Variable displacement pump

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable-displacement vane pump for use in an apparatus using pressurized fluid, such as a power steering unit for reducing force required to steer a steering wheel of an automobile.

2. Description of the Related Art

As a pump for a power steering unit, a positive-displacement vane pump has usually been employed which is directly operated by an engine of an automobile. The discharge flow rate of the foregoing positive displacement pump is changed to correspond to the number of revolutions of the engine. Therefore, the positive displacement pump has a characteristic which is mutually contradictory to auxiliary steering force which must be provided for the power steering unit. The auxiliary steering force must be enlarged when the automobile is stopped or the automobile runs at low speed and reduced when the automobile runs at high speed. Therefore, the positive displacement pump must have a large capacity which enables a discharge flow rate to be maintained with which required auxiliary steering force can be obtained even if the automobile runs at low speed with a small number of revolutions of the engine. Moreover, a flow control valve must be provided which controls the discharge flow rate to be not larger than a predetermined quantity when the automobile runs at high speed with a large number of revolutions of the engine. Therefore, the positive displacement pump involves an increase in the required elements, a complicated overall structure and a complicated structure of passages. Thus, the overall size and costs cannot be reduced.

To solve the problems experienced with the above-mentioned positive displacement pump, variable-displacement vane pumps each of which is capable of reducing a discharge flow rate per revolution (cam cc/rev) in proportion to an increase in the number of revolutions have been disclosed. For example, variable-displacement vane pumps of the foregoing type have been disclosed in Japanese Patent Laid-Open No. 53-130505, Japanese Patent Laid-Open No. 56-143383, Japanese Patent Laid-Open No. 58-93978, Japanese Utility-Model Publication No. 63-1478, and Japanese Patent Laid-Open No. 7-243385. The foregoing variable displacement pumps do not need the flow control valve of the capacity type. Moreover, the variable displacement pump exhibits an excellent energy efficiency because waste of drive horsepower can be eliminated. Since a return to a tank can be prevented, a rise in the temperature of oil can be prevented, a rise in the temperature of oil can be prevented. Moreover, problems of leakage in the pump and deterioration in the capacity efficiency can be prevented.

An example of the foregoing variable-displacement vane pump will simply be described with reference to

FIG. 16

which shows the structure of the pump disclosed in Japanese Patent Laid-Open No. 7-243385. Referring to

FIG. 16

, reference numeral

1

represents a pump body,

1

a

represents an adapter ring and

2

represents a cam ring provided in an elliptic space

1

b

formed in the adapter ring

1

a

of the body

1

, the cam ring

2

being swingably supported through a support shaft portion

2

a

which serves as a fulcrum for a swinging operation. The cam ring

2

is urged by an urging means (compression coil spring) for urging the cam ring

2

in a direction indicated by a hollow arrow F show in FIG.

16

.

Reference numeral

3

represents a rotor eccentrically accommodated at a position adjacent to an end in the cam ring

2

in such a manner that a pump chamber

4

is formed at another end. Since the rotor

3

is rotated by an external power source, the rotor

3

forwards/rearwards moves a vane

3

a

which is held such that the vane

3

a

is able to move in the radial direction. Reference numeral

3

b

represents a drive shaft for the rotor

3

. The rotor

3

is rotated in a direction indicated by an arrow shown in FIG.

16

.

Reference numerals

5

and

6

represent fluid-pressure chambers formed in a pair on the two outer sides of the cam ring

2

, the fluid-pressure chambers

5

and

6

being arranged to serve as high and low pressure portions in the elliptic space

1

b

of the adapter ring

1

a

of the body

1

. In the chambers

5

and

6

, passages

5

a

and

6

a

for introducing fluid pressures across a variable metering orifice

12

provided for a pump discharge-side passage

11

for controlling the swinging operation of the cam ring

2

are opened through a spool-type control valve

10

to be described later. When the fluid pressures across the variable metering orifice

12

in the pump discharge-side passage

11

are introduced through the passages

5

a

and

6

a

, the cam ring

2

is swung to a required direction. Thus, the capacity in the pump chamber

4

is varied so that the discharge flow rate is controlled to correspond to a flow rate in the discharge portion of the pump. That is, the flow rate in the discharge portion is controlled in such a manner that the flow rate in the discharge portion is reduced in inverse proportion to enlargement of the number of revolutions of the pump.

Reference numeral

7

represents an opening (a suction port) in the suction portion of the pump, the opening

7

being opened to face a pump suction-side region

4

A of the pump chamber

4

. Reference numeral

8

represents an opening (a discharge port) in the pump discharge portion, the opening

8

being opened to face a pump discharge-side region

4

B of the pump chamber

4

. The openings

7

and

8

are provided for either of a pressure plate or a side plate (not shown), the plates being securing walls for holding a pump element incorporating the rotor

3

and the cam ring

2

from two side portions.

The cam ring

2

is urged by the compression coil spring from the fluid-pressure chamber

6

, as indicated with symbol F shown in the drawing. The cam ring

2

is pressed in a direction in which the capacity in the pump chamber

4

is maximized. Reference numeral

2

b

shown in the drawing represents a sealing member provided on the outer surface of the cam ring

2

so as to define the fluid-pressure chambers

5

and

6

in association with a bearing portion

2

a

, the chambers

5

and

6

being defined on the right-hand and left-hand portions in the pump chamber

4

.

