Method to control road vehicle provided with servo-assisted transmission during slowing-down phase

Abstract

To provide a control method to improve degradation of riding comfort in downshift caused by a braking operation, when a servo-assisted transmission is in an automatic operation mode.SOLUTION: A downshift is carried out by the steps for: calculating an opening time interval needed to allow a road vehicle to reach an opening speed at which clutches 16A, B of a servo-assisted transmission 7 are reliably opened under the assumption that a pressing of a brake pedal remains constant; calculating the number of times of downshifting that can be carried out in the opening time interval based on a time needed to carry out downshift; and scheduling the downshift to be carried out in order to get from the current gear engaged in the servo-assisted transmission to an opening gear with which the clutch of the servo-assisted transmission is reliably opened.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] [Cross - reference to Related Applications] This patent application claims the priority of Italian Patent Application No. 102019000017510, filed on September 30, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for controlling a road vehicle equipped with a servo - assisted transmission during a deceleration phase.

[0003] The present invention finds advantageous applications in a drive train equipped with a dual - clutch servo - assisted transmission, and for this reason, without loss of generality, it will be explicitly referred to in the following description.

Background Art

[0004] A drive train equipped with a dual - clutch servo - assisted transmission comprises a pair of main shafts that are coaxial with each other, independent of each other, and inserted inside each other, two coaxial clutches each adapted to connect its respective main shaft to the drive shaft of an internal combustion engine, and at least one secondary shaft that transmits movement to the drive wheels and can be coupled to the main shaft by respective gear trains each forming a gear.

[0005] During a gearshift, the current gear couples the secondary shaft to the main shaft, while the following gear couples the secondary shaft to the other main shaft. As a result, the gearshift is performed by crossing the two clutches, that is, by releasing the clutch associated with the current gear and simultaneously closing the clutch associated with the following gear.

[0006] When the drivetrain operates in automatic mode, that is, when gear shifts are not requested by the driver but are determined autonomously by the drivetrain control unit (simulating the behavior of an automatic transmission), and when the road vehicle 1 is moving forward at a medium speed (i.e., when the road vehicle 1 is driven in a non-high-performance mode), the "high" gear is generally 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 revolutions per minute) to minimize fuel consumption. In these conditions, the drivetrain control unit uses lower and upper thresholds to perform a downshift (i.e., engage a new, lower gear) if the engine speed is below the lower threshold, while an upshift (i.e., engage a new, higher gear) is performed if the engine speed exceeds the upper threshold. This control mode is effective in allowing the engine to operate at low speeds, but it carries the risk of causing extremely low speeds when the driver decides to stop the vehicle on the road by applying (more or less forcefully) the brake pedal (i.e., potentially causing the engine to operate very slowly, resulting in irregular operation and even potentially leading to an undesirable stop). This is because a certain amount of execution time is required to ensure the necessary comfort of downshifting (which is essential when the drivetrain is operating in automatic mode), and there may not be enough time to perform all the downshifts required to prevent the engine speed from falling significantly below the lower threshold.

[0007] The solution currently used to prevent internal combustion engines from operating too slowly is to speed up downshifts (i.e., force particularly rapid downshifts), but this solution (due to rapidly executed downshifts) results in a jarring longitudinal acceleration and a sudden increase in the speed of the internal combustion engine, thus significantly reducing the comfortable ride perceived by the driver.

[0008] The patent application, International Publication No. 2015024792, describes a method for controlling a road vehicle equipped with a servo-assisted transmission during the deceleration phase, in which, where conditions permit, multiple downshifts are performed, thereby preventing the engagement of intermediate gears between the first and last gears. [Overview of the project] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a method for controlling a road vehicle equipped with a servo-assisted transmission during the deceleration phase, the method being free from the aforementioned drawbacks, and also being easy and economical to implement. [Means for solving the problem]

[0010] According to the present invention, a method is provided for controlling a road vehicle equipped with a servo-assisted transmission during a deceleration phase, as described in the appended claims.

[0011] The attached claims describe preferred embodiments of the present invention and form an integral part of the main text of the specification. [Brief explanation of the drawing]

[0012] The present invention will now be described with reference to the accompanying drawings illustrating non-limiting embodiments of the present invention. [Figure 1] This is a schematic plan view of a rear-wheel-drive road vehicle equipped with a drivetrain that includes a dual-clutch servo-assisted transmission controlled according to the control method of the present invention. [Figure 2] Figure 1 is a schematic diagram of the drivetrain. [Modes for carrying out the invention]

[0013] In Figure 1, the number 1 represents a road vehicle (in particular, an automobile) as a whole, comprising two front driven (i.e., non-driven) wheels 2 and two rear driven wheels 3. At the front is an internal combustion engine 4 with drive shafts 5 that generate torque transmitted to the driven wheels 3 by the drivetrain 6. The drivetrain 6 comprises a dual-clutch servo-assisted transmission 7 located in the rear-wheel drive assembly and a transmission shaft 8 that connects the drive shafts 5 to the inputs of the dual-clutch servo-assisted transmission 7. The dual-clutch servo-assisted transmission 7 is connected in a train-like manner to a self-locking differential 9, from which a pair of axle shafts 10 extend, each axle shaft 10 being integrated with the driven wheels 3.

