U.S. patent application number 09/793287 was filed with the patent office on 2001-10-25 for hydraulic power steering apparatus for vehicle.
Invention is credited to Ishiwata, Masaru, Serizawa, Akihiko.
Application Number | 20010032750 09/793287 |
Document ID | / |
Family ID | 18634863 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032750 |
Kind Code |
A1 |
Serizawa, Akihiko ; et
al. |
October 25, 2001 |
Hydraulic power steering apparatus for vehicle
Abstract
A hydraulic power steering apparatus for a vehicle is provided
with a main control valve in which a valve opening degree is
controlled on the basis of a relative movement between an input
shaft interlocking with a steering wheel and an output shaft
interlocking with a steering mechanism for turning a steered wheel,
a power cylinder mechanism generating a steering assist force, a
pump apparatus discharging a fixed flow amount of working oil, a
first flow passage including a supply passage communicated with the
main control valve, and a control unit controlling an assist
control valve. The main control valve controls a supply amount of
the working oil in the first flow passage to the power steering
apparatus, and the assist control valve controlling a flow amount
of a part of the working oil discharged from the pump apparatus 1
is controlled to a set valve opening degree set on the basis of a
vehicle speed and an oil pressure of the working oil in the first
flow passage, by the control unit.
Inventors: |
Serizawa, Akihiko; (Tochigi,
JP) ; Ishiwata, Masaru; (Tochigi, JP) |
Correspondence
Address: |
ORUM & ROTH
53 West Jackson Boulevard
Chicago
IL
60604-3606
US
|
Family ID: |
18634863 |
Appl. No.: |
09/793287 |
Filed: |
February 26, 2001 |
Current U.S.
Class: |
180/423 ;
180/417 |
Current CPC
Class: |
B62D 5/062 20130101;
Y10T 137/86654 20150401; B62D 5/0837 20130101; B62D 5/083
20130101 |
Class at
Publication: |
180/423 ;
180/417 |
International
Class: |
B62D 005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2000 |
JP |
2000-124784 |
Claims
What is claimed is:
1. A hydraulic power steering apparatus for a vehicle comprising:
an input member interlocking with a steering wheel; an output
member connected to said input member so as to freely move
relatively; a steering mechanism steering a steered wheel in an
interlocking relationship with said output member; a main control
valve having a first valve portion and a second valve portion in
which a valve opening degree is controlled on the basis of a
relative movement between said input member and said output member;
a power cylinder mechanism generating a steering assist force
applied to said steering mechanism in correspondence to a fluid
pressure in a working chamber in which a working fluid is supplied
and discharged; a first flow passage communicating a pump apparatus
for discharging a fixed flow amount of working fluid with said main
control valve; a second flow passage branched from said first flow
passage and communicated with a low pressure portion via an assist
control valve and said main control valve; a control unit
controlling said assist control valve; said first valve portion
controlling a supply amount of the working fluid in said first flow
passage to said working chamber; and said second valve portion
controlling a discharge amount of the working fluid in said second
flow passage to said low pressure portion in accordance with
cooperation with said assist control valve, wherein a vehicle speed
sensor for detecting a vehicle speed and a pressure sensor for
detecting a fluid pressure of the working fluid in said first flow
passage are provided, and said control unit controls a valve
opening degree of said assist control valve to a set valve opening
degree set on the basis of the vehicle speed detected by said
vehicle speed sensor and the fluid pressure detected by said
pressure sensor.
2. A hydraulic power steering apparatus for a vehicle as claimed in
claim 1, wherein said control unit is arranged and constructed to
set the valve opening degree of said assist control valve to a
fully closed side at a time of a vehicle speed equal to or less
than a predetermined low vehicle speed including a vehicle stop
time, and is arranged and constructed to set the valve opening
degree so as to be increased in accordance with an increase of the
vehicle speed from the predetermined low vehicle speed, in
connection with the vehicle speed detected by the vehicle speed
sensor, and is arranged and constructed to set the valve opening
degree so that the fluid pressure by which the steering assist
force having an optimum magnitude is generated is generated in the
power cylinder mechanism, with respect to the steering torque
generated at a time when the driver operates the steering wheel at
a certain vehicle speed, in connection with the fluid pressure
detected by the pressure sensor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a hydraulic power steering
apparatus for a vehicle, and more particularly to a pressure and
vehicle speed sensitive type hydraulic power steering apparatus
which controls steering assist force in response to an external
load (a road reaction force) correlated with fluid pressure of
working fluid supplied to a power cylinder mechanism and vehicle
speed.
[0003] 2. Description of the Related Art
[0004] Relating to a hydraulic power steering apparatus of this
kind, for example, there has been known a power steering apparatus
disclosed in Japanese Patent Application Publication (JP-B) No.
6-79895. The power steering apparatus is provided with a pump for
pressure feeding an oil, a hydraulic motor connected to a tire
wheel via a linkage and having a piston and a cylinder, and a
rotary valve apparatus for controlling flow of the oil to the
hydraulic motor. An output passage of the pump is communicated with
an inlet side of a vehicle speed sensing valve, and an outlet side
of the speed sensing valve is communicated with a low speed oil
inlet passage and a high speed oil inlet passage. Further, the
rotary valve apparatus has an internal valve member integrally
formed with a steering shaft and a valve sleeve rotatably receiving
the internal valve member and integrally rotating with a pinion.
