Method for controlling a road vehicle with a servo-assisted gearbox during a deceleration phase

Abstract

The invention relates to a method for controlling a road vehicle (1) having a servo-assisted gearbox (7) during a deceleration phase, the control method comprising the following steps when the servo-assisted gearbox (7) is in an automatic operating mode: assuming that the depression of a brake pedal (23) remains constant, calculating a release time interval required for the road vehicle (1) to reach a release speed for eventually releasing a clutch (16) of the servo-assisted gearbox (7); calculating the number of downshifts that can be performed within the release time interval based on the time required to perform the downshift; planning a downshift to be performed from the current gear engaged in the servo-assisted gearbox (7) to the release gear through which the clutch (16) of the servo-assisted gearbox (7) is eventually released, so that no more than the number of downshifts that can be performed within the release time interval is performed; and performing the planned downshift.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000017510 filed on September 30, 2019, the disclosure of which is incorporated herein in its entirety by reference. Technical Field

[0003] The invention relates to a method for controlling a road vehicle having a servo-assisted gearbox during a deceleration phase.

[0004] The invention finds advantageous application in a drive train having a dual-clutch servo-assisted gearbox, to which explicit reference will be made in the following description without loss of generality. Background Art

[0005] 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 clutch 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 shafts by corresponding gear trains, each gear train defining a gear.

[0006] During a gear shift, the current gear couples the countershaft to the 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 releasing the clutch associated with the current gear and simultaneously closing the clutch associated with the subsequent gear.

[0007] When the powertrain is operating in automatic mode, i.e. when gear changes are not requested by the driver but are decided autonomously by the powertrain's control unit (simulating the behavior of an automatic gearbox), and when the road vehicle 1 is travelling at moderate speeds (i.e. the road vehicle 1 is driven in a non-high performance mode), a "high" gear is typically used to allow the internal combustion engine to operate at a low speed (e.g. in the range of approximately 1,500 to 2,500 rpm) to minimize fuel consumption. In these cases, the control unit of the powertrain uses a lower threshold and an upper threshold: when the speed of the internal combustion engine is below the lower threshold, a downshift is performed (i.e. a new, lower gear is engaged), whereas when the speed of the internal combustion engine exceeds the upper threshold, an upshift is performed (i.e. a new, higher gear is engaged); this control mode is effective in running the internal combustion engine at low speeds, but there is a risk of causing too low a speed when the driver decides to stop the road vehicle by acting (more or less hard) on the brake pedal (i.e. it may cause the internal combustion engine to run too slowly, with the result that an operating anomaly may even lead to an undesired stop), since the downshift requires a specified execution time to ensure the necessary comfort (indispensable when the powertrain is operating in automatic mode), and there may not be the time required to perform all the requested downshifts in order to prevent the speed from falling too far below the lower threshold.

[0008] The current approach for preventing the internal combustion engine from running too slowly is an accelerated downshift approach (i.e. forcing a particularly rapid downshift); however, this approach (due to the rapidly executed downshift) results in an impulsive longitudinal acceleration and in a sudden increase in the speed of the internal combustion engine, which significantly reduces the driving comfort perceived by the driver.

[0009] Patent application WO2015024792A1 describes a method for controlling a road vehicle with a servo-assisted gearbox during a deceleration phase, where conditions permit, with a multi-step downshift that prevents engaging intermediate gears between an initial gear and a final gear. Summary of the invention

[0010] The object of the present invention is to provide a method for controlling a road vehicle with a servo-assisted gearbox during a deceleration phase which does not have the above-mentioned disadvantages and which is at the same time easy and economical to implement.