Reference numerals

7

a

and

8

a

represent whisker-like notches formed continuously from ends of the opening

7

in the pump suction portion and the opening

8

in the pump discharge portion. When a pumping operation is performed by rotating the rotor

3

so that the leading end of each vane

3

a

is slid on the inner surface of the cam ring

2

, the notches

7

a

and

8

a

gradually relieve the fluid pressure from the high pressure portion to the low pressure portion in a region from a space adjacent to the ends of the openings

7

and

8

and held between the vanes to a space between the vanes adjacent to the foregoing space. Thus, surge pressure and pulsation are prevented.

The spool-type control valve

10

is operated by dint of different pressures P

1

and P

2

across a variable metering orifice

12

disposed at an intermediate position of the pump discharge-side passage

11

. When fluid pressure P

3

corresponding to the flow rate in the discharge portion of the pump is introduced into the fluid-pressure chamber

5

at a position on the outside of the cam ring

2

, a sufficiently high flow rate can be maintained in the initial stage of the operation of the pump. In particular, in a state where the different pressure across the variable orifice

12

is raised to be a level not lower than a predetermined level when a load is applied because of the operation of the apparatus using the fluid pressure, the control valve

10

introduces the fluid pressure P

1

upstream of the variable orifice

12

into the high-pressure-side fluid-pressure chamber

5

on the outside of the cam ring

2

, the fluid pressure P

1

being introduced as control pressure. Thus, any swing of the cam ring

2

can be prevented.

The variable-displacement vane pump having the above-mentioned structure incorporates elements, for example, the body

1

, each having a complicated structure. What is worse, a large number of elements must be provided. Thus, there arises a problem in that each element cannot easily be machined and assembled. Moreover, the size and weight of the pump cannot easily be reduced. Thus, the foregoing pump is susceptible to improvement.

The conventional variable displacement pump has a structure that a pressure plate is disposed to an end of the rotor

3

and the cam ring

2

which constitute the pump chamber

4

in the body

1

. A discharge chamber into which pressurized oil discharged from the pump chamber is introduced is formed on the backside of the pressure plate. The discharged pressure from the discharge chamber of the pump causes the pressure plate to be brought into contact with the cam ring

2

and the rotor

3

under a predetermined pressure. Thus, the pump chamber

4

is formed between an end surface of a portion of the side plate or the pump body

1

disposed opposite to the cam ring

2

and the rotor

3

. As a result, hydraulic oil can be sucked into the pump chamber

4

and discharged from the same.

The above-mentioned variable displacement pump is different from a usual positive displacement vane pump in that the pump chamber

4

is composed of a pump suction-side region

4

A and a pump discharge-side region

4

B which are disposed at asymmetric positions with respect to the rotational shaft

3

b

. On the other hand, an annular recess is formed on the backside of the foregoing pressure plate except for the portion including the rotational shaft

3

b

. The foregoing recess is formed into a discharge chamber into which pressurized oil discharged from the discharge portion of the pump is introduced.

Therefore, the discharged pressure from the inside portion of the discharge chamber acts on substantially the overall back surface of the pressure plate because of the annular recess. Since the pump suction-side region

4

A of the pump chamber

4

is formed eccentrically, great force for pressing the pressure plate against the pump chamber

4

acts on the above-mentioned portion. If the eccentric force acts on the plate, the portion is deformed. As a result, there is apprehension that the plate is excessively pressed against the cam ring

2

and the rotor

3

.

Therefore, the pressure plate is required to have rigidity capable of during the eccentric force.

If the pressure plate is deformed, a gap is formed between the cam ring

2

and the rotor

3

. What is worse, an amount of internal leakage of pressurized oil is enlarged when the pressure is high. Therefore, a countermeasure must be taken.

As described above, the above-mentioned variable displacement pump is required to have a completely modified overall structure, to enable the structures of the elements to be simplified, the number of the elements to be reduced, the machining and assembling processes to be performed easily, reliability of the operation of the pump to be improved and the size, weight and cost of the pump to be reduced.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is to provide a variable displacement pump arranged such that the overall structure including a pump body is modified, pressure balance is kept between the two sides of the pressure plate disposed between the pump chamber and the discharge-side chamber of the pump and deformation of the plate is prevented so that excessive contact of the plate with the cam ring and the rotor is prevented and thus an mount of internal leakage in the pump is prevented.

To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a variable displacement pump comprising: a cam ring for forming a pump chamber from a rotor in a state in which the rotor having a vane is moved to an eccentric position; a cam case mounted on a portion around the cam ring to swingably support the cam ring such that a swingable pin axially disposed in a portion of an outer periphery of the cam ring in a circumferential direction of the cam ring serves as a fulcrum so that the capacity of the pump chamber is changed, the cam case urging the cam ring in a direction in which the capacity of the pump chamber is maximized; front and rear bodies between which the cam case serving as an intermediate body is disposed and which are disposed on the two sides in the axial direction of the cam case so as to form a pump body; a rotational shaft pivotally supported by the two bodies so as to rotate the rotor; and a pressure plate disposed on the inside of the front body at a position at which the pressure plate is in contact with a portion adjacent to the cam case so as to introduce pressurized oil in a discharge portion of the pump to a back surface of the pressure plate, wherein a low pressure chamber for introducing low level oil pressure is formed between the back surface of the pressure plate and the front body at a position opposite to a suction region of the pump chamber.

The low pressure chamber is provided for the back side of the pressure plate or the front body.

