Hydraulic pressure source device for hydraulic booster of automobile

A hydraulic pressure source device for supplying an actuating hydraulic pressure to an automotive booster, having an accumulator and a hydraulic pump, the pump being interposed in a low-pressure oil passage leading from the control valve of a hydraulic power steering device to an oil tank. In the oil passage is also interposed an electromagnetic valve which is adapted to be opened and closed under control of an intermittent actuator which intermittently energizes the electromagnetic valve when sensing a pressure in the accumulator below a preset level. The pump is actuated by the hydraulic oil which is discharged into the low-pressure oil passage after having actuated the control valve through intermittent opening and closing operation of the electromagnetic valve to replenish the accumulator with the hydraulic pressure. A restrictor may be disposed in the low-pressure oil passage to release the hydraulic oil to an oil tank when the electromagnetic valve is closed, so as to establish a pressure difference between the low-pressure oil passage and a high-pressure oil passage connecting between the control valve and a main hydraulic pump.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to hydraulic pressure source device for a 
hydraulic booster which is employed to actuate, for example, an automotive 
brake by means of boosted oil pressure. 
2. Description of Prior Art 
A conventional hydraulic pressure source device for a hydraulic booster has 
heretofore been arranged such that hydraulic pump which employs an engine 
as its drive source and an accumulator which is connected to the discharge 
side of the pump are connected to an oil supply passage which connects an 
input hydraulic chamber of the booster and an oil tank. 
In these days, many types of automobiles are equipped with a hydraulic 
power steering device. Such a power steering device has as its hydraulic 
pressure source a hydraulic pump which is actuated by an engine. If this 
automobile is equipped with a hydraulic booster of the type described 
above, it is necessary for a hydraulic pump for the power steering device 
and a hydraulic pump for the booster to be connected to the engine through 
respective transmission gears. It is therefore necessary to provide two 
transmission gears, which disadvantageously involves an increase in cost 
as well as increased losses of the engine power. 
SUMMARY OF THE INVENTION 
The present invention is proposed in view of the above-described fact and 
has as its primary object the provision of a hydraulic pressure source 
device of the above-described type wherein an auxiliary hydraulic pump for 
the hydraulic booster is actuated by means of oil pressure discharged from 
a control valve associated with a power steering device which is driven by 
the automotive engine, thereby overcoming the above-described 
disadvantages of the prior art. 
To this end, according to a first aspect of the invention, there is 
provided a hydraulic pressure source device for a hydraulic booster of an 
automobile including a hydraulic power steering device provided with a 
control valve, the control valve of the power steering device being 
connected via a high-pressure oil passage to a main hydraulic pump driven 
by an engine, 
the hydraulic pressure source device comprising: 
an auxiliary hydraulic pump having a working chamber and a pump chamber, 
the working chamber communicating with a low-pressure oil passage which 
connects the control valve with an oil tank, the pump chamber being 
adapted to perform repeated suction and discharge strokes in response to 
intermittent supply of an oil pressure to the working chamber; 
a suction valve connecting the pump chamber to the oil tank; 
a discharge valve connecting the pump chamber to an input hydraulic 
pressure chamber of a hydraulic booster; 
a accumulator connected to a downstream side of the discharge valve; 
an electromagnetic valve interposed in the low-pressure oil passage at a 
position downstream of the auxiliary hydraulic pump for opening and 
closing the low-pressure oil passage; and 
an intermittent actuator connected to the electromagnetic valve to actuate 
the valve so as to be periodically opened and closed when a pressure 
within the accumulator goes down below a predetermined value. 
According to a second aspect of the present invention, there is provided, 
additionally to the above arrangement, with a restrictor which is adapted 
to allow the low-pressure oil passage to be conductive even when the 
electromagnetic valve is closed. 
When the internal pressure in the accumulator goes below a specified value, 
the intermittent actuator causes the electromagnetic valve to be 
periodically opened and closed. When the valve is closed, the outlet 
pressure of the control valve of the power steering device rises, thus 
causing the auxiliary hydraulic pump to effect a discharge operation. On 
the other hand, when the electromagnetic valve is opened, the outlet 
pressure of the control valve lowers, and the auxiliary hydraulic pump 
consequently performs a suction operation. 
