sub.0 (=e.sub.0/r.sub.0, where e.sub.0 is a virtual
minimum diameter of the disk and r.sub.0 is a half-toroidal radius
of curvature)=0.45 and a half vertex angle
.theta..sub.0=57.degree., the amount for correcting the tilting
angle is,
.DELTA..phi.=4.degree. (4)
[0047] for a tire diameter ratio of .alpha.=1.1 (the tire diameter
of the front wheels is smaller than the tire diameter of the rear
wheels by 10%).
[0048] When the tire diameter of the front wheels is smaller than
the tire diameter of the rear wheels by 10%, the ratio ef/er of
nearly 1.1 is maintained over the whole range of speed-changing
ratios if the target tilting angle .phi.cf of the power rollers 42
for the front wheels corresponding to the target speed-changing
ratio ecf for the front wheels in the continuously variable
speed-changing mechanism 6a for the front wheels, is shifted toward
the speed-increasing side by only 4.degree. in relation with the
target tilting angle .phi.cr of the power rollers 42 for the rear
wheels, that corresponds to the target speed-changing ratio ecr for
the rear wheels in the continuously variable speed-changing
mechanism 6b for the rear wheels. The amount .DELTA..phi. for
correcting the tilting angle is determined by the cavity aspect
ratio k.sub.0 and the half vertical angle .theta..sub.0, i.e.,
determined according to the structure of the toroidal type
continuously variable speed-changing mechanism, and is stored as an
initial value in the controller 30.
[0049] FIG. 4 is a graph illustrating changes in the speed-changing
ratio ef for the front wheels and in the speed-changing ratio er
for the rear wheels, wherein the abscissa represents the tilting
angle .phi.r of the power rollers 42 for the rear wheels
(hereinafter simply referred to as tilting angle .phi.r) in the
continuously variable speed-changing mechanism 6b for the rear
wheels. A solid line represents the speed-changing ratio er for the
rear wheels and a broken line represents the speed-changing ratio
ef for the front wheels when the tilting angle .phi.r varies from
20.degree. up to about 88.degree.. As will be understood from FIG.
4, though the relationship is essentially nonlinear between the
tilting angle .phi.f for the front wheels (hereinafter simply
referred to as tilting angle .phi.f) corresponding to the
speed-changing ratio ef for the front wheels and the tilting angle
.phi.r corresponding to the speed-changing ratio er for the rear
wheels in order to obtain the ratio ef/er=1.1, it can be replaced
by an approximation obtained by advancing the tilting angle .phi.f
for the front wheels toward the speed-increasing side by 4.degree.
in relation with the tilting angle .phi.r for the rear wheels.
[0050] FIG. 5 is a graph illustrating a deviation from the true
ratio (1.1 or 1.05) of the ratio (ef/er) of the speed-changing
ratio ef for the front wheels to the speed-changing ratio er for
the rear wheels of when an approximation is set by advancing the
tilting angle .phi.f of the front wheels toward the
speed-increasing side by 4.degree. in relation with the tilting
angle .phi.r for the rear wheels, in the graph the abscissa
representing the tilting angle .phi.r of the power rollers 42 in
the continuously variable speed-changing mechanism 6b for the rear
wheels. The upper graph shows a deviation in the ratio (ef/er) of
when the tire diameter ratio .alpha. is 1.1. In this control
operation, the maximum error is at the most 2.7%
((ef/er)/.alpha.=1.13/1.1=1.027) when the speed-changing ratio is
near 1 (corresponds to the tilting angle .phi.r of about
57.degree.).
[0051] Similarly, when the tire diameter ratio is .alpha.=1.05 (the
tire diameter of the front wheels is smaller than the tire diameter
of the rear wheels by 5%), the amount for correcting the tilting
angle is,
.DELTA..phi.=2.degree. (5)
[0052] As will be understood from the lower graph in FIG. 5,
further, when the tire diameter ratio .alpha.=1.05, the maximum
error from the theoretical value is 1.2%
((ef/er)/.alpha.=1.063/1.05=1.012) at the speed-changing ratio
being nearly 1.
