DESCRIPTION

The present invention relates to a rotor for devices for transmission of the movement to fans for cooling the coolant in vehicles and to a double-armature movement transmission device provided with such a rotor.

It is known, in the technical sector relating to the cooling of the coolants contained in the radiators of motor vehicles, that there exists the need to force air onto the said radiator, in order to obtain as rapid as possible dissipation of heat from the liquid externally, said forced air flow being obtained by causing the rotation of a fan, normally mounted on the shaft of the water pump, or on the driving shaft, or on a fixed driven shaft carrying a pulley which receives movement from a belt operated by the driving shaft.

It is also known that said fan must be made to rotate only upon reaching of a certain predefined water temperature detected by means of a thermostat which operates an electromagnetic friction coupling, closing of which causes the rotation of the fan. In addition to normal devices of the so-called ON/OFF type, there is also a need, in the case of particular operating requirements, for devices able to operate a fan so that it is able to rotate:

- at a lower speed than that of the transmission shaft for cooling in low external temperature conditions ;

- at a speed the same as or even greater than that of the transmission shaft at higher external temperatures or during use in critical conditions which result in overheating of the engine;

- at zero speed, namely with the fan which does not rotate at all and remains in the idle condition with respect to the transmission shaft, in the case of particularly low temperatures at which further cooling is not useful or is even damaging.

Examples of such devices are known from EP 1, 746, 266, in the name of the same present Applicant, which describes devices which comprise an electromagnetic clutch arranged between an actuating rotor and the fan, which clutch transmits the movement to the fan via two armatures which are respectively and selectively recallable against the rotor by means of excitation of the electromagnet for activating the clutch. With references to Figs. 1, 2 and 3, an example of a rotor 30 according to the prior art comprises an annular body 31 integral with a coaxial sleeve 31a extending towards the rear part P and suitable for engagement with a supporting driving shaft 20a (Fig. 3) for transmission of the movement to the fan 1.

Preferably the outer surface of the radially outer edge of the annular body has, formed therein, annular recesses 31b for forming the annular edge of the rotor in the manner of a pulley suitable for engagement with a drive belt driven by the driving shaft of a vehicle, for taking up a rotational movement .

In its front surface the annular body 31 has a circumferential recess 35 formed along a diameter slightly greater than the diameter of the sleeve 31b and filled with a non-magnetic material 35a, as well as radially outer slots 36,37 suitable for creating a magnetic flux deviated along a respective first inner armature 33 and a second outer armature 34 (Fig. 2,3) upon suitable excitation of the coil (s) of the electromagnet 32.

Although functional, these devices have given rise to drawbacks associated with their use on some types of engines subject to high vibrations which cause fractures in some zones of the rotor with consequent breakage of the component and interruption of the magnetic circuit, the flows of which cause the armatures to be recalled against the rotor and stoppage of the vehicle.

DE 10 2004 042687 also discloses a rotor which, in order to solve this problem, envisages filling the said circumferential slots with non-magnetic material; with this solution, however, magnetically isolated annular sectors are created and these prevent the magnetic flux from following a radial path from an outermost diameter towards an innermost diameter. This configuration therefore prevents the operation of the rotor in the case of a fan controlled by an electromagnetic coupling with single electromagnet and double armature.

The technical problem which is posed therefore is that of providing a rotor for devices for transmission of the rotational movement to a fan for cooling the coolant in motor vehicles, which is not damaged by or at least less subject to the damage resulting from particular vibration conditions caused by the engines on which the movement transmission device is mounted and at the same time is able to ensure a regular passage of an electromagnetic flow from a radially outermost zone to a radially innermost zone.

In connection with this problem, conveniently the rotor should also be such as to have both small diametral dimensions and a small axial thickness, while maintaining a high torque transmission performance for operation of fans which are also large in size.

A further object of the present invention is to develop a device for transmission of the rotational movement to a fan for cooling the coolant in motor vehicles, which is provided with such a rotor and is able to cause rotation of the fan at a speed different from that of the driving shaft and able to be determined depending on the actual cooling requirement of the engine, which device has compact dimensions without high and costly projecting rotational masses and is formed by a small number of costly parts.

These technical problems are solved according to the present invention by a rotor for devices for transmission of the movement to a fan for cooling the coolant of a motor vehicle according to the characteristic features of Claim 1 and by an electromagnetic friction coupling according to Claim 10 and by a device for transmission of the movement to a vehicle cooling fan equipped with such a friction coupling according to the characteristic features of Claim 13.

