Fluid pressure circuit

A fluid pressure circuit is provided in which two independent systems are provided with a pressure generator for supplying pressure through each of the circuits so as to operate the brake system of a vehicle in an antiskid mode. The fluid pressure circuits have a phase difference of a half a period with respect to each other so as to provide for a continuous pressure to each of the brake systems of the independent fluid pressure systems. By providing such an arrangement, pulsation effects of each independent system are reduced without adversely influencing the pressure generator apparatus and while decreasing the noise associated with the operation of the fluid pressure system under such operating conditions.

BACKGROUND OF INVENTION 
The present invention relates to a fluid pressure circuit provided with a 
pressure generator, and particularly to a fluid pressure circuit, which 
includes two independent systems provided with a pressure generator for 
supplying pressure to each of circuits, respectively. 
Conventionally, a fluid pressure circuit of such type was disclosed in 
Patent Laid-Open Publication No. 53-43180. This circuit is provided with a 
reduction chamber on the ejecting or output side of a pressure generator. 
The chamber is stiff with respect to the pressure as it is a metal member 
having a cross-sectional surface larger than that of a conduit of the 
fluid pressure circuit, thereby absorbing/reducing the ejecting or output 
pulsation of the pressure generator due to the elasticity of the operating 
fluid in said chamber. Therefore, this type of circuit has promoted the 
reduction of the roar sound or noise associated with operation of the 
circuit and the advancement of the pedal feel (the relief of the shock 
applied to the brake pedal) when the circuit is used in the antiskid 
apparatus. 
However, this apparatus as described above reduces the ejecting or output 
pulsation of the pressure generator according to the operating fluid in 
the reduction chamber. As a result, a problem has arisen in that the 
elasticity of the operating fluid in the reduction chamber is changed 
according to the absolute pressure of the fluid pressure and a sufficient 
reduction effect cannot be obtained as it requires a volume larger than 
the known predetermined volume utilized in this field, which would require 
the size of such circuits to be increased. 
Accordingly, an object of the present invention is to provide a fluid 
pressure circuit which can obtain the predetermined reduction effect 
independent upon the change of the fluid pressure from the pressure 
generator. 
SUMMARY OF THE INVENTION 
The present invention is provided with fluid pressure circuits 
corresponding to two systems which are independent to each other. A 
pressure generator supplies the fluid pressure to each of the fluid 
pressure circuits which have a phase difference of a half period to each 
other. A body is provided with has an inner hole for allowing each of the 
passages on the ejecting side of said pressure generator to be 
communicated with each other. A piston is provided in a fluid-tight manner 
into the inner hole of each body to partition or form a pari of damper 
chambers which open and close the inlet and the outlet of each of passages 
on the ejecting side of each of the pressure generators and an orifice is 
open to the outlet of the ejecting side passages of each of the pressure 
generators. 
According to the present invention as described above, the ejecting or 
output pulsation of one system is transmitted/absorbed through the piston 
to the passage of the ejecting or output side in the other system having a 
phase difference of a half period as the piston is moved according to the 
pressure difference between both damper chambers in the passage of the 
ejecting or output side on the other system having a phase difference of a 
half period. Therefore, the pulsation of each output side can be reduced 
by half without influencing the fluid pressure of the inhalating or 
incoming fluid from the pressure generator to decrease the noise 
associated with operation of the fluid pressure circuit. 
Also, fluid pressure circuits of the present invention are connected to 
each conduit for coupling the brake master cylinder and the antiskid 
actuator through the check valve. The outlet of the passage on the 
ejecting side of the pressure generator allows the fluid to flow only into 
the conduit passage, while the passage of each of inhalating or inlet 
sides of the pressure generators is connected to the reservoir which can 
receive the predetermined amount of the operating fluid, thereby advancing 
the pedal feel by reducing the ejecting pulsation when the circuit is 
utilized with the antiskid actuator.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
One embodiment of the fluid pressure circuit according to the present 
invention will be explained below. 
