FR2899661A1 - TORQUE LIMITER - Google Patents

Abstract

This torque limiter (1) is of the type comprising a flexible flywheel (3) fixed with respect to a driving shaft, a first support plate (13) fixed with respect to said flywheel (3), a second support plate ( 19) movable axially and fixed in rotation with respect to said flexible flywheel (3), a friction (17) interposed between said first (13) and second (19) support plates and intended to drive a driven shaft, and elastic means (22) able to exert an axial force on said second support plate (19) so as to grip said friction (17) between said first (13) and second (19) support plates. Said resilient means (22) are interposed between said flexible flywheel (3) and said second support plate (19).

Description

The present invention relates to a torque limiter. We know

  the prior art torque limiters, intended to be interposed between a driving shaft and a driven shaft: such limiters are used in particular in the automotive field, and allow for example to limit the torque transmitted by a combustion engine to a non-drive transmission. disengageable such as an automatic transmission or a continuously variable transmission (frequently referred to as CVT).

  Conventionally, these torque limiters comprise a friction pinch between two support plates under the effect of elastic means, this pinch being calibrated so that when the torque exerted by the driving shaft exceeds a predetermined threshold, friction can slip between the two support plates and thus dissipate by friction the excess torque exerted by the driving shaft, thus avoiding the ruin of the bodies located downstream of the driven shaft. In other words, the torque limiter acts as a fuse between the driving and driven shafts. A particular type of torque limiter is the flexible flywheel torque limiter: the presence of a flexible flywheel makes it possible to absorb the jerks in axial translation and in nutation transmitted by the driving shaft, in particular when this shaft is driven by an internal combustion engine. The object of the present invention is to propose a particularly simple arrangement for such a torque limiter, making it possible to reduce both the cost of manufacture and the bulk.

  This object of the invention is achieved with a torque limiter, of the type comprising a flexible flywheel fixed relative to a driving shaft, a first support plate fixed relative to said flywheel, a second axially movable and fixed support plate in rotation with respect to said flexible flywheel, a friction interposed between said first and second support plates and intended to drive a driven shaft, and resilient means able to exert an axial force on said second support plate so as to grip said friction between said first and second support plates, limiter in which said elastic means are interposed between said flexible wheel and said second support plate. Due to the fact that the resilient means are supported on the flexible flywheel, it is possible to dispense with a whole series of intermediate parts which hitherto complicated the manufacture of the flexible flywheel torque limiters, and increased their axial and especially axial dimensions. . In this way it is possible to obtain a torque limiter made with a minimum number of parts, which makes it economical and compact.

  According to other optional features of the torque limiter according to the invention: said resilient means comprise a Belleville spring washer, mounted prestressed between said flexible flywheel and said second support plate, said second support plate has a axial thickness substantially greater than said first support plate, - said first support plate is formed in a cover of said limiter, - said torque limiter further comprises means for damping acyclisms, whose input cooperates with said friction and the output is adapted to cooperate with said driven shaft, - said torque limiter comprises a plate contiguous to said flexible flywheel, for distributing the forces of fixing means of said flexible flywheel on said driving shaft, - said torque limiter comprises securing means for securing said flexible flywheel to said drive shaft, and orifices for accessing these means of attachment, said openings through said damping means, said first and second support plates are interconnected by a plurality of tongues allowing a relative axial displacement of these two plates, and prohibiting the rotation of these two trays relative to each other. Other features and advantages of the present invention will appear on examining the attached drawing board, in which: FIG. 1 is a partially cutaway front view of the torque limiter according to the invention, FIG. 2 is a sectional view along the line II-II of FIG. 1 of the limiter according to the invention, when it is mounted on a crankshaft and disposed inside a fixed bell, and FIG. partial view of the torque limiter according to the invention, taken along the direction of the arrow III of FIG.

  As can be seen in FIGS. 1 and 2, the torque limiter 1 according to the invention comprises a metal plate 3 forming a flexible flywheel intended to be fixed on a driving shaft 5 such as an internal combustion engine crankshaft. Fastening means such as hollow-panel screws 7i are used to fix the flexible flywheel 3 on the crankshaft 5. Preferably, it is planned to double the flexible flywheel 3 of a force distribution plate 9 in its zone of fixing on the crankshaft 5. On the flexible flywheel 3 is fixed a rigid cover 11 having an annular portion 13 forming a first support plate.

