TANDEM PUMP VALVE STRUCTURE

Abstract

When the pressure in a main fluid supply channel is lower than a no-load operation start pressure, and auxiliary fluid supply channel is communicated with the main fluid supply channel through the internal flow channel of a spool, and as the pressure rises within the main fluid supply channel, the spool moves against the biasing force of a biasing member, and the area of opening of the auxiliary fluid supply channel is reduced with regards to opening of the internal flow channel. When the pressure in the main fluid supply channel rises and reaches a no-load operation start pressure, the area of opening in the auxiliary fluid supply channel with regards to opening of the internal flow channel becomes smaller and while connected to the main fluid supply channel, the auxiliary fluid supply channel is connected to the return flow channel. When the pressure in the main fluid supply channel rises above the no-load operating start pressure and reaches a no-load operation pressure, the auxiliary fluid supply channel is cut off from the main fluid supply channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.

FIG. 1 is a cross-section view of a tandem pump with the tandem pump valve structure of the present invention;

FIG. 2 is a partial cross section view of the pump body showing the valve bore;

FIG. 3 is an appearance perspective view of the spool;

FIG. 4 is a cross-section view of the tandem pump showing the condition where the oil pressure in the main fluid supply channel is at the no-load operation start pressure;

FIG. 5 is a cross section diagram of a tandem pump showing the condition where the oil pressure in the main fluid supply channel is at the no-load operation pressure; and

FIG. 6 is a cross section diagram of a tandem pump showing the condition where the oil pressure in the main fluid supply channel is at the relief set pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention will be described below while referring to the drawings. FIG. 1 shows a tandem pump 10 constructed with a valve 50 which has the valve structure of the present invention. This tandem pump 10 is an oil pump attached to a vehicle engine, and uses the output shaft from the engine as a drive source to draw in oil for lubrication and cooling which has accumulated in a tank 61 and pump to an oil gallery 62 which is connected to various regions of the engine. The tandem pump 10 comprises a pump body 1 using a part of the engine casing, a drive gear 11 which is housed in a manner which can rotate in a pump chamber 2 formed in the pump body 1, and two driven gears (first driven gear 12 and second driven gear 13).

The drive gear 11 is supported by a drive shaft 11a, and the first and second driven gears 12, 13 are rotatably supported by a first and second driven shaft 12a, 13a respectively. The drive shaft 11a is driven by the engine crankshaft and rotates the drive gear 11 in the direction of the arrow shown in FIG. 1 (counterclockwise). The first and second driven gears 12, 13 follow the rotation of the drive gear 11 and rotate in the opposite direction to drive gear 11 (clockwise).

The drive gear 11 and the first driven gear 12 as well as the drive gear 11 and the second driven gear 13 form conventionally known gear pumps. When the drive gear 11 and the driven gears 12, 13 rotate, oil is drawn in to the pump chamber 2 from the intake opening because of the reduced pressure created when the gear teeth mutually separate because of this rotation and oil is discharged from the pump chamber 2 to the discharge opening at higher pressure by the gear teeth mutually moving together. In the embodiment shown in FIG. 1, the upper side of the engagement region between the drive gear 11 and the first driven gear 12 forms an intake opening 16a, while the lower side forms a discharge opening 16b. Furthermore, the bottom side of the engagement region between the drive gear 11 and the second driven gear 13 becomes an intake opening 17a, while the upper side forms a discharge opening 17b. Hereinafter, the gear pump comprising the drive gear 11 and the first driven gear 12 will be referred to as the main oil pump 16, and the gear pump comprising the drive gear 11 and the second driven gear 13 will be referred to as the auxiliary oil pump 17, the intake opening 16a and the discharge opening 17a of the main oil pump 16 will be referred to as the main intake opening 16a and the main discharge opening 17a respectively, and the intake opening 17a and the discharge opening 17b of the auxiliary oil pump 17 will be referred to as the auxiliary intake opening 17a and the auxiliary discharge opening 17b, respectively.

Therefore the tandem pump 10 comprises a main oil pump 16 and an auxiliary oil pump 17 which are simultaneously driven by one drive source. The pump body 1 contains a main oil intake channel 3 which is connected to the tank 61 and connected to the main intake opening 16a, and an auxiliary oil intake channel 4 which branches off of the main oil intake channel 3 and is connected to the auxiliary intake opening 17a. Furthermore, a main oil supply channel 5 is connected to the main discharge opening 16b and connected to the oil gallery 62, and an auxiliary oil supply channel 6 is connected to the main oil supply channel 5 inside the pump body 1 and is connected to the auxiliary discharge opening 17b.