FIG. 1 and FIG. 2 illustrate an example of one embodiment of the fluid 
pressure circuit of the present invention to the direct controlled 
antiskid control apparatus of the discharge type. In FIG. 1, brake master 
cylinder 10 (below referred to as the master cylinder) is operated by 
means of brake pedal 11. The front pressure chamber of master cylinders 10 
is connected through first conduit passage 13 to brake wheel cylinder 
(below refereed to as the wheel cylinder) 19, 20 of one system, supply 
switchable valves 23, 24 and second conduit passages. The rear pressure 
chamber of master cylinder 10 is connected to wheel cylinders 21, 22 of 
the other system though first conduit passage 16, supply switchable valves 
25, 26 and second conduit passages 17, 18. Each of second conduit passages 
17, 18 is connected through each of discharge switchable valves 29, 30, 
respectively, to reservoir 32 which can receive a predetermined amount of 
the operating fluid. 
Supply switchable valves 23-26 are the electromagnetic actuated 
opening/closing valve type having two ports-two positions which forces 
first conduit passage 13, 16 connected to master cylinder 10 and second 
conduit 14, 15 connected to master cylinder 10 to be communicated with 
each other when deenergized and also interrupts the communication of the 
same conduit passage when energized. Also, discharge switchable valves 
27-30 are of the electromagnetic actuated opening/closing valve type 
having two ports and two positions and interrupts the communication 
between each of second conduit passages and reservoirs 31, 32 when 
deenergized, as well as allows communication between each of second 
conduit passages and reservoirs 31, 32 when energized. The switching 
operation of both of the switchable valves 23-26, 27-30 (deenergization, 
energization) is controlled by control unit 33, so that these valves are 
deenergized together when the brake operation of the vehicle is not 
required, and also when the antiskid apparatus is controlled, the 
denenergization and the energization of these valves is repeated by means 
of control unit 33 in response to the detecting signal from each of speed 
sensors 34-37 for detecting the locking state of each of the car wheels. 
Only, first conduit passage 13 and each of second conduit passages 14, 15 
are connected to each other through check valves 69, 70 bypassing each of 
supply switchable valves 23, 24. First conduit passage 16 and each of 
second conduit passages 17, 18 are connected to each other through check 
valves 71, 72 bypassing each of supply switchable valves 25, 26. Each of 
check valves 69-72 is a one direction valve allowing the fluid to flow 
from second conduit passages into first conduit passages, so that the 
return of the operating fluid during the removal of the brake operation is 
advanced. 
Each reservoir 31, 32 is provided with a piston and spring arrangement, so 
that it can receive the operating fluid discharged through each of 
discharge switchable valves 31-30 therein. Each of the reservoirs 31, 32 
is respectively connected to passages 38a, 39a of the inhalating or intake 
side of fluid pressure pumps 38, 39. Each fluid pressure pump 38, 39 is a 
plunger pump having opposite movement with respect to each other, and is 
operated by means of one electrical power motor 40. The fluid pressure 
pumps 28, 39 and electrical power motor 40 comprise the pressure generator 
of the present invention. Electrical power motor 40 is configured so as to 
be controlled by means of control unit 33 to be simultaneously operated by 
initiating the opening/closing control of each of switchable valves 23-26 
and 27-30. 
Each of the passages 38a, 39a on the ejecting or output side of each of the 
fluid pressure pumps 38, 39 is connected to a reduction apparatus 41 of 
the present invention. In this embodiment, reduction apparatus 41 is shown 
in FIG. 2 and is comprised of a body 42 having inner hole or opening 42a 
for allowing each of the passages 38a, 39a on the ejecting side of each of 
fluid pressure pumps 38, 39 to be communicated with each other. A floating 
piston 45 is received fluid-tightly into inner hole 42a of each of bodies 
42 to partition/form a pair of damper chambers 43, and 44, opening inlets 
38b1, 39b1 and outlets 38b2, 39b2 for each ejecting side passages 38b, 
39b. Springs 46, 47 are mounted elastically in each of the damper chambers 
43, 44 so as to be faced against each other through floating piston 45. 
