Split type oil hydraulic piston pump and pressurized oil feed circuit making use of the same pump

The known swash plate type oil hydraulic piston pump is improved in that three delivery slots each extending over an angular distance of about 60.degree. are formed in a valve plate along one circumference concentric with a rotary cylinder block at an angular interval of 60.degree. and the number of piston-cylinder units provided in the cylinder block is chosen to be a multiple of 6. Pressurized oil delivered through a center delivery slot is fed to one hydraulic actuator, and pressurized oil delivered through the delivery slots on the opposite sides of the center delivery slot is jointly fed to the other hydraulic actuator, whereby variations of flow rates of the pressurized oil fed to the respective hydraulic actuators can be minimized. Preferably, in order to feed more pressurized oil to a more heavily loaded hydraulic actuator, additional delivery slots are formed in the valve plate at the boundary portions between the three main delivery slots, and pressurized oil delivered through these additional delivery slots is fed selectively to a more heavily loaded hydraulic actuator or, if the both actuators are equally loaded, to both the hydraulic actuator through a pressure-sensitive switching valve. More preferably, a pulsation damper is connected across the hydraulic circuits for feeding the pressurized oil to the respective hydraulic actuators.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a split type oil hydraulic piston pump and 
a pressurized oil feed circuit for feeding pressurized oil to two 
hydraulic actuators by making use of a split type oil hydraulic piston 
pump. 
2. Description of the Prior Art 
Heretofore, generally classifying the oil hydraulic piston pumps, axial 
type oil hydraulic piston pumps and radial type oil hydraulic pumps have 
been known, and as oil hydraulic piston pumps adapted for high-speed, 
high-pressure and variable-capacity operations the axial type oil 
hydraulic piston pumps have been commonly used. In these axial type oil 
hydraulic piston pumps is included a swash plate type piston pump which is 
also known as a KV pump. Among these swash plate type piston pumps, a 
piston pump constructed in such manner that a single pressurized oil 
suction slot and a plurality of pressurized oil delivery slots are formed 
in one valve plate that is slidably making contact with a single cylinder 
block provided with a plurality of pistons and pressured oil may be fed 
from these delivery slots to a plurality of hydraulic actuators, is known 
as a split type oil hydraulic pump. 
A difficulty associated with such a split type oil hydraulic pump in the 
prior art was generation of a large variation of a flow rate when the 
pistons deliver the pressurized oil to the respective delivery slots. In 
addition, when each piston passes through the valve plate portion between 
the plurality of delivery slots, the delivered oil is interrupted by the 
valve plate, resulting in generation of a large trapping pressure, and 
hence the oil delivered from the piston cannot be effectively and 
perfectly utilized. Furthermore, in the case where the pressurized oil is 
fed from the plurality of pressurized oil delivery slots to a plurality of 
hydraulic actuators, it is necessary to feed a larger amount of 
pressurized oil to a hydraulic actuator that is more heavily loaded. 
Moreover, the larger a load of a hydraulic actuator is, the more is 
generated oil leakage. 
SUMMARY OF THE INVENTION 
The present invention has been worked out in view of the above-mentioned 
status of the prior art, and a principal object of the present invention 
is to provide a split type oil hydraulic piston pump, in which a large 
variation of a flow rate would not be generated when the respective 
pistons deliver the pressurized oil to the respective delivery slots. 
Another object of the present invention is to provide a pressurized oil 
feed circuit system for use with a split type oil hydraulic piston pump, 
in which a larger amount of pressurized oil can be fed to a hydraulic 
actuator that is more heavily loaded. 
Still another object of the present invention is to provide a split type 
oil hydraulic piston pump, in which a trapped pressure produced when each 
piston passes through a valve plate portion between a plurality of 
delivery slots can be avoided as much as possible and moreover the oil 
delivered from each piston can be effectively utilized to the maximum 
extent, and a pressurized oil feed circuit system making use of the same 
pump. 
Yet another object of the present invention is to provide a pressurized oil 
feed circuit system making use of a split type oil hydraulic piston pump, 
which system can prevent an oil flow rate fed to a hydraulic actuator from 
increasing abruptly. 
In order to achieve the aforementioned various objects of the invention, 
according to a first aspect of the present invention, there is provided a 
split type oil hydraulic piston pump including a plurality of 
piston-cylinder units disposed within a single cylinder block along one 
circumference at an equal angular interval and in parallel to each other 
and a valve plate disposed on the pressurized oil suction/delivery side of 
these piston-cylinder units so as to make slidable contact with the 
above-mentioned cylinder block and having a single suction slot and a 
plurality of delivery slots, in which the plurality of delivery slots are 
disposed along the above-mentioned one circumference as spaced by an 
angular interval of 60.degree. from each other, and the plurality of 
piston-cylinder units are provided as many as a multiple of 6. 
