TECHNICAL FIELD

The present invention refers to a device for driving a water pump of an internal combustion engine for a motor vehicle.

BACKGROUND ART

Manufacturers pay great attention to engine cooling since it is able to significantly contribute to reducing the levels of primary pollutants.

The emission limits are defined at European level by the sequence of Euro standards 1-2-3-4-5-6 for passenger transport vehicles and Euro I-II-III-IV-V for heavy transport.

Evaluation of the above-mentioned limits, for lightweight vehicles, entails the performance of a mission with a speed profile pre-defined according to the time, starting from cold engine conditions (NEDC cycle) .

In performance of the above-mentioned cycle, the engine fully warms up in a time interval which is equivalent to approximately 2/3 of the overall test time (1200 s) . A large part of the test is therefore performed with the engine not yet fully warmed up, and therefore in unfavourable conditions for emission levels.

Rapid engine warm-up at ignition results in a considerable reduction in emissions; said reduction is particularly significant for the above reasons since it determines favourable emission levels in compliance with the current standards. The latest limitations introduced with regard to engines concern C02 emissions, closely correlated with fuel consumption .

More rapid warming-up of the engine also promotes a reduction in consumption for various reasons, including reduction in the power absorbed in friction due to the lubricating oil reaching optimal viscosity conditions more rapidly. The engine is cooled by a cooling fluid, which is circulated by means of a pump (normally called "water pump") . The water pump is normally driven by the engine by means of a drive belt, which takes its movement from a drive pulley rotating with the drive shaft and powers a driven pulley integral with the pump shaft.

In order to reduce the duration of the engine heating transient, and reach normal thermal operating conditions more rapidly, various alternative solutions have been proposed.

A first known solution consists in driving the pump by means of a dedicated electric motor, which can therefore be activated only when necessary and, in particular, de-activated during the heating transient. This solution is costly, however, and not always possible due to the overall dimensions of the electric motor which may be incompatible with the space available in the engine compartment; other negative factors are the high electric power absorption, the vulnerability of the electric motor to the scheduled operating temperatures, and the need to provide failsafe solutions.

Another possible solution is the use of an electromagnetic control clutch to selectively couple the pulley to the water pump shaft. Again, this solution is fairly complex, it involves problems of reliability linked to wear and operating temperature which are not always easy to solve, and requires the use of superior quality magnetic materials.

The adoption of a pump provided with a device adapted to selectively interrupt the circulation of the fluid, for example a shutter, has also been proposed. However, said pumps have larger overall dimensions than conventional pumps, and this prevents use on conventional engines. Furthermore, the solution is not optimal in energy terms since the shutter dissipates the energy released from the pump to the fluid.

Connection of the pump to the drive belt by means of friction wheels, one fixed and splined onto the pump shaft and the other movable, has also been proposed. This solution is complex, bulky and costly, and very difficult to optimise in relation to the conflicting needs in terms of limiting wear and preventing slipping, particularly in the presence of water or humidity.

DISCLOSURE OF INVENTION

The object of the present invention is the production of a driving assembly for driving a water pump of a vehicle, which allows disconnection of the water pump when not necessary but is free from the problems connected with the known art and discussed above.

The above-mentioned object is achieved by a circuit according to claim 1.

BRIEF DECRIPTION OF THE DRAWINGS

For a better understanding of the present invention, two preferred embodiments are described below, with reference to the accompanying drawings, in which:

figure 1 is a schematic perspective view of a driving device according to a first embodiment of the invention; and

figure 2 is a schematic perspective view of a second embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figure 1, the number 1 indicates as a whole a driving assembly for a cooling fluid pump (below, for the sake of brevity, "water pump", not illustrated) of an internal combustion engine for a motor vehicle.

The assembly 1 comprises a pulley 2 adapted to cooperate with a drive belt (not illustrated) , of conventional type, which takes its movement from a drive pulley operated by the engine shaft .

For said purpose, the pulley is expediently provided with an outer annular ring 3, appropriately provided with a poly-V profile (not illustrated) . The pulley 2 can furthermore be selectively coupled, as described below, to a drive shaft 4 of the pump, on which it is idly mounted by means of a bearing 5.

