Patent Description:
In vehicles operated by an internal combustion engine, a clutch, which is disengaged to allow gear change, is arranged along the transmission.

Some prior art clutches are provided with a mechanism, in the form of suitable cams, which tend to open the clutch automatically if the driving wheel or wheels tend to rotate faster than the speed set by the engine. This occurs, for example, when the driver shifts from a higher gear to a lower gear while the vehicle is traveling at high speed, while simultaneously releasing the accelerator, reducing the flow of fuel to the engine. In this case the engine acts as a brake (known as "engine braking effect") and tends to brake the driving wheel or wheels.

In order to prevent an excessive braking effect from negatively affecting the vehicle driving, the clutch can be provided with a device adapted to reduce the torque transmitted through the clutch, when the speed of the driving wheel or wheels, and hence of the driven member of the clutch, tends to exceed the rotation speed of the drive input member of the clutch. The device comprises a pair of cam profiles which coact with each other to generate an axial movement of a driven member of the clutch away from a pressure plate that presses the friction discs against one another, so that they transmit the torque from the drive input member to the driven member by friction. The cam profiles are integral one with the driven member and the other with the pressure plate of the clutch. The axial movement of the driven member and pressure plate away from each other reduces the torque transmitted from the driving wheel toward the engine and thus reduces the engine braking effect.

A clutch of this type, according to the preamble of claim <NUM>, is disclosed in documents <CIT> and <CIT>. This clutch has some drawbacks due to the fact that the axial stroke of the pressure plate relative to the driven member is limited by an axial stop.

According to to the invention, a clutch for transmitting torque from an engine to a driving wheel of a vehicle, according to claim <NUM> is provided. The clutch comprises a housing connected to a drive input member to rotate integrally therewith about a rotation axis of the clutch. First friction discs are rotatingly coupled to the housing and are intercalated with second friction discs rotatingly coupled to a driven member. The driven member is connectable to a drive output member to rotate integrally therewith. A pressure plate is mounted on the driven member and axially movable relative thereto parallel to the rotation axis of the clutch. The pressure plate is elastically stressed toward the driven member to compress the first discs and the second discs against one another. The clutch further comprises a first cam profile integral with the driven member, and coacting with a second cam profile integral with the pressure plate. The first cam profile and the second cam profile are configured so that, if a torque is transferred from the driven member toward the drive input member, the driven member rotates relative to the pressure plate about the axis of the clutch and the rotation movement between the driven member and the pressure plate generates, by means of the first cam profile and the second cam profile, an axial thrust on the pressure plate and an axial movement of the pressure plate away from driven member, reducing the pressure exerted by the pressure plate on the first discs and the second discs. To limit the axial movement of the pressure plate relative to the driven member, an angular stroke limiter is provided, which limits the relative rotation between the driven member and the pressure plate and thereby limits the movement of the pressure plate away from the driven member.

In this way, the movement of the pressure plate and driven member away from each other is obtained without the need for an axial stop, as instead is normally the case in prior art clutches, in which the axial load generated by the impact of the pressure plate against the axial stop is added to the axial load applied by the elastic member that presses the discs of the clutch against one another.

In practice, the angular stroke limiter defines a maximum relative rotation between the driven member and the pressure plate which can correspond to a maximum movement of the pressure plate and driven member away from each other such as to prevent coupling loss between driven discs and driven member.

In general, the angular stroke limiter can be configured in various ways and can comprise at least one pair of mutual stop elements, one integral with the driven member and the other with the pressure plate. These stops can be combined and arranged in any suitable way as a function of the structure of the driven member and of the pressure plate.

In particularly advantageous embodiments, the angular stroke limiter comprises at least one slot formed in the pressure plate and at least one first column of the driven member that extends approximately parallel to the rotation axis of the clutch and engages in the slot. The slot extends in a tangential direction around the rotation axis of the clutch and the size thereof in tangential direction defines the maximum stroke in axial direction of the pressure plate relative to the driven member under the thrust of the first cam and of the second cam. The relative rotation between the driven member and the pressure plate is limited by the first column abutting against the ends of the first slot.

In practical embodiments, several slots and several columns can be provided.