The steering shaft and the pinion are connected to each other via a
torsion rod displacing in a torsional manner, and first and second
valve apparatuses are constituted by the internal valve member and
the valve sleeve. In this case, the first valve apparatus increases
the magnitude of pressure distributed to the hydraulic motor in
correspondence to an increase of the torsional displacement, and
the second valve apparatus controls a returning amount of the oil
to a suction side of the pump in correspondence to the torsional
displacement. Then, the speed sensing valve distributes the oil
only to the first valve apparatus when the vehicle is at a low
speed, and distributes the oil to both of the first and second
valve apparatuses when the vehicle is at a high speed, whereby it
is possible to obtain a proper assist force in correspondence to
the speed of the vehicle and the torsional displacement.
[0005] Since there is no returning amount of the oil during low
speed operation, the assist force is increased and operation of a
steering handle becomes light. Since a predetermined amount of oil
is returned to the suction side of the pump via the second valve
apparatus during high speed operation, an amount of oil distributed
to the hydraulic motor is reduced by the degree of the returning
amount, the assist force is reduced, and the operation of the
steering handle becomes heavy.
[0006] In this case, although the assist force (the steering assist
force) with respect to the displacement is different, a
characteristic of the assist force with respect to the torsional
displacement is definitely determined in accordance with a
geometrical shape of measuring edges of the first and second valve
apparatuses, at every vehicle speed. However, since the
characteristic of the assist force obtained by the same geometrical
shape is not always optimum in all the vehicle speeds, it is
desirable to increase freedom for setting the assist force in
correspondence to the change of the vehicle speed in such a manner
that the assist force can be set with every change of the torsional
displacement at every vehicle speed.
SUMMARY OF THE INVENTION
[0007] The present invention relates to the matter mentioned above.
An object of the present invention is to provide a hydraulic power
steering apparatus for a vehicle which recognizes an external load,
that is, a road reaction force by a fluid pressure of a working
fluid supplied to a power cylinder mechanism, whereby freedom for
setting a steering assist force in correspondence to vehicle speed
is great.
[0008] In accordance with the present invention, there is provided
a hydraulic power steering apparatus for a vehicle comprising,
[0009] an input member interlocking with a steering wheel, and
[0010] an output member connected to the input member so as to
freely move relatively.
[0011] A steering mechanism steering a steered wheel is in an
interlocking relationship with the output member.
[0012] A main control valve has a first valve portion and a second
valve portion in which a valve opening degree is controlled on the
basis of relative movement between the input member and the output
member.
[0013] A power cylinder mechanism generating a steering assist
force applied to the steering mechanism is in correspondence to a
fluid pressure in a working chamber in which a working fluid is
supplied and discharged.
[0014] A first flow passage communicates a pump apparatus for
discharging a fixed flow amount of working fluid with the main
control valve.
[0015] A second flow passage is branched from the first flow
passage and communicates with a low pressure portion via an assist
control valve and the main control valve.
[0016] A control unit controls the assist control valve.
[0017] The first valve portion controls a supply amount of the
working fluid in the first flow passage to the working chamber,
and
[0018] the second valve portion controls a discharge amount of the
working fluid in the second flow passage to the low pressure
portion in accordance with cooperation with the assist control
valve.
[0019] A vehicle speed sensor for detecting a vehicle speed and a
pressure sensor for detecting a fluid pressure of the working fluid
in the first flow passage are provided. The control unit controls a
valve opening degree of the assist control valve to a set valve
opening degree set on the basis of the vehicle speed detected by
the vehicle speed sensor and the fluid pressure detected by the
pressure sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be more fully understood from the
detailed description given below and from the accompanying drawings
which should not be taken to be a limitation on the invention, but
are for explanation and understanding only.
[0021] The drawings
[0022] FIG. 1 is an idiomatic diagram mainly showing an oil passage
of a hydraulic power steering apparatus for a vehicle corresponding
to an embodiment in accordance with the present invention;
[0023] FIG. 2 is a partly cross sectional view of a whole of a gear
box;
[0024] FIG. 3 is a cross sectional view of a main control valve and
an assist control valve;
[0025] FIG. 4 is a cross sectional view on a plane vertically
crossing in an axial direction of the main control valve, which
explains a valve structure of the main control valve;
[0026] FIG. 5 is a partly enlarged view of FIG. 4;
[0027] FIG. 6 is a graph showing a relation between a steering
torque and an opening area of a throttle portion;
[0028] FIG. 7 is a graph showing a relation between a steering
torque and oil pressure in an oil chamber of a power cylinder
mechanism;
[0029] FIG. 8 is a graph showing a relation between a steering
torque and a steering force; and
[0030] FIG. 9 is a valve opening degree map for setting a set valve
opening degree of an assist control valve with respect to an oil
pressure detected by a pressure sensor, in a specific vehicle
speed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] A description will be given below of an embodiment in
accordance with the present invention with reference to FIGS. 1 to
9.
[0032] FIG. 1 is an idiomatic diagram mainly showing an oil passage
of a hydraulic power steering apparatus for a vehicle corresponding
to an embodiment in accordance with the present invention. The
power steering apparatus is provided with a pump apparatus 1 driven
by an internal combustion engine mounted on a vehicle, a reservoir
2, a gear box 3 (refer to FIG. 2), an electronic control unit 4, a
vehicle speed sensor 5, an engine rotational speed sensor 6 and a
pressure sensor 7.