According to the present invention, the assembly 1 comprises a control device 6 housed inside the pulley 2 and adapted to selectively connect the pulley to the shaft 4.

In the example illustrated, the control device 6 is of the hydraulic type and comprises a clutch box 7 splined onto the shaft 4 of the pump by means of a grooved coupling 8. The clutch box 7 is, substantially, a fluid actuator comprising a pair of opposing pistons 9, the stems 10 of which project on opposite sides of the clutch box 7, radially with respect to the pump shaft 4, and carry respective shoes 11 adapted to cooperate by friction with an inner surface 12 of the annular ring 3 of the pulley 2.

The clutch box 7, rotating with the shaft 4, is connected to an engine lubrication oil delivery pipe 15, which is arranged coaxial with the shaft 4 and on the axially opposite side to it with respect to the pulley 2. Expediently, the clutch box 7 is provided with an opening 16 in which one end of the pipe 15 is inserted with the interposition of a seal 17 of conventional type, and is supported with respect to the pipe 15 by means of a bearing 18. The clutch box 7 is lastly provided with return springs 19 acting on the pistons 9 so as to maintain the shoes 11 in a position retracted from the pulley 2. The clutch box 7 is controlled by means of a hydraulic circuit of conventional type and not illustrated, which is adapted to electively supply engine oil to the delivery pipe 15 at a stable pre-defined pressure level. Since the maintenance of a minimum pressure in the engine lubrication circuit is vital for operation of the engine itself, driving by means of engine oil is intrinsically failsafe.

Operation of the assembly 1 is as follows. With the engine "cold", i.e. until a pre-defined threshold temperature of the cooling fluid is reached, the clutch box 7 is not activated and therefore the shoes 11 remain detached from the inner surface 12 of the annular ring 3 of the pulley 2 under the action of the return springs 19.

In this way, the pulley 2 rotates, driven by the belt, but does not drive the pump shaft 4, therefore allowing the engine to rapidly reach normal thermal operating conditions. When the cooling fluid reaches the pre-defined threshold temperature, the hydraulic control circuit sends oil under pressure to the delivery pipe 15 and then to the clutch box 7. The pistons 9 therefore project and push the shoes 11 against the inner surface 12 of the annular ring 3 of the pulley 2, overcoming the resistance of the return springs 18.

In this way, the clutch box 7 is rotated due to the friction between the shoes 11 and the pulley 2, and in turn drives the shaft 4.

Figure 2 illustrates a second embodiment of the driving assembly of the invention, indicated as a whole by 40, which is described below in the aspects that differ from the driving assembly 1, using the same reference numbers to indicate parts the same as or corresponding to parts already described. In the assembly 40, the pulley 2 - idly mounted on the shaft 4 - houses a conical clutch wheel 41 mounted on the shaft 4 in an axially slidable and angularly fixed manner, for example by means of a grooved coupling 42. The friction wheel 41 has an annular friction surface 43 adapted to selectively interact with the inner surface 12, also conical , of the annular ring 3 of the pulley 2.

The friction wheel 41 is loaded axially by a spring 44 towards its position of contact with the surface 12; the load of the spring 44 is sufficient to ensure driving of the pulley 2 by friction. A hydraulic actuator 45, arranged coaxial with the shaft 41 and on the axially opposite side of the pulley 2, is adapted to exert on the clutch wheel 41 an axial thrust such as to overcome the load of the spring 44, and thus detach the friction surface 43 from the inner surface 12 of the annular ring 3 of the pulley 2.

In this embodiment the failsafe function is achieved mechanically, since in the event of a breakdown the engagement between the friction wheel 41 and the pulley 2 is ensured by the spring 44.

From an examination of the characteristics of the driving assemblies 1, 40 described, the advantages offered by the present invention are evident.

The use of a coupling device housed inside the pulley and hydraulically controlled using the engine oil as the operating fluid provides the function of decoupling the pulley from the pump drive shaft without introducing substantial additional bulk or new equipment, since the lubrication oil is intrinsically present in internal combustion engines.

Lastly, it is clear that modifications and variations that do not depart from the protective scope of the claims can be made to the driving assemblies described.