Rotary expansible chamber devices – Trapped fluid relief
Reexamination Certificate
2000-08-17
2001-11-06
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Trapped fluid relief
C418S206400
Reexamination Certificate
active
06312241
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority benefits under 35 USC §119 on the basis of Japanese Patent Application No. 11-251892 (1999), the disclosure thereof being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gear pump which provides a pumping effect by rotation of a pair of gears meshing with each other.
2. Description of Related Arts
Gear pumps which are compact and lightweight with simple constructions are conventionally employed in various industrial fields.
In general, such a gear pump has a gear chamber defined between a pair of side plates fitted in a cavity within a housing. A pair of gears meshing with each other are accommodated in the gear chamber. Support shafts of the gears are respectively supported with opposite ends thereof being fitted in support holes formed in the respective side plates. An operating fluid inlet chamber and an operating fluid outlet chamber are respectively provided on opposite sides of a meshing position of the gears in the gear chamber.
In the gear pump, a so-called trapping phenomenon occurs in the vicinity of the gear meshing position, that is, an operating oil is trapped in a region defined between the respective side plates and the gears meshing with each other. When the operating oil trapped in the aforesaid region is compressed by the rotation of the gears, an extraordinarily high pressure is developed in that region, resulting in vibrations and noises.
One approach to this problem is to form relief channels in the side plates adjacent the gear meshing position for releasing the oil trapped in the trap region. The relief channels are provided in pair and include a high pressure side relief channel extending from the vicinity of the gear meshing position to the outlet chamber and a low pressure side relief channel extending from the vicinity of the gear meshing position to the inlet chamber. The pair of relief channels communicate with the trap region in the vicinity of the gear meshing position. The high pressure side relief channel releases the oil trapped in the trap region into the outlet chamber, while the low pressure side relief channel releases the oil trapped in the trap region into the inlet chamber. For prevention of the trapping phenomenon, either of the relief channels should communicate with the trap region at all times.
In order to ensure the pumping effect of the gear pump, on the other hand, communication between the inlet chamber and the outlet chamber should be prevented. Therefore, the pair of relief channels should be prevented from directly communicating with each other and from simultaneously communicating with the trap region. In this respect, the trap region is first brought into communication with the high pressure side relief channel, and then brought into communication with the low pressure side relief channel with the communication with the high pressure side relief channel being blocked, when the meshing of the gears is progressed by the rotation of the gears.
Immediately before the communication with the low pressure side relief channel, the trap region communicates with the high pressure side relief channel and, therefore, has a high inside pressure which is equal to the inside pressure of the outlet chamber. When the trap region communicating with the high pressure side relief channel under the high pressure is instantaneously brought into communication with the low pressure side relief channel, the high pressure trap region communicates with the inlet chamber under a low pressure through the low pressure side relief channel. As a result, the high pressure oil is released into the low pressure inlet chamber, so that impactive noises and vibrations are generated.
SUMMARY OF THE INVENTION
In order to solve the aforesaid problem, it is an object of the present invention to provide a gear pump which can assuredly prevent the vibrations and the noises which may otherwise occur due to the trapping phenomenon.
In accordance with a preferred mode of the present invention, there is provided a gear pump which includes a pair of gears accommodated in a gear chamber and has a trap region developed in the vicinity of a meshing position of the pair of gears during rotation of the pair of gears, the gear pump comprising: an operating fluid inlet chamber and an operating fluid outlet chamber disposed on opposite sides of the meshing position within the gear chamber; a first relief channel for providing communication between the trap region and the outlet chamber; and a second relief channel for providing communication between the trap region and the inlet chamber. As the pair of gears are rotated, a communication state is sequentially switched among a first state in which the trap region communicates only with the first relief channel, a second state in which communication between the trap region and the first and second relief channels is blocked, and a third state in which the trap region communicates only with the second relief channel. When the inside pressure of the trap region is reduced to a level substantially equal to the inside pressure of the inlet chamber in the second state during the rotation of the pair of gears, the communication state is switched to the third state.
According to this mode, the pressure of the operating fluid in the trap region is gradually reduced as the volume of the trap region is gradually increased in the second state. When the inside pressure of the trap region becomes substantially equal to the inside pressure of the inlet chamber, the communication state is switched to the third state, whereby the trap region is opened to the inlet chamber. Therefore, no impact is generated when the trap region is opened to the inlet chamber, so that the noises and the vibrations can be prevented.
It is preferred that the communication state is switched to the second state when the volume of the trap region is minimized in the first state during the rotation of the pair of gear.
In this case, the switching from the first state to the second state occurs when the trap region has the minimum volume. Therefore, an increase in the volume of the trap region can be enhanced in the second state, so that a reduction in the pressure can be enhanced in the second state. Thus, the inside pressure of the trap region can sufficiently be reduced to be made closer to the inside pressure of the inlet chamber before the trap region is brought into communication with the second relief channel, whereby the vibrations and the noises can assuredly be prevented.
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Kamamoto Shigeo
Yamada Wataru
Yamazaki Takayasu
Denion Thomas
Koyo Seiko Co. Ltd.
Rabin & Berdo P.C.
Trieu Theresa
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