FR2488966A1 - V=belt and pulley transmission - has permanent magnets in belt to increase torque exerted by ferromagnetic pulley - Google Patents

Abstract

The transmission system consists of a driving and a driven pulley with a vee belt drive. One or both of the gullies may be of the variable diameter type. The maximum torque capable of being transmitted is dependent on the tension in the vee belt.S An increased torque capability is achieved by embedding permanent magnets in the vee belt (3) and using a ferromagnetic driving pulley. The magnet inserts in the vee belt consist of transverse cores producing North and South poles on each side (7,8) of the belt. A magnetic field (9) is established between the vee belt and the pulley enabling an increased torque to be transmitted without increasing the belt tension.

Description

The present invention relates to torque converters of the pulley and belt type allowing continuous speed variation and capable of transmitting high torque.

It is known that converters of this type comprise at least one pulley with variable diameter and that, in these converters, the power transmission is effected by friction and not by meshing, precisely to allow the continuous variation of speed.

However, the transmission of a large torque by means of a belt acting by simple friction raises difficulties and has many disadvantages. In fact, the energy losses are permanent and significant due to slipping and it is impossible to obtain high speed ratios between a driving shaft and a driven shaft. In addition, at a given transmitted power, a belt converter must have a larger footprint than a hydraulic or gearbox.

In such torque converters, the only way to increase the transmitted power is to increase the belt tension. I1 therefore results as a consequence of a reduction in mechanical efficiency.

The object of the present invention is to remedy the drawbacks mentioned above by improving the belt torque converters to enable them to transmit high torque, without increasing the tension of the belt.

To this end, according to the invention, the torque converter comprising at least one transmission element of the belt type and two pulleys, at least one of which is of variable diameter, and in which this transmission element and these pulleys are in friction contact, while at least that of said pulleys which is driving is of a ferromagnetic material, is remarkable in that said transmission element is provided with magnetic means permanently magnetized creating north poles and south poles in the walls lateral of said transmission element, these north and south poles cooperating with the lateral walls of the groove of the pulley made of ferromagnetic material to locally generate a magnetic contact pressure, independent of the tension of said transmission element.

Thus, thanks to the addition of an additional contact pressure of magnetic origin, the friction losses are reduced and the mechanical efficiency of the transmission system is increased. It is therefore possible, with given mass and size, to increase the transmitted power, as well as the extreme speed ratio between the driving pulley and the driven pulley.

It will be noted that the pulleys of known torque converters are generally made of steel, that is to say of a ferromagnetic material. Consequently, to adapt a known torque converter to the improvements of the present invention, it suffices to replace its usual transmission element with a transmission element provided with magnetic means according to the invention.

By the American patent N03 208 296 and the French patent 2 106 729 (70 34 339), contact is already made with transmission devices of the pulley and belt type using auxiliary magnetic contact pressures.

In French patent NO 2 106 729, provision is made to produce magnetized pulleys and to incorporate ferromagnetic elements in the belt. It is seen that such a device could not be used in the case of a torque converter with continuously variable speed, since it would be practically impossible to incorporate permanent magnets in the pulleys with variable diameter. In any case, these variable diameter pulleys should be specially made, which would greatly increase the cost of said converters, whereas according to the invention, it is sufficient, in order to obtain a converter according to the invention, to change in a known converter, the belt, without touching the other elements of the latter.

The preferred embodiments described in US Pat. No. 3,208,296 likewise provide magnetic pulleys. However, an example of a device without a magnetic pulley is also described. It will be noted that this last exemplary embodiment cannot be used in a converter. with speed variation, because, the American patent N03 208 296 envisages only systems of pulley of the cylinder type and with flat belt in which the auxiliary magnetic forces are radial compared to the pulleys. In the present invention on the contrary, it is essential that these auxiliary magnetic forces be parallel to the axis of said pulleys.

Thus, the American patent NO 3,208,296 and the French patent NO 2,106,729 could not be applied to the production of a torque converter according to the invention.

In the torque converter according to the invention, the belt can form a flexible continuous link in one piece in which are magnetized elements or else be in the form of a chain of articulated links, each of which includes or consists of a magnetic element.