Further details may be obtained from the following description of non-limiting examples of embodiment of the present invention, provided with reference to the accompanying drawings, in which:

Figures la-lb: a schematic perspective view, from the back and from the front, respectively, of a rotor according to the prior art with a radially inner armature of a movement transmission device schematically shown in Fig. 2;

Figure 2 : shows a partial schematic cross-section of a rotor according to the prior art applied to a double-armature electromagnetic friction coupling for transmission of the movement via a double armature ;

Figure 3 : shows a schematic vertical section through a motor vehicle fan with a movement transmission device according to the prior art;

Figure 4 : shows a front view of a rotor according to the present invention; Figure 5 : shows a cross-section along a vertical diametral plane of the rotor according to Fig. 4 illustrating a first embodiment of a rotor according to the invention;

Figure 6 : shows a cross-section along a vertical diametral plane of the rotor according to Fig. 4 illustrating a second embodiment of a rotor according to the invention;

Figure 7 : shows a cross-section along a vertical diametral plane of the rotor according to Fig. 4 illustrating a third embodiment of a rotor according to the invention;

Figures 8a-8c: show schematic partial cross- sections of a partial detail of the first embodiment of the rotor according to the invention associated with the armatures of an electromagnetic friction coupling, in the idle, first rotational speed and second rotational speed conditions, respectively;

Figures 9a-9c: show schematic partial cross- sections of a partial detail of the second embodiment of the rotor according to the invention associated with the armatures of an electromagnetic friction coupling, in the idle, first rotational speed and second rotational speed conditions, respectively;

Figures lOa-lOb; show schematic partial cross- sections of a partial detail of the third embodiment of the rotor according to the invention associated with the armatures of an electromagnetic friction coupling, in the idle, first rotational speed and second rotational speed conditions, respectively;

Figure 11 : shows a schematic vertical section through a motor vehicle fan with movement transmission device according to the invention in the idle condition.

For the purposes of the description below the layouts shown by way of example will refer to a pair of reference axes, i.e. longitudinal axis X-X, for easier description coinciding with the axis of rotation of the rotor, and transverse/radial axis Y-Y, as well as a front side A and a rear side P situated opposite each other in the axial- longitudinal direction X-X.

With reference to Figs. 4,5,6,7 a rotor according to the invention comprises:

an annular body 131 integral with a coaxial sleeve 131b extending towards the rear side P and designed to be coupled with a fixed supporting shaft 120a shown by way of example in Fig. 11.

Preferably, the radially outer edge of the annular body extends towards the rear part P and has an outer surface on which movement take-up means are provided, for example annular grooves 131b for forming a pulley suitable for engagement with a drive belt 3 driven by the driving shaft and preferably of the toothed type.

According to the invention it is envisaged that the annular body 131 of the rotor comprises always (Fig. 4) : a circumferential recess 135 formed along a diameter slightly greater than the diameter of the sleeve 131 and filled with a bead 135a of non ^¬ magnetic material conventionally applied by means of welding and suitable for interrupting the continuity of magnetic flux through the rotor; as will appear more clearly below, the recess 135 is designed to interrupt the passage of a magnetic flux generated by an electromagnet 232, which flux will be in this way obliged to cross the thickness of the rotor in order to continue along an armature opposite to the rotor and close a magnetic circuit for recalling the said armature; - a continuous, circumferential, outer recess 636 arranged along a first circumference situated between the inner recess 135 and the outer annular edge of the rotor and filled with non-magnetic material 636a providing further reinforcement;

- a continuous, circumferential, intermediate recess 637 arranged along a circumference situated between the inner recess 135 and the said outer recess 636 and in turn filled with non-magnetic material 637a providing further reinforcement.

According to a first embodiment of the rotor according to the invention (Fig. 5) it is also envisaged that:

- the annular body 131 of the rotor has a plurality of radial holes 638, which are angularly spaced from each other, for receiving respective pins 639 made of ferromagnetic material and extending radially from the circle sector comprised between the radially outer edge of the rotor and the circle sector comprised between the radially innermost recess 135 and the intermediate recess 637.

Figure 6 shows a second embodiment of a rotor according to the invention comprising:

- a ferromagnetic annular plate 839 applied on the rear end surface of the annular body 131 and fixed to the latter by suitable fixing means, such as screws 839a, and radially extending between the radially inner surface 131c of the radially outer edge of the rotor and the circle sector comprised between the radially innermost recess 135 and the intermediate recess 637.

