U.S. patent application number 09/800184 was filed with the patent office on 2001-10-11 for vehicle including a variable gear ratio steering device and an electric power steering apparatus.
This patent application is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Kurosawa, Takao, Murata, Makoto, Sasajima, Kouji.
Application Number | 20010027895 09/800184 |
Document ID | / |
Family ID | 18617034 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027895 |
Kind Code |
A1 |
Murata, Makoto ; et
al. |
October 11, 2001 |
Vehicle including a variable gear ratio steering device and an
electric power steering apparatus
Abstract
A vehicle including a variable gear ratio steering device and an
electric power steering apparatus is disclosed. The variable gear
ratio steering device influences on a steering system of the
vehicle and varies a ratio of a steering angle of steerable road
wheels to a steering wheel angle by driving an electric motor in
accordance with a vehicle speed. The electric power steering
apparatus influences on the steering system of the vehicle and
provides an assist steering wheel torque by driving an electric
motor in accordance with a manual steering wheel torque. The
vehicle comprises a power supply voltage detector for detecting a
voltage of a power supply, and a control unit for controlling the
electric motor of said variable gear ratio steering device in
accordance with the detected voltage. When the detected voltage
decreases to a certain voltage or lower, the control unit brings
the variable gear ratio steering device into a slow state and
thereafter stops the same.
Inventors: |
Murata, Makoto; (Wako-shi,
JP) ; Kurosawa, Takao; (Wako-shi, JP) ;
Sasajima, Kouji; (Wako-shi, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha
|
Family ID: |
18617034 |
Appl. No.: |
09/800184 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
180/446 ;
180/400 |
Current CPC
Class: |
Y10T 74/1958 20150115;
B62D 1/166 20130101; B62D 5/0481 20130101; Y10T 74/19555 20150115;
B62D 5/0457 20130101 |
Class at
Publication: |
180/446 ;
180/400 |
International
Class: |
B62D 005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2000 |
JP |
2000-103291 |
Claims
What is claimed is:
1. A vehicle including a variable gear ratio steering device and an
electric power steering apparatus, the variable gear ratio steering
device influencing on a steering system of the vehicle and varying
a ratio of a steering angle of steerable road wheels to a steering
wheel angle by driving an electric motor in accordance with a
vehicle speed, and the electric power steering apparatus
influencing on the steering system of the vehicle and providing an
assist steering wheel torque by driving an electric motor in
accordance with a manual steering wheel torque, the vehicle
comprising: a power supply voltage detector for detecting a voltage
of a power supply; and a control unit for controlling the electric
motor of said variable gear ratio steering device in accordance
with the detected voltage, wherein, when the detected voltage
decreases to a certain voltage or lower, the control unit brings
the variable gear ratio steering device into a slow state and
thereafter stops the variable gear ratio steering device.
2. A vehicle according to claim 1, wherein said control unit
reduces assistance of the assist steering wheel torque from the
electric motor of said electric power steering apparatus when the
detected voltage decreases to the certain voltage or lower, and
said control unit stops the assistance of said assist steering
wheel torque when the voltage further decreases to a lower limit
voltage which is set to be lower than the certain voltage.
3. A vehicle according to claim 2, wherein said control unit
carries out assistance by decreasing said assist steering wheel
torque in accordance with a value of the detected voltage when the
detected voltage is between the certain voltage and the lower limit
voltage.
4. A vehicle according to claim 1, wherein said control unit brings
the variable gear ratio steering device into the slow state when
the detected voltage decreases to the certain voltage or lower
continuously for a certain period of time.
5. A vehicle according to claim 2, wherein said control unit brings
the variable gear ratio steering device into the slow state and at
the same time decreases assistance of the assist steering wheel
torque from the electric power steering apparatus when the detected
voltage decreases to the certain voltage or lower continuously for
a certain period of time.
6. A vehicle according to claim 4, wherein said control unit
cooperatively controls said variable gear ratio steering device
with other equipment, such as an air conditioning system and a car
audio system.
7. A vehicle according to claim 5, wherein said control unit
cooperatively controls said variable gear ratio steering device and
said electric power steering apparatus with other equipment, such
as an air conditioning system and a car audio system.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to vehicles including a
variable gear ratio steering device and an electric power steering
apparatus.
BACKGROUND OF THE INVENTION
[0002] Vehicles including a variable gear ratio steering device and
an electric power steering apparatus have been widely known. The
variable gear ratio steering device influences on a steering system
of the vehicle and continuously varies the steering angle ratio
(also referred to as "transmission rate" or "reduction gear ratio")
or the ratio of the steering angle of the road wheels to the
steering wheel angle. The variable gear ratio steering device sets
the steering angle ratio to a greater value in a low speed range,
at which a steering operation with a large steering input is often
necessary, so that the turn or displacement of the steerable road
wheels is relatively large with respect to a relatively small
steering input. This is so-called quick state. On the other hand,
the variable gear ratio steering device sets the steering angle
ratio to a smaller value in a high speed range, at which a steering
operation with a large steering input is not required, so that the
turn or displacement of the road wheels is relatively small with
respect to a relatively large steering input. This is so-called
slow state. Meanwhile, the electric power steering apparatus
assists a driver's steering wheel torque by making direct use of
the driving force of an electric motor, so as to ease the effort
required for the steering wheel operation. Therefore, the driver is
not required a laboring steering operation.
[0003] The variable gear ratio steering device and the electric
power steering apparatus are provided with an electric motor,
respectively, which is driven by a power supply from a battery.
When controlling the drive of each electric motor, in the variable
gear ratio steering device, the steering angle ratio is increased
or decreased in accordance with a vehicle speed, and in the
electric power steering apparatus, the assist steering wheel torque
is increased or decreased in accordance with the driver's manual
steering wheel torque input.
[0004] However, in these vehicles, in order to prevent an engine
stop due to decreased voltage of the battery, a consideration is
made such that the assistance of the electric power steering
apparatus is stopped and the variable control of the steering angle
ratio (steering ratio characteristics) with the variable gear ratio
steering device is stopped.
[0005] However, since the variable gear ratio steering device
ensures a large displacement of the road wheels with a small
steering input during the quick state in a low speed range, the
steering operation cannot be facilitated without assistance of the
electric power steering apparatus. If the voltage of the battery
lowers when the variable gear ratio steering device is in the quick
state, and the assistance of the electric power steering apparatus
is lowered or stopped and the variable control of the steering
angle ratio with the variable gear ratio steering device is
stopped, the movement of the steering wheel becomes heavy. This is
not preferable. Meanwhile, in order to prevent the engine stop,
decreasing the voltage of the battery has to be restricted.
Further, these fail-and-safe actions are preferably carried out
without giving an uncomfortable feel to the driver.
