ITBO20090516A1 - GEARBOX FOR MOTOR VEHICLES. - Google Patents

Description

DESCRIPTION

Attached to a patent application for INDUSTRIAL INVENTION having the title

"EXCHANGE BOX FOR MOTOR VEHICLES"

The present invention relates to a gearbox for motor vehicles, in particular for high performance motor vehicles and preferably for road use.

Mechanical transmissions of motor vehicles for road use are currently known in which the gearbox is actuated by means of a manually operated lever or, alternatively, by automated manual actuation.

In the first solution, the gear lever, operated directly by the driver, is mechanically connected by means of transmissions to traditional selection and engagement members, that is to say "H" -shaped.

In the second solution, engagement and selection of the gears is obtained by means of one or more hydraulic or electric actuators which act upon command of the driver. In both of the aforementioned solutions, the gears of the gearbox are served by synchronizing devices designed to facilitate the engagement of the gears in order to achieve excellent driving comfort, smooth and silent.

Disadvantageously, the synchronizing devices (including those of the latest generation) have a minimum engagement time, determined by the time required for energy dissipation to bring the primary and secondary shafts to a speed such as to allow easy reciprocal meshing. This minimum time, of the order of 160 ms, cannot be further reduced for the above reasons. A forced engagement to occur in a shorter time can in fact lead to a breakdown of the synchronization devices.

Therefore, gearboxes made with the aforesaid structure are unable to provide performance suitable for a high-performance vehicle, not even following a thorough optimization.

Also known are high-performance motor vehicles whose construction specifications are aimed at transmitting high power, with particular attention to the gearbox.

The gearbox of a high performance motor vehicle, for example for a racing car, is equipped with straight toothed gears with direct front engagement and without synchronizers to create a very ready and robust mechanical transmission, that is to say characterized by very low shift times and the possibility of transmitting very high torques and powers. The absence of synchronizers is due to the need to minimize shift times which would otherwise be excessive and penalize vehicle performance.

The aforementioned type of gearboxes is designed specifically for racing vehicles.

However, it has been noted that in high-performance cars intended for road use, the use of gearboxes thus made causes annoying drawbacks.

These drawbacks are linked to an excessive roughness of the transmission, with particular reference to the engagement of the gears. The direct front engagement, devoid of synchronizing organs, in fact produces a very rough and aggressive shifting which greatly penalizes the comfort of use of the vehicle, making it unsuitable for use on the road.

In this context, the technical task underlying the present invention is to propose a gearbox for motor vehicles which overcomes the aforementioned drawbacks of the known art.

In particular, it is an object of the present invention to provide a gearbox for motor vehicles capable of guaranteeing high performance (in particular comparable to the performance of racing vehicles) and at the same time maintaining a comfort of use suitable for use on the road.

The specified technical task and the specified purpose are substantially achieved by a gearbox for motor vehicles comprising the technical characteristics set out in one or more of the appended claims.

Further characteristics and advantages of the present invention will become clearer from the indicative, and therefore non-limiting, description of a preferred but not exclusive embodiment of a gearbox for motor vehicles as illustrated in the accompanying drawings in which:

Figure 1 is a perspective view of a portion of a gearbox according to the present invention and with some parts removed to better highlight others;

Figure 2 is a sectional view of the gearbox part of Figure 1;

Figure 3 is a simplified schematic view of a control unit used in the gearbox of Figure 1;

Figure 4 is a perspective view of a component of a control unit, according to a different embodiment, used in the gearbox of Figure 1;

Figure 5 is a schematic representation of a part of the lateral surface of the component of Figure 4 projected onto a plane.

In accordance with the attached figures, 1 generally represents a gearbox according to the present invention.

The gearbox 1 comprises a primary shaft 2 and a secondary shaft 3, which can be connected respectively to a power take-off of an internal combustion engine (by means of a disc clutch) and to a power output (driving axle of a vehicle, by means of a differential). The two shafts 2, 3 rotate respectively around rotation axes "X", "Y" parallel to each other.

