Variable displacement oil pump including swing member

In a variable displacement type oil pump, a swing member accommodates a pump forming member, and swings to vary a quantity of change of a volumetric capacity of each pump chamber. A biasing member biases the swing member in a direction to increase the quantity of change of the volumetric capacity of each pump chamber. A first control oil chamber applies a first torque to the swing member in a direction to reduce the quantity of change of the volumetric capacity of each pump chamber. A second control oil chamber applies a second torque to the swing member in a direction to increase the quantity of change of the volumetric capacity of each pump chamber, wherein the second torque is larger than the first torque. A switching mechanism switches between supply and drain of working oil with respect to the second control oil chamber.

TECHNICAL FIELD

The present invention relates to a variable displacement type oil pump for oil supply for lubrication of a slide part such as a crankshaft of an internal combustion engine, and/or for driving of auxiliary equipment of the internal combustion engine.

BACKGROUND ART

Various variable displacement type oil pumps have been provided. A patent document 1 discloses a variable displacement type oil pump as follows.

This variable displacement type oil pump is configured to satisfy a required two-stage characteristic including a low pressure characteristic related to a first rotation region and a high pressure characteristic related to a second rotation region, for application to devices having different request discharge pressures, such as sliding parts such as bearing metal pieces of a crankshaft of an internal combustion engine, and a variable valve device for controlling characteristics of operation of engine valves such as intake valves.

Specifically, a first control oil chamber and a second control oil chamber are formed between an inner peripheral surface of a pump body and an outer peripheral surface of a cam ring; a pump discharge pressure is supplied to the first control oil chamber so as to bias the cam ring in a direction to reduce a quantity of eccentricity of the cam ring (henceforth referred to as coaxial direction); and the pump discharge pressure is supplied to the second control oil chamber so as to bias the cam ring in a direction to increase the quantity of eccentricity of the cam ring (henceforth referred to as eccentric direction). The cam ring is biased by a spring force of a coil spring in a direction to increase the quantity of eccentricity of the cam ring; and a plurality of pump chambers defined by an inner peripheral surface of the cam ring and a plurality of vanes configured to be out of and in an outer peripheral surface of a rotor, wherein internal pressures of the pump chambers cause another biasing force for swing control of the cam ring in the eccentric direction or in the coaxial direction.

Supply and drain of the discharge pressure with respect to the first and second control oil chambers is controlled by an electromagnetic switching valve and a pilot valve so as to control the quantity of eccentricity of the cam ring in accordance with engine rotational speed, thereby satisfying the two-stage request discharge pressure having the low pressure characteristic and the high pressure characteristic.

PRIOR ART DOCUMENT(S)

Patent Document 1: JP 2014-105622 A

SUMMARY OF THE INVENTION

Problem(s) to be Solved by the Invention

In case of the variable displacement type oil pump described above, especially when the pump is rotating at high speed (in the second rotation region), it is likely that many bubbles occur in oil due to aeration and/or cavitation in a process of suction. This causes a phenomenon of collapse and others of the bubbles in a discharge region where oil is compressed and discharged, and thereby brings the internal pressures of the pump chambers out of balance. This may cause behavior of the cam ring to be unstable so that the cam ring swings in the coaxial direction before a set operating oil pressure is reached, and cause control of the high pressure characteristic of the second rotation region to be unstable.

The present invention is made with attention to the technical problem described above, and is targeted for providing a variable displacement type oil pump which is capable of suppressing behavior of a cam ring from becoming unstable even when bubbles occur in pump chambers, and thereby stabilizing control of a high pressure characteristic of the pump.

Means for Solving the Problem(s)

According to the present invention, a variable displacement type oil pump comprises: a pump forming member configured to be rotationally driven so as to change a volumetric capacity of each of a plurality of pump chambers, and suck working oil through a suction part, and discharge working oil through a discharge part; a swing member configured to accommodate the pump forming member inside of the swing member, and swing about a swing fulcrum so as to vary a quantity of change of the volumetric capacity of each of the plurality of pump chambers opened to the discharge part, wherein the swing fulcrum is set at an outer periphery of the swing member; a biasing member mounted with application of a setting load so as to bias the swing member in a direction to increase the quantity of change of the volumetric capacity of each of the plurality of pump chambers; a first control oil chamber configured to be supplied with working oil so as to apply a first torque to the swing member in a direction to reduce the quantity of change of the volumetric capacity of each of the plurality of pump chambers; a second control oil chamber configured to be supplied with working oil so as to apply a second torque to the swing member in a direction to increase the quantity of change of the volumetric capacity of each of the plurality of pump chambers, wherein the second torque is larger than the first torque; and a switching mechanism configured to switch between supply of working oil to the second control oil chamber and drain of working oil from the second control oil chamber.

Effect(s) of the Invention

The present invention serves to suppress behavior of the cam ring from becoming unstable, and thereby stabilize control of the pump under the high pressure characteristic.

MODE(S) FOR CARRYING OUT THE INVENTION

The following describes a variable displacement type oil pump according to an embodiment of the present invention in detail with reference to the drawings. The variable displacement type oil pump according to the present embodiment is exemplified as an oil pump for supply of engine lubricating oil to sliding parts of an internal combustion engine of an automotive vehicle, and/or to a valve timing control device employed for control of opening and closing timings of engine valves of the internal combustion engine.

