Method for controlling a road vehicle with a servo-assisted transmission during a deceleration phase - Patents.com

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 priority to Italian Patent Application No. 102019000017510, filed September 30, 2019, the disclosure of which is incorporated herein by reference in its entirety.

[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 invention finds advantageous application in drivetrains equipped with a dual clutch servo assisted transmission, to which, without loss of generality, explicit reference is therefore made in the following description. [Background technology]

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

[0005] During a gear shift, a current gear connects the secondary shaft to a main shaft, while a following gear connects the secondary shaft to the other main shaft, and as a result, a gear shift is performed by crossing two clutches, i.e. by opening 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, i.e. 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 medium speed (i.e. when the road vehicle 1 is operated 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 revolutions per minute) to minimize fuel consumption. In these conditions, the control unit of the drivetrain uses lower and upper thresholds, and if the rotational speed of the internal combustion engine is lower than the lower threshold, a downshift is performed (i.e. a new lower gear is engaged), whereas if the rotational speed of the internal combustion engine is higher than the upper threshold, an upshift is performed (i.e. a new higher gear is engaged), this control mode is effective to allow the internal combustion engine to operate at low speed, but there is a risk that it will cause a very low speed when the driver decides to stop the road vehicle by acting (more or less strongly) on the brake pedal (i.e. it may operate the internal combustion engine very slowly, which will result in erratic operation and even undesirable stopping), because downshifts require a certain execution time to ensure the necessary comfort (which is essential when the drivetrain operates in automatic mode) and the time required to execute all the downshifts required to prevent the rotational speed from falling too far below the lower threshold may not be present.

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

[0008] Patent application WO2015024792 describes a method for controlling a road vehicle with a servo-assisted transmission during a deceleration phase, whereby, if conditions permit, multiple downshifts are performed, thereby preventing intermediate gears between the first and last gear from being engaged. Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a method for controlling a road vehicle equipped with a servo-assisted transmission during a deceleration phase, said method not suffering from the aforementioned drawbacks and at the same time being easy and economical to implement. [Means for solving the problem]

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

[0011] The appended claims describe preferred embodiments of the invention and form an integral part of the body of the specification. [Brief description of the drawings]

[0012] The present invention will now be described with reference to the accompanying drawings, which show non-limiting embodiments of the invention. [Figure 1] 1 is a schematic plan view of a rear-wheel drive road vehicle having a drivetrain with a dual clutch servo-assisted transmission controlled in accordance with the control method of the present invention; [Diagram 2] FIG. 2 is a schematic diagram of the drive train of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In Figure 1, the numeral 1 generally indicates a road vehicle (in particular an automobile) with two front driven (i.e. non-driven) wheels 2 and two rear driven wheels 3. At the front there is an internal combustion engine 4 with a drive shaft 5 which generates torque transmitted to the drive wheels 3 by a drive train 6. The drive train 6 comprises a dual clutch servo assisted transmission 7 arranged in a rear wheel drive assembly and a transmission shaft 8 connecting the drive shaft 5 to an input 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 extend a pair of axle shafts 10, each axle shaft 10 being integral with a drive wheel 3.

[0014] The road vehicle 1 comprises an engine 4 control unit 11 for controlling the engine 4, a drivetrain 6 control unit 12 for controlling the drivetrain 6, and a bus line 13, for example manufactured according to the CAN (Car Area Network) protocol, which extends throughout the road vehicle 1 and allows the two control units 11, 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 sent 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 absent and all communication between the two control units 11, 12 may be exchanged using the bus line 13.

[0015] According to Fig. 2, the dual clutch servo assisted transmission 7 comprises a pair of main shafts 15, which are coaxial, independent of each other and inserted inside each other. Furthermore, the dual clutch servo assisted transmission 7 comprises two coaxial clutches 16, each adapted to connect the 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 being an oil bath clutch and therefore pressure controlled (i.e. the degree of opening and closing of the clutch 16 is determined by the pressure of the oil in the clutch 16) and according to another embodiment, each clutch 16 being a dry clutch and therefore position controlled (i.e. the degree of opening and closing of the clutch 16 is determined by the position of the movable element of the clutch 16). The dual clutch servo assisted transmission 7 comprises one single countershaft 17 connected to a differential 9 which transmits the movement to the drive wheels 3, and according to another equivalent embodiment, the dual clutch servo assisted transmission 7 comprises two countershafts 17, both of which are connected to the differential 9.

[0016] The dual clutch servo assisted transmission 7 has seven forward gears designated by Roman numerals (first gear I, second gear II, third gear III, fourth gear IV, fifth gear V, sixth gear VI and seventh gear VII) and a reverse gear (designated R). The main shaft 15 and the secondary shaft 17 are mechanically coupled to each other by a number of gear trains, each gear train forming a respective gear and comprising a main gear wheel 18 attached to the main shaft 15 and a secondary gear wheel 19 attached to the secondary shaft 17. To enable correct operation of the dual clutch servo assisted transmission 7, all odd gears (first gear I, third gear III, fifth gear V and seventh gear VII) are coupled to the same main shaft 15, while all even gears (second gear II, fourth gear IV and sixth gear VI) are coupled to the other main shaft 15.