[0014] The road-going vehicle 1 comprises an engine 4 control unit 11 that controls the engine 4, a drivetrain 6 control unit 12 that controls the drivetrain 6, and a bus line 13. The bus line 13 is manufactured, for example, according to the CAN (Car Area Network) protocol, extends throughout the road-going vehicle 1, and allows the two control units 11 and 12 to communicate with each other. In other words, the engine 4 control unit 11 and the drivetrain 6 control unit 12 are connected to the bus line 13 and can therefore communicate with each other by messages transmitted via the bus line 13. Furthermore, the engine 4 control unit 11 and the drivetrain 6 control unit 12 can be directly connected to each other by a dedicated synchronization cable 14, which can directly transmit signals from the drivetrain 6 control unit 12 to the engine 4 control unit 11 without delays caused by the bus line 13. Alternatively, the synchronization cable 14 may be omitted, and all communication between the two control units 11 and 12 may be conducted using the bus line 13.

[0015] As shown in Figure 2, the dual-clutch servo-assisted transmission 7 comprises a pair of main shafts 15 that are coaxial with each other, independent of each other, and inserted inward from each other. Furthermore, the dual-clutch servo-assisted transmission 7 comprises two coaxial clutches 16, each of which connects its respective main shaft 15 to the drive shaft 5 of the internal combustion engine 4 via the interposition of a transmission shaft 8. Each clutch 16 is an oil-bath clutch and is therefore pressure-controlled (i.e., the degree to which the clutch 16 is open or closed is determined by the pressure of the oil in the clutch 16). According to another embodiment, each clutch 16 is a dry clutch and is therefore position-controlled (i.e., the degree to which the clutch 16 is open or closed is determined by the position of the movable element of the clutch 16). The dual-clutch servo-assisted transmission 7 comprises one single sub-shaft 17 connected to a differential 9 that transmits motion to the drive wheels 3. According to another equivalent embodiment, the dual-clutch servo-assisted transmission 7 comprises two sub-shafts 17, both of which are connected to the differential 9.

[0016] The dual-clutch servo-assisted transmission 7 has seven forward gears (Gear I, Gear II, Gear III, Gear IV, Gear V, Gear VI, and Gear VII) indicated by Roman numerals, and a reverse gear (indicated by R). The main shaft 15 and the sub-shaft 17 are mechanically coupled to each other by multiple gear trains, each gear train forming its own gear and comprising a main gear wheel 18 mounted on the main shaft 15 and a sub-gear wheel 19 mounted on the sub-shaft 17. To enable precise operation of the dual-clutch servo-assisted transmission 7, all odd-numbered gears (Gear I, Gear III, Gear V, and Gear VII) are coupled to the same main shaft 15, while all even-numbered gears (Gear II, Gear IV, and Gear VI) are coupled to the other main shaft 15.

[0017] Each main gear wheel 18 is spline-coupled to the main shaft 15 so as to always rotate integrally with the main shaft 15, and permanently meshes with the respective sub-gear wheel 19, while each sub-gear wheel 19 is mounted on the sub-shaft 17 in a free-moving manner. Furthermore, the dual-clutch servo-assisted transmission 7 includes four synchronous devices 20, each mounted coaxially with the sub-shaft 17 and positioned between the two sub-gear wheels 19, and designed to operate in a way that allows each of the two sub-gear wheels 19 to be mounted to the sub-shaft 17 in an alternative manner (i.e., so that each of the two sub-gear wheels 19 is angularly integrated with the sub-shaft 17). In other words, each synchronous device 20 can be moved in one direction to mount a sub-gear wheel 19 to the sub-shaft 17, or it can be moved in the other direction to mount the other sub-gear wheel 19 to the sub-shaft 17.

[0018] The dual-clutch transmission 7 comprises a single sub-shaft 17 connected to a differential 9 that transmits motion to the drive wheels 3. According to another equivalent embodiment, the dual-clutch transmission 7 comprises two sub-shafts 17, both of which are connected to the differential 9.

