Oil pump

Fluid inlet and outlet portions are provided for introducing and discharging a hydraulic fluid. The fluid outlet portion includes a plurality of outlet ports. A drive shaft is provided that rotates about its axis. A plurality of volume variable pump chambers are arranged about the drive shaft and rotated by the same. The pump chambers are arranged between the fluid inlet and outlet portions for compressing the hydraulic fluid from the fluid inlet portion before discharging the same from the fluid outlet portion. The pump chambers are exposed to the outlet ports separately one after another when the pump chambers are rotated by the drive shaft. A discharge rate varying mechanism is provided that varies a fluid discharge rate of each of the outlet ports by varying the amount of the fluid led to the outlet ports.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to oil pumps applicable to automotive engines and automotive transmissions, and more particularly to the oil pumps of a type that not only feeds elements of the engine (or transmission) with a less pressurized oil to lubricate and cool the same but also feeds hydraulically operated actuating devices of the engine (or transmission) with a highly pressurized oil to drive the same.

That is, for example, in case wherein two hydraulic circuits are provided which separately need of introducing hydraulic fluids that are different in pressure (or introducing rate), usage of two oil pumps may be easily thought out. However, in this case, high-cost and complicated construction of the hydraulic system is inevitably induced due to usage of the two oil pumps.

In view of such drawback, various measures have been hitherto proposed and put into practical use in the field of the hydraulic system. One of them is an oil pump as disclosed in Japanese Laid-open Application (tokkaihei) 8-114186, which is provided with two (or more) outlet ports that separately discharge hydraulic fluids that are different in pressure (or fluid discharge rate).

The oil pump of the publication is a so-called internal trochoid pump that comprises mutually meshed toothed outer and inner rotors each having trochoidal tooth profile. That is, the toothed outer and inner rotors are meshed to each other keeping a mutual eccentricity therebetween, so that under operation a plurality of volume variable pump chambers are continuously formed between the internal teeth of the outer rotor and the external teeth of the inner rotor.

An operating chamber of a pump housing that accommodates the two rotors is formed at a bottom portion thereof with an inlet port that is exposed to a volume increasing zone in which each pump chamber is shifted from the smallest volume position to the largest volume position along a given way defined by the two rotors. While, to a volume reducing zone in which each pump chamber is shifted from the largest volume position to the smallest volume position, there are exposed two independent outlet ports (viz., first and second outlet ports) having a seal land portion located at a predetermined circumferential position.

Under operation, the hydraulic fluid in each pump chamber shifted from the largest volume position to the seal land portion is led (or discharged) to the first outlet port and the hydraulic fluid in the pump chamber shifted from the seal land portion to the smallest volume position is led (or discharged) to the second outlet port. Accordingly, the first and second outlet ports can discharge two types of hydraulic fluid separately in accordance with the circumferential position of the seal land portion.

SUMMARY OF THE INVENTION

In case wherein the oil pump is employed in a motor vehicle, the first outlet port of the oil pump is connected to a first hydraulic circuit to discharge a hydraulic pressure for lubricating and cooling various elements of the engine (or transmission) and the second outlet port of the oil pump is connected to a second hydraulic circuit to discharge a hydraulic pressure for driving hydraulically operated actuating devices.

In this case, the followings are important.

That is, in the first hydraulic circuit, feeding a pressure stable hydraulic fluid is constantly needed, and in the second hydraulic circuit, feeding a high pressure fluid is needed only when the hydraulically operated actuating devices are actually operated.

However, in the above-mentioned known oil pump, the fluid discharge rate is substantially proportional to the rotation speed of the oil pump. Thus, when the second hydraulic circuit connected to the second outlet port of the oil pump needs a fluid introducing rate that is higher than that needed by the first hydraulic circuit connected to the first outlet port, it is inevitably necessary to increase the rotation speed of the oil pump with the aid of an electric motor or the like.

However, under such condition, the hydraulic pressure or fluid discharge rate of the hydraulic fluid discharged from the first outlet port is wastefully increased, which brings about a useless work of the oil pump even though the work of the oil pump satisfies the fluid feeding to the second hydraulic circuit. Even when the seal land portion is set at an optimum position for minimizing the wasteful work of the oil pump, energization of the electric motor for increasing the rotation speed of the oil pump brings about useless consumption of electric power.

Accordingly, an object of the present invention is to provide an oil pump which is free of the above-mentioned drawbacks.

According to the present invention, there is provided an oil pump that is constructed to reduce a wasteful pumping work as small as possible.

According to the present invention, there is provided an oil pump that comprises a fluid outlet portion that includes a plurality of outlet ports and a discharge rate varying mechanism that varies the fluid discharge rate of each of the outlet ports, so that the fluid discharging ratio between the outlet ports is also varied.

In accordance with a first aspect of the present invention, there is provided an oil pump which comprises a fluid inlet portion for introducing a hydraulic fluid; a fluid outlet portion for discharging the hydraulic fluid, the fluid outlet portion including a plurality of outlet ports; a drive shaft that rotates about an axis thereof; a plurality of volume variable pump chambers arranged about the drive shaft and rotated by the same, the pump chambers being arranged between the fluid inlet portion and the fluid outlet portion for compressing the hydraulic fluid from the fluid inlet portion before discharging the same from the fluid outlet portion, the pump chambers being exposed to the outlet ports separately one after another when the pump chambers are rotated by the drive shaft; and a discharge rate varying mechanism that varies a fluid discharge rate of each of the outlet ports by varying the amount of the fluid led to the outlet ports.

In accordance with a second aspect of the present invention, there is provided an oil pump which comprises a fluid inlet portion for introducing a hydraulic fluid; a fluid outlet portion for discharging the hydraulic fluid, the fluid outlet portion including a plurality of outlet ports; a drive shaft that rotates about an axis thereof; a plurality of volume variable pump chambers arranged about the drive shaft and rotated by the same, the pump chambers being arranged between the fluid inlet portion and the fluid outlet portion for compressing the hydraulic fluid from the fluid inlet portion before discharging the same from the fluid outlet portion, the pump chambers being exposed to the outlet ports separately one after another when the pump chambers are rotated by the drive shaft, each outlet port extending in a circumferential direction around the axis of the drive shaft; and a discharge rate varying mechanism that varies an actual open range of each of the outlet ports relative to the pump chambers thereby to vary a fluid discharge rate of each outlet port.

In accordance with a third aspect of the present invention, there is provided an oil pump which comprises an inner rotor rotated by a drive shaft; an outer rotor rotatably disposed around the inner rotor keeping an eccentricity relative to the inner rotor; a plurality of volume variable pump chambers defined between the inner and outer rotors when the inner and outer rotors make a relative rotation; a fluid inlet portion exposed to a circumferential range that induces increase in volume of each pump chamber when the inner and outer rotors make the relative rotation; a fluid outlet portion exposed to a circumferential range that induces decrease in volume of each pump chamber when the inner and outer rotors make the relative rotation; and a discharge rate varying mechanism that varies a degree of the eccentricity of the outer rotor relative to the inner rotor.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following, three embodiments100,200and300of the present invention and one modification100′ of the embodiment100will be described in detail with reference to the accompanying drawings.

