GB2158517A

GB2158517A - Sliding vane pump

Info

Publication number: GB2158517A
Application number: GB08508794A
Authority: GB
Inventors: Siegfried Hertell; Robert Lange
Original assignee: Barmag Barmer Maschinenfabrik AG
Current assignee: Oerlikon Barmag AG
Priority date: 1984-04-09
Filing date: 1985-04-04
Publication date: 1985-11-13
Also published as: FR2568952A1; ES8701309A1; ES542021A0; JPS60256582A; IT1218467B; GB2158517B; FR2568952B1; GB8508794D0; IT8520098A0; JPH0684755B2

Abstract

The pump has a pair of hook- shaped vanes 5, 6 in slidable contact with each other in a guide slot 4 of a rotor 2, the thickness of the hook head 7, 8 of each vane being equal to the combined thickness of the stems 9, 10 of the two vanes, which is adapted to the width of the slot, and the base of each stem combining with the hook head of the other vane to form a hook chamber 15.1, 15.2 which is enclosed in the rotor slot over part of the rotation of the rotor. The hook chambers 15.1 and 15.2 are enclosed during the part of the rotation ranging from 90 DEG before to 90 DEG after the lower dead centre point (i.e. the position shown of vane 6), and each hook chamber is filled with oil during the part of the rotation of the rotor 2 extending from 90 DEG before the lower dead centre point to the lower dead centre point and is drained by way of a restrictor during the part of the rotation extending from the lower dead centre point to 90 DEG after the lower dead centre point. <IMAGE>

Description

SPECIFICATION Vane Cell Pump This invention relates to a vane cell pump.

Japanese Utility Model 26-6486 discloses a vane cell pump having a pair of hook-shaped vanes in slidable contact with each other in a guide slot of the rotor, the thickness of the hook head of each vane being equal to the combined thickness of the stems of the two vanes, which is adapted to the width of the slot, and the base of each stem combining with the hook head of the other vane to form a hook chamber which is immersed in the rotor slot over part of the rotation of the rotor.

One problem in this as in every vane cell pump is that the vanes must keep in close contact with the circumference of the housing in every angular position of the rotor and must therefore constantly move radially inwards and outwards. In the known pump, this problem may give rise to particular difficulties because in the angular position of the rotor in which the total length of the vanes is equal to the radius of the housing and therefore at its maximum (maximum position of the rotor), i.e. the position in which the withdrawn vane is completely immersed in the rotor slot (lower dead centre position), the centre of gravity of the vane is very close to the centre of the rotor and may even lie beyond the rotor axis.There is therefore a certain range of rotation of the rotor during which the centrifugal forces acting on the vanes may be insufficient to keep the head of this vane in contact with the circumferential wall of the housing, and may even be non-existent.

In the known embodiment, a spring is provided for this purpose to push the two vanes apart. This has the disadvantage that the spring forces are at their weakest when the rotor is in its maximum position where they are most required for enabling the vane to move outwards from the lower dead centre point. When the rotor is turned through 90" from its maximum position and the total length of the vanes is therefore at its minimum (minimum position of the rotor), the spring forces are greatest and the centre of gravity of each vane is clearly on that side of the rotor axis to which the vane should move out. From the minimum position onwards, therefore, the centrifugal forces acting on the head of the vane are unnecessarily assisted by the spring forces which are then at their maximum.The increase in friction thereby produced results in a corresponding power loss by dissipation.

The problem therefore arises of effectively assisting the radially outward movement of the vanes of a vane cell pump by the introduction of an additional force but only so long as the centrifugal forces are not sufficient to produce this outward movement.

According to the invention, the rotor and the vanes are so designed for this purpose that the hook chamber (i.e. the rectangular gap between the hook head of one vane and the base of the stem of the other vane) is immersed in the rotor slot when the rotor moves into the minimum position (90 position before the lower dead centre point). The hook chamber is thereby hermetically sealed on all sides and the underside of the hook head is immersed in the rotor slot in the 90" position before the lower dead centre point. Furthermore, according to the invention, the hook chamber is filled with oil between the 90" position and the lower dead centre point.This filling with oil is assisted by the fact that within this range of rotation the hook chamber automatically increases in volume since the total length of the vanes increases. In some cases, leakages may on their own suck a sufficient quantity of lubricating oil into the hook chamber but the hook chamber may be connected to a source of oil, preferably the source of lubricating oil, at some point or over part or all of the range of rotation between the 90" position and the lower dead centre point. Furthermore, the invention provides that in the range of rotation between the lower dead centre point and the following minimum position behind the lower dead centre point, the hook chamber receives a restricted connection to the interior of the pump chamber or also to the outside, in particular to the reserve of lubricating oil.The restriction is so designed that owing to the inevitable reduction in the size of the hook chamber in this region of rotation between the lower dead centre point and the minimum position behind the lower dead centre point, sufficient pressure develops in the hook chamber to push the outwardly moving vane out into the position of contact with the circumferential wall of the housing.

Just as the hook chamber is immersed in the slot when it is in the minimum position before the lower dead centre point so it emerges from the slot when it is in the minimum position behind the lower dead centre point so that it is in this position at the latest that the additional pressure on the outwardly moving vane ceases.

