GB2116258A - Rotary positive-displacement pump - Google Patents

Abstract

In a pump of the slipper-vane type for e.g. a vehicle hydraulic power- steering system, a chamber for the rotor 30 is defined by a cam ring 3 and side plates 4, 5 furnished with suction and discharge parts, respectively, Figs. 5-8 (not shown). To prevent injury thereto due to thermal expansion, friction, and pressure pulsations the cam ring and side plates may be fastened together with longitudinally-resilient screws 20, each of which has either a reduced diameter portion 21 or a screw-threaded portion (24), Fig. 15 (not shown), whereat the strain (caused by the heat and pressure of the working fluid in the rotor chamber) is greater than that at the thicker or non-threaded adjacent portions of the screw. A reservoir 2 for the working fluid may be mounted on the side plates. <IMAGE>

Description

SPECIFICATION Pump This invention relates to improvement in and relating to pumps and more particularly, to an oil pump adapted to pump pressurized oil to the power cylinder in a power steering device which assists a steering wheel in a vehicle, for example.

Generally, the oil pump employed in a power steering device of a vehicle is required to make minimum noise, stand against high load and enjoy long service life even when the pump is operated under a wide range number of rotations of the vehicular engine in an environment where high temperature and dust exist. In order to meet such requirements, almost all conventional pumps are the vane pumps or their modified slipper-vane pumps.

The slipper-vane pump generally comprises a cam ring having a cam face on the inner surface thereof, side plates disposed on the opposite sides of the cam ring and having suction and discharge ports, a rotor positioned in a sealed space defined by the cam ring and side plates for rotation therein and a plurality of slippers disposed about the outer surface of the rotor for slidable movement in contact therewith. In the pump of the type as mentioned above, as the rotor rotates, oil is introduced through the suction ports into the sealed space to be compressed therein and the compressed oil is discharged through the discharge ports out of the pump. However, in order to maintain the efficiency of the pump high, the suction and discharge ports and oil passages are complicately formed so that the pumping pressure can be adjusted.Therefore, the entire pump has a complicated construction and requires a substantial number of parts resulting in an expensive device.

In conventional pumps, since the cam-ring and the side plates on the opposite sides of the cam ring all of which constitute the pump body are rigidly fastened together by rigid bolts, the pump has the disadvantage that when the pump body components expand or contract as the environment temperature varies and/or the pressure of oil being pumped changes, the rotor is subjected to an excessive load or force, the rotor can not rotate smoothly. Furthermore, in the conventional pump, since both the opposite side plates have suction and discharge ports, when oil is sucked and discharged, the cam ring and/or rotor are applied a great force to their opposite sides and the interface between the cam ring and rotor tends to wear severely which in turn makes a noise.In addition, in the conventional pump, oil seals are necessarily provided in spaces between the cam ring and the opposite side plates to prevent leakage of oil there and thus, the pump is required to be manufactured with a high precision and necessarily expensive. Still furthermore, in the conventional pump, when oil is discharged the opposite side plates tend to move away from the cam ring and thus, spring means are required to urge the side plates against the cam ring resulting in a massive and expensive pump.

One object of the present invention is to provide a pump which comprises a pump body which consists of a cam ring and side plates on the opposite sides of the cam ring fastened together with a predetermined prefastening force by elastic bolts which absorb thermal expansion of the components and variation in internal pump pressure caused by variation in temperature whereby the pump can accommodate severe environmental conditions.

Another object of the present invention is to provide a pump in which one of the side plates is formed as the suction plate and the other of the side plates is formed as the discharge side plate so that a single oil passage is defined by the suction side plate, cam ring and discharge side plate and oil can flow in the oil passage with minimum resistance.

Another object of the present invention is to provide a pump in which no oil seals as provided in the conventional pump are provided between the connected components of the pump.

Another object of the present invention is to provide a pump in which the entire pump body is surrounded by a reservoir tank and directly connected to a drive system.