The annular plate 839 is designed to short-circuit the non-magnetic intermediate recess 637 and outer recess 636 so as to close the magnetic flux circuit Fl for recalling the inner armature 33 (Fig. 9b) . The axial thickness of the annular plate is such as to determine a passage of magnetic flux sufficient for ensuring the required force for recalling the inner armature, for example a passage of flux equal to that determined by the pins 639 of the preceding embodiment .

As shown in Fig. 7, a third embodiment of the rotor according to the invention is envisaged, said embodiment comprising in this case an annular plate 739 radially extending between the inner surface 131c of the radially outer edge of the rotor 130 and the circle sector comprised between the radially innermost recess 135 and the intermediate recess 637; the plate 739 is provided with an edge 739a extending in the axial direction towards the rear side P and arranged in contact with the radially inner surface 131c of the axial extension of the radially outer edge of the rotor; with this configuration the passage of the magnetic flux is further improved, said flux finding a greater passage area when crossing the two axial elements in order to continue then radially along the annular plate.

Preferably, the plate 739 is applied to the rotor via means designed to prevent any deformation thereof, ensuring the planarity of the plate, and therefore the best possible contact between the two parts intended for the passage of magnetic flux. An example of these means is illustrated in Fig. 6 by a spot weld 740.

Both in the case of Fig. 6 and in the case of Fig. 7 the annular body 131 has, preferably, a depression 741 extending in the radial section comprised between the outermost recess 636 and the innermost recess 637; along this section the plate 639, 739 is not in contact with the rotor, it thus being possible to reduce the dispersion of magnetic flux in the annular sector not affected by the recall of the innermost armature. With this solution a further advantage is also obtained from the fact that the elimination of the screws allows the recess 636 with the associated non-magnetic material 636a to be arranged closer to the annular edge of the rotor, thus allowing better use of the front surface area thereof which, for the same radial dimensions, results in an increase in the useful magnetic flux and therefore torque applicable to the armature, or, for the same torque, a possible reduction in the radial dimensions of the rotor.

Preferably, the rotor is formed with tempered magnetic steel in order to reduce the magnetic hysteresis once the excitation of the electromagnet has been deactivated.

Preferably, the bead 636,637 filling the slots 136, 137 has a thickness such as to leave a void in the axial thickness on the front end face of the rotor; this therefore ensures iron/iron contact between the surfaces of the rotor and the armatures of the electromagnetic friction coupling 200 designed to ensure the calculated magnetic circuit and therefore the torque which can be transmitted via the friction coupling. Fig. 11 shows the implementation of an electromagnetic coupling 200 comprising an electromagnet 232 fixed to a fixed part 10 and with a coaxial winding; the electromagnet is coaxially, at least partially, inserted inside the rotor 131 according to the invention.

Two armatures, i.e. a radially innermost armature 33 with a smaller diameter and a radially outermost armature 34 with a larger diameter, are positioned on the outside of the rotor and in a position opposite the electromagnet and are respectively connected to a load to be rotated, via respective resilient elements, in the example resilient membranes 33a, 34a with a different resilience which are described in detail below.

According to a preferred embodiment, the winding of the electromagnet comprises two windings, which are preferably concentric, i.e. one winding 232a and one winding 232b, suitable for conducting two different amounts of current and in turn suitable for generating two different magnetic fluxes for recall of a corresponding armature against the different resistive force of the respective resilient membrane. Alternatively the electromagnet may be realized with a single coil PWM-controlled by reducing the power supply so as to determine the correct excitation for attracting only the inner armature 33 or both the armatures 33,34.

Although not shown, it is envisaged that the membranes may be replaced by springs.

In the device for transmission of the movement to vehicle fans 1 illustrated the cooling fan 1 is attached to a supporting bell member la arranged on a bearing lb mounted on a fixed shaft 120a of the vehicle, so as to be coaxial with the axis of rotation thereof.

The same fixed shaft 120a also has mounted thereon, locked in rotation therewith, a rotor 131 according to the invention - shown in the third embodiment thereof in Fig. 7 - which forms the rotating element of a first coupling 200 comprising the annular electromagnet 232 concentric with the rotor 131 and mounted on the outer ring of a bearing 11 arranged between the shaft 120a and the sleeve 131a of the rotor;

the electromagnet 232 is electrically connected by means of wires to a control unit with control logic management based for example on measurement of the temperature of the cooling fluid.

The first armature 33 is arranged on the opposite side to the electromagnet 232, relative to the rotor 131, and is connected to an annular flange 40 joined together with an outer ring 21a of a bearing 21 in turn keyed onto the shaft 120a.