[0033] The pump apparatus 1 supplying a working oil corresponding
to a working fluid to the gear box 3 is provided with a vane-type
hydraulic pump 8, a flow amount control valve 9, a fixed orifice 10
and a relief valve 11. The hydraulic pump 8 driven by a crank shaft
of the internal combustion engine sucks the working oil stored in
the reservoir 2 via a suction passage 12 and discharges the working
oil which has developed a high pressure to a discharge passage 13.
The discharge passage 13 is communicated with a supply passage 14
for supplying the working oil to a main control valve 29 mentioned
below provided in the gear box 3 via the fixed orifice 10, and is
communicated with the suction passage 12 via a return passage 15 in
which the flow amount control valve 9 is provided. Then, the flow
amount control valve 9 moving in response to a differential
pressure between the discharge passage 13 and the supply passage 14
adjusts a flow amount returning to the suction passage 12 via the
return passage 15 in cooperation with the fixed orifice 10. A flow
amount of the working oil discharging to the supply passage 14
becomes fixed in a rotational number range equal to or more than a
predetermined rotational number of the hydraulic pump 8
corresponding to an idling rotational number of the internal
combustion engine. Further, the supply passage 14 and the suction
passage 12 are communicated with each other via the relief valve
11, and the relief valve 11 is opened when the oil pressure in the
supply passage 14 becomes a value over a set allowable maximum
value so as to keep the oil pressure in the supply passage 14 in a
level equal to or less than the allowable maximum value.
[0034] The reservoir 2 is communicated with the main control valve
29 of the gear box 3 via a circulating passage 16 so as to
temporarily store the working oil discharged from the main control
valve 29. The stored working oil is supplied to the hydraulic pump
8 via the suction passage 12.
[0035] The gear box 3 is, as illustrated in FIG. 2, provided with a
cylindrical housing 18 for receiving a rack shaft 17 in such a
manner as to freely move in an axial direction thereof (also
corresponding to a lateral direction in this embodiment), and a
valve housing 19 connected to one end portion of the housing 18.
One end portion of each of a pair of tie rods 20 and 20 is
connected to each of both end portions of the rack shaft 17 via a
pair of ball joints, and another end portion of each of the tie
rods 20 and 20 is connected to the steered wheel via a connecting
mechanism (not shown). In this case, the rack shaft 17, the tie
rods 20 and 20 and the connecting mechanism constitute a steering
mechanism.
[0036] A power cylinder mechanism 21 setting a part of the housing
18 to a power cylinder 21 is provided in a middle portion of the
housing 18. The power cylinder mechanism 21 is provided with the
power cylinder 21, a power piston 23 adhered to the rack shaft 17
so as to be fitted within the power cylinder 21 in such a manner as
to freely swing in the axial direction, and a left oil chamber 24
and a right oil chamber 25 corresponding to a pair of working
chambers respectively formed in both side portions of the power
piston 23.
[0037] An input shaft 26 corresponding to an input member connected
to a steering wheel (not shown) in an interlocking manner, and an
output shaft 28 connected to the input shaft 26 via a torsion bar
27 are rotatably received in the valve housing 19, respectively, as
shown in FIG. 3. Accordingly, the input shaft 26 and the output
shaft 28 are structured such as to be capable of relatively moving
in a rotational direction within a torsional range of the torsion
bar 27. A pinion 28a engaged with rack teeth formed in the rack
shaft 17 is formed in a lower end portion of the output shaft 28
within the housing 18.
[0038] Further, a main control valve 29 constituted by a rotary
valve for controlling supply and discharge of the working oil with
respect to the left oil chamber 24 and the right oil chamber 25 is
disposed in the valve housing 19. An oil supply port (not shown)
communicated with the supply passage 14 and an oil discharge port
31 communicated with the circulating passage 16 which are
communicated with the main control valve 29, are respectively
provided.
[0039] An assist control valve 32 constituted by a linear solenoid
valve is mounted to a side surface of the valve housing 19. The
assist control valve 32 is provided with a valve body 33 fastened
to the valve housing 19 by a bolt, a spool 34 swingably fitted
within the valve body 33, a return spring 35, and a solenoid 36
driving the spool 34 in an axial direction against the return
spring 35. An oil passage 37 communicated with the oil supply port
is formed in the valve body 33. The oil passage 37 is communicated
with a connecting port 38 of the valve housing 19 in the main
control valve 29, and an oil passage 39 branched from the oil
passage 37 is open to a position communicated with and shut from a
ring-like control groove 40 provided on an outer peripheral surface
of the spool 34. An oil passage 41 is provided having one end
always communicated with the control groove 40 and another end
communicated with the connecting port 42 of the valve housing 19.
The oil passage 39 and the control groove 40 are in a
non-communicative state when the vehicle speed is equal to or less
than a predetermined low vehicle speed, and are in a communication
state when the spool 34 is moved by the solenoid 36 and the vehicle
speed becomes greater than the predetermined low vehicle speed. The
result of this structure is that a communication area between both
elements is increased in correspondence to an increase of the
vehicle speed. In this case, a space in which the return spring 35
is received is communicated with a center hole 50 mentioned below
via an oil passage 43 provided in the spool 34 and the valve body
33. In this case, each of axes of the main control valve 29 and the
assist control valve 32 is in a torsional positional relation as
illustrated in FIG. 2, and a cross section in FIG. 3 shows a cross
section passing through each of the axes.