The present invention has the low pressure chamber formed on the backside of the pressure plate at a position opposite to the suction region of the pump chamber. Thus, hydraulic pressure balance can be kept on the two sides of the pressure plate. Thus, deformation of the plate can be prevented.

A recess portion for forming the low pressure chamber is sealed with a sealing member, such as an “O” ring so that separation from the discharge-side pressure chamber (a discharge chamber) formed on the backside of the pressure plate is performed.

The variable displacement pump is a vane-type oil pump for discharging hydraulic pressure. For example, the variable displacement pump is employed as an oil pressure source adaptable to, for example, a power steering unit for a vehicle. The present invention is not limited to this.

The cam ring is swingably supported in a space formed in the pump body by a support portion including a swingable pin having a portion which serves as a fulcrum of swinging. The cam ring is swung by dint of hydraulic pressures in first and second hydraulic pressure chambers formed on the two sides of a segment passing through the support portion and an urging means provided for the low-pressure hydraulic pressure chamber.

The pump body is constituted by the two bodies and the cam case manufactured by precise casting processes, such as aluminum die-cast. The internal passages, the internal spaces and the hole portions, such as the valve hole, are formed by casting or boring The present invention is not limited to the foregoing methods.

The shape of the shaft serving as the rotational shaft is formed into a straight shape as much as possible. The shaft serving as the rotational shaft is pivoted on each body at each position by using bushes, such as wrapping bearings each having a dual structure and made of aluminum and white metal. Thus, the shaft is supported by a two-point support structure. The present invention is not limited to the foregoing structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a vertical cross sectional view showing an essential portion of an embodiment of a variable displacement pump according to the present invention;

FIG. 2

is a horizontal cross sectional view taken along line II—II shown in FIG.

1

and showing a portion in the vicinity of a pump chamber of the variable displacement pump;

FIG. 3

is a horizontal cross sectional view taken along line III—III shown in FIG.

1

and showing the portion in the vicinity of a pump chamber of the variable displacement pump;

FIG. 4

is a side view taken along line IV—IV shown in FIG.

1

and showing a front body portion of the variable displacement pump;

FIGS. 5A-C

,

5

A is a side view showing the variable displacement pump shown in

FIG. 1

when viewed from the front body,

FIG. 5B

is a cross sectional view taken along line V—V shown in

FIG. 5A

and

FIG. 5C

is a diagram showing a conventional example corresponding to

FIG. 5B

;

FIGS. 6A-B

,

6

A is a front view of a cam case of the variable displacement pump shown in FIG.

1

and

FIG. 6B

is a cross sectional view taken along line VI—VI shown in

FIG. 6A

;

FIGS. 7A-E

,

7

A is a cross sectional view showing an essential portion of the cam case of the variable displacement pump shown in FIG.

1

and

FIGS. 7B

to

7

E are cross sectional views taken along lines B—B, C—C, D—D and E—E, respectively;

FIGS. 8A-C

,

8

A is a side view showing a rear body of the variable displacement pump shown in

FIG. 1

when viewed from the surface for joining the cam case,

FIG. 8B

is a cross sectional view taken along line VIIIb—VIIIb shown in FIG.

8

B and

FIG. 8C

is a cross sectional view taken along line VIIIc—VIIIc shown in FIG.

8

A and showing an essential portion;

FIG. 9

is a side view showing the rear body portion of the variable displacement pump shown in

FIG. 1

;

FIGS. 10A-C

,

10

A is a side view showing a portion of a pressure plate adjacent to a pump chamber of the variable displacement pump shown in

FIG. 1

,

FIG. 10B

is a side cross sectional view and

FIG. 10C

is a diagram showing a modification of the structure shown in

FIG. 10B

;

FIG. 11

is a cross sectional view taken along line XI—XI shown in

FIG. 5

;

FIG. 12

is an enlarged cross sectional view taken along line XII—XII shown in FIG.

9

and showing an essential portion;

FIG. 13

is a side cross sectional view showing a modification of the variable displacement pump according to the present invention;

FIGS. 14A

to

14

C show another embodiment of the variable displacement pump according to present invention, in which

FIG. 14A

is a side view showing the rear body when viewed from the joining surface with the cam case,

FIG. 14B

is a side cross sectional view and

FIG. 14C

is a cross sectional view showing an essential portion of a portion for receiving a relief valve;

FIG. 15

is a side cross sectional view showing another embodiment of the variable displacement pump according to the present invention; and

FIG. 16

is a diagram showing the structure of an essential portion of a conventional variable displacement pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodiments of the present invention with reference to the accompanying drawings.

FIGS. 1

to

12

show an embodiment of a variable displacement pump according to the present invention. Referring to the drawings, the variable displacement pump is a vane-type oil pump which serves as a source for generating hydraulic pressure for a power steering unit.

As shown in

FIGS. 1

,

4

to

9

, a vane-type variable displacement pump

20

incorporates a front body

21

, a rear body

22

and a cam case

23

serving as an intermediate body which forms a pump body.

As shown in

FIGS. 1

,

4

,

5

A and

5

B, the front body

21

has a small-diameter portion

21

a

projecting to either end. In the central portion of the front body

21

, a shaft hole

21

b

through which a rotational shaft of a rotor

33

to be described later is inserted is formed.