The primary shaft 2 has a plurality of first toothed profiles 21, 22, 23, 24, 25, 26 while the secondary shaft 3 has a second plurality of toothed profiles 31, 32, 33, 34, 35, 36. The two plurality of toothed profiles are mutually conjugated and maintained in permanent reciprocal meshing to achieve different speed ratios between primary shaft 2 and secondary shaft 3. In particular, the two pluralities of toothed profiles define a sequence of pairs of toothed profiles MI, M2, M3 , M4, M5, M6 (of which one toothed profile is arranged on the primary shaft 2 while the other on the secondary shaft 3) each of which having a specific ratio between the pitch diameters to achieve a specific transmission ratio between the two shafts 2, 3 different from the transmission ratios of the other pairs. Each pair of toothed profiles MI, M2, M3, M4, M5, M6 therefore realizes a specific gear, starting from the lowest gear or first gear (Mi) up to the highest gear (M6). In the present description reference is made to a 6-speed gearbox (M1-M6) defined by six distinct pairs of toothed profiles, however the present invention is similarly applicable to gearboxes having a different number of gears.

The second plurality of toothed profiles 31, 32, 33, 34, 35, 36 is defined by toothed wheels distinct from each other, mounted idle on the secondary shaft 3, while the first plurality of toothed profiles 21, 22, 23, 24, 25 , 26 is permanently integral with the primary shaft 2 (by mechanical machining for material removal and / or by mounting and stable fixing of respective toothed wheels).

The aforementioned toothed profiles 3, 4 are configured in such a way as to define a train of pairs of toothed profiles MI, M2; M3, M4; M5, M6 sorted from a higher gear ratio (first gear) to a lower gear ratio (sixth gear).

A group of gears "R" defining the reverse gear is arranged alongside the pair of toothed profiles Mi defining the first gear. The group of gears "R" defining the reverse gear comprises a respective first toothed profile 40 mounted on the primary shaft 2 and integral with it, and a second respective toothed profile 50 mounted idle on the secondary shaft 50. The two profiles 40, 50 of the reverse gear are not directly meshing with each other, and for this reason the group of gears "R" defining the reverse gear also comprises an idle wheel (not shown and of a known type) meshing with the aforementioned two toothed profiles 40, 50 of the reverse gear to put rotation of the primary shaft 2 and the secondary shaft 3 in the same direction of rotation.

Between the first pair of toothed profiles MI of the first gear and the gears "R" of the reverse gear, first support bearings 4 are arranged to support the shafts 2, 3 with respect to the crankcase (not shown) of the gearbox 1.

At the opposite end (i.e. facing the pair of toothed profiles M6 defining the sixth gear) of the two shafts 2, 3, second support bearings 5 are arranged.

The gearbox 1 also has selection means active between the secondary shaft 3 and the second toothed profiles 31, 32, 33, 34, 35, 36 to make each second toothed profile 31, 32, 33, 34, 35 rotationally integral. , 36 with the secondary shaft 3.

In greater detail, the selection means comprise a first synchronizer 6 designed to rotationally constrain the second toothed profile 31 of the first gear Mi and the secondary shaft 3 to each other. The structure of the first synchronizer 6 is of a substantially known type. In other words, the first synchronizer 6 is slidably mounted on the secondary shaft 3 by means of a splined coupling which allows the translation of the first synchronizer 6 along the axis of rotation "X" of the secondary shaft 3 but which does not allow their reciprocal rotation. . The first synchronizer 6 can be stably associated with the second toothed profile 31 of the first gear Mi by meshing with suitable toothings so as to make the second toothed profile 31 of the first gear Mi rotationally integral with the secondary shaft 3 and therefore connect the primary shaft 2 to the secondary shaft 3 by means of the first pair of profiles M1 defining the first gear.

In accordance with an embodiment of the invention, the first synchronizer 6 is active, on the opposite side to the first pair Mi of toothed profiles of the first gear, also with the second pair M2 of toothed profiles defining the second gear. The first synchronizer 6 can therefore also be stably associated with the aforementioned second toothed profile 32 of the second gear M2 by engaging appropriate front toothing so as to connect the primary shaft 2 to the secondary shaft 3 by means of the second pair of toothed profiles M2 defining the second gear.

