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FIELD OF THE INVENTION
The present invention relates to a power steering apparatus which depends
on DC power as an energy source for generating an auxiliary steering
force; and more specifically, the present invention relates to
motor-driven power steering apparatus which is profitable for a passenger
car using a DC motor as an actuator for generating an auxiliary steering
force.
BACKGROUND OF THE INVENTION
A conventional power steering apparatus comprises a motor for generating an
auxiliary steering force, a control apparatus for regulating current of
the motor corresponding to the steering force, and a battery as a current
source, for instance, as disclosed on FIG. 1 of Japanese Patent Laid-Open
No. 59-156863 (1984), published on Sept. 6, 1984, and entitled "Power
Steering Apparatus of Automobile".
The apparatus of the prior art uses a standard battery which is used in the
automobile as a current power source for all electric devices thereof.
However, the standard battery does not have the function of providing an
output corresponding to the current value of the load of the automobile.
On the other hand, a generator for charging batteries which has two
armature windings connected in star connection, respectively, for
generating two similar voltages is disclosed in FIG. 3 of the U.S. Pat.
No. 4,045,718, entitled "Multiple Winding Multiple Voltage Alternator
Electrical Supply System". However, the prior art discloses that the
connection of these windings to the load is not carried out, respectively,
and these two windings are the same in electrical structure.
In the conventional power steering apparatus sufficient consideration is
not given to the large current consumption of the motor for generating an
auxiliary steering force and the affect thereof an other electrical
systems in the vehicle. Especially, the conventional power steering
apparatus has a drawback in that the illumination provided by the
headlights of the automobile is reduced and the electrical devices mounted
on the vehicle, such as lights, wiper, and air-conditioner, etc. are
undesirably influenced by the steering of the wheel at night when the
automobile stops or while the engine is idling.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a motor-driven power
steering apparatus which can operate properly without exerting a bad
influence upon other electrical devices which use the same battery in the
automobile.
The object of the present invention is attained in such a manner that two
different DC voltages are output from a generator driver by the engine
which is equipped for charging at least one battery, one DC voltage from
the generator being supplied to the power steering, while the other DC
voltage therefrom is supplied to a battery used for other electrical
devices mounted on the automobile.
According to the present invention, since separate DC voltages are supplied
from different electric power systems to the power steering system and to
the other devices in the electrical system, respectively, the other
electrical devices are not affected by the operation of the power steering
apparatus. And further, since the supplied voltage to the power steering
system can be increased without being affected by other electrical
apparatuses mounted on the automobile, the operation of the power steering
system can be reliable.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the first embodiment of the present invention;
FIG. 2 shows a sectional view of the generator applied to the present
invention;
FIG. 3 is a circuit diagram of the generator shown in FIG. 2;
FIG. 4 shows the second embodiment of the present invention;
FIG. 5 shows the third embodiment of the present invention;
FIG. 6 is a circuit diagram of the third embodiment shown in FIG. 5;
FIG. 7 is a diagram for explaining the operation of the circuit shown in
FIG. 6 when a predetermined voltage is obtained from the generator by
rotation of the engine;
FIG. 8 is a diagram for explaining the operation of the circuit shown in
FIG. 6 when the engine stops; and
FIG. 9 shows the 4th embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a steering shaft 1A, which is rotatable freely by the
steering wheel 1, is connected to a gear box 4 of a gear rack 5 through an
universal joint 2. The rotating force of the steering shaft 1A is
transmitted to the gear rack 50 through the gear box having a pinion gear
(not shown) which is rotated by the universal joint 2.
A torque detector 3 is mounted on the gear box 4 for detecting the torque
of the steering shaft 1A. The detected output of the torque detector 3 is
input to a controller 10.
A tie rod 7 is connected to the respective ends of the gear rack 5. The
steering of the wheel 8 takes place by the operation of the gear rack 5
and the tie rod 7, as is well known.