[0053] The toroidal type continuously variable speed-changing
mechanism of the above-mentioned model (the cavity aspect ratio
k.sub.o for defining the toroidal plane is 0.45, and the half
vertical angle .theta..sub.0 is 57.degree.) is practicable to a
sufficient degree even when the amount .DELTA..phi. for correcting
the tilting angle is approximated to be 4.degree. or 2.degree. at
the tire diameter ratio .alpha. is 1.1 or 1.05. For other tire
diameter ratios .alpha. (usually, the tire diameter ratio .alpha.
does not greatly deviate from these values), therefore, the amount
for correction can be sufficiently approximated by using a primary
function. That is, the amount .DELTA..phi. for correcting the
tilting angle can be expressed by the following approximate
equation using the tire diameter ratio .alpha. only as a
variable,
.DELTA..phi.=4.degree..times.(.alpha.-1).times.10 (6)
[0054] As for the toroidal speed-changing units having cavity
aspect ratios k.sub.0 and half vertical angles .theta..sub.0 of
different values, the coefficient related to .alpha. of the
equation (6) becomes a value different from 4.degree. and can be
stored in the map as an initial value corresponding to the model of
the toroidal type continuously variable speed-changing mechanism.
This method greatly facilitates the four-wheel-drive operation by
the controller 30.
[0055] As will be understood from FIG. 5, some error occurs in the
ratio (ef/er) of the speed-changing ratios in response to the
tilting angle .phi.r of the power rollers 42 in the continuously
variable speed-changing mechanism 6b for the rear wheels. In order
to eliminate this error, therefore, the amount .DELTA..phi. for
correcting the tilting angle may be further corrected in response
to the magnitude of the tilting angle .phi.r. By effecting the
correction again, it becomes possible to more highly precisely
avoid the inconvenience such as loss of power ascribed to a
difference in the tire diameters during the four-wheel-drive
traveling.
[0056] Next, described below with reference to FIG. 3 is a
relationship between the tilting angle .phi. of the power rollers
42 and the rotational speed N.sub.3 of the output shafts of the
continuously variable speed-changing mechanisms 6a and 6b. In FIG.
3, when the rotational speeds of the input disk 40 and the output
disk 41 are denoted by N.sub.1 and N.sub.3, the radii (contact
radii) at the contact points C.sub.1, C.sub.3 of the input disk 40,
output disk 41 and the power rollers 42 are denoted by r.sub.1 and
r.sub.3, the shortest diameter between the main shaft 5 and the
extension of a contact surface between the input disk 40 and the
output disk 41 (extension of an arcuate surface of the two disks 40
and 41 shown in cross section in FIG. 3) is denoted by e.sub.o, the
angle between one contact point C.sub.1, C.sub.3 and an axially
symmetrical surface between the two disks on the tilting axis 55 of
the trunnions 43 (surface that passes through the axial center
between the two disks 40 and 41 and through the tilting line 55 and
is at right angles with the axes of the two disks 40 and 41 in FIG.
3) is regarded to be a tilting angle .phi., one-half of a vertical
angle between the tilting axis and the two contact points C.sub.1
and C.sub.3 is regarded to be a half vertical angle .theta..sub.0,
a distance from the tilting axis 55 of the trunnions 43 to the
contact points C.sub.1, C.sub.3 of the power rollers 42, i.e., the
radius of curvature of the half toroidal is denoted by r.sub.0, and
a virtual minimum radius of the disk is denoted by e.sub.0, there
holds the following equation from the geometrical relationship, 1 r
0 + e 0 = r 0 cos + r 1 = r 0 cos ( 2 0 - ) + r 3
[0057] On the other hand, the ratio of r.sub.1 and r.sub.3 is
inversely proportional to the rotational speed of the input disk 40
and the output disk 41 through the rotation of the power rollers 42
as an intermediary rotation. From the ratio of r.sub.1 and r.sub.3,
the speed-changing ratio e that is a ratio of the rotational speed
N.sub.3 of the output disk 41 to the rotational speed N.sub.1 of
the input disk 40, can be obtained in compliance with the following
equation (3). Here, in this specification, the speed-changing ratio
is a value obtained by dividing the output rotational speed by the
input rotational speed. 2 e = N 3 / N 1 = r 1 / r 3 = ( 1 + k 0 -
cos ) / [ ( 1 + k 0 - cos ( 2 0 - ) ] ( 7 )
[0058] where k.sub.0 is a value representing a geometrical feature
of the cavity and is called cavity aspect ratio (=e.sub.0/r.sub.0)
as described earlier.
