Method of controlling a shift to a lower gear with the accelerator pedal released

Abstract

A method for controlling a downshift in a powertrain (6) having a dual clutch servo-assisted transmission (7) in the case of releasing the accelerator pedal (22), providing the following steps: opening the disengaging clutch (16A) at a first moment (t1); closing the engaging clutch (16B) at the first moment (t1); fully opening the disengaging clutch (16A) at a second moment by a first linear ramp; synchronizing the rotational speed (ω E ) of the internal combustion engine (4) with the rotational speed (ω B ) of the engaging clutch (16B) between the second moment and a third moment (t4); closing the engaging clutch (16B) from a fourth moment (t2) by a second linear ramp, the fourth moment being before or coinciding with the second moment; fully closing the engaging clutch (16B) at a fifth moment (t3), the fifth moment coinciding with or being after the second moment; and starting the internal combustion engine (4) between the fourth moment (t2) and the third moment (t4) to generate a torque (T E ).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000017528, filed on September 30, 2019, the disclosure of which is incorporated herein in its entirety by reference. Technical Field

[0003] The present invention relates to a method of controlling a shift to a lower gear (ie a shift where the subsequent or incoming gear is lower than the previous or outgoing gear) with the accelerator pedal released in a powertrain having a dual clutch servo-assisted gearbox. Background Art

[0004] The powertrain with a dual-clutch servo-assisted gearbox comprises: a pair of main shafts, which are coaxial, independent of each other and inserted into each other; two coaxial clutches, each of which is designed to connect the corresponding main shaft to the drive shaft of the internal combustion engine; and at least one secondary shaft, which transmits movement to the drive wheels and can be coupled to the main shaft by a corresponding gear train, each defining a gear.

[0005] During a gear shift, the current gear couples the countershaft to one main shaft, while the subsequent gear couples the countershaft to the other main shaft; as a result, the gear shift is performed by alternating the two clutches, ie by opening the clutch associated with the current gear and simultaneously closing the clutch associated with the subsequent gear.

[0006] Currently, a change to a lower gear with the accelerator pedal released requires opening the outgoing clutch (i.e. the clutch associated with the previous gear), increasing the speed of the internal combustion engine by turning it on (i.e. by causing it to generate a positive torque that determines the acceleration of the drive shaft), and finally closing the incoming clutch (i.e. the clutch associated with the subsequent gear). In this way, a synchronization (increase) between the speed of the internal combustion engine and the speed imparted by the subsequent gear (i.e. by the incoming clutch) is produced when both clutches are open, causing the internal combustion engine to generate a positive torque (however, during the remaining time, the internal combustion engine is off and operates as an engine brake, generating a resistance, i.e. a braking torque).

[0007] This mode of execution of the change to a lower gear with the accelerator pedal released is "fun" (i.e. appreciated by the driver because it provides a feeling of sporty driving also due to the sound produced by the internal combustion engine during its own speed synchronization), but on the other hand it is not very comfortable because, due to the interruption of the torque transmission to the drive wheels, an uncomfortable longitudinal acceleration profile of the road vehicle is determined: in fact, the longitudinal acceleration of the road vehicle suddenly changes from the initial deceleration to zero acceleration in order to then quickly return to a final deceleration that is greater than before (the resulting feeling is of a rapid pull backwards and then forwards, which is not very comfortable overall).

[0008] Furthermore, this shift execution mode generates a certain metallic noise (usually perceptible to the driver, especially at low rpm) due to the simultaneous opening of both clutches determining the unloading of the driveline with subsequent recovery of play when the incoming clutch closes.