This oil pump10is provided at a front end part of a cylinder block or balancer device of an internal combustion engine not shown. As shown inFIGS.1to4, oil pump10includes: a pump housing including a pump body11and a cover member12, wherein pump body11includes a first end side opened, and has a U-shaped longitudinal section, and forms a pump accommodation chamber13inside, and wherein cover member12closes the opening of the first end of pump body11; a drive shaft14rotatably supported by the pump housing, and configured to be rotationally driven by a crankshaft or balancer shaft not shown, wherein drive shaft14extends through a substantially central portion of pump accommodation chamber13; a cam ring15accommodated in pump accommodation chamber13for movement (swing), and configured as a swing member to vary a quantity of change of a volumetric capacity of each of pump chambers24described below as operating oil chambers, in cooperation with first and second control oil chambers31,32and a coil spring33described below; a pump forming member accommodated radially inside of cam ring15, and configured to be rotationally driven by drive shaft14in a clockwise direction inFIG.4so as to increase and reduce the volumetric capacity of each pump chamber24defined between the pump forming member and cam ring15, and thereby perform a pumping action; a pilot valve40coupled to cover member12, and configured as a control mechanism to control supply and drain of oil pressure to and from second control oil chamber32described below; and an electromagnetic switching valve60disposed in an oil passage (second introduction passage72described below) formed between pilot valve40and a discharge opening22adescribed below, and configured as a switching mechanism to perform a switching control of supply of discharged oil to pilot valve40.

The pump forming member includes: a rotor16accommodated rotatably radially inside of cam ring15, and including a central portion coupled to an outer periphery of drive shaft14; vanes17each of which is accommodated in a corresponding one of slits16aso as to be out of and in slit16a, wherein slits16aare formed at an outer periphery of rotor16and extending radially; and a pair of ring members18,18disposed at corresponding sides of an inside portion of rotor16.

Pump body11is formed integrally of an aluminum alloy, and includes an end wall11aas a first end wall of pump accommodation chamber13, wherein a bearing hole11bis formed at a substantially central portion of end wall11a, and is configured to support a first end portion of drive shaft14rotatably, as also shown inFIG.5. A support hole11cis formed as a recess at a predetermined portion of an inner peripheral wall of pump accommodation chamber13, and has a substantially semicircular section for supporting the cam ring15via a rodlike pivot pin19for swing of cam ring15.

The inner peripheral wall of pump accommodation chamber13further includes a first seal slide surface11dconfigured to be in sliding contact with a first seal member20aprovided at an outer periphery of cam ring15, wherein first seal slide surface11dis located above a line M (henceforth referred to as cam ring reference line) inFIG.4, where line M connects a center of bearing hole11band a center of support hole11c. The first seal slide surface11dis formed to have an arc shape having a predetermined semidiameter R1from the center of support hole11c, and have a length in a circumferential direction such that first seal slide surface11dis constantly in sliding contact with first seal member20awhile cam ring15swings with eccentricity within its range of swing. Similarly, a second seal slide surface11eis formed below the cam ring reference line M inFIG.4, and is configured to be in sliding contact with a second seal member20bprovided at the outer periphery of cam ring15. The second seal slide surface11eis formed to have an arc shape having a predetermined semidiameter R2from the center of support hole11c, and have a length in a circumferential direction such that second seal slide surface11eis constantly in sliding contact with second seal member20bwhile cam ring15swings with eccentricity within its range of swing.

As shown inFIGS.4and5in particular, the inside surface of the end wall11aof pump body11is formed with a suction port21and a discharge port22as recesses, wherein suction port21is a suction part in the form of a recess having a substantially arc shape, and is opened in a region radially outside of bearing hole11bwhere the volumetric capacity of each pump chamber24increases along with pumping action by the pump forming member (henceforth referred to as suction region), and wherein discharge port22is a discharge part in the form of a recess having a substantially arc shape, and is opened in a region radially outside of bearing hole11bwhere the volumetric capacity of each pump chamber24decreases along with pumping action by the pump forming member (henceforth referred to as discharge region), and wherein suction port21and discharge port22are substantially opposite to each other through the bearing hole11b.

Suction port21includes: an introduction portion23formed integrally at its substantially central portion in a circumferential direction, wherein introduction portion23extends to a spring accommodation chamber26described below; and a suction opening21aformed in vicinity to a boundary between introduction portion23and suction port21, and extending through the end wall11aof pump body11to the outside. In this configuration, oil stored in an oil pan not shown of the internal combustion engine is sucked to into each pump chamber24in the suction region via the suction opening21aand suction port21, under a negative pressure caused by the pumping action of the pump forming member.

The suction opening21ais configured to communicate with introduction portion23and a low-pressure chamber35, wherein low-pressure chamber35is formed in the suction region radially outside of cam ring15, and wherein low-pressure oil (the suction pressure) is introduced also into low-pressure chamber35.

Discharge port22includes a starting end portion formed with discharge opening22a, wherein discharge opening22aextends through the end wall11aof pump body11and opens to the outside. Accordingly, oil is discharged to discharge port22under pressure by the pumping action of the pump forming member, and is supplied through the discharge opening22aand a main oil gallery27, which is formed inside of the cylinder block, for lubrication of sliding parts of the engine and for driving of the valve timing control device.