This arrangement is particularly advantageous as it allows an angular stroke limiter to be provided in a clutch that, in a known manner, comprises guide columns, which guide the movement of the pressure plate relative to the driven member, and around which elastic members are arranged, typically in the form of helical compression springs, which stress the pressure plate toward the driven member, pressing the friction discs against one another. In this way, a particularly compact configuration with a limited number of components is obtained.

Further advantageous features and embodiments of the clutch are defined in the appended claims, which form an integral part of the present description, and in the following description of exemplary embodiments.

The invention will be better understood by following the description and the accompanying drawings, which illustrate a non-limiting example of embodiment of the invention. More in particular, in the drawing:.

The clutch has a generally known configuration and operation and will be described briefly with reference to the main members, for a better understanding of the invention. The clutch is indicated as a whole with <NUM> and comprises a housing <NUM> rotatingly connected to a drive input member <NUM>, in such a way that the housing <NUM> rotates integrally with the drive input member <NUM> about a rotation axis A-A of the clutch <NUM>. An elastic joint <NUM> acting as flexible coupling element can be arranged between the drive input member <NUM> and the housing <NUM>.

In the illustrated embodiment, the drive input member <NUM> is a gear, which can receive motion, directly or indirectly, from a drive shaft, not shown.

First friction discs <NUM> are mounted in the housing, coaxial to the housing <NUM> and rotatingly coupled to the housing <NUM> by means of radially external tabs <NUM>, which engage in grooves <NUM> of the housing <NUM>. The first friction discs <NUM> are intercalated with second friction discs <NUM>, coaxial to the first friction discs <NUM>. By means of a grooved profile <NUM> of the driven member <NUM> and respective internal teeth <NUM> of the second discs <NUM>, these discs are rotatingly coupled to a driven member <NUM> of the clutch <NUM>, coaxial to the housing <NUM>. By pressing the discs <NUM> and <NUM> against one another a friction force is generated on the surfaces in mutual contact between the discs <NUM>, <NUM>, by means of which the torque is transmitted from the drive input member <NUM> to a drive output member <NUM> (shown only in <FIG>). This latter can be mechanically connected to a gearbox, not shown, by means of which the torque is then transmitted to the driving wheel or wheels of the vehicle (not shown) with a suitable transmission ratio.

A grooved profile <NUM> of the driven member <NUM> rotatingly couples the drive output member <NUM> to the driven member <NUM>.

The driven member <NUM> is mechanically connected to a pressure plate <NUM>, coaxial to the driven member <NUM> and axially movable to move toward and away from the driven member <NUM>, i.e., movable in a direction parallel to the rotation axis A-A of the clutch <NUM>. In addition to a possible axial movement, the pressure plate <NUM> is provided also with a possible angular movement relative to the driven member <NUM>. In other words, the driven member <NUM> and the pressure plate <NUM> can rotate relative to each other about the axis A-A of the clutch, for the purposes described below.

The pressure plate <NUM> is pushed toward the driven member <NUM> by means of elastic members <NUM>. In the embodiment illustrated, the elastic members <NUM> comprise three helical compression springs <NUM> arranged parallel to the axis A-A of the clutch <NUM>. Each compression spring <NUM> is housed in a respective seat <NUM> formed in the pressure plate <NUM>. Each helical spring <NUM> surrounds a column <NUM> which is part of, or integral with, the driven member <NUM>. Each spring <NUM> is maintained partially compressed between the bottom <NUM> of the respective seat <NUM> and a stop <NUM>, which is rigidly connected to, or is part of, the driven member <NUM>. More specifically, in the illustrated example the stop <NUM> is substantially annular in shape and has a plurality of protrusions <NUM> coaxial to the columns <NUM>. Screws <NUM> extend coaxially to each protrusion <NUM> and to the respective column <NUM>, so as to rigidly connect the stop <NUM> to the columns <NUM> and hence to the driven member <NUM>.

While the illustrated embodiment shows a single stop <NUM> of annular shape to hold the three helical compression springs <NUM> in position, constrained to the three columns <NUM>, three separate stops could also be used, each fixed to the respective column <NUM> by means of a proper screw <NUM>.