[0006] In view of the above, the present invention seeks to provide
a vehicle, which solves the drawbacks of the prior art.
SUMMARY OF THE INVENTION
[0007] According to a first aspect of the invention, there is
provided a vehicle including a variable gear ratio steering device
and an electric power steering apparatus, the variable gear ratio
steering device influencing on a steering system of the vehicle and
varying a ratio of a steering angle of steerable road wheels to a
steering wheel angle by driving an electric motor in accordance
with a vehicle speed, and the electric power steering apparatus
influencing on the steering system of the vehicle and providing an
assist steering wheel torque by driving an electric motor in
accordance with a manual steering wheel torque, the vehicle
comprising: a power supply voltage detector for detecting a voltage
of a power supply; and a control unit for controlling the electric
motor of said variable gear ratio steering device in accordance
with the detected voltage, wherein, when the detected voltage
decreases to a certain voltage or lower, the control unit brings
the variable gear ratio steering device into a slow state and
thereafter stops the variable gear ratio steering device.
[0008] In such a construction, when the voltage of the power supply
decreases to a certain voltage or lower, the variable gear ratio
steering device is stopped, thereby saving the life of the power
supply or recovering the power supply. This can prevent or restrict
occurrence of a trouble, such as an engine stop. It should be noted
that when the voltage of the power supply lowers and so does the
assist steering wheel torque of the electric power steering
apparatus, in some conditions of the variable gear ratio steering
device, a difficulty will a rise in a steering operation.
Therefore, the variable gear ratio steering device is preferably
brought into the slow state (dull) where the steering angle ratio
is small, such that the steering operation is carried out with
decreased assistance of the assist steering wheel torque. Herein,
"a certain voltage" is set higher than the voltage that respective
control means (computers) for controlling vehicle-mounted equipment
can be operated without any troubles and that is extremely low in
comparison with the normal state of use. The certain voltage also
indicates the critical voltage, below which the variable gear ratio
steering device and/or the electric power steering apparatus may
not be operated normally, otherwise the engine may stop when
starting the variable gear ratio steering device and/or the
electric power steering apparatus. The certain voltage is for
example 9.5V.
[0009] According to a second aspect of the invention, said control
unit reduces assistance of the assist steering wheel torque from
the electric motor of said electric power steering apparatus when
the detected voltage decreases to the certain voltage or lower, and
said control unit stops the assistance of said assist steering
wheel torque when the voltage further decreases to a lower limit
voltage which is set to be lower than the certain voltage.
[0010] In such a construction, assistance of the assist steering
wheel force (assist steering wheel torque) of the electric power
steering apparatus is reduced when the power supply voltage becomes
the certain voltage or lower, and the assistance is stopped under
the lower limit voltage, thereby saving the life of the power
supply or recovering the power supply. Therefore, reduction of the
power supply voltage can be prevented in a reliable manner. The
certain voltage may be the same as that recited in the
aforementioned construction. The lower limit voltage is defined as
a low voltage, in which for example electric equipment may not be
actuated but at least the engine can manage to move. The lower
limit voltage is for example 8V.
[0011] According to a third aspect of the invention, said control
unit carries out assistance by decreasing said assist steering
wheel torque in accordance with a value of the detected voltage
when the detected voltage is between the certain voltage and the
lower limit voltage.
[0012] In such a construction, assistance is reduced in accordance
with the detected voltage, and thereby the power supply is not
subject to a heavy load. Further, except that the voltage lowers
instantly and abruptly, the driver does not experience any
uncomfortable feel even if the driver carries out a steering
operation while the voltage lowers. Also, except that the voltage
recovers instantly, the driver does not experience any
uncomfortable feel during the steering operation even if the
voltage recovers and increases.
[0013] Preferably, control means is provided for restricting
electric power consumption of the equipment which is unnecessary to
drive the engine or which does not affect safety of the vehicle,
such as an air conditioning system or a car audio system. The
control means controls an operation of such equipment based on the
detected voltage such that when the detected voltage decreases to
the certain voltage or lower, the operation amount of the equipment
is preferably reduced or alternatively the equipment is stopped. As
mentioned above, a cooperative control of the variable gear ratio
steering device and the electric power steering apparatus with
other equipment ensures a smooth steering operation as well as an
improved battery life extending operation (battery recovering
operation).
[0014] Further, in the a fore-mentioned constructions, preferably
the control unit determines under voltage when the detected voltage
decreases to the certain voltage or lower continuously for a
certain period of time, and then as a fail-safe action, the control
unit reduces assist of the assist steering wheel torque and brings
said variable gear ratio steering device into a slow state and
thereafter stops said variable gear ratio steering device.
Preferably, when the detected voltage decreases to the certain
voltage or lower continuously for the certain period of time, the
control unit cooperatively controls said variable gear ratio
steering device and said electric power steering apparatus with
other equipment. This is because the voltage lowers due to noise or
voltage fluctuation even in the normal state of use, and a
fail-and-safe action is not always required. The lowered voltage
due to noise or voltage fluctuation recovers after a relatively
short period of time, such as less than 0.2 or 0.5 seconds.
Therefore, a judgement can be made as to whether or not a
fail-and-safe action is required by setting the certain period of
time. An unnecessary fail-and-safe action is avoidable when the
voltage lowers in the normal state of use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Preferred embodiments of the present invention will be
described below, by way of example only, with reference to the
accompanying drawings, in which:
[0016] FIG. 1 is a schematic view illustrating the overall
arrangement of a variable gear ratio steering device and an
electric power steering apparatus according to the invention;
[0017] FIG. 2 is a sectional view showing the variable gear ratio
steering device of FIG. 1;
[0018] FIG. 3 is an exploded perspective view showing a shaft of
the variable gear ratio steering device of FIG. 1;
[0019] FIG. 4 is a sectional view taken on line A-A in FIG. 2;
[0020] FIG. 5 is an explanatory view showing the working principal
of the variable gear ratio steering device;
[0021] FIG. 6 is a graph showing steering ratio characteristics of
the variable gear ratio steering device;
[0022] FIG. 7 is a block diagram showing a control unit of the
variable gear ratio steering device;
[0023] FIG. 8 shows a construction of a motor driver of FIG. 7;
[0024] FIG. 9 is a block diagram showing a target eccentricity
amount setting means of FIG. 7;
[0025] FIG. 10A is a block diagram showing details of a target
current value setting means of FIG. 7, and
[0026] FIG. 10B is a map showing relations between voltage signal
to be looked up at a target current value setting section and
correction coefficient.
