Water pump for pumping coolant in a low temperature and in a high temperature circuit

In a water pump for pumping coolant in a low temperature and a high temperature circuit with low temperature and high temperature housings each including a spiral flow guide structure, and a single rotor disposed in the joined housings and having a low temperature rotor part for pumping coolant through the low temperature circuit and a high temperature rotor part for pumping coolant through the high temperature circuit, the housings are joined with a heat isolating structure disposed between the flow guide structures of the high temperature and the low temperature housings to limit heat transfer from the high temperature coolant pumped through the high temperature housing to the low temperature coolant pumped through the low temperature housing.

BACKGROUND OF THE INVENTION

The invention resides in a water pump for pumping coolant in a low temperature and in a high temperature circuit including a low temperature housing with an internal low temperature housing, a high temperature housing with an internal high temperature spiral, a water pump impeller for pumping at the same time coolant in the low temperature housing spiral and in the high temperature housing spiral, and a drive shaft for driving the water pump impeller.

DE 41 14 704 C1 discloses a cooling circuit for two-stage charge air cooling. The cooling circuit comprises, a high-temperature and a low-temperature circuit. In the high temperature circuit, in series, a high temperature heat exchanger, a high temperature charge air cooler provided as a first cooling stage, a water pump for circulating coolant in the high-temperature circuit and the internal combustion engine are arranged. In the low temperature circuit, in series, a low-temperature heat exchanger, a low temperature charge air cooler forming a second cooling stage, an engine-oil heat exchanger, a transmission fluid heat exchanger and a second water pump for circulating coolant in the low-temperature circuit are arranged.

In praxis, the first and the second coolant pumps are double suction pumps disposed on a common drive shaft in a two-part housing. In order to keep the weight and the power requirements of the coolant pumps low, the housing and the coolant pump rotors consist of aluminum. In order to further reduce weight, the coolant pump rotor for circulating coolant in the low-temperature circuit is formed integrally with the coolant pump rotor for circulating the coolant in the high-temperature circuit. It is noted however that, with the good heat conductivity of the aluminum and the temperature difference between the high temperature and the low temperature circuit of for example 40° C., an undesirable heat transfer occurs between the two cooling circuits. This heat transfer can be compensated for in the low temperature circuit only by an increased heat removal for example via larger heat exchangers.

It is the object of the present invention to provide a water pump for pumping coolant in a low temperature and a high temperature coolant circuit in which the heat transfer via a common pump rotor is reduced.

SUMMARY OF THE INVENTION

In a water pump for pumping coolant in a low temperature and a high temperature circuit with low temperature and high temperature housings each including a spiral flow guide structure, and a single rotor disposed in the joined housings and having a low temperature rotor part for pumping coolant through the low temperature circuit and a high temperature rotor part for pumping coolant through the high temperature circuit, the housings are joined with a heat isolating structure disposed between the flow guide structures of the high temperature and the low temperature housings to limit heat transfer from the high temperature coolant pumped through the high temperature housing to the low temperature coolant pumped through the low temperature housing.

In the assembled water pump a first plane is defined between the high temperature and the low temperature spiral by a first mounting surface formed on the low-temperature housing and an abutting adjacent mounting surface which is formed on the high-temperature housing. In this first plane, a heat insulation structure consisting for example of a stainless steel sheet is arranged.

For reducing the heat transfer at the water pump rotor itself, the rotor consist of a low-temperature rotor part and a high temperature rotor part joined with an insulating gap which is arranged therebetween and forms a heat barrier. The connecting area between the rotor parts defines a second plane which, generally coincides with the first plane, that is, the two planes are in radial alignment.

It has been determined in test measurements that, with the measures according to the present invention, the heat flow from the high temperature to the low temperature circuit could be reduced by up to 70%. Since, as a result, less heat energy reaches the low temperature circuit, either the cooling system may be made smaller, lighter and less costly or the temperature level in the low-temperature circuit may be kept at a lower level which is advantageous for example for the cooling of electronic components.

The invention will become more readily apparent from the following description of a preferred embodiment thereof on the basis of the accompanying drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1shows a water pump1with details X and Y all shown in sectional views. The detail X (FIG. 1X) shows enlarged an area of the water pump rotor. The detail Y (FIG. 1Y) shows enlarged the connecting area of the pump housings at the outer circumference of the water pump.FIG. 2shows the water pump rotor in a sectional view. The following description is provided referring to all the figures,FIG. 1,FIG. 1x,FIG. 1YandFIG. 2.