For ease and simplification, substantially same elements, parts and portions are designated by the same numerals throughout the description and drawings, and repeated explanation on the same elements, parts and portions will be omitted in the following description.

As will become apparent as the description proceeds, in the embodiments100,200and300and the modification100′, the oil pump of the invention will be described as a hydraulic pressure supplier that supplies both an automotive engine (viz., internal combustion engine) and an associated transmission with respective hydraulic pressures.

Referring toFIGS. 1 to 10, there is shown an oil pump100which is a first embodiment of the present invention.

As is understood fromFIG. 7, the oil pump100is arranged to be driven by an electric motor3and feeds both a constant pressure circuit5and a high pressure circuit6with respective pressurized hydraulic pressures. As will be described in detain hereinafter, constant pressure circuit5is connected to a first outlet port21of the pump100and high pressure circuit6is connected to a second outlet port22of the pump100.

Electric motor3is controlled by an electronic control unit (ECU)2. Under operation, oil pump100sucks a drained hydraulic fluid from an oil pan4through a pipe23aand discharges compressed hydraulic fluid to both constant pressure circuit5and high pressure circuit6through respective pipes24aand25a, as shown.

Designated by numeral7inFIG. 7is a pressure sensor that senses a hydraulic pressure appearing in pipe25aand feeds electronic control unit (ECU)2with a corresponding information on the sensed hydraulic pressure.

Constant pressure circuit5is the circuit to provide various elements of the engine and transmission with hydraulic fluid for lubricating and cooling the same. Such elements are, for example, a crankshaft, camshaft, pistons and the like of the engine and rotation shafts and gear drive members of the transmission.

High pressure circuit6is the circuit to provide hydraulically operated actuating devices with hydraulic fluid (viz., hydraulic pressure) to drive the actuating devices. Such devices are, for example, actuators of a variable valve timing mechanism of the engine and actuators of hydraulic clutches and hydraulic brakes of the transmission.

As is seen inFIG. 7, high pressure circuit6is connected to pressure sensor7that monitors the pressure of the hydraulic fluid fed from oil pump100to high pressure circuit6. Based on the pressure information signal from pressure sensor7, electronic control unit2controls electric motor3.

As is seen fromFIGS. 5 and 6, oil pump100is integrated with electric motor3to constitute a unit. That is, oil pump100and electric motor3are coupled together in a so-called face-to-face connecting manner. That is, as is seen fromFIG. 5, upon coupling, an output shaft3aof electric motor3projects into oil pump100.

As is best seen fromFIG. 5, oil pump100comprises a pump housing11that has a generally cylindrical rotor receiving bore14, a drive shaft15that is rotatably installed in rotor receiving bore14and connected at one end (viz., right end in the drawing) to output shaft3aof electric motor3, an annular outer rotor16that is rotatably received in rotor receiving bore14, an inner rotor17that is tightly disposed on drive shaft15and rotatably received in the annular outer rotor16, and a discharge rate varying mechanism30that is arranged at a side of pump housing11opposite to electric motor3.

As will be apparent hereinafter, discharge rate varying mechanism30functions to vary the rate of fluid discharge (which will be referred to “fluid discharge rate” hereinafter) of oil pump100to each of the above-mentioned constant pressure circuit5and high pressure circuit6.

As is seen fromFIGS. 5 and 6, pump housing11comprises a pump body12that has one end portion formed with the rotor receiving bore14and the other end portion fixed to electric motor3, and a cover member13that is connected to the open side of pump body12to cover rotor receiving bore14. For this connection, four connecting bolts10aare used and as is best seen fromFIG. 5, three elongate connecting bolts10bare used for connecting cover member13, pump body12and electric motor3together.

As is seen fromFIGS. 2 and 5, pump body12made of an aluminum alloy is cylindrical with an octagonal external appearance.

As is seen fromFIG. 5, pump body12has in an end wall thereof a bearing bore12athat bears or rotatably receives an after-mentioned larger diameter part15bof drive shaft15.

It is to be noted that cylindrical rotor receiving bore14is somewhat eccentric with respect to bearing bore12a. In other words, the center axis of the cylindrical bore14is eccentric to an axis that passes through a center of bearing bore12a.

As is understood fromFIG. 6, the cylindrical wall of bearing bore12ais formed with an annular groove12hfor receiving therein a seal member19. With this seal member19, undesired leakage of the hydraulic fluid from the cylindrical bore14toward electric motor3is suppressed.

As is seen fromFIG. 6, cover member13fixed to the open side of pump body12is formed at a center part with a bearing blind bore13ainto which an end of an after-mentioned smaller diameter part15aof drive shaft15is rotatably received. That is, bearing blind bore13aconcentrically faces the above-mentioned bearing bore12a.

Furthermore, cover member13is formed with a drain passage13bthat communicates bearing blind bore13awith an after-mentioned back pressure chamber36a, so that the hydraulic fluid that has been led into bearing blind bore13afrom rotor receiving bore14through a clearance defined around smaller diameter part15aof drive shaft15is led to the back pressure chamber36a.

Drive shaft15is a stepped shaft including the smaller diameter part15athat is press-fitted into a center opening (no numeral) of inner rotor17and the larger diameter part15bthat is detachably connected to output shaft3aof electric motor3.

For the detachable connection of larger diameter part15bwith output shaft3a, as will be understood fromFIG. 6, the larger diameter part15bis formed with a hexagonal blind bore15cwith which a hexagonal top3bof output shaft3ais intimately engaged to achieve a coupling therebetween. That is, upon energization of electric motor3, output shaft3adrives drive shaft like a single unit.

As is seen fromFIGS. 1,3and5, outer rotor16is rotatably received in rotor receiving bore14permitting a cylindrical outer surface thereof to slide on and along a cylindrical inner surface of the bore14.

Outer rotor16is formed with a plurality of internal teeth16aeach having a trochoidal profile.

Inner rotor17is formed with a plurality of external teeth17aeach having a trochoidal profile. Upon coupling between inner and outer rotors17and16, the external teeth17aof inner rotor17are operatively engaged with the internal teeth16aof outer rotor16.

It is to be noted that the number of the external teeth17ais less than that of the internal teeth16aby one. In the illustrated embodiment100, the number of the external teeth17ais eight, and that of the internal teeth16ais nine.

As is seen fromFIG. 3, upon assembly, inner rotor17is operatively received in outer rotor16keeping an eccentric arrangement therebetween. That is, under operation, some of external teeth17aof inner rotor17are practically engaged with some of internal teeth16aof outer rotor16.

As will become apparent as the description proceeds, upon rotation of inner rotor17, outer rotor16is forced to make a rotation relative to inner rotor17keeping the mutually eccentric arrangement.

As is seen fromFIG. 3, under the relative rotation therebetween, inner and outer teeth16aand17aare forced to contact continuously thereby continuously defining a plurality of pump chambers V1to V9therebetween, each pump chamber gradually increasing or decreasing.

