Method for controlling a road vehicle by performing a multi-step downshift in a powertrain having a servo-assisted gearbox

Abstract

The invention relates to a method for controlling a road vehicle (1) by performing a multi-step downshift in a powertrain having a servo-assisted gearbox (7), the control method comprising the steps of: detecting a deceleration of the road vehicle (1) and simultaneously detecting a multi-step downshift request by the driver; performing the multi-step downshift continuously and in an autonomous manner independent of further intervention by the driver while the road vehicle (1) is decelerating; determining the duration of a shift time interval (Δt); and performing each downshift after a first downshift when exactly the shift time interval (Δt) has elapsed since the preceding downshift.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000017507 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 for controlling a road vehicle by performing a multi-step downshift in a powertrain having a servo-assisted gearbox.

[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] There is a function (called "sequential downshift") which allows the driver to downshift multiple times while braking in order to engage the lowest possible gear (depending on the maximum speed of the internal combustion engine) at the end of braking, thereby having the greatest possible acceleration when starting again (which actually occurs at the end of braking). This function called "sequential downshift" is activated by the driver during braking (i.e. while depressing the brake pedal) by pressing the downshift paddle shifter for a long time (i.e. for a time exceeding a predetermined time threshold), which is usually pressed briefly to request a single-step downshift (i.e. to engage a new gear lower than the current gear).

[0008] In other words, to control the dual-clutch servo-assisted gearbox, the driver can rely on upshift paddle shifters, which are briefly depressed to request a single-step upshift (i.e., to engage a new gear that is higher than and adjacent to the current gear), and downshift paddle shifters, which are briefly depressed to request a single-step downshift (i.e., to engage a new gear that is lower than and adjacent to the current gear). During braking (obviously, for a long time), the driver can continuously depress the downshift paddle shifters while depressing the brake pedal to activate a function called "sequential downshifting", which automatically engages lower gears multiple times while braking, so that at the end of braking (i.e., when the brake pedal is released), the lowest possible gear is engaged.

[0009] When racing on a track, a feature known as "Sequential Downshift" is often used at the end of a straight section when the driver chooses to ask the function to handle the selection of the ideal gear while they concentrate on preparing for the next corner.

[0010] The function known as "sequential downshifting" currently requires setting a series of threshold values ​​for the speed of the internal combustion engine, so that a gear change is automatically performed each time the speed of the internal combustion engine reaches the corresponding speed threshold value. However, the software that generates the series of speed threshold values ​​of the internal combustion engine requires long and complex adjustments; in addition, the operating mode of the function known as "sequential downshifting", although effective, is generally not recognized by the driver, who often finds it "unnatural" (i.e., contrary to the driver's expectations).

[0011] Some implementation examples of the so-called “sequential downshift” function are described in patent applications WO2013153309A1 and EP2921746A1. Summary of the invention

[0012] The object of the present invention is to provide a method for controlling a road vehicle by performing a multi-step downshift in a driveline with a servo-assisted gearbox which does not suffer from the above-mentioned disadvantages and which is easy and economical to implement.

[0013] According to the present invention, there is provided a method for controlling a road vehicle by performing a multi-step downshift in a powertrain having a servo-assisted gearbox, the control method comprising the following steps:

[0014] detecting a deceleration of a road vehicle and simultaneously detecting a driver's request for a multiple-step downshift; and

[0015] performing multiple downshifts continuously and in an autonomous manner independent of further intervention by the driver while the road vehicle is decelerating;

[0016] The control method is characterized in that the control method further comprises the following steps:

[0017] determining a duration of a single shift time interval common to all multi-speed downshifts; and

[0018] After the first downshift, each downshift is performed when exactly the shift time interval has elapsed since the preceding downshift.

[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 thereof, in which:

[0021] · 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 present invention;

[0022] · Figure 2 yes Figure 1 A schematic diagram of a powertrain system; and

[0023] · Figure 3 Indicates the time changes in the rotational speeds of the two clutches and the drive shaft during execution of a multi-speed downshift.

[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; A Speed; B Speed; time T1; time T2; time T3; time T4; time T5; Δt time interval. 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] When the road vehicle 1 is decelerating (due to the driver acting on the brake pedal 23) and the driver keeps the downshift paddle shifter 25 depressed for a long time (i.e. for a time exceeding a predetermined time threshold), since the downshift paddle shifter is usually depressed for a short time to request a single-step downshift, the control unit 12 of the powertrain 6 activates a function (called "sequential downshift") which allows the driver to engage a lower gear multiple times while braking in order to engage the lowest possible gear (depending on the maximum speed of the internal combustion engine) at the end of braking and thus have the maximum possible acceleration when starting again (which actually occurs at the end of braking). This function called "sequential downshift" determines the continuous automatic execution of multiple downshifts (i.e. without driver intervention) until the deceleration of the road vehicle 1 is interrupted (i.e. until the driver stops depressing the brake pedal 23).