[0009] Patent application EP3139070A1 describes a method for controlling a change to a lower gear while releasing the accelerator pedal in a powertrain having a dual-clutch servo-assisted gearbox. The method comprises the following steps: at a first moment, opening the outgoing clutch associated with the current gear and closing the incoming clutch associated with the subsequent gear; at a second moment, fully opening the outgoing clutch and fully closing the incoming clutch; between the second moment and a third moment, synchronizing the speed of the internal combustion engine with the speed of the incoming clutch, i.e. with the speed imparted by the transmission ratio of the subsequent gear; and between the second moment and the third moment, controlling the incoming clutch so that the incoming clutch temporarily transmits a torque greater than the braking torque of the internal combustion engine, thereby using the kinetic energy possessed by the road vehicle to accelerate the internal combustion engine. Summary of the invention

[0010] The object of the present invention is to provide a method for controlling the change to a lower gear when the accelerator pedal is released in a powertrain having a dual-clutch servo-assisted gearbox, which method does not have the above-mentioned disadvantages and is easy and economical to implement.

[0011] According to the present invention, a method for controlling a shift to a lower gear when an accelerator pedal is released in a power transmission system having a dual-clutch servo-assisted transmission is provided, thereby shifting a current gear to a subsequent gear lower than the current gear. The power transmission system includes a dual-clutch servo-assisted transmission having: two main shafts; at least one secondary shaft connected to a driving wheel; and two clutches, each of which is interposed between a driving shaft of an internal combustion engine and a corresponding main shaft. The control method includes the following steps:

[0012] disengaging an off-going clutch associated with the current gear at a first moment;

[0013] closing an incoming clutch associated with a subsequent gear at a first moment;

[0014] Fully opening the off-going clutch at a second time by means of a first linear ramp;

[0015] closing the incoming clutch via a second linear ramp starting from a third moment in time, the third moment in time being before or coinciding with the second moment in time;

[0016] between the second and fourth moments, synchronizing the speed of the internal combustion engine with the speed of the incoming clutch, ie with the speed imparted by the transmission ratio of the subsequent gear; and

[0017] The incoming clutch is fully engaged at a fifth time instant, which coincides with the second time instant or is after the second time instant.

[0018] The control method is characterized in that it further includes the following step: starting the internal combustion engine between the third time and the fourth time to generate torque, thereby increasing the rotation speed of the internal combustion engine.

[0019] The appended claims describe preferred embodiments of the invention and form an integral part of the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described with reference to the accompanying drawings showing non-limiting embodiments of the invention, in which:

[0021] Figure 1 is a schematic plan view of a rear-wheel drive road vehicle provided with a powertrain having a dual-clutch servo-assisted gearbox and controlled according to the control method of the present invention;

[0022] Figure 2 yes Figure 1 A schematic diagram of the powertrain; and

[0023] Figures 3 to 6 Shown are the time developments of the torque transmitted by the two clutches of a dual-clutch transmission, the rotational speed of the drive shaft of the internal combustion engine, the longitudinal deceleration of the road vehicle and the torque generated by the internal combustion engine during a corresponding change to a lower gear by means of the control method according to the invention. DETAILED DESCRIPTION

[0024] exist Figure 1In the figure, reference numeral 1 generally denotes a road vehicle (in particular a car) having two front driven (ie non-driven) wheels 2 and two rear driven wheels 3. In the front position there is an internal combustion engine 4 having a drive shaft 5 which generates a torque T transmitted to the drive wheels 3 via a drivetrain 6. E The powertrain 6 includes a dual-clutch servo-assisted gearbox 7 disposed in the rear-wheel drive assembly and a transmission shaft 8 connecting the drive shaft 5 to the input end of the dual-clutch servo-assisted gearbox 7. The dual-clutch servo-assisted gearbox 7 is connected to a self-locking differential 9 in a gear train manner, and a pair of half shafts 10 originate from the self-locking differential 9 and are each integral with the drive wheel 3.