Under operation of oil pump100, the four pump chambers V1to V4placed in a volume increasing range (viz., left half portion inFIG. 3) that brings about a gradual increase of the volume in response to rotation of the two rotors16and17are forced to suck the hydraulic fluid from oil pan4through an inlet port18due to the work of negative pressure produced in the pump chambers V1to V4in response to increase of the volume of the same.

The inlet port18is arranged to straddle over the four pump chambers V1to V4and thus has a generally U-shaped cross section.

While, under operation of oil pump100, the other five pump chambers V5to V9placed in a volume decreasing range (viz., right half portion inFIG. 3) that brings about a gradual decrease of the volume in response to rotation of the two rotors16and17are forced to discharge the hydraulic fluid therefrom to the outside through an outlet port20due to the work of positive pressure produced in the pump chambers V5to V9in response to decrease of the volume of the same.

Like the inlet port18, the outlet port20is arranged to straddle over the five pump chambers V5to V9and has a generally U-shaped cross section.

As is understood fromFIG. 1, outlet port20comprises first and second outlet ports21and22that are isolated from each other.

That is, first outlet port21is exposed to pump chambers V6and V7that are placed at a leading portion of the above-mentioned volume decreasing range and thus show relatively large volume, and second outlet port22is exposed to pump chambers V8and V9that are placed at a trailing portion of the volume decreasing range and thus show relatively small volume.

In pump chambers V6to V9, reduction in volume gradually takes place and thus each pump chamber discharge the compressed hydraulic fluid to first and second outlet ports21and22.

As is seen fromFIG. 2, on an inner surface of the other wall of pump body12, there is defined a rotor sliding surface12bto which one axial end surface of each rotor16or17slidably contacts under rotation of the rotor.

As is seen fromFIGS. 1 and 2, rotor sliding surface12bis formed with a fixed inlet port23in a circumferential range corresponding to the above-mentioned volume increasing range, that is exposed to pump chambers V1to V4of intake side. Fixed inlet port23constitutes one side portion of the above-mentioned inlet port18.

Furthermore, rotor sliding surface12bis formed with an arcuate first fixed outlet port24in a range corresponding to a leading portion of the above-mentioned volume decreasing range, that is exposed to pump chambers V6and V7of discharge side. First fixed outlet port24constitutes one side portion of the above-mentioned first outlet port21. Furthermore, rotor sliding surface12bis formed with an arcuate second fixed outlet port25in a range corresponding to a trailing portion of the volume decreasing range, that is exposed to pump chambers V8and V9of discharge side. Second fixed outlet port25constitutes one side portion of the above-mentioned second outlet port22.

As is seen fromFIG. 3, fixed inlet port23is formed at a circumferential middle portion thereof with an inlet opening23athat extends radially outward. Although not shown in the drawings, inlet opening23ais connected to the above-mentioned oil pan4through a pipe. That is, under operation, the hydraulic fluid is sucked into fixed inlet port23from oil pan4through inlet opening23a.

Furthermore, as is well seen fromFIG. 3, fixed inlet port23is formed at the circumferential middle portion thereof with a recess23bthat is depressed radially outward. Due to provision of recess23b, there is formed an inlet port communicating is passage18athat extends around outer rotor16to communicate fixed inlet port23with an after-mentioned movable inlet port33.

While, the above-mentioned arcuate first fixed outlet port24is formed at a circumferential middle portion thereof with a first outlet opening24athat extends radially outward. Although not shown in the drawings, through a pipe connected to first outlet opening24a, the hydraulic fluid compressed by pump chambers V6and V7is led to the above-mentioned constant pressure circuit5.

Furthermore, first fixed outlet port24is so shaped as to extend radially outward beyond outer rotor16, that is, beyond the inside surface of rotor receiving bore14, and first fixed outlet port24has an extension part24bthat extends in a direction of rotation of the two rotors16and17. For convenience sake, the extension part24bwill be called first communication auxiliary groove24bhereinafter. Due to provision of first communication auxiliary groove24b, there is provided a first outlet port communicating passage21athat extends around outer rotor16to communicate first fixed outlet port24with an after-mentioned first movable outlet port34. Actually, first outlet port communicating passage21acomprises a peripheral part of first fixed outlet port24and first communication auxiliary groove24b.

Like the above, the above-mentioned arcuate second fixed outlet port25is formed at a radially outside part thereof with a second outlet opening25a. Although not shown in the drawings, through a pipe connected to second outlet opening25a, the hydraulic fluid compressed by pump chambers V8and V9is led to the above-mentioned high pressure circuit6.

Second fixed outlet port25is further formed at another radially outside part thereof with a second communication auxiliary groove25bthat extends in the direction of rotation of the two rotors16and17. Due to provision of second communication auxiliary groove25b, there is provided a second outlet port communicating passage22athat extends around outer rotor16to communicate second fixed outlet port25with an after-mentioned second movable outlet port35. Actually, second outlet port communicating passage22acomprises a peripheral part of first fixed outlet port24and second communication auxiliary groove25b.

As is seen fromFIG. 2, between fixed inlet port23and fixed outlet port24, there is arranged a first fixed side seal land12cthat constitutes part of the above-mentioned rotor sliding surface12b, and between fixed inlet port23and second fixed outlet port25, there is arranged a second fixed side seal land12dthat constitutes part of the rotor sliding surface12b.

As will be seen fromFIGS. 2 and 3, first fixed side seal land12chas a circumferential length that is generally the same as the pitch of the external teeth17aof inner rotor17. That is, as is understood fromFIG. 3, first fixed side seal land12cis so arranged and sized as to completely cover pump chamber V5that exhibits the maximum volume when leaving the volume increasing range and entering the volume decreasing range.

While, as is seen fromFIG. 2, second fixed side seal land12dhas a circumferential length that is generally the same as the distance between adjacent two bottoms of the internal teeth16aof outer rotor16. As is understood fromFIG. 3, second fixed side seal land12dis so arranged and sized not to cover two pump chambers V1and V9at a time when pump chamber V1shows the minimum volume in the volume increasing range and pump chamber V9shows the maximum volume in the volume decreasing range.

As is seen fromFIG. 2, between arcuate first fixed outlet port24and arcuate second fixed outlet port25, there are arranged first and second fixed side seal lands12cand12dand a third fixed side seal land12ethat constitutes the above-mentioned rotor sliding surface12b. Third fixed side seal land12eserves to divide outlet port20, as shown.

It is now to be noted that by changing a circumferential position of third fixed side seal land12e, respective circumferential ranges of first and second outlet ports21and22are changed and thus the fluid discharge rate of oil pump100relative to each of the two ports21and22is changed.

As is seen fromFIGS. 1 and 3, pump body12is formed is formed at the open end wall thereof with a generally cylindrical recess26for receiving an after-mentioned rotary plate31. Cylindrical recess26is concentric with the above-mentioned bearing bore12a, and rotary plate31constitutes part of the discharge rate varying mechanism30.