The inside surface of end wall11ais formed with a communication groove25aas a recess configured to allow communication between discharge port22and bearing hole11b, wherein oil is supplied to bearing hole11bthrough the communication groove25a, and is supplied also to side portions of rotor16and vanes17for ensuring preferable lubrication of the sliding parts.

As shown inFIGS.1and3, cover member12has a substantially plate shape, and is attached to the open end surface of pump body11by a plurality of bolts29, and includes a bearing hole12aat a position facing the bearing hole11bof pump body11, wherein bearing hole12asupports a second end side of drive shaft14rotatably. The inside surface of cover member12also includes a suction port, a discharge port, and a communication groove not shown, which are arranged to face the suction port21, discharge port22, and communication groove25aof pump body11, respectively.

As shown inFIG.3, drive shaft14includes a first axial end portion extending through the cover member12to the outside and coupled to the crankshaft or the like, and is configured to be rotated by a torque transmitted from the crankshaft or the like so as to rotate the rotor16in the clockwise direction inFIG.4. As shown inFIG.4, a line N (henceforth referred to as cam ring eccentric-direction line), which passes through the center of drive shaft14, and perpendicularly crosses the cam ring reference line M, is a line of boundary between the suction region and the discharge region.

As shown inFIGS.1and4, rotor16is formed with slits16aas recesses extending radially and outwardly from the central side of rotor16, and back pressure chambers16bat proximal end portions of corresponding slits16a, wherein each back pressure chamber16bhas a substantially circular cross-section and is configured to receive introduction of the discharge pressure. By the centrifugal force accompanying the rotation of rotor16and the internal pressure of back pressure chamber16b, each vane17is pressed outwardly.

While rotor16is rotating, a distal end surface of each vane17is in sliding contact with the inner peripheral surface of cam ring15, and a proximal end surface of each vane17is in sliding contact with an outer peripheral surface of each of ring members18,18. Specifically, each vane17is configured to be pressed up by ring members18,18outwardly in the radial direction of rotor16, so that even when the engine rotational speed is low and the centrifugal force and the pressure of back pressure chamber16bare small, the distal end of each vane17is maintained in sliding contact with the inner peripheral surface of cam ring15so as to separate the pump chambers24liquid-tightly from each other.

Cam ring15is formed integrally of so-called sintered metal to have a substantially cylindrical shape, and include a pivot portion15aat a predetermined position of the outer periphery of cam ring15, wherein pivot portion15ais an arc-shaped recess extending in the axial direction, and is configured to be fitted with pivot pin19so that the axial center forms a swing fulcrum F. Cam ring15also includes an arm portion15bat a position opposite to the pivot portion15athrough the center of cam ring15, wherein arm portion15bextends in the radial direction, and is associated with a coil spring33, wherein coil spring33is a biasing member having a predetermined spring constant. The arm portion15bincludes a pressing projection not shown at a side facing in a direction of movement (rotation), wherein the pressing projection has an arc shape and is constantly in contact with a distal end portion of coil spring33, so that arm portion15bis associated to coil spring33.

Pivot pin19, which serves as swing fulcrum F, is disposed outside of a substantially central portion of discharge port22in the circumferential direction, in the discharge region where the volumetric capacity of each of pump chambers24decreases, namely, on the right side of cam ring eccentric-direction line N inFIG.4.

As shown inFIGS.4and5, the inside of pump body11includes a spring accommodation chamber26disposed at a position opposite to the support hole11c, wherein spring accommodation chamber26accommodates and holds coil spring33, and extends substantially along the cam ring eccentric-direction line N inFIG.4, and is adjacent to pump accommodation chamber13. Coil spring33is mounted between a first end wall of spring accommodation chamber26and the underside of arm portion15b, in a state compressed by a predetermined setting load W1.

A second end wall of spring accommodation chamber26is configured to serve as a restricting surface26ato restrict the range of movement of cam ring15in the eccentric direction. Further movement of cam ring15in the eccentric direction is restricted by contact of restricting surface26awith a second side portion of arm portion15b.

Coil spring33is disposed outside of a substantially central portion of suction port21in the circumferential direction, in the suction region where the volumetric capacity of each of pump chambers24increases, namely, on the left side of cam ring eccentric-direction line N inFIG.4.

In this way, cam ring15is constantly biased by the biasing force of coil spring33via the arm portion15bin the direction to increase the quantity of eccentricity of cam ring15(in the clockwise direction inFIG.4). In an inactive state, cam ring15is in a state where the second side portion of arm portion15bis pressed onto the restricting surface26a, and cam ring15is restricted in a position where the quantity of eccentricity maximized.

The outer periphery of cam ring15is formed with a pair of first and second seal forming portions15c,15dprojecting and facing the first and second seal slide surfaces11d,11eformed in the inner peripheral wall of pump body11. Each seal forming portion15c,15dincludes a seal holding recess holding a corresponding one of first and second seal members20a,20bin sliding contact with a corresponding one of first and second seal slide surfaces11d,11ewhen cam ring15swings with eccentricity.

