The present invention relates to a coolant pump for a coolant circuit of an internal combustion engine. The coolant pump has a pump housing in which is mounted a drivable shaft, to one end of which is attached an impeller which has vanes extending into a suction chamber and is connected to a cover plate. As a result of the rotation of the cover plate and the vaned impeller, fluid is drawn into the suction chamber through an intake port of the pump housing and conveyed further into the pump housing by the vanes. A guide plate, which is axially displaceable by an actuation unit, is disposed between the impeller and the cover plate. The guide plate has a contour corresponding to the impeller and a collar oriented toward the impeller.
BACKGROUND
In order to achieve rapid heating of the internal combustion engine and to selectively adjust the engine temperature, the coolant pump should be switchable or ideally controllable. This is accomplished selectively by adjusting the flow rate. In order to adjust the flow rate or volumetric flow, the guide plate is axially displaced in the pump within the impeller. This must be accomplished by an actuator that is preferably axially mounted in as neutral a manner as possible in terms of space requirements. A coolant pump of the aforementioned type is known from German Patent Application DE 2008 046 424 A1.
SUMMARY OF THE INVENTION
Tests have shown that, depending on the rotational speed, the adjusted position and the pump design, the resulting hydraulic forces on the guide plate may assume values above 150N. This required amount of force must be provided by an actuator which must be capable of adjusting the guide plate at all speeds, temperatures and as frequently as needed. This fact requires an actuating mechanism which is of a certain size and/or operates according to a certain basic principle. For this reason, the actuators used are mostly expensive and require a large space.
It is an object of the present invention to provide a switchable or controllable coolant pump whose actuator does not require additional cost or space to provide the forces needed to adjust the guide plate.
The present invention provides that the guide plate has at least one opening. The opening provided reduces the effective pressure difference between the front and rear sides of the guide plate, which in turn reduces the axial force required to displace the guide plate. Fluid communication between the front and rear sides of the guide plate is facilitated. The fluid conveyed radially behind the guide plate has a centrifugal pressure typical of impellers. In conjunction with a certain dynamic pressure component, which is generated when the flow impinges axially on the rear wall of the impeller after entry through the holes, a mean pressure is generated behind the guide plate. Thus, the pressurized fluid has a force component directed in the guide-plate-closing direction. The guide-plate-closing direction refers to the axial displacement of the guide plate toward the cover plate. This leads to a reduction in the resultant force in the guide-plate-opening direction. The guide-plate-opening direction refers to the axial displacement of the guide plate toward the impeller. In this manner, the actuator is relieved of load during the displacement operation in terms of the force to be exerted.
It has proved advantageous to provide the guide plate with more than one opening. The openings can have different shapes, such as, for example, flow-optimized shapes in order to make use of flow effects, or radial openings extending in the guide plate, or shapes which are optimized for economical manufacture. Regardless of the specific embodiment, the greatest effect is achieved when the openings are located in the region near the axis of rotation of the guide plate.
Further, the graph of FIG. 4 illustrates the change in the fluid forces as a function of the degree of opening of the guide plate. Ideally, the fluid force is zero, which would allow the actuator to axially displace the guide plate without requiring additional force. As can be seen from the graph, a fluid force of zero cannot be achieved with a guide plate without openings. The greater the number of openings, the faster the decrease in the force level. However, the graph also shows that the force level becomes negative above a certain degree of opening of the guide plate and a certain number of openings. A negative force level; i.e., negative fluid forces, means that the guide plate moves toward the cover plate, thus preventing the passage of fluid within the water pump, which is to be avoided. In order to enable the actuator to exert sufficient force against the negative fluid forces, it would have to be designed stronger and larger, which in turn would result in additional costs.
To avoid this, the actuation unit may optionally include a spring. This spring applies pressure to the guide plate indirectly via the shaft in the guide-plate-opening direction. This embodiment provides a fail-safe solution. If the actuator fails and the guide plate is pulled by a negative fluid force in the guide-plate-closing direction, thereby reducing the coolant flow, the spring produces a counterpressure to prevent the guide plate from closing. However, in this embodiment, all of the force curves would have to be increased by the preload of the spring. This would partially cancel out the previously achieved force reduction.
