GB2315815A

GB2315815A - Vane Pump

Info

Publication number: GB2315815A
Application number: GB9716010A
Authority: GB
Inventors: Yoshiyuki Takeuchi; Tuyosi Ikeda
Original assignee: Toyoda Koki KK
Current assignee: Toyoda Koki KK
Priority date: 1996-07-30
Filing date: 1997-07-29
Publication date: 1998-02-11
Also published as: GB9716010D0; JPH1047261A

Abstract

The pump comprises a housing, a cam ring 17 with internal cam surface 17a, and a rotor inside the cam ring having vane 21 retaining support slits S. Pump chambers P1 (P2) are formed by the cam ring, rotor and adjacent vanes. A pair of intake ports 25a (25b Fig. 1) exhaust ports 27a(b) are radially oppositely formed on a side plate (18) for inhaling and discharging fluid from the pump chambers which communicate via notch 33 and communication groove 35 formed on the side plate. When running at speed, pressure overshoot is not fully absorbed by the communication groove 35, therefore between A and B a clearance O forms between vane 21 and the communication groove such that the pump chambers communicate, through the communication groove, with a vane back pressure groove 32 to absorb the overshoot.

Description

TITLE OF THE INVENTION A VANE PUMP BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a vane pump for supplying an operational fluid to a power steering apparatus used in an automotive vehicle.

Description of the Background: A conventional vane pump provides a cam ring therein formed with an internal cam surface which distance from an center axis changes periodically in correspondence withaphaseangle, inwhicharotor is rotatablycoaxially supported. A plurality of radially extensible vanes are supported in vane support slits formed in the rotor, an outer end of which contacts with the internal cam surface of the cam ring. A volume of a pump chamber changes by the rotation of the rotor, which chamber is defined by the rotor, the internal cam surface of the cam ring and adjacent two of the vanes. A pair of intake ports and a pair of exhaust ports are respectively provided at positions corresponding to the pump chambers for performing an expansion operation and a compression operation, in which an operational fluid is inhaled from the intake port to the pump chamber and discharged to the exhaust port. Usually, a period of a cam curve on the internal cam surface of the cam ring is 180 degrees, each of the pair of intake ports and each of the pair of exhaust ports is provided radially oppositely. In such a pressure balance type vane pump as described above, a force acting on an outer surface of the rotor usually is radially balanced. However, an impermanent pressure difference is generated between the both pump chambers formed oppositely radially due to an error such as a machining error and an assembling error, so that a vibration is generated by this unbalance, whereby it is a problem to generate noise.

To solve such a problem as described above, in a slidable surface of the pump housing facing with a side surface of the rotor, there are formed a pair of notches opening to the both pump chambers which are proceed to the pre-compression operation (between the expansion operation and compression operation), and a communication groove communicating one of the notches with the other thereof, as shown in Japanese Utility Model Publication (JIKKAISHO) No. 57-30396. In this configuration, the both pump chambers are communicated through the both notches and the communication groove, so that the impermanent pressure difference between the both pump chambers which is caused by a timing inconsistency (unbalance) can be absorbed.

Thus, in this matter that the pump chambers are communicated each other through the notches and the communication groove, a variable components (so-called an overshoot hereinafter) caused by the pressure changing is relatively small in case that the pump rotates at a low speed, so that the overshoot is led from one of the pump chambers to the other thereof through the communication groove, whereby the pressure difference between the pump chambers can be absorbed. However, when the pump rotates at a high speed in such a high-speed traveling of a vehicle, the overshoot caused in the pre-compression operation is jaggedly increased, so that all of the jagged overshoot can not be led to the other of the pump chambers. Therefore, the communication effect is deteriorated, so that all of the overshoot can not be absorbed. With the result that all of theovershoot can not be absorbed, the pulsation of the operational fluid is caused, the vibration and noise of the pump can not be dissolve.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a vane pump which is capable of absorb the overshoot.