Orifices 48, 49 are open to outlets 38b2, 39b2 of each ejecting side 
passages 38b, 39b. Floating piston 45 is provided with a pair of land 
portions 45a, 45b and an O ring 52 fixedly disposed between each of the 
land portions 45a, 45b, both sides of which are narrowed between backup 
rings 50, 51, thereby maintaining fluid tightness between both of the 
damper chambers 43, 44. Also, outlets 38b2, 39b2 of each of ejecting side 
passages 38b, 39b is respectively connected through orifices 48, 49 to 
each of the first conduit passages 13, 16. Check valves 55, 56 for 
allowing the fluid to flow into only first conduit passages 13, 16 are 
disposed in each of outlets 38b2, 39b2. EAch check valve 55, 56 comprises 
seat members 57, 58 inserted fluid-tightly into holes or openings which 
are respectively perforated in body 42 in the middle of each of the 
outlets 38b2, 39b2. Balls 59, 60 are positioned on the seat surface of the 
opening side on first conduit passages 13, 16 which are formed in each of 
the seat members 57, 58. Springs 63, 64 in contact at one end with plugs 
61, 62, are inserted into the openings formed in body 42 in the middle of 
each of the outlets 38b2, 39b2, to apply an elastic force in the direction 
for urging seating of each of the balls 59, 60 on the seat surface. Cup 
type members 67, 68 are inserted into the passage formed by seat members 
57, 58. Orifices 48, 49 are formed in each of the cup type members 67, 68. 
Reference numbers 59, 54 denote plugs inserted fluid-tightly into the 
opening of both ends of hole or opening 42a in body 42, and reference 
numbers 65, 66 are O rings inserted into a circular groove formed around 
the periphery of seat members 57, 58. Proportional valves 77, 78 mounted 
in the middle of each of second conduit passages 15, 18. 
In operation, brake pedal 11 is depressed to generate the fluid pressure in 
both of the pressure chambers of master cylinder 10. Since each of the 
switchable valves is kept at the position of deenergization as shown in 
FIG. 1, the fluid pressure in master cylinder 10 is applied to wheel 
cylinders 19-22 through each of first conduit passages 13, 16, each of 
supply switchable valves 23-26 and each of second conduit passages 14-18, 
thereby performing the braking of each of the vehicle wheels. 
When the wheel axle is braked as described above during movement of the 
vehicle at a predetermined speed, if the control unit 33 detects the state 
of incipient lock of the wheel 73 on the basis of the detected signal from 
speed sensor 34 of the vehicle, supply switchable valve 23 and discharge 
switchable valve 27 are energized to reduce the fluid pressure of wheel 
cylinder 19 as well as electrical power motor 40 is energized to operate 
fluid pressure pumps 38, 39. If the fluid pressure of wheel cylinder 19 is 
reduced so as to permit the restoration of the original rotation speed of 
wheel 73 based on the detecting signal from speed sensor 34 of the 
vehicle, each of the switchable valves 23, 27 is deenergized, and the 
ejecting or output pressure from fluid pressure pump 38 is applied with 
the fluid pressure from master cylinder 10 to wheel cylinder 19, so that 
the fluid pressure in wheel cylinder 19 is increased, or discharge 
switchable valve 27 is deenergized to retain the fluid pressure in wheel 
cylinder 19. 
In this manner, responsive to the signal from speed sensor 34 of the 
vehicle, each switchable valve 23, 27 are repeatedly energized or 
deenergized to reduce or increase and maintain the fluid pressure in the 
wheel cylinder, with the result that lock-up of the wheel is accurately 
prevented. Also, this embodiment is illustrating the antiskid control when 
wheel 73 is reached at the state of incipient lock-up, but the 
energization and deenergization of each of the switchable valves is 
controlled in the same manner with respect to the other wheel according to 
the signal representative of wheel speed. 