First and second seal forming portions15c,15dhave seal surfaces having predetermined semidiameters slightly smaller than semidiameters R1, R2of first and second seal slide surfaces11d,11e, respectively, such that a predetermined small clearance is formed between each seal slide surface11d,11eand the seal surface of the corresponding seal forming portion15c,15d. On the other hand, each of first and second seal members20a,20bis made of a material such as a fluorocarbon-based resin having a low friction property, and has a thin rectangular shape extending straight in the axial direction of cam ring15, and is pressed onto the seal slide surface11d,11eby an elastic force of an elastic member, wherein the elastic member is made of rubber and disposed at a bottom portion of the holding recess, so that liquid tightness is held between the seal slide surface11d,11eand the seal surface of seal forming portion15c,15d.

In the outside region of cam ring15, a pair of first and second control oil chambers31,32are defined by pivot pin19and first and second seal members20a,20b. An in-engine oil pressure corresponding to the pump discharge pressure is introduced via a control oil introduction passage70to each control oil chamber31,32, wherein control oil introduction passage70is formed to branch from main oil gallery27.

Specifically, first control oil chamber31is configured to receive supply of a pump discharge pressure via a first introduction passage71that is one of two branch passages branched from control oil introduction passage70. On the other hand, second control oil chamber32is configured to receive supply of a pump discharge pressure (referred to as second discharge pressure) via a second introduction passage72after pressure reduction via pilot valve40, wherein second introduction passage72is another branch passage branched from control oil introduction passage70via electromagnetic switching to valve60as a switching mechanism.

Application of these oil pressures to first and second pressure-receiving surfaces15e,15fof the outer peripheral surface of cam ring15facing the first and second control oil chambers31,32, causes first and second torques to cam ring15in the clockwise direction and in the counterclockwise direction, to apply a force of movement (force of swing) to cam ring15.

Specifically, cam ring15receives a biasing force by the spring force of coil spring33in the direction to increase the quantity of change of the volumetric capacity of each pump chamber, and a further biasing force by operating oil pressure acting from first control oil chamber31to first pressure-receiving surface15ein cam ring15in the direction to reduce the quantity of eccentricity against the spring force of coil spring33. Furthermore, cam ring15receives a biasing force by operating oil pressure acting from second control oil chamber32to second pressure-receiving surface15fin the direction to increase the quantity of eccentricity in cooperation with the spring force of coil spring33.

The second pressure-receiving surface15fis set to have a larger area than first pressure-receiving surface15e, so that when the same oil pressure acts on both, cam ring15is biased totally in the direction to increase the quantity of eccentricity of cam ring15(in the clockwise direction inFIG.4).

The difference between the first and second torques (biasing forces) based on the difference in area between first pressure-receiving surface15eand second pressure-receiving surface15fcan be expressed by vectors as shown inFIG.4. This force can be decomposed into a component of a first vector B1(semidiameter R1) in a direction to first seal member20a(endpoint) from swing fulcrum F of cam ring15as a start point, and a component of a second vector B2(semidiameter R2) in a direction to second seal member20b(endpoint) from swing fulcrum F, where swing fulcrum F is the axial center of pivot pin19. The second vector B2is set to be larger than first vector B1.

By the configuration described above, in oil pump10, when the biasing force (vector) based on the internal pressures of control oil chambers31,32is smaller than setting load W1of coil spring33, cam ring15is put in a maximally eccentric state shown inFIG.4. On the other hand, when the biasing force (vector) based on the internal pressure of first control oil chamber31exceeds the setting load W1of coil spring33as the discharge pressure rises, cam ring15is moved in the coaxial direction (in the counterclockwise inFIG.4) depending on the discharge pressure.

As shown inFIGS.1and4, pilot valve40includes: a valve body41formed integrally with a first side portion of cover member12, and having a cylindrical shape, and including a valve accommodation hole41ahaving an open lower end side in its axial direction; a plug42closing the lower end opening of valve body41; a spool valve element43accommodated radially inside of valve body41and configured to slide in the axial direction, and employed for control of supply and drain of oil pressure to and from second control oil chamber32in accordance with a slide position of spool valve element43; and a valve spring44disposed between plug42and spool valve element43radially inside of a lower end portion of valve body41, and mounted in a state compressed by a predetermined setting load W2, and thereby configured to constantly bias the spool valve element43toward an upper end side of valve body41.

The valve accommodation hole41aaccommodates spool valve element43inside, and includes an upper end wall opened and formed with an introduction port51that is connected to electromagnetic switching valve60via first branch passage72abranched from a downstream side of second introduction passage72. Plug42is press-fitted and fixed in the lower end opening part of valve accommodation hole41a.

Moreover, the peripheral wall of valve accommodation hole41aincludes an intermediate portion in the axial direction, which is opened and formed with a supply-drain port52having a first end side connected to second control oil chamber32and a second end side connected constantly to a relay chamber57described below, wherein supply-drain port52is employed for supply and drain of oil pressure with respect to second control oil chamber32. The lower end side of valve accommodation hole41ain the axial direction is opened and formed with a first drain port53, wherein first drain port53includes a first end side connected to a suction side, and is configured to drain oil pressure from second control oil chamber32via the relay chamber57by switching of communication with relay chamber57.

The peripheral wall of the lower end side of valve body41is opened and formed with a second drain port54, wherein second drain port54overlaps with a back pressure chamber58described below, and is configured to communicate with the suction side, similar to first drain port53.

