Servo-assisted gearshift control device for a motor-vehicle dual-clutch transmission

The device comprises four shift forks, each slidable among a first engagement position, a second engagement position and an intermediate neutral position between the two engagement positions, and an operating unit comprising four double-acting hydraulic actuators identical to each other and arranged to control each the displacement of a respective shift fork among the two engagement positions and the neutral position. The operating unit further comprises a support plate having holes for fixing to the gear case, and an actuator block accommodating the hydraulic actuators. The support plate and the actuator block are integrated to form a single body. In the assembled condition of the operating unit on the gear case, the actuator block is disposed on the side of the support plate facing towards the inside of the gear case.

BACKGROUND OF THE INVENTION

The present invention relates in general to a motor-vehicle dual-clutch transmission with six or seven forward gears and reverse gear, and more specifically to a servo-assisted gearshift control device for a transmission of this type.

A gearshift control device for a robotized gearbox, in particular for a gearbox with six forward gears, is known from European Patent EP-B-1 216 371 and comprises four shift forks, each of which is slidably mounted along a respective stationary rod fixed to the gear case so as be alternatively movable to first and second engagement positions, each corresponding to the engagement of a respective gear, eight single-acting hydraulic actuators associated in pairs to each fork to control the movement thereof to the first or second engagement positions, and a hydraulic control circuit for controlling the eight hydraulic actuators independently of each other. More particularly, the two hydraulic actuators associated to each shift fork are arranged on opposite sides with respect to a nose of the fork which extends perpendicularly to the corresponding rod and act on that nose to move the fork to the first or second engagement positions.

This known gearshift control device has the advantage of allowing to control the hydraulic actuators independently of each other, but it has however the shortcoming of requiring a great number of components, since two hydraulic actuators are provided for each shift fork.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a servo-assisted gearshift control device for a motor-vehicle dual-clutch transmission with six or seven forward gears and reverse gear, which has a smaller number of components than the prior art, which makes it possible to carry out in “power-shift” mode and in non-sequential mode all the multiple gear changes allowed by the transmission architecture, which can be used as such when converting a dual-clutch transmission into a single-clutch robotized transmission without requiring changes either to the gear case or to the gearshift forks, and which further allows to maintain the same gear case and the same gearshift forks when converting a motor-vehicle dual-clutch transmission into a single-clutch manual transmission.

This and other objects are fully achieved according to the invention by virtue of a servo-assisted control device for a motor-vehicle dual-clutch transmission as defined in independent claim1.

Further advantageous characteristics of the invention are set forth in the dependent claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first toFIGS. 1 and 2, a motor-vehicle dual-clutch transmission with six or seven forward gears and reverse gear is generally indicated10and comprises a clutch unit (not shown) housed in a casing12, and a gearbox14(which can be partially seen inFIG. 2) housed in a gear case16. The gearbox14includes, in per-se-known manner, two coaxial input shafts (not shown) and two output shafts (also not shown) arranged parallel to the two input shafts and carrying a plurality of idle gear wheels (not shown) which can be coupled for rotation each with the respective output shaft by means of four engagement sliding sleeves (also not shown), three of which are always associated to two gears while the remainder is associated to one gear only or to two gears depending on the gearbox having six or seven forward gears, respectively.

The displacement of the engagement sliding sleeves for the engagement of the different gears of the gearbox is controlled by a servo-assisted gearshift control device, generally indicated18inFIG. 1. The control device18basically includes four shift forks denoted by the reference numerals20,22,24and26, respectively, and an operating unit28comprising four double-acting hydraulic actuators, identical to each other, denoted by the reference numerals30,32,34and36, respectively. The actuator30is arranged to control the displacement of the shift fork20, the actuator32is arranged to control the displacement of the shift fork22, the actuator34is arranged to control the displacement of the shift fork24and the actuator36is arranged to control the displacement of the shift fork26. In the illustrated embodiment, the shift forks are mounted in pairs on two stationary rods38and40of the gearbox (which can be better seen inFIG. 5) orientated parallel to the output shafts. More specifically, the two shift forks20and22are slidably mounted on the rod38, while the other two shift forks24and26are slidably mounted on the rod40. The shift forks20,22,24and26illustrated in the figures are advantageously formed according to the teaching of the non-published European Patent Application N. 06425148.1 in the Applicant's name, that is to say, with identical bodies suitably shaped to allow a partially overlapping arrangement of each pair of shift forks mounted on the same rod. It is however clear that the shift forks may have any other configuration.