Fluid pressure pumps 38, 39 of the opposed plunger type has a phase 
difference of a half period is operated during the antiskid control, and 
the ejecting or outlet pressure from each of fluid pressure pumps 38, 39 
is applied through reduction apparatus 41 to first conduit passages 13, 
16. The characteristic of ejecting or outlet pressure Pa, Pb in each of 
fluid pressure pumps 38, 39 is represented by the solid line as shown in 
FIG. 3. That is to say, when the plunger of fluid pressure pump 38 moves 
to the discharge stroke, the plunger of fluid pressure pump 39 moves to 
the intake stroke. If reduction apparatus 41 is not installed therein, the 
characteristics of the ejecting pressure are represented by the dotted 
line as drawn in FIG. 3 and pulsations having a pulsation width of P 
occur, respectively. According to the present invention, that is, when 
fluid pressure pump 38 is in the ejecting or discharge stroke and fluid 
pressure pump 39 is in the inhalating or inlet stroke, floating piston 45 
in FIG. 2 is moved leftwardly in response to the pressure difference 
between both of the damper chambers 43 and 44 to increase the volume of 
damper chamber 43 and transmits the fluid pressure of fluid pressure pump 
38 to fluid pressure pump 39 as well as transferring the operating fluid 
ejected or discharged from fluid pressure pump 38 to fluid pressure pump 
39 alternately repeated per half period as the floating piston 45 is moved 
so as to provide continuous output. Accordingly, the ejecting pressure is 
smoothly represented as shown in FIG. 3 and the pulsation pressure P is 
slightly reduced by half. As a result, the roar sound or noise level 
created by the ejecting pulsation of the fluid pressure pump can be 
reduced, and the undesirable shock of brake pedal 11 due to the pulsation 
can be relieved to increase the pedal feel. Also, the pulsation width and 
the fluid amount transferred/absorbed from one of the fluid pressure pumps 
during discharge to the other fluid pressure pump during intake can be 
changed if the diameter of each of springs 46, 47 and each of orifice 48, 
49 and the diameter of floating piston 45 is properly selected. Also this 
embodiment illustrates an example of an antiskid control apparatus which 
is directly controlled such as the discharge type, but the present 
invention can be used in various antiskid control apparatus by properly 
selecting the switchable valve. 
FIG. 4 represents a modified example of the pressure reduction apparatus of 
the present invention. This embodiment is configured so that inner hole 
142a formed in body 142 of reduction apparatus 41 is in the form of the 
step having large diameter portion 142al and small diameter portion 142a2, 
each of land portions 145a, 145b of floating piston 145 is guided into 
small diameter portions 142a2, each of damper chambers 143, 144 is formed 
in large diameter portions 142a1 respectively, retainers 79, 80 engaged 
with the step of inner hole 142a by means of springs 146, 147 being 
elastically mounted in each of damper chambers 143, 144 are respectively 
contacted with land portions 145a, 145b of floating pistons 145, and 
floating piston 145 is moved, when the predetermined pressure difference 
overcoming the load of springs 146, 147 is generated between damper 
chambers 143 and 144. Except for it, other configuration and acting are 
same as those of FIG. 2, and then their detail explanation are omitted 
herein. Only, the part members same as those of FIG. 2 have the reference 
adding 100 to the reference used in FIG. 2. 
While a preferred embodiment of the present invention has been described, 
the present invention should not be limited to the configuration of the 
embodiments and obviously variations and modifications may not be properly 
allowed without the appended claim. 
According to the present invention, as the piston is moved by the pressure 
difference between both of damper chambers, the ejecting pulsation of one 
system is transmitted/absorbed through the piston to the passage of the 
ejecting side in the other system having the phase difference of the half 
period. Therefore, each of the ejecting pulsation can be reduced by half 
without influencing on the fluid pressure of the operating fluid from the 
pressure generator and the roar sound of the circuit can be decreased. 
Also, according to the present invention, the ejecting pulsation can be 
reduced to advance the pedal feeling. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing application. The invention 
which is intended to be protected herein should not, however, be construed 
as limited to the particular forms disclosed, as these are to be regarded 
as illustrative rather than restrictive. Variations and changes may be 
made by those skilled in the art without departing from the spirit of the 
present invention. Accordingly, the foregoing detailed description should 
be considered exemplary in nature and not limited to the scope and spirit 
of the invention as set forth in the appended claims.