Supply-drain port52is configured to constantly communicate with second control oil chamber32via a communication passage59that is formed inside of the lower part of valve body41.

Furthermore, valve body41is formed with a communication port55between introduction port51and first drain port53, wherein communication port55extends in a radial direction, and is configured to allow communication between relay chamber57and a second branch passage72bwhen spool valve element43is in an upper position (seeFIG.7A) inFIG.4, wherein second branch passage72bis branched from a further downstream end of second introduction passage72with respect to first branch passage72a.

Spool valve element43includes a first land portion43aincluding an upper end surface formed as a pressure-receiving surface56configured to receive a discharge pressure introduced through the introduction port51, wherein first land portion43aand a second land portion43bare provided at an upper end portion and a lower end portion respectively in the axial direction. Spool valve element43includes a small-diameter shaft portion43cbetween land portions43a,43b, and is formed with relay chamber57radially outside of small-diameter shaft portion43c, wherein relay chamber57has a cylindrical shape, and is configured to connect the supply-drain port52to introduction port51(communication port55) or to first drain port53, depending on the axial position of spool valve element43.

Back pressure chamber58is formed between second land portion43band plug42, and is employed for draining oil that leaks from relay chamber57via the outer peripheral side (infinitesimal clearance) of second land portion43b.

By the configuration described above, when the discharge pressure acting from introduction port51to pressure-receiving surface56is lower than or equal to a predetermined pressure (operating oil pressure of spool valve element43described below), spool valve element43of pilot valve40is positioned in a first region of valve accommodation hole41aby the biasing force of valve spring44based on the setting load W2, wherein the first region is a predetermined region of the upper end side of valve accommodation hole41a(seeFIGS.4and7A).

The condition that spool valve element43is positioned in the first region, allows communication between second branch passage72band relay chamber57via communication port55, and prevents communication between first drain port53and relay chamber57by second land portion43b, and allows communication between second control oil chamber32and relay chamber57via supply-drain port52, simultaneously.

As the discharge pressure acting on pressure-receiving surface56exceeds the predetermined pressure, spool valve element43moves from the first region toward the lower side of valve accommodation hole41aagainst the spring force of valve spring44, and gets positioned in a second region that is a predetermined region in the lower side of valve accommodation hole41a(seeFIG.8B). The condition that spool valve element43is positioned in the second region, maintains communication between second control oil chamber32and relay chamber57via supply-drain port52, and prevents communication between communication port55and relay chamber57by first land portion43a, and allows communication between relay chamber57and the oil pan or the like via first drain port53, simultaneously.

As the discharge pressure acting on the pressure-receiving surface56decreases slightly as compared to the condition that the discharge pressure is maintained higher than or equal to the predetermined pressure, spool valve element43gets positioned in a third region slightly above the second region by the spring force of valve spring44. As shown inFIG.9, this condition causes the first land portion43aof spool valve element43to close the communication port55so as to prevent its communication with relay chamber57, and causes the second land portion43bto close the first drain port53so as to prevent its communication with relay chamber57. This puts the second control oil chamber32, communication passage59, supply-drain port52, and communication port55in a state of closed circuit.

As shown inFIG.4, electromagnetic switching valve60generally includes: a valve body61disposed between control oil introduction passage70and second introduction passage72, and having a substantially cylindrical shape inside which an oil passage65extends through in the axial direction; a valve element accommodation portion66formed in a first end portion of valve body61by extension of the diameter of oil passage65; a seat member62press-fitted and fixed in an outer end portion of valve element accommodation portion66, and including a central portion including an introduction port67as an upstream end opening connected to an upstream side passage of second introduction passage72; a ball valve element63configured to be on and off a valve seat62aformed at an inner end opening edge of seat member62, and configured to be employed for opening and closing of introduction port67; and a solenoid64provided at a second end portion (right end portion inFIG.4) of valve body61.

Valve body61is formed with a valve seat66asimilar to valve seat62aof seat member62, wherein valve seat66ais formed at an inner end opening edge of valve element accommodation portion66, wherein valve element accommodation portion66is formed radially inside of the first end side of valve body61, and accommodates the ball valve element63. The peripheral wall of valve body61is formed with a supply-drain port68and a plurality of drain ports69, wherein supply-drain port68is formed in a first end side of the peripheral wall radially outside of valve element accommodation portion66, and extends through in a radial direction, and serves as a downstream side opening portion connected to an upstream side of second introduction passage72, and is employed for supply and drain of oil pressure to and from pilot valve40, and wherein each drain port69is formed in a second end side of the peripheral wall radially outside of oil passage65, and extends through in a radial direction, and is connected to a drain side including the oil pan.

Solenoid64includes a casing64aand a rod64b, wherein casing64ahouses a coil not shown, and rod64bis fixed to an armature arranged radially inside of the coil. Solenoid64is configured to move the armature and rod64bin the leftward direction inFIG.4by an electromagnetic force generated by energization of the coil. Solenoid64is applied with an excitation current from an on-board ECU not shown based on a state of operation of the engine which is sensed or calculated from predetermined parameters such as oil temperature, water temperature, and engine speed of the internal combustion engine.