A gear box 6 of the gear rack 5 is connected to a motor 11 through a
reducer 20. The motor 11 is driven by a control signal of the controller
10.
A pulley 14 is fixed on the rotational axis of the engine 13. A pulley 16
is fixed on the rotational axis of a generator 17. A belt 15 is suspended
between the pulley 14 and the pulley 16. The generator 17 has first output
terminals 21 and the second output terminals 22. Batteries 9 and 18 are
connected to these output terminals 21 and 22, respectively. The
controller 10 is connected to the output terminals of the battery 9. Most
other electrical loads 12 of the vehicle are connected to the output
terminals of the battery 18.
When the steering wheel 1 is operated, the torque detector 3 detects the
torque of the steering shaft 1A to input a detecting signal to the
controller 10. The motor 11 is driven by a control signal from the
controller 10, and gives the auxiliary steering force to overcome the road
surface friction generated between the wheel 8 and the road surface.
Referring to FIG. 2, the generator 17 outputs a first DC output voltage A
of a comparatively low voltage for charging the battery 18 of 12 volts and
supplying electric power to the various kinds of loads 12, and a second DC
output voltage B of a comparatively high voltage (48 volts) for driving
the motor 7 of the power steering system. The generator comprises two sets
of armature windings 112 and 113 and two sets of rectifiers (diodes) 115
and 117. Other than that, the generator is almost the same as a standard
generated (called an AC dynamo). The pulley 16 is connected to the shaft
101 which is suspended by two sets of bearings 107. The rotor is formed by
the iron core 102 of rundle configuration and the field winding 103 is
mounted on the shaft 101.
The field winding 103 is connected to the outside through a slip ring 104
and a brush 105. A predetermined exciting current is supplied from a
voltage regulator (not shown). As a result, a three-phase AC voltage is
generated by the armature windings 112 and 113 when the engine 13 is
driven. The three-phase AC voltage is supplied to the rectifiers 115 and
117 through lead wires 114 and 116. First and second DC voltages are
generated at the terminals A.sub.1 and A.sub.2 of the rectifier 117 and
the terminals B.sub.1 and B.sub.2 of the rectifier 115, respectively. In
FIG. 2, 106 denotes a brush holder, 109 and 110 brackets, and 111 armature
iron.
Referring to FIGS. 2 and 3, two sets of armature windings are arranged
independently in electrical structure, and the field winding 103 is
arranged in common to supply flux to two sets of armature windings 112 and
113.
In the embodiment shown in FIG. 1, the battery 9 constitutes the first
voltage supplier, and the battery 18 constitutes the second voltage
supplier.
When a driver operates the steering wheel 1, the steering shaft 1A is
driven rotatably. The torque caused by the rotational movement of the
steering shaft 1A is detected by the torque detector 3. The detected
signal is input to the controller 10 from the torque detector 3. The
controller 10 inputs the electric power of the battery 9 and supplied it
to the motor 11 at a level corresponding to the detected signal, and the
motor 11 supplies an auxiliary steering force corresponding to the
detected signal. Since the general load 12, such as the lights, the
ignition system, etc. is connected to the battery 18, for instance, the
intensity of illumination of the head lights is not decreased by the
operation of the motor-driven power steering apparatus. Accordingly, the
safe operation of the automobile is not affected by the operation of the
motor-driven power steering apparatus when the automobile is running at
night or through a tunnel.
Since the voltage of the first output terminals 21 is set at a high voltage
level, current flowing through a semiconductor element of the power
steering apparatus connected to the first output terminal 21 can be
reduced so that the semiconductor element can be miniaturized and the cost
of manufacture thereof can be reduced. The battery 9 as the voltage
supplier is able to connect to the power steering apparatus by changing
the specification of the armature winding (turn and diameter of winding)
of the generator 17, so that the size of the apparatus does not become
large and the cost of producing the apparatus can be reduced.
Referring to FIG. 4, a condenser 120 is used in the embodiment as the first
voltage supplier instead of the battery 9 used in the embodiment of FIG.