As shown in

FIGS. 1

,

4

,

5

A and

5

B, a circular space

24

for accommodating a pressure plate

31

which is one of pump elements

30

is formed in the joining surface of the front body

21

in the large-diameter portion with which the cam case

23

is joined. Moreover, an annular recess

24

a

is formed at the back of the circular space

24

. The annular recess

24

a

is formed in such a manner that a discharge chamber

25

is formed between a pressure plate

31

to be described later and the annular recess

24

a

, the discharge chamber

25

being a chamber into which pressurized oil in the discharge portion of the pump is introduced.

As shown in

FIGS. 1

,

2

,

3

,

5

A-

5

C,

6

A-

6

B and

7

, the cam case

23

has, in the central portion thereof, an accommodating space

32

for accommodating a pump cartridge which is the pump element

30

. The accommodating space

32

has an ellipse-like shape extending to the right and left in

FIGS. 2 and 3

. The accommodating space

32

swingably supports a cam ring

34

mounted on a portion around a rotor

33

in a state where the rotor

33

having a vane

33

a

is moved eccentrically to either side such that a swingable pin

35

disposed in a portion in the circumferential direction and placed in the axial direction is used as a fulcrum. Thus, the capacity of the pump chamber

36

can be varied.

The cam ring

34

forms a pump chamber

36

between an inner surface and an outer surface of the rotor

33

. The cam ring

34

is urged in a direction in which the capacity of the pump chamber

36

is maximized by a compression coil spring

37

disposed on either side of the cam case

23

and serving as an urging means.

The cam case

23

is a member corresponding to an adapter ring (

1

a

shown in

FIG. 16

) for swingably holding the cam ring

34

in the pump body. The rear body

22

is joined in contact with the rear portion of the cam case

23

. In corporation with a pressure plate

31

disposed in the circular space

24

adjacent to the front body

21

, the cam case

23

forms the pump chamber

36

between the rotor

33

and the cam ring

34

.

Reference numeral

40

represents a drive shaft serving as a rotor for rotating the rotor

33

of the pump elements

30

from an outer position. The drive shaft

40

penetrates the front body

21

and the rotor

33

. The inner end of the drive shaft

40

is received by a shaft hole

22

a

formed in the rear body

22

.

As shown in

FIG. 1

, the drive shaft

40

is arranged to be integrally rotated with the rotor

33

by dint of serration joint (or a key joint). The drive shaft

40

is rotatively supported at two points by bushes

41

and

42

provided for shaft holes

21

b

and

22

a

of the front body

21

and the rear body

22

.

The bushes

41

and

42

are wrapping bearings made of, for example, aluminum and white metal and having a dual structure. The bushes

41

and

42

are disposed for a predetermined length in the axial direction so as to rotatively support the drive shaft

40

with required strength.

Referring to

FIG. 1

, reference numeral

43

represents an oil seal disposed at the opened end of the small-diameter portion

21

a

of the shaft hole

21

b

of the front body

21

, the shaft hole

21

b

having the bush

41

. Reference numeral

44

represents a pulley

44

provided for a pulley support ring

44

a

disposed at an outer end of the drive shaft

40

by press fitting or the like. When rotative force is transmitted from an outer power source, such as a electric motor, to the pulley

44

, the drive shaft

40

can be rotated.

In this embodiment, the pump body for constituting the variable displacement pump

20

incorporates the front and rear bodies

21

and

22

and the cam case

23

manufactured by precise casting, such as aluminum die-cast. The shape of the drive shaft

40

serving as the rotational shaft is formed to have the straight shape as much as possible. Moreover, the drive shaft

40

is borne at each of the front and rear bodies

21

and

22

by the bushes

41

and

42

. Therefore, the following advantages can be obtained.

That is, the conventional pump has a structure that the ball bearing for bearing the drive shaft

40

is provided at a position adjacent to the pulley

44

. Moreover, a needle bearing and a bush are disposed in the body. Thus, the drive shaft

40

is borne at three points. On the other hand, this embodiment has the structure that the drive shaft

40

is supported at two points by the bushes

41

and

42

. Moreover, the drive shaft

40

is formed into the straight shape as much as possible. Therefore, the outer diameter of the pump body can be reduced and the number of the elements can be reduced. Thus, the cost can be reduced.

In this embodiment, the length of the bush

41

in the front body

21

in the axial direction is elongated and the bush

41

is positioned adjacent to the pulley

44

in the small-diameter portion

21

a

. Therefore, resistance against a bending load can be raised despite the small diameter of the shaft. Moreover, the load capacity (a PV value) as the pump can be enlarged. Since the drive shaft

40

is borne by the bushes

41

and

42

at the positions adjacent to the rotor

33

, a problem which arises because of an eccentric load occurring due to the hydraulic pressure can be prevented.

Since the drive shaft

40

is formed into the substantially straight shape as described above, the hole

31

a

in the pressure plate

31

for introducing high hydraulic pressure into a base portion (

33

b

) of the vane

33

a

can be formed into a straight shape in the axial direction in place of the conventional diagonal hole. Therefore, the passage for introducing hydraulic oil can be enlarged. Moreover, the straight hole can easily be formed in the pressure plate

31

by a machining process. When the straight hole is formed when the pressure plate

31

is manufactured by casting, the cost can be reduced.

The front body

21

, the rear body

22

and the cam case

23

holding the front and rear bodies

21

and

22

are stacked in a state in which the internal elements have been accommodated. Then, the stacked elements are joined by four joining bolts

45

which are joining means so that the elements are integrally assembled. An end surface of the rear body

22

which is in contact with an end of the cam case

23

has a function to serve as a side plate of the pump elements

30

.

