VEHICLES"

TECHNICAL FIELD

The present invention relates to a dual clutch transmission architecture, in particular a dual clutch transmission architecture for an off road vehicle such as an agricultural vehicle and to a related method for controlling the gear shifting of such dual clutch transmission.

BACKGROUND OF THE INVENTION

Transmissions for off road vehicles such as agricultural vehicles offer different configuration, for instance:

• manual shifted transmissions, in which all gears of the transmissions are engaged directly by the driver through lever mechanisms which command clutches, synchronizers and dog clutches to select the gear;

• semi-powershift transmission, in which some gears are engaged, manually or automatically, thanks to servo actuated mechanisms in powershift mode, i.e. by swapping the torque by a couple of clutches, and in which other gears are actuated by lever mechanisms which commands clutches, synchronizers and dog clutches to select the gear or by a servo-actuated mechanism which is not in powershift mode, i.e. which uses a single clutch and, when such clutch is opened, torque cannot pass through the transmission; and

• full powershift transmission, in which all gears of the transmission are engaged through servo actuated mechanism in powershift mode.

An important request that must be satisfied in modern mechanical transmission for agricultural vehicles is to have high efficiency across the full ground speed range, in order to improve the vehicle fuel consumption. In this respect a large use of wet clutches to build the semi-powershift or the full-powershi f t transmissions , generates more power losses inside the transmission when compared to the use of synchroni zers and dog-clutches and, as consequence , a penalty of ef ficiency as consequence .

For this reason, in the art , the dual-clutch transmis sion, DCT , architecture is considered the most valuable layout for powershi ft transmissions in order to satisfy all the previous demands :

• it provides an high number of speed ratios with a mechanism that allow for a comfortable powershi ft (by swapping one couple of clutches ) ; and

• it performs high ef ficiency, because a powershi ft layout is provided by only few couples of wet clutches accompanied by many synchroni zers and dog-clutches .

Because of these advantages , recently DCT architecture has been applied in the field of the transmissions for agricultural vehicles . An example of such DCT architecture is disclosed in patent document WO2019091953 Al .

However such known architectures used big wet clutches that dissipate a considerable amount of energy, in particular for allowing shi ft between range gears .

Moreover, during shi fting between gear ratio or range gear ratio , the inertia of the carried transmission elements is considerable . Therefore resistant torque is high and the fuel consumption is not neglectable during shi fting .

In conclusion, the need is felt to improve existing DCT architecture for agricultural vehicle in order to improve their performances in all its working speed ranges and to improve the comfort during all gears shi fting .

Aim of the present invention is to satis fy the above mentioned needs in a cost-ef fective and optimi zed way .

SUMMARY OF THE INVENTION

The aforementioned aim is reached by an architecture for a dual clutch transmission and a related control method as claimed in the appended set of claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawings wherein:

• Figure 1 is a schematic representation of a dual clutch transmission architecture according to the present invention;

• Figures 2 to 5 are schematic representations of the dual clutch transmission architecture of figure 1 in different operational conditions; and

• Figures 6A, 6B are tables indicating the activation of elements of the transmission architecture according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 discloses a dual clutch transmission 1, in the following "transmission", for an off road vehicle, such as an agricultural vehicle, e.g. a tractor (not illustrated) , comprising an engine input shaft 2, operatively connected to a torque source (not shown) , such as an internal combustion engine of the work vehicle, and an output shaft 3, which can be coupled to a drive axle of the off road vehicle.

The transmission 1 essentially comprises, operatively connected in series one to the other between input shaft 2 and output shaft 3, an input stage A, a gear ratio stage B and a range gear ratio stage C.

The input stage A may be realized in different manner to provide torque to a first main clutch 5, hereinafter "forward clutch", and torque in reversed direction to a second main clutch 6, hereinafter "rearward clutch", both carried by the engine input shaft 2 .

In disclosed exemplarily embodiment , input stage A comprises a gearing 4 compri sing a first wheel 4 ' configured to mesh with a first wheel 4 a rotatably fixed to the forward clutch 5 and to a third wheel 4c configured to engage a second wheel 4b rotatably fixed to the rearward clutch 6 .

As per se known, the forward clutch 5 couples the engine input shaft 2 to the output shaft 3 in order to allow a forward motion of the work vehicle while the rearward clutch 6 couples the engine input shaft 2 to the output shaft 3 in order to allow a rearward motion of the work vehicle . In the disclosed exemplarily embodiment , such occurrence is given by the peculiar construction of gearing 4 as described above .