Another object of the present invention is to provide a pump which has a maximum number of rotations within the range of 1,800--5,000 r.p.m. as compared with a conventional maximum number of rotations within the range of 800--1,000 r.p.m. in the power steering of a vehicle whereby the necessary power is substantially reduced and the pump body can be reduced in size.

A still further object of the present invention is to provide a pump the construction of which is simplified by the elimination of means adapted to urge the side plates against the cam ring.

According to the present invention, there has been provided a pump which essentially comprises a cam ring, a suction side plate disposed on one side of the cam ring and a discharge side plate disposed on the other side of the cam ring. The cam ring and suction and discharge side plates are integrally connected together by means of elastic bolts. Rotatably disposed within a sealed space defined by the cam ring and suction and discharge side plates is a rotor. The shaft of the rotor has the shaft of a motor, for example, directly connected thereto. A plurality of slippers are disposed about the rotor and always slidably urged against the cam face on the inner surface of the cam ring by means of the respectively associated springs. The pump body comprising the cam ring, rotor and suction and discharge side plates is entirely surrounded by an oil-tight reservoir tank.

The above and other objects and attendant advantages of the present invention will be more readily apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawings which show one preferred embodiment of the present invention for illustration purpose only, but not for limiting the scope of the same in any way.

Fig. lisa vertically sectional view of the pump embodying the principle of the present invention; Fig. 2 is a front elevational view of said pump; Fig. 3 is a front elevational view of the cam ring in said pump; Fig. 4 is a side elevational view in partial section of said cam ring as shown in Fig. 3; Fig. 5 is a front elevational view of the suction side plate of said pump; Fig. 6 is a side elevational view in section of said suction side plate as shown in Fig. 5; Fig. 7 is a front elevational view of the discharge side plate of said pump; Fig. 8 is a side elevational view in section of said suction side plate as shown in Fig. 7; Fig. 9 is a front elevational view of the reservoir tank in said pump; Fig. 10 is a side elevational view of said reservoir tank as shown in Fig. 9;; Fig. 11 is a schematic view of the pump body as being received in said reservoir tank; Fig. 12 is a side elevational view of Fig. 1 1; Fig. 1 3 is an analytic diagram of stress applied to bolts which connect the components of the pump body together; Fig. 14 is a side view of one embodiment of the elastic bolt to be employed to connect the components of the pump body together; Fig. 1 5 is a side view of another embodiment of the elastic bolt to be employed to connect the components of the pump body together; and Fig. 1 6 is a detailed fragmentary view in section showing the relationship between the elastic bolt and the pump body components fastened together thereby.

The present invention will be now described referring to the accompanying drawings and more particularly, to Fig. 1 thereof in which the entire pump embodying the present invention is shown. The pump generally comprises a pump body 1 and a reservoir tank 2 which receives the pump body 1 therein. The interior of the reservoir tank 2 is filled with fluid such as oil. The pump body 1 comprises a cam ring 3, a suction side plate 4 on one side of the cam ring 3 and a discharge side plate 4 on the other or opposite side of the cam ring. The cam ring 3 has a center opening 6 of the inner periphery of which is formed as a cam face which pumps the fluid in the conventional manner in cooperation with slippers of which description will be made hereinafter.

The center opening 6 in the cam ring 3 serves as a sealed pump chamber defined by the opposite suction and discharge side plates 4, 5 which are disposed on the opposite sides of the cam ring 3 in close contact therewith.

The suction side plate 4 is disposed on one or the right-hand side of the cam ring 3 (as seen in Fig.

1) in close contact therewith and as more particularly shown in Figs. 5 and 6. The suction side plate 4 comprises a larger diameter portion 7 and a smaller diameter portion 8, the latter of which is formed with a pair of larger arcuate outer suction ports 9, 9' and a pair of smaller arcuate inner suction ports 10, 10'. The smaller diameter portion of the suction side plate 4 is further formed with an inlet 11 which is in communication with the outer and inner arcuate suction ports 9, 9' and 10, 10'.