According to the invention, an outlet with variable restrictor may be provided over the range of rotation between the lower dead centre point and the 90" position behind the lower dead centre point.

This restrictor may in particular be so formed that the pressure in the hook chamber falls abruptly before the minimum position behind the lower dead centre point is reached. For this purpose, an additional outlet, e.g. in the form of a radially bound notch on the front side of the hook head, may provide a premature connection between the hook chamber and the interior of the housing.

The inflow of oil into the hook chamber and the restricted outflow of oil from the hook chamber may be brought about, for example, by a groove or slot in the end wall of the housing. This opening may vary in cross-section according to the required restrictor effect and extends along the part of the circle over which the hook chamber sweeps between the minimum positions before and behind the lower dead centre point.

The oil inflow and restricted oil outflow may also be formed by a recess in an end wall of the rotor.

The external radius of this recess is calculated to ensure that the hook chamber sweeps over the recess in its movement between the 90" position and the lower dead centre point, whereby the hook chamber is connected to the oil supply. After the hook chamber has passed through the lower dead centre point, the oil which has entered it is expelled through the recess. The limited depth of the recess produces the desired restrictor effect. The recess preferably varies in depth in the radial direction, being deepest in the outer regions and reaching such a depth just before the minimum position behind the lower dead centre point that it provides for almost unrestricted escape of the oil from the hook chamber.

In a preferred embodiment, at least one end wall is provided with an additional, substantially radially directed groove or recess situated just before the minimum position behind the lower dead centre point and so formed that the hook chamber sweeps over the recess as it moves into this region of rotation. It is this additional opening which produces the abrupt elimination of the restrictor effect.

The vane cell pump according to the invention is preferably used as a vacuum pump, for example for increasing the braking force or for boosters in motor vehicles, in particular those with fuel injection. It has the advantage of providing a very high volumetric output for a very compact design and, by virtue of the invention, also having a very low power dissipation.

When the pump is used as air pump or vacuum pump, measures are provided to facilitate "cold start" ofthe pump. The problem in cold starting is that the lubricating oil is very viscous. In addition, impurities in the oil may become so firmly deposited during periods of standstill that the movement of the vanes is permanently impaired. In one embodiment, this is overcome by providing a spring with limited spring excursion in the hook chamber, either on the base of the stem or on the underside of the hook head, to press the two vanes apart in the minimum position and over a certain, as far as possible very small range of rotation in front of and behind the minimum position. The spring is a bimetal spring designed so that it only projects into the hook chamber when cold.

Cold start may also be facilitated by subjecting the hook chambers immersed in the rotor slot or one of the hook chambers to the oil pressure.

In a preferred embodiment, the vane cell pump used as vacuum pump is lubricated with lubricating oil free from pressure but a valve device is provided which closes in the cold. This effect may be achieved, for example, by lengthwise contraction as the temperature falls or by a bimetal effect.

In another embodiment of the pump which is lubricated with lubricating oil, the pressure of the lubricating oil is used to advantage for moving the vanes out of their minimum position. The pumps of this embodiment are used mainly as vacuum pumps, in particular vacuum pumps in motor vehicles with fuel injection for increasing the braking power orfor driving other servo motors which are connected to the lubricating oil system of the engine and in which the outlet communicates with the oil sump of the engine.

In this pump, the housing, rotor and vanes are again so designed that the hook chambers are immersed in the guide slot of the rotor during the part of the rotation ranging from 90 before to 90 behind the lower dead centre point. In this range, the hook chambers communicate with an oil supply pipe which communicates with the source of lubricating oil, in particular a lubricating oil pump.

For this purpose, one end face of the rotor or one end face of the housing may, as already described above, have a circular disc-shaped recess into which the oil supply duct opens and which is covered by the hook chambers after they have entered the rotor slot. The oil supply duct is preferably concentric to the rotor. The problem in such an arrangement is that the lubricating oil is sucked into the pump chambers which are at a lower pressure.

Furthermore, in such a vacuum pump, the outlet chamber is also provided with a non-return valve, with the result that the outlet chamber is also under vacuum until it acquires the external pressure by suitable compression. The power required in such a vacuum pump can be considerably reduced since the pressure difference between the two sides of a vane is very small. This entails the risk, however, that oil may be sucked into the outlet chamber, whereby the oil consumption of the pump is greatly increased. This leads to a deficiency in oil in other lubricated parts of the motor vehicle engine precisely when the engine is driven at a high speed and the pump therefore takes in an unnecessarily high vacuum.

To limit the oil supply and establish a controlled oil flow, thevane cell pump is provided with a type of slide valve control in that the stems of both vanes have recesses or clearances extending radially from the base of thestem over part of the length of the vane, and by intermittently covering the oil supply duct which is concentric to the rotor, these clearances control the oil flow between the oil supply duct and the hook chambers in dependence upon the angular position of the rotor by means of their end edges sweeping over the oil supply duct.

The supply of oil to the hook chambers is thereby controlled so that the oil pressure sufficiently assists the radially outward movement of the vanes without producing an excessive contact pressure which would cause excessive wear and dissipation of power and without causing any unwanted discharge of oil into the intake and/or output chamber of the pump or the oil sump of the vehicle engine.