Preferably, the selection means further comprise a second synchronizer 7, also of a substantially known type, designed to engage reverse gear. The second synchronizer 7 is slidably mounted on the secondary shaft 3 by means of a splined coupling which allows the translation of the second synchronizer 7 along the rotation axis "X" of the secondary shaft 3 towards and away from the corresponding second toothed profile 50 of the reverse gear. The second synchronizer 7 can be stably associated with the aforementioned second toothed profile 50 of the reverse gear by engaging suitable front toothing so as to connect the primary shaft 2 to the secondary shaft 3 by means of the reverse gear "R".

The aforementioned synchronizers 6, 7 have a substantially known structure, in particular they engage with the respective second toothed profiles 31, 32, 50 by means of conical engagement surfaces which make a gradual engagement with the respective second toothed profiles 31, 32, 50 to achieve a gradual speed adjustment between the primary shaft 2 and the secondary shaft 3.

The aforementioned synchronizers 6, 7 can be moved axially, along the rotation axis of the secondary shaft 3, by means of known movement forks and therefore not illustrated.

Advantageously, the selection means also comprise two front engagement rings 10, 11 slidingly mounted on the secondary shaft 3, the first of which is arranged between the third pair of toothed profiles 33 defining the third gear M3 and the fourth pair of toothed profiles 34 defining the fourth gear M4, and the second of which arranged between the fifth pair of toothed profiles 35 defining the fifth gear M5 and the sixth pair of toothed profiles 36 defining the sixth gear M6. In other words, the first 10 of the two front engagement rings 10, 11 performs the engagement and disengagement of the third and fourth gear while the second front engagement ring 11 performs the engagement and disengagement of the fifth and sixth gear .

The two front engagement rings 10, 11 operate according to a substantially known principle by direct engagement of their front teeth 12 with respective front teeth 13 of the toothed profiles 33, 34, 35, 36 of the secondary shaft 3. The front engagement made by two front coupling rings 10, 11 is a coupling without synchronization devices. Each front engagement ring 10, 11 has the front teeth 12 on both sides to allow the engagement of two different gears M3, M4; M5, M6.

In all the illustrated embodiments, the pairs of toothed profiles M1, M2 defining the first two gears have helical teeth while the other pairs of toothed profiles M3, M4, M5, M6 have straight teeth.

Preferably, the reverse gears "R" also have helical teeth.

More generally, all the pairs of toothed profiles associated with a synchronizing device have helical teeth.

In accordance with an embodiment variant not shown, however, all the toothed profiles can have straight teeth.

Figure 3 shows a first embodiment of an actuator device 14 for controlling the gearbox described above.

The actuator device, of the "AMT" (automated manual transmission) type, comprises a pair of linear actuators 15, 16 of the hydraulic or electromechanical type, active along two transversal directions, preferably perpendicular to each other. A first 15 of the aforementioned linear actuators 15, 16 defines a selection movement, i.e. a movement adapted to select and move (by means of the forks not shown) one of the following selectors:

- first synchronizer 6 of the first / second gear; - second reverse gear synchronizer 7;

- first ring with front coupling 10;

- second ring with front coupling 11.

The selection movement therefore has, in the illustrated embodiment, four operating positions (R; M1-M2; M3-M4; M5-M6).

The second linear actuator 16 acts with a clutch movement to engage, in each of the four operating positions, one of the available gears (there are two gears available for all the operating positions of the first linear actuator 15 except in the case of reverse, which represents the only gear that can be engaged when the second synchronizer is selected 7).

The engagement movement therefore has, in the illustrated embodiment, two operating positions in the case of engagement of the forward gears (MI, M2, M3, M4, M5, M6) and one operating position in the case of engagement of the reverse gear (R).

In the embodiment illustrated in Figure 3, the gearbox 1 according to the present invention comprises an electronic control unit 17 which governs the stroke of the two linear actuators 15, 16. The electronic control unit 17 determines the stroke of each linear actuator 15, 16 as a function of commands expressed by the driver of the vehicle (for example by means of selection levers, buttons or other selection members).