[0017] Each main gear wheel 18 is splined to the respective main shaft 15 so as to always rotate together with the main shaft 15 and is permanently meshed with a respective secondary gear wheel 19, while each secondary gear wheel 19 is loosely mounted on the secondary shaft 17. Furthermore, the dual clutch servo assisted transmission 7 comprises four synchronizers 20, each of which is mounted coaxially with the secondary shaft 17, disposed between the two secondary gear wheels 19 and designed to be operated to alternatively mount the two respective secondary gear wheels 19 to the secondary shaft 17 (i.e., to make the two respective secondary gear wheels 19 angularly integral with the secondary shaft 17). In other words, each synchronizer 20 can be moved in one direction to mount the secondary gear wheel 19 to the secondary shaft 17, or moved in the other direction to mount the other secondary gear wheel 19 to the secondary shaft 17.

[0018] The dual clutch transmission 7 has one single secondary shaft 17 connected to a differential 9 that transmits motion to the drive wheels 3, and according to another equivalent embodiment, the dual clutch transmission 7 has two secondary shafts 17, both of which are connected to the differential 9.

[0019] 1, a road vehicle 1 comprises a passenger compartment providing a driving position for a driver, comprising a seat (not shown), a steering wheel 21, an accelerator pedal 22, a brake pedal 23 and two paddle shifters 24, 25 connected to either side of the steering wheel 21 controlling a dual clutch servo assisted transmission 7. The upshift paddle shifter 24 is operated (by a short pressure) by the driver to request an upshift (i.e. engagement of a new gear higher than and adjacent to the current gear), whereas the downshift paddle shifter 25 is operated (by a short pressure) by the driver to request a downshift (i.e. engagement of a new gear lower than and adjacent to the current gear).

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

[0021] In use, when the drivetrain 6 operates 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 , as well as detecting the current gear engaged in the servo-assisted transmission 7 and detecting depression of the brake pedal 23 (e.g. by detecting the brake fluid pressure in the hydraulic circuit of the brake system). At this point, the control unit 12 of the drivetrain 6 calculates, assuming that the depression of the brake pedal 23 remains constant, the release time interval necessary to enable the road vehicle 1 to reach an opening speed at which the clutch 16 of the servo-assisted transmission 7 is reliably opened (taking into account the upcoming stopping of the road vehicle 1), and furthermore, the control unit 12 of the drivetrain 6 calculates, based on the time required to perform a downshift (and taking into account the fact that when the drivetrain operates in automatic mode, downshifts must be performed with maximum comfort and therefore require a certain execution time, for example in the range of 800-900 milliseconds), how many downshifts can be performed within the internal opening time.

[0022] The control unit 12 of the drivetrain 6 then schedules downshifts to be performed from the current gear engaged in the servo-assisted transmission 7 to a release gear (generally second gear II) that ensures the release of the clutch 16 of the servo-assisted transmission 7, performing a number of downshifts not exceeding (if necessary less than) the number of downshifts that can be performed in the release time interval, and finally, during the release time interval, the control unit 12 of the drivetrain 6 performs the already scheduled downshifts, so that at the end of the release time interval, the release gear (generally second gear II) is engaged in the servo-assisted transmission 7, thus ensuring the release of the clutch 16.

[0023] According to a preferred embodiment, the disengaging gear is the second gear II, the road vehicle 1 is stopped with the clutch 16 disengaged and, after the road vehicle 1 is stopped, the first gear I is engaged with the servo-assisted transmission 7.

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

[0025] According to a preferred embodiment, the control unit 12 of the drivetrain 6 periodically detects the depression of the brake pedal 23, recalculates the release time interval (if the depression of the brake pedal 23 changes), recalculates the number of downshifts that can be performed in the release time interval (if the depression of the brake pedal 23 changes), and then reschedules the downshifts to be performed from the current gear engaged in the servo-assisted transmission 7 to the released gear (if the depression of the brake pedal 23 changes).

[0026] The control unit 12 of the drive train 6 determines the rotation speed ω E The control unit 12 of the drivetrain 6 schedules downshifts to prevent the rotational speed ω of the internal combustion engine 4 from falling below a predetermined lower threshold, so that the internal combustion engine 4 does not operate too slowly, i.e. E downshifts are scheduled to ensure that the maximum torque always exceeds a predetermined lower threshold.

[0027] According to a preferred embodiment, the control unit 12 of the drivetrain 6 measures (by means of a suitable sensor) the rotational speed ω2 of the countershaft 17 of the servo-assisted transmission 7 and calculates the longitudinal deceleration of the road vehicle 1 by calculating the time derivative of the rotational speed ω2 of the countershaft 17 of the servo-assisted transmission 7. The control unit 12 of the drivetrain 6 then calculates the disengagement time interval based on the longitudinal deceleration of the road vehicle 1, i.e. the control unit 12 of the drivetrain 6 calculates the time required for the road vehicle 1 to reach the disengagement speed (the speed at which the clutch 16 of the servo-assisted transmission 7 is reliably disengaged) based on the longitudinal deceleration of the road vehicle 1.

[0028] Even when the drive train 6 of the road vehicle 1 is equipped with a single clutch servo assisted transmission, what has been disclosed above is applicable without major modifications.

[0029] The above described control method has several advantages.

[0030] First of all, the above-described control method makes it possible to stop the road vehicle 1 when the drivetrain 6 operates in automatic mode without running the internal combustion engine 4 too slowly and in particular without affecting the ride comfort perceived by the driver.

[0031] Furthermore, the above described control method is easy and economical to implement since its implementation requires limited storage space and low computing power. [Explanation of symbols]

[0032] 1. Road vehicles 2 Front wheels 3 Rear wheel 4 Engine 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 Secondary shaft 18 Main gear wheel 19 Secondary gear wheel 20 Synchronous Device 21 Steering Wheel 22 Accelerator pedal 23 Brake pedal 24 Upshift paddle shifter 25 Downshift paddle shifter ω E Rotational speed ω2 rotation 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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