The clearances in the vanes may be so designed that the connection between the oil supply duct and a hook chamber is increased immediately after the hook chamber is immersed in the rotor slot and decreased immediately before the hook chamber re-emerges from the rotor slot.

The clearances may advantageously be formed as recesses at one or both lateral edges of each vane.

Recesses may also be formed on the back of each vane facing away from the hook head. Cut-outs extending in the radial direction from the base of the stem over part of the length of the vane at one or both lateral edges of each vane do not affect the forces with which the vanes are pressed in contact with each other.

As already mentioned, the oil supply duct may be placed concentrically to the rotor in an end wall of the housing. In that case, the oil supply duct is preferably inside the rotor and its diameter is greater than the width of the rotor slot so that a half-moon shaped channel is left on each side of the pair of vanes. The recesses or cut-outs intermittently connect these half-moon shaped channels with the hook chambers.

Cut-outs at the lateral edges of the vanes can be used not only to control the oil supply to the hook chambers by ensuring that the overlap between the cut-outs and the oil supply duct has the required size but they can also be used for the particularly important function of controlling the oil flow from the oil supply duct into the housing by suitably designing the recesses in relation to each other. In particular, the cut-outs of the two vanes are so arranged that they do not overlap even when the vanes are in the dead centre position. In this dead centre position of the two vanes, one of the hook chambers is completely outside the rotor. In this position, the connection between the oil supply duct and the hook chamber outside the rotor is prevented by the fact that the vanes are in contact with each other over their whole width so that the cut-outs do not overlap.

In order to obtain a sufficiently tight seal between the oil supply duct and the housing, the hook chambers should enter the rotor slot before the clearances or cut-outs overlap the oil supply duct, and preferably up to 15 before this overlap occurs.

The invention cannot and is not intended to prevent oil enclosed in the hook chamber from flowing out of the rotor slot into the housing, in particular into the outlet chamber, when the hook chamber re-emerges from the rotor slot, since these places also require oil, in particular for lubricating the vanes against the housing and the rotor. The invention is, however, intended to prevent these quantities of oil returning into the crank case of the engine through the outlet openings, firstly because the expulsion of these quantities of oil from the outlet duct and in particular from the outlet valve entails a considerable dissipation loss and secondly because it is precisely when the output capacity of the oil pump is exhausted by the high oil consumption of other consuming devices that the outflow of lubricating oil is undesirable.

According to the invention, preferably a train of grooves bent at angles is provided in one end wall of the housing at the end of the outlet chamber. The essential components of this train of grooves are: A circumferential branch extending over part of the outlet chamber, preferably over the end region of the outlet chamber. It is particularly important that this circumferential branch should cover that part of the outlet chamber which is situated behind the end of the outlet opening. It should be noted that for reasons of manufacture as well as for the sake of efficient sealing, the outlet opening cannot extend as far as the dead centre point. The outermost end of the outlet chamber is therefore a dead space. A radial branch of the system extends from the end of the circumferential branch to just before the oil supply.The radial branch is substantially bounded by the plane containing the dead centre point. A connecting branch extends from the end of the radial branch in a direction substantially parallel to the circumferential branch and ends in a point which is about 30 but preferably more than 30 , preferably 30 to 60 before the line containing the dead centre point (measured from the centre of the rotor). The end region of the outlet chamber is connected to the oil supply by way of the circumferential branch, the radial branch and the connecting branch of this system of grooves and by the cut-outs of the vane which is approaching its upper dead centre position as the other vane approaches the lower dead centre position.The contents of the remaining outlet chamber are then transferred to the oil supply along the train of grooves but a powerful throttling effect is produced since the grooves are relatively shallow and the train of grooves are sharply bent at angles, especially between the circumferential branch and the radial branch. Oil is thereby prevented from overflowing from the oil supply into the outlet chamber so long as the latter is still under a vacuum and at the same time the oil collecting in this end region of the outlet chamber is transferred to the oil supply by the system of grooves when the oil pressure is reached in the oil supply. The oil is then again available in the oil supply for lubrication and for assisting the outward movement of the hook vanes.

The invention will now be described with reference to embodiments illustrated by way of example in the drawings, in which Figs. 1,3 are normal sections, each through a different embodiment, Figs. 2,4 are radial sections through the same embodiments, Figs. 58 illustrate a valve arrangement for supplying pressure oil.

Figs. 9, 10 are a normal section and a radial section through a combined vacuum/oil hydraulic pump.

Fig. 11 is a radial section through an exemplary embodiment, Figs. 12A and B are perspective views of hook vanes, Figs. 13A to 13E are normal sections through the embodiment shown in Fig. 11 with the rotor in different angular positions, and Figs. 14Aand B show details ofthe outlet valve.