[0019] According to Figure 1, the road vehicle 1 is equipped with an occupant compartment that provides a driving position for the driver, which includes a seat (not shown), a steering wheel 21, an accelerator pedal 22, a brake pedal 23, and two paddle shifters 24, 25, which control a dual-clutch servo-assisted transmission 7 and are connected to both sides of the steering wheel 21. The upshift paddle shifter 24 is operated by the driver (with a short pressure) to request an upshift (i.e., meshing a new gear higher than the current gear and adjacent to the current gear), while the downshift paddle shifter 25 is operated by the driver (with a short pressure) to request a downshift (i.e., meshing a new gear lower than the current gear and adjacent to the current gear).

[0020] The drivetrain 6 can operate in automatic mode, meaning that gear shifts are not requested by the driver and are determined autonomously by the control unit 12 of the drivetrain 6 (simulating the behavior of an automatic transmission).

[0021] When in use, if the drivetrain 6 is operating in automatic mode, during the deceleration phase, the control unit 12 of the drivetrain 6 detects the current speed of the road vehicle 1 and controls the rotational speed ω of the internal combustion engine 4. E The control unit 12 of the drivetrain 6 detects the current gear engaged with the servo-assisted transmission 7 and detects the depression of the brake pedal 23 (for example, by detecting the pressure of the brake fluid in the hydraulic circuit of the brake system). At this point, assuming that the depression of the brake pedal 23 remains constant, the control unit 12 of the drivetrain 6 calculates the release time interval required to allow the road vehicle 1 to reach a release speed at which the clutch 16 of the servo-assisted transmission 7 will be reliably released (taking into account the upcoming stop of the road vehicle 1). Furthermore, the control unit 12 of the drivetrain 6 calculates several downshifts that can be performed within the internal release time based on the time required to perform a downshift (and taking into account the fact that a predetermined execution time in the range of 800 to 900 milliseconds is required, for example, since the downshift must be performed with maximum comfort when the drivetrain is operating in automatic mode).

[0022] Thereafter, the control unit 12 of the drive train 6 schedules a downshift to be executed to reach a release gear (generally the second gear II) that reliably releases the clutch 16 of the servo assist transmission 7 from the currently engaged gear of the servo assist transmission 7, and executes a number of downshifts that does not exceed (and, if necessary, is less than) the number of downshifts that can be executed within the release time interval. Finally, during the release time interval, the control unit 12 of the drive train 6 executes the previously scheduled downshifts, whereby, at the end of the release time interval, the release gear (generally, the second gear II) is engaged in the servo assist transmission 7, and thus the clutch 16 is reliably released.

[0023] According to a preferred embodiment, the release gear is the second gear II, the road vehicle 1 is stopped with the clutch 16 released, and after the road vehicle 1 is stopped, the first gear I is engaged in the servo assist transmission 7.

[0024] Generally speaking, the control unit 12 of the drive train 6 always attempts to schedule a single downshift (i.e., the subsequent gear is consecutive to the previous gear), but if the number of downshifts that can be executed within the release time interval is less than the number of gears existing between the currently engaged gear of the servo assist transmission 7 and the release gear, the downshift scheduling necessarily involves at least one multiple downshift (i.e., for example, in the case of a downshift from the seventh gear VII to the fourth gear IV or in the case of a downshift from the sixth gear VI to the third gear III, the subsequent gear is not consecutive to the previous gear). The control unit 12 of the drive train 6 preferably prepares for the multiple downshift (i.e., immediately executes the possible multiple downshift) such that the last downshift of the downshift schedule is a single downshift at the beginning of the downshift schedule (i.e., at the beginning of the schedule).

[0025] According to a preferred embodiment, the control unit 12 of the drive train 6 periodically detects the depression of the brake pedal 23 and recalculates the release time interval (when the depression of the brake pedal 23 changes), and also recalculates the number of downshifts that can be performed during the release time interval (when the depression of the brake pedal 23 changes). Then, it reschedules the downshifts to be performed so as to reach from the current gear engaged with the servo-assisted transmission 7 to the release gear (when the depression of the brake pedal 23 changes).

[0026] The control unit 12 of the drive train 6 is configured to schedule a downshift to prevent the rotational speed ω of the internal combustion engine 4 from falling below a predetermined lower threshold value, so that the internal combustion engine 4 does not operate overly slowly. That is, the control unit 12 of the drive train 6 schedules a downshift so that the rotational speed ω of the internal combustion engine 4 can always exceed a predetermined lower threshold value. E が所定の下限閾値を下回ることを防止するダウンシフトをスケジュールして、内燃エンジン4が過度に遅く作動しないようにし、すなわち、ドライブトレイン6の制御ユニット12は、内燃エンジン4の回転速度ω E が所定の下限閾値を常に超えることができるようにするべくダウンシフトをスケジュールする。

[0027] According to a preferred embodiment, the control unit 12 of the drive train 6 measures the rotational speed ω2 of the secondary shaft 17 of the servo-assisted transmission 7 (by means of a suitable sensor), 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 transmission 7. Then, the control unit 12 of the drive train 6 calculates the release time interval based on the longitudinal deceleration of the road vehicle 1. That is, the control unit 12 of the drive train 6 calculates the time required for the road vehicle 1 to reach the release speed (the speed at which the clutch 16 of the servo-assisted transmission 7 is reliably released) based on the longitudinal deceleration of the road vehicle 1.