[0059] Next, described below is a relationship between the tilting
angle .phi.f of the power rollers 42 in the continuously variable
speed-changing mechanism 6a for the front wheels and the tilting
angle .phi.r of the power rollers 42 in the continuously variable
speed-changing mechanism 6b for the rear wheels. If the rotational
speeds of the front wheels 10 and of the rear wheels 14 are denoted
by Nf and Nr, then, .alpha.=Nf/Nr from the equation (1) when the
tire diameter ratio is being corrected. The reduction ratio of the
output disk 41 of the continuously variable speed-changing
mechanism 6a for the front wheels to the front wheels 10 is
generally equal to the reduction ratio of the output disk 41 of the
continuously variable speed-changing mechanism 6b for the rear
wheels to the rear wheels 14. Therefore, if the rotational speeds
of the output disks 41 of the continuously variable speed-changing
mechanism 6a for the front wheels and of the continuously variable
speed-changing mechanism 6b for the rear wheels are denoted by
Nf.sub.3 and Nr.sub.3, the ratio (Nf.sub.3/Nr.sub.3) becomes equal
to .alpha..
[0060] The input rotational speeds of the continuously variable
speed-changing mechanisms 6a and 6b for the front and rear wheels
are the rotational speed of the main shaft 5 and assume the same
value. If tilting angles .phi.f and .phi.r of the power rollers
42,42 of the continuously variable speed-changing mechanisms 6a and
6b are used for the equation (7), therefore, there hold the
following equations, 3 ef = Nf 3 / N 1 = ( 1 + k 0 - cos f ) / [ (
1 + k 0 - cos ( 2 0 - f ) ] er = Nr 3 / N 1 = ( 1 + k 0 - cos r ) /
[ ( 1 + k 0 - cos ( 2 0 - r ) ] ( 8 )
[0061] From the ratio of the above two, the following equation
holds, 4 ef / er = Nf 3 / Nr 3 = = { ( 1 + k 0 - cos f ) / [ ( 1 +
k 0 - cos ( 2 0 - f ) ] } / { ( 1 + k 0 - cos r ) / [ ( 1 + k 0 -
cos ( 2 0 - r ) ] } ( 9 )
[0062] The speed-changing ratio er of the equation (8) is a
function of the tilting angle .phi.r of the power rollers 42 in the
continuously variable speed-changing mechanism 6b for the rear
wheels. The tilting angle .phi.f is obtained by substituting the
value of the tire diameter ratio .alpha. and the value of the
tilting angle .phi.r for the equation (9). It is also allowable to
store in advance the tilting angle .phi.f for each tilting angle
.phi.r in the form of a map (see FIG. 4). As will be obvious from
the foregoing description, the tilting angle .phi.f of the power
rollers 42 of the continuously variable speed-changing mechanism 6a
for the front wheels corresponds to the speed-changing ratio ef of
the continuously variable speed-changing mechanism 6a for the front
wheels, and the tilting angle .phi.r of the power rollers 42 of the
continuously variable speed-changing mechanism 6b for the rear
wheels corresponds to the speed-changing ratio er of the
continuously variable speed-changing mechanism 6b for the rear
wheels. In other words, the speed-changing ratio ef of the
continuously variable speed-changing mechanism 6a for the front
wheels can be replaced by the tilting angle .phi.f of the power
rollers 42 of the continuously variable speed-changing mechanism 6a
for the front wheels, and the speed-changing ratio er of the
continuously variable speed-changing mechanism 6b for the rear
wheels can be replaced by the tilting angle .phi.r of the power
rollers 42 of the continuously variable speed- changing mechanism
6b for the rear wheels. Further, the tilting angle .phi.r can be
replaced by the target tilting angle .phi.cr for the rear wheels,
and the tilting angle .phi.f can be replaced by the target tilting
angle .phi.cf for the front wheels.