As is seen fromFIGS. 2 and 6, cylindrical recess26has an outer diameter sufficiently larger than that of rotor receiving bore14, so that there is defined therebetween a plate seat portion on and around which rotary plate31moves.

Under a condition wherein the two rotors16and17are properly set in rotor receiving bore14, axially outer surfaces of the rotors16and17are flush with a seating surface of rotary plate31.

As is best seen fromFIG. 2, cylindrical recess26is formed at a cylindrical wall thereof with an arcuate groove27that is depressed in radially outward. As is seen from the drawing, arcuate groove27is concentric with cylindrical recess26.

As may be understood fromFIG. 1, discharge rate varying mechanism30is of a mechanism including two major parts that make a relative rotation therebetween. More specifically, discharge rate varying mechanism30comprises pump housing11that constitutes one of the major parts, rotary plate31that is slidably received in cylindrical recess26to rotate by an angular range corresponding to the circumferential length of cylindrical recess26thereby defining inlet port18and first and second outlet ports21and22, and a spring32that is received in one end portion of arcuate groove27to bias rotary plate31in a given direction, that is, in a clockwise direction inFIG. 1. As will be described in the following, for being biased by the spring32, rotary plate31is formed with a lever portion31b.

As is understood fromFIG. 6, rotary plate31has a thickness that is substantially the same as the depth of the plate receiving recess (or cylindrical recess)26, and rotary plate31is circular in shape. Under rotation of rotary plate31, one surface slides on cover member13and the other surface slides on the outside surfaces of the two rotors16and17. Rotary plate31is formed with a shaft receiving opening31athrough which smaller diameter part15aof drive shaft15passes. Thus, rotary plate31is permitted to make a relative rotation to drive shaft15.

As is seen fromFIG. 1, rotary plate31is formed at a peripheral part with the above-mentioned lever portion31bthat, under rotation of rotary plate31, slidably contacts an outer cylindrical surface of arcuate groove27to divide the interior of the groove27into two chambers. With such arrangement, under a condition wherein rotary plate31is set in plate receiving recess26having cover member13hermetically connected thereto, the arcuate groove27forms therein a back pressure chamber36athat is placed at a position opposite to the rotation direction of the two rotors16and17to receive therein the spring32, and a pressure chamber36bthat is placed at the rotational direction of the rotors16and17to introduce the discharge pressure from first outlet port21.

Although not shown in the drawings, cover member13is formed with stopper pins to which lever portion31bof rotary plate31abuts for regulating the rotating range of rotary plate31.

As is seen fromFIGS. 1 and 5, rotary plate31is formed with movable inlet port33and first and second movable outlet ports34and35that constitute counter-portions of the above-mentioned inlet port18and first and second outlet ports21and22.

Movable inlet port33and first and second movable outlet ports34and35are sized to correspond to fixed inlet port23and fixed first and second fixed outlet ports24and25that are formed in rotor sliding surface12bof pump body12.

More specifically, as is seen fromFIGS. 1,8and9, movable inlet port33has a shape similar to that of fixed inlet port23. However, a circumferential length of movable inlet port33is shorter than that of fixed inlet port23. Thus, throughout the entire rotation range of rotary plate31, movable inlet port33is permitted to overlap with fixed inlet port23.

As is seen fromFIG. 4, like the above-mentioned fixed inlet port23, movable inlet port33of rotary plate31is formed at a circumferentially middle part thereof with a radially outwardly depressed recess33a. At the position where recess33aoverlaps with recess23bof fixed inlet port23, there is defined the above-mentioned inlet port communicating passage18a.

With the above-mentioned arrangement, part of the hydraulic fluid led into fixed inlet port23through the above-mentioned inlet opening23ais led into movable inlet port33through inlet port communicating passage18a, so that also from movable inlet port33, the hydraulic fluid is led into pump chambers V1to V4.

First movable outlet port34has a shape identical to first fixed outlet port24, and in a radial direction, throughout the entire rotating range of rotary plate31, first movable outlet port34is exposed to first fixed outlet port24, and as is seen fromFIG. 9, in a circumferential direction, when rotary plate31takes the counterclockwise-most position, the port34fully overlaps with first fixed outlet port24.

Thus, as is seen fromFIG. 1, at a radially outward side of outer rotor16where first movable outlet port34overlaps with first fixed outlet port24, there is defined the above-mentioned first outlet port communicating passage21a. The hydraulic fluid discharged to first movable outlet port34through the communicating passage21ais discharged from first outlet port24atogether with the hydraulic fluid discharged to first fixed outlet port24.

Second movable outlet port35has a shape similar to the above-mentioned second fixed outlet port25. However, a circumferential length of the port35is somewhat shorter than that of second fixed outlet port25, and in a radial direction, throughout the entire rotating range of rotary plate31, the outlet port35is fully mated with second fixed outlet port25, and as is seen fromFIG. 8, in a circumferential direction, when rotary plate31is rotated to the clockwise-most position, the outlet port35is fully mated with second fixed outlet port25.

As is seen fromFIG. 1, like the above-mentioned first movable outlet port34, second movable outlet port35is formed, around outer rotor16at a position where second movable outlet port35and first fixed outlet port25are mated, with the above-mentioned second outlet port communicating passage22a, so that the hydraulic fluid discharged to second movable outlet port35through the communicating passage22ais discharged from a second outlet port25atogether with the hydraulic fluid discharged to second fixed outlet port25.

As is described hereinabove, movable ports33to35are arranged to constitute respective passage units together with communicating passages18a,21aand22aand fixed outlet ports23,24and25. More specifically, movable port33and fixed inlet port23constitute the inlet port18, first movable outlet port34and first fixed outlet port24constitute the first outlet port21and second movable outlet port35and second fixed outlet port25constitute second outlet port22.

As will be understood from the above description, the movable ports33to35are arranged eccentric to the corresponding fixed ports23to25. This is because of the followings. That is, a first movable side seal land31cof rotary plate31between movable inlet port33and first movable outlet port34and a second movable side seal land31dof rotary plate31between movable inlet port33and second movable outlet port35have circumferential lengths that are greater than those of the corresponding first and second fixed side seal lands12cand12d, and a third movable side seal land31cof rotary plate31between first movable outlet port34and second movable outlet port35has a circumferential length that is smaller than that of third fixed side seal land12eand generally equal to the pitch of the external teeth17aof inner rotor17.

Due to the above-mentioned arrangement, throughout the entire rotation range of rotary plate31, first and second movable side seal lands31cand31dcan overlap with the corresponding first and second fixed side seal lands12cand12d, and thus, under operation, the first and second fixed side seal lands12cand12dserve as an actual seal land means.

While, third movable side seal land31ehas a circumferential length that is smaller than that of third fixed side seal land12e, and throughout the entire rotation range of rotary plate31, third fixed side seal land12ecan constantly overlap with third movable side seal land31e, and thus, under operation, third movable side seal land31eserves as an actual seal land means.