[0027] FIG. 11 is a control time chart of a vehicle including the
variable gear ratio steering device and the electric power steering
apparatus in an under voltage state; and
[0028] FIG. 12 is a control time chart of the vehicle including the
variable gear ratio steering device and the electric power steering
apparatus in a voltage recovery state.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] With reference to the drawings, a vehicle including a
variable gear ratio steering device and an electric power steering
apparatus will be described. Herein, the vehicle is not limited to
a particular type, and as long as equipped with a motor (engine
and/or driving motor),the vehicle may be a normal passenger car, a
vehicle for construction work, an advanced specification vehicle,
and the like.
[0030] The vehicle including a variable gear ratio steering device
and an electric power steering apparatus comprises a power supply
voltage detector for detecting a voltage of a power supply and a
control unit for controlling both an electric motor of the variable
gear ratio steering device and an electric motor of the electric
power steering apparatus. And when the voltage of the power supply
lowers to a certain voltage, the control unit decreases assistance
of the electric power steering apparatus (or an assist steering
torque) and brings the variable gear ratio steering device into to
a slow state. Further, the control unit carries out assistance in
accordance with the voltage of the power supply if the voltage is
in the range of from the certain voltage to a lower limit voltage.
The voltage of the power supply (battery) lowers due to secular
deterioration, decreased battery electrolyte level, and the
like.
[0031] Firstly, constructions of the variable gear ratio steering
device and the electric power steering apparatus will be
described.
[0032] FIG. 1 illustrates the overall arrangement of the variable
gear ratio steering device and the electric power steering
apparatus. The variable gear ratio steering device and the electric
power steering apparatus 1 include a variable gear ratio device 10
and a controller or control unit 60 (referring to FIG. 7). The
variable gear ratio device 10 is provided in a steering system S
from a steering wheel 2 to steerable road wheels W. The control
unit 60 controls the variable gear ratio device 10, viz. a motor
for the variable gear ratio steering device (hereinafter referred
to as VGS motor) 27 in accordance with a vehicle speed.
[0033] In the steering system S, a steering wheel 2 is integrally
attached to a steering shaft 3, and a lower end of the steering
shaft 3 is connected to an input shaft of the variable gear ratio
device 10 via a connecting shaft 4 including a pair of universal
joints 4a, 4b. The variable gear ratio device 10 continuously
varies the ratio (.beta./.alpha.) of the rotational angle .beta. of
the output shaft to the rotational angle a of the input shaft. The
output shaft of the variable gear ratio device 10 is provided with
a pinion 5. The pinion 5 meshes with rack teeth on a rack shaft 6
such that the rotational movement of the output shaft is converted
into the linear movement (L) of the rack shaft 6, which is in turn
converted into the steering movement (T) of the front wheels or the
steerable road wheels W via tie rods 7 and knuckle arms.
[0034] In the variable gear ratio steering device and the electric
power steering apparatus 1, a motor for the electric power steering
apparatus (hereinafter referred to as EPS motor) 8 for generating
an assist steering torque is provided laterally and coaxially of
the rack shaft 6. And the rotation of EPS motor 8 is converted into
a thrust force via a ball screw mechanism 9 coaxial with the rack
shaft 6, and the thrust force works on a rack-ball screw shaft 9A
(rack shaft 6). The EPS motor 8 is controlled by the control unit
60 (referring to FIG. 7). The control unit also controls VGS motor
27.
[0035] Next, with reference to FIGS. 2 to 4, one embodiment of the
variable gear ratio device will be described.
[0036] As shown in FIG. 2, a supporting member 14 is rotatably
supported on an upper casing 13a via a ball bearing 12, and at an
offset position of the supporting member 14 the input shaft 11 is
rotatably supported via a ball bearing 15. One end of the input
shaft 11 is received in a lower casing 13b, and is integrally
formed a coupling 16 for transmitting a rotational force to the
output shaft 17. The input shaft 11 is also connected to a
connecting shaft 4 as illustrated in FIG. 1, therefore the input
shaft 11 can be rotated through the connecting shaft 4 with the
rotation of the steering wheel 2.
[0037] The output shaft 17 is rotatably supported on the lower
casing 13b via a pair of ball bearings 18a, 18b. The pinion 5
meshing with the rack shaft 6 is integrally formed on the output
shaft 17. One end of the output shaft 17 protrudes into the lower
casing 13b. An intermediate shaft 19 projects from the end of the
output shaft 17 in a position eccentrically offset from the center
of the output shaft 17. The intermediate shaft 19 and the coupling
16 integral with the input shaft 11 are connected via a slider 21
and a tapered roller bearing 22. A pair of flat needle bearings 20
is interposed between the slider 21 and the coupling 16. A seal
member 35 having a flexible tubular portion is fitted between the
input shaft 11 and the upper casing 13a so as to seal the variable
gear ratio device 10.
[0038] As best seen in FIG. 3, agroove 23 having a trapezoidal
section is formed in the lower surface of the coupling 16. The
slider 21 is slidably engaged with the opposing slant surfaces of
the groove 23 through the pair of flat needle bearings 20. The
intermediate shaft 19 is engaged with the center portion of the
lower surface of the slider 21 through the tapered roller bearing
22 so that the intermediate shaft 19 and the tapered roller bearing
22 are relatively rotatable to each other.
[0039] As shown in FIG. 2, an adjust screw 24 is threadably fitted
into a lower end of the lower casing 13b, and the inner end of this
adjust screw 24 abuts on the outer race of the ball bearing 18b
supporting the lower end of the output shaft 17 so that, by
appropriately turning the adjust screw 24, the pinion 5 is moved
axially and a desired preload can be applied between the input
shaft 11 and the output shaft 17 with the coupling 16 interposed
therebetween. Therefore, it is possible to remove any play which
the coupling 16 may have, and improved rigidity of the torque
transmitting train can be achieved.
[0040] As shown in FIG. 4, a fan-shaped partial worm wheel 25 is
formed at a part of an outer periphery of the supporting member 14.
The partial worm wheel 25 is meshed with a worm 28 which is driven
by a motor 27 for the variable gear ratio steering device
(hereinafter referred to as VGS motor) via a worm reduction
mechanism 26, and when rotating the VGS motor 27, rotational
movement can be applied to the supporting member 14 in a
predetermined angle range. The worm 28 is supported on the upper
casing 13a via a backlash-removing member 29 making use of an
eccentric cam. A hexagon socket 30 is formed at one end of the
backlash-removing member 29, and when inserting a hexagon coupling
bolt into the hexagon socket 30 and turning the same with regard to
the upper casing 13a, the center of axis of the backlash-removing
member 29 displaces so as to vary the meshing point with the
partial worm wheel 25. Further, in order to allow displacement of
the center of axis of the worm 28, the worm 28 and the worm
reduction mechanism 26 are connected via Oldham's coupling 31.