In order to be able to use a conventional inexpensive actuator, it has proved advantageous to match the degree of opening of the guide plate to the number in a suitable manner. As a result, a fluid force of 20-50 N develops which acts on the guide plate, forcing it toward the impeller, and thus opening the coolant pump. This is intended to prevent negative fluid forces, which in turn eliminates the need for the use of a fail-safe spring. In a specific embodiment of the present invention, it is therefore proposed that the impeller have an additional closing contour pointing in a direction toward the guide plate, and that the closing contour be engageable into the at least one opening of the guide plate, partially or completely closing the same.
Moreover, provision is made for the closing contour to be configured in the manner of a pin, the closing contour having more than one pin-like closing element, and the individual closing elements differing in their dimensions (length and/or diameter).
The axially stepped closing contour may be disposed in the injection-molded portion of the impeller or in the insert thereof. In accordance with the present invention, the pins have different lengths, so that when the guide plate is displaced toward the closing contour, first a longer pin-like closing element closes one opening, and when the guide plate is advanced further toward the closing contour, a shorter pin-like closing element closes another opening. It would also be possible to conceive of closing elements having different diameters and corresponding openings in the guide plate.
Another option in accordance with the present invention is to configure at least one closing element in a stepped manner, which allows for partial closure of the opening.
In another preferred embodiment of the present invention, the actuation unit includes an actuator adapted to actuate independently of the rotational speed of the impeller.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the present invention are shown in FIGS. 1 through 4, which are described in detail below, without limiting the invention to such embodiments.
In the drawing,
FIG. 1 is a cross-sectional view of a controllable coolant pump having a guide plate provided with openings, shown with the guide plate closed;
FIG. 2
a is a schematic view of the guide plate, where its openings are closed by closing elements;
FIG. 2
b is a schematic view of the guide plate, where only one opening is closed by a closing element;
FIG. 2
c is a schematic view of the guide plate, shown with the openings open;
FIG. 3 is a detail view of the guide plate, shown with a stepped closing element; and
FIG. 4 is a graph showing different fluid force curves as a function of the number of openings and the degree of opening of the guide plate.
DETAILED DESCRIPTION
FIG. 1 shows a coolant pump for a coolant circuit of an internal combustion engine, the coolant pump having a pump housing 1, in which is mounted a drivable shaft 2a having an impeller 4 attached to one end thereof. Impeller 4 has vanes 6 extending into suction chamber 7. Impeller 4 and cover plate 9 are joined to one another. When impeller 4 rotates, fluid is conveyed into suction chamber 7 through an intake port 10 of pump housing 1. A guide plate 12, which is axially displaceable by an actuation unit 3, is disposed between impeller 4 and cover plate 9. Guide plate 12 has a contour corresponding to impeller 4 and a collar 13 oriented toward impeller 4. In order to achieve rapid heating of the internal combustion engine and to selectively adjust the engine temperature, the coolant pump must be controllable or switchable. To this end, a volume flow rate is adjusted in accordance with demand. In order to adjust the volume flow rate, guide plate 12 is axially displaced in pump housing 1. As guide plate 12 is displaced between impeller 4 and cover plate 9, it changes the degree of opening, thereby controlling the passage of the flow. Actuation unit 3 includes both the shaft 2a and a push rod 2b axially displaceable in shaft 2a, as well as an actuator 14 actuating push rod 2b. Push rod 2b is directly connected to guide plate 12. The displacement of guide plate 12 is controlled by actuator 14. Actuator 14 should be incorporated into the coolant pump in as neutral a manner as possible in terms of space requirements. For this reason, the forces resulting from the volume flow and acting on guide plate 12 should be kept as low as possible to be able to choose an actuator 14 that is convenient in terms of space. According to the present invention, to be able to reduce the force level on guide plate 12, and thus on actuator 14, openings 11 are formed in guide plate 12. The openings 11 formed reduce the effective pressure difference between the front side of the