Pumps – Three or more cylinders arranged in parallel – radial – or...
Reexamination Certificate
1999-07-19
2001-02-13
Walberg, Teresa (Department: 3742)
Pumps
Three or more cylinders arranged in parallel, radial, or...
C091S006500
Reexamination Certificate
active
06186748
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an axial piston pump.
2. Description of the Related Art
An axial piston pump performs a pump action by receiving a fluid from a suction port into a piston chamber and discharging the fluid to a discharge port while relatively rotating a cylinder block with respect to a valving element. During this time, a fluctuation in pressure is caused in each of the piston chambers formed in the cylinder block. The fluctuation in the pressure acts as a vibromotive force on the pumping device and vibrates the pumping device. Consequently, noises are made. A process of the fluctuation in the pressure of one piston chamber includes a pressure rise process and a pressure drop process. If the pressure rapidly fluctuates in the pressure rise process and the pressure drop process, a pressure fluctuation curve includes many harmonic components. Consequently, the noises are particularly offensive to the ear.
There is an attempt to form a notch and a bypass port on a valving element in order to make the pressure fluctuation curve smooth in the pressure rise process and the pressure drop process (see Japanese Unexamined Patent Publication No. Sho 54-44208, for example). In an axial piston pump, a notch is formed continuously with respect to a discharge port, thereby making the pressure fluctuation curve in a piston chamber smooth in an early stage of the pressure rise process. The bypass port communicating with a suction port is formed on the valving element to make the pressure of the piston chamber escape to the suction port through the bypass port before the pressure of the piston chamber reaches that of the discharge port. Consequently, the pressure can be prevented from being rapidly raised in a late stage of the pressure rise process.
Moreover, a notch is formed continuously with respect to the suction port, thereby making the pressure fluctuation curve of the piston chamber smooth in an early stage of the pressure drop process. The bypass port communicating with the discharge port is formed in the valving element to lead the pressure of the discharge port to the piston chamber through the bypass port before the pressure of the piston chamber reaches that of the suction port. Thus, the pressure can be prevented from being rapidly dropped in a late stage of the pressure drop process.
As far as the pressure fluctuation curve of each of the piston chambers is concerned, it can be said that the above-mentioned structure can make the pressure fluctuation curve smoother. Pump noises, however, are made from all the pistons. Accordingly, even if the pressure fluctuation curve of each of the piston chambers is smooth, there are instances where the noises made by all the piston chambers include many harmonics.
SUMMARY OF THE INVENTION
It is an object of the invention not only to make a pressure fluctuation curve of each of piston chambers smooth, but also to regulate the mutual pressure rise and drop timing among the piston chambers, thereby decreasing harmonics of noises made by all the piston chambers.
In order to achieve the object, the invention provides an axial piston pump comprising a plurality of pistons, a cylinder block provided with a plurality of piston chambers in which the pistons slide, a valving element having a suction port and a discharge port formed therein, and a casing accommodating the cylinder block; the axial piston pump causing the pistons to reciprocate while relatively rotating the cylinder block with respect to the valving element, thereby receiving a fluid from the suction port into the piston chamber and discharging the fluid to the discharge port, the axial piston pump comprising a first opening portion formed in the valving element to be connected to the discharge port for making a pressure fluctuation curve of each of the piston chambers smooth in an early stage of a pressure rise process, a second opening portion formed in the valving element to be connected to at least one of the suction ports and an inside of the casing for making the pressure fluctuation curve of the piston chamber smooth in an early stage of a pressure drop process, a first bypass port formed on the valving element communicating with at least one of the suction ports and the inside of the casing, and a second bypass port formed on the valving element communicating with the discharge port, wherein during rotation of the cylinder block an opening of the first bypass port is positioned so as to start overlapping with an opening of the piston chamber before a pressure of the piston chamber reaches that of the discharge port after the opening of the piston chamber starts to overlap with the first opening portion, and an opening of the second bypass port is positioned so as to start overlapping with an opening of the piston chamber before a pressure of the piston chamber reaches that of the suction port after the opening of the piston chamber starts to overlap with the second opening portion, an opening of one of the piston chambers starts overlapping with the second opening portion when a pressure of another piston chamber substantially reaches that of the discharge port, and an opening of one of the piston chambers starts overlapping with the first opening portion when a pressure of the another piston chamber substantially reaches that of the suction port.
With such a structure, the pressure fluctuation curve in the pressure rise process and the pressure drop process of each of the piston chambers becomes smooth. The completion point of the pressure rise process in one of the piston chambers overlaps with the start point of the pressure drop process of another piston chamber. Furthermore, the completion point of the pressure drop process of one of the piston chambers overlaps with the start point of the pressure rise process of another piston chamber. Accordingly, the vibromotive forces generated by all the piston chambers resemble closely a sine-wave curve as a whole. Therefore, harmonic components included in noises are decreased. Accordingly, the harmonic components of the noises made from all the piston chambers can be decreased.
The axial piston pump may further comprise a swash plate such that the piston reciprocates according to an inclination of the swash plate. More specifically, the axial piston pump may be constituted as a swash plate-type axial piston pump.
In the axial piston pump, the pressure fluctuation curve of a piston chamber in the pressure rise process can be made substantially equal to a sine-wave curve from a local minimum; to a local maximum, and the pressure fluctuation curve of the piston chamber in the pressure drop process is substantially equal to a sinewave curve from a local maximum to a local minimum.
In order to achieve the object, furthermore, the invention provides an axial piston pump comprising a plurality of pistons, a cylinder block provided with a plurality of piston chambers in which the pistons slide, a valving element having a suction port and a discharge port formed therein, and a casing accommodating the cylinder block, the axial piston pump causing the pistons to reciprocate while relatively rotating the cylinder block with respect to the valving element, thereby receiving a fluid from the suction port into the piston chambers and discharging the fluid to the discharge port, the axial piston pump comprising a first opening portion formed on the valving element to be connected to the discharge port for making a pressure fluctuation curve of each of the piston chambers smooth in an early stage of a pressure rise process, a second opening portion formed on the valving element connected to at least one of the suction ports and an inside of the casing for making the pressure fluctuation curve of the piston chamber smooth in an early stage of a pressure drop process, a first bypass port formed on the valving element communicating with at least one of the suction ports and the inside of the casing, and a second bypass port formed on the valving element communicating with the discharge po
Kawabata Sachio
Matsuda Kazuhide
Sakai Ryuji
Umeda Tokihiko
Fastovsky Leonid
Kawasaki Jukogyo Kabushiki Kaisha
Walberg Teresa
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