[0011] According to the invention, a method for controlling a road vehicle with a servo-assisted gearbox during a deceleration phase is provided, the control method comprising the following steps when the servo-assisted gearbox is in automatic operating mode:

[0012] Detecting the current speed of road vehicles;

[0013] detecting the current gear engaged in a servo-assisted transmission; and

[0014] Detecting depression of the brake pedal;

[0015] The control method is characterized in that the control method further comprises the following steps:

[0016] Assuming that the depression of the brake pedal remains constant, calculate the release time interval required to bring the road vehicle to the release speed required to finally release the clutch of the servo-assisted gearbox;

[0017] calculating a number of downshifts that can be performed within the release time interval based on the time required to perform the downshift;

[0018] planning a downshift to be performed from a current gear engaged in the servo-assisted transmission to a disengaged gear by which a clutch of the servo-assisted transmission is ultimately disengaged so as to perform no more downshifts than can be performed within the disengagement time interval; and

[0019] Implement a planned downshift.

[0020] The appended claims describe preferred embodiments of the invention and form an integral part of the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will now be described with reference to the accompanying drawings showing non-limiting embodiments thereof, in which:

[0022] · Figure 1 is a schematic plan view of a rear-wheel drive road vehicle having a powertrain with a dual-clutch servo-assisted gearbox controlled according to the control method of the invention; and

[0023] · Figure 2 yes Figure 1 Schematic diagram of the powertrain system.

[0024] Reference numerals list

[0025] 1 road vehicle; 2 front wheels; 3 rear wheels; 4 engine; 5 drive shaft; 6 powertrain; 7 gearbox; 8 transmission shaft; 9 differential; 10 axle; 11 engine control unit; 12 powertrain control unit; 13 BUS line; 14 synchronization cable; 15 main shaft; 16 clutch; 17 secondary shaft; 18 main gear; 19 secondary gear; 20 synchronizer; 21 steering wheel; 22 accelerator pedal; 23 brake pedal; 24 upshift paddle shifter; 25 downshift paddle shifter; ω E Speed; ω2 speed. DETAILED DESCRIPTION

[0026] 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 which is transmitted to the drive wheels 3 via a drive train 6. The drive train 6 comprises a dual-clutch servo-assisted gearbox 7 arranged in a rear-wheel drive assembly and a transmission shaft 8 connecting the drive shaft 5 to the input of the dual-clutch servo-assisted gearbox 7. The dual-clutch servo-assisted gearbox 7 is connected in a train-like manner to a self-locking differential 9 from which a pair of axles 10, each integral with the drive wheels 3, originate.

[0027] The road vehicle 1 comprises: a control unit 11 of the engine 4 controlling the engine 4, a control unit 12 of the powertrain 6 controlling the powertrain 6, and a BUS line 13, which is made, for example, according to the CAN (Car Area Network) protocol, extends to 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 engine 4 and the control unit 12 of the powertrain 6 are connected to the BUS line 13 and can therefore communicate with each other by means of messages sent through the BUS line 13. In addition, the control unit 11 of the engine 4 and the control unit 12 of the powertrain 6 can be directly connected to each other by a dedicated synchronization cable 14, which is capable of directly transmitting signals from the control unit 12 of the powertrain 6 to the control unit 11 of the engine 4 without the delay 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 can be exchanged using the BUS line 13.

[0028] 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 insertion of the transmission shaft 8; each clutch 16 is an oil bath clutch and is therefore pressure-controlled (i.e., the degree of release / closure of the clutch 16 is determined by the pressure of the oil 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 release / closure 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.

[0029] The dual-clutch servo-assisted transmission 7 has seven forward gears (first gear I, second gear II, third gear III, fourth gear IV, fifth gear V, sixth gear VI and seventh 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 mounted on the main shaft 15 and a counter gear 19 mounted on the countershaft 17. In order for the dual-clutch servo-assisted transmission 7 to operate correctly, all odd-numbered gears (first gear I, third gear III, fifth gear V, seventh gear VII) are coupled to the same main shaft 15, while all even-numbered gears (second gear II, fourth gear IV and sixth gear VI) are connected to another main shaft 15.

[0030] Each main gear 18 is splined to the corresponding main shaft 15 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 mounted 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 mounted on the countershaft 17, disposed between two sub-gears 19, and designed to be operated so that the corresponding two sub-gears 19 are alternately assembled 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 assemble the sub-gear 19 to the countershaft 17, or can move in the other direction to assemble another sub-gear 19 to the countershaft 17.