Preferably, the belt according to the invention has a trapezoidal section and each magnetized element has a south pole on one of the oblique faces of the belt and a north pole on the other of said oblique faces of the latter, every pale south being on an oblique face of the belt and all the north poles being on the other of said oblique faces. Thus, when a magnetic element comes into contact with the oblique faces of the groove of the corresponding pulley, the lines of magnetic forces close from one oblique face of the groove to the other, through said pulley, generating a force d important attraction which presses the belt against said groove.

The magnetized elements can be constituted by wires or studs transverse to said belt or by blocks, each of which forms a link in a chain. In this case, it is advantageous for a longitudinal non-magnetic textile or metallic weaving to be interlaced with said transverse magnetic elements.

The figures of the appended drawing will make it clear how the invention can be implemented.

FIG. 1 schematically illustrates a variable speed torque converter, in gear reduction.

Figure 2 is a schematic section along the line
II-II of Figure 1.

FIG. 3 schematically illustrates a variable speed torque converter in overdrive transmission.

Figure 4 is a schematic section along the line IV-IV of Figure 1.

Figure 5 illustrates the principle of the present invention.

Figure 6 is a partial longitudinal section of a first embodiment of the belt for the converter according to the invention.

Figure 7 is a cross section along the line
VII-VII of figure 6.

Figure 8 is a partial longitudinal section of a second embodiment of the belt for the converter according to the invention.

FIG. 9 is a cross section along the line IX-IX of FIG. 8.

FIG. 10 is a longitudinal section along the line X-X in FIG. 8.

Figure 11 is a partial front view of a third embodiment of the belt for the converter according to the invention.

Figure 12 is a view along the line XII-XII of Figure 11.

Figure 13 is a section along line XIII-XIII of Figure 11.

In these figures, identical references designate similar elements.

The continuously variable torque converter, shown diagrammatically in FIGS. 1 and 3, comprises a driving pulley 1 and a driven pulley 2 connected by a transmission belt 3.

Each of the pulleys 1 and 2 has a known structure, not shown in detail, allowing it to vary the diameter of its groove: for this purpose, as illustrated diagrammatically in FIGS. 2 and 4 with regard to the driven pulley 2, each of the pulleys 1 and 2 can consist of two conical flanges 4 and 5, which interpenetrate and whose axial spacing is variable.

In the case of FIG. 1, the diameter of the groove of the driving pulley 1 is greater than that of the groove of the driven pulley 2, so that it is a gear reduction. Conversely, in the case of FIG. 3, the diameter of the groove of the driving pulley 1 is smaller than that of the groove of the driven pulley 2, so that it is an overdrive transmission.

The tangential force F transmitted by such a system is equal to the difference of the respective tensions T and T 'of the driving strand and the driven strand of the belt 3. Consequently, if the driving pulley 1 provides the same torque in both cases of Figures 1 and 3, the force F will be lower in the case of Figure 1 than in the case of Figure 3, since then the radius of the groove of the pulley 1 is greater in the system of Figure 1 than in the system of FIG. 3. Thus, in overdrive transmission (FIG. 3), the force F to be transmitted is greater, so that in this case the operation of the system 1, 2, 3 is less satisfactory for the reasons explained above. -above.

In addition, we know that the voltage T is equal to
T = T 'ef denoting the coefficient of friction; it follows that F = T-T '= T (1- f), that is to say that the value
e of the force F varies as a direct function of the winding angle a. The transmitted torque is therefore strongly influenced by the value of the winding angle a. As in the case of Figure 1, the winding angle X takes a value al greater than that a2 of the system of Figure 3, we see that the latter system is not likely to transmit torques as high as the Figure 1 system.

Thus, these few remarks show that, all other things being equal, the high speed ratios do not benefit from favorable conditions. I1 follows that, when the coefficient of friction f, the winding angle a and the speed of the driving pulley 1 are given, the only way to increase the transmitted power, without increasing the bulk, is to increase belt tension T, which is to the detriment of mechanical efficiency.

To increase the transmissible force F, without increasing the belt tension T, the present invention provides a local magnetic attraction between the belt 3 and at least the pulley 1.