The structure of a valve 50 for the tandem pump 10 with the aforementioned oil channel structure will be described while referring to FIG. 1 through FIG. 3. As will be described later, the valve 50 functions as a no-load valve and also functions as a relief valve, and is comprising a spool 30 established to slide in the valve bore 20 which is formed to be a part of the auxiliary oil supply channel 6 in the pump body 1, and a return spring 40 which biases the spool 30 to the right side within the valve for 20. Hereinafter, the section in the auxiliary oil supply channel 6 which connects the auxiliary discharge opening 17b and the valve bore 20 will be referred to as the upstream section 6a while the section which connects the valve bore 20 and the main oil supply channel 5 will be referred to as the downstream section 6b.

As shown in FIG. 2, the valve bore 20 is closed on the right end, has an opening 20b on the left end which is connected to the outside of the pump body 1, and has a recessed region 20c which is formed to recess further to the right side from the center region of the right bottom surface 20d. The valve bore 20 has three ports 21 to 23 mutually separated in the axial direction and formed in a cylindrical shape with a diameter larger than the inner circumferential surface 20a of the valve bore 20. Of these ports, the first port 21, which is located on the left side, forms a part of the upstream section 6a of the auxiliary oil supply channel 6 and is connected to the auxiliary discharge opening 17b, the second port 22, which is located on the right side, forms a part of the downstream section 6b of the auxiliary oil supply channel 6 and is connected to the main supply channel 5, and the third port 23 which is located between the first and second ports 21, 22, is a part of the return flow channel 7 formed in the pump body 1 and is connected to the auxiliary intake opening 17a.

The spool 30 is integrally comprising a main unit 30A which has an internal flow channel 30a extending the axial direction, and a spring housing section 30B with a spring chamber 30b which extends in the axial direction and is connected in the axial direction to the main body 30A, and the spool 30 is inserted into the valve bore 20 through the opening 20b from the main unit 30A side.

With the spool 30 inserted in the valve bore 20, the return spring 40 is housed in the spring chamber 30b though the opening 20b with a portion housed in the recessed region 45a of the cylinder with bottom shaped retainer 45. Furthermore, the pump body 1 has a pin insertion hole 29 which passes through the left end of the valve bore 20 and extends in an axial orthogonal direction, and when the return spring 40 and the retainer 45 are inserted in the valve bore 20, a locking pin 49 is inserted into this pin insertion hole 29. Assembled in this manner, one end of the return spring 40 will contact the bottom surface 30c of the spring chamber 30b, while the other end will contact with the inside bottom surface 45b of the retainer 45, and the outside bottom surface 45c of the retainer 45 will contact the locking pin 49 and be retained inside the valve bore 20. Therefore, the return spring 40 will provide a biasing force to the right side on the bottom surface 30c of the spring chamber 30b.

The spool 30 which is biased to the right side in the valve bore 20 by the return spring 40, makes contact to the right bottom surface 20d of the valve bore 20 on the right end surface 30d of the main unit 30A, D and is restricted from moving to the right. The position of the spool 30 at this time is referred to as the “initial position”. On the other hand, when the spool 30 moves to the farthest left position in the valve bore 20 against the bias, the left end surface 30f of the spring housing section 30B will contact with the opening end surface 45d of the retainer 45 (refer to FIG. 6). The position of the spool 30 at this time is referred to as the “maximum left travel position”.

As shown in FIG. 3, the main unit 30A of the spool 30 is formed in a stepped cylindrical shape, and integrally has three land parts 31 to 33 which are mutually spaced apart in the axial direction and which slide 1 along the inner circumferential surface 20a of the valve bore 20, and two rod parts 34, 35 which are connected between adjacent land parts and which have a cylindrical shape with a diameter smaller than the three land parts 31 to 33, and each of the land parts has a donut shaped stepped surface extending in an axial orthogonal direction which connects to the rod parts at the ends. Note, hereinafter when the spool 30 is housed in the valve bore 20, of the three land parts 31 to 33, the land part positioned on the right side is referred to as the first land part 31, the land part positioned on the left side is referred to as the second land part 32, and the land part positioned between the first and second land parts 31, 32 is referred to as the third land part 33, and of the two rod parts 34, 35, the rod part positioned on the right side and which connects the first and third land parts 31, 33 is referred to as the first rod part 34, and the rod part positioned on the left side which connects the second and third land parts 32, 33 is referred to as the second rod part 35. The spool 30 is established inside the valve bore 20 such that the land parts 31 to 33 are engaged, and therefore a first and second groove 24, 25 are formed to be encompassed by the outer circumferential surface of the first and second rod parts 34, 35, the inner circumferential surface 20a of the valve bore 20, and the stepped surfaces.