The water pump as shown inFIG. 1pumps coolant in a low temperature cooling circuit and, at the same time, coolant in a high-temperature circuit. The water pump1comprises the following main design groups: a low temperature housing2, a high-temperature housing5, a water pump rotor8for pumping the coolant, a drive shaft9for driving the water pump rotor8and a first bearing housing20. In the low temperature housing2, a low temperature spiral passage3is provided. The inlet of the low temperature coolant housing is designated inFIG. 1by the reference sign NT IN. As shown in detail inFIG. 1Y, a first mounting surface4is formed at an end face of the low temperature housing2. The high temperature housing5includes a high temperature spiral guide structure6. The inlet of the high temperature coolant is marked inFIG. 1by the reference sign HT IN. At its front end, seeFIG. 1Y, the high temperature housing5is provided with a second mounting surface7.

A drive torque is supplied to the drive shaft9via a gear wheel22, which is formed integrally with the drive shaft9. The drive shaft9drives the water pump rotor8. The drive shaft9is radially and axially supported in the low temperature housing2by way of a cone ball bearing18and, via a cylindrical roller bearing23, by the bearing housing20, seeFIG. 1. The ball bearing18is rendered play-free by the application of an axial force by the first bearing housing20via a second bearing housing21which is resilient, so that it acts as a spring engaging the outer housing ring19of the conical ball, bearing18.

By means of a shaft seal ring24and a friction seal ring connection14, the low temperature housing2and the drive shaft9are sealed relative to one another. For the removal of leakages, a leakage bore15with an elastomer ball16is arranged in the low temperature housing2. The elastomer ball16is movably disposed in the leakage channel15and forms a one-way valve which prevents, upon flow reversal, any water from entering the water pump for example during underwater operation.

During operation, there is a temperature difference between the high-temperature and the low temperature circuit of up to 40° C. Since the housings of the water pump1and the water pump rotor8consist of aluminum, heat is transferred from the hotter medium (high temperature) to the cooler medium (low temperature) via the housing of the water pump and via the rotor. For reducing the heat transfer two measures are provided.

The first measure serves to reduce the heat transfer from the high temperature housing5to the low-temperature housing2. To this end, there is a first separation plane E1defined between the first assembly surface4of the low temperature housing2and the second assembly surface7of the high temperature housing5and between the low temperature spiral duct structure3and the high temperature spiral duct structure6. As shown inFIGS. 1 and 1Y, the two assembly surfaces4and7are disposed in engagement with each other via an intermediate heat insulator10. As heat insulator10, typically a stainless steel sheet or plastic material insert may be used. Additionally, the heat insulator10may be coated by a sealing material.

The second measure serves to reduce the heat transfer within the water pump rotor8. To this end, the water pump rotor8comprises a low-temperature rotor part11and a high-temperature rotor part12with an intermediate insulation gap13disposed therebetween, seeFIG. 2. The water pump rotor8is mounted on the drive shaft9via a steel sleeve17which is mounted to the drive shaft9by a press-fit. The low temperature rotor part11pumps the coolant in the low-pressure circuit via the low temperature spiral guide structure3. The high temperature rotor12pumps the coolant in the high temperature circuit via the high temperature spiral guide structure6. The radially extending isolation gap13is formed by a corresponding shaping of the adjacent backsides of the rotor parts11and12. The back side is the side of the rotor part opposite the pump blades. The low temperature rotor part11and the high-temperature rotor part12are interconnected in a fluid-tight manner for example by cementing or by welding, particularly by electron beam welding. During the welding procedure, the insulation gap13is evacuated so that it forms a highly effective heat barrier because of the fluid tight evacuated space provided by this procedure. With the fluid-tight cementing an air-filled isolation gap remains which in this case forms the heat barrier. The connection area of the low-temperature rotor part11and the high temperature rotor part12defines a second plane E2(FIG. 2). In a first embodiment, the second plane E2coincides with the first plane E1which is defined by the first and the second mounting surface area. In a second embodiment, seeFIG. 1X, the diameter d1of the low temperature rotor part11is smaller than the diameter d2of the high temperature rotor part12. By a corresponding contour of the low temperature housing2and the high temperature housing5a labyrinth seal structure is formed. However, a mirror-reversed arrangement of the labyrinth seal structure is also possible that is that d1is larger than d2. In the second embodiment then the second plane E2is axially displaced with respect to the first plane E1by half the width of the labyrinth seal so as to form the labyrinth structure.

The water pump according to the present invention has the following advantages:

The heat transfer from the high temperature to the low temperature circuit is substantially reduced, in the test example by up to 70%.

The heating of the low temperature circuit is reduced so that the cooling system can be made smaller, lighter and at lower costs.

Alternatively, the low temperature circuit can be operated at a lower temperature level whereby the cooling for example of electronic components is improved.