Another object of the present invention is to provide an vane pump which can dissolve the pulsation of fluid by absorption of the overshoot.

Briefly, according to the present invention, a vane pump is composed of a pump housing, a cam ring disposed in the pump housing and formed with an internal cam surface therein and a rotor which is rotatably supported in the cam ring and has a plurality of vane support slits formed equiangularly therein.

A 'drive shaft is rotatably disposed in the pump housing and a plurality of vanes are respectively supported in the vane support slits of the rotor. A pair of intake ports are radially oppositely formed on a side plate for leading fluid into a pump chamber defined by the internal cam surface of the cam ring, the rotor and adjacent two of the plurality of vanes in correspondence with an expansion operation, and a pair of exhaust ports are radially oppositely formed on the side plate for discharging the fluid from the pump chamber in correspondence with a compression operation, respectively. In a pre-compression operation proceeding from the expansion operation to the compression operation, one of the pump chambers communicates with the other of pump chambers from a communication groove formed on the side plate for communicating to a vane back pressure groove formed on the side plate through a clearance which is formed on the one end of vanes such that the one of pump chambers communicates with the other of vanes from through the communication groove to the vane back pressure groove when the pump chamber is positioned between the intake port and the exhaust port.

With this configuration, the overshoot generated in both pump chambers during the pre-compression operations all of which can not absorbed by the communication groove, is led from the clearance formed between the one end of the vane and the communication groove through the vane support slit to the vane back pressure groove, so that the pressure changing can be absorbed due to the overshoot in the both pump chambers.

Further, in the vane pump according to the present invention, the overshoot generated in the pump chambers is led each other through the clearance formed on the one end of vanes positioned aside of the intake port to the vane back pressure groove, so that the overshoot can be absorbed.

Furthermore, in the vane pump according to the present invention, the communication groove and the vane back pressure groove are formed coaxially relative to the rotor on a slide surface of one of the side plate, and the communication groove is formed outside of the vane back pressure groove. In this situation, the communication groove is communicated with the vane support slit in a case that a top end of the vane is brought contact with the internal cam surface of the cam ring. As a result, the overshoot can be led to the vane back pressure groove through the vane support slit.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1 shows a cross-sectional view of a vane pump according to the present invention; Fig. 2 is a cross-sectional view of the vane pump taken along the line II-II in Fig. 1; Fig. 3 is an expansion plan of a part shown in Fig.

1; and Fig. 4 is a graph indicating a pressure changing in a pump chamber corresponding to time changing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, an embodiment according to the present invention will be described with reference to Fig. 1 to Fig. 4.

In Figs. 1 and 2, 10 denotes a pump housing which is formed therein with a receiving bore 12 communicating with a hollow chamber 11. The hollow chamber 11 opens to one end of the pump housing 10 and the receiving bore 12 opens to the other end thereof, respectively. In a rear housing 13 closing an opening portion of the pump housing 10, a drive shaft 15 is rotatably supported by a bearing 16a disposed in the receiving bore 12 and a bearing 16b disposed in the concave portion 14.

In the hollow chamber 11, there are disposed a cam ring 17 facing with an internal surface of the rear housing 13 and a side plate 18 which faces with an opposite side of the cam ring 17 facing with the rear housing 13.

In an internal surface of the cam ring 17, there are formed a pair of internal cam surfaces 17a wherein a period of a cam curve is 180 degrees. Further, in the cam ring 17, there is rotatably disposed a rotor 22 which slidably supports a plurality of radially extensible vanes 21 which outer end contacts with the internal cam surface 17a slidably. In Fig. 2, both right sides of the rotor 22 and the vane 21 are fluidly closed by the internal surface of the rear housing 13, and both left side thereof are fluidly closed by a side surface of the side plate 18, so that a plurality of blocked pump chambers P1 and P2 are formed between the internal cam surface 17a and the rotor 22 and divided by adjacent two of the plurality of vanes 21, whereby a volume of each of the pump chambers P1 and P2 is changed by a rotation of the rotor 22.