Transmission 1 further comprise a first clutch 7 , hereinafter "even clutch" , and a second clutch 8 , hereinafter "odd clutch" . The even clutch 7 is configured to couple a first auxiliary shaft 11 , hereinafter "even shaft" , with the forward clutch 5 . The odd clutch 8 is configured to couple a first auxiliary shaft 12 , hereinafter "odd shaft" , with the rearward clutch 6 .

Advantageously, the forward clutch 5 is coupled to the even clutch 7 by a first housing 10 ' and the rearward clutch 6 is coupled to the odd clutch 8 by a second housing 10 ' ’ . The first and the second housing 10 ' , 10 ' ’ are coupled together by an intermediate gear 9 , e . g . carried in a rotatable free manner by engine input shaft 2 .

Preferably the intermediate gear 9 is configured to be coupled to the first housing 10 ' through a first gear ratio and to be coupled to the second housing 10 ' ’ through a second gear ratio . The first and the second gear ratio are preferably di f ferent .

In view of above , thanks to the coupling of the housings 10 ' , 10 ' ’ with the intermediate gear 9 , the even shaft 11 may be coupled to the rearward clutch 6 and the odd shaft 12 may be coupled to the forward clutch 5 according to their actuation .

The even shaft 11 and the odd shaft 12 each comprise a plurality of selection elements 17 e.g. synchronizer or dug clutches, fixedly carried by the respective shaft 11, 12 and therefore rotate together with to these latter. Obviously selection elements 17 may comprise other equivalent connection means such as joint clutches.

The gear ratio stage B comprises a plurality of gears 14, 15 accommodated on respectively even or odd shafts 11, 12 and having a different size one with respect to the other and that are supported in a rotatable free manner the respective shaft 11, 12, e.g. by means of bearings, so that they are not forced to rotate to the same speed of the respective shaft 11, 12 when the engaging dog clutch 17 is in their neutral position.

Preferably the even shaft 11 may comprise four gears 14, namely a first gear 14 ¹ having the biggest diameter, a fourth gear 14 ^IV having the smallest diameter and a second and third gears 14 ¹¹ , 14 ¹¹¹ having respective diameters comprised between the ones of first and the fourth gears 14 ¹ , 14 ^IV .

Similarly, the odd shaft 12 may comprise four gears 15, namely a first gear 15 ¹ having the biggest diameter, a fourth gear 15 ^IV having the smallest diameter and a second and third gears 15 ¹¹ , 15 ¹¹¹ having respective diameters comprised between the ones of first and the fourth gears 15 ¹ , 15 ^IV .

Advantageously the gear 14 ¹ has the same diameter of gear 15 ¹ , gear 14 ¹¹ has the same diameter of gear 15 ¹¹ , gear 14 ¹¹¹ has the same diameter of gear 15 ¹¹¹ and gear 14 ^IV has the same diameter of gear 15 ^IV .

The gears of gears sets 14, 15, when selected, represent the different speed ratios of the transmission ; namely first speed ratio selecting gear 15 ¹ , second speed ratio selecting gear 14 ¹ , third speed ratio selecting gear 15 ¹¹ , fourth speed ratio selecting gear 14 ¹¹ , fifth speed ratio selecting gear 15 ¹¹¹ , sixth speed ratio selecting gear 14 ¹¹¹ , seventh speed ratio selecting gear 15 ^IV or eighth speed ratio selecting gear 14 ^IV .

As said above , gears of the gears sets 14 , 15 may be selected by a dog clutch 17 configured to couple the shaft with the chosen gear . Preferably the even shaft 11 may comprise two dog clutches 17 interposed respectively between the gear 14 ¹ - 14 ¹¹ and 14 ¹¹¹ - 14 ^IV . Similarly the odd shaft 12 may comprise two dog clutches 17 interposed respectively between the gear 15 ¹ - 15 ¹¹ and 15 ¹¹¹ - 15 ^IV .

The transmission 1 further comprises an intermediate shaft 20 configured to engage with gear wheels 14 , 15 and with gear range stage C . In particular, the intermediate shaft 20 is configured to carry a number of wheels 21 corresponding to the wheels of the gear ratio stage B .