According to a second aspect of the present invention, there is provided a 
split type oil hydraulic piston pump according to the above-mentioned 
first aspect of the invention, in which the valve plate is further 
provided with outlet slots serving as additional delivery slots between 
adjacent delivery slots among the plurality of delivery slots. 
According to a third aspect of the present invention, there is provided a 
pressurized oil feed circuit system making use of a split type oil 
hydraulic piston pump for connecting first and second hydraulic actuators 
with a split type oil hydraulic piston pump including a plurality of 
piston-cylinder units disposed within a single cylinder block along one 
circumference at an equal angular interval and in parallel to each other 
and a valve plate disposed on the pressurized oil suction/delivery side of 
the piston-cylinder units so as to make slidable contact with the 
above-mentioned cylinder block and having a single suction slot and first, 
second and third delivery slots disposed along the above-mentioned one 
circumference as spaced by an angular interval of 60.degree. from each 
other, the plurality of piston-cylinder units being provided as many as a 
multiple of 6, which system comprises a first circuit for connecting the 
above-mentioned first and third delivery slots jointly to the 
above-mentioned first hydraulic actuator and a second circuit for 
connecting the above-mentioned second delivery slot to the above-mentioned 
second hydraulic actuator. 
According to a fourth aspect of the present invention, there is provided a 
pressurized oil feed circuit system making use of a split type oil 
hydraulic piston pump for connecting first and second hydraulic actuators 
with a split type oil hydraulic piston pump including a plurality of 
piston-cylinder units disposed within a single cylinder block along one 
circumference at an equal angular interval and in parallel to each other 
and a valve plate disposed on the pressurized oil suction/delivery side of 
the piston-cylinder units so as to make slidable contact with the 
above-mentioned cylinder block and having a single suction slot and first, 
second and third delivery slots disposed along the above-mentioned one 
circumference as spaced by an angular interval of 60.degree. from each 
other, the plurality of piston-cylinder units being provided as many as a 
multiple of 6, which system comprises a first circuit for connecting the 
above-mentioned first and third delivery slots jointly to the 
above-mentioned first hydraulic actuator, a second circuit for connecting 
the above-mentioned second delivery slot to the above-mentioned second 
actuator, and first and second outlet slots formed in the valve plate 
between the above-mentioned first and second delivery slots and between 
the above-mentioned second and third delivery slots, respectively, said 
first and second outlet slots being jointly and selectively connected to 
either one having a higher pressure of the above-mentioned first and 
second circuits or to both the first and second circuits if they have an 
equal pressure, via one switching valve. 
According to a fifth aspect of the present invention, there is provided a 
pressurized oil feed circuit system according to the above-mentioned 
fourth aspect of the invention, in which the circuit for connecting the 
above-mentioned first and second outlet slots to the above-mentioned 
switching valve is provided with check valve means. 
According to a sixth aspect of the present invention, there is provided a 
pressurized oil feed circuit system according to the above-mentioned 
fourth or fifth aspect of the invention, which system comprises a 
pulsation damper connected between the most downstream ends of the 
aforementioned first and second circuits for feeding pressurized oil to 
the above-mentioned first and second hydraulic actuators, respectively. 
The above and many other advantages, features and additional objects of the 
present invention will become manifest to those versed in the art upon 
making reference to the following detailed description and accompanying 
drawings in which preferred structural embodiments incorporating the 
principles of the present invention are shown by way of illustrative 
example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
At first, a first embodiment of a split type oil hydraulic piston pump 
according to the present invention and a first embodiment of a pressurized 
oil feed circuit to be used jointly with the split type oil hydraulic 
piston pump will be described with reference to FIGS. 1 and 2. 