[0063] When the vehicle is stably traveling straight at a constant
speed and the tires slip little, the controller 30 disconnects the
clutch 35 which is the driving power disconnection device, and
calculates the tire diameter ratio .alpha. in a state where the
vehicle travels in the two-wheel-drive state. The tire diameter
ratio .alpha. is calculated from a ratio of the average values of
the rotational speeds of the front wheel drive shafts 9,9 detected
by the front wheel rotational speed sensors 91,91 to the average
values of the rotational speeds of the rear wheel drive shafts
13,13 detected by the rear wheel rotational speed sensors 131,131.
Due to this calculation, the tire diameter ratio .alpha. can be
relatively easily and reliably obtained. It is also possible to
obtain the tire diameter ratio .alpha. from a difference in the
reaction forces obtained by measuring them in the hydraulic servo
circuits 21 and 22 of the continuously variable speed-changing
mechanisms 6a and 6b without providing the clutch 35. In this case,
the four-wheel-drive vehicle is constituted more simply, making it
possible to decrease the weight and the cost. The controller 30
further sets the target speed-changing operation conditions of the
vehicle detected by the detector means to be the target
speed-changing ratio ecr for the rear wheels in the continuously
variable speed-changing mechanism 6b for the rear wheels (this has
been specifically described already and is, hence, not repeated
here again). The rear wheels 14,14 are substantially rotatively
driven at the target speed-changing ratio (=target speed-changing
ratio for the rear wheels).
[0064] The controller 30 further sets the target speed-changing
ratio obtained based on the operation conditions of the vehicle
detected by the detector means to be the target speed-changing
ratio ecr for the rear wheels in the continuously variable
speed-changing mechanism 6b for the rear wheels, and sets the
speed-changing ratio obtained by correcting the target
speed-charging ratio on the basis of the tire diameter ratio
.alpha. to be the target speed-changing ratio ecf for the front
wheels. As described earlier in this embodiment, the controller 30
adds the amount .DELTA..phi. for correcting the tilting angle which
is the amount for correcting the speed-changing ratio obtained
based on the tire diameter ratio .alpha. to the target tilting
angle .phi.cr for the rear wheels, and sets the result to be the
target tilting angle .phi.cf for the front wheels, i.e., to be the
target speed-changing ratio ecf for the front wheels in the
continuously variable speed-changing device 6a for the front
wheels. The controller 30, then, connects the clutch 35 to change
the two-wheel-drive state over to the four-wheel-drive state. The
front wheels 10,10 are rotatively driven at substantially the
target speed-changing ratio ecf for the front wheels.
[0065] That is, when the tire diameter has changed between the
front wheels and the rear wheels, the target speed-changing ratio
ecf for the front wheels is corrected based on the tire diameter
ratio .alpha. on the basis of the target speed-changing ratio ecr
set to the continuously variable speed-changing mechanism 6b for
the rear wheels as a reference, so that the peripheral velocities
of the front wheels 10,10 are brought into agreement with the
peripheral velocities of the rear wheels 14,14. As a result, loss
of power ascribed to the difference in the peripheral velocity is
eliminated, and a smooth four-wheel-drive traveling is realized.