In both embodiments, a rotor 2 is rotatably mounted in a housing 1. The rotor 2 and shaft 3 are made in one piece. The shaft 3 is driven by a motor (not shown) e.g. by way of the cam shift of a car engine. The rotor is subdivided across its whole width by a slot 4 in which two vanes 5 and 6 are slidably movable. The vanes 5, 6 are hook shaped in cross-section. Each vane has a stem 9, 10 and a so-called hook head 7,8 which is twice as thick as the stem 9, 10. The vanes 5, 6 are placed with their stems 9, 10 in sliding contact. To prevent the stems sticking together, especially at cold start, both stems or only one may be provided with a recess extending over all or part of the width of the stem.In the radial direction, however, the recesses are too short to emerge from the rotor slot in any angular position of the rotor, so that they are sealed off by the end walls 11, 12 of the housing 1 in every angular position. The so-called hook chambers 15.1 and 15.2 are formed by-the underside 13 of each hook head and the base 14 of the stem 9 or 10, respectively, of the other vane.

For the sake of clarity it should be noted that the vanes 5,6 are congruent. Furthermore, the angular position of the rotor 2 shown in Figs. 1 and 3 will be referred to as the maximum position. In this maximum position, the vanes have their greatest overall length in the radial direction from the hook head of one vane to the hook head of the other. This overall length is equal to the internal radius of the housing 1. In the maximum position illustrated, the vane 6 reaches its radially innermost position (lower dead centre position) relative to the rotor while the vane 5 reaches its radially outermost position (upper dead centre position). This means that in the maximum position, the hook chambers 15 also have their maximum size.Furthermore, the angular position of rotor 2 and corresponding position of the vanes indicated in dotted lines in Figs. 1 and 3 will be referred to as the minimum position. In this position, the overall length of the vanes in the radial direction of the rotor is at its minimum due to the eccentric position of the rotor 2 in the housing. The volume of the hook chambers is therefore also smallest in this position. The radial length of the hook heads 7,8 and the radial length of the vanes 9, 10 are so calculated that the hook chambers 15 have as small a volume as possible in the minimum position,l.e. the lower edge 13 of the hook head 7 or 8 almost abuts against the base 14 of the stem 9 or 10 of the other vane. In both exemplary embodiments, the inlet 32 and outlet 33 are closed in the counterflow direction by a non-return valve 34 and 35.Oil is thereby prevented from flowing back in the opposite direction through inlet 32 while in outlet 33 a reduction in output is obtained.

According to the invention, the length of each hook head in the radial direction and the radius of the rotor are such that the undersides 13 of the hook heads are completely immersed in the rotor slot in the region of the minimum position. This means that from the minimum position onwards, the hook chambers 15 are sealed off by the rotor slot 4 and the end walls 11,12 of the housing.

According to the invention, the hook chambers 15 become filled with oil in their movement from the minimum position to the maximum position and the oil is then expelled through a restrictor between the maximum position or lower dead centre point and the minimum position.

For this purpose, the example illustrated in Figs. 1 and 2 has sickle-shaped openings 16 and 17 in the end walls 11 and 12 connected to an oil supply 20 through ducts 18, 19. The oil may be at a very slight excess pressure and may serve as lubricating oil for the pump. The openings 16, 17 are so arranged that the hook chambers 15 sweep over them when the rotor rotates. Their cross-section increases from the minimum position to the lower dead centre position and then decreases from the lower dead centre position to a point near the minimum position.

Shortly before reaching the minimum position, the cross-section increases abruptly to form an outlet region 21.

The mode of operation is as follows: As the rotor 2 rotates in the sense indicated by the arrow 22, the volume of the hook chamber 15.1 immersed in the rotor slot 4 increases between the minimum position and the lower dead centre point. Since the hook chamber 15.1 sweeps over the opening 16 or 17 during this part of the rotation, the hook chamber sucks oil out of this opening. At the lower dead centre point, the particular vane (say, the vane 5) reaches its innermost radial position with respect to the rotor. At the same time, the other vane (6) reaches its outermost radial pOsition, known as the upper dead centre point.This means that from the lower dead centre point onwards, the volume of the hook chamber begins to decrease and the oil enclosed in it is squeezed out through the openings 16, 17. Since the openings 16, 17 have only a narrow, limited cross-section, the flow of oil through them is restricted so that a pressure is established in the hook chamber 15, and this pressure is sufficient to push the vane (5) radially outwards from the dead centre position. About 10 to 20 before the minimum position is reached, the hook chamber 15 sweeps over the outlet region 21 which has a wider crosssection so that the pressure in the hook chamber 15 suddenly drops. This arrangement prevents unnecessarily high forces being exerted on the outwardly moving vane.The same effect is obtained when the vane 6 with the hook chamber 15.2 rotates from minimum position to maximum position to minimum position. It will be seen that the particular form of cross-section of the opening enables the pressure variation in the hook chamber 15 and therefore also the contact pressure with which the vanes are pushed outwards to be adjusted to the optimum. This pressure variation should in particular conform to the variations in position of the centre of gravity on the vane.

According to the invention, the centre of gravity of each vane is modified by the introduction of a weight 23, such as a metal rod, in each hook head.

This fulfils or assists the purpose of locating the centre of gravity of each vane 5 or 6 by a suitable geometrical configuration and mass distribution so that it will not move beyond the central axis 24 of the rotor even when the vane is in the lower dead centre position.

According to the invention, each vane is so placed that the hook chambers face forwards in the direction of movement of the vanes. This has the result that pressure forces acting on the top and underside of each hook head on the pressure side are equalized and the vacuum on the intake side of the pump assists the radially outward movement of the vanes.