[0041] A displacement sensor 33, such as a differential
transformer, is mounted on the upper casing 13a so as to engage
with a pin 32 projecting from the upper surface of the supporting
member 14. The displacement sensor 33 detects the rotational angle
of the supporting member 14. The rotation amount detected by the
displacement sensor 33, viz. an eccentricity amount signal (actual
eccentricity amount) 33a of the input shaft 11 which is supported
by the supporting member 14 is outputted as a digital signal to VGS
controller 70A in the control unit 60.
[0042] As shown in FIG. 7, the VGS controller 70A drives the VGS
motor 27 by feedback control in such a way that the target
eccentricity amount 71a corresponding to the steering angle ratio
which is set based on the vehicle speed (viz. the target steering
angle ratio) coincides with the actual eccentricity amount
(equivalent to the actual steering angle ratio) 33a detected by the
displacement sensor 33.
[0043] Operational principle of the variable gear ratio steering
device will now be described with reference to FIGS. 5 and 6, in
which FIG. 5 is an explanatory view showing the working principal
of the variable gear ratio steering device, and FIG. 6 is a graph
showing input angle/output angle characteristics indicating the
steering ratio characteristics of the variable gear ratio steering
device.
[0044] In the diagram of FIG. 5, A and B denote the rotational
centers of the input shaft 11 and the output shaft 17, C denotes
the point of engagement of the intermediate shaft 19, b denotes the
distance between B and C, a denotes the eccentricity amount between
the input shaft 11 and the output shaft 17 or the distance between
A and B, .alpha. denotes the rotational angle of the input shaft 11
or the steering angle of the steering wheel 2, and .beta. denotes
the rotational angle of the output shaft 17 or the rotational angle
of the pinion 5. According to the geometric relationship between
the various parts, the following mathematical relationship
holds:
b.multidot.sin.beta.=(b.multidot.cos.beta.-a) tan .alpha.
[0045] This can be also written as given in the following:
.alpha.=tan.sup.-1(b.multidot.sin .beta./(b.multidot.cos
.beta.-a))
[0046] When the input shaft 11 is turned by the driver's steering
wheel operation, the intermediate shaft 19 turns in the manner of a
crank around the axial center of the output shaft 17 by virtue of
the engagement between the coupling 16 of the input shaft 11 and
the slider 21. As best seen in FIG. 5, when the rotational angle
.alpha.1 of the input shaft 11 is 90 degrees, the output shaft 17
takes a rotational angle as shown in the same figure.
[0047] Further, by turning the supporting member 14, the eccentric
cam action of the supporting member 14 makes the center of axis of
the input shaft 11 change in the range of between A0 and A2
indicated in FIGS. 3 and 4. Because of the change in the center of
axis of the input shaft 11, when the eccentricity amount a between
the input shaft 11 and the output shaft 17 is determined to a
certain value and the centers of axes of the input shaft 11 and the
output shaft 17 are positioned eccentrically to each other, the
rotational angle of the output shaft 17 is not generally
proportional to the rotational angle of the input shaft 11. More
specifically, as indicated by the solid lines a1 and a2 given in
FIG. 6, the change in the angle of the output shaft 17 for a given
increment of the rotational angle of the input shaft 11
progressively increases as the rotational angle of the input shaft
11 increases.
[0048] When the eccentricity amount a between the centers of axes
of the input shaft 11 and the output shaft 17 is continuously
changed within the range of between a2 to a0 (a2>a1>a0=0), it
is possible to change the ratio (.beta./.alpha.) of the rotational
angle of the output shaft 17 for a given rotational angle of the
input shaft 11 or the effective steering angle ratio. If the
eccentricity amount a between the input shaft 11 and the output
shaft 17 is increased, progressiveness is enhanced as to the rate
of change of the output angle .beta. for the input angle .alpha.,
and if the eccentricity amount a is 0, the input angle .alpha. is
equal to the output angle .beta., as indicated by the dashed line
(a0) given in FIG. 6.
[0049] If the change of the steering angle ratio is controlled in
such a way that it shifts to a0 in a low speed vehicle cruising
range and to a2 in a high speed vehicle cruising range, more
sensitive response or quick characteristics can be achieved in the
low speed vehicle cruising range with the rate of the rack stroke
for the steering angle a of the steering wheel set higher than the
conventional steering apparatus. Meanwhile, less sensitive response
or dull and slower characteristics can be achieved in the high
speed vehicle cruising range with the rate of the rack stroke for
the steering angle a of the steering wheel set lower than the
conventional steering apparatus. Therefore, the relation between
the effective steering angle and the vehicle cruising speed can be
a flat characteristic.
[0050] Next, with reference to FIGS. 7 and 8, a control unit for a
vehicle including the variable gear ratio steering device and the
electric power steering apparatus will be described, in which FIG.
7 is a block diagram showing a control unit of the variable gear
ratio steering device according to this preferred embodiment, and
FIG. 8 shows a construction of a motor driver of FIG. 7.
[0051] As shown in FIG. 7, the control unit 60 comprises a
controller 70 and a motor driver 80. The variable gear ratio
steering device and the electric power steering apparatus 1
comprise a vehicle speed sensor 41 for detecting vehicle speed, a
steering torque sensor 42 for detecting manual steering torque, a
voltage sensor 43 as a power supply voltage detector, a motor
current sensor 44 for detecting electric current supplied to the
motor, and the aforementioned displacement sensor 33. The vehicle
speed sensor 41 is for outputting a vehicle speed signal 41a
corresponding to the revolutions of the output shaft of the
non-shown transmission, the steering torque sensor 42 is for
outputting a steering torque signal 42a corresponding to a manual
steering torque of the driver, and the voltage sensor 43 detects an
ignition voltage (hereinafter referred to as IG voltage) and
outputs a voltage signal 43a. The IG voltage is lower than the
battery voltage. The motor current sensor 44 detects an electric
current supplied to EPS motor 8 and outputs a current signal 44a.
In these sensors, a non-shown AD converter converts the signal into
a digital signal. These equipments such as the control unit 60 and
motors 8, 27 are driven by the power supply BAT as a power source
(12V). The controller 70 and the like can be operated at 5V.
[0052] As shown in FIG. 7, the controller 70 comprises VGS
controller 70A and EPS controller 70B. As hardware constitution,
the controller 70 is equipped with an input/output interface to the
displacement sensor 33, the vehicle speed sensor 41, the steering
torque sensor 42, the voltage sensor 43, the motor current sensor
44, the VGS motor driver 81, the EPS motor driver 82 and the like,
ROM which stores various data and programs, RAM which provisionally
stores various data, and logic circuits for various calculating
processes. Meanwhile, the VGS motor driver 81 and the EPS motor
driver 82 of the motor driver 80 are each equipped with a gate
driving circuit GC and a bridge circuit BC, such as shown in FIG.
8.
[0053] [VGS Controller & VGS Motor Driver]
[0054] VGS controller controlling the variable gear ratio steering
device will be described below.