  Faced with this first support plate are the lining 15 of a friction 17. On the other side of the lining 15 is a second support plate 19 of substantially annular shape, having an axial thickness preferably greater than the first support plate 13.

  The second support plate 19 is mounted fixed in rotation relative to the cover 11 and the flexible flywheel 3, and axially movable relative to these two members. This free movement in translation and locked in rotation is obtained by means of a plurality of resilient tongues 21a, 21b, 21c distributed evenly around the limiter (see Figures 1 and 3).

  Between the flexible flywheel 3 and the second support plate 19 is a spring washer 22, Belleville type washer, centered in this plate or in the flexible flywheel 3. This elastic washer 22 may include a chamfer, a radius or a striking on its outer diameter and on its inside diameter, in its support zones respectively on the plate 19 and on the flywheel 3, for a part to reduce the stresses and on the other hand to present an improved support on this plate and on this wheel. This washer is prestressed in such a way as to permanently exert a calibrated pressure force on the second support plate 19, allowing the friction pads 17 to be clamped between this second support plate and the first support plate 13. In a simplified variant and not shown, the friction 17 could be connected directly to a driven shaft, which may itself cause for example an automatic transmission or a continuous variable transmission.

  In the variant shown, the torque limiter according to the invention comprises, as is known per se, means for damping the acyclisms transmitted by the crankshaft 5. These damping means comprise two guide rings 23, 25 between which extends a damping web 27 itself secured to a hub 29 adapted to drive a driven shaft (not shown). Between the two guide rings 23 and 25 are arranged a plurality of springs or groups of springs 31a to 31d, cooperating with the damping veil 27.

  The guide washer 25 is itself integral with the friction 15. It is provided, both in the two guide washers 23, 25 that in the web 27, orifices 33i for the passage of a screwing tool fixing means 17. It will be noted that it is advantageous to provide that the heads 35i of the fastening means 7i are too large to pass through the orifices 33i so that these fastening means 7i can be considered to be in fact prisoners to the inside the torque limiter according to the invention. A single or multiple hysteresis system (variable hysteresis), known per se, is provided in the damping means.

  This system comprises in particular a friction washer 36 having Ei notches and pins Ti uniformly distributed at its periphery. The nipples Ti make it possible to connect the friction washer 36 to the guide washer 25. The arrangement of the notches Ei and the nipples Ti makes it possible not to obstruct the orifices 33i, so as to let a screwing tool pass. As is known per se, the torque limiter 1 is disposed inside a protective bell 37 and disposed, if necessary, between an internal combustion engine and an automatic transmission or continuous variable (not shown).

  The mode of operation and the advantages of the torque limiter according to the invention result directly from the foregoing description. The crankshaft 5, the flexible flywheel 3, the cover 11, the first support plate 13, the second support plate 19, the elastic washer 22 rotate continuously in one piece.

  As long as the torque transmitted by the crankshaft 5 is less than a predetermined value imposed by the calibration of the spring washer, the linings 15 of the friction 17 are held clamped between the first 13 and second 19 support plates.

  When the torque transmitted by the crankshaft 5 exceeds said predetermined value, the linings 15 of the friction 17 slide between the first 13 and second 19 bearing plates, so that a part of the torque is lost by friction, thereby limiting the torque effectively transmitted to the driven shaft, and to avoid damaging organs driven by this shaft.

  The damping means comprising the two guide washers 23, 25, the damping web 27 and the plurality of springs 31a to 31d allow them to reduce the acyclisms transmitted by the crankshaft 5. Note that the flexible steering wheel 3 allows to absorb the jerks in axial translation and nutation transmitted by the crankshaft 5.