The operating unit28of the control device is shown in detail inFIG. 3. With reference to that figure, the operating unit28includes a support plate42and an actuator block44, advantageously integrated to form a single body. The support plate42has holes46which can be brought into alignment with corresponding holes48provided in the gear case16(FIG. 2) for fixing the operating unit28to the gear case16. The actuator block44accommodates the four hydraulic actuators30,32,34and36, each of which is basically constituted by an elongated plunger50forming at its opposite ends first and second head portions52and54, which are slidably and fluid-tightly arranged in first and second pressure chambers56and58, respectively, provided in the actuator block44. In its intermediate region between the head portions52and54, the plunger50of each hydraulic actuator has a recess60on its cylindrical side surface and, in the diametrically opposite position, three equally-spaced positioning indentations62,64and66. For ease of illustration, reference numerals50to66are represented inFIG. 3only in connection with the hydraulic actuator32. In the recess60of the plunger50of each hydraulic actuator30-36engages a nose68of the shift fork20-26associated to that actuator, in such a manner that the translation movement of each hydraulic actuator is transmitted to the associated shift fork. The recesses60of the plungers50of the four hydraulic actuators30,32,34and36are arranged, in the neutral middle position, in a single selection plane corresponding to the selection plane of the gearshift lever in the manual version of the gearbox.

A hydraulic control circuit (not shown) is arranged to supply pressurised fluid to the pressure chambers56and58of the four hydraulic actuators30,32,34and36or to vent these latter so as to bring about every time the disengagement of the engaged gear or the engagement of a different gear depending on the commands directly imparted by the driver or by an electronic control unit of the transmission. By supplying pressurised fluid to the chamber56of a hydraulic actuator and venting the other chamber58the respective plunger50is caused to move to the right (relative to the observer ofFIG. 3) in a first engagement position, whereas by supplying pressurised fluid to the chamber58and venting the chamber56the plunger50is caused to move to the left in a second engagement position. A neutral middle position corresponding to the idling condition is further provided for each plunger50.

With reference again toFIG. 3, a snap-locking device is associated to the plunger50of each hydraulic actuator and is provided with a position-marking ball70arranged to engage alternatively in one of the three positioning indentations62,64and66in order to hold the plunger50in the neutral middle position (middle indentation64) or in one of the two engagement positions (side indentations62and66).

Moreover, each hydraulic actuator integrates a position sensor (not shown) adapted to provide an electronic control unit (also not shown) with a position signal for the closed-loop position control of the actuator itself.

The upper side (facing towards the outside of the gearbox) of the support plate42of the operating unit28can be seen in the perspective view ofFIG. 4, on which side a labyrinth72is formed in order to provide the connections between the hydraulic control circuit and the pressure chambers56and58of the actuators30,32,34and36, which chambers are arranged on the opposite side of the support plate42, i.e. towards the inside of the gearbox.

In view of the foregoing description, the advantages offered by the servo-assisted gearshift control device according to the present invention becomes apparent.

First of all, the use of only four hydraulic actuators allows to minimize the number of components of the control device.

Secondly, the hydraulic actuators are identical to each other and are controllable independently of each other, which allows to bring about non-sequential gear changes in “power-shift” mode, i.e. with simultaneous engagement of two gears.

Moreover, the hydraulic actuators of the operating unit are arranged on the side of the support plate facing towards the inside of the gear case, which allows to minimize the outer overall size of the operating unit. hindrance

In addition, since in the neutral position the recesses of the plungers of the hydraulic actuators, in which the noses of the shift forks engage, are arranged in a single selection plane and the support plate of the operating unit can be fixed to the same attachment portion as the one provided on the gear case in the manual version of the gearbox, the operating unit of the servo-assisted gearshift control device according to the invention can be used as such to convert a motor-vehicle dual-clutch transmission into the corresponding robotized single-clutch version and also allows to maintain the same gear case and the same shift forks when converting a motor-vehicle dual-clutch transmission into a manual single-clutch transmission. It is not therefore necessary to modify either the gear case or the shift forks with the respective noses in order to convert the dual-clutch version into the single-clutch version. Since the dual- and single-clutch versions can share some of the components of the servo-assisted gearshift control device, significant cost-savings are obviously achieved.

Finally, since a snap-locking device adapted to hold the respective plunger in the neutral middle position or in one of the two engagement positions is associated to each hydraulic actuator, it is possible to avoid additional machining operations and additional parts on the gear case and on the shift forks.

Naturally, the principle of the invention remaining unchanged, the embodiments and constructional details may vary widely with respect to those described and illustrated purely by way of non-limiting example.

For example, even though the description refers to shift forks slidably mounted on stationary rods, the invention is also applicable to a servo-assisted gearshift control device having shift forks secured to slidable support rods.