The connection between the armature 33 and the flange 40 is realized via a resilient element 33a designed to allow axial movements of the armature 33, but prevent relative rotation of armature and flange 40.

Said flange 40 also carries the first part 310 of a second coupling 300, the other part 320 of which is joined together with the bell member la of the fan 1.

In greater detail, said first part 310 of the coupling comprises the said flange 40 which is made of magnetic material and which carries permanent magnets 314.

The second coupling part 320 is formed by a ring 321, which is arranged radially opposite the said permanent magnets 314 and is made of conductive material and is joined together with the bell member la which is also made of non-magnetic material such as die-cast aluminium.

With this first configuration, the first part 310 of the second coupling forms the rotor part for generating the movement of the said coupling which, by means of the flange 40 and the permanent magnets 314, causes the generation of eddy currents with induction concatenation via the driven ring 321, which is rotationally driven, causing rotation of the bell member la and therefore the fan 1.

Concentrically with the first armature 33 a second armature 34 is arranged radially more externally with respect to the first armature and is connected to the bell member la via a resilient element, for example, a resilient membrane 34a which is designed to allow axial movements of the armature 34, but prevent the relative rotation of armature and bell member .

The membrane 34a of the second armature 34 has a greater resistance in the axial direction than that of the membrane 33a of the first armature, therefore requiring a greater recall force in order to allow displacement of the armature towards the rotor . The second armature 34 also has a radial dimension much greater than that of the first armature 33 and a plurality of circle-arc slots 34b arranged along the same circumference and designed to cause a deviation of the magnetic flux so as to increase the force of magnetic attraction and therefore the torque which can be transmitted from the rotor to the armature and therefore to the fan 1.

With this configuration and with either one of the embodiments of the rotor according to the invention it is possible to obtain the different required speeds of rotation of the fan 1 and in particular: a) in conditions where the electromagnet 232 is not excited (Fig.8a; 9a; 10a) and therefore the friction coupling is disengaged, the movement of the driving shaft 20 is not transmitted to the armatures 33 and/or 34 and therefore to the fan 1 which remains idle;

b) in the condition where the electromagnet 232 is excited by means of the first winding 232b (Fig.8b; 9b; 10b) , a circuit Fl is created for the magnetic flux which, passing from the electromagnet to the rotor 131, is deviated from the annular recess 135 onto the first armature 33, causing recall of only the first smaller-size armature 33 which, overcoming the reduced resistance in the axial direction of the membrane 33a, engages with the rotor 131 and transmits the movement to the fan via the Foucault coupling 300; since the transmission occurs with relative slipping of the flange 40 and the bell member la, the latter rotates a slower speed than that of the driving shaft 20;

c) in the conditions where the electromagnet 232 is excited (Figs .8c; 9c; 10c) by means of the simultaneous excitation of the first winding 232a and the second winding 232b, a circuit F2 is created for the magnetic flux which passes from the electromagnet through the rotor 131, is alternately deviated from the rotor to the armature 34 and from the latter back again to the rotor, via the series of outer slots 136 and the series of intermediate slots 137 of the rotor and the slots 34b of the second armature 34, and is again closed on the first armature as described for the first flux circuit Fl; in this way the second armature 34 is also recalled and, overcoming the resistance of the associated membrane 34a, engages with the rotor 31, transmitting the movement of the driving shaft directly to the bell member la and resulting in a speed of rotation of the fan which is the same as the speed of rotation of the said driving shaft. Although described in relation to an example (Fig. 11) where the movement is transmitted to the rotor by a pulley connected thereto, the situation is also possible where the said support means (120a) form an extension of the driving shaft of the vehicle (Fig. 3) and are joined together with the rotor 131 for transmission of the rotational movement thereto.

It is therefore clear how the rotor according to the invention provides a solution to the technical problem posed, as a result of the hollow slots formed on the said rotor being filled with non ^¬ magnetic material, achieving in particular a greater mechanical resistance to the vibrations produced by the engines of the vehicles on which it is mounted, while maintaining at the same time high levels of magnetic flux and therefore torque which the device may transmit, both in the case of reduced excitation for recall of only the innermost armature and in the case of full excitation for recall of both the armatures.

Similar characteristic features distinguish electromagnetic friction couplings and double- armature devices according to the invention designed to achieve the required operation at several speeds and in the idle condition with smaller dimensions both axially and radially and a smaller number of parts, thus avoiding also the use of special bearings with a consequent reduction in the associated production, assembly and maintenance costs .