The internal flow channel 30a formed in the main unit 30A is formed as a cylinder with bottom which has an opening 30e in the right end surface 30d. The first land surface 31 has a plurality of first through-holes 36 formed along the outer circumferential surface, the second rod part 35 as a plurality of second through-holes 37 formed along the outer circumferential surface, and the second through-holes 37 open into the second groove 25 when the spool 30 is housed in the valve bore 20. Furthermore, the first and second through-holes 36, 37 are all connected to the internal flow channel 30a, are formed to extend in the radial direction with regards to the internal flow channel 30a, and are formed in a cylindrical shape in the outer circumferential surface of the spool 30.

Next, the function of the tandem pump 10 and the valve 50 will be described while referring to FIG. 4 through FIG. 6. When the engine is stopped, the tandem pump 10 is stopped, and the spool 30 receives a biasing force from the return spring 40 and is in the initial position. In this initial position, the internal flow channel 30a is connected to the recessed part 20c through the opening 30e. Furthermore, the first port 21 has a first through-hole 36 and the second port 22 is connected to the second groove 25. Therefore, the first port 21 is connected to the second port 22 through the first through-holes 36, the internal flow channel 30a, the second through-holes 37, and the second groove 35. On the other hand, the third port 23 is cut off from the first and second ports 21, 22.

When the engine starts, the gears 11 to 13 will be made to rotate, and pumping action will be performed by both oil pumps 16, 17. In other words, the main oil pump 16 will draw in oil which has accumulated in the tank 61 from the main intake opening 11a which has been guided through the main oil intake channel 3, and will discharge the oil to the main discharge opening 16b. The auxiliary oil pump 17 will draw in the oil, which has been guided from inside the main oil intake channel 3 through the auxiliary oil intake channel 4, from the auxiliary intake opening 17a, and will discharge the oil to the auxiliary discharge opening 17b. When the spool 30 is in the initial position, the oil is discharged from the auxiliary discharge opening 17b, flows into the first port 21 through the upstream section 6a of the auxiliary oil supply channel 6, and the entire quantity flows into the internal flow channel 30a. The oil which flows into the internal flow channel 30a is discharged from the second port 22 and is introduced into the main oil supply channel 5. Therefore, the oil discharged from the main oil pump 16 and the oil discharged from the auxiliary pump 17 will be merged together and will be sent from the main oil supply channel 5 to the oil gallery 62.

The oil gallery 62 which is the destination of the discharged oil is formed inside the casing of the engine, and is constructed such that the supply pressure rises as the amount of oil supplied increases. Therefore, when the rotational speed of the pump (rotational speed of the drive shaft 11a) is low such as immediately after the engine starts, the discharge flow rate from both oil pumps 16, 17 will be low, and the oil pressure in both oil supply channels 5, 6 will also be low. However, the oil discharged from both oil pumps 16, 17 is combined and supplied to the oil gallery 62, and therefore when looking at the tandem pump 10 overall, the amount of supplied oil necessary for lubrication will still be discharged.

Furthermore, the oil which flows into the internal flow channel 30a will flow through the opening 30e and into the recessed region 20c. Therefore, the right end surface 30d of the spool 30 will be acted on by the oil pressure of the oil in the internal flow channel 30a and will be pushed to the left against the biasing force of the return spring force. The spool 30 will compress the return spring 40 by moving to the left, and will move to a position where the pushing force created by the oil pressure is balanced with the biasing force of the return spring 40.

Note, the diameter of the first through-holes 36 and the axial length of the first port 21 are nearly equal, and when the spool 30 is in the initial position, the entire area of the openings of the first through-holes 36 are facing the first port 21. As the spool 30 moves, the first through-holes 36 will move to the left relative to the first port 21, and the area of that portion of the first through-holes 36 which face the first port 21 will gradually be reduced. Therefore, the area of the first through-holes 36 which are open to the first port 21 will become smaller, and the oil channel will be constricted from the first port 21 to the second port 22, and the farther the spool 30 moves towards the left from the initial position, the area of the opening will decrease and the amount of constriction will increase. Therefore the valve 50 of this embodiment has a constricting structure which changes the degree of constriction depending on the degree of oil pressure supplied, and because of this constricting structure, although the discharge flow rate increases for the tandem pump 10 as a whole as the rotational speed of the pump increases, the tendency thereof can be relaxed.