  Note also that the provision of a relatively large axial thickness for the second support plate 19 allows to play the second support plate the role of a flywheel, and to facilitate the dissipation of the heat from the friction of the friction linings 17. In the case where the need for inertia is low, one can alternatively use a thin bearing plate, which can then be steel and made by cutting press. Note that making the fastening means 7i captive torque limiter can transport the torque limiter without risk of losing these fastening means. The presence of the orifices 33i makes it possible to actuate these fastening means in view of their cooperation with the crankshaft 5 despite the fact that they are prisoners. Thanks to these characteristics, the torque limiter according to the invention can be fully pre-assembled before being actually mounted on the crankshaft 5: this modular character greatly facilitates the integration of this torque limiter in a manufacturing process.

  Note that to remove the torque limiter of the crankshaft 5, it may be necessary to rotate the friction 17 and its associated damping means, so as to bring the orifices 33i in front of the fixing means 35i: to do this, a fluted tool is provided capable of coming into engagement with the hub 29. This is imperative in the case where the cover 11 is fixed irremovably (for example by rivets) on the flexible web 3.

  On the other hand, when this cover is fixed on the flexible web by removable means such as screws / nuts, as shown, the fastening means 35i can be accessed by disconnecting the cover 11 from the flexible web 3. In addition, it will be noted that that the fact of providing that the orifices 33i are smaller than the heads 35i fastening means 7i limits the size of the areas without material of the web 27, and thus to strengthen its mechanical strength. The fact that the elastic washer 22 is interposed between the flexible wheel 3 and the second support plate 19, without any additional intermediate piece, is a very simple arrangement, can be expensive and can be particularly bulky axially. Such an arrangement had never been envisaged until now, because it was thought, wrongly, that it was excluded that the spring washer 22 is supported on a member having a certain flexibility such as the flexible steering wheel 3. Of course the present invention is not limited to the example described and shown, provided for illustrative and non-limiting. Thus, for example, the elastic washer 22 could be replaced by cutouts (for example in the form of tabs) made directly in the flexible steering wheel. This would remove the spring washer 22 and thus save a room.

Claims (12)

  1. Torque limiter (1), of the type comprising a flexible flywheel (3) fixed relative to a driving shaft, a first support plate (13) fixed relative to said flywheel (3), a second support plate (19) movable axially and fixed in rotation with respect to said flexible flywheel (3), a friction (17) interposed between said first (13) and second (19) support plates and intended to drive a driven shaft, and means elastic members (22) adapted to exert an axial force on said second support plate (19) so as to grip said friction (17) between said first (13) and second (19) support plates, limiter in which said means elastic members (22) are interposed between said flexible flywheel (3) and said second support plate (19).   2. Torque limiter (1) according to claim 1, wherein said resilient means comprise a spring washer (22) of the Belleville type mounted preload between said flexible wheel (3) and said second support plate (19).   The torque limiter (1) according to claim 1, wherein said resilient means is cut into said flexible flywheel.   4. torque limiter (1) according to any one of claims 1 to 3, wherein said second support plate (19) has an axial thickness substantially greater than said first support plate (13).   The torque limiter (1) according to any one of claims 1 to 3, wherein said second support plate (19) is of thin steel.   Torque limiter (1) according to any one of the preceding claims, wherein said first support plate (13) is formed in a cover (11) of said limiter (1).   7. torque limiter (1) according to any one of the preceding claims, further comprising means for damping the acyclisms (23, 25, 27, 31a to 31d), whose input cooperates with said friction (17) and the output is adapted to cooperate with said driven shaft.   8. Torque limiter (1) according to any one of the preceding claims, comprising a plate (9) contiguous to said flexible wheel (3) for distributing the forces of fixing means of said flexible wheel (3) on said drive shaft.   9. Torque limiter (1) according to any one of the preceding claims, comprising fastening means (7i) trapped to fix said flexible flywheel (3) on said drive shaft, and orifices (33i) for accessing these fastening means.   10. A torque limiter (1) according to claims 7 and 9, wherein said orifices (33i) pass through said damping means (23, 25, 27).   11. The torque limiter (1) according to claim 10, wherein said damping means comprise at least one friction washer (36) having notches (Ei) and fixing studs (Ti) arranged so as not to obstruct said orifices (33i).   Torque limiter (1) according to any one of the preceding claims, wherein said first (13) and second (19) support plates are interconnected by a plurality of tongues (21a to 21c) allowing movement. relative axial of these two trays, and prohibiting the rotation of these two trays relative to each other.