[0040] The main control valve 29 is provided with a rotary valve
body 44 integrally formed with the input shaft 26, and a sleeve 45
within which the rotary valve body 44 is fitted in such a manner as
to freely swing in a rotational direction. The sleeve 45 is
connected to the output shaft 28 so as to integrally rotate
therewith, and is fitted within the valve housing 19 in such a
manner as to freely swing in the rotational direction. Accordingly,
the rotational valve body 44 constitutes an input side valve
element interlocking with the input shaft 26, and the sleeve 45
constitutes an output side valve element interlocking with the
output shaft 28.
[0041] Referring to FIG. 4 in combination, four inflow grooves 46a,
46a, 46b and 46b and four return grooves 47, 47, 47 and 47 which
extend in an axial direction are alternately provided on an outer
peripheral surface of the rotary valve body 44 at a uniform
interval in a peripheral direction. Two first lands 48a and 48b and
two second lands 49a and 49b which are positioned between the
adjacent return grooves 47 and 47 are alternately provided in a
peripheral direction. The first lands 48a, 48a, 48b and 48b are
constituted by a pair of left first lands 48a and 48a opposing each
other in a diametrical direction and a pair of right first lands
48b and 48b opposing each other in a diametrical direction. The
second lands 49a, 49a, 49b and 49b are constituted by a pair of
left second lands 49a and 49a opposing each other in a diametrical
direction and a pair of right second lands 49b and 49b opposing
each other in a diametrical direction. The inflow grooves 46a, 46a,
46b and 46b are constituted by two first inflow grooves 46a and 46a
and two second inflow grooves 46b and 46b. Each of the first inflow
grooves 46a and 46a is positioned between the left and right first
lands 48a and 48b, and each of the second inflow grooves 46b and
46b is positioned between the left and right second lands 49a and
49b. Each of the return grooves 47, 47, 47 and 47 is communicated
with a center hole 50 provided along the rotary axis of the rotary
valve body 44 via oil passages 51, 51, 51 and 51. The center hole
50 is communicated with the oil discharge port 31 via an oil
passage 52 provided in the valve housing 19.
[0042] Two first inflow passages 53 and 53 communicated with the
supply passage 14 via the connecting port 38 and the oil passage 37
and two second inflow passages 54 and 54 communicated with the
connecting port 42 and the oil passage 41 are respectively provided
at positions opposing to both of the first inflow grooves 46a and
46a and positions opposing to both of the second inflow grooves 46b
and 46b Relative positions of the rotary valve body 44 and the
sleeve 45 are in a state that no relative movement exists between
the input shaft 26 and the output shaft 28, that is, a neutral
position of the main control valve 29, on an inner peripheral
surface of the sleeve 45. In the neutral position, a pair of left
first control grooves 55a and 55a and a pair of right first control
grooves 55b and 55b are respectively provided in such a manner as
to oppose a pair of left first lands 48a and 48a, and to oppose a
pair of right first lands 48b and 48b. A pair of left second
control grooves 56a and 56a and a pair of right second control
grooves 56b and 56b are respectively provided in such a manner as
to oppose a pair of left second lands 49a and 49a, and to oppose a
pair of right second lands 49b and 49b.
[0043] Each of the left first control grooves 55a and 55a is
communicated with a left supply and discharge port 60 provided in
the valve body 33 via left first supply and discharge passages 57a
and 57a in the sleeve 45. A connecting port 58 in the valve housing
19 and an oil passage 59 in the valve body 33, and the left supply
and discharge port 60 is communicated with the left oil chamber 24
via a left oil passage 61. In the same manner, each of the right
first control grooves 55b and 55b is communicated with a right
supply and discharge port 64 provided in the valve body 33 via
right first supply and discharge passages 57b and 57b in the sleeve
45. A connecting port 62 in the valve housing 19 and an oil passage
63 in the valve body 33, and the right supply and discharge port 64
is communicated with the right oil chamber 25 via a right oil
passage 65.
[0044] The supply passage 14, the oil supply port, the oil passage
37, the connecting port 38 and the first inflow passages 53 and 53
constitute a first flow passage, and the oil passage 39, the oil
passage 41, the connecting port 42, the second inflow passages 54
and 54, the oil passage 51, the center hole 50, the oil passage 52,
the oil discharge port 31 and the circulating passage 16 constitute
a second flow passage. Then, the reservoir 2 to which the working
oil is returned via the circulating passage 16 constitutes a low
pressure portion.
[0045] As is well illustrated in FIG. 5, both corner portions in a
peripheral direction of each of the first lands 48a, 48a, 48b and
48b respectively have two beveled first control portions 66a and
66b. Two left and right first throttle portions 68a and 68b are
respectively formed in accordance with cooperation of both of the
first control portions 66a and 66b and both edges 67a and 67b in
the peripheral direction of each of the first control grooves 55a,
55a, 55b and 55b. Accordingly, a first valve portion is constituted
by the first lands 48a, 48a, 48b and 48b and the first control
grooves 55a, 55a, 55b and 55b. A magnitude of an opening area of
the first throttle portions 68a and 68b is determined in accordance
with a valve opening degree of the first valve body.