[0055] As shown in FIG. 7, VGS controller 70A controlling the
variable gear ratio steering device comprises a target eccentricity
amount setting means 71, a deviation calculating means 72, a PID
control means 73 and PWM signal generating means 74.
[0056] The target eccentricity amount setting means 71 is equipped
with ROM and the like and sets the target eccentricity amount 71a
of the variable gear ratio device 10 in order to obtain certain
steering characteristics (or steering angle ratio) in accordance
with a vehicle speed. For this reason, the target eccentricity
amount setting means 71 map-searches the target eccentricity amount
71a (71Aa) from the data area with the use of a vehicle speed
signal 41a inputted as a digital signal, and then outputs the
result to the deviation calculating means 72. The map of the
vehicle speed signal 41a and the target eccentricity amount 71a
(71Aa) is set based on experimental results or logic operations so
that the target eccentricity amount becomes larger as the vehicle
speed increases. The target eccentricity amount setting means 71
sets the maximum eccentricity amount as the target eccentricity
amount 71a when the voltage signal 43a digitalized and inputted
decreases to a certain voltage (9.5V in this embodiment) or lower.
This will be described later.
[0057] The deviation calculating means 72 has a subtracter as
hardware or a subtracting function controlled by software. The
target eccentricity amount 71a from the target eccentricity amount
setting means 71 and the digitalized actual eccentricity amount 33a
from the displacement sensor 33 are inputted into the deviation
calculating means 72, and the deviation calculating means 72
outputs the deviation signal 72a to the PID control means 73.
[0058] The PID control means 73 is equipped with a logic circuit
and the like, and carries out an operation such as P (proportion),
I (integration) and D (differentiation) with regard to the
deviation signal 72a from the deviation calculating means 72. And
in order to make the deviation closer to zero, the PID control
means generates and outputs a drive control signal 73a which
indicates a direction of the electric currents supplied to the
motor 27 and its current value.
[0059] The PWM signal generating means 74 is equipped with a logic
circuit and the like. The PWM signal generating means 74 generates
and outputs a PWM (pulse width modulation) signal 74a, which is
corresponding to the current value and the polarity of the drive
control signal 73a, to the motor driver 80 (VGS motor driver
81).
[0060] As shown in FIG. 8, the VGS motor driver 81 is equipped with
a gate drive circuit GC and a bridge circuit BC. The bridge circuit
BC comprises four field effect transistors FET, and each gate Ge of
the field effect transistor FET is driven by the gate drive circuit
GC. With such arrangement, the VGS motor 27 is PWM-driven
corresponding to the duty ratio of the PWM signal, ON signal and
OFF signal.
[0061] With reference to FIG. 9, details of the aforementioned
target eccentricity amount setting means 71 will be described,
which, in the normal state, sets the target eccentricity amount 71a
in accordance with the vehicle speed or the vehicle speed signal
41a, and which sets the target eccentricity amount 71a for the
maximum value when the voltage decreases to a certain voltage K1 or
lower. Herein, FIG. 9 is a block diagram showing details of the
target eccentricity amount setting means.
[0062] As shown in FIG. 9, the target eccentricity amount setting
means 71 comprises at least a target eccentricity amount setting
section 71A, a voltage reference value storage section 71B, a
comparison/selection section 71C, and a target eccentricity amount
switching section 71D.
[0063] The target eccentricity amount setting section 71A is
equipped with ROM and the like. The target eccentricity amount
setting section 71A map-searches the target eccentricity amount
71Aa from the data area with the use of the digitalized vehicle
speed signal 41a, and outputs the result. As mentioned above, the
map is set so that the target eccentricity amount 71Aa becomes
larger as the vehicle speed signal 41a increases.
[0064] The voltage reference value storage section 71B is equipped
with ROM and the like, and stores the certain voltage K1. In this
embodiment, the certain voltage K1 is 9.5V for IG voltage. The
certain voltage K1 is inputted to the comparison/selection section
71C to be described later.
[0065] The comparison/selection section 71C is equipped with a
logic circuit, ROM, a comparator and the like. The
comparison/selection section 71C compares the digitalized voltage
signal 43a and the certain voltage K1, and determines whether the
voltage signal 43a is less than the certain voltage K1, that is
whether or not in a low voltage state. And based on the comparison
result, it outputs a low voltage signal LV1 to the target
eccentricity amount switching section 71D. Herein, the low voltage
signal LV1 is an H level signal when in the low voltage state and
is an L level signal when in the normal state. The low voltage
state is determined when the voltage signal 43a is lower than the
certain voltage K1 continuously for over 0.5 seconds. Further, the
comparison/selection section 71C selects and outputs the target
eccentricity amount 71Ca that is stored in the data area to the
target eccentricity amount switching section 71D when the low
voltage state is determined. Herein, the target eccentricity amount
71Ca in the low voltage state is to bring the eccentricity amount
of the variable gear ratio device 10 to the maximum (or the
proximity of the maximum value) so as to achieve the slowest
steering ratio characteristics.
[0066] The target eccentricity amount switching section 71D is
equipped with a switching element and the like, and based on the
level (H or L) of the low voltage LV1 from the comparison/selection
section 71C, it switches the target eccentricity amounts 71Aa and
71C a to be inputted. More specifically, when the low voltage
signal LV1 is at L level, which is not in the low voltage state,
the target eccentricity amount switching section 71D outputs the
target eccentricity amount 71Aa from the target eccentricity amount
setting section 71A as the target eccentricity amount 71a to the
deviation calculating means 72 (FIG. 7) to be described later.
Meanwhile, when the low voltage signal LV1 is at H level, which is
in the low voltage state, the target eccentricity amount switching
section 71D outputs the target eccentricity amount 71Ca in the low
voltage state as the target eccentricity amount 71a to the
deviation calculating means 72 to be described later. Accordingly,
when turning to the low voltage state, the steering ratio
characteristic swiftly shifts to the slow state (as a fail-safe
performance), thereby facilitating the driver's steering operation.
Such a fail-safe action continues until the eccentricity amount
increases to the maximum, even if the voltage of the battery BAT
decreases to 8V (a lower limit voltage K2 to be described later) or
lower while the eccentricity amount is enlarged.
[0067] When turning to the low voltage state, the VGS controller
70A lights on VGS warning lamp WL1 so as to indicate the driver
that the variable gear ratio steering device is in the slow state,
viz. the operation of the variable gear ratio steering device is
stopped. For this reason, the comparison/selection section 71C
outputs the low voltage signal LV1, which is based on the judgement
result whether or not in the low voltage state, to the VGS warning
lamp WL1. The VGS warning lamp WL1 is lit when the low voltage
signal LV1 at H level is inputted.