Furthermore, as shown in FIG. 4, when the pump rotational speed further increases and the oil pressure in the main oil supply channel 5 increases to reach the no-load operation start pressure, the right end of the first land part 31 (left end of first rod part 34) will be located at the right end of the first port 21. Therefore, the first groove 24 will begin to connect with the first port 21, a part of the openings of the first through-holes 36 will face the first port 21, and the first and second ports 21, 22 will be maintained in a connected condition as described above.

When the oil pressure in the main oil supply channel 5 exceeds the one load operating start pressure, the axial length of the region where the first groove 24 is connected to the first port 21 will increase. Thus, the first part 21 will be connected to the third port 23 through the first groove 24 by being connected to the first groove 24. Therefore, when the no-load operating start pressure is exceeded, a portion of the oil which flows into the first port 21 will recirculate to the auxiliary intake opening 17a through the return flow channel 7. In this manner, the load on the auxiliary oil pump 17 is eliminated and the oil pressure in the upstream section 6a of the auxiliary oil supply channel 6 will drop because the oil is recirculated to the auxiliary intake opening 17a.

As shown in FIG. 5, when the oil pressure in the main oil supply channel 5 further rises above the no-load operation start pressure, the first through-holes 36 will move to the left of the first port 21 and the entire opening will face the inner circumferential surface 20a of the valve bore 20. Thereby, the first port 21 will be cut off from the internal flow channel 30a, and will be connected to the third port 23 through the second groove 24. Therefore, the total quantity of oil which is discharged to the auxiliary discharge opening 17b and flows into the first port 21 will be recirculated to the auxiliary intake opening 17a and the auxiliary oil pump 17 will be in a no-load condition.

Furthermore, as shown in FIG. 5, immediately prior to the oil pressure in the main oil supply channel 5 reaching the no-load operation pressure and the first port 21 being completely cut off from the internal flow channel 30a, the left end of the second groove 25 will be positioned at the left end of the third port 23, and the second groove 25 will begin to be b connected to the third port 28. Thereby the oil discharged from the main oil pump 16 will begin to be relieved. In other words, a high pressure relief cracking pressure will be established immediately prior to the no-load operation pressure.

FIG. 6 shows the condition where the oil pressure in the main oil supply channel 5 rises above the cracking pressure to reach the relief set pressure and the spool 30 is in the maximum left travel position. At this time, the first port 21 is connected only to the third port 23 and is in a no-load operation condition. Furthermore, the second port 22 is connected to the third port 23 through the second groove 25, and the second groove 25 is connected to the internal flow channel 30a through the second through-holes 37. Therefore the oil pressure in the main oil supply channel 5 will be held to the relief set pressure because the second port 22 is connected to the third port 23. Furthermore, the second part 37 is always connected to the internal flow channel 30a, regardless of the position of travel of the spool 30, and therefore even though the auxiliary oil pump 17 is in the no-load operation condition, oil pressure to push the spool 30 against the biasing force will be supplied to the internal flow channel 30a.

Furthermore, when the engine rotational speed decreases after the spool 30 is in the maximum left travel position, the rotational speed of the pump will drop and the oil pressure in the main oil supply channel 5 will drop, and the spool 30 will move to the right. As the spool 30 moves to the right, the function of the high pressure relief will end and the no-load operation condition will be over.

In this manner, using a simple structure consisting of a spool 30 and a return spring 40, the valve 50 of the present embodiment can function both as a no-load valve to place the auxiliary oil pump 17 of a tandem pump 10 in a no-load operation condition, and also function as a relief valve to adjust the discharge oil pressure from the main oil pump 16, and can also make the size of the overall tandem pump 10 more compact. The no-load valve function works to reduce the loss of engine output to the drive source by reducing the excess supply of oil, and the relief valve function can prevent pressures which exceed the relief set pressure from acting on the oil gallery 62 side and can ensure the safety of the oil pressure system on the oil gallery 62 side.