In the example illustrated in Figs. 3 and 4, the oil is supplied through a disc-shaped recess 26 in one end face of the rotor 2. This recess 26 is sealed off from the circumference of the rotor 2 by the radial ridge 27. The recess 26 communicates with the internal channel 29 of the hollow shaft 3 through an annular gap 28. The oil supply pipe 30 is directed into the internal channel 29.

The oil supply pipe 30 carries oil free from pressure into the internal channel 29. Since the diameter of the internal channel 29 is greater than the width of the slot 4, the oil is able to flow over both vanes. It should be noted that in Fig. 4, the rotor has been represented as if the vanes were not inserted in the slot. The contours of the vanes are merely indicated by the dotted lines.

It should also be noted that the slot is continued for a short length into the shaft 3 as a recess 31 through which oil can enter the region of the bearings for the purpose of lubrication.

The recess 26 is shallow and its depth preferably varies in the radial direction. Each hook chamber 15 absorbs oil from the recess 26 between the minimum position and the lower dead centre point and expels this oil as it continues on its rotation from the lower dead centre point to the minimum position. The flow of oil is, however, restricted by the shallowness of the recess 26. The particular variation in the depth of the recess causes the restrictor effect to vary in the course of the rotation.

Each hook chamber sweeps over the region of greatest depth, where the restrictor effect is virtually eliminated, shortly before reaching the minimum position, so that the pressure in the hook chamber is again reduced.

This release of pressure before the minimum position is reached behind the dead centre point may also be achieved by a notch 36 formed in front of the hook head, as indicated by the broken line in Fig. 3, this notch connecting the recess 26 of the rotor with the circumference of the rotor through the ridge 27 in a selected, narrow region before the minimum position where the complete elimination of pressure is desired. This arrangement may be used in particular as an alternative to the circumferential increase in depth of the recess 26.

When a vacuum pump is started from the cold, in particular at temperatures below 0 C, the lubricating oil is found to be highly viscous. This may prevent the movement of the vanes, so that the pumping action does not set in. When such a vacuum pump is used, for example, for increasing the braking force, such a failure in function has adverse consequences.

According to the invention, this difficulty is overcome by briefly supplying oil under pressure through pipe 20 in the embodiment illustrated in Figs. 1,2. The pressure is chosen to be sufficiently high to push the vanes outwards into sealing contact with the wall of the housing. A suitable thermosensitive valve may be provided for putting the oil under pressure. In the embodiment illustrated in Figs. 3, 4, the thermosensitive valve consists of a ring 47 inserted in a groove 48 in the hollow shaft. When the system is cold, the ring 47 restricts the cross-section of outflow between the oil supply pipe 30 and the internal circumference of the channel 29 sufficiently to cause a pressure to build up in the channel 29. Details are shown in Figs. 5 to 8. The ring 47 is split at one point, as shown in Figs.

6 and 7, and the two ends of the ring 47 overlap. The ring is lined on its internal circumference by a highly heat-sensitive, metallic insert 39 in the form of an open ring which, as shown in Fig. 8, is firmly attached to the main body. The ring 47 itself consists of a material which is not heat-sensitive, e.g. a plastics material which contracts only slightly on cooling compared with the metal insert 39. Owing to the large amount of contraction of the metal insert 39 in the cold, the internal diameter of the ring 47 decreases owing to the resulting bimetal effect. The width of the gap between the duct 29 and the oil supply pipe 30 is therefore also reduced so that an oil pressure can build up in the duct 29. As the temperature rises, the internal diameter of the ring 47 increases so that the oil can flow out of the duct 29 without restriction.

The example illustrated in Figs. 9 and 10 is a hook vane pump functioning both as vacuum pump and as oil pressure pump. The pump may be used both for driving pneumatic servo consumers such as servo brakes and for hydraulic consumers such as level regulators in motor vehicles. It should be noted that the axial section through the pump shown in Fig. 9 is substantially similar to that shown in Fig. 2.

Reference will therefore be made to Fig. 2 in the description which follows.

The rotor 2 is eccentrically mounted in the housing 1 and driven to rotate by the shaft 3 in the sense indicated by the arrow 22.

The two vanes of the pump are supported to be slidably movable against each other in a rotor slot 4.

The vanes are hook shaped. The end of each vane, referred to as hook head 7, 8 in this application, is equal in thickness to the sum of the two stems 9, 10 of the vanes sliding on each other.

In the embodiment illustrated in Fig. 10, which shows a detail of one of the hook heads, each hook head has a bearing sleeve 40 in which a roller 38 is rotatably mounted with a sliding fit. The bearing sleeve is connected to its respective hook chamber 15.1 or 15.2 by a plurality of pressure equalizing ducts 39 arranged one behind the other in the axial direction.

The pump is so designed that when the rotor rotates in the sense of arrow 22, the hook chamber 15.1 enters the rotor slot 4 in or shortly before the minimum position (90 position) indicated in broken lines so that the hook chamber 15.1 constitutes an enclosed chamber in this position. As the rotor continues to rotate, this closed hook chamber 15.1 first engages with the curved inlet slot 37 until it reaches the lower dead centre point and thereafter engages with the outlet slot 45 which extends between the lower dead centre point and the following minimum position but in such a manner that the hook chamber 15.1 or 15.2 does not establish a direct connection between the outlet slot and inlet slot at the lower dead centre point.