Accordingly, when solenoid64is energized, rod64bmoves forward so that ball valve element63disposed at the distal end portion of rod64bis pressed onto valve seat62aof seat member62, thereby preventing communication between introduction port67and supply-drain port68, and allowing communication between supply-drain port68and drain port69through the oil passage65. On the other hand, when solenoid64is de-energized, ball valve element63is moved backward by the discharge pressure introduced via introduction port67so that ball valve element63is pressed onto valve seat66aof valve body61, thereby allowing communication between introduction port67and supply-drain port68, and preventing communication between supply-drain port68and drain port69.

<Actions of Oil Pump>

The following describes actions of oil pump10according to the present embodiment with reference toFIGS.7to9.

First, the following describes a required oil pressure of the internal combustion engine which is a reference for control of the discharge pressure of oil pump10, with reference toFIG.6, in advance to description of actions of oil pump10. InFIG.6, P1represents a first engine request oil pressure corresponding to a request oil pressure of a device such as a valve timing control device for fuel efficiency improvement when such a device is employed, and P2represents a second engine request oil pressure which is required for lubrication of bearing parts of the crankshaft when the engine is rotating at high speed. It is ideal to change the discharge pressure (required oil pressure) P depending on engine rotational speed N of the internal combustion engine, in accordance with request oil pressures P1, P2.

InFIG.6, a solid line represents a characteristic of oil pressure of oil pump10according to the present invention, and a long-dashed short-dashed line represents a characteristic of oil pressure of the conventional oil pump from a point C-A where discharge pressure P2is reached.

In oil pump10according to the present embodiment, in a section “a” inFIG.6corresponding to a region of rotation from engine start to low-speed region, solenoid64is energized with an excitation current so as to prevent communication between introduction port67and supply-drain port68, and allow communication between supply-drain port68and drain port69, as shown inFIG.7A. This prevents the discharge pressure P from being introduced into second control oil chamber32(pilot valve40) so that spool valve element43of pilot valve40is positioned in the first region.

Accordingly, as shown by an arrow in the figure, oil in second control oil chamber32is drained through communication passage59, supply-drain port52, relay chamber57, second branch passage72b, and oil passage65, and then through drain port69of electromagnetic switching valve60, while discharge pressure P is supplied only to first control oil chamber31.

In this engine rotation region, discharge pressure P is lower than an operating oil pressure with which cam ring15swings, so that cam ring15is maintained in the state of maximum eccentricity, and discharge pressure P has a characteristic of increasing substantially in proportion to engine rotational speed N.

Thereafter, as engine rotational speed N rises and discharge pressure P reaches the operating oil pressure with which cam ring15swings, solenoid64is maintained energized so as to continue to supply discharge pressure P only to first control oil chamber31, as shown inFIG.7B. This causes the biasing force based on the internal pressure of first control oil chamber31to exceed the biasing force W1of coil spring33, and thereby causes cam ring15to move in the coaxial direction. This reduces the discharge pressure P, and a quantity of increase of discharge pressure P becomes smaller (in the section “b” inFIG.6) than when cam ring15is in the state of maximum eccentricity.

Thereafter, as engine rotational speed N further rises and the engine operating state requires second engine request oil pressure P2, solenoid64is de-energized so as to allow communication between introduction port67and supply-drain port68, and prevent communication between supply-drain port68and drain port69, as shown inFIG.8A. This causes the discharge pressure P introduced through second introduction passage72to be introduced to pressure-receiving surface56of pilot valve40via the first branch passage72a. In this situation, the discharge pressure P has not yet reached the operating oil pressure with which spool valve element43operates, so that spool valve element43of pilot valve40is maintained in the first region, and communication among communication port55, relay chamber57, and supply-drain port52is allowed, and first drain port53is closed by second land portion43b, and the second discharge pressure is supplied to second control oil chamber32.

Accordingly, a resultant force of the biasing force W1of coil spring33and the biasing force based on the internal pressure of second control oil chamber32becomes a biasing force to cam ring15in the eccentric direction, wherein this biasing force exceeds the biasing force based on the internal pressure of first control oil chamber31in the coaxial direction, so that cam ring15is moved back in the direction to increase the quantity of eccentricity of cam ring15, and the quantity of increase of discharge pressure P increases again (in the section “c” inFIG.6).

Thereafter, as discharge pressure P rises with the characteristic of increase described above, and reaches the operating oil pressure of spool valve element43, spool valve element43of pilot valve40receives the discharge pressure P acting from introduction port51to pressure-receiving surface56, and moves in the downward direction (toward the plug42) against the biasing force W2of valve spring44, and the position of spool valve element43shifts from the first region to the second region, as shown inFIG.8B. This causes the first land portion43ato close the opening of communication port55at the valve accommodation hole41a, and allows communication between supply-drain port52and first drain port53via relay chamber57, so that oil in second control oil chamber32is drained and discharge pressure P is supplied only to first control oil chamber31. This causes the biasing force based on the internal pressure of first control oil chamber31in the coaxial direction to exceed the biasing force in the eccentric direction based on the resultant force of the biasing force W1of coil spring33and the biasing force based on the internal pressure of second control oil chamber32, and thereby causes the cam ring15to move in the coaxial direction, and reduces the discharge pressure P.