In a manner known per se, the springs <NUM> generate a thrust of the pressure plate <NUM> against the assembly of the first discs <NUM> and second discs <NUM> and against the driven member <NUM>. The pressure of the discs <NUM> against the discs <NUM> generates the friction force that allows the torque to be transmitted from the drive input member <NUM> to the driven member <NUM>.

To disengage the clutch, for example to change the transmission ratio toward the driving wheel or wheels, in a known manner the pressure plate <NUM> can be moved away from the driven member <NUM> by means of compression of the springs <NUM>. This movement can be controlled by an actuator, for example a manually controlled actuator, operated by means of a lever on the handlebar of a vehicle on which the clutch <NUM> is installed. The actuator can act directly on the pressure plate <NUM>, moving it away from the driven member <NUM> with an axial movement.

The driven member <NUM> comprises at least one first cam profile <NUM>, which coacts with at least one second cam profile <NUM> integral with the pressure plate <NUM>. In the embodiment illustrated, in actual fact the driven member <NUM> comprises three first cam profiles <NUM>, coacting with the same number of second cam profiles <NUM> integral with the pressure plate <NUM>. The cam profiles are configured such that a mutual rotation about the axis A-A of the driven member <NUM> relative to the pressure plate <NUM> causes a thrust in axial direction between the driven member <NUM> and the pressure plate <NUM> oriented in a direction opposite to the thrust exerted by the springs <NUM>. The thrust generated by the first and second cam profiles <NUM>, <NUM> coacting with each other thus causes an axial movement of the pressure plate <NUM> away from the driven member <NUM>. More precisely, the pressure plate <NUM> moves away from the driven member <NUM> moving relative to the housing <NUM> in a direction such as to compress the springs <NUM>.

This axial movement occurs when the torque applied to the driven member <NUM> by the drive output member <NUM> exceeds the torque applied by the engine to the drive input member <NUM>. This circumstance occurs, for example, when the driver of the vehicle engages a lower gear and releases the accelerator, so that the engine acts as brake (engine braking effect). In this circumstance, it is advisable for the clutch <NUM> to be able to slip slightly, reducing the torque transmitted therethrough and hence ultimately reducing the engine braking effect. This is obtained as a result of the thrust of the cam profiles <NUM> against the cam profiles <NUM> and consequent compression of the helical compression springs <NUM>. The movement of the pressure plate <NUM> and the driven member <NUM> away from each other reduces the friction force transmitted by the second discs <NUM> to the first discs <NUM> and allows mutual sliding therebetween, with consequent rotation of the driven member <NUM> relative to the drive input member <NUM>.

To prevent the movement of the pressure plate <NUM> and the driven member <NUM> away from each other in the direction of the rotation axis A-A from causing undesirable effects, it is advisable to provide a member for limiting this movement. For example, limiting the relative movement away from each other is advisable so that the outermost friction disc <NUM>, i.e., farthest from the bottom of the housing <NUM>, is prevented from leaving its position concentric with the axis A-A, which would otherwise make subsequent correct and complete re-engagement of the clutch not possible.

Characteristically, to limit the movement of pressure plate <NUM> and driven member <NUM> away from each other, an angular stroke limiter is provided, i.e., a limiter of the relative rotation between driven member <NUM> and pressure plate <NUM>, i.e., a limiter of the angular stroke between driven member <NUM> and pressure plate <NUM>. By limiting this rotation, and hence imposing a maximum angular misalignment between driven member <NUM> and pressure plate <NUM>, this consequently limits the axial movement of the pressure plate <NUM> relative to the driven member <NUM>, without the need for axial stops against which the pressure plate <NUM> impacts.

In the illustrated embodiment, the angular stroke limiter comprises a plurality of slots <NUM>, each of which is provided in the bottom <NUM> of each seat <NUM>. The respective column <NUM> of the driven member <NUM> extends through each slot <NUM>.