When the tire diameter (average value) of the front wheels 10 has
decreased, the speed-changing ratio for the front wheels 10 is
brought to the speed-increasing side to rotate the front wheels at
a higher speed thereby to eliminate a difference in the peripheral
velocity from the rear wheels 14, by utilizing the fact that the
speed-changing ratio can be controlled for the front wheels 10
only. Conversely, when the tire diameter (average value) of the
front wheels 10 has increased, the speed-changing ratio for the
front wheels 10 is brought to the speed-decreasing side by
utilizing the fact that the speed-changing ratio can be controlled
for the front wheels 10 only, to rotate the front wheels at a lower
speed thereby to eliminate a difference in the peripheral velocity
from the rear wheels 14. It needs not be pointed out that when the
tire diameter (average value) of the front wheels 10 has decreased,
the amount .DELTA..phi. for correcting the tilting angle added to
the target tilting angle .phi.cr for the rear wheels assumes a
positive value and when the tire diameter (average value) of the
front wheels 10 has increased, the amount .DELTA..phi. for
correcting the tilting angle added to the target tilting angle
.phi.cr for the rear wheels assumes a negative value. In the
above-mentioned embodiment, the controller 30 is so constituted as
to obtain the target speed-changing ratio for the front wheels by
adding the amount for correcting the speed-changing ratio
calculated based on the tire diameter ratio .alpha. to the target
speed-changing ratio. Upon executing a relatively simple control
operation, therefore, inconvenience such as loss of power caused by
a difference in the tire diameter between the front wheels and the
rear wheels is avoided, and a smooth four-wheel-drive traveling is
realized. Besides, since the correction for obtaining the target
speed-changing ratio for the front wheels is effected by adding the
amount for correcting the speed-changing ratio calculated based on
the tire diameter ratio to the target speed-changing ratio for the
rear wheels, the speed-changing ratio is simply operated by the
controller, the operation time is short, and the CPU and the memory
need bear a decreased amount of burden.
[0066] According to the device for changing the speeds of the front
and rear wheels in a four-wheel drive vehicle of the present
invention as will be obvious from the foregoing description, the
controller 30 calculates the tire diameter ratio .alpha. of the
front wheels 10 to the rear wheels 14 during the vehicle travels
straight, sets the target speed-changing ratio obtained based on
the operation conditions of the vehicles detected by the detector
means to be the target speed-changing ratio for the rear wheels in
the continuously variable speed-changing mechanism 6b for the rear
wheels, and sets the speed-changing ratio obtained by correcting
the target speed-changing ratio on the basis of the tire diameter
ratio .alpha. to be the target speed-changing ratio for the front
wheels in the continuously variable speed-changing mechanism 6a for
the front wheels. Consequently, inconvenience such as loss of power
caused by the difference in the tire diameter between the front
wheels and the rear wheels is avoided and a smooth four-wheel-drive
traveling is realized. Further, the controller 30 detects changes
in the tire diameters of the front and rear wheels during traveling
straight and, when a difference is detected in the tire diameter
between the front wheels and the rear wheels, the controller 30
separately controls the speed-changing ratios for the front and
rear wheels in response to the difference so that the front and
rear wheels will have an equal peripheral velocity, to thereby
avoid inconvenience such as loss of power and realize a smooth
four-wheel-drive traveling. Upon executing a relatively simple
control operation, further, inconvenience such as loss of power
caused by a difference in the tire diameter between the front
wheels and the rear wheels is avoided, and a smooth
four-wheel-drive traveling is realized.
[0067] In the above-mentioned embodiment, the target speed-changing
ratio is set to be the target speed-changing ratio for the rear
wheels in the continuously variable speed-changing mechanism 6b for
the rear wheels, and the speed-changing ratio obtained by
correcting the target speed-changing ratio based on the tire
diameter ratio .alpha. is set to be the target speed-changing ratio
for the front wheels in the continuously variable speed-changing
mechanism 6a for the front wheels. However, there also holds
another embodiment in which the target speed-changing ratio is set
to be the target speed-changing ratio for the front wheels in the
continuously variable speed-changing mechanism 6a for the front
wheels, and the speed-changing ratio obtained by correcting the
target speed-changing ratio based on the tire diameter ratio
.alpha. is set to be the target speed-changing ratio for the rear
wheels in the continuously variable speed-changing mechanism 6b for
the rear wheels. This embodiment, too, makes it possible to obtain
the actions and effects substantially the same as those in the
earlier-mentioned embodiment.
[0068] According to the present invention, the controller 30 is
capable of setting a speed-changing ratio obtained by correcting
the target speed-changing ratio according to the predetermined
equation using the target speed changing ratio and the tire
diameter ratio .alpha. as variables, to be the target
speed-changing ratio for the front wheels or the target
speed-changing ratio for the rear wheels. Specifically, the above
equation (9) is stored in the controller 30, and the speed-changing
ratio to be set as the target speed-changing ratio for the front
wheels or as the target speed-changing ratio for the rear wheels is
calculated from the target speed-changing ratio and the tire
diameter ratio .alpha. in accordance with the equation (9).