[0034] In other words, to control the dual clutch servo-assisted gearbox 7, the driver can rely on the upshift paddle shifter 24, which is briefly depressed to request a single-step upshift (i.e., to engage a new gear that is higher than and adjacent to the current gear), and the downshift paddle shifter 25, which is briefly depressed to request a single-step downshift (i.e., to engage a new gear that is lower than and adjacent to the current gear). During braking (obviously, for a long time), the driver can continuously depress the downshift paddle shifter 25 while depressing the brake pedal 23 to activate a function called "sequential downshifting", which automatically engages lower gears multiple times during braking, so that at the end of braking (i.e., when the brake pedal 23 is released), the lowest possible gear is engaged.

[0035] When racing on a track, a feature known as "Sequential Downshift" is often used at the end of a straight section when the driver chooses to ask the function to handle the selection of the ideal gear while they concentrate on preparing for the next corner.

[0036] The control unit 12 of the powertrain 6 detects a deceleration of the road vehicle 1 (by determining the degree of depression of the brake pedal 23, for example by detecting the pressure of the brake fluid in the hydraulic circuit of the brake system) and simultaneously detects a multi-step downshift request by the driver (if the driver keeps the downshift paddle shifter 25 depressed for a long time); therefore, if both of the above situations occur, the control unit 12 of the powertrain 6 performs a multi-step downshift continuously and in an autonomous manner independent of further intervention by the driver while the road vehicle 1 is decelerating. In particular, the control unit 12 of the powertrain 6 determines the duration of a single shift time interval Δt common to all multi-step downshifts (i.e., said single shift time interval Δt applies in the same way to all downshifts of the multi-step downshift) and, after the first downshift, performs each downshift when exactly said shift time interval Δt has elapsed since the previous downshift.

[0037] According to a preferred embodiment, the control unit 12 of the powertrain 6 detects the driver's multi-speed downshift request at the same time T1 (at Figure 3 ) a first downshift is performed, and (after the first downshift) all further downshifts are performed each time exactly a shift time interval Δt has elapsed since the preceding downshift; in this way, all downshifts are equally spaced in time from one another by the same shift time interval Δt (which is always constant, i.e., always the same). That is, the duration of the shift time interval Δt always remains constant for all downshifts performed one after the other.

[0038] Obviously, the control unit 12 of the powertrain 6 determines a multi-step downshift when the deceleration situation of the road vehicle 1 ceases, ie when the driver releases the brake pedal 23, thereby ending braking.

[0039] It should be noted that downshifting may cause the speed ω of the internal combustion engine 4 to increase. E In the case of excessive increase (ie, in the case of a possible increase in the rotation speed ω of the internal combustion engine 4 E In the case where the maximum speed allowed is exceeded), the control unit 12 of the powertrain 6 delays the downshift; that is, when necessary, the downshift is delayed until the downshift can be performed without causing the speed ω of the internal combustion engine 4 to increase. E excessive increase.

[0040] According to a preferred embodiment, the control unit 12 of the powertrain 6 determines the rotation speed ω of the internal combustion engine 4 at the time T1 when the driver's multi-step downshift request is detected. E , the duration of the shift time interval Δt is determined based on the gear engaged in the dual-clutch servo-assisted transmission 7 at the time T1 when the driver's multi-step downshift request is detected and / or based on the degree of depression of the brake pedal 23 at the time T1 when the driver's multi-step downshift request is detected.

[0041] According to a possible embodiment, the control unit 12 of the powertrain 6 may have in its memory a speed ω based on the internal combustion engine 4. E , the gear engaged in the dual-clutch servo-assisted transmission 7 and the degree of depression of the brake pedal 23 to provide a mapping of the duration of the shift time interval Δt.

[0042] For example, when the brake pedal 23 is depressed to a large extent, the shift time interval Δt may last for 3 to 4 tenths of a second, while when the brake pedal 23 is depressed to a small extent, the shift time interval Δt may last for 10 to 12 tenths of a second.

[0043] According to a preferred but non-binding embodiment, the control unit 12 of the powertrain 6 determines the value of a comfort index (referred to as "CMFidx") at the moment T1 when the driver's multi-step downshift request is detected, and therefore, the control unit 12 of the powertrain 6 adjusts the execution speed of the downshift based on the value of the comfort index; that is, in the case where the comfort index indicates that the driver cares about comfort, the downshift is performed more slowly (smoothly), thus triggering smaller longitudinal oscillations, and in the case where the comfort index indicates that the driver does not care about comfort, the downshift is performed faster (suddenly), thus triggering larger longitudinal oscillations. For example, the control unit 12 of the powertrain 6 can determine the value of the comfort index based on the position of a selector (also referred to as a "handle") controlled by the driver to indicate the type of desired driving style.