In the side plate 18, there are radially oppositely formed a pair of intake ports 25a and 25b corresponding to the pump chamber performing an expansion operation, and a pair of exhaust ports 27a and 27b performing a compression operation, respectively.

A back pressure groove 32 communicating to a vane back pressure chamber 31 is coaxially formed relative to the rotor 22 at one side surface of the side plate 18 facing with the left side of the rotor 22, to which the exhaust ports 27a and 27b are communicated through a communication groove (not shown).

Further, in the same side surface of the side plate 18, a pair of notches 33 and 34 are radially oppositely formed between the intake ports 25a and 25b and the exhaust ports 27a and 27b, respectively. The notches 33 and 34 are communicated with a communication groove 35 which is coaxially formed relative to the rotor 22 at the same side surface of the side plate 18. The pair of notches 33 and 34 are respectively opened to the pump chambers P1 and P2 at sections proceeding from the expansion operation to the compression operation therein, wherein the pump chamber P1 is communicated with the pump chamber P2 through the notches 33 and 34 and the communication groove 35.

The intake ports 25a and 25b are communicated with a supply passage 44 communicated with a reservoir (not shown) through a supply chamber 41 formed in the rear housing 13 and a bypass passage 28 formed in the pump housing 10, while the exhaust ports 27a and 27b formed in the side plate 18 communicate the operational fluid with a discharge port (not shown) through a pressure chamber 20 formed in the pump housing 10. Between the bypass passage 28 and the pressure chamber 20, a valve fitting bore 45 is formed in which a flow control spool valve (not shown) is provided for returning an excess part of the operational fluid to the bypass passage 28 to control the amount of the operational fluid discharged from the discharge port at a constant flow rate.

As shown in Fig. 3, the vanes 21 are slidably supported in vane support slits S which are radially formed in the rotor 22, in which outer ends of the vanes 21 slidably contact with an expansion curve section (A), a pre-compression curve section (B) and a compression curve section (C) which are formed on the internal cam surface 17a of the cam ring 17. In a special pre-compression operation such that one of the vanes 21 closes the intake port 25a and the pump chamber P1 dose not open to the exhaust port 27a, i.e., while the vane 21 reaches from a rotational position A to a rotational position B (corresponding to a position where the over-shoot occurs in the pump chamber P1), a length L of the vane 21 is set such that the pre-compression curve section is formed so as to generate a clearance 0 between the communication groove 35 and a lower end 21a of the vane 21 aside thereof.

Next, an operation of the vane pump described above will be explained.

When the rotor 22 rotates with the drive shaft 15 by the rotation of a power source (not shown), the operational fluid in the reservoir (not shown) is inhaled to the pump chamber P1, P2 from the intake ports 25a and 25b through the supply port 44, the bypass passage 28 and the supply chamber 41. On the other hand, the operational fluid led to the pump chamber P1, P2 is discharged to the pressure chamber 20 through the exhaust ports 27a and 27b.

In such a situation that the pre-compression operation proceeds from the expansion operation to the compression operation, i.e., when the situation of the pump chamber Pi blocked by the pair of vanes 21 as shown in Fig. 3 (only a situation in the pump chamber P1 is presented herein, but a situation in the pump chamber P2 is same as that in the pump chamber P1) proceeds from the situation in the expansion operation that the pump chamber P1 opens to the intake port 25a to the situation in the pre-compression operation that the pump chamber P1 is completely closed from the intake port 25a by one of the pair of vanes 21, the overshoot that the pressures in the both pump chambers P1 and P2 jaggedly increase occurs. In that time, the both pump chambers P1 and P2 are communicated through the notches 33 and 34 and the communication groove 35 communicated therewith, so that the overshoot can be absorbed. However, in a high-speed traveling, the rotor 22 is rotated at a high speed, so that the overshoot generated in the both pump chamber P1 and P2 jaggedly increase, thereby not being absorbed by the communication groove 35 only.