The pressure of oil which is discharged from the auxiliary hydraulic pump 
as the result of the repetition of such operations of this pump is stored 
in the accumulator and employed to actuate the hydraulic booster. 
The restrictor which operates to make the low-pressure oil passage 
conductive allows proper discharge of the working oil from the control 
valve even when the electromagnetic valve is closed so as to prevent 
disappearance of a difference in pressure between the high- and 
low-pressure oil passages.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described hereunder with 
reference to the accompanying drawings. 
FIG. 1 shows a first embodiment of the invention, in which are illustrated 
a tandem type master cylinder M for a dual type hydraulic brake of an 
automobile and hydraulic booster B adapted to actuate the master cylinder 
M by means of boosted hydraulic pressure. 
In FIG. 1, the master cylinder M includes a cylinder body 1 having an oil 
tank 2 formed on an upper side of the body. The inside of the tank 2 is 
divided at a lower-half part thereof by a partition wall 2a into a front 
oil reservoir 2.sub.1 and a rear oil reservoir 2.sub.2. These oil 
reservoirs 2.sub.1 and 2.sub.2 communicate with a cylinder bore 1a formed 
in the cylinder body 1 through respective front relief ports 3.sub.1, 
3.sub.2 and respective rear supply ports 4.sub.1, 4.sub.2. The cylinder 
bore 1a has a front piston 7.sub.1 and a rear piston 7.sub.2 slidably 
received therein. 
In the cylinder bore 1a, a front hydraulic pressure chamber 8.sub.1 is 
defined between the front piston 7.sub.1 and the front end wall of the 
bore 1a, and a rear hydraulic pressure chamber 8.sub.2 between both the 
pistons 7.sub.1 and 7.sub.2. These hydraulic pressure chambers 8.sub.1 and 
8.sub.2 respectively communicate with hydraulic circuits of the dual type 
hydraulic brake through output ports, not shown. The pistons 7.sub.1 and 
7.sub.2 are mounted with piston cups 9.sub.1 and 9.sub.2 disposed at their 
front ends respectively. The pistons 7.sub.1 and 7.sub.2 have their 
intermediate portions reduced in diameter to form annular oil replenishing 
chambers 10.sub.1 and 10.sub.2 on their outer peripheries. The oil 
chambers 10.sub.1 and 10.sub.2 respectively communicate with the back 
portions of the piston cups 9.sub.1 and 9.sub.2 via through-holes 11.sub.1 
and 11.sub.2 which are provided at the respective front end portions of 
the pistons 7.sub.1 and 7.sub.2. 
In the front hydraulic pressure chamber 8.sub.1 is housed a front return 
spring 12.sub.1 which biases the front piston 7.sub.1 in its retracting 
direction, while in the rear hydraulic pressure chamber 8.sub.2 is 
disposed a rear return spring 12.sub.2 which biases the rear piston 
7.sub.2 in its retracting direction and a distance maintaining device 14 
which limits stretching of the spring 12.sub.2 within a predetermined 
range. The distance maintaining device 14 comprises a pair of movable and 
fixed (front and rear) seat members 15 and 16 which respectively retain 
both ends of the rear return spring 12.sub.2, and a support shaft 17 which 
is mounted on the rear piston 7.sub.2 and slidably carries the movable 
seat member 15. The support shaft 17 has an expanded head portion 17a 
which serves to limit the forward movement of the movable seat member 15. 
Accordingly, the support shaft 17 allows the movable seat member 15 to 
approach the rear piston 7.sub.2 but by means of its expanded head portion 
17a prevents the movable seat member 15 from separating from the rear 
piston 7.sub.2 by more than a predetermined distance, thereby regulating 
the maximum distance between the movable seat member 15 and the rear 
piston 7.sub.2, and this regulation provides a limitation to the 
stretching of the return spring 12.sub.2. 
A booster cylinder 20 of the hydraulic booster B is continuously formed 
with the rear part of the cylinder body 1 of the master cylinder M. The 
booster cylinder 20 comprises a smaller-diameter cylinder 20a which is 
formed integrally with the cylinder body 1 so as to project from the rear 
end of the body, and a larger-diameter cylinder 20b which is secured to 
the rear end of the cylinder body 1 by bolts 21 and extends rearwardly of 
the smaller-diameter cylinder 20a while covering the same. A cylinder bore 
22b of the larger-diameter cylinder 20b is made larger in diameter than a 
cylinder bore 22a of the smaller-diameter cylinder 20a and is disposed 
rearwardly of the latter. 