The inlet slot and outlet slot are connected into the fluid circuit of a consuming device which is only indicated schematically in Fig. 9. This circuit includes a consuming device 42, a controllable valve 43, the tank 44 and a pressure limiting valve 46. The inlet slot constitutes the intake side of the hydraulic pump connected to the tank 44. In the region of the inlet slot, the hook chambers absorb oil as their volume increases from the minimum position to the lower dead centre point. As rotation continues from the lower dead centre point to the following minimum position, the oil taken in by each hook chamber is expelled as the volume of the chamber decreases and is delivered under pressure to the consuming device 42. A pressure limiting valve 46 is arranged between the consumer pipe which extends from the outlet slot and the tank pipe which leads to the inlet slot.This valve 46 may be adjusted to a particular optimum pressure which ensures that the hook heads of the vane cell pump will always lie close up against the housing wall 1 of the vacuum pump without producing unnecessary friction.

In the embodiment of Figs. 11 to 14, the rotor 2 with shaft 3 is rotatably mounted in the housing 1.

The rotor and shaft are made in one piece. The shaft and rotor have an internal channel 29. The internal channel 29 communicates with an oil supply pipe.

The oil supply pipe extends from a lubricating oil pump (not shown). The oil supply pipe 30 is sealed off againstthe internal channel 29 buy a ring 47 which is situated in a groove 48. When the system is cold, the ring 47 reduces the outflow cross-section between the oil pipe 30 and the internal circumference ofthe internal channel 29 sufficiently to cause a pressure to build up in the channel 29.

Details of th is arrangement are illustrated in Figs. 5 to 8 which have been described above.

The rotor has a slot 4 lying in a normal plane. The width of this slot is equal to the sum of the thicknesses of vanes 5,6. The diameter of the internal channel 29 is greater than the width of the slot 4 so that half-moon shaped channels are formed on the two sides of the vanes 5, 6 inside the rotor slot and extend through the length of the rotor.

The two vanes 5,6 have each a hook head 7,8 and a stem 9, 10. The stems both have the same thickness and the thickness of each hook head is equal to the combined thickness of the two stems. The underside 13 of each hook head 7 or 8 and the base 14 of each stem 9 or 10 of the other vane together form the hook chambers 15.1 and 15.2. The pump has an inlet 32 which is closed by a non-return valve and an outlet 33 also closed by a non-return valve.

As may be seen from Figs. 14A and 14B, the outlet 33 is a slot which is closed in the direction of outflow by a blade spring 49. The blade spring is attached by a screw 50 to the end which faces away from the sense of rotation. This is of decisive importance for the orderly functioning of the spring 49 as non return valve.

The vanes have cut-out portions 50 at each lateral edge at the end of the stem, as shown in Figs. 1 2A and 1 2B. These cut-outs extend from the end of the base 14 of the stem towards the hook head. As shown in Figs. 12B, the cut-out portions may be replaced by recesses 52 extending from the base 14 of the stem in the direction of the hook head.

The flow resistance of the oil flow described below can be determined by suitable choice of the depth of the recesses or cut-outs.

The dimensions of the vanes, in particular of their hook heads 7, 8 and their cut-outs 50 and other details of the embodiment illustrated are described below with reference to Figs. 13Ato 13E.

Line Tin the figures represents the plane through the dead centre point. This plane contains the axis of housing 1 and the axis of rotor 2, and the rotor makes sealing contact with the housing in this plane. In the angular position of rotor 2 shown in Fig. 13C in which the vanes lie in the plane of the dead centre point, vane 6 is completely withdrawn into the rotor (lower dead centre point) while vane 5 extends to its furthermost position outside the rotor (upper dead centre point). The plane passing through the centre of the rotor perpendicularly to the dead centre point plane is marked by the reference E. It is referred to in this application as the narrow or 90" position. This position is characterised in that the distance between the hook heads 7, 8 of the vanes 5, 6 is here at a minimum, as can be seen from Fig. 13E.

The sense of rotation is indicated in all the figures by the arrow 22. It should be noted that the hook chambers must always face in the sense of rotation.

In the angular position of Fig. 13A, the hook chamber 15.2 formed by the hook head 8 and the stem 10 of the vane 6 is completely immersed in the rotor slot 4. The hook chamber 15.2 communicates with the oil supply 29 through the cut-out 50 in the stem 10. The hook chamber 15.2 is therefore subjected to the oil pressure of the lubricating oil in the supply duct 29. At the same time, the stem 9 of the vane 5 covers the oil supply duct 29 so that the oil supply duct 29 has no communication with the outlet chamber and the hook chamber 15.1 situated therein.

A train of grooves 53 set at angles to each other and 1 to 2 mm in depth is provided in one end wall of the housing, as indicated in Fig. 11 This train of grooves comprises a circumferential branch 54 extending from the dead centre point plane T into the outlet chamber against the sense of rotation.