[0025] The road vehicle 1 comprises a control unit 11 of an internal combustion engine 4, which controls the internal combustion engine 4, a control unit 12 of a drivetrain 6, which controls the drivetrain 6, and a bus line 13, which is made, for example, according to the CAN (Car Area Network) protocol, extends over the entire road vehicle 1 and allows the two control units 11 and 12 to communicate with each other. In other words, the control unit 11 of the internal combustion engine 4 and the control unit 12 of the drivetrain 6 are connected to the bus line 13 and can therefore communicate with each other by means of information sent via the bus line 13. Furthermore, the control unit 11 of the internal combustion engine 4 and the control unit 12 of the drivetrain 6 can be directly connected to each other via a dedicated synchronization cable 14, which is capable of directly transmitting signals from the control unit 12 of the drivetrain 6 to the control unit 11 of the internal combustion engine 4 without delays caused by the bus line 13. Alternatively, the synchronization cable 14 may not be present and all communications between the two control units 11 and 12 may be exchanged using the bus line 13.

[0026] according to Figure 2 , the dual-clutch servo-assisted gearbox 7 comprises a pair of main shafts 15, which are coaxial, independent of each other and inserted into each other. In addition, the dual-clutch servo-assisted gearbox 7 comprises two coaxial clutches 16, each of which is designed to connect the corresponding main shaft 15 to the drive shaft 5 of the internal combustion engine 4 through the intervention of the transmission shaft 8; each clutch 16 is an oil bath clutch and is therefore pressure-controlled (i.e., the degree of opening / closing of the clutch 16 is determined by the oil pressure in the clutch 16); according to an alternative embodiment, each clutch 16 is a dry clutch and is therefore position-controlled (i.e., the degree of opening / closing of the clutch 16 is determined by the position of the movable element of the clutch 16). The dual-clutch servo-assisted gearbox 7 comprises a single secondary shaft 17 connected to the differential 9, which transmits movement to the drive wheels 3; according to an alternative and equivalent embodiment, the dual-clutch servo-assisted gearbox 7 comprises two secondary shafts 17, both of which are connected to the differential 9.

[0027] The dual-clutch servo-assisted transmission 7 has seven forward gears (1st gear I, 2nd gear II, 3rd gear III, 4th gear IV, 5th gear V, 6th gear VI and 7th gear VII) indicated by Roman numerals and a reverse gear (indicated by R). The main shaft 15 and the countershaft 17 are mechanically coupled to each other through a plurality of gear trains, each of which defines a corresponding gear and includes a main gear 18 fixed to the main shaft 15 and a counter gear 19 fixed to the countershaft 17. In order for the dual-clutch servo-assisted transmission 7 to operate correctly, all odd-numbered gears (1st gear I, 3rd gear III, 5th gear V, 7th gear VII) are coupled to the same main shaft 15, while all even-numbered gears (2nd gear II, 4th gear IV and 6th gear VI) are coupled to another main shaft 15.

[0028] Each main gear 18 is connected to the corresponding main shaft 15 by a spline so as to always rotate in an integral manner with the main shaft 15, and is permanently meshed with the corresponding sub-gear 19; on the other hand, each sub-gear 19 is installed on the countershaft 17 in an idling manner. In addition, the dual-clutch servo-assisted transmission 7 includes four synchronizers 20, each of which is coaxially installed on the countershaft 17, disposed between two sub-gears 19, and designed to be operated to alternately fix the corresponding two sub-gears 19 to the countershaft 17 (that is, alternately make the corresponding two sub-gears 19 angularly integral with the countershaft 17). In other words, each synchronizer 20 can move in one direction to fix one sub-gear 19 to the countershaft 17, or can move in the other direction to fix another sub-gear 19 to the countershaft 17.

[0029] The dual-clutch gearbox 7 comprises a single layshaft 17 connected to the differential 9 , which transmits the movement to the drive wheels 3 ; according to an alternative and equivalent embodiment, the dual-clutch gearbox 7 comprises two layshafts 17 each connected to the differential 9 .