[0031] 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 .

[0032] 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) in order 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) in order to request a downshift (i.e., to engage a new gear that is lower than and adjacent to the current gear).

[0033] The powertrain 6 may be operated in automatic mode, ie gear changes are not requested by the driver but are autonomously decided by the control unit 12 of the powertrain 6 (simulating the behavior of an automatic gearbox).

[0034] In use, when the powertrain 6 is operated in automatic mode, during the deceleration phase, the control unit 12 of the powertrain 6 detects the current speed of the road vehicle 1, the rotation speed ω of the internal combustion engine 4 E , detecting the current gear engaged in the servo-assisted gearbox 7, and detecting the depression of the brake pedal 23 (e.g. by detecting the pressure of the brake fluid in the hydraulic circuit of the brake system). At this point, the control unit 12 of the powertrain 6 calculates the disengagement time interval required for the road vehicle 1 to reach the disengagement speed for the final disengagement of the clutch 16 of the servo-assisted gearbox 7 assuming that the depression of the brake pedal 23 remains constant (taking into account that the road vehicle 1 is about to stop); in addition, the control unit 12 of the powertrain 6 calculates the number of downshifts that can be performed within the disengagement time interval based on the time required to perform the downshift (and taking into account that when the powertrain is operating in automatic mode, the downshift must be performed with maximum comfort and therefore requires a specified execution time, for example in the range of 800-900 milliseconds).

[0035] Subsequently, the control unit 12 of the powertrain 6 plans a downshift from the current gear engaged in the servo-assisted transmission 7 to a disengaged gear (usually the second gear II) through which the clutch 16 of the servo-assisted transmission 7 is finally released, thereby performing no more than (or less than if necessary) the number of downshifts that can be performed within the release time interval; finally, during the release time interval, the control unit 12 of the powertrain 6 performs a pre-planned downshift, so that at the end of the release time interval, the disengaged gear (usually the second gear II) is engaged in the servo-assisted transmission 7, so that the clutch 16 is finally released.

[0036] According to a preferred embodiment, the released gear is the second gear II, the road vehicle 1 is stopped with the clutch 16 released, and after the road vehicle 1 has stopped, the first gear I is engaged in the servo-assisted gearbox 7 .

[0037] Generally speaking, the control unit 12 of the powertrain 6 always attempts and plans a single-step downshift (i.e., the subsequent gear is adjacent to the previous gear); however, if the number of downshifts that can be performed within the release time interval is less than the number of gears that exist between the current gear engaged and the released gear in the servo-assisted transmission 7, the downshift plan must involve at least one multi-step downshift (i.e., the subsequent gear is not adjacent to the previous gear, for example, a downshift from the seventh gear VII to the fourth gear IV or a downshift from the sixth gear VI to the third gear III). The control unit 12 of the powertrain 6 preferably arranges a multi-step downshift at the beginning of the downshift plan (i.e., first in the plan) (i.e., it immediately performs a possible multi-step downshift) so that the last downshift of the downshift plan is a single-step downshift.

[0038] According to a preferred embodiment, the control unit 12 of the powertrain system 6 periodically detects the depression of the brake pedal 23, recalculates (in the event of a change in the depression of the brake pedal 23) the release time interval, recalculates (in the event of a change in the depression of the brake pedal 23) the number of downshifts that can be performed within the release time interval, and then replans (in the event of a change in the depression of the brake pedal 23) the downshift to be performed from the current gear engaged in the servo-assisted transmission 7 to the released gear.

[0039] The control unit 12 of the drivetrain 6 plans a downshift so as to prevent the speed ω of the internal combustion engine 4 from decreasing. E drops below a predetermined lower threshold, thereby ensuring that the internal combustion engine 4 does not run too slowly; that is, the control unit 12 of the powertrain 6 plans the downshift so as to always allow the speed ω of the internal combustion engine 4 to E Exceeds a predetermined lower threshold.