Advantageously, the electronic control unit 17 determines, for the second linear actuator 16 responsible for the engagement movement, a variable stroke according to the current position assumed by the first linear actuator 15, that is to say according to the available gears. In other words, the electronic control unit 17 determines, for the second linear actuator 16, a variable stroke according to the selector on which the second linear actuator 16 acts, and in particular:

- the electronic control unit 17 sets, for the second linear actuator 16, a greater stroke in the case of operation of a synchronizer 6, 7 (therefore when the first linear actuator 15 has selected the first synchronizer 6 or the second synchronizer 7) ; - the electronic control unit 17 sets, for the second linear actuator 16, a shorter stroke in the case of operation of one of the aforementioned two front coupling rings 10, 11 (therefore when the first linear actuator 15 has selected one of the two rings front coupling 10, 11).

In other words, the stroke necessary for the aforementioned synchronizers 6, 7 to fully engage is greater than the stroke required for the front engagement rings 10, 11, and to take this into account the electronic control unit 17 is able to vary the stroke of the second actuator 16 depending on whether the latter has to act on one of the aforementioned synchronizers 6, 7 or on one of the aforementioned front engagement rings 10, 11.

In accordance with a different embodiment, the actuator device is of the sequential type and comprises a selection drum of the type illustrated in Figure 4 and indicated with reference 18.

The selection drum 18 has a first peripheral groove 19 and a second peripheral groove 20, side by side along an axis of rotation "Z" of the drum 18.

The first groove 19 is designed to house a pair of pins for moving the respective forks (not shown as they are of a substantially known type) for moving the synchronizers 6, 7, therefore responsible for engaging the first and second gears, as well as the reverse gear. The conformation of the first slot 19 is illustrated in Figure 5, which illustrates a view in development on a plane to highlight the angular position with respect to the "Z" axis of the various parts making up the first slot 19.

The second groove 20 is designed to house a further pair of pins for moving the respective forks (not shown as they are of a substantially known type) for moving the front engagement rings 10, 11, therefore responsible for engaging the gears between the third and sixth.

Each groove 19, 20 has a circular section 19a, 20a, that is to say annular in shape around the "Z" axis of the drum 18, and a zig-zag section 19b, 20b defining a cam for controlling the aforementioned pins (defining cam followers) of the forks in such a way that a rotation of the drum 18 around its axis "Z" causes a translation of the forks, preferably along the axis "Z" itself.

Advantageously, the zig-zag section 19b of the first groove 19 (illustrated with a continuous line in Figure 5) has an extension, away from the annular section 19a and along the "Z" axis of the drum 18, which is greater than the corresponding section a zig-zag 20b of the second groove 20 (illustrated with a hidden line in Figure 5). This greater extension has the purpose of producing a translation of a greater entity of the pivot of the respective selection forks in order to achieve a greater translation of the synchronizers 6, 7 compared to the front engagement rings 10, 11. This compensates for the greater stroke required to the synchronizers 6, 7 to make a complete engagement with respect to the front engagement rings 10, 11.

The two zigzag sections 19b, 20b can be angularly spaced around the "X" axis by an angle sufficient to allow the gears (six plus reverse) to engage correctly one at a time. Alternatively, the two zig-zag sections 19b, 20b can be arranged in the same angular position around the "X" axis and, in this case, the correct exclusive engagement of one gear at a time is delegated to an appropriate angular spacing of the pins of the selection forks inside the slots 19, 20.

The selection drum 18 also has a safety slot 21 arranged on the periphery of the selection drum 18 and extending along a partial angular development of the drum 18 itself (Figure 4). The safety slot 21 is able to be stably engaged by a fixed pin (not illustrated, not illustrated as it is substantially known) which allows the rotation of the selection drum 18 around the "Z" axis only for the angular extension defined by the slot safety 21. In this way the extreme positions assumed by the selection drum 18 during rotation around the "Z" axis are automatically defined.

An auxiliary peripheral slot 22 is also provided on the selection drum 18, also extending along a partial angular development of the selection drum 18. The auxiliary slot 22 can be engaged by an auxiliary pin (not illustrated, not illustrated as it is substantially known) normally pushed by a spring into the auxiliary slot 22. The auxiliary pin can be unlocked by pulling on it to extract the pin from the auxiliary slot 22 allowing the selection drum 18 to reach angular positions otherwise prevented by the auxiliary pin, which it can therefore function, for example, as a locking and unlocking element for reverse gear.