Referring to

FIG. 2

, reference numeral

47

represents an “O” ring mounted on a recess grove

47

a

formed in the side portion of the cam case

23

and arranged to seal the pump chamber

36

formed by the pump elements

30

and the first and second fluid-pressure chambers

38

and

39

for swinging the cam ring

34

. The “O” ring

47

has an enlarged portion

47

b

for bypassing the relief valve

74

.

In addition to the above-mentioned structure according to this embodiment, a swingable pin

35

for swingably supporting the cam ring

34

in the cam case

23

is provided as one of means for locating the three-piece structure composed of the front body

21

, the rear body

22

and the cam case

23

serving as the intermediate body which is held between the front and rear bodies

21

and

22

.

Since the above-mentioned structure incorporates the swingable pin

35

of the cam ring

34

which is a conventional element as the locating member, any redundant element is not required. Thus, the number of elements of the pump can be reduced and the cam case and the two bodies can reliably be located at the joining surfaces in the directions of the planes and the circumferential directions. That is, it might be considered to locate the above-mentioned members by using two means for only locating the positions, such as the locating pins. In this embodiment, the swingable pin

35

having another functions is employed as at least either of the locating means.

In this embodiment, another locating means is arranged such that a reamer bolt

45

A arranged to be received in a reamer hole

45

B is employed as at least one of the joining bolts

45

for joining the two bodies

21

and

22

to each other. Therefore, the number of elements can be reduced. Since the reamer bolt

45

A is able to reliably bear an eccentric load generated by dint of the hydraulic pressure which acts on the two bodies

21

and

22

and the cam case

23

, the reliability of the assembled pump

20

can be maintained.

In the above-mentioned embodiment, the reamer bolt

45

A is employed as one of the joining bolts serving as the locating means together with the swingable pin

35

. The present invention is not limited to the above-mentioned structure. For example, the structure shown in

FIG. 1

may be structured such that locating pins

46

and

48

may be provided between the front body

21

and the cam case

23

and between the cam case

23

and the rear body

22

. Even if the reamer bolt

45

A is not provided, the two bodies

21

and

22

and the cam case

23

can easily be located and assembled. In this case, when holes formed when the two bodies

21

and

22

and the cam case

23

have been precisely cast are used as holes into which the locating pins

46

and

48

are inserted, the machining process can easily be performed. Since the joining bolts

45

is able to freely be tightened, the assembling process can easily be performed.

Although the structure shown in

FIG. 1

incorporates the two locating pins

46

and

48

, the present invention is not limited to this. One locating pin may be inserted into a required portion to as well as have the locating function. The essential portion lies in that the cam case

23

which is held between the front and rear bodies

21

and

22

paired with each other is located in the rotational direction and the direction of the plane in each joining surface by using the swingable pin

35

which swingably supports the cam ring

34

.

Reference numeral

50

represents a suction port formed in a portion of the rear body

22

. The port

50

has a suction-side pipe

50

a which is a connector in the suction portion of the pump

20

. Hydraulic oil for the suction portion is introduced from a tank. Hydraulic oil is allowed to pass through a suction-side passage

51

formed in the rear body

22

, and then allowed to pass through a suction-side opening

52

opened in a suction-side region

36

A of the pump chamber

36

formed in the cam ring

34

of the cam case

23

from the rotor

33

. Then, hydraulic oil is sucked into the pump chamber

36

. Then, hydraulic oil undergoes a pumping action because of the operation of the vane

33

a

so that hydraulic oil is discharged through a discharge-side opening

53

and the discharge-side passage

54

adjacent to the pressure plate

31

opened in a discharge-side region

36

B. Then, hydraulic oil is, on the backside of the pressure plate

31

, introduced into the discharge chamber

25

(a discharge-side pressure chamber) which is a high pressure chamber formed by the annular recess

24

a

of the front body

21

.

In the embodiment shown in FIGS.

1

and

8

A-

8

C, the suction port

50

and the suction-side passage

51

in the rear body

22

are constituted by the passage holes formed by machining. The present invention is not limited to this. When holes formed by using cores when the rear body

22

is cast are employed, for example, as shown in

FIGS. 14A and 14B

, the machining process can easily be performed and the cost can be reduced. Since the basic structure is the same as that shown in

FIG. 1

, the foregoing method is omitted from description.

The discharge chamber

25

is, through hydraulic-pressure passages

56

and

57

, connected to a high-pressure chamber of the control valve

55

formed in a portion of the cam case

23

shown in FIG.

5

B and FIG.

3

and serving as the high-pressure portion. On the other, as shown in

FIG. 12

, hydraulic oil is allowed to pass through a discharge-side passage

60

having a metering orifice

60

a

, and then introduced into the second fluid-pressure chamber

39

and an internal passage in a discharge-side connector

58

so as to be discharged through a discharge-side port

59

.

In the discharge-side passage

60

, there is formed the variable metering orifice

60

a

which is capable of changing the opened area by the fluid-pressure passage hole

60

opened in the second fluid-pressure chamber

39

and the side portion of the cam ring

34

. The variable metering orifice

60

a

is formed when the small-diameter opened end of the discharge-side passage

60

is opened/closed in the side wall portion because the cam ring

34

is displaced. When the amount of opening/closing of the orifice

60

a

is arranged to be controlled in accordance with the level of the fluid pressure in the discharge portion, the displacement of the cam ring

34

can be controlled as desired. Thus, the flow rate characteristic can be varied.