[0040] According to a preferred embodiment, the control unit 12 of the drivetrain 6 measures (via appropriate sensors) the rotational speed ω2 of the secondary shaft 17 of the servo-assisted gearbox 7 and calculates the longitudinal deceleration of the road vehicle 1 by calculating the time derivative of the rotational speed ω2 of the secondary shaft 17 of the servo-assisted gearbox 7. The control unit 12 of the drivetrain 6 then calculates the release time interval based on the longitudinal deceleration of the road vehicle 1; i.e., the control unit 12 of the drivetrain 6 calculates how much time the road vehicle 1 needs to reach the release speed (at which the clutch 16 of the servo-assisted gearbox 7 is finally released) based on the longitudinal deceleration of the road vehicle 1.

[0041] Even if the drivetrain 6 of the road vehicle 1 has a single-clutch servo-assisted gearbox, what is disclosed above is applicable without significant changes.

[0042] The above control methods have different advantages.

[0043] Firstly, when the powertrain system 6 is operating in automatic mode, the control method described above allows the road vehicle 1 to be stopped without causing the internal combustion engine 4 to run too slowly, and in particular without affecting the driving comfort perceived by the driver.

[0044] Furthermore, the control method described above is easy and economical to implement, since its execution requires limited storage space and reduced computing power.

Claims

1. A control method for controlling a road vehicle (1) having a servo-assisted gearbox (7) during a deceleration phase, when the servo-assisted gearbox (7) is in automatic operating mode, the control method comprising the following steps: Detecting the current speed of the road vehicle (1); detecting the current gear engaged in the servo-assisted gearbox (7); as well as Detecting depression of a brake pedal (23); The control method is characterized in that the control method further comprises the following steps: Assuming that the depression of the brake pedal (23) remains constant, calculating the release time interval required for the road vehicle (1) to reach a release speed for finally releasing the clutch (16) of the servo-assisted gearbox (7); calculating a number of downshifts that can be performed within the release time interval based on the time required to perform the downshift; planning a downshift to be performed from a current gear engaged in the servo-assisted gearbox (7) to a disengaged gear by which a clutch (16) of the servo-assisted gearbox (7) is finally disengaged so as to perform no more downshifts than can be performed within the disengagement time interval; and Implement a planned downshift.

2. The control method according to claim 1, characterized in that: In the event that the number of downshifts that can be performed within the release time interval is less than the number of gears between the currently engaged gear and the released gear in the servo-assisted gearbox (7), the downshift plan involves at least one multi-step downshift.

3. The control method according to claim 2, characterized in that: A multi-speed downshift is always scheduled first in the downshift schedule.

4. The control method according to claim 2, characterized in that: At least the last downshift of a downshift schedule is always a single-stage downshift.

5. The control method according to claim 1, characterized in that: The control method further comprises the following steps: Periodically detecting depression of the brake pedal (23); recalculating the release time interval in the event of a change in depression of the brake pedal (23); In case of a change in depression of the brake pedal (23), recalculating the number of downshifts that can be performed within the release time interval; and In the event of a change in the depression of the brake pedal (23), a downshift to be performed from the currently engaged gear in the servo-assisted transmission (7) to the released gear is replanned.

6. The control method according to claim 1, characterized in that: The release gear is the second gear (II); stopping the road vehicle (1) with the clutch (16) released; and After the road vehicle (1) has come to a stop, a first gear (I) is engaged in the servo-assisted gearbox (7).

7. The control method according to claim 1, characterized in that: A downshift plan is implemented to prevent the speed (ω) of the internal combustion engine (4) of the road vehicle (1) from decreasing. E ) drops below a predetermined lower threshold.

8. The control method according to claim 1, characterized in that: The control method further comprises the following steps: determining a longitudinal deceleration of the road vehicle (1); and The release time interval is calculated based on a longitudinal deceleration of the road vehicle (1).

9. The control method according to claim 8, characterized in that: The control method further comprises the following steps: measuring the rotation speed (ω2) of the secondary shaft (17) of the servo-assisted gearbox (7); and The longitudinal deceleration of the road vehicle (1) is calculated by calculating the time derivative of the rotation speed (ω2) of the secondary shaft (17) of the servo-assisted gearbox (7).

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