Furthermore, when the spool 30 moves from the initial position to the position where all of the opening of the first through-holes 36 are facing the inner circumferential surface 20a of the valve bore 20, the oil discharged from the auxiliary oil pump 17 will be merged with the oil discharged from the main oil pump 16, but will be constricted based on the oil pressure in the main oil supply channel 5. The effect of this constriction gradually reduces the ratio of the oil discharged from the auxiliary oil pump 17 with regards to the total supplied oil, and although the overall amount of oil discharged from the tandem pump 10 increases as the rotational speed of the pump increases, this tendency is relaxed. Furthermore, the structure which creates this constricting effect is a very simple structure and can change the degree of constriction of the internal flow channel 30a and the upstream section 6a of the auxiliary oil supply channel 6 by changing the area with regards to the first port 21 of the openings of the first through-holes 36 which are formed in the spool 30.

Furthermore, when the oil pressure in the main oil supply channel 5 reaches the no-load operation start pressure and rises further, the first port 21 is connected to the internal flow channel 30a through the first through-holes 36 and is connected with the third port 23, and therefore the oil pressure in the upstream section 6a of the auxiliary oil supply channel 6 will drop. At this time, the spool 30 will move to the left from the initial position so the area of the opening of the first through-holes 36 with regards to the first port 21 will be reduced, and the upstream section 6a of the auxiliary oil supply channel 6 will be connected to the internal flow channel 30a in a more constricted condition than when the spool 30 is in the initial position. Therefore, the oil pressure in the main oil supply channel 5 (internal flow channel 30a) will not be strongly affected by the drop in pressure of the upstream sections 6a of the auxiliary oil supply channel 6. The valve 50 of the present embodiment can reduce the possibility of chattering, including from the no-load operation start pressure to the no-load operation pressure.

Furthermore, the first through-holes 36 for connecting the first port 21 to the internal flow channel 30a were a plurality of holes extending in the radial direction of the spool 30, and when the no-load operation start pressure is exceeded, the first groove 24 for connecting the first port 21 to the third port 23 will be formed as a donut shaped space encompassed by the outer circumferential surface of the first rod part 34 and the inner circumferential surface 20a of the valve bore 20. Thus a structure is provided such that when the no-load operation start pressure is exceeded and the spool 30 moves to the left, the volume of the section of the first groove 24 which is connected to the first port 21 will suddenly increase with regards to the amount of change in the region of the first through-holes 36 which are open to the first port 21. Therefore, the pressure in the upstream section 6a of the auxiliary oil supply channel 6, which is reduced by the flow into the first groove 24, can be rapidly reduced with less risk of having an effect on the internal flow channel 30a side through the first through-holes 36.

Furthermore, as the pressure in the main oil supply channel 5 reaches the no-load operating pressure and rises further the area of the opening of the first port 21 with regards to the internal flow channel 30a is gradually reduced, so when the no-load operation start pressure is reached, the first port 21 will be cut off from the internal flow channel 30a. Therefore even in the region of the no-load operation pressure where the first port 21 and the internal flow channel 30a open and close, the total amount of oil discharged from the tandem pump 10 will not be largely affected and the changes in the supplied oil pressure associated with the conventional design will not readily occur. Therefore, by using the valve 50 of this embodiment, the risk of chattering can be reduced even under these conditions.

Similarly, the structure where the first port 21 and the internal flow channel 30a are cut off in order to create the no-load operation condition (in other words, the structure with a check valve function) shunts the first through-holes 36 formed in the spool 30 in the axial direction with regards to the first port 21, and therefore a structure similar to a conventional structure where the internal flow channel 30a is closed using a separate member such as a tappet can be avoided. Therefore, the structure will be simple, and even if the spool 30 moves back and forth in the axial direction, there is no risk of creating abnormal noises.

Furthermore, the relief start pressure is set to a slightly lower pressure than the no-load operation pressure, and therefore the second port 22 in the third port 23 will already start to be connected while the entire opening of the first through-holes are facing the internal circumferential surface 20a of the valve bore 20 and the first port 21 is completely cut off from the internal flow channel 30a, and some of the oil which has flowed from the main oil supply channel 5 into the downstream section 6b of the auxiliary oil supply channel 6 will be discharged to the return flow channel 7. Therefore, from the relief start pressure until the relief set pressure, the pressure change in the internal flow channel 30a can be minimized compared to the form where relief begins while the first port 21 is completely cut off from the internal flow channel 30a. Thus, with the valve 50 of the present embodiment, chattering can be suppressed even after the start of oil pressure relief in the main oil supply channel 5.