Alongside the aforementioned slots 19, 20, 21, 22, the selection drum 18 has a plurality of recesses 23, arranged according to a peripheral development around the "Z" axis in an equidistant position, and can be engaged by means of a spring pusher (not shown as substantially known) to stabilize the position of the selection drum 18 in correspondence with predefined angular positions of the recesses 23. In the illustrated embodiment, the recesses 23 are nine and are arranged in an angularly equidistant position of 40 ° from each other.

In accordance with an embodiment not shown, the selection drum 18 can have four distinct slots, one for engaging the reverse gear and the other three each for engaging two consecutive gears, therefore each slot in this circumstance is engaged by a single pin of a single selector fork. More generally, the selection drum has, in this latter embodiment, at least a first groove for engaging the reverse gear, a second groove for engaging the first and second gear and a third groove for engaging the third gear. and fourth gear (with possible fourth groove for the engagement of fifth and sixth gear), in which the first and second grooves are responsible for the movement of a synchronizer while the third groove is responsible for the movement of a ring with frontal couplings. Therefore, the first and second grooves are shaped in such a way as to achieve an axial displacement greater than the displacement made by the third groove.

The present invention achieves the proposed object, overcoming the drawbacks complained of in the known art.

The use of synchronizing devices associated with the lower gears (first and possibly second gear, as well as reverse) and the use of front clutches without synchronizers for the higher gears contribute, in cooperation with each other, to achieving a comfort suitable for use road and, at the same time, typical performance of "racing" vehicles.

The use of front clutches (further assisted by the use of respective straight-toothed gears) allows the shifting time to be reduced to very low levels (of the order of 20 milliseconds), suitable for high performance cars and in particular for racing .

At the same time, the provision of synchronizers to assist first gear and reverse (possibly assisted by helical toothing for first gear and / or reverse) allows a gear engagement, starting from neutral gear, very smooth if compared to a front engagement without synchronizer. Since with the clutch released, the primary shaft is still driven into rotation with a very low torque to facilitate the engagement of the first gear or reverse gear (with the primary and secondary shafts completely stopped, it may not be possible to engage in certain angular configurations of the shafts same), the clutch with synchronizer creates a smooth and progressive meshing which is perceived in a non-annoying way by the driver.

Moreover, the engagement of the first gear from neutral does not penalize the performance of the vehicle as this engagement usually takes place before the vehicle starts and, therefore, at a time not subject to the need for high performance.

Claims (13)