[0030] according to Figure 1 , the road vehicle 1 comprises a passenger compartment accommodating a driving position for a driver; the driving position comprises: a seat (not shown); a steering wheel 21; an accelerator pedal 22; a brake pedal 23; and two paddle shifters 24 and 25, which control a dual-clutch servo-assisted gearbox 7 and are connected to opposite sides of the steering wheel 21. The upshift paddle shifter 24 is operated by the driver (by means of a short pressure) to request an upshift (i.e., to engage a new gear that is higher than and adjacent to the current gear), while the downshift paddle shifter 25 is operated by the driver (by means of a short pressure) to request a downshift (i.e., to engage a new gear that is lower than and adjacent to the current gear).

[0031] In the following, the execution mode of downshifting from a higher current gear A to a lower subsequent gear B when the accelerator pedal 22 is released is described (when the accelerator pedal 22 is released, the internal combustion engine 4 is running in a closed state and acts as an engine brake); that is, the current gear A has a larger transmission ratio than the subsequent gear B (therefore, when the speed of the road vehicle 1 is the same, the current gear A causes the internal combustion engine 4 to run slower than the subsequent gear B).

[0032] In the initial situation (i.e. before the gear change), the outgoing clutch 16B is closed in order to transmit the motion to the main shaft 15A, which in turn transmits the motion to the secondary shaft 17 through the engaged current gear A; on the other hand, the incoming clutch 16B is open, thus isolating the main shaft 15B from the transmission shaft 8. Before starting the upshift, the subsequent gear B is engaged in order to connect the main shaft 15B to the secondary shaft 17 through the gear B. When the driver sends a gear change command, the gear change is performed by opening the outgoing clutch 16A in order to disconnect the main shaft 15A (thus the gear A) from the transmission shaft 8 (i.e. the drive shaft 5 of the internal combustion engine 4) and (substantially) simultaneously closing the incoming clutch 16B in order to connect the main shaft 15B (thus the gear B) to the transmission shaft 8 (i.e. the drive shaft 5 of the internal combustion engine 4).

[0033] Figure 3 The manner in which a shift to a lower gear is performed is shown, with the driver issuing a downshift command by operating the downshift paddle shifter 25 while releasing the accelerator pedal 22 . Figure 3 Starting from the top it shows:

[0034] shows the speed ω of the internal combustion engine 4 E , the speed of the clutch 16A that is leaving ω A and the speed of the clutch 16B entering B The first diagram of the temporal development of

[0035] The torque T transmitted by the two clutches 16A and 16B is shown. A , T B The second diagram of the temporal development of

[0036] shows the torque T generated by the internal combustion engine 4 E The third diagram of the time development of (before and after the downshift, the internal combustion engine 4 is in the off state, so it operates in the engine braking mode to generate a negative torque T E );as well as

[0037] The fourth diagram shows the time development of the longitudinal acceleration α of the vehicle 1 (it should be noted that since the internal combustion engine 4 generates a substantially negative torque T E , that is, braking is performed, and therefore the vehicle 1 operates in engine braking mode, so the longitudinal acceleration α of the vehicle 1 is always negative, that is, the vehicle 1 is decelerating).

[0038] As soon as the control unit 12 of the driveline 6 receives a gear change command from the driver (time t0), the control unit 12 of the driveline 6 immediately starts filling the incoming clutch 16B, i.e. it immediately starts supplying pressurized oil into the incoming clutch 16B; in fact, the incoming clutch 16B associated with the subsequent gear B can only transmit a significant torque to the rear drive wheels 3 when the filling of the pressurized oil is completed and the pressurized oil therefore exerts a thrust that compresses the plates of the incoming clutch 16B because it cannot occupy more volume in the incoming clutch 16B. As a result, before the incoming clutch 16B associated with the subsequent gear B can actually start to transmit a significant torque to the rear drive wheels 3, it is necessary to wait for a specified delay time interval (usually 80 to 220 thousandths of a second), during which the filling of the incoming clutch 16B is completed by oil. The completion of filling of the incoming clutch 16B is usually monitored by a pressure sensor which detects the oil pressure in the incoming clutch 16B: when the oil pressure in the incoming clutch 16B exceeds a predetermined threshold, this means that the internal volume of the incoming clutch 16B is completely filled, and therefore the oil in the clutch 16B begins to compress. As a result, a moment t1 is established when the oil pressure in the incoming clutch 16B exceeds the predetermined threshold, wherein (after a delay time) the incoming clutch 16B is filled with oil and is ready to transmit significant torque.