For example, in the case where the pulley is made of metal or magnetic metal alloy, said belt is produced so that it includes magnetic elements capable of applying said belt against the walls of the pulley groove. As shown in FIG. 5 in the case of a trapezoidal belt 3 cooperating with a pulley 6 with a fixed groove, the belt 3 is such that on one of its oblique faces 7 appear magnetic poles south S and on its other face oblique 8 of the north magnetic poles N
Thus, the pulley 6 being made of a magnetic material, the magnetic force lines 9 close, from face 8 to face 7, through said pulley, which generates the desired magnetic attraction and therefore the application of the oblique faces 7 and 8 of the belt 3 against the corresponding oblique faces 10 and 11 of the groove 12 of the pulley 6. It is thus easy to obtain a contact pressure of magnetic origin of several bars at least equal to the pressure generated by the tension of the belt.

In the embodiment of Figures 6 and 7, the belt 3 is made of a reinforced elastomeric material 13, in which are incorporated sections of magnetized wires 14. Each of the sections of magnetized wires 14 is transverse to the belt 3 and is flush with the oblique faces 7 and 8 thereof. In the plane of the oblique face 7, the ends of the wires 14 all form a south pole, while in the plane of the forced face 8, the ends of the wires 14 all form a north pole. The sections of threads 14 can be divided into several longitudinal layers. The frame of the elastomeric material 13 is formed at least in part by a non-magnetic longitudinal or textile weaving 16, interlaced with said threads 14.

In the embodiment of FIGS. 8, 9 and 10, the sections of wires 14 are replaced by transverse magnetic pads 15, embedded in the elastomer 13.

In this case, the north and south poles created by these studs 15 in the oblique faces 7 and 8 are less numerous, but their surfaces are larger than in the embodiment of FIGS. 6 and 7. Reinforcing wires 16 are also provided to reinforce the belt 3.

Figures 11, 12 and 13 illustrate another embodiment, according to which the belt 3 is produced in the form of a chain, each link of which consists of a pyramidal magnetic block 17; the blocks 17 are hinged together by means of longitudinal bars 18, freely rotating around transverse axes 20, linked to said blocks. The blocks 17 are magnetized so that south poles appear on their oblique face 7 and north poles on their oblique face 8.

Of course, the magnets 14, 15 or 17 must be sufficiently non-magnetizable depending on the conditions of use of the transmission system. Most of the time, iron-based magnets can be used, however, in cases requiring high reliability, samarium-cobalt magnets will be used. At least the friction surfaces 7 and 8 can be covered with a wear-resistant film protecting the magnets and their magnetization. So the thickness of this
film (not shown in the drawings) would leave a slight gap between the belt and the pulleys. Of course, this film could completely coat the belt and not cover only the oblique side faces 7 and 8 thereof.

Claims (7)

1.- Torque converter comprising at least one transmission element of the belt type and two pulleys, at least one of which is of variable diameter, and in which this transmission element and these pulleys are in frictional contact, while at least that of said pulleys which is driving is made of a ferromagnetic material, characterized in that said transmission element is provided with magnetic means permanently magnetized creating north poles and south poles in the side walls of said transmission element, these poles north and these south poles cooperating with the side walls of the groove of the pulley (s) made of ferromagnetic material to locally generate a magnetic contact pressure, independent of the tension of said transmission element. 2.- Torque converter according to claim 1, characterized in that its belt forms a continuous link in one piece in which are incorporated transverse magnetic elements interleaved with at least one non-magnetic reinforcing weave whose general direction is longitudinal . 3.- Torque converter according to claim 1, characterized in that its belt is in the form of a chain of articulated links, each of which comprises or consists of a magnetic element. 4.- Torque converter according to any one of claims 2 or 3, having a trapezoidal section characterized in that each magnetized element has a south pole on one of the oblique faces of the belt and a north pole on the other of said oblique faces, of the latter, all the south poles being on one of said oblique faces, while all the north poles are on the other. 5.- Torque converter according to claim 2, characterized in that the magnetized elements consist of wires or studs transverse to said belt. 6.- Torque converter according to claim 3, characterized in that the magnetized elements consist of blocks each of which forms a link in a chain. 7.- Torque converter according to any one of claims 4 to 6, characterized in that at least the oblique faces of its belt are coated with a non-magnetic wear layer protecting the ends of the magnetized elements.