guide plate (the face facing the cover plate) and the rear side of the guide plate (the face facing the impeller). This, in turn, leads to a reduction in the fluid forces exerted by the fluid flow on guide plate 12. This facilitates the fluid communication between the front and rear sides of the guide plate. Further, the radially conveyed fluid forms a pressure cushion on the rear side of the guide plate. This pressure results in a force component in the guide-plate-closing direction, which in turn reduces the resultant force in the guide-plate-opening direction, thereby relieving actuator 14 of load during the displacement operation. Guide plate 12 is closed when its front side rests against cover plate 9 and flow is no longer possible. The degree of opening of guide plate 12 is an indication of the amount of flow through the coolant pump. The graph of FIG. 4 illustrates the relationship between the number of openings 11 formed in guide plate 12, the degree of opening of guide plate 12, and the fluid forces acting on guide plate 12. For a constant degree of opening of guide plate 12, the force curves decrease as the number of openings 11 increases. However, above a certain degree of opening, the force curves become negative in some regions. This results in a force acting on guide plate 12 in the guide-plate-closing direction and, therefore, a fail-safe solution is needed. This means that guide plate 12 must be prevented from being unintentionally closed as long as the engine needs to be cooled. One way to achieve this would be to use an additional spring 8. The spring disposed within actuation unit 3 and acts on push rod 2b. This spring must have a preload such that even if actuator 14 fails, guide plate 12 is moved back via push rod 2b in the direction of impeller 4 to a normal position. In order for these negative forces to be compensated by a so-called “fail-safe spring”, all of the force curves would have to be elevated by the preload of this spring 8. This, in turn, would partially cancel out the force reduction achieved by openings 11. This would require the use of a powerful actuator 14 which would occupy more space.
Therefore, a refinement of the present invention proposes that the openings 11 of guide plate 12 be variably activated and deactivated according to the degree of opening. This is achieved by a closing contour 5 formed in the impeller 4 provided with vanes 6. This contour may be formed in the steel insert of impeller 4 or in the injection-molded portion thereof, as illustrated in FIGS. 2 through 3. As guide plate 12 is displaced toward impeller 4, pin-like closing elements 5a engage into one or more openings 11 and close the same. In the graph of FIG. 4, an idealized force curve 20 is shown. Idealized force curve 20 shows a nearly constant force acting on guide plate 12, regardless of its degree of opening. This idealized force curve 20 can only be achieved if each time one of the marked operating points Sx is reached, a jumps is made to one of the nearest operating points. This is achieved by changing the number of openings 11 of guide plate 12 and the degree of opening of guide plate 12. This is implemented using an axially stepped closing contour 5 having pin-like closing elements 5a. Closing elements 5a engage into openings 11 of guide plate 12 as it is displaced between impeller 4 and cover plate 9. The displacement of guide plate 12 causes a change in the degree of opening. Moreover, because of closing contour 5, different numbers of openings 11 are cleared or closed. FIG. 2a shows guide plate 12 in an open position with the openings closed. This corresponds to an operating range from an opening degree of 100% to operating point S1 in the graph. FIG. 3 shows a stepped, pin-like closing element 5a, which permits implementation of half-closed openings 11. This corresponds to the operating range between operating points S1 and S2 in the graph. FIG. 2b shows guide plate 12 in a position after having been displaced in the closing direction, and in which one opening 11 is closed. This corresponds to the operating range between operating points S2 and S3 in the graph. FIG. 2c shows guide plate 12 in the closed position in which two openings are open. This corresponds in the graph to the operating range from operating point S3 to operating point S4 or an opening degree of 0%, respectively, depending on the degree of opening.
LIST OF REFERENCE NUMERALS
1 pump housing
2
a shaft
2
b push rod
3 actuation unit
4 impeller
5 closing contour
5
a closing element
6 vane
7 suction chamber
8 spring
9 cover plate
10 intake port
11 opening
12 guide plate
13 collar
14 actuator
20 idealized force curve
- S1 operating point 1
- S2 operating point 2
- S3 operating point 3
- S4 operating point 4
Patent Application
20140037432