Reference numeral 1 designates a cylinder block adapted to be rotated 
jointly with a rotary shaft 6. In this cylinder block 1 are formed a 
plurality of cylinder bores 2 as arrayed along a concentric circumference 
at an equal angular interval and in parallel to each other, pistons 3 are 
respectively fitted in these cylinder bores 2 so as to make slidable 
contact with the bore inner surfaces to form respective cylinder chambers 
4, and the respective pistons 3 are coupled to a swash plate 5. In 
addition, between the cylinder block 1 and a valve body 7 is disposed a 
valve plate 8, and in this valve plate 8 are formed a suction slot 9 
extending nearly over a semi-circumference and first, second and third 
delivery slots 10.sub.1, 10.sub.2 and 10.sub.3 as aligned along the same 
circumference. On the other hand, in the valve body 7 are formed a suction 
port 11 opening to the suction slot 9, a first delivery port 12.sub.1 
opening to the first delivery slot 10.sub.1, a second delivery port 
12.sub.2 opening to the second delivery slot 10.sub.2 and a third delivery 
port 12.sub.3 opening to the third delivery slot 10.sub.3. The first 
delivery port 12.sub.1 and the third delivery port 12.sub.3 are jointly 
connected to a first hydraulic actuator A.sub.1 through a first circuit 
L.sub.1, and the second delivery port 12.sub.2 is connected to a second 
hydraulic actuator A.sub.2 through a second circuit L.sub.2. The first, 
second and third delivery slots 10.sub.1, 10.sub.2 and 10.sub.3 are formed 
so as to be arrayed along one circumference having its center at a center 
O of the valve plate 8 as spaced by an angular interval of 60.degree. from 
each other, and the number of the pistons 3 is equal to a multiple of 6 
(6, 12, 18, . . . ). As a result of the above-mentioned arrangement, a 
variation of a flow rate of pressurized oil fed to each hydraulic actuator 
by the pistons 3 can be reduced. The reason for the reduction of the flow 
rate variation will be explained in the following. 
Since a theoretical instantaneous delivery rate per one piston 3 depicts a 
sine curve as shown in FIG. 3, in order to equalize a sum of delivery 
amounts Q.sub.1 and Q.sub.3 per one cycle of the first and third delivery 
slots 10.sub.1 and 10.sub.3 to a delivery amount Q.sub.2 per one cycle of 
the second delivery slot 10.sub.2, it is only necessary to form the first 
delivery slot 10.sub.1 over the range of 180.degree. to 240.degree., the 
second delivery slot 10.sub.2 over the range of 240.degree. to 300.degree. 
and the third delivery slot 10.sub.3 over the range of 300.degree. to 
360.degree., and hence the first, second and third delivery slots 
10.sub.1, 10.sub.2 and 10.sub.3 could be formed in the valve plate 8 along 
one circumference as spaced by an angular interval of 60.degree. from each 
other. 
In the above-described split type oil hydraulic piston pump, variations of 
instantaneous flow rates through the second delivery slot 10.sub.2 and 
through the first and third delivery slots 10.sub.1 and 10.sub.3 in 
combination when the number of the pistons 3 is smaller than 6 and when 
the number of the pistons 3 is equal to 6, respectively, are shown by the 
graphs in FIGS. 4 and 5, in which in the case where the number of the 
pistons 3 is smaller than 6, slits s and peaks p are generated in the flow 
rate waveforms, resulting in a large variation of a flow rate (FIG. 4), 
but when the number of the pistons 3 is selected to be 6, the slits s and 
peaks p in the flow rate waveforms become extremely small and hence a flow 
rate variation can be reduced (FIG. 5). 
More particularly, when the number of the pistons 3 is selected to be 6, 
the variations of the theoretical instantaneous delivery rates for the 
respective ones of the successive pistons 3 as shown in FIG. 3 would 
appear as delayed by a phase angle of 360.degree./6=60.degree. 
successively so as to deliver the pressurized oil by the amounts per one 
cycle of Q.sub.1, Q.sub.2 and Q.sub.3, respectively, through the first, 
second and third delivery slots 10.sub.1, 10.sub.2 and 10.sub.3, and hence 
the slits s and peaks p in the resultant flow rate waveforms would become 
small as shown in FIG. 5, whereas when the number of the piston 3 is 
smaller than 6, the variations of the theoretical instantaneous delivery 
rates for the respective ones of the successive pistons as shown in FIG. 3 
would appear as delayed by a phase angle larger than 60.degree. 