[0046] As shown in FIG. 6, each of the first control portions 66a
and 66b is formed so as to have such a geometrical shape that when
the rotary valve body 44 rotates leftward from the neutral
position, the opening area of each of the left first throttle
portions 68a becomes small in correspondence to an increase of a
leftward rotational displacement and becomes zero at a
predetermined rotational position. The opening area of each of the
right first throttle portions 68b becomes large in correspondence
to an increase of a leftward rotational displacement. When the
rotary valve body 44 rotates rightward from the neutral position,
the opening area of each of the right first throttle portions 68b
becomes small in correspondence to an increase of a rightward
rotational displacement and becomes zero at a predetermined
rotational position. The opening area of each of the left first
throttle portions 68a becomes large in correspondence to an
increase of a rightward rotational displacement.
[0047] Further, both corner portions in the peripheral direction of
each of the second lands 49a, 49a, 49b and 49b respectively have
two second control portions 69a and 69b formed in a beveling manner
and extending in the peripheral direction longer than the first
control portions 66a and 66b. Two left and right second throttle
portions 71a and 71b are respectively formed in accordance with
cooperation of both of the second control portions 69a and 69b and
both edges 70a and 70b in the peripheral direction of each of the
second control grooves 56a, 56a, 56b and 56b. A second valve
portion is constituted by the second lands 49a, 49a, 49b and 49b
and the second control grooves 56a, 56a, 56b and 56b, and a
magnitude of an opening area of the second throttle portions 71a
and 71b is determined in accordance with a valve opening degree of
the second valve body.
[0048] As shown in FIG. 6, each of the second control portions 69a
and 69b is formed so as to have such a geometrical shape that when
the rotary valve body 44 rotates leftward from the neutral
position, the opening area of each of the left second throttle
portions 71a becomes small in correspondence to an increase of a
leftward rotational displacement and becomes zero at a
predetermined rotational position. The opening area of each of the
rightward second throttle portions 71b becomes large in
correspondence to an increase of a leftward rotational
displacement. When the rotary valve body 44 rotates rightward from
the neutral position, the opening area of each of the right second
throttle portions 71b becomes small in correspondence to an
increase of a rightward rotational displacement and becomes zero at
a predetermined rotational position. The opening area of each of
the left second throttle portions 71a becomes large in
correspondence to an increase of a rightward rotational
displacement.
[0049] With respect to the working oil supplied to the first inflow
grooves 46a and 46a from the supply passage 14 via the oil passage
37 by the main control valve 29, a flow amount flowing into the
return grooves 47, 47, 47 and 47 is controlled by each of the first
throttle portions 68a and 68b in the first valve portion, so that a
supply amount of the working oil to the left oil chamber 24 and the
right oil chamber 25 in the power cylinder mechanism 21 is
controlled. With respect to the working oil supplied to the second
inflow grooves 46b and 46b from the oil passage 39 via the oil
passage 41 by the assist control valve 32, a flow amount flowing
into the return grooves 47, 47, 47 and 47 is controlled by the
valve opening degree of the assist control valve 32 and each of the
second throttle portions 71a and 71b in the second valve body, so
that a discharge amount of the working oil to the reservoir 2 is
controlled.
[0050] A vehicle speed signal output from the vehicle speed sensor
5 for detecting a speed of the vehicle, an engine rotational number
signal output from the engine rotational speed sensor 6 for
detecting the rotational number of the internal combustion engine,
and an oil pressure signal output from the pressure sensor 7
provided in the supply passage 14 and detecting an oil pressure
corresponding to a fluid pressure of the working oil in the supply
passage 14 are input to the electronic control unit 4 for
controlling an operation of the assist control valve 32. Since the
oil pressure in the supply passage 14 indicates a value dependent
on the valve opening degrees of the first and second valve portions
in the main control valve 29 in correspondence to the steering
torque, an external load, that is, a road reaction force is
reflected together with the steering torque.
[0051] The electronic control unit 4 has serial processing means
executing processes until outputting a drive signal to the solenoid
36 on the basis of the input signal from each of the sensors. Among
these processing means are means for searching a valve opening
degree map in which a set valve opening degree of the assist
control valve 32 is set by using the vehicle speed and the oil
pressure as parameters. The basis of the input vehicle speed signal
and oil pressure signal constitutes valve opening degree setting
means, and means for outputting a drive signal corresponding to the
calculated set valve opening degree, for example, a current having
a predetermined duty ratio controlled in a duty manner to the
solenoid 36 constitutes valve drive controlling means.
[0052] The solenoid 36 continuously moves the spool 34 in an axial
direction so as to form a straight line in correspondence to the
supplied drive signal, whereby the spool 34 controls the oil
passage 39 and the control groove 40 in a communicated state and a
shut state. In this case, the engine rotational number corresponds
to a control allowing signal which confirms whether or not the
internal combustion engine is in an operated state so as to allow
the control of the assist control valve 32 or not. When the
internal combustion engine is stopped, the assist control valve 32
is in a non-operating state, and the spool 34 is arranged at a
position where the oil passage 39 and the control groove 40 are
communicated with each other, due to spring force of the return
spring 35.