The discharge side plate 5 is disposed on the other or left-hand side of the cam ring in close contact therewith (as seen in Fig. 1) and as more particularly shown in Figs. 7 and 8. The discharge side plate 5 is formed with a pair of outer larger arcuate discharge ports 12, 12', a pair of inner smaller arcuate discharge ports 13, 13' and a cylindrical outlet 14 which is in communication with the outer and inner discharge ports. The discharge side plate 5 is formed with a passage 1 5 which is in communication with the outer and inner discharge ports. One end of the passage is open to the interface between the cam ring and discharge side plate.

The cam ring 3 includes a plurality of holes 1 6 (four holes in the illustrated embodiment) adjacent to the periphery of the ring in alignment with holes 17 in the discharge side plate 5 and similarly, the suction side plate is formed with the corresponding number of threaded holes 1 8 in alignment with the corresponding holes and in the discharge side plate and cam ring, respectively. In assembling the components of the pump body together, elastic bolts 20 are first passed through the aligned holes in the cam ring and discharge side plate and then screwed into the threaded holes 1 8 in the suction side plate 4 whereby the suction and discharge side plates and cam ring are firmly connected together.In such a case, it is to be noted that no oil seals are provided between the suction and discharge side plates and the cam ring. Different embodiments of the elastic bolt 20 are in detail shown in Figs. 14 and 15. The elastic bolt shown in Fig. 14 has an intermediate elastic portion 21 between the head 22 and shank 23 of the bolt and the intermediate elastic portion 21 is designed to extend and contract by a suitable degree. In the illustrated embodiment, the elastic bolt is reduced in diameter in the intermediate elastic portion 21. In the embodiment shown in Fig. 15, the elastic portion 20 is externally threaded at 24 to function as a coiled spring. The function of the intermediate elastic portion will be described hereinafter.

A rotor 30 is provided within the interior of the pump chamber. A plurality of slippers 40 are provided about the periphery of the rotor 30 in slidable contact with the cam face of the cam ring (see Fig. 3). The slippers 40 are freely received in the corresponding recesses 31 formed in the periphery of the rotor 30 and the slippers have contact faces 41 on their faces opposing to the cam face on the cam ring 3. A compression spring 50 is interposed between the face of the slipper remote from the cam face thereof and the bottom of the corresponding recess in the rotor 30 so as to always urge the slipper contact face against the cam face on the cam ring. As in the conventional pumps, the pump of the invention is formed with the suction zone S and the discharge zone D (see Fig. 3).The suction ports in the suction side plate are positioned at the suction zone and similarly, the discharge ports in the discharge side plate are positioned at the discharge zone.

The slippers and rotor have such a width that they can be smoothly inserted into the spaces between the suction and discharge side plates. Although not shown, the rotor has a drive means such as a motor drive shaft 60 directly connected to the central area of the rotor. In the illustrated embodiment of the pump, the rotor and drive shafts are connected together by means of serrations. The motor drive shaft is journaled in a bearing 70 which are in turn provided on the motor mounting member 80.

The reservoir tank 2 comprises a plastic housing and has an opening 91 fitted on the larger diameter portion of the suction side plate 4 with an oil seal 90 interposed therebetween and an opening 92 fitted on the outer periphery of the discharge side plate 5 with an oil seal 93 interposed therebetween. The reservoir 2 further includes an oil injection port 2a and an oil inlet 2b in communication with the inlet in the suction side plate (see Figs. 9 and 10). Reference numeral 95 denotes a filter provided in the oil inlet. In this arrangement, the reservoir tank 2 receives the pump body 1 in sealing relationship.