Therefore, the above-mentioned control operation is easily and
correctly executed.
[0069] According to the present invention, further, the controller
30 obtains the target speed-changing ratio for the front wheels or
the target speed-changing ratio for the rear wheels by adding the
amount for correcting the speed-changing ratio calculated based on
the tire diameter ratio .alpha. to the target speed-changing. The
actions and effects of this control operation are as described in
detail in the foregoing embodiment.
[0070] According to the present invention, further, the controller
30 can calculate the amount for correcting the speed-changing ratio
in accordance with the predetermined equation or the approximate
equation using the tire diameter ratio .alpha. as a variable. The
amount for correcting the speed-changing ratio that is the
difference between the target speed-changing ratio for the front
wheels and the target speed-changing ratio for the rear wheels, can
be easily operated from the above equation (9). Further, by using
the approximate equations, i.e.,
.phi.cf=.phi.cr+.DELTA..phi. (3)
[0071] and
.DELTA..phi.=4.degree..times.(.alpha.-1).times.10 (6)
[0072] .DELTA..phi. can be easily calculated and, hence, .phi.cf
can be very easily calculated. It needs not be pointed out that
.DELTA..phi. assumes either a positive value or a negative value
depending upon the value of the tire diameter ratio .DELTA.. It
also needs not be pointed out that the equation for obtaining
.phi.cr by adding .DELTA..phi. to .phi.cf which is a reference is
expressed by .phi.cr=.phi.cf+.DELTA..phi.- .
[0073] According to the present invention, further, the controller
30 can obtain the amount for correcting the speed-changing ratio
from a map prepared in advance based on the values calculated or
approximated by the predetermined equation or approximate equation
determined in advance by using the tire diameter ratio .alpha. as a
variable. The map is as explained with reference to FIG. 4, and
from the map, there can be very easily obtained the amount for
correcting the speed-changing ratio, corresponding to the tire
diameter ratio. The map is prepared in advance based on the
approximate values for correcting the speed-changing ratios
calculated from the approximate equation. The amounts for
correcting the speed-changing ratios obtained by the approximate
equation lie within a narrow range for the target speed-changing
ratios for the rear wheels based on the tire diameter ratios
.alpha. that are considered to take place and on the operation
conditions and can, hence, be approximated by using a simple
approximate function. The speeds for the front and rear wheels can
be favorably controlled also by correcting the target
speed-changing ratio for the rear wheels or the target
speed-changing ratio for the front wheels based on the amount for
correcting the speed-changing ratio obtained in accordance with the
approximate function, and by setting the thus obtained
speed-changing ratio to be the target speed-changing ratio for the
front wheels or to be the target speed-changing ratio for the rear
wheels. It is further allowable to form a map by making a graph by
correctly plotting the ratios of ef to er in accordance with the
equation (9) in FIG. 4.
[0074] According to the present invention, further, the controller
30 can obtain an approximate amount for correcting the
speed-changing ratio calculated according to a predetermined
approximate equation using the tire diameter ratio as a variable
from a map prepared in advance by using approximate values that
have been further corrected based on a deviation of the ratio of
the target speed-changing ratio for the front wheels to the target
speed-changing ratio for the rear wheels at the above tire diameter
ratio. This deviation is as described with reference to FIGS. 4 and
5. The difference in the peripheral velocity between the front
wheels and the rear wheels can be more reliably eliminated by
further correcting the amount for correcting the speed-changing
ratio calculated from the map or the approximate function, based on
the tire diameter ratio .alpha..