CLAIMS 1. Automotive gearbox, comprising: - a first shaft (2) having a plurality of first toothed profiles (21, 22, 23, 24, 25, 26); - a second shaft (3) having a plurality of second toothed profiles (31, 32, 33, 34, 35, 36) engaged simultaneously by meshing with the first toothed profiles (21, 22, 23, 24, 25, 26) of said first shaft (2) to define distinct pairs (MI, M2, M3, M4, M5, M6) of toothed profiles having different transmission ratios and included between a lower gear, or first gear (MI), and a lower gear high (M6)? - selection means (6, 7, 10, 11), active on a part of said first (21, 22, 23, 24, 25, 26) and / or second (31, 32, 33, 34, 35, 36 ) toothed profiles to rotationally connect said first and said second shaft (2, 3) to each other by means of one of said pairs (MI, M2, M3, M4, M5, M6) of toothed profiles in such a way as to select a desired gear; characterized in that said selection means (6, 7, 10, 11) comprise at least a first synchronizer (6), associated with the pair of toothed profiles (Mi) defining the first gear, and at least one selector with front coupling (10; 11) without synchronizer, associated with at least one of the remaining pairs of toothed wheels (M3, M4, M5, M6) defining the highest gears. 2. Gearbox according to claim 1, further comprising at least one group of gears (R) defining the reverse gear, wherein said selection means (6, 7, 10, 11) comprise at least a second synchronizer (7) associated with said group of gears (R) defining the reverse gear. Gearbox according to claim 2, wherein said first synchronizer (6) is also active on a second pair (M2) of toothed profiles defining the second gear to rotationally connect said first and said second shaft (2, 3 ) by means of said second pair of toothed profiles (M2). 4. Gearbox according to any one of the preceding claims, wherein at least one of the toothed profiles (21, 22, 31, 32) associated with a synchronizer (6, 7) has external helical toothing while the other toothed profiles (23, 24 , 25, 26, 33, 34, 35, 36), associated with a frontal coupling selector (10; 11) without synchronizer, have external teeth with straight teeth. Gearbox according to any one of claims 1 to 3, wherein all said first (21, 22, 23, 24, 25, 26) and second (31, 32, 33, 34, 35, 36) profiles toothed are straight-toothed. 6. Gearbox according to any one of the preceding claims, further comprising an actuator device (14) active on said selection means (6, 7, 10, 11) and controllable by a user to engage the gear selected by the user, said gearbox (1) comprising an electronic unit (17) for controlling said actuator device (14), said electronic control unit (17) being adapted to set a forward / return stroke of said first and / or second synchronizer (6; 7) different, and preferably greater, with respect to the forward / return stroke of said frontal clutch selector (10; 11). 7. Gearbox according to claim 6, wherein said actuator device (14) comprises two linear actuators (15, 16), a first of which (15) is designed to select one of said selection means (6, 7, 10, 11 ) according to a selection movement, and the second (16) designed to control an engagement movement of the selection means (6, 7, 10, 11), preferably perpendicular to said selection movement; said electronic control unit (17) being able to impart to said second linear actuator (16) a stroke which varies according to the gear to be engaged, preferably said electronic control unit (17) being able to impart to said second linear actuator (16 ) a greater stroke in the case of insertion of the first gear (MI), associated with said first synchronizer (6), compared to the case of insertion of a higher gear (M3, M4, M5, M6) associated with said front clutch selector ( 10; 11). Gearbox according to claim 6 or 7, wherein said actuator device (14) is an H-type automated actuator. 9. Gearbox according to any one of the preceding claims 1 to 5, further comprising a sequential actuator active on said selection means (6, 7, 10, 11) and controllable by a user to engage the gear selected by the user , said sequential actuator comprising a selection drum (18) active on said selection means (6, 7, 10, 11) and shaped in such a way as to set a forward / return stroke of said first and / or second synchronizer (6 , 7) different, and preferably greater, with respect to the forward / return stroke of said frontal clutch selector (10; 11). Gearbox according to claim 9, wherein said selection drum (18) has at least a first peripheral slot (19) for controlling said first and / or second synchronizer (6, 7) by means of a first cam system - cam follower, and a second peripheral slot (20) for controlling said frontal coupling selector (10, 11) by means of a second cam-follower system; said first peripheral groove (19) and said second peripheral groove (20) being shaped in such a way that a rotation of said selection drum (18) around its own axis (Z) determines a displacement of said first and / or second synchronizer ( 6, 7) along said axis (Z) which is different, and preferably greater, than a displacement along said axis (Z) of said front clutch selector (10, 11). 11. Gearbox according to claim 10, wherein each of said first and second grooves (19, 20) of the selection drum (18) has a predominantly annular shaped portion (19a, 20a) extending around the axis of rotation (Z) of the selection drum (18) and has at least one zig-zag section (19b, 20b) adapted to generate the movement of said synchronizer (6, 7) or of said frontal coupling selector (10, 11) forward and backward along said axis of rotation (Z) of the selection drum (18); the zig-zag portion (19b) of said first peripheral slot (19) having a greater extension along the rotation axis (Z) of the selection drum (18) than the zig-zag portion (20b) of said second peripheral cavity (20). Gearbox according to any one of the preceding claims, wherein said first shaft (2) is a primary shaft connectable to a power take-off of an internal combustion engine and in which said second shaft (3) is a secondary shaft connectable to a power output, preferably a differential connected to the wheels of a vehicle; said first toothed profiles (21, 22, 23, 24, 25, 26) being integral with the primary shaft while said second toothed profiles (31, 32, 33, 34, 35, 36) being mounted idle on said secondary shaft and being made integral in an alternating manner to the secondary shaft by means of said selection means (6, 7, 10, 11). 13. Road vehicle, in particular high-performance, comprising a gearbox (1) according to any one of the preceding claims.