[0068] However, if the low voltage signal LV1 at H level is once
inputted, it is retained until the ignition switch is turned OFF
and then turned ON, and the low voltage signal LV1 is released and
changed from H level to L level when the voltage of the power
supply BAT is more than 9.5V upon turning ON the ignition switch.
Alternatively, the low voltage signal LV1 is released and changed
from H level to L level when the system reset is performed and the
voltage of the power supply BAT after reset is more than 9.5V.
Therefore, once the low voltage state is determined, even if the
voltage recovers over 9.5V (9.68V or more), the low voltage signal
LV1 at H level is not changed to the low voltage signal LV1 at L
level and the variable gear ratio steering device remains in the
slowest state unless performing ON-and-OFF operations of the
ignition switch. And the VGS warning lamp WL1 also remains ON.
Unstableness of the system or the device is thereby overcome.
[0069] With such a construction, switching means is preferably
provided in the power supply line between the power supply BAT and
the VGS motor driver 81 to switch ON and OFF the power supply line
so that the switching means is OFF when in the low voltage state
and the actual eccentricity amount 33a of the displacement sensor
33 is proximate to the maximum value, thereby stopping the supply
from the power supply BAT to the VGS motor driver 81. This is for
securely preventing decrement of the voltage of the power supply
BAT. Preferably, the switching means turns ON when the voltage is
over 9. 5V after turning OFF and turning ON the ignition switch.
This is for conforming to the indication of the VGS warning lamp
WL1.
[0070] [EPS Controller & EPS Motor Driver]
[0071] EPS controller for controlling the electric power steering
apparatus will be described.
[0072] As shown in FIG. 7, the EPS controller 70B for controlling
the electric power steering apparatus comprises a target current
value setting means 76, a deviation calculating means 77, a PID
control means 78 and PWM signal generating means 79.
[0073] The target current value setting means 76 sets a target
current 76a of the EPS motor 8 in order to obtain a certain assist
steering torque in accordance with a manual steering torque. Forth
is reason, the target current value setting means 76 is equipped
with ROM and the like. The target current value setting means 76
map-searches the target current 76a (76Aa) from the data area with
the use of a steering torque signal 42a inputted as a digital
signal, and then outputs the result to the deviation calculating
means 77. The map of the steering torque signal 42a and the target
current 76a (76Aa) is set based on experimental results or logic
operations so that the target current becomes larger as the
steering torque signal 42a increases. The target current value
setting means 76 decreases the target current value 76a when the
voltage signal 43a digitalized and inputted decreases to a certain
voltage k1 (K1=9.5V in this embodiment) or lower, and makes the
target current value 76a zero when the voltage signal 43a decreases
to a lower limit voltage K2 (k2=8V in this embodiment) or lower.
When the voltage signal 43a is between K1 and K2, the target
current value setting means 76 decreasingly corrects the target
current value 76a in accordance with the value of the voltage
signal 43a and generates an assist steering torque. This will be
described later.
[0074] The deviation calculating means 77 has a subtracter as
hardware or a subtracting function controlled by software. The
target current value 76a from the target current value setting
means 76 and the digitalized current signal (or current value) 44a
from the motor current sensor 44 are inputted into the deviation
calculating means 77, and the deviation calculating means 77
outputs the deviation signal 77a to the PID control means 78.
[0075] The PID control means 78 is equipped with a logic circuit
and the like, and carries out an operation such as P (proportion),
I (integration) and D (differentiation) with regard to the
deviation signal 77a from the deviation calculating means 77. And
in order to make the deviation closer to zero, the PID control
means generates and outputs a drive control signal 78a, which
indicates a direction of the electric currents supplied to the EPS
motor 8 and its current value.
[0076] The PWM signal generating means 79 is equipped with a logic
circuit and the like. The PWM signal generating means 79 generates
and outputs a PWM signal 79a, which is corresponding to the current
value and the polarity of the drive control signal 78a, to the
motor driver 80 (EPS motor driver 82).
[0077] As shown in FIG. 8 and similar to the VGS motor driver 81,
the EPS motor driver 82 is equipped with a gate drive circuit GC
and a bridge circuit BC. The bridge circuit BC comprises four field
effect transistor FET, and each gate Ge of the field effect
transistor FET is driven by the gate drive circuit GC. With such
arrangement, the EPS motor 8 is PWM-driven corresponding to the
duty ratio of the PWM signal, ON signal and OFF signal.
[0078] With reference to FIG. 10, details of the aforementioned
target current value setting means 76 will be described, which, in
the normal state, sets the target current value 76a in accordance
with the manual steering torque or the steering torque signal 42a,
and which decreasingly corrects the target current value 76a in
accordance with the value of the voltage signal 4 3a when the
voltage is between the certain voltage K1 and the lower limit
voltage K2.
[0079] As shown in FIG. 10A, the target current value setting means
76 comprises at least a target current value setting section 76A, a
voltage reference value storage section 76B, a comparison/selection
section 76C, multiplication means 76D, and a target current value
switching section 76E. Herein, FIG. 10A is a block diagram showing
details of the target current value setting means 76.
[0080] The target current value setting section 76A is equipped
with ROM and the like. The target current value setting section 76A
map-searches the target current value 76Aa from the data area with
the use of the digitalized steering torque signal 42a, and outputs
the result. As mentioned above, the map is set so that the target
current value 76Aa becomes larger as the steering torque signal 42a
increases.
[0081] The voltage reference value storage section 76B is equipped
with ROM and the like, and stores the certain voltage K1. The
certain voltage K1 is 9.5V for IG voltage, which is the same as the
above-described certain voltage K1 stored in the voltage reference
value storage section 71B of the target eccentricity amount setting
means 71.
[0082] The comparison/selection section 76C is equipped with a
logic circuit, ROM, a comparator and the like. The
comparison/selection section 76C compares the digitalized voltage
signal 43a and the certain voltage K1, and determines whether the
voltage signal 43a is less than the certain voltage K1, that is
whether or not in the low voltage state. Because the basis of the
judgement is exactly the same as the comparison/selection section
71C of the aforementioned target eccentricity amount setting means
71, further explanation will be omitted. Further, the
comparison/selection section 76C searches the map, which is stored
in the data area, with the use of the voltage signal 43a as an
address, and outputs the corresponding correction coefficient C to
the multiplication means 76D to be described later. The map is
shown in FIG. 10B. In this map, when the voltage (or the voltage
signal 43a) is at the certain voltage K1 or more, the correction
coefficient C is "1", and when the voltage is at the lower limit
voltage K2 or less, the correction coefficient C is "0". And when
the voltage is between the certain voltage K1 and the lower limit
voltage K2, the correction coefficient C decreases in proportion to
the voltage. With the provision of the map, the
comparison/selection section 76C does not have to compare
(determine) the voltage signal 43a and the lower limit voltage K2.