[0053] In the valve opening degree map, in relation to the vehicle
speed detected by the vehicle speed sensor 5, the set valve opening
degree is set to zero at a time of a vehicle speed equal to or less
than the predetermined low vehicle speed including a vehicle stop
time. At this time, the solenoid 36 moves the spool 34 against the
return spring 35 so as to shut the communication between the oil
passage 39 and the control groove 40, and the set valve opening
degree is set so that the communicating area between the oil
passage 39 and the control groove 40 is increased in accordance
that the vehicle speed is increased over the predetermined low
vehicle speed. In relation to the oil pressure detected by the
pressure sensor 7, the set valve opening degree is set so that the
oil pressure for generating the steering assist force having an
optimum magnitude is generated in the left oil chamber 24 or the
right oil chamber 25 of the power cylinder mechanism 21, with
respect to the steering torque generated at a time when the driver
operates the steering wheel.
[0054] In this embodiment, as an embodiment of the valve opening
degree map, as shown in FIG. 9, at a low vehicle speed S.sub.L
equal to or less than the predetermined low vehicle speed, the set
valve opening degree of the assist control valve 32 is zero, that
is, fully closed without relation to the oil pressure detected by
the pressure sensor 7. As an embodiment of the vehicle speed in the
vehicle speed range where the vehicle speed becomes larger than the
predetermined low vehicle speed and the assist control valve 32 is
in an open valve state, at a high vehicle speed S.sub.H, when the
oil pressure generated due to the steering torque is equal to or
more than a first predetermined value P.sub.1, the set valve
opening degree of the assist control valve 32 is gradually
increased from a predetermined value A.sub.1 so as to become a
second predetermined value A.sub.2 when the oil pressure is equal
to or more than a second predetermined value P.sub.2.
[0055] Next, a description will be given of an operation and an
effect of the embodiment structure in the manner mentioned
above.
[0056] When the internal combustion engine is operated and a fixed
flow amount of working oil is discharged to the supply passage 14
in an upstream side of the branch portion of the oil passage 39
from the pump apparatus 1, the engine rotational number signal is
input to the electronic control unit 4, and the assist control
valve 32 is in a state capable of being controlled. The electronic
control unit 4 controls the assist control valve 32 to the set
valve opening degree set in accordance with the valve opening
degree map on the basis of the vehicle speed detected by the
vehicle speed sensor 5 and the oil pressure detected by the
pressure sensor 7.
[0057] Further, when the vehicle speed is the low vehicle speed
S.sub.L, the set valve opening degree of the assist control valve
32 is set to zero without relation to the magnitude of the oil
pressure obtained by reflecting the external load (the road
reaction force), as shown in FIG. 9. In this state, the oil passage
39 and the control groove 40 are shut, all amount of the working
oil in the supply passage 14 flows into a pair of first inflow
grooves 46a and 46a from a pair of first inflow passages 53 and 53,
and the working oil is not supplied from the second inflow passages
54 and 54.
[0058] When the steering wheel is not operated, the main control
valve 29 is at a neutral position, and the working oil flowing into
the first inflow grooves 46a and 46a is returned to the return
grooves 47, 47, 47 and 47, the oil passages 51, 51, 51 and 51 and
the center hole 50 via the throttle portions 68a and 68b of the
first valve portion and further to the reservoir 2 through the
circulating passage 16. Since both of the left oil chamber 24 and
the right oil chamber 25 are in a low oil pressure state and the
differential pressure applied to the power piston 23 hardly exists,
the steering assist force is not generated.
[0059] When the steering wheel is leftward rotated (rightward
rotated) (hereinafter, descriptions in parentheses show motions
when the steering wheel is rightward rotated), the pinion 28a is
engaged with the rack teeth, the rack shaft 17 is rightward rotated
(leftward rotated), and the tie rods 20 and 20 are rightward
rotated (leftward rotated) integrally together with the rack shaft
17, whereby the left and right tire wheels are turned. In the main
control valve 29, the working oil flowing from the supply passage
14 via the first inflow passages 53 and 53, the first inflow
grooves 46a and 46a, the left first control grooves 55a and 55a
(the right first control grooves 55b and 55b) and the left first
supply and discharge passages 57a and 57a (the right first supply
and discharge passages 57b and 57b) is supplied to the left oil
chamber 24 (the right oil chamber 25) via the left oil passage 61
(the right oil passage 65). The amount of the working oil supplied
to the left oil chamber 24 (the right oil chamber 25) at this time
is determined by the amount of the working oil which is controlled
by the first throttle portions 68a and 68a (the first throttle
portions 68b and 68b) of the first valve portion so as to flow into
the return grooves 47, 47, 47 and 47.
[0060] At the same time, the working oil supplied from the right
oil chamber 25 (the left oil chamber 24) passes through the right
oil passage 65 (the left oil passage 61) and returns to the
reservoir 2 via the right first supply and discharge passages 57b
and 57b (the left first supply and discharge passages 57a and 57a)
of the main control valve 29, the right first control grooves 55b
and 55b (the left first control grooves 55a and 55a), the return
grooves 47 and 47 and the center hole 50 and further through the
circulating passage 16.
[0061] As a result, as shown in FIG. 7, the oil pressure in
correspondence to the steering torque is generated in the left oil
chamber 24 or the right oil chamber 25 in the power cylinder
mechanism 21, and the steering assist force generated on the basis
of the differential pressure of both of the oil chambers 24 and 25
is added to the steering mechanism.