That is, since the third seal land portion that separates first and second outlet ports21and22moves in a circumferential direction upon rotation of rotary plate31, the ranges of first and second outlet ports21and22are subjected to a change, and as a result, the fluid discharge rate of oil pump100relative to each of the two outlet ports21and22is changed.

As is seen fromFIGS. 1 and 4, rotary plate31is formed on an outer side surface (viz., the surface opposite to the surface to which end surfaces of two rotors16and17slidably contact) with a pressure relief groove31fthat constantly connects one end (near first movable side seal land31c) of movable inlet port33and the above-mentioned back pressure chamber36a. That is, due to presence of such groove31f, movable inlet port33and back pressure chamber36akeeps their mutual fluid communication even under rotation of rotary plate31. More specifically, due to presence of such pressure relief groove31f, the hydraulic fluid led to the back pressure chamber36acan be returned to movable inlet port33.

As is seen fromFIG. 1, within back pressure chamber36a, there is installed the above-mentioned spring32for constantly biasing rotary plate31to rotate in the same direction as the rotation of the two rotors16and17.

While, as is seen fromFIGS. 1 and 4, on the outer side surface of rotary plate31, there is further formed a pressure induction groove31gthat constantly connects one end (viz., the end near first movable side seal land31c) of first movable outlet port34and the above-mentioned pressure chamber36b. That is, even under rotation, the fluid communication between the port34and the chamber36bis assuredly kept. Due to presence of such groove31g, the discharge pressure of first outlet port21is led to the pressure chamber36bto press lever portion31bof rotary plate31thereby to bias rotary plate31to rotate in a direction opposite to the direction in which the two rotors16and17rotate. That is, inFIG. 1, rotary plate31is biased to rotate in a counterclockwise direction.

As will be understood from the above description, in the discharge rate varying mechanism30, rotary plate31rotates in accordance with a difference between the discharge pressure at first outlet port21and the biasing force of spring32thereby changing the circumferential position of third movable side seal land31e. With this, a circumferential open range of first outlet port21relative to pump chambers V6and V7and that of second outlet port22relative to pump chambers V6and V7are changed, so that the fluid discharge rate to each of first and second outlet ports21and22is changed.

In the following, with reference to the drawings, especially,FIGS. 1,8and9, operation of oil pump100of the present invention will be described with respect to operation of the discharge rate varying mechanism30.

FIG. 8shows a condition wherein oil pump100is about to start its pumping work. Under this condition, due to the biasing force of spring32, rotary plate31is biased in a clockwise direction in the drawing and takes the clockwise-most position. That is,FIG. 8shows a condition wherein rotary plate31assumes the clockwise-most position in the rotating range. Due to provision of the stopper pins (not shown) provided by cover member13, excessive clockwise rotation of rotary plate31is suppressed.

When rotary plate31assumes the position as shown inFIG. 8, first outlet port21shows such a state that first fixed outlet port24and first movable outlet port34are most displaced away from each other maximizing the open range exposed to pump chambers V6and V7. In this condition, the hydraulic fluid from first outlet port21shows the maximum fluid discharge rate. While, when rotary plate31assumes the position ofFIG. 8, second outlet port22shows such a state that second fixed outlet port25and second movable outlet port35fully overlap with each other minimizing the open range exposed to pump chambers V8and V9. In this condition, the hydraulic fluid from second outlet port22shows the minimum fluid discharge rate.

In response to increase of rotation speed of oil pump100, the discharge pressure appearing at first discharge port21increases. When the discharge pressure exceeds a predetermined value (viz., set pressure), rotary plate31is forced to rotate counterclockwise to a position, such as the position as shown inFIG. 1, against the biasing force of spring32.

In such position, third fixed side seal land12eassumes a circumferential middle position relative to third movable side seal land31eshowing a small circumferential distance between first fixed outlet port24and first movable outlet port34as compared with the case shown inFIG. 8and producing a certain circumferential distance between second fixed outlet port25and second movable outlet port35. That is, in accordance with a counterclockwise rotation of rotary plate31inFIG. 1, the fluid discharge rate of first outlet port21is gradually reduced and that of second outlet port22is gradually increased.

When thereafter the discharge pressure in first discharge port21is further increased, rotary plate31is further rotated counterclockwise in the drawing due to the force of the increased discharge force, and finally, rotary plate31is rotated to the position as shown inFIG. 9.

When rotary plate31is at the position ofFIG. 9, first outlet port21takes such a condition that first fixed outlet port24and first movable outlet port34are fully mated with each other, so that the open range exposed to pump chambers V6and V7is minimized and thus the fluid discharge rate of first outlet port21is minimized. While, when rotary plate31is at the position ofFIG. 9, second outlet port22takes such a condition that second fixed outlet port25and second movable outlet port35are maximally placed away from each other in a circumferential direction, so that the open range exposed to pump chambers V8and V9is maximized and thus the fluid discharge rate of second outlet port22is maximized.

As is described hereinabove, rotary plate31is continuously rotated in accordance with the discharge pressure of first outlet port21applied to the right side (inFIGS. 8 and 9) of lever portion31bof rotary plate31. When the discharge pressure of first outlet port21is lowered, rotary plate31is rotated clockwise in the drawings due to the force of spring32thereby increasing the fluid discharge rate of first outlet port21.

In the discharge rate varying mechanism30, by rotating rotary plate31in accordance with the discharge pressure at first outlet port21, the fluid discharge rate of first or second outlet port21or22is increased or decreased for keeping the discharge pressure of first outlet port21at a predetermined degree (viz., set pressure).

In the following, operation of oil pump100practically set in an actual hydraulic circuit will be described with reference toFIGS. 7 and 10. That is, as is seen fromFIG. 7, under operation, oil pump100feeds the hydraulic fluid to both constant pressure circuit5and high pressure circuit6.

For operating constant pressure circuit5, the following facts are to be considered. That is, for lubricating and cooling the elements of the engine and transmission (viz., elements benefiting from constant pressure circuit5), constant pressure circuit5needs a relatively low pressurized (viz., pressure P1) and constantly stable hydraulic fluid. However, as is known to those skilled in the art, clearances between mutually contacting portions of the elements are varied in accordance with rotation speed of the engine, and thus, the amount of hydraulic fluid needed for keeping the pressure P1is varied in accordance with the rotation speed of the engine.

While, for operating high pressure circuit6, the following facts are to be considered. When the actuator of the variable valve timing mechanism of the engine and the actuators of the hydraulic clutches and hydraulic brakes of the transmission are at rest, it is only necessary to feed the high pressure circuit6with a hydraulic fluid of low pressure (P2). That is, only when such actuators are in operation, it becomes necessary to feed the circuit6with a hydraulic fluid of high pressure (P3).

Thus, in the present invention, as is seen fromFIG. 7, first outlet port21of oil pump100is connected to constant pressure circuit5through pipe24a. That is, by the rotation of rotary plate31in accordance with the discharge pressure in first outlet port21, the fluid discharge rate of first outlet port21or second outlet port22is varied keeping the discharge pressure in first outlet port21at the relatively low predetermined pressure P1.