It is noticed, even i f visually schemati zed, that the intermediate shaft 20 is preferably arranged vertically adj acent , i . e . over/below, the even and odd shafts 11 , 12 in order to provide a compact arrangement of the transmission 1 .

Accordingly, intermediate shaft carries a first wheel 21 ¹ , a second wheel 21 ¹¹ , a third wheel 21 ¹¹¹ and a fourth wheel 21 ^IV .

The gear range stage C is configured to engage a number of the wheels 21 carried by intermediate shaft 20 to the output shaft 3 by choosing among a plurality of gear ratios , defined by respective range gears 22 , which are multiplied by the gear ratio of gear ratio stage B .

In the disclosed exemplarily embodiment , the gear range stage G comprises a first range gear 22 ¹ called " low" range , a second range gear 22 ¹¹ "medium" range , and a third range gear 22 ¹¹¹ called " fast" ; the three range gears have di f ferent dimensions . In this way, the transmission provides twenty four possible gear ratios , due to the eight gear ratios repeated over the three range gear ratios . According to the invention, the gear ratio wheels 22 are al l carried in a rotatably free manner on a support shaft 23 and selectively engageable in rotation to this latter thanks to selection means 24 preferably design are semisynchroni zers .

Consequently, some of the wheels 21 carried by intermediate shaft 20 are carried in in a rotatably free manner on this latter and selectively engageable in rotation to this latter thanks to the aforementioned selection means 24 .

The selection means 24 are controlled in order to al low a power shi ft change during gear shi fting between gear wheels 14 , 15 and/or range gear wheels 22 as detailed below .

In particular, the support shaft 23 is coupled to output shaft 3 , e . g . via a gearing 30 compri sing a first gear 30 ' rigidly carried to the support shaft 23 and a second gear 30 ' ’ rigidly carried by output shaft 3 .

In the disclosed embodiment , a pair of wheels 21 are carried in a rotatably free manner with respect to the intermediate shaft 20 and carrying respective range gears 22 , in particular first wheel 21 ¹ carries first range gear 22 ¹ and fourth wheel 21 ^IV carries third range gear 22 ¹¹¹ .

One of the wheel 21 is instead carried in a fixed manner with respect to intermediate shaft 20 and carries one range gear 22 ; in particular, second wheel 21 ¹ carries second range gear 22 ¹¹ .

The exceeding wheels of wheels 21 are preferably rotationally engaged with one of the wheels 21 carried in free manner by intermediate shaft 20 . In particular, in the disclosed arrangement , third wheel 21 ¹¹¹ is rotationally fixed with respect to fourth wheel 21 ^IV , i . e . they are carried by the same support that freely rotates on intermediate shaft 20 .

Preferably, according to the shown embodiment , the wheels 21 are operatively connected to range gear wheels 22 via idler wheels 25 . In particular, according to the above , each gear wheel 21 coupler to range gear wheel 22 is coupled by a respective idler wheel 25 .

Preferably, each idler wheel 25 compri ses a first wheel 25 ' conf igured to engage with a respective gear wheel 21 and a second wheel 25 ' ’ configured to engage with a respective range gear wheel 22 .

The above described clutches 5 , 6 , 7 , 8 , selection elements 17 and selection means 24 can be selected by respective actuators (not shown) that are controlled by an electronic control unit (not shown) . The electronic control unit controls said clutches or said electronic motors by sending control electric signals directed to the respective clutches or motors to be controlled .

Electronic control unit can be either the ECU of the vehicle or driveline ECU of the vehicle . The electronic unit is configured to control the above cited elements of the transmission 1 as per direct input command of the user of the vehicle or in automatic way following the shi ft control logic deployed into a speci fic software code , which can be memori zed into the electronic unit .

The operation of the transmission 1 according to the invention are described in the following .

In particular, the operation is described making the assumption that the transmission 1 is providing torque to output shaft 3 in the " first slow" gear ratio .

In a first example of operation, shown in figure 2 , it is represented a standard operation in " f irst slow" . In such configuration, the torque provided by input stage A passes through forward clutch 5 , odd clutch 8 to odd shaft 12 . First gear wheel 15 ¹ is engaged via selection elements 17 and therefore transmits torque to the first wheel 21 ¹ that is engaged via selection means 24 to the intermediate shaft 20 . On the opposite side , selection means 24 couple the fourth wheel 21 ^IV to the intermediate shaft 20 and torque is transmitted, via idle wheel 25 , towards third range gear wheel 22 ¹¹¹ that is coupled to the support shaft 23 via selection means 24 . Then, thanks to gearing 25 the torque is provided to the output shaft 3 .