[0028] Even when the drive train 6 of the road vehicle 1 includes a single-clutch servo-assisted transmission, what has been disclosed previously can be applied without major changes.

[0029] The aforementioned control method has various advantages.

[0030] Firstly, the aforementioned control method enables the vehicle 1 on the road to be stopped without excessively slowing down the internal combustion engine 4 when the drivetrain 6 is operating in automatic mode, and in particular without affecting the comfortable ride perceived by the driver.

[0031] Furthermore, the aforementioned control method is easy and economical to implement because its execution requires limited memory space and low computing power. [Explanation of symbols]

[0032] 1. Vehicles on the road 2 Front wheels 3 Rear wheels 4 engines 5. Drive shaft 6 Drivetrain 7 Transmission 8. Transmission shaft 9 Differential device 10 Axle shaft 11. Engine control unit 12. Drivetrain control unit 13 Bus Line 14 Sync Cable 15 Main shaft 16 Clutch 17 Sub-shaft 18 Main gear wheel 19 Sub-gear wheel 20 Synchronizing device 21 Steering Wheel 22 Accelerator pedal 23 Brake pedal 24 Upshift Paddle Shifter 25 Downshift paddle shifters ω E Rotation speed ω² rotational speed

Claims

1. A method for controlling a road vehicle (1) equipped with a servo-assisted transmission (7) during a deceleration phase, the method comprising, when said servo-assisted transmission (7) is in an automatic operating mode, the steps of: detecting a current speed of the road vehicle (1); detecting a current gear engaged in the servo-assisted transmission (7); Detecting depression of a brake pedal (23); In a control method comprising: Calculating a release time, which is the time required for the road vehicle (1) to reach a release speed at which the clutch (16) of the servo-assisted transmission (7) is finally released, assuming that the depression of the brake pedal (23) remains constant; calculating a number of downshifts that may be performed during said opening time based on the time required to perform the downshifts; scheduling the downshifts to be performed from the current gear engaged in the servo-assisted transmission (7) to a release gear that will finally release the clutch (16) of the servo-assisted transmission (7) in order to perform a number of downshifts not exceeding the number of downshifts that can be performed during the release time; performing a scheduled downshift; The control method further comprises:

2. 2. The control method of claim 1, wherein the scheduling of downshifts involves at least one multiple downshift when the number of downshifts that can be performed during the open time is less than the number of gears that exist between the current gear engaged in the servo-assisted transmission and the open gear.

3. 3. The method of claim 2, wherein the scheduling of downshifts always places multiple downshifts first.

4. 4. A method according to claim 2 or 3, wherein at least the last downshift of said scheduling of downshifts is always a single downshift.

5. a step of periodically detecting depression of the brake pedal (23); recalculating the release time when the depression of the brake pedal (23) changes; recalculating the number of downshifts that can be performed during said release time when the depression of the brake pedal (23) changes; rescheduling a downshift to be performed from the current gear engaged in the servo-assisted transmission (7) to the disengaged gear when the depression of the brake pedal (23) changes; The control method according to claim 1 , further comprising:

6. the opening gear is a second gear (II), The road vehicle (1) is stopped with the clutch (16) released, After the road vehicle (1) is stopped, a first gear (I) is engaged with the servo-assisted transmission (7). A control method according to any one of claims 1 to 5.

7. The scheduling of downshifts is based on the rotational speed (ω Ｅ The control method according to claim 2 , wherein the control is performed so that the difference (i) between the first and second thresholds does not fall below a predetermined lower threshold.

8. The step of calculating the opening time includes: determining a longitudinal deceleration of the road vehicle (1); calculating said release time based on the longitudinal deceleration of said road vehicle (1); The control method according to claim 1 , comprising:

9. The step of determining the longitudinal deceleration comprises: The rotation speed (ω) of the secondary shaft (17) of the servo-assisted transmission (7) ２ ) measuring the The rotation speed (ω ２ calculating the longitudinal deceleration of the road vehicle (1) by calculating the time derivative of The control method of claim 8 , comprising:

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