In the pump described hereinabove, when the motor is rotated, the rotor 30 is rotated thereby whereby the slippers 40 slidably move along the cam face on the cam ring 3 so as to introduce the fluid or oil through the oil inlet, the inlet 2b in the reservoir tank 2 and the suction ports 9, 9' and 10, 1 0' in the suction side plate 4 into the seal space within the cam ring 3 at the suction zone S and compress the introduced oil which is in turn discharged through the discharge ports 12, 12' and 13, 13' and outlet 14 in the discharge side plate at the discharge area of the pump body 1. It is to be noted that when the pump of the invention is applied to the steering device of a vehicle, for example, the number of rotations of the rotor is set over at least three times as high as that of idling rotations of the vehicular engine.

Since the conventional pump for the power steering of a vehicle is driven by the engine, in order to exhibit the maximum capacity of the pump while the vehicle is parking or enters its garage, the pump is designed to provide a predetermined maximum pressure and a predetermined maximum displacement at 600-1,000 r.p.m. in proportion to the number of rotations at such a particular time and thus, notwithstanding the fact that the number of rotations of the pump increases when the vehicular speed and accordingly, the engine rotation rate increases, a substantial portion of the displaced oil is released by a pressure regulation valve or drooper valve.Thus, when the pump rotates at a rate within the range of 600-1,000 r.p.m., the efficiency of the pump is high, but when the rotational rate of the pump is within the range of 1,000-8,000 r.p.m., the pump is not only low in efficiency, but the pump becomes expensive because the components of the pump should be formed of high quality materials by taking wear-resistance and durability called for the pump when operated at a high rotational rate into consideration within the range of 1,000--8,000 r.p.m.

On the other hand, the pump of the present invention is designed to rotate at a rotational rate within the range of 1,800-5,000 r.p.m. at an engine rotational rate within the range of 600-1 000 r.p.m. when the vehicle is parking or enters the garage and the rotation of the pump is stopped or reduced when the vehicle speed or engine rotational rate exceeds the range. Thus, the capacity of the cam ring of the pump body is one third - one fifth that of the component of the corresponding conventional pump.In the illustrated embodiment of the pump, the maximum frictional movement velocity of the slidable parts of the pump is only one sixth - one eighth that of the corresponding parts in the conventional pump. in the pump of the invention, the maximum circumferential velocity of the slidable parts is 4.5 m/sec. whereas the maximum circumferential velocity of the corresponding parts in the conventional pump is 1 6 m/sec. From the low circumferential velocity of the slidable parts in the pump of the invention, it will be understood that the costs of the materials of the cam ring slippers, the suction and discharge side plates and the heat-treatment and processing of these parts can be substantially reduced.Thus, in the illustrated embodiment of the pump according to the present invention, the suction and discharge side plates are usually formed of light metal alloy such as aluminum or die cast aluminum and the cam ring and rotor are formed of sintered alloy not subjected to any specific treatment (cementation) without difficulties.

Figs. 11 and 1 2 are schematic view showing comparison between the capacity of the pump of the invention (with the reservoir tank) and that of the conventional pumps. The weight of the pump of the invention shown by reference character C is 0.4 kg whereas the weight of the conventional pumps shown by reference characters A and B, respectively, is 3.4 kg and 3.2 kg, respectively.

From these Figures, it will be understood that the pump C of the invention is quite smaller than the conventional pumps A, B.

One of the important features of the present invention is that the cam ring 3 and the suction and discharge side plates 4, 5 have the holes by which these components are positioned in place and the elastic bolts 20 passing through these three components connect the components together to thereby provide the pump body.As mentioned hereinabove, although the suction and discharge side plates can be formed of light metal alloy such as aluminum or die cast aluminum, since the aluminum, steel and sintered alloy components of the pump are fastened together in side-by-side relationship by means of the steel bolts, it is necessary to consider the possibility that the pump may suffer from lowering in efficiency or get trouble due to yielding and/or fatigue destruction of the components resulting from sudden change in the fastening force caused by difference between the thermal expansion coefficients of the components and at the same time, it is necessary to suitably absorb pulsation of oil pressure caused by the pressure within the pump varying from 0 atmospheric pressure to about 70 atmospheric pressures and vane rotation. Fig. 1 3 is an analytic diagram showing stress applied to the elastic bolt employed for connecting the components of the pump according to the present invention.