In this situation, at a position where the overshoot occurs in the pump chamber P1 (from the situation that the pump chamber P1 opens to the intake port 25a, to the situation that the pump chamber P1 is completely closed from the intake port 25a by the vane 21), i.e., in such an area that the vane 21 as shown in Fig.

3 exists between the rotational position A and the predetermined rotational position B, the clearance 0 is formed between the lower end 21a of the vane 21 and the communication groove 35, so that the overshoot in the pump chamber P1 introduced to the communication groove 35 via the notch 33 is led to the vane back pressure groove 32 via the vane support slit S from the clearance 0, whereby the overshoot can be absorbed. Further, the overshoot generated in the pump chamber P1 that is a high pressure is led to the vane back pressure groove 32 which pressure is a high similar to the pump chamber P1, the volume of the pump chamber P1 can not be changed jaggedly.

For example, the pressure changing in the pump chamber P1 from the expansion operation through the pre-compression operation to the compression operation is presented by a graph in Fig. 4. As understood in Fig. 4, the vane pump according to the present invention can absorb the overshoot compared with the conventional vane pump. In Fig. 4, time tl, time t2 and time t3 present start time of the expansion operation, the precompress ion operation and the compression operation, respectively.

Further, the pulsation of the operational fluid can also be decreased largely by the absorption of the overshoot.

As described above, according to the present invention, in the pre-compression operation proceeding form the expansion operation to the compression operation, the clearance is formed between the end portion of the vane and the communication groove, so that the overshoot generated in the pump chamber can be led from the communication groove through the vane support slit to the vane back pressure groove when the pump is rotated at a high speed in such a high-speed traveling especially, whereby it can largely absorb the overshoot compared with the conventional vane pump in which the overshoot is led by the communication groove only. In this situation, the overshoot in the pump chamber is led to the vane back pressure groove which pressure is similar to that in the pump chamber, so that the volume in the pump chamber can not be changed jaggedly. Therefore, the pulsation of the operational fluid can be largely decreased by the absorption of the overshoot.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

What is claimed is:

1. A vane pump comprising: a pump housing; a cam ring disposed in said pump housing and formed with an internal cam surface therein; a rotor rotatably supported in said cam ring and having a plurality of vane support slits formed equiangularly therein; a drive shaft rotatably disposed in said pump housing for rotating said rotor; a plurality of vanes respectively supported in said vane support slits of said rotor, said vanes being radially extensible from said rotor for moving along said internal cam surface of said cam ring when said rotor is rotated; at least one side plate disposed in said pump housing in contact with one end surface of said cam ring; a pair of intake ports radially oppositely formed on said at least one side plate for leading fluid into a pump chamber defined by said internal cam surface of said cam ring, said rotor and adjacent two of said plurality of vanes; a pair of exhaust ports radially oppositely formed on said at least one side plate for discharging the fluid from said pump chamber; a vane back pressure groove formed on said at least one side plate for leading the fluid in said exhaust to one end of all of said vanes supported in said vane support slits; and a communication groove formed on said at least one side plate for communicating one of said pump chambers positioned between one of said intake ports and one of said exhaust ports with the other of said pump chambers positioned between the other of said intake ports and the other of said exhaust ports through notches formed on said at least one side plate; wherein a clearance is formed on said one end of vanes such that said one of pump chambers communicates with said other of pump chambers from said notch through said communication groove to said vane back pressure groove when said pump chamber is positioned between said intake port and said exhaust port.

2. A vane pump according to claim 1, wherein said pump chambers are communicated to a reservoir through said clearance.

3. A vane pump according to claim 1, wherein said one of pump chambers defined by said adjacent two of vanes communicates with said other of chambers through said clearance formed on said one end of vanes positioned aside of said intake port.

4. A vane pump according to claims 2 or 3, wherein said communication groove and said vane back pressure groove are formed coaxially relative to said rotor on a slide surface of one of said at least one side plate and said rotor; and wherein said communication groove is formed outside of said vane back pressure groove.