In this embodiment, the first and second fluid pressure chambers

38

and

39

are formed between the outer surface of the cam ring

34

and the cam-ring accommodating space

32

in the cam case

23

so as to swing the cam ring

34

. Hydraulic pressure which is supplied to the first and second fluid pressure chambers

38

and

39

is controlled by a control valve

55

which is disposed in a portion of the cam case

23

. The control valve

55

controls the hydraulic pressure through passage holes

38

a

and

39

a

to correspond to the flow rate of the pressurized fluid from the pump chamber

36

. As shown in FIGS.

5

B and

7

A-

7

E, a hydraulic-pressure passage in the high pressure portion is constituted by a diagonal hole

56

formed from the discharge chamber

25

in the front body

21

and opened in an end surface which is a joining surface for joining the cam case

23

. Moreover, also a hole

57

for establishing the connection between the end surface of the cam case

23

and the valve hole

55

a

of the control valve

55

is an element for constituting the foregoing hydraulic-pressure passage.

Since the above-mentioned structure is, as shown in

FIG. 5C

, arranged such that the high-pressure portion, such as the control valve

55

, is disposed in the conventional front body

21

, the high-pressure hydraulic passage for establishing the connection between the front body

21

and the discharge chamber

25

can be formed by combining the two passage holes

56

a

and

56

b

which penetrate the front body

21

through two different positions on the outer surface of the front body

21

. Moreover, the structure for closing the opened ends with blind caps can be omitted. Therefore, the number of manufacturing processes can considerably be reduced and the blind caps and the like can be omitted. Thus, the cost can significantly be reduced. Since the above-mentioned structure is able to eliminate apprehension that oil leaks in the foregoing blind caps, reliability can be improved.

In the above-mentioned structure, the space for accommodating the conventional cam ring

34

and forming the first and second fluid pressure chambers

38

and

39

is created by the adapter ring inserted into the front body

21

. Since the adapter ring is formed into a separate structure by the cam case

23

which serves as the intermediate body, the structure of the pump including the passages and grooves can be simplified. Thus, the passage holes and the like can easily be machined and the pump can easily be assembled.

In place of the conventional structure that the front body

21

and the rear body

22

are joined by a socket-and-spigot joint method, the rear body

22

can be formed to have a large thickness in the axial direction. Moreover, the suction port

50

can be provided for the rear side or the front side. The foregoing structure is able to improve the rigidity of the rear body

22

. Since the front body

21

and the rear body

22

do not require close tolerance, the machining process can easily be performed.

Referring to

FIGS. 2 and 3

, reference numeral

35

a

represents a sealing member for defining the first and second fluid pressure chambers

38

and

39

formed in a pair disposed at symmetrical positions with respect to the swingable pin

35

. Passage holes

38

a

and

39

a

for introducing fluid pressure across the metering orifice

60

a

from the control valve

55

are formed on the two sides of the sealing member

35

a

(see

FIGS. 3

,

6

A-

6

B and

7

). Moreover, a passage hole

55

b

(see

FIGS. 1

,

6

A-

6

B and

8

A-

8

C) is formed from the control valve

55

to suction-side passages

51

and

51

a.

Since the other structures of the vane-type variable displacement pump

20

are known, the other structures are omitted from description.

In this embodiment, the spool valve is employed as the control valve

55

for controlling the fluid pressure for swinging the cam ring

34

. The valve hole

55

a

for placing the spool-type control valve

55

is, as shown in

FIGS. 1 and 3

, formed in a direction perpendicular to the axial direction of the rotational shaft

40

such that an end of the valve hole

55

a

is outwards opened in a portion of the cam case

23

. Then, the valve elements for constituting the control valve

55

are introduced into the valve hole

55

a

. Separation of a plug

71

which is a plug element is prevented as shown in

FIGS. 3

,

7

A,

7

E and

11

such that a through hole

72

a

is formed adjacent to an opened end of the valve hole

55

a

in a direction perpendicular (in the axial direction of the rotational shaft

40

) to the valve hole

55

a

, the through hole

72

a

penetrating the cam case

23

. Moreover, a pin, for example, a spring pin

72

is inserted into the through hole

72

a

. The two ends of the pin

72

are received by the end surfaces of the front body

21

and the rear body

22

which are joined to the two ends of the cam case

23

and which close the opened ends of the through hole

72

a

. Thus, separation is prevented.

The conventional structure is arranged such that the opened ends of the valve hole

55

a

of the spool-type control valve

55

are secured by mounting a stopper plug after the valve elements have been mounted. On the other hand, this embodiment has the structure that the simple spring pin

72

is employed to secure the opened end. Two ends of the spring pin

72

can be secured and stopped. Therefore, the thread cutting process required for the portion which receives the control valve

55

can be omitted. Moreover, the size can be reduced.

Moreover, generation of foreign matter, such as dust and iron powder, because of the conventional method of screwing the plug can be prevented. Since the spring pin

72

is employed, undesirably of the valve element can easily be prevented.

In this embodiment, a relief valve

74

for relieving hydraulic oil to the suction side of the pump

20

when the fluid pressure in the discharge portion of the pump

20

is made to be not lower than a predetermined level is provided for the rear body

22

at a position between the discharge portion and the suction portion of the pump

20

, as shown in

FIGS. 8A

,

8

C and FIG.

12

. That is, a valve hole

75

for receiving the relief valve

74

is formed by a blind hole having an end which is opened in the joining surface with the cam case

23

in the rear body

22

. Valve elements

74

a

placed in the valve hole

75

are secured at the joining surface (or a portion of the front body

21

) with the cam case

23

.