1. In the embodiment shown in FIG. 4, the condenser 120 has the effect of
absorbing the noise caused by switching of the semiconductor element of
the controller 10. Other structure, operation and effect of the embodiment
shown in FIG. 4 is same to that of FIG. 1.
According to the embodiments shown in FIGS. 1 and 4, the power source to
other electric parts is not changed; for instance, the intensity of the
illumination of the head lights is not reduced by the operation of the
motor-driven power steering apparatus. And also, the motor-driven power
steering apparatus can be supplied in small size and low manufacturing
cost.
FIG. 5 shows one embodiment of the present invention applied to a rack and
pinion system. Referring to FIG. 5, 1 denotes the steering wheel, 23 a
steering shaft, 24 a middle shaft, 25 a pinion, 7 a rack shaft, 5 a
steering gear box, 11 a DC motor in high voltage specification as an
actuator for generating an auxiliary steering force, 20 a reducer, 26 a
pinion for the auxiliary steering force, 20 a reducer, 26 a pinion for the
auxiliary steering force, 10 a torque detector, 10-1 a chopper controller,
12 electrical devices mounted on the vehicle (load), 13 an engine, 14 and
15 pulleys, 15 a belt, 17 a generator for charging a battery, 18 a battery
10-2 a chopper, and 27 a diode.
When the steering is carried out by turning the steering wheel 1, the gear
rack 5 held slidably within the steering gear box 4 is moved through the
pinion 25 along the axial direction of the gear rack, and a torque is
applied to the steering shaft 23, the torque is detected by the torque
detector 3, and a signal is generated corresponding to the torque. The
signals from the torque detector and a steering angle sensor (not shown)
are input to the chopper controller 10-1, which outputs a control signal
to the chopper 10-2 to generate a predetermined torque by controlling the
power supplied to the motor 11. The torque is applied to the gear rack 5
through the reducer 20, the pinion 26 and gear box 6. Thereby, an
auxiliary steering force is generated in the motor-driven power steering
apparatus.
FIG. 6 is a circuit diagram of a motor-driven power steering apparatus
forming one embodiment of the present invention. Referring to FIG. 6, the
chopper 10-2, which is shown as a switching transistor therein, is
connected to the motor 11 in series and is connected directly to the DC
output (high voltage) of the rectifier 115, which is powered from
generator 17 through the lead wire 114. A flywheel diode 28 is connected
across motor 11. On the other hand, the DC output (low voltage), which is
obtained as an output of the rectifier 117 from the armature winding 113
of the generator 17 through the lead wire 116, is connected to the battery
18 and the load 12 in parallel to supply electrical power to them, and
also is connected to the DC output from rectifier 115 through the diode 27
of the blocking inverse current type. Although a control circuit is
necessary for changing over the rotational direction of the motor 11
reciprocally, the control circuit is not shown in FIG. 6.
The power supply source for driving the motor which generates the auxiliary
power steering force, is changed over automatically depending on the
running or stopping of the generator 17 for generating a predetermined
electric power, since the diode 27 is provided in the embodiment shown in
FIG. 7. Hereunder, we will explain the operation of the circuit shown in
FIG. 6 referring to FIGS. 7 and 8.
Referring to FIG. 7, the generator 17 generates the voltage V.sub.B =48
volts via rectifier 115 and the voltage V.sub.A =12 volts via rectifier
117 with the revolution of the engine 13. The diode 27 is turned OFF by
reverse biasing. The rectifier 115 supplies the voltage V.sub.B to the
motor 11. The chopper 10-2 is operated by the control signal from the
chopper controller 10-1 so that the motor 11 is supplied with a
predetermined current I.sub.1, to provide a predetermined auxiliary
steering force. At this time, since the voltage specification of the motor
11 48 volts, the current I.sub.1 for generating a required auxiliary
steering force is reduced to 1/4 compared with a conventional motor which
is excited by 12 volts.