That end of the circumferential branch 54 which extends into the outlet chamber also covers in the circumferential direction the end of the curved outlet slot 33 which is formed in the opposite housing wall.

The train of grooves 53 further comprises a radial branch 55 which lies on the dead centre point plane and extends to a short distance before the internal channel (oil supply) 29 of the shaft 3 and rotor 2.

Lastly, the train of grooves 53 comprises a connecting branch 56 which extends in a direction parallel to the circumferential branch 54 and also faces away from the sense of rotation. As may be seen from Figs. 1 3A to 13E, the connecting branch 56 and radial branch 55 of the train of grooves are joined together to form a recess covering an area indicated by the dash-dot line. The broken line thus does not exist in reality but only serves to illustrate the course taken by the system of grooves 53. It should, however, be particularly noted that the circumferential branch 54 and the radial branch 55 must not be integrated in a common recess forming a wide two-dimensional area since a powerful restrictor effect which is particularly important for the function of this system of grooves is produced at the point of intersection of these two branches.

Fig. 13A should be further noted for the functioning of this system of grooves 53. This figure shows how the cut-out 50 of the vane 6 is brought into communication with the connecting branch 56 so that a connection is established between the end portion of the discharge chamber and the oil supply.

This end portion is situated between the vane 5 and the dead centre point plane. If the discharge chamber, which communicates with the crank case of the motor vehicles through the outlet 33 and non-return valve 34, is still under a vacuum or if the outlet slot 33 establishes a direct connection between the discharge chamber and the chamber in front of it which is bounded by the two vanes 5,6 and which is also under a vacuum, only a small quantity of oil can flow over into the discharge chamber from the oil supply duct 29 since the system of grooves 53 is severely throttled, particularly at the angle between the radial branch 55 and the circumferential branch 54. In particular, the pressure of lubricating oil in the internal channel 29 is preserved.On the other hand, as soon as an excess pressure is established in the discharge chamber which is reduced to a very small volume, the system of grooves 53 enables the oil or oil/air mixture in this chamber to be forced back into the oil supply 29. At this stage, the throttling effect on this oil supply decreases since the cut-out 50 progressively overlaps the connecting branch 56.

In the angular position shown in Fig. 13B, there is no longer any connection between the discharge chamber and the outlet slot 33. The entire contents of this chamber, consisting mainly of oil, is now transferred to the oil supply duct 29 by way of the system of grooves 53 and the recess 50.

It is only at the dead centre point position of Fig.

1 3C that the connection between the discharge chamber and the oil supply ducts 29 is cut off since the rear boundary to the radial groove lies substantially in the plane of the dead centre point and the stem 9 of the vane 6 now completely covers the radial groove. At the same time, the hook chamber 15.2 remains connected to the oil supply 29 so that it is precisely at this stage that the pressure of the lubricating oil acts on the vane 6 tending to push it outwards as the rotation continues. This is particularly important because the vane 5 is in its inner dead centre position and the centrifugal forces between one end, carrying the hook head 8, and the other end comprising the stem 9 are to a large extent balanced so that only a very small centrifugal force acts on the vane in a radially outward direction.This unfavourable situation is compensated by the connection according to the invention between the hook chamber 15.2 and the oil supply which provides the pressure of lubricating oil to assist the outward movement.

As the rotation continues, the hook chamber 15.2 re-emerges from the rotor slot 4 shortly after passing through the minimum position, as shown in Fig. 13E. At that moment, however, the stem 10 of the vane 6 again completely covers the oil supply duct 29 so that the cut-out 50 no longer provides any communication between the pump chamber or hook chamber 15.2 and the oil supply 29.

The hook chamber 15.1, on the other hand, enters the rotor slot just before reaching the minimum position, as shown in Fig. 13D, and shortly thereafter the stem 10 of the vane 6 opens the communication between the oil supply 29 and the hook chamber 15.1 through the cut-out 51. This means that the vane 5 is now subjected to the oil pressure of the lubricating oil at the base 14 of the stem so that its outward movement continues to be assisted by the pressure of the lubricating oil.

It is important that the immersion and subjection to pressure of one hook chamber 15.1 (angular position of Fig. 13D) and the re-emergence of the other hook chamber 15.2 can take place in a fixed sequence, preferably without any time gap, if the pump with rotor and vanes are so designed that the control edges of the hook heads and the control edges of the cut-outs establish the communication to the oil pressure and remove the oil pressure at the required times.

Claims

1. Vane cell pump having a pair of hook-shaped vanes in slidable contact with each other in a guide slot of the rotor, the thickness of the hook head of each vane being equal to the combined thickness of the stems of the two vanes, which is adapted to the width of the slot, and the base of each stem combining with the hook head of the other vane to form a hook chamber which is immersed in the rotor slot over part of the rotation of the rotor, characterised in that the hook chambers are immersed during the part of the rotation ranging from 90" before to 90" behind the lower dead centre point, and each hook chamber is filled with oil during the part of the rotation of the rotor extending from 90" before the lower dead centre point to the lower dead centre point and is opened by way of a restrictorduring the part of the rotation extending from the lower dead centre point to 90" after the lower dead centre point.