As is seen fromFIG. 7, second outlet port22is connected to high pressure circuit6. Thus, the discharge pressure in second outlet port22is detected by pressure sensor7and an information signal on the detected discharge pressure is fed to the electronic control unit2. That is, when the above-mentioned actuators are at rest, control unit2controls the rotation speed of electric motor3(viz., oil pump100) to keep the discharge pressure in second outlet port22to the low level P2, while when the actuators are in operation, control unit2controls the rotation speed of electric motor3to keep the discharge pressure in second outlet port22to the high level P3.

In a low speed operation condition wherein the engine rotation speed is low, constant pressure circuit5needs a relatively small amount (Q1) of hydraulic fluid of the predetermined pressure P1, and high pressure circuit6needs a small amount (Q3) of hydraulic fluid of the predetermined low pressure P2.

While, in a normal operation condition wherein the engine rotation speed is higher than that of the above-mentioned low speed operation condition, constant pressure circuit5needs a relatively larger amount (Q2) of hydraulic fluid of the predetermined pressure P1, and high pressure circuit6needs a smaller amount (Q3) of hydraulic fluid of the predetermined low pressure P2. While, upon operation of the actuators, high pressure circuit6needs a much larger amount (Q4) of hydraulic fluid of the predetermined pressure P3.

In view of the above description, the following inequalities are established.

As will be understood from the above description, each of constant pressure circuit5and high pressure circuit6is subjected to a marked fluctuation in both hydraulic pressure and fluid amount in accordance with the engine operation condition. Particularly in fluid amount, the general fluid discharge rate of oil pump100and the fluid discharge rate of each of the two outlet ports21and22of the pump100is subjected to a marked change.

In the following, operation of oil pump100itself will be described concretely with reference to the drawings.

When oil pump100is at rest, the open degree of first outlet port21shows the maximum value as is mentioned hereinabove.

When, upon starting of the engine, oil pump100starts its operation and comes into the low speed operating condition, rotary plate31is rotated in a counterclockwise direction inFIG. 1to reduce the open degree of first outlet port21, so that the discharge pressure of first outlet port21shows the predetermined pressure P1.

When now pressure sensor7senses that the hydraulic pressure applied to high pressure circuit6is higher than the low predetermined level P2, control unit2reduces the rotation speed of electric motor3, and when the sensor7senses that the pressure applied to high pressure circuit6is lower than the low predetermined level P2, control unit2increases the rotation speed of electric motor3. That is, in accordance with the hydraulic pressure in high pressure circuit6, control unit2controls electric motor3.

When the rotation speed of electric motor3is reduced, the rotation speed of oil pump100is accordingly reduced and thus the hydraulic pressure in first outlet port21is reduced. Accordingly, by rotating rotary plate31to a desired angular position, the fluid discharge rate of first outlet port21is increased keeping the discharge pressure in first outlet port21at the predetermined level P1.

While, when the rotation speed of electric motor3is increased, the rotation speed of oil pump100is increased and thus the hydraulic pressure in first outlet port21is increased. Accordingly, by rotating rotary plate31to a desired angular position, the fluid discharge rate of first outlet port21is reduced keeping the discharge pressure in first outlet port21at the predetermined level P1.

Due to the change of rotation speed of electric motor3and the change of the fluid discharge rate of first outlet port1, the hydraulic pressure in high pressure circuit6is subjected to a change. Thus, by processing a feedback signal, control unit2controls electric motor3in a manner to keep the discharge pressure of second outlet port22at the lower level P2.

By turning rotary plate31and controlling the rotation speed of electric motor3in the above-mentioned manner, each of control pressure circuit5and high pressure circuit6is fed with a desired amount Q1or Q3of the hydraulic fluid of the predetermined pressure P1or P2.

When then the engine shifts from the low speed operation condition to the normal operation condition, the amount of hydraulic fluid fed to constant pressure circuit5changes from Q1to Q2. The hydraulic pressure of the fluid fed to this circuit5is not changed. While, upon such change, the amount of hydraulic fluid and pressure fed to high pressure circuit6do not change.

That, if the amount of hydraulic fluid led to constant pressure circuit5is lower than the level Q2, the hydraulic pressure appearing in first outlet port21lowers. Thus, for keeping the hydraulic pressure in constant pressure circuit5at the predetermined level P1, rotary plate31is turned to an angular position to increase the fluid discharge rate of first outlet port21. That is, in such case, the hydraulic pressure in constant pressure circuit5is increased to the predetermined level P1.

In response to the increase of the fluid discharge rate of first outlet port21, the fluid discharge rate of second outlet port22tends to be decreased. Thus, if the discharge pressure at second outlet port22does not reach the low level P2that is needed by high pressure circuit6, control unit2controls electric motor3to increase the rotation speed of the same.

When, due to increase of the rotation speed of electric motor3, the rotation speed of oil pump100is increased, the change in pressure of the hydraulic fluid fed to constant pressure circuit5affects or controls the fluid discharge rate of each of first and second outlet ports21and22. Thus, the change in pressure of the hydraulic fluid fed to high pressure circuit5affects or controls the rotation speed of electric motor3.

Thus, like in the above-mentioned low speed operation condition, each of constant pressure circuit5and high pressure circuit6is fed with a desired amount Q2or Q3of the hydraulic fluid of the predetermined pressure P1or P2.

In order to operate the actuators employed in the engine and transmission, it is necessary to feed high pressure circuit6with a large amount of highly pressurized hydraulic fluid. Accordingly, control unit2controls or increases the rotation speed of electric motor3until the time when the hydraulic pressure in the circuit6is increased to the level P3.

While, under such condition, constant pressure circuit5does not need the increase of hydraulic pressure and fluid amount. That is, since the increase in fluid discharge rate of first outlet port21caused by the increase of rotation speed of oil pump100induces an excessive fluid discharge pressure, rotary plate31is rotated in a counterclockwise direction in the drawing to reduce the fluid discharge rate of first outlet port21thereby to keep the hydraulic pressure at the level P1.

In second outlet port22, the hydraulic pressure and hydraulic fluid are increased due to increase of rotation speed of oil pump100and increase of fluid discharge rate. That is, control unit2controls or increases the electric motor3until the time when the hydraulic fluid fed to high pressure circuit6shows a target amount Q4and the hydraulic pressure P3.

Accordingly, when the rotation speed of oil pump100is increased, only the fluid discharge rate of second outlet port22can be increased without increase in the fluid discharge rate of first outlet port21. Thus, each of constant pressure circuit5and high pressure circuit6is fed with a desired amount Q1or Q3of the hydraulic fluid of the predetermined pressure P1or P2.

As is described hereinabove, the hydraulic pressure in constant pressure circuit5affects or controls the fluid discharge rate of first outlet port21and that of second outlet port22, and the hydraulic pressure in high pressure circuit6affects or controls the rotation speed of electric motor3, so that the general discharge rate of oil pump100is controlled. Thus, each pressure circuit5or6is fed with a desired amount of hydraulic fluid of desired pressure.