[0039] From the time t0 when the drivetrain control unit 12 immediately starts closing the incoming clutch 16B to the time t1 when, after a delay time, the incoming clutch 16B is filled with oil and ready to transmit significant torque, there is no change in the dynamics of the road vehicle 1, i.e., the full torque T generated by the internal combustion engine 4 E (It is the negative torque T E , that is, the braking torque T E , because the internal combustion engine 4 is in the off state and therefore operates as an engine brake) is completely transmitted by the outgoing clutch 16A, just as before the start of the gear change. At time t1, the incoming clutch 16B begins to transmit the torque T B (i.e., torque T B begins to increase), while commanding the off-going clutch 16A to open (ie, torque T A starts to decrease); it should be noted that the opening of the outgoing clutch 16A associated with the current gear A occurs without delay, because the outgoing clutch 16A is already full of pressurized oil and at this stage only part of the oil needs to be discharged by opening the solenoid valve (the action of which is therefore instantaneous).

[0040] Between the instants t1 and t2, there is a partial and reduced torque transfer between the two clutches 16A and 16B, i.e. the torque transmitted by the outgoing clutch 16A is reduced in a step-like manner, and the torque transmitted by the incoming clutch 16B is increased by the same amount in a step-like manner. Subsequently, between the instants t2 and t3, there is a complete torque transfer between the two clutches 16A and 16B, i.e. the torque transmitted by the outgoing clutch 16A is gradually reduced (the outgoing clutch 16A is opened by a linear ramp), while the torque transmitted by the incoming clutch 16B is gradually increased (the incoming clutch 16B is closed by a linear ramp), thereby determining the alternation between the two clutches 16A and 16B. The clutches 16A and 16B are opened and closed by means of linear ramps, i.e. the respective torques T A and T B Changes (decreases and increases) linearly over time.

[0041] exist Figure 3 In the embodiment shown, the outgoing clutch 16A is fully opened in the same time required to fully close the incoming clutch 16B, so that a symmetrical alternation is obtained. At time t3, the outgoing clutch 16A is fully open (so it no longer transmits any torque), while the incoming clutch 16B transmits the entire torque T of the internal combustion engine 4. E There is a shift time between the instants t1 and t3, during which the torque transmitted by the outgoing clutch 16A decreases until it becomes zero, while the torque transmitted by the incoming clutch 16B increases until it reaches the torque T generated by the internal combustion engine 4. E (As mentioned above, the internal combustion engine 4 is in the off state and therefore operates as an engine brake, thereby generating a negative torque T E ), that is, during this period, the outgoing clutch 16A separates itself from the drive wheel 3 and the incoming clutch 16B connects itself to the drive wheel 3.

[0042] The speed ω of the internal combustion engine 4 E Before the gear shift until time t3, it is equal to the speed ω given by the transmission ratio of the current gear position A. A , which during the gear shift is imparted to the speed ω of the subsequent gear ratio B Gradually increases and becomes equal to the speed ω after the gear shift B .according to Figure 3 Before time t3, the clutch 16A is not fully opened, so the speed ω of the internal combustion engine 4 E is equal to (corresponds to) the speed ω imparted by the transmission ratio of the current gear A associated with the offgoing clutch 16A A As a result, the speed of the internal combustion engine 4 ω E It only increases after the off-going clutch 16A is fully opened.

[0043] There is a synchronization time between the times t3 and t4, during which the speed ω of the internal combustion engine 4 is E The speed ω given by the transmission ratio of the current gear A A Increase to the speed ω given by the transmission ratio of the subsequent gear B B , that is, the speed ω E With speed ω B synchronous.