A passage

76

which is connected a suction-side passage

51

in the suction side of the pump

20

through the passage hole

51

b

and the shaft hole

22

a

is connected to a portion of a valve hole

75

for the relief valve

74

in the form of a blind hole formed in the rear body

22

. Reference numeral

76

a

represents a blind cap for closing an opened end formed by machining the passage

76

from the outside of the rear body

22

.

A pressure detection switch

91

for detecting a state in which the fluid pressure in the discharge portion of the pump

20

has been made to be not lower than a predetermined level is disposed in a portion of the rear body

22

. A passage

92

for establishing the connection between the low pressure portion of a switch hole

91

a

for receiving the pressure detection switch

91

is formed when the passage hole

51

b

is formed in the rear body

22

by machining such that the passage

92

is formed to penetrate the shaft hole

22

a

. Thus, the machining process can easily be performed and the cost can be reduced (see FIGS.

1

and

8

A-

8

C).

The conventional structure has an arrangement that the stopper plug which is inserted into the opened end of the valve hole

75

of the relief valve

74

is a screw inserted into the opening formed in the outer surface of the rear body

22

. In this embodiment, the plug is the straight plug (

74

a

) having the “O” ring. Moreover, the plug

74

a

can simply be borne by the cam case

23

or the front body

21

. Therefore, the overall structure of the valve

74

can be simplified. Moreover, generation of foreign matter, such as dust and iron powder experienced with the conventional stopper plug can be prevented. In addition, the movement of the plug in the axial direction can be stopped at a required position.

Since the relief valve

74

and the passages

76

and

92

for connecting the low-pressure portion of the pressure detection switch

91

to the suction-side portion of the pump

20

are provided for the rear body

22

by a simple machining process, the number of machining processes and the cost can be reduced. Although the specific structure of the pressure detection switch

91

is omitted, any one of arbitrary pressure detection switch structures, for example, disclosed in Japanese Utility-Model Publication No. 2540145 may be employed.

The first and second fluid pressure chambers

38

and

39

for swinging the cam ring

34

by dint of the fluid pressure which is introduced in accordance with the flow rate discharged from the pump chamber

36

are formed on the two sides of the position between the swingable pin

35

and an opposite position (the sealing member

35

a

) in the cam case

23

. In this embodiment, the coil spring

37

serving as an urging means for urging the cam ring

34

in a direction in which the capacity in the pump chamber

36

is maximized is disposed in a hole

94

formed from the outer surface of the pump body (the cam case

23

), the cam ring

34

being provided for the fluid-pressure chamber

39

of the two fluid-pressure chambers. Moreover, the discharge-side connector

58

for forming the discharge port (the discharge port

59

) for the pressurized oil in the discharge portion of the pump is provided for the hole

94

.

The above-mentioned structure enables the portion for receiving the coil spring

37

for urging the cam ring

34

and the discharge-side connector

58

to be used commonly. Therefore, the number of machining processes and the cost can be reduced. Moreover, the overall size of the pump can be reduced. Moreover, the cost can be reduced because the number of elements can be decreased.

In this embodiment, the pressure plate

31

is disposed in the inside portion of the front body

21

to be in contact with the cam case

23

, the pressure plate

31

being arranged to form the discharge chamber

25

for introducing pressurized oil in the discharge portion to the backside. A low-pressure chamber

80

for introducing low pressure hydraulic oil is formed into a recess, the low-pressure chamber

80

being formed between the backside of the pressure plate

31

and the front body

21

at a position opposite to the suction-side region

36

A of the pump chamber

36

, as shown in

FIGS. 1 and 4

.

Reference numeral

81

represents an “O” ring in the form of an arc shape for sealing the low-pressure chamber

80

from the portion adjacent to the discharge chamber

25

.

The above-mentioned structure is able to keep a balance of hydraulic pressure on the two sides of the pressure plate

31

which is in contact with the pump chamber

36

formed by the rotor

33

and the cam ring

34

. Thus, deformation of the pressure plate

31

can be prevented.

When the ratio of the area of the recess portion which is formed into the low-pressure chamber

80

for low-pressure hydraulic pressure is determined properly, the pressure plate

31

can adequately be deformed. By using a state of the deformation, the degree of contact with the cam ring

34

which forms the pump chamber can be adjusted. Thus, internal leakage occurring when the pressure is high can be prevented.

Referring to

FIGS. 1 and 4

, reference numeral

82

represents a return passage for returning hydraulic oil leaked to the portion including the oil seal

43

to the suction portion of the pump

20

.

Referring to FIGS.

1

and

10

A-

10

C, reference numerals

83

and

83

a

represent recess grooves which connect the low-pressure chamber

80

with the suction portion of the pump

20

and which serve as a passage hole and an opening in the suction portion for maintaining the low pressure. Reference numeral

31

B shown in the drawings represents a shaft hole of the pressure plate

31

. Reference numeral

31

c

represents a groove portion connected through the hole portion

31

a

for introducing the pressure in the discharge portion of the pump

20

into the base portion of the vane

33

a.

In this embodiment, the pressure plate

31

is arranged as shown in

FIGS. 1

,

10

A and

10

B such that a bridge portion

54

a

is provided for at least either (which is discharge-side passage

54

in this case) of the recess groove

83

a

or the discharge-side opening

53

provided for the pressure plate

31

to correspond to the suction-side region

36

A and the discharge-side region

36

B of the pump chamber

36

.