A preferred embodiment of the present invention has been described above, but the scope of the present invention is not restricted to the aforementioned embodiment. The second through-holes 37 may be formed in the thud land part 33 so long as the structure allows the second port 22 to always be connected to the internal flow channel 30a. The aforementioned no-load operation start pressure, no-load operation pressure, and relief pressure can easily be changed by changing the axial length of the land parts 31 to 33 or the rod parts 34, 35 or by changing the spring characteristics of the return spring 40. Furthermore, a plate member of prescribed thickness may be placed between the outer side bottom surface of the retainer 45 and the locking pin 49. Thereby the initial displacement of the return spring 40 can easily be set.

Note, an example where the tandem pump is an oil pump on an automotive engine for pumping oil for lubrication to an oil gallery has been shown, but this is not a restriction and the present invention may be used for other applications with other devices, and furthermore, the discharge fluid is not restricted to oil and instead may be water or air. Furthermore, the tandem pump was made from gear pumps, but may also be made from other types of pumps such as a vane pump.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No. 2006-221582 filed on Aug. 15, 2006, which is incorporated herein by reference.

Claims

1. A tandem pump valve structure, comprising: a tandem pump having a main fluid pump and an auxiliary fluid pump which are simultaneously driven by a drive source;a main fluid supply channel which extends from a discharge opening of the main fluid pump to a fluid supply subject;an auxiliary fluid supply channel extending from a discharge opening of the auxiliary fluid pump and connecting to the main fluid supply channel;a spool which has an internal flow channel extending in an axial direction of the spool and which is fitted by insertion to be able to move inside a valve bore which forms a part of the auxiliary fluid supply channel;a biasing member which applies a bias to one side in the axial direction of the spool in the valve bore; anda return flow channel which is connected to the valve bore, whereinthe spool receives pressure from the main fluid supply channel and is able to move in the axial direction toward a second end side of the spool, counteracting the biasing force of the biasing member,the auxiliary fluid supply channel is communicated with the main fluid supply channel through the internal flow channel when the pressure in the main fluid supply channel is lower than a no-load operation start pressure,the spool is moved against the biasing force of the biasing member and an opening area of the auxiliary fluid supply channel becomes smaller with regards to the internal flow channel when the pressure in the main fluid supply channel rises,the auxiliary fluid supply channel is connected to the return flow channel, with the auxiliary fluid supply channel which has a reduced opening area with regards to the internal flow channel being communicated with the main fluid supply channel, when the pressure in the main fluid supply channel rises to the no-load operation start pressure, andthe auxiliary fluid supply channel is cut off from the main fluid supply channel when the pressure in the main fluid supply channel rises above the no-load operation start pressure to reach a no-load operation pressure.

2. The tandem pump valve structure according to claim 1, wherein when the pressure in the main fluid supply channel reaches a relief set pressure which is higher than the no-load operation pressure, the spool further moves against the biasing force of the biasing member, and the auxiliary fluid supply channel and the main fluid supply channel are communicated with the return flow channel.

3. The tandem pump valve structure according to claim 1, wherein the spool comprises a main unit having the internal flow channel, and a biasing force effector which receives a biasing force from the biasing member and which is connected to the other end of the main unit;the spool main unit comprises a first end land part middle end part, and second end land part, all of which are cylindrically shaped and separated in the axial direction of the spool, a first end rod part which is formed in a cylindrical shape with a smaller diameter than the middle land part and which links the first end land part and the middle land part, and a second end rod part which is formed in a cylindrical shape with a smaller diameter than the middle land part and which links the middle land part and the second end land part;the first end land part, middle land part, and second end land part are fitted in the valve bore, one end groove is formed to be encompassed by an outer circumferential surface of the first end rod part and an inner circumferential surface of the valve bore, and a second end groove is formed to be encompassed by an outer circumferential surface of the second end rod part and an inner circumferential surface of the valve core.

4. The tandem pump valve structure according to claim 3, wherein a first end through-hole is formed to pass through the outer circumferential surface and communicate with the inside flow channel at the first land part, and a second end through-hole is formed to pass through the outer circumferential surface and communicate with the inside flow channel at one of either the second end rod part or the second end land part;the first end through-hole communicates the main fluid channel with the inside flow channel regardless of a travel position of the spool; andthe second end through-hole is configured such that area of the opening to the auxiliary fluid channel changes depending on the travel position of the spool.

5. The tandem pump valve structure according to claim 1, wherein the tandem pump comprises a drive gear which is driven by a drive source, and a gear pump comprising a first driven gear and a second driven gear which externally mesh with the drive gear.

6. The tandem pump valve structure according to claim 1, wherein the return flow channel is connected to an intake opening of the auxiliary fluid pump.