In a second example of operation, shown in figures 3 to 5 , it is shown a gearshi ft operation from, for instance , first slow to second slow . In the initial condition, the torque flows as above described making reference to figure 2 . Then, the selection element 17 associated to wheel 14 ¹ connects this latter so that the even shaft 11 is make rotate ( figure 3 ) . Accordingly, the clutches 7 , 8 are swapped, as per se known, so that the torque passes from even clutch 7 to wheel 14 ¹ and then downstream to range stage C ( figure 4 ) . When swapping is complete , than the wheel 15 ¹ is disengaged by the associated selection element 17 .

In a third example of operation, not shown in figures , it is described an upshi ft between to eight slow to first medium . In the initial condition, the torque flows from even shaft 11 / wheel 14 ^IV to range stage C passing via gear 21 ^IV that free to rotate and makes rotate via idler gear 25 the wheel 22 ¹¹¹ that is coupled to support shaft 23 .

Then, the wheels 22 ¹¹ and 14 ¹ are engaged via selection means 24/element 17 thereby allowing odd shaft 12 and intermediate shaft 20 rotate . Accordingly, clutches 8 , 7 are swapped and torque passes through the new path defined by wheels 14 ¹ and range gear 22 ¹¹ via idler gear 25. When swapping is complete, wheels 15 ^IV and 22 ¹¹¹ are disengage from the respective shafts 11 , 23.

The vehicle may be provided by a dedicated control software code in the ECU of the transmission configured to recognize signals from sensors installed on the vehicle, e . g . the torque demand at the output shaft 3 and the speed of the engine input shaft 2 , and automatically define the gearshift without any user intervention .

The invention also relates to a method for operating a transmission 1 as described above for shifting from a gear 14 , 15 of a gear ratio stage B in combination a gear 22 of range gear stage C to a further gear 14 , 15 of the gear ratio stage B in combination the gear 22 of range gear stage C :

• receiving an input for shifting from an initial gear 14 , 15 of the gear ratio stage B in combination with an initial gear 22 of range gear stage C to a further gear 14 , 15 of the gear ratio stage B in combination with the same and/or a further gear 22 of the range gear stage C;

• coupling the further gear 14 , 15 with the respective shaft 11 , 12 if the same range gear 22 is requested otherwise coupling the further gear 14 , 15 with the respective shaft 11 , 12 and the further gear 22 to the support shaft 23 ;

• swapping even and odd clutches 7 , 8 thereby allowing torque to flow from the clutch 7 , 8 associated to the initial gear 14, 15 to the clutch 7 , 8 associated to the further gear 14 , 15;

• uncoupling the initial gear 14 , 15 from the respective shaft

11 , 12 if the same range gear 22 is requested otherwise uncoupling the initial gear 14 , 15 from the respective shaft

11 , 12 and the initial gear 22 from the support shaft 23.

In view of the foregoing, the advantages of a dual clutch transmission 1 according to the invention and the related method are apparent .

The transmission architecture 1 according to the invention increases the efficiency of the system. Indeed, the power losses due to the presence of clutches to allow power-shift between range gears is avoided.

Furthermore, the use of semi-synchronizers as selection means 24 provides a very compact and economic arrangement for coupling or uncoupling the support shaft gear wheels and range gear wheels .

It is furthermore noticed, that the range gear wheels may be designed smaller since the inertia carried by the range gear wheel is smaller with respect to known transmission architecture . Indeed the torque is split into different paths thanks to the specific arrangement of wheels on the intermediate shaft 20 and of the range wheels on the support shaft 23.

Since the clutch in range gears is not present and since the range gear wheels are smaller, the overall dimensions of the transmission 1 is more compact with respect to known architectures .

It is clear that modifications can be applied to the described transmission 1 which do not extend beyond the scope of protection defined by the claims .

For example, the number and typology of gears of gear ratio, range and idler gears may be varied according to vehicle necessity.

Further, the transmission may comprise different elements with respect to the described one, e . g . the number and/or typologies of clutches , gears and dog clutches may be varied. Accordingly, input stage A may be realized in any convenient manner .

Moreover, the control and typology of selection elements/means 17 , 24 may be implemented with any typology of control, e . g . a hydraulic, electric or pneumatic in alternative or in combinations .