Also, the voltage reference value storage section 76B does not have
to store the lower voltage K2. As a result, the overall arrangement
of the system can be simplified.
[0083] Further, the comparison/selection section 76C outputs the
low voltage signal LV2 to the target current value switching
section 76E based on the comparison result. Similar to the low
voltage signal LV1, the low voltage signal LV2 is an H level signal
when in the low voltage state and is an L level signal when in the
normal state.
[0084] The multiplication means 76D has a multiplier as hardware or
a multiplying function controlled by software. The multiplication
means 76D multiplies the target current value 76Aa outputted from
the target current value setting section 76A by the correction
coefficient C outputted from the comparison/selection section 76C,
and outputs the thus corrected target current value 76Da
(=C.times.76Aa) to the target current value switching section
76E.
[0085] The target current value switching section 76E is equipped
with a switching element and the like, and based on the level (H or
L) of the low voltage signal LV2 from the comparison/selection
section 76C, it switches the target current value 76Aa and 76Da to
be inputted. More specifically, when the low voltage signal LV2 is
at L level, which is not in the low voltage state, viz. in the
normal state, the target current value switching section 76E
outputs the target current value 76Aa from the target current value
setting section 76A as the target current value 76a to the
deviation calculating means 77 (FIG. 7) to be described later.
Meanwhile, when the low voltage signal LV2 is at H level, which is
in the low voltage state, the target current value switching
section 76E outputs the corrected target current value 76Da in the
low voltage state as the target current value 76a to the deviation
calculating means 77 to be described later. Accordingly, when
turning to the low voltage state, the assist steering torque is
decreasingly corrected in accordance with the voltage of the power
supply BAT. Therefore, the driver does not experience any
uncomfortable feel. Preferably, decreasing the assist amount may be
carried out in accordance with voltage, rather than in accordance
with time. This is because the power supply BAT is not subject to a
heavy load. Namely, in the case that the assist amount is decreased
in accordance with time, a greater assist amount may be required
even if the voltage abruptly drops, which leads to acceleration of
decreased voltage of the power supply BAT.
[0086] When turning to the low voltage state, the EPS controller
70B lights on EPS warning lamp WL2 so as to indicate the driver
that the assist amount of the electric power steering apparatus is
decreased. For this reason, the comparison/selection section 76C
outputs the low voltage signal LV2, which is based on the judgement
result whether or not in the low voltage state, to the EPS warning
lamp WL2. The EPS warning lamp WL2 is lit when the low voltage
signal LV2 at H level is inputted.
[0087] When the voltage of the power supply BAT recovers, the EPS
controller 70B changes the low voltage signal LV2 from H level to L
level so as to assist with the normal assist steering torque.
[0088] Whether or not the voltage of the power supply BAT has been
recovered is determined based on the judgement whether the voltage
(IG voltage) is over 9.68V continuously for more than 0.5
seconds.
[0089] Such conditions may be determined in consideration of noise,
hysteresis and the like.
[0090] For this reason, the voltage reference value storage section
76B of the aforementioned EPS controller 70B (or the target current
value setting means 76) stores a recovery voltage K0 other than the
certain voltage K1. The value of the recovery voltage K0 is 9.68V
as previously mentioned in relation to the IG voltage. Other than
the aforementioned comparative function made by the comparator and
the like, the comparison/selection section 76C has another
comparative function to compare the voltage signal 43a and the
recovery voltage K0 and to determine whether the voltage signal 43a
is over the recovery voltage K0 continuously for more than 0.5
seconds.
[0091] The comparison/selection section 76C determines that the
voltage of the power supply BAT has been recovered, if the voltage
signal 43a is over the recovery voltage K0 continuously for more
than 0.5 seconds. When the voltage recovers, the
comparison/selection section 76C changes the level of the low
voltage signal LV2 from H level to L level. Therefore, the EPS
warning lamp WL2 is turned off. At the same time, the target
current value 76a selected at the target current value switching
section 76E is switched to the target current 76Aa outputted from
the target current value setting section 76A, thereby allowing an
assistance with the normal assist steering torque. Meanwhile, when
the voltage is over 9.5V, the correction coefficient C is "1", and
therefore the assistance is carried out with the normal assist
steering torque regardless of the level of the low voltage signal
LV2.
[0092] As mentioned above, the variable gear ratio steering device
and the electric power steering apparatus have different recovery
conditions upon recovering the voltage of the power supply BAT.
This is because the electric power steering apparatus affects the
driver's steering operation rather than the variable gear ratio
steering device. Also, it is not preferable to operate the variable
gear ratio steering device under unstable conditions of the power
supply BAT. If the variable gear ratio steering device is
continuously operated under unstable conditions of the power supply
BAT, it may stop in the quick state when the voltage again
drops.
[0093] [Air Conditioner ECU]
[0094] In the case that the vehicle is equipped with an air
conditioning system (hereinafter referred to as an "air
conditioner"), the controller 70 sends a low voltage signal LV2 to
an air conditioner ECU which entirely controls the air conditioner,
as indicated in FIG. 7. The air conditioner ECU reduces or stops
the output of the air conditioner when it receives a low voltage
signal LV2 at H level. Reducing the output of the air conditioner
is achieved by reducing the output of a fan of the air conditioner
or by reducing (or stopping) the output of a compressor. Meanwhile,
the air conditioner ECU recovers the output of the air conditioner
to the normal condition or restarts the operation when it receives
a low voltage signal LV2 at L level.
[0095] With reference to FIGS. 11 and 12, and to FIGS. 1 to 10 if
necessary, operation of a vehicle including the aforementioned
variable gear ratio steering device and the electric power steering
apparatus 1 will be described, in which FIG. 11 is a control time
chart when the voltage decreases, and FIG. 12 is a control time
chart when the voltage recovers.
[0096] [Under Voltage State]
[0097] At first, the control time chart shown in FIG. 11 will be
described.
[0098] As shown in the figure, at the section between Point a and
Point b, the power supply BAT supplies a certain constant voltage
(IG voltage) over 9.5V. Therefore, the variable gear ratio steering
device drives the VGS motor in accordance with the vehicle speed,
and changes the eccentricity amount so as to achieve the optimal
steering ratio characteristics for the vehicle speed.
[0099] Meanwhile, the electric power steering apparatus generates a
normal assist steering torque associated with the driver's steering
torque input so as to ease the driver's steering operation.
[0100] At Point b, the voltage starts to decrease. And at the
section between Point band Point c, the voltage decreases. However,
since the voltage is still over the certain voltage (9.5V), the low
voltage state is not determined by the controller 70 (or the
comparison/selection section 71C, 76C). As a result, similar to the
section between a and b, the optimal steering ratio characteristics
in accordance with the vehicle speed and an assistance associated
with the driver's steering torque input can be achieved.