[0062] When the vehicle speed is increased, for example, to the
high vehicle speed S.sub.H mentioned above, the assist control
valve 32 is set to the set valve opening degree having a
predetermined value A.sub.1 when the oil pressure in correspondence
to the steering torque is equal to or less than a first
predetermined value P.sub.1. In this state, a part of the working
oil discharged from the pump apparatus 1 flows into the main
control valve 29 from the oil passage 39 via the assist control
valve 32, and the remaining working oil flows into the main control
valve 29 via the oil passage 37 and the connecting port 38.
[0063] The working oil supplied from the second inflow passages 54
and 54 is returned to the reservoir 2 via the throttle portions 71a
and 71b of the second valve portion after passing through the
return grooves 47, 47, 47 and 47, the oil passages 51, 51, 51 and
51 and the center hole 50 and further the circulating passage 16.
The amount of the circulating working oil is determined in
accordance with the amount of the working oil which is controlled
by the second throttle portions 71a, 71a, 71b and 71b of the second
valve portion so as to flow into the return grooves 47, 47, 47 and
47 when the steering wheel is not operated, and is determined in
accordance with the amount of the working oil which is controlled
by the second throttle portions 71a and 71b (the second throttle
portions 71b and 71b) of the second valve portion so as to flow
into the return grooves 47, 47, 47 and 47 when the steering wheel
is leftward rotated (rightward rotated).
[0064] On the contrary, the working oil flowing into the first
inflow grooves 46a and 46a from the connecting port 38 via the
first inflow passages 53 and 53 is controlled by the first throttle
portions 68a and 68b in correspondence to the steering torque so as
to be supplied to the left oil chamber 24 or the right oil chamber
25 of the power cylinder mechanism 21. At this time, since the
amount of the working oil flowing into the first inflow passages 53
and 53 is set to be smaller than that when the assist control valve
32 is closed, in the same manner as that at the low vehicle speed
S.sub.L mentioned above, the oil pressure in which the oil pressure
in correspondence to the steering torque is generated in the left
oil chamber 24 or the right oil chamber 25 of the power cylinder
mechanism 21 due to the working oil having the amount of the
working oil controlled by the first and second valve portions and
supplied to the left oil chamber 24 or the right oil chamber 25,
has a small value in the same steering torque in comparison with
the low vehicle speed S.sub.L mentioned above, as shown in FIG. 7.
The steering assist force generated on the basis of the
differential pressure of both of the oil chambers 24 and 25 becomes
small, and as shown in FIG. 8, required steering force becomes
large in the same steering torque. In this case, steering force
when the steering assist force is not generated is shown in FIG. 8
by using a single dot chain line.
[0065] When the steering torque becomes greater and the oil
pressure detected by the pressure sensor 7 becomes greater than the
first predetermined value P.sub.1, the set valve opening degree of
the assist control valve 32 is made large and becomes the valve
opening degree having the predetermined value A.sub.2 at the second
predetermined value P.sub.2 or more. In a range of the steering
torque having the oil pressure greater than the first predetermined
value P.sub.1, in comparison with the case that the set valve
opening degree of the assist control valve 32 becomes the
predetermined value A.sub.1, that is, the oil pressure of both of
the oil chambers 24 and 25 is determined only on the basis of the
geometrical shape of the control portions 66a, 66b, 69a and 69b of
the first and second valve portions, the amount of the working oil
supplied to the power cylinder mechanism 21 is reduced. As a
result, as shown in FIGS. 7 and 8, in comparison with the
characteristic shown by a two-dot chain line when the set valve
opening degree of the assist control valve 32 is kept to be the
predetermined value A.sub.1, in the same steering torque, the oil
pressure in both of the oil chambers 24 and 25 becomes smaller, and
the steering assist force generated on the basis of the oil
pressure becomes smaller, so that the required steering force
becomes larger. In the manner mentioned above, a condition that the
steering assist force is small is maintained in the range of the
large steering torque, whereby it is possible to improve steering
stability at the high vehicle speed S.sub.H.
[0066] In this case, even when the assist control valve 32 is
opened, in the case that the steering torque becomes large and the
opening area of the throttle portions 71a and 71b in the second
valve portion becomes zero, all the amount of the working oil
supplied from the pump apparatus 1 is supplied to the first inflow
passages 53 and 53, so that a large assist steering force is
generated.
[0067] As mentioned above, the assist control valve 32 is
controlled to the set valve opening degree in correspondence to the
vehicle speed and the oil pressure in the supply passage 14 in
which the oil pressure obtained by reflecting the external load is
generated by the first and second valve portions having the valve
opening degree corresponding to the steering torque generated
through the relative movement in the rotational direction of the
input shaft 26 and the output shaft 28 connected to each other via
the torsion bar 27 (that is, the twist of the torsion bar 27). The
discharge amount of the working oil in the oil passage 39 branched
from the supply passage 14 to the reservoir 2 is controlled by the
assist control valve 32, even at the same vehicle speed, with
respect to the particular steering torque at that time. The flow
amount of the working fluid to the first valve portion after
passing through the first inflow passages 53 and 53 from the supply
passage 14 is controlled by suitably setting the set valve opening
degree of the assist control valve 32 with respect to the oil
pressure generated in the supply passage 14 obtained by reflecting
the external load. The structure can be made such that the oil
pressure for obtaining the steering assist force having an optimum
magnitude at the vehicle speed is generated in the left oil chamber
24 and the right oil chamber 25 in the power cylinder mechanism
21.