2. Vane cell pump according to claim 1, characterised in that the cross-section of the restrictor widens over the part of the rotation ranging from the lower dead centre point to the 90" position behind the lower dead centre point.

3. Vane cell pump according to claim 2, characterised in that the cross-section of the restrictorwidens unevenly shortly before the 90" position behind the lower dead centre point.

4. Vane cell pump according to claim 3, characterised in that the widening of the restrictor cross-section is brought about by a short radial notch formed in the front of the hook chamber.

5. Vane cell pump according to any one of claims 1 to 3, characterised in that the oil supply to the hook chamber can be connected to a source of pressure oil.

6. Vane cell pump according to any one of the preceding claims, characterised in that the oil inlet and the oil outlet open into a pressureless system.

7. Vane cell pump according to claim 1, characterised in that the oil inlet and oil outlet form part of an oil circulation containing a hydraulic consuming device which produces the restrictor effect.

8. Vane cell pump according to any one of the preceding claims, characterised in that the hook heads each comprise a roller with which they lie in contact with the wall of the housing, the bearing sleeve ofthe roller being connected to the respective hook chamber by pressure equalization ducts.

9. Vane cell pump according to claim 7 or 8, characterised in that the oil inlet slot and oil outlet slot are curved and lie on the turning circle of the hook chambers in an end wall, the inlet slot extending from the minimum position before the lower dead centre point to the lower dead centre point while the outlet slot extends from a position which is at a distance of more than the thickness of a vane from the lower dead centre point to the 90" position.

10. Vane cell pump according to any one of the preceding claims, characterised by a temperature dependent restrictor valve in the oil inflow and/or oil outflow.

11. Vane cell pump having a pair of hook-shaped vanes in slidable contact with each other in a guide slot of the rotor, the thickness of the hook head of each vane being equal to the combined thickness of the hook stems of the two vanes in contact with each other, which is adapted to the width of the slot, the base of each stem together with the hook head of the other vane forming a hook chamber which is immersed in the rotor slot during part of the rotation of the rotor, characterised in that the hook chambers are immersed during the part of the rotation ranging from 90" before to 90" behind the lower dead centre point, and during the part of the rotation of the rotor from 90" before the lower dead centre point to the lower dead centre point each hook chamber is filled with oil and connected to an oil supply channel, and the connection to the oil supply channel is interrupted before the re-emergence from the rotor slot.

12. Vane cell pump according to claim 11, characterised in that the stems of the two vanes have clearances each extending in the radial direction from the base of the stem over part of the length of the vane, which clearances intermittently cover an oil supply duct which is concentric to the rotor and thereby control the flow of oil between the oil supply duct and the hook chambers in dependence upon the angular position of the rotor by means of their end edges sweeping over the oil supply duct.

13. Vane cell pump according to claim 12, characterised in that the connection between the oil supply duct and the hook chambers is increased by the end edges of the recesses immediately after immersion of the hook chamber in the rotor slot and decreased immediately before re-emergence of the hook chamber from the rotor slot.

14. Vane cell pump according to any one of claims 11 to 13, characterised in that the clearances are recesses formed in the back of each vane.

15. Vane cell pump according to any one of claims 11 to 14, characterised in that the clearances are formed by cut-outs provided at one or both lateral edges of each vane and extending from the base of the stem along part of a radial length of the vane.

16. Vane cell pump according to claim 14 or claim 15, characterised in that the oil supply duct is placed concentrically in the rotor and that the diameter of the oil supply duct is greater than the width of the guide slot and in that the oil supply duct extends into the region of the rotor where the clearances or cut-outs are situated.

17. Vane cell pump according to claim 16, characterised in that the cut-outs of the two vanes do not overlap even when the vanes are in the dead centre position.

18. Vane cell pump according to any one of claims 11 to 17, characterised in that immersion of the hook chambers takes place in the range of rotation before the lower dead centre point before, preferably 5 to 15 before the clearance/cut-out begins to cover the oil supply duct.

19. Vane cell pump according to any one of the preceding claims, characterised in that one end wall of the pump housing has a train of grooves set at different angles in the region of the outlet, comprising a circumferential branch extending in the circumferential direction and covering part of the outlet chamber of the pump, a radial branch which is directed substantially radially and substantially bounded by the plane containing the dead centre point and extends radially from the end point of the outlet chamber to shortly before the oil supply duct, and a connecting branch which is parallel to the circumferential branch and is brought into communication with the cut-outs of the vanes at the latest 30" before the lower dead centre point.

20. Vane cell pump according to claim 19, wherein the part of the outlet chamber which is covered is in the end region thereof.

21. Vane cell pump according to claim 20, the said part is that part of the end region which is situated behind the outlet.

22. Vane cell pump according to any one of claims 19 to 21, characterised in that the connecting branch is formed by a widening of the radial branch in the opposite direction to the rotation and is brought into communication with the cut-out of the vanes between the minimum position and the dead centre position.

23. Vane cell pump according to claim 22, wherein the said connecting branch is brought into communication with the cut-out at latest at 45" before the dead centre position.

24. Vane cell pump according to any one of claims 11 to 23, characterised in that the outlet which extends over part of the circumference is closed by a non-return valve.

25. A vane cell pump substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.