[0044] Figure 3 An example of a multi-step downshift during (prolonged) braking is shown:

[0045] At time T1, the driver (who has depressed the brake pedal 23) depresses the downshift paddle shifter 25 and keeps the downshift paddle shifter 25 depressed for a long time; therefore, at time T1, the control unit 12 of the powertrain 6 performs a first-stage downshift (it should be noted that, starting from time T1, the speed ω of the internal combustion engine 4 is E From the speed ω of the clutch 16B B becomes the speed ω of the clutch 16A A ), and calculate the duration of the shift time interval Δt;

[0046] At time T2 (exactly separated from time T1 by a shifting time interval Δt), the control unit 12 of the powertrain 6 autonomously (i.e., without further command from the driver) performs a second downshift (it should be noted that, starting from time T2, the speed ω of the internal combustion engine 4 is E From the speed ω of the clutch 16A A becomes the speed ω of clutch 16B B );

[0047] At time T3 (exactly separated from time T2 by a shifting time interval Δt), the control unit 12 of the powertrain 6 autonomously (i.e., without further command from the driver) performs a third-stage downshift (it should be noted that, starting from time T3, the speed ω of the internal combustion engine 4 is E From the speed ω of the clutch 16B B becomes the speed ω of the clutch 16A A ).

[0048] At time T4 (exactly separated from time T3 by a shifting time interval Δt), the control unit 12 of the powertrain 6 autonomously (i.e., without further command from the driver) performs a fourth-speed downshift (it should be noted that, starting from time T4, the speed ω of the internal combustion engine 4 is E From the speed ω of the clutch 16A A becomes the speed ω of clutch 16B B );

[0049] At time T5 (which is less than the shift time interval Δt from time T4 and is therefore too early for a downshift and no downshift actually occurs), the driver releases the brake pedal 23 (i.e. ends the braking phase) and, as a result, the control unit 12 of the powertrain 6 ends the multi-stage downshift as the deceleration of the road vehicle 1 ceases.

[0050] 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.

[0051] The embodiments described here can be combined with one another without thereby exceeding the scope of protection of the present invention.

[0052] The above control methods have different advantages.

[0053] Firstly, the control method described above allows the regulation phases to be reduced and simplified to a considerable extent, since the law providing the duration of the shifting time interval Δt can be determined and established in a relatively simple and rapid manner.

[0054] Furthermore, the control method described above controls the dual clutch servo-assisted transmission 7 in a driver-understandable manner that is generally perceived by the driver as "natural" (ie corresponds to the driver's expectations).

[0055] Finally, 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 by performing a multi-step downshift in a powertrain having a servo-assisted gearbox, the control method comprising the following steps: detecting a deceleration of the road vehicle (1) and simultaneously detecting a driver's multi-stage downshift request; as well as performing a multi-speed downshift while the road vehicle (1) is decelerating, continuously and in an autonomous manner independent of further intervention by the driver; The control method is characterized in that the control method further comprises the following steps: determining a duration of a single shift time interval (Δt) common to all multi-speed downshifts; as well as After the first downshift, each downshift is performed when exactly the shift time interval (Δt) has elapsed since the previous downshift.

2. The control method according to claim 1, characterized in that: The first-speed downshift is performed at the same timing (T1) at which the driver's multi-speed downshift request is detected.

3. The control method according to claim 1, characterized in that: Downshifting will cause the speed (ω) of the internal combustion engine (4) connected to the power transmission system (6) to increase. e ) increases excessively, delay downshifting.

4. The control method according to claim 1, characterized in that: Based on the speed (ω) of the internal combustion engine (4) at the time (T1) when the driver's multi-step downshift request is detected e ) to determine the duration of the shift time interval (Δt).

5. The control method according to claim 1, characterized in that: The duration of the shift time interval (Δt) is determined based on the gear engaged in the servo-assisted transmission (7) at the time (T1) when the driver's multi-step downshift request is detected.

6. The control method according to claim 1, characterized in that: The duration of the shift time interval (Δt) is determined based on the degree of depression of the brake pedal (23) at the time (T1) when the driver's multi-step downshift request is detected.

7. The control method according to claim 1, characterized in that: The duration of the shifting time interval (Δt) always remains constant for all downshifts.

8. The control method according to claim 1, characterized in that: When the deceleration of the road vehicle (1) ceases, the multi-step downshift ends.

9. The control method according to claim 1, characterized in that: A deceleration of the road vehicle (1) is detected by determining the degree of depression of an actuator pedal (23).

10. The control method according to claim 1, characterized in that: In the case where the driver keeps pressing the downshift paddle shifter (25) for a long time, a multi-step downshift request of the driver is detected.

11. The control method according to claim 1, characterized in that: The control method further comprises the following steps: determining a value of a comfort index at a time (T1) when a multi-step downshift request by the driver is detected; and A speed at which the downshift is executed is adjusted based on the comfort index.

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