The booster cylinder 20 has a booster piston 23 slidably received therein. 
The extremity of the rearward movement of the booster piston 23 is limited 
by the rear end wall of the larger-diameter cylinder 20a. The booster 
piston 23 has a smaller-diameter portion 23a slidably received in the 
front cylinder bore 22a and a larger-diameter portion 23b slidably 
received in the rear cylinder bore 22b. The inside of the rear cylinder 
bore 22b is divided by the larger-diameter portion 23b into a front input 
hydraulic pressure chamber 24 and a rear output hydraulic pressure chamber 
25. The output hydraulic pressure chamber 25 is, as a matter of course, 
larger than the input hydraulic pressure chamber 24 in terms of 
pressure-receiving area. The hydraulic pressure source device S according 
to the present invention is connected to the input hydraulic pressure 
chamber 24. 
The booster piston 23 has an inlet valve 29 and an outlet valve 30 disposed 
side by side. 
The inlet valve 29 is of normally-closed type and comprises: a tubular 
valve chamber 32 formed axially of the booster piston 23 at an 
intermediate portion of an oil passage 31 which provides communication 
between the input and output hydraulic pressure chambers 24 and 25; a 
spherical valve body 33 adapted to open and close the oil passage 31 in 
cooperation with a valve seat which is formed on the rear end wall of the 
valve chamber 32; a valve spring 34 disposed within the valve chamber 32 
so as to bias the valve body 33 in its closing direction; and an actuator 
rod 35 capable of moving the valve body 33 in its opening direction 
against the force of the valve spring 34. The actuator rod 35 is fitted in 
the booster piston 23 in a manner slidable in the axial direction of the 
piston 23, the rear end portion of the rod 35 projecting into the output 
hydraulic pressure chamber 25. 
The outlet valve 30 comprises a valve cylinder 36 which is fitted in the 
piston 23 so as to extend axially of the piston 23, and a valve piston 38 
which is slidably received in an inner bore, that is, a valve bore 37, of 
the valve cylinder 36. The rear end portion of the valve piston 38 extends 
oil-tightly through the rear end wall of the booster cylinder 20 and is 
connected to a brake pedal 40 through a push rod 39. The valve cylinder 36 
has an outlet port 41 communicating with the output hydraulic pressure 
chamber 25, while the valve piston 38 has an annular groove 42 which comes 
in and out of communication with the outlet port 41 in response to the 
forward and rearward movements of the valve piston 38, and also has an oil 
passage 43 which communicates with the annular groove 42. The oil passage 
43 communicates with an oil chamber 45, defined in front of the booster 
piston 23, through an oil passage 44 which is formed in the booster piston 
23. Further, the oil chamber 45 communicates with the rear oil reservoir 
2.sub.2 in the oil tank 2 through an oil passage 46 which is formed in the 
cylinder body 1. The oil passage 46 also provides communication between 
the rear oil reservoir 2.sub.2 on one hand and the relief port 3.sub.2 and 
the supply port 4.sub.2 on the other. 
In the output hydraulic pressure chamber 25, an interlocking plate 47 is 
secured to the valve piston 38 by means of a pair of front and rear 
circlips 48. The interlocking plate 47 faces the rear end of the actuator 
rod 35 of the inlet valve 29 so as to push the rod 35 forwardly in 
response to the forward movement of the valve piston 38. The interlocking 
plate 47 further serves to limit the extremity of rearward movement of the 
valve piston 38 in cooperation with a stopper ring 49 which is attached to 
the booster piston 23. The interlocking plate 47 is biased in the 
direction to abut against the stopper ring 49 by means of the force of a 
return spring 50 compressed between the valve cylinder 36 and the plate 
47. 