[0075] According to the present invention, further, the
continuously variable speed-changing mechanism 6a for the front
wheels and the continuously variable speed-changing mechanism 6b
for the rear wheels are, respectively, constituted by a toroidal
type continuously variable speed-changing device 6 comprising an
input disk 40 which receives the driving force, an output disk 41
that is arranged opposite to the input disk 40 and is drive-coupled
to the front wheel drive shafts 9,9 or to the rear wheel drive
shafts 13,13, and power rollers 42 arranged between the input disk
40 and the output disk 41 so as to rotate in a tilted manner and to
continuously change the rotational speed of the input disk 40 and
transmit it to the output disk 41 by changing the contact points to
the input disk 40 and to the output disk 41. The thus constituted
toroidal type continuously variable speed-changing device 6 can
transmit a large torque compared with the belt-type continuously
variable speed-changing device and is, further, capable of quickly
changing the speed, contributing to easily changing the speed by
the controller 30.
[0076] According to the present invention, further, the controller
30 sets the target tilting angle .phi.cf of the power rollers 42
for the front wheels in the continuously variable speed-changing
mechanism 6a for the front wheels and the target tilting angle
.phi.cr of the power rollers 42 for the rear wheels in the
continuously variable speed-changing mechanism 6b for the rear
wheels, correspondingly to the target speed-changing ratio for the
front wheels and to the target speed-changing ratio for the rear
wheels. The controller 30 then controls the continuously variable
speed-changing mechanism 6a for the front wheels and the
continuously variable speed-changing mechanism 6b for the rear
wheels, based on the target tilting angle .phi.cf for the front
wheels and on the target tilting angle .phi.cr for the rear wheels.
Upon executing a relatively simple control operation, therefore,
the controller 30 avoids the inconvenience such as loss of power
caused by a difference in the tire diameter between the front
wheels and the rear wheels, and realizes a smooth four-wheel-drive
traveling.
[0077] In the toroidal type continuously variable speed-changing
device 6, the power rollers 42 are rotatably supported by the
trunnions 43 which can be moved in the directions of tilted axes by
the actuators. The controller 30 controls the operation of the
actuators in the continuously variable speed-changing mechanism 6a
for the front wheels and in the continuously variable
speed-changing mechanism 6b for the rear wheels, based on a
deviation between the target speed-changing ratio for the front
wheels or the target speed-changing ratio for the rear wheels and
the true speed-changing ratio for the front wheels or the true
speed-changing ratio for the rear wheels calculated based on the
rotation of the output disk 41, thereby to control the tilting
angle of the power rollers 42 by feedback. This control operation
makes it possible to avoid inconvenience such as loss of power
caused by a difference in the tire diameter between the front
wheels and the rear wheels and to realize a smooth four-wheel-drive
traveling.
[0078] In response to the target speed-changing ratio for the front
wheels and the target speed-changing ratio for the rear wheels, the
controller 30 sets the target tilting angle .phi.cf of the power
rollers 42 for the front wheels in the continuously variable
speed-changing mechanism 6a for the front wheels or the target
tilting angle .phi.cr of the power rollers 42 for the rear wheels
in the continuously variable speed-changing mechanism 6b for the
rear wheels, respectively, and further controls the continuously
variable speed-changing mechanism 6a for the front wheels and the
continuously variable speed-changing mechanism 6b for the rear
wheels based on the target tilting angle .phi.cf for the front
wheels and the target tilting angle .phi.cr for the rear wheels.
When the tilting angle is to be controlled by feedback, the
operation of the actuator is controlled based on the deviation
between the target tilting angle and the actually detected tilting
angle so that the deviation is canceled. This control operation
makes it possible to avoid inconvenience such as loss of power
caused by a difference in the tire diameter between the front
wheels and the rear wheels and to realize a smooth four-wheel-drive
traveling.
[0079] The present invention can be preferably put into practice as
a device for changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle capable of variably driving the front
wheels and the rear wheels independently from each other by using
the toroidal type continuously variable speed-changing device. The
invention can be preferably put into practice also as a device for
changing the speeds of the front and rear wheels in a
four-wheel-drive vehicle capable of variably driving the front
wheels and the rear wheels independently from each other by using
the belt-type continuously variable speed-changing device. In the
above-mentioned embodiment, the clutch 35 which is the driving
force disconnection device is provided for the front wheel drive
shafts 9. However, the clutch 35 may be provided for the rear wheel
drive shafts 13, instead.
* * * * *