Patent Application
20190170141
The invention relates to a vacuum pump having a housing which limits a working space and having a rotor, which is rotatably mounted in the housing about a rotor axis, wherein the rotor guides at least one vane being movably mounted in the radial direction, wherein the vane has a transverse extent, and wherein the vane divides the working space into a suction side having a suction inlet and a pressure side having a pressure outlet.
Generally vacuum pumps have a sickle-shaped pump space, which is divided by the at least one vane into pressure chambers. Due to rotation of the rotor, which is eccentric to the wall enclosing, a pressure gradient can be provided between the suction side having a suction inlet and a pressure side with the pressure outlet.
Vacuum pumps are used in many applications, especially in motor vehicles. During operation, vacuum pumps are regularly lubricated with oil. If the combustion engine is cut off, the vacuum pump runs fully off oil, as it is normally located far down on the combustion engine, and thus excess oil runs from the combustion engine into the working space. If the combustion engine is switched on again, the excess oil must be ejected. This is especially critical when the combustion engine has cooled in the meantime and the oil is thus viscous and hard to eject. Such problems occur particularly in hybrid motor vehicles, because a great many “starts” have to be carried out with them.
In a cold start of the vacuum pump with high accelerations, comparatively high torques act on the pump vane. In a cold start however, this results in major problems, as the cooled oil in the working space has a higher viscosity. Thus, in a cold start the pump vane works against the resistance of the cold and in particular highly viscous oil to convey the collected oil out of the work space. In the worst case, a pump vane can break under this load. In order to counteract this, it is known from the prior art to use the largest possible leaf springs at the pressure outlet, which open up a large transverse section and thus reduce the starting torque and the load on the vane or vanes. In addition, the use of ventilation holes lead to permanently increased power consumption.
The object of the invention is therefore to create a remedy for the named problems of the prior art.
This object is achieved by a vacuum pump with the features of claim 1. It is accordingly provided that the housing has at least one oil outlet different from the pressure outlet, wherein the oil outlet is closed by a relief valve. The relief valve assumes an open position, when a limit pressure lying above a nominal pressure is exceeded in the working space. Furthermore, the transverse extent of the vane is large enough that when the vane passes the oil outlet, the oil outlet is closed by the vane, so that there is no fluid connection between the suction side and the pressure side over the oil outlet.
The nominal pressure is here the operating pressure during normal operation of the vacuum pump. The transverse extent of the pump vane is the extent transverse to the displacement plane of the vane. Because of the oil present in the working space, this nominal pressure is regularly exceeded during a cold start of the vacuum pump. As soon as the pressure is so high that the limit pressure is also exceeded, the relief valve opens so that oil can flow out of the oil outlet. Due to an especially small and fast-reacting relief valve, the highly viscous oil can be quickly discharged from the working space, so that the resistance forces on the vane can be advantageously reduced. And when the vane passes the oil outlet, the latter closes off the oil outlet in order to avoid a “short circuit.” Consequently, the suction side cannot communicate via the oil outlet with the pressure side; rather, they are separated from one another. It goes without saying that several oil outlets can also be provided.
In a cold start, pressures of 10 to 15 bar can regularly arise, while the limit pressure can lie at 0.3 to 0.7 bar, in particular at 0.5 bar. This is significantly higher than the nominal pressure.
Thus, all in all, the cold start torque acting on the vane during a cold start can be limited without reducing performance in normal operation. The pump function and its power consumption are thus not negatively impaired.
Here in particular it can be provided that the vane along with the rotor at any rate in the so-called neutral position can be divided into a suction side with a suction inlet, a pressure side with a pressure outlet, and a pump side. The volume of the pump side hereby defines the cubic capacity of the pump. The oil outlet can in particular be provided on the pump side, and thus terminate in the pump side of the working space. In particular, in this way a performance reduction of the pump can be avoided, while oil can be efficiently discharged from the pump during a cold start.
Advantageously the relief valve is made comparatively small and in particular comparatively fast-reacting. Thus a high efficiency can be achieved in the vacuum pump despite the provision of an additional oil outlet additionally to the pressure outlet.
An advantageous further development of the invention provides that at the outlet an outlet valve is provided for opening or closing the outlet, wherein the outlet valve assumes an open position when the nominal pressure in the working space is exceeded, and wherein the nominal pressure is lower than the limit pressure. Thus, the relief valve remains closed in normal operation. Such an outlet valve thus controls normal operation.
A further advantageous embodiment of the invention provides that the oil outlet on the housing is provided in the axial direction. Thus, the vane tip does not move over the oil outlet. Instead, the oil outlet is covered during passage of the vane by the transverse extent of the vane.
It is also advantageous when the housing has a housing cover extending transversely to the rotor axis, wherein the oil outlet is provided in the housing cover. Thus the oil outlet can be covered especially simply by the transverse extent of the vane during passage of the vane.
