GB2516244A

GB2516244A - Switchable water pump for an internal combustion engine

Info

Publication number: GB2516244A
Application number: GB1312652.9A
Authority: GB
Inventors: Luca Borgia
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-07-15
Filing date: 2013-07-15
Publication date: 2015-01-21
Also published as: GB201312652D0; CN204419672U

Abstract

A switchable water pump 600 comprises a housing 610, a shaft 650 which drives an impeller 660, a bearing 640 which is press-fitted in the housing 610 and supports the shaft, and a coil 640 inserted in a coil cage 630. The coil cage is integral with the housing. Therefore the only press-fit tolerance is between the outer diameter of the bearing and the inner diameter of the housing. The press-fit interference may range between 10 and 80 Âµm (microns). The housing may be made of aluminium. The parallelism between a first datum plane A of the housing, and a second datum plane B of the housing may range between 0.05 and 0.1 mm. The pump may be an internal combustion engine coolant pump.

Description

SVV7TCHABLE WATER PUMP FOR AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a switchable water pump for the cooling system of an internal combustion engine.

BACKGROUND

It is known that internal combustion engines generate mechanical power by extracting energy from heat flows. Engines are inefficient, so more heat energy enters the engine than comes out as mechanical power; the difference is waste heat which must be removed. Internal combustion engines remove waste heat through cool intake air, hot exhaust gases, and explicit engine cooling. CooTing is also needed because high temperatures damage engine materials and lubricants. Most internal combustion engines are fluid cooled using a liquid coolant run through a heat exchanger (radiator) cooled by air. Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors.

One of the most important component for a liquid cooling system is the coolant pump, normally a water pump. In modern engines, the coolant circuit can be provided with a switchable water pump, which can be switched off during engine startup. The coolant pump is either driven by the fan belt or the timing belt on some newer vehicles. The pump moves coolant from the radiator, through the engine, and back into the radiator.

The pump has a shaft with a pulley on one end and a pump rotor or impeller on the other end. When the pulley is spun by a belt, the rotor moves the coolant. The pump shaft is supported by means of bearings, normally cylindrical or needle roller bearings. The pulley is driven by the crankshaft of the internal combustion engine and the impeller can be switched by means of a friction pair with the pump shaft.

With reference to Fig. 1, representing a prior art embodiment of a switchable water pump 500, a pump main bearing 520 is press fitted into the pump housing 510 to avoid any displacement during working condition, due to axial force components. The bearing is made of steel, while the pump housing is made of aluminium. In addition and differently from a standard water pump (which does not need a switchable actuation), also a steel coil cage 530, for the disengaging of the pump, is press fitted on the outer diameter of the aluminum housing. All components are machined to have suitable press fit interferences and press loads. This leads to have a press fit tolerance chain which consists of tolerances about the following dimensions: coil cage (steel) inner diameter vs. housing (aluminium) outer diameter and housing inner diameter vs. bearing (steel) outer diameter.

Taking into account that the machining tolerance of the bearing outer diameter is in the order of microns and the tolerances of the inner and outer housing diameter and inner coil cage diameter are in the order of 0,01 mm, since the aluminum has twice the thermal expansion coefficient compared to steel, and considering that for automotive application it has to be consider a range of at least -40 °C to + 140 °C, it is necessary to increase the interference of the bearing press-fit to avoid, in unfavorable thermal conditions, the potential loss of press out load. This leads to overload the bearing rows, causing balls and rollers deformation.

Therefore a need exists for a new switchable water pump design which would be able to reduce the current press fit tolerance chain, in order not to overload the pump bearing.

An object of an embodiment of the invention is a switchable water pump having a press fit tolerance chain equivalent to the press fit tolerance chain of a standard water pump.

Another object of the invention is to improve the pulley axial run-out, improving the parallelism between two characteristic datum planes of the switchable water pump.

These objects are achieved by a switchable water pump and by an internal combustion engine having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a switchable water pump comprising a housing, a shaft, which drives an impeller, a bearing, which is press filled in the housing and supports the shaft, a coil inserted in a coil cage, wherein said coil cage is realized as an unique piece with the housing.

An advantage of this embodiment is that a coil cage integrated in the pump housing reduces the tolerance chain of the pump, thus allowing to decrease the press fit interference of the bearing and, consequently, to increase the bearing lifetime. Moreover, a further advantage is that the pump as a whole is cheaper, because of missing machining operation on coil cage inner diameter and housing outer diameter, missing press fit operation between coil cage and housing, less material cost.

According to an aspect of this embodiment, the housing is made of aluminium.

The fact that the coil cage is integrated in the pump housing, and therefore is made of aluminium as well, leads to the reduction of the magnetic losses.

According to a further embodiment, a press fit tolerance chain only and exactly consists in the tolerance of a housing inner diameter and in the tolerance of a bearing outer diameter.

An advantage of this embodiment is that the new solution allows a press fit tolerance chain as the one of a standard water pump.

