Note: Descriptions are shown in the official language in which they were submitted.
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POWER STE~RING DEVICE
This invention relates to a power steering (or assisting)
device of an energy saving type, by which s-teering assis-tance
can be changed in response to rotating speed of an engine or
vehicle speed.
In general, it is well known that, preferably, in a
power steering device, supply of power fluid to a power cylinder
(actuator) is increased to effect steering assistance to a
steering wheel at a stopping state or a lower speed running
state of a vehicle, while the supply of the power fluid is
decreased to reduce the steering assistance to the steering
wheel at a higher speed running state to thereby elevate
running stability.
Heretofore, in order to obtain the above characteristic
in a power steering device, there has been provided a power
steering device as disclosed in Japanese Patent Publication
No. 54-9774, said device using an electromagnetic clutch for
driving and controlling an oil pump which discharges the po~er
fluid by utilizing the rotation of engine so that, in notice
that a larger rotating angle of a steering wheel is required
at the stopping state or the lower speed running state, the
electromagnetic clutch is operated to assist steering when
the rotating angle of the steering wheel exceeds a predetermined
value~ However, in such a conventional device, since the
degree of power steering is determined ~y the rotating angle
o~ the steering wheel, the steering assistance is suddenly
applied in the proximity of the predetermined rotating angle
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and this unstable state therefore may invite a dangerous
condition.
Further, as disclosed in Japanese Patent Publication
No. 54-111707, there has been provided a power steering device
in which the supply of the power fluid from an oil pump to a
power cylinder is controlled by an electromagnetic by-pass
valve or is adjusted by a flow adjusting valve in response to
a running state of a vehicle. However, the power steering
device of this type spends much energy and cannot meet the
needs of the energy saving times because, at a higher speed
running state of the vehicle, most of the power fluid dis-
charged from an oil pump which rotates continuously at higher
speed in proportional to rotating speed of an engine is
successibly returned to an oil tank without working in effect.
Recently, a measure to save energy shows a -tendency to
decrease the number of rotation of an engine at an idling
state and to raise the maximum rotating speed area so as to
miniaturize and lighten in weight the engine. However, in a
conventional oil pump discharging power fluid in response to
rotating speed of an engine, there are disadvantages that
steering power fails at a stopping state or an extremely low
speed state, nevertheless the steering power is sufficiently
required, and if an amount of power fluid discharged from the
pump is increased at a lower speed state then the discharging
amount is increased in excess and the consumptlon of energy
becomes large.
The present invention provides an improved power
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steerlng device by which the above-mentioned disadvantages
can be overcome.
It is, therefore, an object of the present invention
to provide a power steering device oE an energy saving type.
Another object of the present invention is to provide
a power steering device in which the number of rotation of
an oil pump can be changed in response to vehicle speed and
a steering angle of a-steering wheel to thereby change steering
power.
These and other objects and advantages of the present
invention will be appear more clearly from the following
detailed disclosure read in conjunction with the accompanying
drawings.
Fig. 1 is a diagramatic view of a preferred embodim nt
of the power steering device of -the present invention;
Figs. 2 and 3 are character.Lstic curves showing a
relationship between the vehicle speed and the number of
rotation of the oil pump of the preferred embodiment as shown
in Fig. l; and
Fig. 4 is a characteristic curve showing a relationship
between the number of rotation and the discharging amount of
the oil pump in comparison between the present invention and
a prior artO
Fig. 1 shows a preferred embodiment of a power steering
device of the present invention~ A steering wheel 1 is coupled
through a control valve 2 and a s-teering gear 3 to an actuator
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4, and the actuator 4 and a communicating valve 5 are connected
through the control valve 2 to an oil pump 6 by means of lines
A and s. The control valve 2 controls an amount and a flow
direction of power fluid which is discharged from the oil
pump 6 to the actuator 4 in response to steering operation of
the steering wheel 1. The communicating valve 5 acts to
close a by-pass path between the supply lines A and B of the
actuator 4 when a valve member of the valve is actuated by
the power fluid in a pilot line C which transmits oil pressure
applied by the rotation of the oil pump 6, thereby effecting
a power steering state, while the valve 5 acts to open the
by-pass path between -the supply lines A and B when the oil
pump 6 stops or the rotation thereof is in an extremely low
speed state, thereby losing the steering power and effecting
a manual steering state. A rotating shaft of an engine 7 is
~oupled to the oil pump 6 through an electromagnetic clutch
8 having a linear transmission characteristic.
Provided on the steering wheel 1 is also a steering
sensor 9 which comprises, for example, a small-sized d.c.
generator and outputs an electric signal in accordance with
the steering operation of the steering wheel 1. An engine
rotation sensor 10 provided on the engine 7 detects, for
example, an ignitlon pulse or converts into an analog
signal by inteyrating the pulse to output an electric signal
corresponding to the number of rotation of the engine. Also,
a speed sensor 12 detects the number of rotation of a wire
cable of a speed meter coupled to a transmission gear 11 and
outputs electric siynals corresponding to vehicle speed.