[0044] In order to increase the speed ω of the internal combustion engine 4 after the incoming clutch 16A is fully opened E , the internal combustion engine 4 is turned on between time t2 and t4 to generate a positive torque T E (i.e., driving torque rather than braking torque); that is, the internal combustion engine 4 is turned on at time t2 and turned off at time t4. In other words, in order to make the speed ω of the internal combustion engine 4 E and the speed ω of the clutch 16B entering B Synchronize to make the torque T generated by the internal combustion engine 4 E Temporarily increases (so that it becomes a driving torque and no longer a braking torque between times t2 and t4).

[0045] The longitudinal acceleration α of the road vehicle 1 is approximately constant immediately before the gear change and is equal to the value α A (which is negative because the vehicle is decelerating), and is approximately constant and equal to the value α immediately after the gear change B (It is negative because the vehicle is decelerating and its absolute value is greater than the value α A During the gear shift, the longitudinal acceleration of the vehicle 1 changes from the initial value α A Gradually decreases to the final value α B .

[0046] exist Figure 3 In the embodiment shown, the off-going clutch 16A is fully open with respect to the full torque T of the internal combustion engine 4. E The lead amount for the full transfer to the incoming clutch 16B (occurring at time t3) is zero, ie, the full torque T of the internal combustion engine 4 is transmitted to the outgoing clutch 16A. E The clutch 16B is fully opened at the moment t3 when the clutch 16B is fully transmitted to the incoming clutch 16B; the advance amount is Figure 3 AMT indx represents, and is zero (i.e., minimum). Figure 4 In the variant shown, by Figure 3 Downshifting occurs in the same manner as described above, with the only difference being that the off-going clutch 16A is fully open relative to the full torque T of the internal combustion engine 4. E AMT fully transferred to the incoming clutch 16B indxis no longer zero (on a scale of 0 to 100, it is approximately 40), ie the clutch 16A that is disengaged has a full torque T of the internal combustion engine 4. E is fully opened before being fully transmitted to the incoming clutch 16B (occurring at time t3); in other words, the outgoing clutch 16A is fully open relative to the torque T of the internal combustion engine 4 E The moment t3 at which the clutch 16B is fully opened is advanced. Figure 5 In another variation shown, by Figure 3 Downshifting occurs in the same manner as described above, with the only difference being that the off-going clutch 16A is fully open relative to the full torque T of the internal combustion engine 4. E AMT fully transferred to the incoming clutch 16B indx is no longer zero, but is maximum (on a scale of 0 to 100, this is 100), ie the clutch 16A is off-loaded at the full torque T of the internal combustion engine 4 . E is fully opened at time t2 long before being fully transmitted to the incoming clutch 16B (occurring at time t3); in other words, the outgoing clutch 16A is fully opened relative to the full torque T of the internal combustion engine 4. E The moment t3 at which the incoming clutch 16B is fully transmitted is significantly earlier than the moment t2 at which it is fully opened.

[0047] In other words, advance AMT indx The clutch 16A that is off is fully opened relative to the total torque T of the internal combustion engine 4. E The degree of advance of full transfer to the incoming clutch 16B (occurring at time t3) and ranges from a minimum value of 0 (eg Figure 3 In the embodiment shown, the full opening of the off-going clutch 16A occurs at the full torque T of the internal combustion engine 4. E The same moment t3) is fully transmitted to the incoming clutch 16B to a maximum value of 100 (such as Figure 5 In the embodiment shown, full opening of off-going clutch 16A occurs at time t2).

[0048] By changing the advance amount AMT indx , the execution mode of downshifting is also changed; therefore, the control unit 12 of the powertrain system 6 can advance the amount of AMT indx The throttle is operated to achieve different downshifts according to the needs expressed by the driver (the driver can operate a selector called a "handle" to choose a preferred driving style, that is, a style more focused on comfort or a style more focused on fun / sport). In fact, it should be noted that in Figure 3 , Figure 4 and Figure 5In the embodiment shown, the time curve of the longitudinal deceleration α of the road vehicle 1 is variable.