The reduction of discharge pressure P causes the oil pressure (discharge pressure P) acting on the pressure-receiving surface56of spool valve element43to be lower than the operating oil pressure of spool valve element43, so that the biasing force W2of valve spring44exceeds the biasing force based on discharge pressure P, and spool valve element43moves toward introduction port51, as shown inFIG.8A. This allows communication between communication port55and supply-drain port52of pilot valve40, and thereby causes the second discharge pressure to be supplied to second control oil chamber32again. This moves the cam ring15back in the eccentric direction, and increases the discharge pressure P again.

Thereafter, as the increase of discharge pressure P causes the oil pressure acting on the pressure-receiving surface56of spool valve element43to exceed the operating oil pressure of spool valve element43, spool valve element43moves again into the second region against the biasing force W2of valve spring44, as shown inFIG.8B. This causes the oil in second control oil chamber32to be drained, and causes the discharge pressure P to be supplied only to first control oil chamber31, as described above.

As a result, the biasing force based on the internal pressure of first control oil chamber31in the coaxial direction exceeds the biasing force in the eccentric direction which is the resultant force of the biasing force W1of coil spring33and the biasing force based on the internal pressure of second control oil chamber32, so that cam ring15moves in the coaxial direction, and discharge pressure P decreases again.

In this way, oil pump10according to the present embodiment is configured to perform an adjustment to maintain the discharge pressure P at the operating oil pressure of spool valve element43by continuing to alternately switch between communication between communication port55and supply-drain port52connected to second control oil chamber32, and communication between first drain port53and supply-drain port52by spool valve element43of pilot valve40. Since this pressure regulation is implemented by switching of supply-drain port52by pilot valve40, it is not influenced by the spring constant of coil spring33. Moreover, since the pressure regulation is performed within a significantly small range of stroke of spool valve element43related to the switching of supply-drain port52, it is not influenced by the spring constant of valve spring44. As a result, in the section “d”, as engine rotational speed N rises, the discharge pressure P of oil pump10does not increase in proportion but has a substantially flat characteristic.

As described above, oil pump10according to the present embodiment can maintain the discharge pressure P at the predetermined high pressure P2by the pressure regulation control of pilot valve40, in the engine rotation region (in the section “d” inFIG.6) where it is requested to maintain at least the predetermined high pressure (spool valve operating oil pressure) equal to the second engine request oil pressure P2.

Specifically, in case of oil pump10according to the present embodiment, when discharge pressure P exceeds the predetermined pressure that is the operating oil pressure of spool valve element43, after the condition that discharge pressure P is higher than the operating oil pressure of cam ring15, and lower than or equal to the operating oil pressure of spool valve element43, spool valve element43moves from the first region to the second region so as to reduce the quantity of eccentricity of cam ring15, and discharge pressure P becomes below the spool valve operating oil pressure again, and spool valve element43moves back to the first region. Thus, switching of communication via supply-drain port52by spool valve element43continues to be repeatedly performed, so that discharge pressure P can be maintained at the operating oil pressure of spool valve element43, and the predetermined high pressure characteristic P2can be maintained.

Moreover, as described above, in oil pump10according to the present embodiment, immediately before the slide position of spool valve element43of pilot valve40shifts from the first region to the second region, and oil is drained from second control oil chamber32through relay chamber57to first drain port53, the first land portion43aof spool valve element43closes the opening of communication port55at valve accommodation hole41a, and the second land portion43bcloses the opening end of first drain port53simultaneously, thereby putting the second control oil chamber32, communication passage59, and supply-drain port52temporarily in the state of closed circuit, as shown inFIG.9.

Accordingly, the condition that second control oil chamber32is filled with oil is maintained, so that cam ring15is maintained stably in the position in the direction to increase the quantity of eccentricity by the resultant force of the spring force of coil spring33and the operating oil pressure (second vector B2) acting on the second pressure-receiving surface15fof second control oil chamber32which has a larger area than the first pressure-receiving surface15eof first control oil chamber31.

In the conventional oil pump described above, when engine rotational speed N rises, many bubbles occur in oil and the bubbles collapse in pump chambers24in the discharge region, so that the internal pressures of pump chambers24get out of balance, and the behavior of cam ring15becomes unstable. As a result, in the state of high pressure characteristic P2, it is possible that discharge pressure P falls and a desired discharge pressure cannot be obtained, as shown by the long-dashed short-dashed line inFIG.6.

In contrast, according to the present embodiment, even if bubbles in pump chambers24collapse to bring the internal pressures of pump chambers24in the discharge region out of balance in the high engine speed region, cam ring15is maintained in the position to which cam ring15is moved in the direction to increase the quantity of eccentricity, because the second pressure-receiving surface15fis formed to have a larger area than the first pressure-receiving surface15e, and the second vector B2acting on the side of second control oil chamber32is larger than the first vector B1acting on the side of first control oil chamber31, as described above. This serves to suppress the behavior of cam ring15from becoming unstable, and thereby maintain the high pressure characteristic P2flat.

Second Embodiment

FIG.10shows a variable displacement type oil pump according to a second embodiment, which has basic configuration similar to that of the first embodiment, but differs in that a third control oil chamber80is formed between first control oil chamber31and second control oil chamber32.

Specifically, first seal slide surface11dof pump body11is moved and arranged toward arm portion15bof cam ring15in the circumferential direction, and the whole of first control oil chamber31is moved in the same direction, and third control oil chamber80is formed between first control oil chamber31and support hole11cof pump body11supporting the pivot pin19.