Each slot <NUM> extends according to a tangential direction, i.e., is elongated according to a circumference which is co-axial with the rotation axis A-A of the clutch. When the driven member <NUM> tends to rotate relative to the pressure plate <NUM> about the rotation axis A-A, each column <NUM> tends to move along the respective slot <NUM> through which it extends. If there are no other constraints, the maximum mutual rotation between the pressure plate <NUM> (with which each slot <NUM> is integral) and the driven member <NUM> (with which the columns <NUM> are integral) is determined by the tangential extension of the slots <NUM>. The size of each slot <NUM> in tangential direction, i.e., the angle subtended by the arc of circle representing the centerline of each slot, is such that the maximum movement of the columns <NUM> inside the slots <NUM> corresponds to a mutual axial movement between the pressure plate <NUM> and the driven member <NUM> that compresses the springs <NUM> without taking them to the condition of maximum compression. In any case, the axial movement is sufficient to cause a sliding between discs <NUM> and discs <NUM>, but is sufficiently limited to prevent the last disc from displacing radially away from its correct position.

<FIG> and <FIG> show, in a section transverse to the axis A-A and in a section according to the lines VII-VII and VIII-VIII, the two mutual positions of the slots <NUM> and of the columns <NUM> (and hence of the pressure plate <NUM> and of the driven member <NUM>) in neutral conditions (<FIG> and <FIG>) and in a position of maximum mutual rotation (<FIG> and <FIG>, where the columns <NUM> are abutting against the respective ends of the slots <NUM>.

It is understood that tangential size of the slots <NUM> is a function of the thickness of the discs <NUM> and in particular of the last disc <NUM>, of the diameter of the columns <NUM> and of the inclination of the cam profiles <NUM>, <NUM>. In fact, the axial stroke of the pressure plate <NUM> relative to the driven member <NUM> is linked to the mutual rotation angle between pressure plate <NUM> and driven member <NUM> through the inclination of the cam profiles. The greater the inclination relative to a plane orthogonal to the rotation axis A-A is, the greater the axial movement will be, with the same angular movement.

To reduce impacts and consequent vibrations, it is advantageous for the edges of the slots <NUM> to be coated with an elastically yielding material, or in any case a material having an impact absorbing effect, as shown at <NUM>.

Claim 1:
A clutch (<NUM>) for transmitting a torque from an engine to a driving wheel of a vehicle, comprising:
a housing (<NUM>) connected to a drive input member (<NUM>) to rotate integrally therewith about a rotation axis (A-A) of the clutch (<NUM>);
first friction discs (<NUM>) mounted in the housing (<NUM>) and rotating therewith;
a driven member (<NUM>), on which there are mounted second friction discs (<NUM>) coaxial to the first friction discs (<NUM>) and intercalated therebetween; wherein the driven member (<NUM>) is connectable to a drive output member (<NUM>) to rotate integrally therewith;
a pressure plate (<NUM>) mounted on the driven member and axially movable relative thereto parallel to the rotation axis (A-A) of the clutch (<NUM>); wherein the pressure plate (<NUM>) is elastically stressed toward the driven member (<NUM>) to compress the first friction discs (<NUM>) and the second friction discs (<NUM>) against one another, and wherein a movement of the pressure plate (<NUM>) away from the driven member (<NUM>) causes a reduction of pressure between the first friction discs (<NUM>) and the second friction discs (<NUM>);
a first cam profile (<NUM>) integral with the driven member (<NUM>) and coacting with a second cam profile (<NUM>) integral with the pressure plate (<NUM>); wherein the first cam profile (<NUM>) and the second cam profile (<NUM>) are configured so that, if a torque is transferred from the driven member (<NUM>) toward the drive input member (<NUM>), the driven member (<NUM>) rotates relative to the pressure plate (<NUM>) about the rotation axis (A-A) of the clutch (<NUM>) and the rotation movement between the driven member (<NUM>) and the pressure plate (<NUM>) generates, by means of the first cam profile (<NUM>) and the second cam profile (<NUM>), an axial thrust on the pressure plate (<NUM>) and an axial movement of the pressure plate (<NUM>) away from the driven member (<NUM>), reducing the pressure exerted by the pressure plate (<NUM>) on the first friction discs (<NUM>) and on the second friction discs (<NUM>);
characterized by an angular stroke limiter (<NUM>, <NUM>), which limits the relative rotation between the driven member (<NUM>) and the pressure plate (<NUM>) and thereby limits the axial movement of the pressure plate (<NUM>) away from the driven member (<NUM>) generated by the first cam profile (<NUM>) and the second cam profile (<NUM>).