[0049] exist Figure 3 , Figure 4 and Figure 5 In the embodiment shown, the internal combustion engine 4 is in a shut-off state before the downshift (therefore, it acts as a brake torque T E The engine brake is operated by the driver) and remains closed even after the downshift; that is, the driver keeps the accelerator pedal 22 fully released before, during and after the downshift. However, it may happen that the driver decides to depress the accelerator pedal 22 after requesting the downshift (that is, after time t0) and thus request the internal combustion engine 4 to generate a positive torque T E (i.e., driving torque); this situation exists when Figure 6 In the embodiment shown, the driver depresses the accelerator pedal 22 at time t6 (e.g., between time t2 and time t3) after requesting a downshift (i.e., after time t0). Obviously, the control unit 12 of the powertrain 6 must complete the downshift that has already started, but can try and respond immediately to the driver's new (and unpredictable) request, giving the driver a feeling of extreme sensitivity; as a result, starting from time t6, the control unit 12 of the powertrain 6 requests the control unit 11 of the internal combustion engine 4 to increase the torque T generated by the internal combustion engine 4. E (upon request of the driver who has depressed the accelerator pedal 22), and at the same time accelerates the closing of the incoming clutch 16B (i.e. closes the incoming clutch 16B more quickly), which obviously now has to transmit a greater torque T overall due to the internal combustion engine 4 being turned on. B .

[0050] The above control methods have different advantages.

[0051] Firstly, the above-described method of controlling the change to a lower gear with the accelerator pedal released is very comfortable because a comfortable longitudinal acceleration curve for the road vehicle is determined due to the uninterrupted transmission of torque to the drive wheels 3: in fact, the longitudinal acceleration of the road vehicle changes gradually from an initial deceleration to a final deceleration that is greater than the previous one without a gradient reversal (the transmission ratio is reduced during the downshift, so that the engine braking has a more decisive effect on the dynamics of the road vehicle 1); in this way, the driver always has the feeling of a continuous deceleration.

[0052] In addition, the above-mentioned method of controlling the shift to a lower gear when the accelerator pedal is released does not produce any perceptible metallic noise because both clutches 16A and 16B are never open at the same time, so the powertrain 6 is always "stressed"; that is, because the gear system of the powertrain 6 is always "stressed", the clearance is greatly reduced, and as a result, the noise is also greatly reduced.

[0053] The above method of controlling the shift to a lower gear with the accelerator pedal released also allows for a new strategy (also known as "change of mind") to be implemented, which allows for the torque T of the incoming clutch 16B to be adjusted if the driver depresses the accelerator pedal 22 during a downshift. B , thereby allowing the road vehicle 1 to respond more promptly and quickly to the driver's instructions.

[0054] The above method of controlling the shift to a lower gear when the accelerator pedal is released allows the full torque T of the internal combustion engine 4 to be fully opened by fully opening the off-going clutch 16A based on the driver's preference. E AMT fully transferred to the incoming clutch 16B indx Simple adjustments are made to customize the time profile of the longitudinal acceleration α of the road vehicle 1 .

[0055] Finally, the control method described above is easy and economical to implement, since it does not require the installation of additional physical components and does not require expansion of the control unit 12 of the powertrain 6 , since no additional computing power is required.