In this Figure, the broken lines show stress applied to the conventional bolt when the bolt is tightened and the solid lines show stress applied to the elastic bolt employed in the pump of the invention when the bolt is tightened.

In the illustrated embodiment of the pump of the invention, it is assumed that the pressure within the pump is 300 kg at normal temperature and the fastening force by each elastic bolt at normal temperature is 300 kg. Variations in the fastening force by the bolts are shown in the following Table. TABLE

Fastening Difference External Energy force at Fastening Fastening in fastening force absorbed by normal force at force at force at -35 C applied components temperature -35 C 100 C and 100 C to bolt fas tened Stress applied to conventional 300 kg 242 kg 388 kg 146 kg 30 kg 45 kg bolt (kg/mm2) Stress applied to inventive 300 kg 260 kg 358 kg 98 kg 20 kg 55 kg elastic bolt (kg/mm2) As clear from the above-given Table, the elastic bolt is well within the elastic and fatigue limits designed for the bolt and stress applied to the aluminum contact face on the head of the bolt is also within the yielding and fatigue limits designed for the bolt whereby reliance in the strength of the elastic bolt can be substantially improved.

Fig. 1 6 is a fragmentary sectional view showing the relationship between the elastic bolt and the components fastened together by the bolt. When the pump is in its inoperative position or rotates at a low rotational rate, that is, at a low pressure, the side plates are urged towards the rotor under the fastening force provided by the bolt as shown by the solid line a and on the other hand, when the pump is at a high pressure or rotating at a high rotational rate, the side plates move away from the rotor as shown by the dotted line b to provide suitable clearances between the rotor and side plates whereby the pressurized oil is evenly applied to the interface between the rotor and side plates so as to maintain the rotor and slippers in their neutral position.In this way, the interface between the rotor and side plates can be protected against potential flaw, burn and wear and pulsation of oil pressure can be effectively absorbed.

Furthermore, this effect prevents the inclination of the rotor and slippers which may be otherwise caused by the differential pressure applied to the opposite sides of the rotor and slippers whereby the oil can flow in the one-way passage with a minimum resistance.

Furthermore, since the pump body of the invention has no oil seal rings, the oil is allowed to leak through the areas of the components fastened together by the bolts, but the leaked oil is immediately recycled to the reservoir tank and thus, the efficiency of the pump will not be adversely affected by the leaked oil.

While only one embodiment of the invention has been shown and described in detail, it will be understood that the same is for illustration purpose only and not to be taken as a definition of the invention, reference being had for this purpose to the appended claims.

Claims (6)

1. A pump comprising a cam ring defining a pump chamber therein and having a cam face on the inner surface, a rotor disposed within said pump and a plurality of slippers disposed about said rotor in slidable contact with said cam face on the cam ring, a suction side plate disposed on one side of said cam ring and having suction ports and a discharge side plate disposed on the other side of said cam ring and having discharge ports whereby fluid flows from said suction side plate through said pump chamber to said discharge side plate.

2. The pump as set forth in Claim 1, in which said discharge side plate has means adapted to urge the side plate towards said cam ring when said fluid is pumped.

3. A pump comprising a pump body having a cam ring and side plates disposed on the opposite sides of said cam ring: and a reservoir tank receiving said pump body, said cam ring and side plates being fastened together by means of elastic bolts.

4. A pump comprising a pump body having a cam ring defining a pump chamber therein and a rotor disposed within said pump chamber; and a reservoir tank receiving said pump body therein, said rotor being directly connected to a drive member.

5. The pump as set forth in Claim 4, in which the number of rotations of said rotor is set at least three times as high as that of the engine of a vehicle when the engine Is idling.

6. A pump substantially as herein described with reference to Figs. 1 to 14 and 1 6 or Figs. 1 to 13, 1 5 and 1 6 of the accompanying drawings.