The booster piston 23 is formed with a larger-diameter bore 51 which opens 
to the front of the booster piston 23, and a smaller-diameter bore 52 
which extends from the larger-diameter bore 51 to the valve bore 37. In 
the larger-diameter bore 51, an elastic piston 53 of rubber and a 
pressure-receiving piston 54 with the same diameter as that of the piston 
53 are slidably received in the mentioned order. On the other hand, the 
smaller-diameter bore 52 slidably receives a reaction piston 55 which is 
able to abut at both its ends against the respective surfaces of the valve 
piston 38 and the elastic piston 53. 
The pressure-receiving piston 54 has an output rod 56 projecting from its 
front side and abutting against the rear end of the rear piston 7.sub.2. 
In the above-described arrangement, the pressure-receiving piston 54, the 
elastic piston 53 and the reaction piston 55 constitute in combination a 
reaction mechanism 57 which transmits the reaction force as the result of 
the action of the master cylinder M to the piston 38. 
Thus, when the brake pedal 40 is in an inoperative state, the valve piston 
38, together with the interlocking plate 47, is, as illustrated, 
maintained at the extremity of the rearward movement thereof by means of 
the force of the return spring 50, and the annular groove 42 is placed at 
the position where it is in communication with the outlet port 41. The 
outlet valve 30 is therefore open. In the inlet valve 29, on the other 
hand, the actuator rod 35 is released from the interlocking plate 47, and 
the valve body 33 is caused to be seated on the valve seat of the valve 
chambers 32 by means of the force of the valve spring 34. For the reason, 
the inlet valve 29 is closed. Accordingly, the input and output hydraulic 
pressure chambers 24 and 25 are shut off from each other by the inlet 
valve 29, and the output hydraulic pressure chamber 25 is communicated 
with the oil tank 2 through the outlet port 41, the annular groove 42, the 
oil passages 43, 44, the oil chamber 45 and the oil passage 46 and is 
therefore under atmospheric pressure. In consequence, the front and rear 
pistons 7.sub.1, 7.sub.2 and the booster piston 23 are maintained at the 
extremities of their respective rearward movements by the urging force of 
the return springs 12.sub.1 and 12.sub.2. 
Further, in this case, the oil pressure accumulated in an accumulator 62, 
described later, of the hydraulic pressure source device S has been 
introduced into the input hydraulic pressure chamber 24 and acts on the 
front surface of the larger-diameter portion 23b of the booster piston 23, 
which also allows the booster piston 23 to be maintained at the extremity 
of its rearward movement. Further, since the spherical valve body 33 has a 
high valve closing ability, it is possible for it to reliably prevent any 
leakage of hydraulic oil from the input hydraulic pressure chamber 24 into 
the output hydraulic pressure chamber 25. 
As the brake pedal 40 is pressed for the purpose of braking the automobile, 
its depression causes the valve piston 38 and the interlocking plate 47 to 
be pushed forwardly through the push rod 39. Thereupon, the annular groove 
42 is first shut off from the outlet port 41, that is, the outlet valve 30 
is closed. Then, the interlocking plate 47 abuts against the rear end of 
the actuator rod 35 and pushes the same forwardly, whereby the valve body 
33 is separated from the valve seat, that is, the inlet valve 29 is 
opened. As a result, the output hydraulic pressure chamber 25 is out of 
communication with the oil tank 2, and the hydraulic pressure which has 
been introduced in the input hydraulic pressure chamber 24 is also 
introduced into the output oil hydraulic chamber 25 through the oil 
passage 31 and the valve chamber 32. In consequence, the booster piston 23 
which receives the hydraulic pressure at its rear surface is moved 
forwardly, thus causing the front and rear pistons 7.sub.1 and 7.sub.2 to 
move forwardly through the reaction mechanism 57 and the output rod 56 
while compressing their respective return springs 12.sub.1 and 12.sub.2. 
Then, after the piston cups 9.sub.1 and 9.sub.2 have respectively passed 
the relief ports 3.sub.1 and 3.sub.2, the pistons 7.sub.1 and 7.sub.2 
respectively cause hydraulic pressures to be produced in the hydraulic 
pressure chambers 8.sub.1 and 8.sub.2 in response to the respective 
forward movements of the pistons 7.sub.1 and 7.sub.2, thereby allowing the 
corresponding brake hydraulic circuits to be actuated. 