The bridge portions

54

a

is formed in the recess groove

83

a

which is formed into the suction-side opening

52

and the recess groove

53

a

of the discharge-side opening

53

, the bridge portions

54

a

being disposed apart from the end surface adjacent to the pump chamber

36

.

As shown in

FIGS. 10A and 10B

, the recess groove

53

a

forming the discharge-side opening

53

has the circular through passage hole (the portion given reference numeral

54

). The present invention is not limited to this. A structure shown in

FIG. 10C

may be employed.

That is,

FIG. 10C

shows each portion between circular holes

54

which is formed into the bridge portion

54

a

by forming the discharge-side opening (or the suction-side opening

52

) of the pump

20

with a plurality of the circular holes

54

.

Deterioration in the rigidity of the pressure plate

31

occurring because of the existence of the suction-side opening

52

and the discharge-side opening

53

can be prevented by the bridge portions

54

a

, the suction-side opening

52

and the discharge-side opening

53

having substantially circular-arc shapes provided for the pressure plate

31

to correspond to the suction-side region

36

A and the discharge-side region

36

B of the pump chamber

36

. Thus, required rigidity can be maintained.

The numbers and positions of the bridge portions

54

a

may arbitrarily be determined in consideration of the required rigidity for the pressure plate

31

. The suction-side opening

52

and the discharge-side opening

53

having the bridge portions

54

a

can be formed to have arbitrary shapes by molds (or casting molds) When the bridge portions

54

a

are formed by combining the circular holes

54

, simple molded holes (cast holed) obtainable when the pressure plate

31

is manufactured may be employed. Thus, the cost can be reduced.

The present invention is not limited by or to the above-mentioned embodiment. The shapes and structures may be modified and changed and a variety of modifications may be employed.

Although the above-mentioned embodiment has the structure that the suction port

50

of the pump

20

is provided for the rear body

22

, the present invention is not limited to this. The suction port

50

may be provided for the front body

21

so as to be connected to the suction-side passage

51

provided for the rear body

22

through the low pressure portion of the valve hole

55

a

constituting the control valve

55

provided for the cam case

23

, as shown in FIG.

13

. Reference numeral

50

b represents a passage hole for connecting the suction port

50

of the front body

21

to the portion including the cam case

23

.

In the structure shown in

FIG. 13

, the passage

76

for establishing the connection between a portion of the valve hole

75

for the relief valve

74

in the form of a blind hole formed in the rear body

22

to the suction portion of the pump

20

is formed by a core cast hole when the rear body

22

is manufactured by casting. As a result, the processes for forming the passage holes of the rear body

22

can be minimized and an advantage can be obtained when the machining operation is performed, as shown in FIGS.

13

and

14

A-

14

C. Moreover, an advantage can be obtained as compared with the structure shown in

FIG. 12

that the blind cap

76

a

can be omitted. As can be understood from a comparison between FIGS.

12

and

14

A-

14

C, the structures of the passages can freely be designed.

Also the passage

92

for connecting, to the suction portion of the pump

20

, the low pressure portion of the switch hole

91

a

for receiving the pressure detection switch

91

disposed in a portion of the rear body

22

and arranged to detect a state in which the fluid pressure in the discharge side of the pump

20

has been made to a level not lower than a predetermined level may be formed by using a core in a molding process for casting the rear body

22

. In this case, the machining operation can easily be performed and the cost can be reduced.

As described above, the passages

76

and

92

for connecting the low pressure portions of the relief valve

74

and the pressure detection switch

91

to the suction portion of the pump

20

are simultaneously molded by using cores when the rear body

22

is manufactured by casting. Therefore, the number of machining processes and the cost can be reduced.

In the foregoing embodiment, the discharge-side connector

58

having the discharge-side port

59

and disposed in the discharge portion of the pump

20

has the structure that the discharge side port

59

is opened in the direction perpendicular to the axial direction of the discharge-side connector

58

, as shown in FIG.

3

. The present invention is not limited to this. A simple structure may be employed in which the discharge-side port

59

is opened in the axial direction of the discharge-side connector

58

, as shown in FIG.

15

.

The vane-type variable displacement pump

20

having the above-mentioned structure is not limited to the above-mentioned embodiment. The pump

20

may be applied to any one of various apparatuses and units as well as the power steering unit according to the embodiment.

As was described above, the variable displacement pump according to the present invention is able to keep the oil pressure balance between the two sides of the pressure plate

31

having one side surface which is contact with the pump chamber

36

and the other ends surface on which the pump discharge chamber is formed. Thus, deformation of the plate can be prevented.

According to the present invention, determination of the area of the region which is formed into the low pressure chamber for the low level hydraulic pressure realized by a recess enables an amount of internal leakage occurring when the pressure level is high by using adequate deformation of the pressure plate.

Number	Name	Date
4421462	Ohe	Dec 1983
5141418	Ohtaki et al.	Aug 1992
5290155	Snow et al.	Mar 1994
5538400	Konishi et al.	Jul 1996
5562432	Semba et al.	Oct 1996

Number	Date	Country
53-130505	Nov 1978	JP
56-143383	Nov 1981	JP
58-93978	Jun 1983	JP
63-14078	Apr 1988	JP
5-278622	Oct 1993	JP
7-243385	Sep 1995	JP

Variable displacement pump

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (5)

Foreign Referenced Citations (6)