[0101] The voltage becomes 9.5V at Point c. However, the low
voltage state is not determined-yet. At Point d, the voltage is
below 9.5V continuously for more than 0.5 seconds, and fail and
safe F/S is fixed. Therefore, the low voltage state is determined
by the comparison/selection section 71C of the target eccentricity
amount setting means 71, and the comparison/selection section 71C
outputs a low voltage signal LV1 at H level. The target
eccentricity amount 71a then becomes the maximum value so that the
variable gear ratio steering device is smoothly brought into the
slow state. At the same time, the VGS warning lamp WL1 is lit. The
low voltage state is also determined by the comparison/selection
section 76C of the target current value setting means 76, and the
comparison/selection section 76C outputs a low voltage signal LV2
at H level. Thereby, the target current value 76Aa outputted from
the target current value setting section 76A is multiplied by the
correction coefficient C and the target current value 76a is
decreasingly corrected. As a result, assistance of the assist
steering torque is decreased. Additionally, the air conditioner is
stopped (A/C restricted) because the low voltage signal LV2 at H
level is also sent to the air conditioner ECU. By these operations,
a life extension or recovery of the power supply BAT is
performed.
[0102] At the section between Point d and Point e, because the
voltage of the power supply BAT is less than 9.5V but is more than
8V, the variable gear ratio steering device has been brought into
the slow state. The VGS motor 27 does not consume electric power
after turning to the slow state, and hence a life extension or
recovery of the power supply BAT is performed. Further, when the
voltage decreases in the range of between 9.5V and 8V, the electric
power steering apparatus generates an assist steering torque
associated with the voltage, with the use of the correction
coefficient C which decreases in accordance with the voltage, and
with such an assist steering torque, the driver's steering
operation is assisted. At the section between d and e, because the
assist steering torque is decreasing smoothly in accordance the
voltage, the driver does not experience any uncomfortable feel even
if the voltage of the power supply BAT decreases during the
steering operation. Further, because the assist steering torque is
changed in accordance with the voltage, the power supply BAT is not
subject to a heavy load. Decrement of the voltage of the power
supply BAT from 9.5V to 8V takes at least 10 seconds, and usually
more. The VGS warning lamp WL1 and the EPS warning lamp WL2 remain
on, and the air conditioner remains stopped. This can attract the
driver's attention as well as perform a life extension or recovery
of the power supply.
[0103] At Point e, the voltage of the power supply BAT becomes 8V,
viz. the lower limit voltage K2, and as shown in FIG. 10B, the
correction coefficient C becomes 0 (zero). The electric power
steering apparatus then stops to generate an assist steering
torque, i.e., assistance is wholly stopped, so that an improved
life extension or recovery of the power supply BAT is performed. It
should be noted that even if the assistance is wholly stopped, the
variable gear ratio steering device is in the slow state, enabling
the steering operation by the driver's manual steering torque
input. If the variable gear ratio steering device has not been
brought into the slow state at Point e, the VGS motor 27 is
continuously driven so as to bring into the slow state. This is for
making the variable gear ratio steering device stop merely in the
slow state.
[0104] As mentioned above, an abrupt voltage drop can be prevented
because of the life extension or recovery performance of the power
supply BAT during the under voltage state. Further, the driver does
not experience any uncomfortable feel because the electric power
steering apparatus decreasingly corrects the assist steering torque
in accordance with the voltage. Moreover, the driver's steering
operation is not disturbed because the variable gear ratio steering
device is brought into the slow state.
[0105] [Voltage Recovery State]
[0106] Next, the control time chart shown in FIG. 12 will be
described, in which the voltage recovers.
[0107] As shown in the figure, at Point g, the voltage (IG voltage)
of the power supply BAT is less than 9.5V but is more than 8V.
Therefore, the variable gear ratio steering device has been stopped
in the slow state. And as mentioned above, the assist steering
torque of the electric power steering apparatus is corresponding to
the voltage of the power supply BAT. The VGS warning lamp WL1 and
the EPS warning lamp WL2 remain on, and the air conditioner remains
stopped. In other words, a life extension or recovery of the power
supply BAT is being performed.
[0108] As a result of the life extension performance, decrement of
the voltage stops at Point h, and at the same time, recovery or
increment of the voltage starts. At the section between Point h and
Point i, because the voltage is less than 9.68V that is the
recovery voltage K0, the life extension remains performed. However,
the assist steering torque generated by the electric power steering
apparatus increases in accordance with the increased voltage.
[0109] At Point i, the voltage reaches to the recovery voltage K0,
viz. 9.68V. However, the normal state is not determined at Point i.
At Point j, the voltage is over 9.68V continuously for more than
0.5 seconds (viz. recovery fixed). Then, the normal state is
determined by the comparison/selection section 76C of the target
current value setting means 76, and the comparison/selection
section 76C outputs a low voltage signal LV2 at L level. Therefore,
the electric power steering apparatus generates a normal assist
steering torque, and the EPS warning lamp WL2 is off, and further
the air conditioner is restarted. The driver is assisted by the
normal assist steering torque, and the vehicle is air-conditioned
(A/C recovered). The assist steering torque substantially recovers
to the normal value (referring to correction coefficient C of FIG.
10) after the voltage is over 9.5V that is the certain voltage
K1.
[0110] Meanwhile, the variable gear ratio steering device remains
in the slow state even if the voltage of the power supply BAT is
over 9.68V continuously for 0.5 seconds. The VGS warning lamp WL1
remains on. The variable gear ratio steering device is operated in
a usual manner with the VGS warning lamp W11 turned off, such as
when the voltage of the power supply BAT is over 9.5V after turning
off and then on the ignition switch. In this occasion, the
comparison/selection section 71C of the target eccentricity amount
setting means 71 outputs a normal low voltage signal LV1 at L
level.
[0111] As mentioned above, because the assist steering torque of
the electric power steering apparatus is increased when the voltage
recovers, the driver does not experience any uncomfortable feel.
Further, the variable gear ratio steering device is kept in the
slow state even if the voltage of the power supply BAT recovers, so
as to prepare for an unstable state after the recovery. This is for
making the variable gear ratio steering device stop merely in the
slow state even if the voltage decreases again. Moreover, the
recovery of the voltage is promoted.
[0112] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof. For example, the assist steering torque of the electric
power steering apparatus may be decreasingly corrected by way of
fade-out control means of the electric power steering apparatus
disclosed in the applicant's Japanese patent application No. Hei
10-377614 (unpublished). Further, decreasing correction of the
assist steering torque is not always necessary. Means for bringing
the variable gear ratio steering device into the slow state is not
limited to the specific embodiments mentioned above. It is also
possible to compulsively stop the supply to the power supply of the
electric power steering apparatus when the voltage decreases to the
lower limit voltage or less.
* * * * *