[0068] Since the steering assist force with respect to the steering
torque at each of the vehicle speeds can be set to various
magnitudes by suitably changing the set valve opening degree of the
assist control valve 32 with respect to the oil pressure of the
supply passage 14 obtained by reflecting the external load in the
steering torque, the freedom for setting the steering assist force
with respect to the steering torque becomes great at the vehicle
speed, so that it is possible to set the steering assist force to
an optimum magnitude at each of the vehicle speeds.
[0069] In the main control valve 29, at the first throttle portions
68a and 68b of the first valve portion and the second throttle
portions 71a and 71b of the second valve portion which control the
supply amount of the working oil to the power cylinder mechanism
21, since the geometrical shape of the first control portions 66a
and 66b and the second control portions 69a and 69b may be formed
in accordance with working to such a degree that the steering
torque is reflected, working at a high accuracy is not required and
cost can be reduced.
[0070] Since it is possible to set the steering assist force with
respect to each of the steering torque by changing the set valve
opening degree of the assist control valve 32 with respect to the
oil pressure obtained by reflecting the external load in connection
with the steering torque, it is possible to easily change the set
of the steering assist force with respect to each of the steering
torque in correspondence to a kind of vehicle and a driver's taste.
Using the main control valve 29 having the same structure, due to a
common use of the main control valve 29, and since it is not
required to change the first control portions 66a and 66b and the
second control portions 69a and 69b corresponding to the portion
for controlling the amount of the working oil in the first throttle
portions 68a and 68b of the first valve portion and the second
throttle portions 71a and 71b of the second valve portion in
accordance with the working or the like, it is possible to reduce
cost.
[0071] In this case, in the embodiment mentioned above, the set
valve opening degree is increased within the range of the
predetermined steering torque. In some cases, it is possible to
reduce the set valve opening degree within a certain steering
torque range. Further, at a time of being equal or less than the
predetermined low vehicle speed, the set valve opening degree of
the assist control valve 32 is set to zero. It is possible to set
the set valve opening degree to be more than zero so as to open the
assist control valve 32 within the range of the steering torque,
for example, that the steering assist force rapidly increases. The
pressure sensor 7 is provided in the supply passage 14, however,
the pressure sensor 7 may be provided everywhere the first flow
passage is constituted, in addition to the supply passage 14.
[0072] As heretofore explained, embodiments of the present
invention have been described in detail with reference to the
drawings. However, the specific configurations of the present
invention are not limited to those embodiments but those having a
modification of the design within the range of the present
invention are also included in the present invention.
[0073] In accordance with the present invention, the assist control
valve is controlled to the set valve opening degree in
correspondence with the vehicle speed and the fluid pressure of the
first flow passage in which the fluid pressure obtained by
reflecting the external load (the road reaction force) by the first
and second valve portions having the valve opening degree in
correspondence to the steering torque during the relative movement
between the input member and the output member. The discharge
amount of the working fluid in the second flow passage to the low
pressure portion is controlled by the assist control valve
mentioned above. The flow amount of the working fluid supplied from
the first flow passage to the first valve portion is controlled by
suitably setting the set valve opening degree of the assist control
valve with respect to the fluid pressure generated in the first
flow passage obtained by reflecting the external load, with respect
to the particular steering torque even at the same vehicle speed,
so that it is structured such that the oil pressure for obtaining
the steering assist force having an optimum magnitude at the
vehicle speed is generated in the operating chamber in the power
cylinder mechanism.
[0074] Since the steering assist force with respect to the steering
torque at each of the vehicle speeds can be set to various
magnitudes by suitably changing the set valve opening degree of the
assist control valve with respect to the fluid pressure of the
first flow passage obtained by reflecting the external load at the
steering torque, the freedom for setting the steering assist force
with respect to steering torque at the vehicle speed becomes great,
so that it is possible to set steering assist force to an optimum
magnitude at each of the vehicle speeds.
[0075] Since the portion which controls the flow amount of the
first and second valve portions in the main control valve may be
formed in accordance with the working to such a degree that the
steering torque can be reflected to the first flow passage, it is
not required to work at a high accuracy and it is possible to
reduce cost.
[0076] Since it is possible to set the steering assist force with
respect to each of the steering torque by changing the set valve
opening degree of the assist control valve with respect to the
fluid pressure obtained by reflecting the external load to the
steering torque, it is possible to easily change the setting of the
steering assist force with respect to each of the steering torque
in correspondence to the kind of vehicle and the driver's taste
upon using the main control valve having the same structure. Due to
the common use of the main control valve and since it is not
required to change the portion for controlling the flow amount in
the first and second valve portions in accordance with the working
or the like, it is possible to reduce cost.
[0077] Although the invention has been illustrated and described
with respect to several exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made to the
present invention without departing from the spirit and scope
thereof. Therefore, the present invention should not be understood
as limited to the specific embodiment set out above, but should be
understood to include all possible embodiments which can be
embodied within a scope encompassed and equivalents thereof with
respect to the features set out in the appended claims.
* * * * *