[0056] Reference numerals list

[0057] 1 road car

[0058] 2 Front wheels

[0059] 3 Rear wheels

[0060] 4 Engine

[0061] 5 Drive shaft

[0062] 6 Powertrain

[0063] 7 Gearbox

[0064] 8 Drive shaft

[0065] 9 Differential

[0066] 10 Half shaft

[0067] 11 Engine control unit

[0068] 12 Powertrain control unit

[0069] 13 Bus lines

[0070] 14 Sync Cable

[0071] 15 Spindle

[0072] 16 Clutch

[0073] 17 Countershaft

[0074] 18 Main gear

[0075] 19 Secondary gear

[0076] 20 Synchronizer

[0077] 21 Steering Wheel

[0078] 22 Accelerator pedal

[0079] 23 Brake pedal

[0080] 24 Upshift paddle shifters

[0081] 25 Downshift paddle shifters

[0082] ω E Speed

[0083] ω A Speed

[0084] ω B Speed

[0085] T E Torque

[0086] T A Torque

[0087] T B Torque

[0088] α Acceleration

[0089] Time t0

[0090] Time t1

[0091] Time t2

[0092] Time t3

[0093] t4 time

[0094] t5

[0095] t6 time

[0096] AMT indx Fully open lead

Claims

1. A control method for controlling a shift to a lower gear when an accelerator pedal (22) is released in a powertrain (6) having a dual-clutch servo-assisted gearbox (7) to shift from a current gear (A) to a subsequent gear (B) lower than the current gear (A), wherein the powertrain (6) includes a dual-clutch servo-assisted gearbox (7) having: two main shafts (15); at least one secondary shaft (17) connected to a drive wheel (3); and two clutches (16A, 16B) each interposed between a drive shaft (5) of an internal combustion engine (4) and the corresponding main shaft (15), The control method comprises the following steps: opening an off-going clutch (16A) associated with the current gear position (A) at a first time (t1); closing an incoming clutch (16B) associated with a subsequent gear (B) at a first time (t1); Fully opening the off-going clutch (16A) at a second moment via a first linear ramp; closing the incoming clutch (16B) via a second linear ramp starting from a third time (t2) that is before or coincides with the second time; Between the second time and the fourth time (t4), the speed (ω) of the internal combustion engine (4) is increased. E ) and the speed (ω) of the incoming clutch (16B) B ), that is, the speed (ω) given by the transmission ratio of the subsequent gear (B) B )synchronous; as well as fully closing the incoming clutch (16B) at a fifth time (t3) which coincides with or is after the second time, The control method further comprises the following steps: starting the internal combustion engine (4) between the third moment (t2) and the fourth moment (t4) to generate a torque (T E ), thereby increasing the speed (ω) of the internal combustion engine (4) E ).

2. The control method according to claim 1, characterized in that: The fifth moment (t3) coincides with the second moment.

3. The control method according to claim 1, characterized in that: The fifth time (t3) is after the second time.

4. The control method according to claim 1, characterized in that: The third time (t2) is before the second time.

5. The control method according to claim 1, characterized in that: The third moment (t2) coincides with the second moment.

6. The control method according to claim 1, characterized in that: The longitudinal deceleration (α) of the road vehicle (1) increases between the third instant (t2) and the fifth instant (t3).

7. The control method according to claim 1, characterized in that: The control method further comprises the following steps: Detecting driver preferences; and Based on the driver's preference, the off-going clutch (16A) is changed to be fully open relative to the full torque (T E ) is fully transferred to the incoming clutch (16B) (AMT indx ).

8. The control method according to claim 7, characterized in that: The off-going clutch (16A) is fully open relative to the full torque (T E ) is fully transferred to the incoming clutch (16B) (AMT indx ) may vary between a minimum value when the off-going clutch (16A) is fully open at the fifth time (t3) and a maximum value when the off-going clutch (16A) is fully open at the third time (t2).

9. The control method according to claim 1, characterized in that: The internal combustion engine (4) is in a shut-down state before the shift to the lower gear and is also in a shut-down state after the shift to the lower gear.

10. The control method according to claim 9, characterized in that: Before, during and after shifting to a lower gear, the driver keeps the accelerator pedal (22) fully released.

11. The control method according to claim 1, characterized in that: The control method further comprises the following steps: detecting depression of an accelerator pedal (22) by a driver during a shift to a lower gear; In the event that the driver depresses the accelerator pedal (22) during a shift to a lower gear, the torque (T E );as well as In the event that the driver depresses the accelerator pedal (22) during a shift to a lower gear, the incoming clutch (16B) is accelerated to close.

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