In the meantime, the pressure-receiving piston 54 receives from the rear 
piston 7.sub.2 the reaction force created by the action of the master 
cylinder M and is thereby actuated so as to compress the elastic piston 
53. A part of the compressing force is fed back to the valve piston 38 
through the reaction piston 55 and further to the brake pedal 40 through 
the push rod 39, whereby it is possible for the driver of the automobile 
to sense the magnitude of the braking force. 
The hydraulic pressure source device S according to the present invention 
will now be described. 
The device S comprises: a main hydraulic pump 60 of a hydraulic power 
steering device P; an auxiliary hydraulic pump 61 which is actuated by the 
main hydraulic pump 60; an accumulator 62 in which hydraulic pressure is 
accumulated by the operation of the auxiliary hydraulic pump 61; an 
electromagnetic valve 63 which controls the operation of the auxiliary 
hydraulic pump 61; and an intermittent actuator 69 which controls the 
electromagnetic valve 63. 
The main hydraulic pump 60 is actuated by an engine E through a 
transmission device 64 so as to feed the working oil pumped up from an oil 
tank 65 to a high-pressure oil passage 66h under pressure. The working oil 
fed to the high-pressure oil passage 66h is passed to a low-pressure oil 
passage 66l via a control valve 68 which is operated through a steering 
wheel 67 and then returns to the oil tank 65. When the control valve 68 is 
operated through the steering wheel 67, the hydraulic pressure in the 
high-pressure oil passage 66h is supplied to a power cylinder (not 
shown), whereby the power cylinder is actuated so as to assist the driver 
in operating the steering wheel 67. The power steering device P of the 
type described above is known. 
The auxiliary hydraulic pump 61 comprises a pump body 70 which has first 
and second cylinder bores 71 and 72 defined therein in series, and a 
piston assembly 76 which is composed of first and second pistons 73 and 74 
which are slidably received in the respective cylinder bores 71 and 72 and 
interconnected through a piston rod 75. In the first cylinder bore 71, the 
first piston 73 defines a working chamber 77 on its front side, while, in 
the second cylinder bore 72, the second piston 74 defines a pump chamber 
78 on its front side. In the pump chamber 78 is compressed a return spring 
79 in such a manner as to bias the piston assembly 76 toward the working 
chamber 77. 
The working chamber 77 is connected with the low-pressure oil passage 66l 
in such a manner that the working oil in the low-pressure oil passage 66l 
passes through the working chamber 77. On the other hand, the pump chamber 
78 is connected through a suction valve 82 with a suction oil passage 80 
which extends from the oil tank 2 of the master cylinder M or an 
independent oil tank. The pump chamber 78 is further connected through a 
discharge valve 83 with a dischage oil passage 81 which leads to the input 
hydraulic pressure chamber 24 of the hydraulic booster B. Further, the 
accumulator 62 is connected to the discharge oil passage 81. 
The electromagnetic valve 63 is interposed in the low-pressure oil passage 
66l on the downstream side of the auxiliary hydraulic pump 61. The valve 
63 is formed in a normally-open type valve which is closed when excited. 
The low-pressure oil passage 66l is further provided therein with a 
restrictor 90 which allows the oil passage 66l to be conductive even when 
the electromagnetic valve 63 is closed. The restrictor 90 may be provided 
integrally on the electromagnetic valve 63 itself in such a manner that 
the restrictor 90 communicates with the low-pressure oil passage 66l when 
the electromagnetic valve 63 is closed, as shown in FIG. 1. Alternatively, 
the restrictor 90 may be separately disposed in a by-pass passage 91 which 
is connected to the low-pressure oil passage 66l so as to by-pass the 
electromagnetic valve 63, as shown in FIG. 2. 
The intermittent actuator 69 is constituted by an oscillator 85 and a 
pressure-responsive switch 86. 
The oscillator 85 is interposed in an energization circuit 88 which 
connects a power source 87 to the solenoid of the electromagnetic valve 
63. The oscillator 85 is adapted to deliver periodical actuating pulses to 
the electromagnetic valve 83 during energization. 
To control the energization of the oscillator 85, the pressure-responsive 
switch 86 is inserted into the energization circuit 88, the switch 86 
being adapted to be closed when sensing that the internal pressure of the 
accumulator 62 goes below a specified value. 