It is especially preferred when the housing has a pot-shaped housing section having a housing bottom, wherein the oil outlet is provided in the housing bottom. The cylindrical section of the pot-shaped housing section is then configured to be advantageously completely fluid-tight, so that the vane tip can slide thereon, allowing a comparatively high efficiency.
It is also conceivable that both in the housing cover and in the housing bottom, an oil outlet is provided in order to allow especially fast emptying of the working space.
Here it is especially preferred when the oil outlet extends transversely to the rotor axis in the radial direction. In this way especially simple coverage of the oil outlet is possible when the vane passes it, so as to prevent a short circuit.
It is further especially preferred when several oil outlets are provided, wherein the oil outlets can be arranged rotationally-symmetrically around the rotor axis. Here an n-fold rotational symmetry can be present, depending on how many oil outlets are provided. These oil outlets can in particular open sequentially in a cascading manner, as the pressure before the vane reaches the respective oil outlet is regularly the highest, and thus in this region the limit pressure may possibly be exceeded.
Advantageously the oil outlet is configured in the shape of a slot, wherein the slot width is smaller than the vane width. If the slot extends in the radial direction, the slot width is the length of the slot perpendicular to the radial direction.
On the other hand, the oil outlet may also be circular, wherein the opening diameter is smaller than the vane width. Such outlet geometries can be configured especially simply in the housing and can be opened or closed especially quickly by means of a valve.
The transverse length of the vane can be 9 mm, for example. The slot width can be 7 mm, or with a circular design of the oil outlet the diameter can be 7 mm. Thus when the vane passes the oil outlet it can seal the latter.
An especially preferred development of the invention follows from the fact that the relief valve comprises a closing body and a return element, wherein the return element forces the closing body into a closed position in which the oil outlet is sealed.
Such a relief valve closes or opens especially quickly and can be made comparatively small in order to be able to discharge oil from the working space quickly and efficiently without significantly impairing the efficiency in any negative way.
An especially preferred further development of the invention provides that the closing body comprises an elastically pliable locking tongue. Here the locking tongue can be made for example of steel, in particular spring steel, or plastic, and permits quick and precise opening or closing of the relief valve in a simple manner.
Here it is especially preferred when the return element comprises a leaf spring. The leaf spring can in particular be configured as spring-elastic valve and can comprise several leaves. The return element in particular can be secured using a fastening means such as a screw with one end on the pump housing. Such a return element can be produced especially simply and when needed allows fast opening of the relief valve when the limit pressure is exceeded.
Advantageously, the locking tongue is configured from the leaf spring. Such a relief valve is especially simple to produce, so that a reasonably priced yet still effective relief valve is provided.
The outlet valve can also be made of leaf springs. These leaf springs however are significantly weaker than those of the relief valve, so that in normal operation the relief valve is closed, while the outlet valve is open in order to release the pumped medium.
Preferably a stop is provided, which limits the motion of the locking tongue from a closed position to the open position. Accordingly, a precise and efficient opening or closing of the relief valve is allowed.
On the other hand, it is conceivable that the closing body comprises a closing ball. In addition, or alternatively, the return element can be a spring, in particular a screw spring. Such a relief valve especially can be made especially simply and compactly. Furthermore, using the screw spring the oil outlet can also be efficiently closed in such a vacuum pump system, in which gravity does not act in the direction of the closed part of the relief valve. By contrast, a leaf spring in particular can be used when gravity acts on the leaf spring in the direction of the closed position, so that the leaf spring is pressed by gravity against the valve seat.
Further details and advantageous configurations of the invention may be found in the following description, with reference to which the embodiments of the invention shown in the figures are described and explained in more detail:
In a cold start of the pump 10, the situation is entirely different from the above. Actually, the pump 10 is lubricated with oil. Residual oil in the working space 14 can be present in the working space 14 during a cold start. Furthermore, oil can be located in the lines and in the internal combustion engine. Since the pump is regularly arranged very far down in a motor vehicle, the pump 10 runs completely full a few seconds after engine cutoff. In a cold start the oil has a high viscosity. Thus, during a cold start of the pump, very high accelerations occur in the vane 26. Thus, a high torque acts on the pump vane, since it works against the force of the oil. Consequently, a pressure arises in the pump 10 which exceeds a limit value. If the limit value is exceeded in the working space, such a high pressure force acts against the return force of the relief valve that the locking tongue 40 lifts off from the valve seat, so that the oil outlet 36 opens. In this way the oil can be discharged from the working space 14. This can occur very quickly. Nonetheless the relief valve 38 can be kept comparatively small, so that the effectiveness of the vacuum pump is comparatively high despite the provision of a second outlet. All in all, therefore, a quick and efficient pressure reduction can occur during a cold start via the oil outlet 36, without negatively impairing the function of the pump 10 and its power consumption.
The vane 26 has a transverse extent d1 (cf.
Consequently, all in all a vacuum pump 10 can be provided that limits the cold start torque action on the vane 26 without reducing the performance in normal operation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 128 972.0 | Dec 2017 | DE | national |