successively so as to deliver the pressurized oil by the amounts per one 
cycle of Q.sub.1, Q.sub.2 and Q.sub.3, respectively, through the first, 
second and third delivery slots 10.sub.1, 10.sub.2 and 10.sub.3, and so, 
the slits s and peaks p in the resultant flow rate waveforms would become 
large as shown in FIG. 4. In addition, when the number of the pistons 3 is 
chosen to be larger than 6 and smaller than 12, and when it is chosen to 
be equal to 12, the resultant delivery flow rates through the second 
delivery slot 10.sub.2 and through the first and third delivery slots 
10.sub.1 and 10.sub.3 in combination, respectively, are shown by the 
graphs in FIGS. 6 and 7, in which it is observed that when the number of 
the pistons 3 is larger than 6 and smaller than 12, the slits s and peaks 
p in the resultant flow rate waveforms would become large similarly to the 
above-mentioned case where the number of the pistons 3 is smaller than 6, 
and when it is chosen to be 12, the slits s and peaks p would become 
smaller than the above-mentioned case where it is chosen to be 6. If the 
number of the pistons 3 is selected to be 18, then the slits s and peaks p 
in the resultant flow rate waveforms would become further small. However, 
when the number of the pistons 3 is increased up to 18, the overall size 
of the piston pump would become large, and yet the effect obtained by 
increasing the number of the pistons so large, is small. Therefore, the 
number of 12 is most preferable. 
Subsequently, another embodiment of the abovedescribed valve plate 8 and 
the pressurized oil feed circuit will be described with reference to FIG. 
8. 
As shown in FIG. 8, in addition to the first, second and third delivery 
slots 10.sub.1, 10.sub.2 and 10.sub.3, the valve plate 8 is provided with 
first and second outlet slots 20.sub.1 and 20.sub.2 serving similarly to 
the delivery slots, between the first and second delivery slots 10.sub.1 
and 10.sub.2 and between the second and third delivery slots 10.sub.2 and 
10.sub.3, respectively. The locations where these first and second outlet 
slots 20.sub.1 and 20.sub.2 are provided, correspond to the positions 
where a trapping pressure is produced by the piston 3 in the case of the 
above-described first embodiment, and in terms of the rotational phase 
angle of the cylinder block the locations correspond to the points of 
240.degree. and 300.degree. as viewed in FIG. 3. In a pressurized oil feed 
circuit for first and second hydraulic actuators A.sub.1 and A.sub.2 to be 
connected to this valve plate 8 according to the second embodiment, as 
shown in FIG. 8, a first delivery port 12.sub.1 opening to the first 
delivery slot 10.sub.1 and a third delivery port 12.sub.3 opening to the 
third delivery slot 10.sub.3 are connected via a first circuit L.sub.1 to 
the first hydraulic actuator A.sub.1, a second delivery port 12.sub.2 
opening to the second delivery slot 10.sub.2 is connected via a second 
circuit L.sub.2 to the second hydraulic actuator A.sub.2, a first outlet 
port 22.sub.1 opening to the above-mentioned first outlet slot 20.sub.1 
and a second outlet port 22.sub.2 opening to the above-mentioned second 
outlet slot 20.sub.2 are connected via check valves 13.sub.1 and 13.sub.2, 
respectively, to an inlet port 23 of a switching valve V, and further led 
to two outlet ports 24.sub.1 and 24.sub.2 of the switching valve V via 
chokes 14.sub.1 and 14.sub.2 provided within the switching valve V when 
the switching valve V takes a neutral position or to either one of the two 
outlet ports 24.sub.1 and 24.sub.2 when the switching valve V is actuated 
in either direction, and thus eventually, the first and second outlet 
slots 20.sub.1 and 20.sub.2 are jointly and selectively connected to 
either one or both of the above-mentioned first and second circuits 
L.sub.1 and L.sub.2. 
The above-described switching valve V is normally held, by resilient forces 
of associated biasing springs, at a first position I for feeding 
pressurized oil delivered from the first and second outlet ports 22.sub.1 
and 22.sub.2 to the first and second circuits L.sub.1 and L.sub.2 through 
the chokes 14.sub.1 and 14.sub.2, respectively. However, in the event that 
the oil pressure in the first circuit L.sub.1 is higher than the oil 
pressure in the second circuit L.sub.2, the switching valve V occupies a 
second position II for feeding pressurized oil delivered from the first 
and second outlet ports 22.sub.1 and 22.sub.2 to the first circuit 
L.sub.1, while in the event that the oil pressure in the second circuit 
L.sub.2 is higher than the oil pressure in the first circuit L.sub.1, the 
switching valve V occupies a third position III for feeding pressurized 
oil delivered from the first and second outlet ports 22.sub.1 and 22.sub.2 
to the second circuit L.sub.2. 
