Tandem Pump No-Load Operation Device

Abstract

When the pressure in the main oil supply channel is lower than the no-load operation start pressure, the pressurized oil within the secondary oil supply channel passes through the internal flow channel of the spool and flows into the main oil supply channel. At this time oil output from both the main and secondary oil pumps is merged and supplied to the oil supply destination. When the pressure within the main oil supply channel rises and reaches the no-load operation start pressure, the spool moves in opposite direction to the direction of the force of the spring, the pressurized oil within the secondary oil supply channel is drained, the poppet contacts the spool and blocks the internal flow channel of the spool. At this time, the secondary oil pump enters the no-load operation state, and oil output from the main oil pump only is transmitted to the oil supply destination.

1 . A tandem pump no-load operation device, comprising:
 a tandem pump comprising a main fluid pump and a secondary fluid pump that are simultaneously driven by a drive source;   a main fluid supply channel that extends from an outlet of the main fluid pump to a fluid supply destination;   a secondary fluid supply channel that extends from an outlet of the secondary fluid pump and is connected to the middle of the main fluid supply channel;   a valve bore that forms a part of the secondary fluid supply channel;   a spool, disposed by fitting and insertion within the valve bore so that the spool can freely move, having an internal flow channel that extends in an axial direction;   an urging member that urges the spool within the valve bore toward connection with the main fluid supply channel; and   a poppet disposed within the valve bore so as to be able to freely move, that is closer to the connection with the main fluid supply channel than the spool within the valve bore, and that can move to a closed position in which an end portion of the poppet contacts and closes an end of the internal flow channel of the spool, and move to an open position in which the poppet is separated from the end of the internal flow channel, wherein   a drain flow channel is provided that is connected to the valve bore, and when the spool is acted on by the pressure within the main fluid supply channel the spool can move against the force of the urging member; when the pressure within the main fluid supply channel is smaller than a no-load operation start pressure, the spool is moved by the force of the urging member towards the connection with the main fluid supply channel, the link with the drain channel is closed, and the secondary fluid supply channel and the main fluid supply channel are linked by the internal flow channel; and when the pressure within the main fluid supply channel rises higher than the no-load operation start pressure, the spool moves against the force of the urging member, and the secondary fluid supply channel is connected to the drain flow channel, and the poppet is moved into the closed position against the spool by a difference in pressure between the secondary fluid supply channel and the main fluid supply channel resulting from pressurized oil within the secondary fluid supply channel being drained.   
   
   
       2 . The tandem pump no-load operation device according to  claim 1 , wherein the tandem pump comprises gear pumps comprising a drive gear driven by the drive source and a first driven gear and a second driven gear that circumscribes and meshes with the drive gear. 
   
   
       3 . The tandem pump no-load operation device according to  claim 1 , wherein the spool comprises: an intermediate portion having the internal flow channel; and an urging member housing portion, at one end of the intermediate portion, that is acted on by the force of the urging member, wherein
 the external periphery of the intermediate portion is provided, in the center in the axial direction, with a small diameter spool rod portion, and spool land portions are provided to the left and right of the spool rod portion, the left and right spool land portions mate with the valve bore, and the spool is inserted and installed within the valve bore so as to be able to move freely.   
   
   
       4 . The tandem pump no-load operation device according to  claim 3 , wherein linking holes that penetrate the external peripheral surface and link to the internal flow channel are provided in the left spool land portion, so that within the range of movement of the spool the linking holes are always connected to the outlet side of the secondary fluid pump in the secondary fluid supply channel. 
   
   
       5 . The tandem pump no-load operation device according to  claim 3 , wherein when the pressure within the main fluid supply channel exceeds the no-load operation start pressure and the spool is moved against the force of the urging member, the secondary fluid supply channel is connected to the drain flow channel via the spool rod portion. 
   
   
       6 . The tandem pump no-load operation device according to  claim 1 , wherein a flow channel serving also as a drain that opens to both the main fluid supply channel and the external peripheral surface of the poppet is provided within the poppet, and when the pressure within the main fluid supply channel exceeds the no-load operation start pressure and reaches a relief setting pressure that is still higher than the no-load operation start pressure, the spool is acted on by the force of the relief setting pressure and is moved to a position where the flow channel serving also as a drain and the drain flow channel are connected, and the pressurized fluid within the main fluid supply channel is drained from the drain flow channel. 
   
   
       7 . The tandem pump no-load operation device according to  claim 6 , wherein the spool comprises: an intermediate portion having the internal flow channel; and an urging member housing portion at one end of the intermediate portion of which is acted on by the force of the urging member, wherein
 the external periphery of the intermediate portion is provided with, in the center in the axial direction, a small diameter spool rod portion, and spool land portions are provided to the left and right of the spool rod portion, the left and right spool land portions mate with the valve bore, and the spool is inserted and installed within the valve bore so as to be able to move freely.   
   
   
       8 . The tandem pump no-load operation device according to  claim 7 , wherein drain apertures are provided in the right spool land portion that penetrate the external peripheral surface, and that links with a part closer to the main fluid supply channel than a part blocked by the poppet in the internal flow channel, and
 when the pressure in the main fluid supply channel reaches the relief setting pressure, the spool is acted on by the relief setting pressure and moves to a position where the drain apertures link with the drain flow channel, and the flow channel serving also as a drain is connected to the drain flow channel.   
   
   
       9 . The tandem pump no-load operation device according to  claim 4 , wherein when the pressure within the main fluid supply channel exceeds the no-load operation start pressure and the spool is moved against the force of the urging member, the secondary fluid supply channel is connected to the drain flow channel via the spool rod portion.