In the first embodiment, rotary plate31is rotatably mounted to pump housing11. First and second outlet ports21and22are provided by a unit that consists of rotary plate31and pump housing11. First outlet port21comprises first fixed outlet port24defined by pump body12and first movable outlet port34defined by rotary plate31, and second outlet port22comprises second fixed outlet port25defined by pump body12and second movable outlet port35defined by rotary plate31. Accordingly, by rotating rotary plate31, the circumferential open range of first outlet port21exposed to pump chambers V6and V7and that of second outlet port22exposed to pump chambers V8and V9are varied, and thus, the fluid discharge rate of first and second outlet port21and22is variable.

Accordingly, constant pressure circuit5and high pressure circuit6that are respectively connected to first and second outlet ports21and22enjoy the variable fluid discharge rate separately. In other words, elements of the engine and transmission benefiting from constant pressure circuit5and elements of the engine and transmission benefiting from high pressure circuit6are supplied with a sufficient amount of hydraulic fluid from oil pump100without forcing electric motor3to do excessive work. This brings about a compact construction of electric motor3and energy saving of a motor vehicle that employs the oil pump100.

Referring toFIGS. 11 to 14, there is shown a modification100′ of oil pump100of the above-mentioned first embodiment.

As is seen fromFIG. 12, in this modification100′, unlike the first embodiment100, first outlet port21is connected to high pressure circuit6and second outlet port22is connected to constant pressure circuit5. Furthermore, rotary plate31is rotated by the discharge pressure appearing in second outlet port22.

Because of similar construction, modification100′ enjoys substantially same advantages as those possessed by the above-mentioned first embodiment100.

Referring toFIGS. 15 to 22, there is shown an oil pump200which is a second embodiment of the present invention.

Since this second embodiment200is similar in construction to the above-mentioned first embodiment100, only portions or parts that are different from those of the first embodiment100will be described in the following.

That is, as is seen fromFIGS. 15,19and20, oil pump200has no drive shaft like the drive shaft15used in the first embodiment100. That is, in the second embodiment200, inner rotor17is directly connected to output shaft3aof electric motor3. Cover member13has no bore like the bearing blind bore13aused in the first embodiment100. That is, output shaft3ais rotatably held by only bearing bore12aof pump body12.

More specifically, in oil pump200of the second embodiment, inner rotor17is fixed to a leading end of output shaft3awith across flat. Unlike the first embodiment100in which drive shaft15passes through rotary plate31, rotary plate31has no opening like the shaft receiving opening31aemployed in the first embodiment.

As is seen fromFIGS. 15 to 17, there is no need of providing pump body12with a recess for receiving rotary plate31that corresponds to the cylindrical recess26employed in first embodiment100. That is, in the second embodiment200, rotary plate31is received in rotor receiving bore14together with outer rotor16.

As is seen fromFIG. 15, rotary plate31is sized to have the generally same diameter as outer rotor16. Thus, movable inlet port33and first and second movable outlet ports34and35of rotary plate31are each shaped like a recess provided at the periphery of rotary plate31.

That is, as is seen fromFIG. 18, rotary plate31employed in this second embodiment200has no annular rim portion. That is, unlike in first embodiment100, movable inlet port33and first and second movable outlet ports34and35of rotary plate31are recesses, not enclosed openings (seeFIG. 4).

It is to be noted that also in second embodiment200, first outlet port21is connected to constant pressure circuit5and second outlet port22is connected to high pressure circuit6.

Accordingly, in this second embodiment200, substantially same advantageous operation as in the first embodiment100is carried out. Furthermore, since in the second embodiment200rotary plate31and outer rotor16are received in the common rotor receiving bore14, production of pump body12is easily achieved as compared with pump body12used in the first embodiment100. That is, in the first embodiment100, cylindrical recess26is provided by pump body12in addition to rotor receiving bore14. As is known, easy production brings about reduction in cost of oil pump200.

Referring toFIGS. 23 to 29, there is shown an oil pump300which is a third embodiment of the present invention.

Since this third embodiment300is similar in construction to the above-mentioned first embodiment100, only portions or parts that are different from those of the first embodiment100will be described in the following.

As is seen fromFIGS. 23,26and27, pump body12has a shape different from that of first embodiment100. That is, as is seen fromFIG. 26, pump body12is shaped to have a triangular projection.

As is best understood fromFIG. 26, pump body12has a generally cylindrical pump element receiving bore40that is coaxial with the bearing bore12aformed in one end wall thereof.

The depth of the receiving bore40is substantially the same as the thickness of outer and inner rotors16and17.

Within the receiving bore40, there is rotatably received a rotary ring41that constitutes part of an after-mentioned discharge rate varying mechanism30.

Rotary ring41comprises outer and inner cylindrical walls (no numerals) that are eccentric to each other. Rotary ring41is formed with a lever portion41a.

Within rotary ring41, there is operatively received a unit of outer and inner rotors16and17in substantially the same manner as in case of the first embodiment100. In this third embodiment300, inner rotor17is provided with drive shaft15that is connected to output shaft3aof electric motor3.

As is seen fromFIG. 26, on the inner surface of an axial wall portion of pump body12, there is defined a rotor sliding surface12bto which one axial end surface of each rotor16or17slidably contacts under rotation of the rotors16and17.

As is best shown inFIG. 24, rotor sliding surface12bis formed with inlet port18and first and second outlet ports21and22around bearing bore12a. As shown, these ports18,21and22are similar to the fixed ports23,24and25(seeFIG. 2) provided by oil pump100of the first embodiment.

As is seen fromFIG. 26, rotary ring41is a member corresponding to the above-mentioned rotary plate31employed in the first embodiment100. However, rotary ring41has no openings corresponding to movable and fixed ports33,34and35as shown.

As is seen fromFIG. 24, first, second and third seal lands12c,12dand12eare defined on rotor sliding surface12blike in case of the first embodiment100. First and third seal lands12cand12ehave each a circumferential length that is generally the same as the pitch of external teeth17aof inner rotor17, and second seal land12dhas a circumferential length that is generally the same as the distance between adjacent two bottoms of the internal teeth16of outer rotor16.

As is seen fromFIGS. 24 and 26, cylindrical recess40is formed at a cylindrical wall thereof with an arcuate groove27that is depressed in radially outward. As shown, arcuate groove27extends from the position of third seal land12eto the position of second seal land12din a direction of rotation of the rotors16and17.

As is seen fromFIG. 24, arcuate groove27has an extension28that extends in a tangential direction. Rotor sliding surface12bof pump body12is further formed with a pressure relief groove12fthat extends from inlet port18to the extension28of arcuate groove27and a pressure induction groove12gthat extends from first outlet port21to arcuate groove27.

As is understood fromFIGS. 23 and 26, around outer rotor16, there is arranged discharge rate varying mechanism30that functions to change a meshing position where internal teeth16aof outer rotor16and external teeth17aof inner rotor17are actually meshed. With such mechanism30, the fluid discharge rate of each of first and second outlet ports21and22is continuously varied.