According to another embodiment of the invention a press fit interference between the housing inner diameter and the bearing outer diameter ranges between 10 and 80 jim.

An advantage of this embodiment is that, thanks to the increased tolerance freedom, the bearing lifetime increases up to the bearing lifetime of bearings for standard water pump.

According to a still further embodiment, the parallelism between a first datum plane of the housing and a second datum plane of the housing ranges between 0.05 e 0.1 mm.

An advantage of this embodiment is that a better parallelism between the first datum plane and the second datum plane, which is interfaced with the pulley, leads to an improved axial run-out of the pulley.

A further embodiment of the disclosure provides an internal combustion engine comprising a switchable water pump according to the previous embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a switchable water pump, according to a prior art design.

Figure 2 shows a switchable water pump according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to Fig. 2, a switchable water pump 600 is shown. It comprises a housing 610, a shaft 650, which drives an impeller or rotor 660 and is driven by a pulley 670. The shaft is supported by means of bearings 620, normally cylindrical or needle roller bearings. The pulley is driven by the crankshaft of the internal combustion engine and the impeller 660 can be switched by means of a friction pair with the pump shaft 650.

A pump bearing 620 is press filled into the pump housing 610 to avoid any displacement during working condition, due to axial force components. The bearing is made of steel, while the pump housing is made of aluminium. Moreover the pump comprises a coil 640 and a coil cage 630 for the disengaging of the pump. The main feature of this switchable water pump is that the coil cage 630 is realized as an unique piece with the housing 610, differently from known solutions according to which the coil cage is a separate piece and is press filled externally to the housing. This new housing, integrating the coil cage, is preferably made of aluminium. In a known switchable water pump the housing is made of aluminium as well, while the separate coil cage is made of steel. According to an embodiment of the invention, the fact that the coil cage is integrated in the pump housing and therefore is made of aluminium as well, leads to the reduction of the magnetic losses, since aluminium and its alloys are non-magnetic.

Adopting this new solution, the main advantage is to reduce the press fit tolerance chain: in fact, with respect to a known switchable water pump design, where the press fit tolerance chain consists of the tolerances of the coil cage inner diameter vs. the housing outer diameter and the housing inner diameter vs. the bearing outer diameter, the new solution imp!ies a press fit tolerance chain consisting only of the housing 610 inner diameter 611 and the bearing 620 outer diameter 621. In other words, this is the press fit tolerance chain of a standard water pump (i.e. a non-switchable water pump). As a consequence, even for extreme temperature conditions, the press out load increases, due to increased tolerance freedom, or in other words the required interference values between the housing and the bearing can have a larger range, for example between 10 and 80 1sm. This leads to a bearing lifetime increasing, at least equivalent to the bearing lifetime as for standard water pump.

Furthermore, the reduced press fit tolerance chain leads to the advantage of a better parallelism between a datum plane A, which represents the sealing surface of the pump on the engine, and a datum plane B, which represents the pump surface that is interfaced with the pulley 670, via an axial bearing 680. The parallelism between the two planes will range between 0.05 and 0.1 mm. As a consequence the pulley axial run-out can be improved.

Summarizing, this new design of the switchable water pump, with a coil cage integrated in the housing, leads to several improvements: the bearing lifetime increases due to less severe press fit interferences; the pulley run-out is improved, due to better parallelism between two fundamental datum planes of the pump; the pump as a whole is cheaper because of missing machining operation on coil cage inner diameter and housing outer diameter, missing press fit operation between coil cage and housing and less material cost.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

500 switchable water pump (known design) 510 housing 520 bearing 530 coil cage 600 switchable water pump (new design) 610 housing 611 housing inner diameter 620 bearing 621 bearing outer diameter 630 coil cage as unique piece with the housing 640 coil 650 shaft 660 impeller 670 pulley 680 axial bearing A, B datum planes

Claims

CLAIMS1. Switchable water pump (600) comprising a housing (610), a shaft (650), which drives an impeller (660), a bearing (620), which is press fitted in the housing (610) and supports the shaft, a coil (640) inserted in a coil cage (630), wherein said coil cage (630) is realized as an unique piece with the housing (610).
2. Switchable water pump (600) according to claim 1, wherein the housing (610) is made of aluminium.
3. Switchable water pump (600) according to claim I or 2, wherein a press fit tolerance chain only and exactly consists in the tolerance of a housing (610) inner diameter (611) and in the tolerance of a bearing (620) outer diameter (612).
4. Switchable water pump according to claim 3, wherein a press fit interference between the housing (610) inner diameter (611) and the bearing (620) outer diameter (612) ranges between 10 and 80 psm.
5. Switchable water pump according to any of the preceding claims, wherein the parallelism between a first datum plane (A) of the housing (610) and a second datum plane (B) of the housing (610) ranges between 0.05 and 0.1 mm.
6. Internal combustion engine (110) comprising a switchable water pump (600) according to any of the preceding claims.