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An electronic control circuit (not shown) receives
output signals from an operating device 13, that is, the
respective output signals from the steering sensor 9, the
~ engine xotation sensor 10 and the speed sensor 12 and, when
the steering wheel 1 is operated and the output signal from
the steering sensor 9 therefore is received, amplifies an AND
amount of the output signal from the engine rotation sensor
10 and the output signal from the speed sensor 12 to apply
the amplified AND signal to the electromagnetic clutch 8.
Accordingly, a vehicle speed responsible characteristic is
added to the electromagnetic clutch 8 having the linear trans-
mission characteristic, whereby when the vehicle is stopped
an exciting current of a solenoid coil of the electromagnetic
clutch 8 comes to a maximum value to transmit the rotation of
the engine 7 to the oil pu~lp 6 without sliding and when the
vehicle speed is increased the exci.ting current is decreased
to increase the sliding. Thus~ the magnetic field generated
by means of the solenoid coil of the electromagnetic clutch 8
is controlled to change electrically the degree of the sliding
transmission 50 that the steering power can be obtained in
response to the vehicle speed. Although, in the preferred
embodiment, the electromagnetic clutch 8 is operated the '
detected signal from the steering sensor 9 only at the steer-
ing in accordance with the preset transmitting amount -to
thereby drive the oil pump 6, it is possible that the electro-
magnetic clutch 8 is continuously operated by the detected
signals from both the speed sensor 12 and the engine rotation
sensor 10 over a preset variable area of the transmitting
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amount so as to drive the oil pump 6. Also, it is easily
effected that the electromagnetic clutch 8 is operated in
accordance wi~h a variable transmitting amount on the basis
of the detected signal from the engine rotation sensor lO to
control the discharging amount o the oil pump 6. Further,
although the preferred embodiment provides a communicating
valve 5 to by-pass both chambers of the actuator 4 and to
reduce oil path resistance of the steering at a non-assisting
state when the oil pump 6 is stopped or rotated at the
extremely low speed, the communicating valve may be removed
from the oil lines in view of slight increase in the steering
torque at the manual steering state when the oil pump 6 does
not discharge the power fluid and mechanical strength of the
control valve 2 (torsion bar). Preferably, a powder clutch,
a hysteresis clutch and the like are available for the electro-
magnetic clutch having the linear transmission characteristic,
the former using magnetic powder so that, in an excited condi-
tion, torque is transmitted by mutually attracting force of
the magnetic powder and frictional force ~etween the powder
and a transmitting surface of the clutch, and the latter being
such that non-contact coupling is magnetically accomplished
without using mechanically frictional force.
Fig. 2 shows a vehicle speed-rotation of pump character-
istic of the power steering device of the present invention
and, in the drawing, _ denotes a fixed rotation characteristic
of the oil pump, a2 denotes an attenuating rotation character-
istic of the oil pump, b denotes a vehicle speed responsible
linear attenuating rotation characteristic, and D denotes an
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operating point of the communicating valve. Further, Fig. 3
shows a vehicle speed-rotation of pump characteristic illus-
trating an energy saving effect of the power steering device
of the present invention and, in the drawing, c'l denotes an
oil pump rotating characteristic at the steering, c`7. denotes
an oil pump stopping characteristic at the non-steering, and
~3 denotes a warming-up, an extremely low-speed, rotating
characteristic of the oil pump at the non-steering. According
to Fig. 3, it is apparent that the supply of the powex fluid
from the oil pump is reduced or stopped when the power steering
is not required. Also, the communicating valve is operated
at a higher speed point D' to by-pass the both chambers of the
actuator to cause a manual steering state.
Fig. 4 shows a dischaxging amount-rotation characteristic
lS of the oil pump to compare a discharging characteristic of
. the oil pump of the present inventi.on with a discharging
characteristic of the oil pump as used in the conventional
power steering device in which the supply of the power fluid
from the oil pump to the power cylinder is adjusted by the
flow adjusting valve in accordance with the running state of
the vehicle and, in the drawing, dl denotes an apparent
discharging characteristic of the oil pump, d2 denotes a
general discharging characteristic of the oil pump to which
a vehicle speed responsible characteristic is not added (under
this condition, disused discharging oil is returned to the
tank by means of the flow adjusting valve) and e denotes-a
discharging characteristic of the oil pump of the presen-t
invention. Accordingly/ in Fig. 4, ~rea I is an invalid
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discharging area and, according to the present invention, if
the electromagne~ic clutch having the linear transmission
characteristic is operated in the proximity of a point P
. then the oil pump can be effectively operated in ~rea II,
that is, a valid discharging area.
Although, in the preferred embodiment as shown in Fig.
l, the electromagnetic clutch 8 is porvided to be directly
coupled to the oil pump 6, even if an oil pump having smaller
size, light weight a.nd a smaller discharging amount is used,
it is possible to provide a transmission means for increasing
the rotating speed of the oil pump between the clutch and the
oil pump to thereby obtain desired steering power at an idling
state of the engine or a lower speed running state.
As described above, the present invention, in contrast
with an ON-OFF control, can provide the variable steering
assistance in accordance with the preset vehicle speed and
this, therefore, does not give an operator unstable feeling
at the steering. Also, according to the present invention,
. the changing between the power steering state and the manual
steering state can be smoothly effected by the operation of
the communicating valve, thereby stabilizing the operation of
the steering wheel.