The following is a description of the operation of the above-described 
embodiment. 
Assuming now that the internal pressure of the accumulator 62 goes below 
the specified value, the pressure-responsive switch 86 is closed. 
Thereupon the oscillator 85 is actuated to deliver periodical actuating 
pulses to the electromagnetic valve 63. In consequence, the 
electromagnetic valve 63 repeats opening and closing operations, thereby 
periodically opening and closing the low-pressure oil passage 66l. 
Thus, when the electromagnetic valve 63 is closed, the outlet pressure of 
the control valve 68 rises, and the pressure acts on the working chamber 
77 of the auxiliary hydraulic pump 61, thus causing the piston assembly 76 
to be pushed toward the pump chamber 78 against the force of the return 
spring 79. In consequence, the pump chamber 78 is pressurized. More 
specifically, the pump chamber 78 carries out a discharge stroke in which 
the working oil inside the pump chamber 78 is fed under pressure to the 
discharge oil passage 81 through the discharge valve 83. 
Even when the electromagnetic valve 63 is thus closed, the low-pressure oil 
passage 66l is maintained in a conductive state through the restrictor 90. 
Accordingly, discharge of the working oil from the control valve 68 to the 
oil tank 65 is permitted to a proper degree. As a result, there is no risk 
of disappearance of a differential pressure between the high- and 
low-pressure oil passages 66h and 66l. It is therefore possible to ensure 
a reliable operation of the power steering device P during a steering 
operation, and there is no large change in the operation feeling when the 
driver actuates the steering wheel 67. 
When the electromagnetic valve 63 is opened, the piston assembly 76 is 
pushed back in the auxiliary hydraulic pump 61 toward the working chamber 
77 by means of the force of the return spring 79. In consequence, the 
pressure in the pump chamber 78 is reduced. More specifically, the pump 
chamber 78 effects a suction stroke in which the oil stored in the oil 
tank 2 is sucked into the pump chamber 78 through the suction oil passage 
80. 
By virtue of such a pump operation of the auxiliary hydraulic pump 61, the 
hydraulic pressure for actuating the hydraulic booster B is accumulated in 
the accumulator 62. When the hydrualic pressure accumulated in the 
accumulator 62 exceeds a specified value, the pressure-responsive switch 
86 is opened, and the operation of the oscillator 85 is thereby suspended. 
In consequence, the electromagnetic valve 63 returns to its open state. 
As has been described above, according to the first aspect of the present 
invention, the control valve of the hydraulic power steering device is 
connected through the high-pressure oil passage to the main hydraulic pump 
which is actuated by the engine, and the working chamber of the auxiliary 
hydraulic pump is communicated with the low-pressure oil passage which 
connects the control valve and the oil tank. The auxiliary hydraulic pump 
has a pump chamber in which suction and discharge strokes are repeated 
when the working chamber is intermittently supplied with hydraulic 
pressure. The pump chamber is communicated with the oil tank through the 
suction valve and with the input hydraulic chamber through the discharge 
valve. The accumulator is connected to the downstream side of the 
discharge valve. Further, the electromagnetic valve is interposed in the 
low-pressure oil passage on the downstream side of the auxiliary hydraulic 
pump, the electromagnetic valve being adapted to open and close the 
low-pressure oil passage. The electromagnetic valve is connected with the 
intermittent actuator which causes the electromagnetic valve to be 
periodically opened and closed. By virtue of this arrangement, it is 
possible for the auxiliary hydraulic pump for the hydraulic booster to be 
actuated by means of the outlet oil pressure of the control valve of the 
power steering device. Accordingly, it is unnecessary for the auxiliary 
hydraulic pump to be provided with any transmission device for connecting 
the pump to the engine, which advantageously contributes to reduction in 
the cost and power losses. 
Further, according to the second aspect of the present invention, there is 
provided additionally to the above-described arrangement according to the 
first aspect of the invention with the restrictor which allows the 
low-pressure oil passage to be conductive even when the electromagnetic 
valve is closed. It is therefore possible to prevent disappearance of a 
differential pressure between the high- and low-pressure oil passages when 
the electromagnetic valve is closed. Thus, it is possible to suppress 
changes in the operation feeling when the driver actuates the power 
steering device.