Referring to FIG. 8, the output of rectifier 115 and the output of
rectifier 117 are zero, since the generator 17 is not driven by the engine
13. Therefore, the voltage V.sub.A is 12 volts as a result of the battery
18. At this time, the diode 27 is caused to be forwarded biased. When the
chopper 10-2 is operated by the chopper controller 10-1 the electric power
I.sub.2 is supplied to the motor 11 from the battery 18 so that the motor
11 generates a torque to supply an auxiliary steering force. At this time,
the motor 11, which has a voltage specification of 48 volts, is driven by
the voltage of 12 volts supplied from the battery 18 so that the response
speed of the motor is insufficient. However, the magnitude of the current
I.sub.2 can be maintained equivalently to an approximate same value by
changing the duty ratio of the current flowing through the chopper
provided as transistor 10-2. Consequently, the same auxiliary steering
force can be obtained in case of FIG. 8 as provided in the case of FIG. 7.
At this time, there is no problem with the generator 17, since reverse
current to the generator 17 is blocked by the rectifiers 115 and 117, as
well known.
In the embodiment, the output voltage of the generator 17 is selected to be
12 volts at the first DC output and 48 volts at the second DC output,
respectively. A transistor is used as the chopper in the described
embodiment; however, a gate turn-off transistor, a thyristor, or field
effect transistor (FET), etc. can be used instead. Also, the DC motor 11
is used as an auxiliary steering force generating actuator. However, the
invention is not limited to use of the DC motor. For instance, an AC motor
such as induction motor, a brushless type motor (synchronous motor) of a
DC motor, or other motors can be used instead. Of course, any other DC
motors can be employed without respect to their magnetic field types.
FIG. 9 shows one embodiment of the present invention in which a brushless
DC motor is employed as an actuator for generating an auxiliary steering
force. In FIG. 9, the same parts as in FIG. 6 are indicated by the same
reference symbols. The difference between FIG. 9 and the previous
embodiment in FIG. 6 is that the second DC output B, namely an output of
high voltage, is connected to the synchronous brushless DC motor 11
through an invertor 50; and common earth wires of the inverse current
blocking diode 27 and the high and low voltage rectifiers are equipped
between the invertor 50 and the rectifier 115.
In the embodiment shown in FIG. 9, the chopper can be omitted, and the
brushless DC motor can be operated by the high voltage rectifier 115
during running of the engine and by the battery 18 when the engine is not
running. Incidentally, the motor 11 can be an induction motor, instead.
In the embodiments, the motor of the motor-driven power steering is
connected as a high voltage load. The present invention is not limited
thereto. For instance, when an ignition system is connected to the high
voltage rectifier 115, it can resolve a drawback that the voltage of the
ignition device is not increased based on a short ignition duration when
an automobile is running at a high speed. Further, when all of the general
motors, such as the car cooler motor, are connected to the high voltage
side of the generator, the motor current can be reduced.
According to the embodiments shown in FIGS. 5 and 9, the chopping
transistor and the motor can be driven by high voltage when the engine is
running, and the current flowing through the motor can be reduced in
proportion to the magnitude of a reciprocal of a ratio of the high voltage
to the low voltage of the generator 17. Since the general load and the
control apparatus are driven by the low voltage battery which is equipped
separately from the high voltage battery used for the motor-driven power
steering, the intensity of the light is not reduced when the automobile is
driven at night.
Since the apparatus shown in FIG. 9 does not need the build-up chopper
shown in FIG. 6, it has a long durability and becomes a compact system.
According to the embodiments shown in FIGS. 6 and 9, since the motor-driven
power steering motor can be driven by low current when the engine is not
running, the power steering can be driven when the automobile is
transported by a wrecker truck in the event of an engine failure.
In the embodiments of FIGS. 1, 4 and 5, the present invention is applied to
the motor-driven power steering apparatus. However, the present invention
also can be applied to a motor-driven oil pressure type power steering
apparatus.
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