The invention generally relates to pumps, and more particularly relates to a positive-displacement pump with a vane for mutually separating the two chambers in the interior of the pump housing.
A positive-displacement pump of this type is already known from FIG. 2A of DE 41 07 720 A1. In this case, both end faces of the vane that separates the two chambers of the pump housing interior from one another and is guided in a restricted fashion respectively carry one sealing strip that is movably guided in the longitudinal direction of the vane and adjoins the inner circumferential wall of the housing interior.
In order to realize this movable arrangement of the sealing strips, they are realized with a T-shaped cross section, with the cross section of the outside of the T-bar being convexly curved and consequently contacting the circumferential wall along only one surface line.
The central web of the strip is engaged with a longitudinal groove machined into the end face of the vane such that it can be moved in the longitudinal direction of the vane, so that the sealing strips automatically adjoin the inner circumferential wall of the housing when the drive shaft rotates due to the effect of centrifugal force.
The disadvantage of this construction can be seen in the fact that the sealing strips only adjoin the inner circumferential wall of the housing interior in a sealing fashion due to the centrifugal force once a certain rotational speed of the drive shaft is reached. This means that a chamber seal which ensures a reliable transport of the gaseous or aqueous medium is not realized until this time.
Positive-displacement pumps of this type consequently are, for example, not suitable for evacuating a brake booster of a motor vehicle since an evacuation needs to be ensured at slow rotational speeds in this case.
The present invention is based on the objective of disclosing a positive-displacement pump, in which a transport of the respective medium starts at a rotational speed greater than 0 or when the centrifugal force during the start of the motor-driven pump does not yet suffice for displacing the sealing strips of the vane into their maximum radial sealing position.
Due to the fact that the vane is equipped with an energy storing device, a permanent contact of both sealing strips with the circumferential wall of the housing interior is also ensured while the shaft is at a standstill, so that the respective medium is displaced or transported at the beginning of the shaft rotation.
In this context, it should be mentioned that FIG. 4 of DE 41 07 720 A1, which was cited above with reference to the state of the art, discloses a pump construction, in which the vane is already equipped with energy storing devices in the form of compression springs. In contrast to the construction according to the invention, the sealing strips are immovably held on the vane ends, i.e., the compression springs do not serve for holding the sealing strip in constant contact with the inner circumferential wall of the housing interior, but rather for supporting the end of the vane that moves into the lower dead center in the oval housing interior in order to compensate for the effects of centrifugal force (see column 5, lines 5 ff.).
According to one advantageous embodiment of the invention, the vane may be guided such that it can be radially displaced on the drive shaft or in a pump rotor that is driven by said drive shaft. In this case, it may, as mentioned above, already suffice to merely arrange one energy storing device between the vane and one of its sealing strips. However, it is preferred to arrange both sealing strips such that they can be moved in the longitudinal direction of the vane, with both sealing strips being supported by one respective energy storing device.
The movable arrangement of the sealing strips may be realized in accordance with FIG. 2A of DE 41 07 720 A1. In this case, the energy storing devices may be respectively arranged between the base of the vane groove and the web of the T-shaped cross section of the sealing strips.
One preferred arrangement of the movable sealing strips on the vane makes it possible to eliminate mold slides for forming guide grooves on the end face of the slide vane as well as on the strip during the injection molding of the vane and the sealing strips. In addition, the sealing strips that are attached to or overlap the vane end in this construction have a higher stability because the bending moments during the vane rotation which result from radial support forces can be favorably absorbed by the U-limbs of the sealing strips.
The energy storing device that is realized in the form of a leaf spring can be advantageously positioned such that the vane and the sealing strips simultaneously remain exactly aligned relative to one another in the lateral direction.
An alternative arrangement of the energy storing device is disclosed wherein this construction is primarily advantageous if the interior of the pump housing has a shape that highly deviates from a circular cylindrical circumference and the sealing strip or strips need to be displaced by relatively large radial distances during the rotation of the vane.
Another advantageous vane construction is disclosed wherein the sealing strips are arranged on the vane ends such that they can be moved in the longitudinal direction of the vane.
It should also be mentioned that the invention can be utilized in an equally advantageous fashion on the vane of vane-cell pumps.