More specifically, the outer periphery of cam ring15is formed with a third seal forming portion15hprojecting and facing a third seal slide surface11fof the inner peripheral wall of pump body11. A third seal member20cis accommodated and held in a seal holding recess formed in the outer surface of third seal forming portion15h, wherein third seal member20cis in sliding contact with third seal slide surface11fwhen cam ring15swings with eccentricity.

Third seal member20cis similar to first and second seal members20a,20b, and is made of a material such as a fluorocarbon-based resin having a low friction property, and has a thin rectangular shape extending straight, and is pressed onto third seal slide surface11fby an elastic force of an elastic member, wherein the elastic member is made of rubber and disposed at a bottom portion of the holding recess, so that liquid tightness is held between third seal member20cand third seal slide surface11f.

Third control oil chamber80is defined by pivot pin19and third seal member20c, and is configured to communicate with the low pressure part such as the inside of the oil pan via a drain port81.

The provision of third control oil chamber80between pivot pin19and first control oil chamber31serves to set the first vector B1(semidiameter R1) larger than in the first embodiment, even if the area of first pressure-receiving surface15eof cam ring15facing the first control oil chamber31is equal to that of the first embodiment. Namely, first and second control oil chambers31,32may be arbitrarily arranged around the outer periphery of cam ring15, if the second vector B2serving for the force of swing of cam ring15is larger than the first vector B1.

The operations of pilot valve40and electromagnetic switching valve60are similar to those of the first embodiment, wherein it is possible to obtain a two-stage control including a high pressure characteristic and a low pressure characteristic of discharge pressure by control of the swing position of cam ring15by control of valves40,60, as in the first embodiment.

Oil leaked from first control oil chamber31and second control oil chamber32via third seal member20cand pivot pin19and others is collected in third control oil chamber80, and can be drained to the outside via drain port81. This allows to precisely control the quantity of oil supplied in first control oil chamber31and second control oil chamber32. This serves to further stabilize the control of the swing position of cam ring15.

Third Embodiment

FIG.11shows a third embodiment where third control oil chamber90is formed in a modified position. First control oil chamber31is formed in the same position as in the first embodiment, and third control oil chamber90is formed between second control oil chamber32and support hole11cof pump body11supporting the pivot pin19.

Specifically, the outer periphery of cam ring15is formed with a third seal forming portion15iprojecting and facing a third seal slide surface11gof the inner peripheral wall of pump body11. A third seal member20dis accommodated and held in a seal holding recess formed in the outer surface of third seal forming portion15i, wherein third seal member20dis in sliding contact with third seal slide surface11gwhen cam ring15swings with eccentricity.

Third seal member20dis similar to first and second seal members20a,20b, and is made of a material such as a fluorocarbon-based resin having a low friction property, and has a thin rectangular shape extending straight, and is pressed onto third seal slide surface11gby an elastic force of an elastic member, wherein the elastic member is made of rubber and disposed at a bottom portion of the holding recess, so that third control oil chamber90is liquid-tightly separated between pivot pin19and third seal slide surface11g, and is configured to communicate with the low pressure part such as the inside of the oil pan via a drain port91.

In spite of the provision of third control oil chamber90between pivot pin19and second control oil chamber32, the second vector B2of the semidiameter R2from pivot pin19to second seal slide surface11eis larger than the first vector B1of the semidiameter R1from pivot pin19to first seal slide surface11dsuch that a torque vector (second torque) based on the oil pressure of second control oil chamber32is larger than a torque vector (first torque) based on the oil pressure of first control oil chamber31, and the position of cam ring15can be stably held in the state of high pressure characteristic P2.

The operations of pilot valve40and electromagnetic switching valve60are similar to those of the first embodiment, wherein it is possible to obtain a two-stage control including a high pressure characteristic and a low pressure characteristic of discharge pressure by control of the swing position of cam ring15by control of valves40,60, as in the first embodiment.

Oil leaked from first control oil chamber31and second control oil chamber32via third seal member20dand pivot pin19and others is collected in third control oil chamber90, and can be drained to the outside via drain port91. This allows to precisely control the quantity of oil supplied in first control oil chamber31and second control oil chamber32. This serves to further stabilize the control of the swing position of cam ring15.

The present invention is not limited to the configurations according to the embodiments described above. For example, the first and second engine request oil pressures P1, P2, the operating oil pressure of cam ring15, and the operating oil pressure of spool valve element43may be changed arbitrarily depending on specifications of the internal combustion engine and valve timing device and others of the vehicle where oil pump10is mounted.

The embodiments are exemplified such that the quantity of discharge can be varied by swing of cam ring15. However, variation of the quantity of discharge is not limited to the swing means described above, but may be implemented by moving the cam ring15straight in a radial direction. In other words, the form of movement of cam ring15is unlimited, if the configuration is capable of varying the quantity of discharge (the configuration is capable of varying the quantity of change of the volumetric capacity of pump chamber24).

The embodiments are exemplified as the variable displacement type oil pump. For example, the present invention may be applied to a trochoid type pump. In such a case, an outer rotor forming an external gear corresponds to the swing member. The varying mechanism is configured by arranging the outer rotor to move with eccentricity similar to cam ring15, and arranging control oil chambers and a spring radially outside of the outer rotor.