Since the pressurized oil feed circuit system shown in FIG. 8 is 
constructed in the above-described manner, the circuit L.sub.1 or L.sub.2 
on the side of the hydraulic actuator A.sub.1 or A.sub.2 that is more 
heavily loaded is additionally fed with pressurized oil delivered from the 
first and second outlet ports 22.sub.1 and 22.sub.2, and thereby the 
pressurized oil can be fed at a larger flow rate to the hydraulic actuator 
that is more heavily loaded. Therefore, the hydraulic actuator that is 
more heavily loaded, can be operated at a high speed and at a high 
pressure, and also leakage of pressurized oil in the more heavily loaded 
hydraulic actuator can be compensated. It is to be noted that in the case 
where the oil pressures in the first and second circuits L.sub.1 and 
L.sub.2 are equal to each other, the switching valve V is held at the 
first position I, where it feeds the pressurized oil delivered from the 
first and second outlet ports 22.sub.1 and 22.sub.2 to the first and 
second circuits L.sub.1 and L.sub.2 via the chokes 14.sub.1 and 14.sub.2, 
respectively, at equal flow rates. 
Moreover, according to the construction of the above-described second 
embodiment, pressurized oil trapped at the valve plate portions between 
the delivery slots in the split type piston pump can be fed through the 
first and second outlet slots 20.sub.1 and 20.sub.2 to either one having a 
higher pressure or both of the first and second circuits L.sub.1 and 
L.sub.2. Accordingly it becomes possible to reduce the trapping pressure, 
and hence it is possible to obviate the disadvantages of the split type 
oil hydraulic piston pump in the prior art that the output pressure is 
lowered and the power loss caused by leakage of pressurized oil is 
increased. 
Here it is to be noted that the aperture area A.sub.s of the outlet slots 
20.sub.1 and 20.sub.2 is determined in the following manner. Since the 
theoretical instantaneous delivery rate per one piston produced as a 
result of rotation of the cylinder block 1 would vary as shown in FIG. 3 
as described above, it will be readily seen that the oil flow rate through 
the outlet slots 20.sub.1 and 20.sub.2 disposed at the positions of 
rotational phase angles of 240.degree. and 300.degree. is 0.866 times as 
large as the maximum delivery flow rate per one piston. Accordingly, it is 
preferable to select the aperture area A.sub.s of the outlet slots 
20.sub.1 and 20.sub.2 to be 0.866 times as large as the outlet aperture 
area A.sub.p of the cylinder chamber 4. 
A third embodiment of the above-described pressurized oil feed circuit is 
illustrated in FIG. 9. According to this embodiment, a pulsation damper 25 
is provided across the first and second circuits L.sub.1 and L.sub.2 as 
connected to the downstream of the respective circuits on the side of the 
hydraulic actuators. 
This pulsation damper 25 is constructed in such manner that a free piston 
27 is provided within a cylinder 26 so as to form first and second 
hydraulic chambers 28 and 29 and the free piston 27 is held at a neutral 
position by means of first and second springs 30 and 31. The first and 
second hydraulic chambers 28 and 29 are respectively connected to the 
first circuit L.sub.1 and the second circuit L.sub.2. Therefore, in the 
event that the flow rate through either one of the first and second 
circuits L.sub.1 and L.sub.2 has been momentarily and impulsively 
increased, then the increment of the oil flow is fed to the corresponding 
one of the first and second hydraulic chambers 28 and 29 and urges the 
free piston 27 towards the opposite end of the cylinder 26 against the 
resilient force of the first and second springs 30 and 31, so that the 
impulsive variation of the oil feed rate through the circuit L.sub.1 or 
L.sub.2 can be obviated. 
In the case where means for allowing a trapping pressure to escape is 
provided, a variation of an instantaneous oil flow rate corresponding to 
about 50% of an average delivery rate of all the working pistons 3, must 
be absorbed (although this is a specific value in the case where the 
number of the pistons is 12). This amount of absorption is sufficiently 
approximated, in terms of a volume change, by about 10% of a stroke of one 
piston, and hence the pulsation damper 25 is only necessitated to have a 
capacity equal to about 1/10 times that of the piston 3, so long as it has 
a response of about 500 Hz. In other words, if it is assumed that the 
diameter of the piston 3 and the diameter of the free piston 27 are 
identical and the response of the pulsation damper is 500 Hz, the stroke 
of the free piston 28 could be selected to be about 1/10 times the stroke 
of the piston 3. 
In addition, as shown in FIG. 11, notches 21.sub.1 and 21.sub.2 could be 
formed in the outlet slots 20.sub.1 and 20.sub.2, respectively, for the 
purpose of reducing noises and improving a mechanical strength of the 
outlet slot portions.