The discharge rate varying mechanism30generally comprises the above-mentioned rotary ring41that changes the meshing portion when rotated and an elongate biasing mechanism42that functions to bias rotary ring41in a given direction (viz., in a counterclockwise direction inFIG. 23) through lever portion41aof rotary ring41.

As is seen fromFIG. 27, rotary ring41has the same thickness as the two rotors16and17. As is mentioned hereinabove, rotary ring41comprises outer and inner cylindrical walls that are eccentric to each other. As shown, one axial end surface of rotary ring41slidably contacts the inner surface of cover member13and the other axial end surface of the ring41slidably contacts rotor sliding surface12bof pump body12.

As is seen fromFIG. 28, lever portion41aof rotary ring41is movably placed in arcuate groove27of pump body12. As shown, due to provision of lever portion41a, arcuate groove27is divided into two chambers that are back pressure chamber36aand pressure chamber36b. As shown back pressure chamber36ais placed in a trailing area with respect to the rotation direction of the two rotors16and17and contains therein elongate biasing mechanism42, and pressure chamber36is placed in a leading area with respect to the rotation direction of the rotors16and17and communicated with first outlet port21through pressure induction groove12g. The back pressure chamber36ais communicated with inlet port18through pressure relief valve12f.

Elongate biasing mechanism42comprises an elongate spring guide43that includes telescopically connected first, second and third pin members, spherical portions43aand43cthat are formed on axially opposed ends of the spring guide43, flanges43band43dthat are provided on the axially opposed ends within spherical portions43aand43cand a coil spring44that is disposed about spring guide43and compressed between the flanges43band43dto bias spring guide43in a direction to expand the guide43.

As shown inFIG. 28, one spherical portion43ais pivotally received in a round cut41bformed in the lever portion41aof rotary ring41, and the other spherical portion43cis pivotally received in a round recess28aformed in a leading end of the extension28of arcuate groove27. Thus, due to the biasing force of biasing mechanism42, rotary ring41is biased to rotate in a counterclockwise direction inFIG. 28.

In the following, with reference toFIGS. 23,28and29, operation of oil pump300of the third embodiment will be described with respect to operation of discharge rate varying mechanism30.

FIG. 28shows a condition wherein oil pump300is about to start its pumping work. Under this condition, due to the biasing force of biasing mechanism42, rotary ring41is biased in a counterclockwise direction (viz., in a direction opposite to the direction in which the two rotors16and17rotate) in the drawing and takes the counterclockwise-most position. Due to provision of stopper pins (not shown) provided by cover member13, excessive counterclockwise rotation of rotary ring41is suppressed.

Under this condition, a relative eccentricity between outer and inner rotors16and17takes a mating line M1with respect to which mutually meshed internal and external teeth16aand17aof the two rotors16and17are balanced, and the mating line M1passes through a circumferential middle position of second outlet port22. That is, under this condition, the pump chamber exposed to second outlet port22shows the minimum volume causing the fluid discharge rate of second outlet port22to be minimum (almost zero), and at the same time, the other pump chamber exposed to first outlet port21shows the maximum volume causing the fluid discharge rate of first outlet port21to be maximum. Since the mating line M1is inclined relative to inlet port18, the intake side pump chambers V1, V2, V3and V4take smaller open area relative to intake port18, and thus, the total fluid discharge from oil pump300is restricted.

In response to increase of rotation speed of oil pump300, the discharge pressure appearing at first discharge port21increases. When the discharge pressure exceeds a predetermined value (viz., set pressure), rotary ring41is forced to rotate clockwise to a position, such as the position as shown inFIG. 23, against the biasing force of spring44.

In such position ofFIG. 23, the relative eccentricity between outer and inner rotors16and17takes a mating line M2with respect to which mutually meshed internal and external teeth16aand17aof the two rotors16and17are balanced, and the mating line M2passes through respective circumferential middle positions of first and second seal lands12cand12d. That is, under this condition, an open degree of intake side pump cambers V1, V2, V3and V4to the ports18,21and22and that of exhaust side pump chambers V6, V7, V8and V9to the ports18,21and22are balanced, and thus, the total fluid discharge from oil pump300shows the maximum. That is, under such condition, each of first and second outlet ports21and22discharges the hydraulic fluid in the amount based on the angular position of third seal land12e.

When then the discharge pressure of first outlet port21further increases, rotary ring41is further turned in clockwise direction inFIG. 23due to the force of the discharge pressure, and finally, rotary ring41takes the clockwise-most position ofFIG. 29.

When rotary ring41is in such clockwise-most position, the relative eccentricity between outer and inner rotors16and17takes a mating line M3with respect to which mutually meshed internal and external teeth16aand17aof the two rotors16and17are balanced, and the mating line M3passes through a circumferential middle position of first outlet port21. Under this condition, the pump chamber exposed to the circumferential middle portion of first outlet port21shows the maximum volume causing the fluid discharge rate of this first outlet port21to be minimum (almost zero), and at the same time, the other pump chamber exposed to second outlet port22shows the minimum volume causing the fluid discharge rate of this second outlet port22to be maximum. Since the mating line M3is inclined relative to inlet port18, the fluid intake rate of oil pump300is reduced and thus the total fluid discharge from oil pump300is restricted.

As is described hereinabove, in accordance with the discharge pressure of first outlet port21applied to lever portion41a, rotary ring41is forced to rotate, and when the discharge pressure of first outlet port21is reduced, rotary ring41is rotated in a counterclockwise direction inFIG. 29thereby to increase the fluid discharge rate from first outlet port21.

In the discharge rate varying mechanism30, rotary ring41is rotated in accordance with the discharge pressure appearing in first outlet port21thereby to continuously change the eccentric direction of each rotor16or17.

With this, the fluid discharge rate of each of first and second outlet ports21and22is varied. Of course, the discharge distribution rate between first and second outlet ports21and22is continuously varied. By adjusting the discharge distribution rate, the discharge pressure of first outlet port21can be kept at a predetermined level (viz., set pressure).

As is described hereinabove, in the third embodiment300, when one outlet port21or22exhibits the maximum discharge rate, the other outlet port22or22exhibits the minimum discharge rate. Accordingly, oil pumps100,200and300can be selectively used in accordance with required characteristics of constant pressure and high pressure circuits5and6.

In the foregoing description, discharge rate varying mechanism30is applied to oil pumps100,200and300of a so-called trochoidal type. However, if desired, the mechanism30may be applied to other type oil pumps, which are for example, a variable displacement vane pump and the like.

In first and second embodiments100and200, the circumferential position of third fixed side seal land12eand that of third movable side seal land31emay change in accordance with the user's needs. Also, in third embodiment300, the circumferential position of third seal land12emay change in accordance with such needs.

Furthermore, in embodiments200and300, the connection of first and second outlet ports21and22to constant pressure circuit5and high pressure circuit6may be reversed like the circuit shown inFIG. 12. That is, in such case, rotary plate31or rotary ring41is rotated in accordance with the discharge pressure of second outlet port22.

The entire contents of Japanese Patent Application 2008-24638 filed Feb. 5, 2008 are incorporated herein by reference.

Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.