Method for controlling a road vehicle to perform multiple downshifts in a drivetrain with a servo-assisted transmission - Patents.com

Abstract

To naturally, easily and economically execute an operation mode to execute multiple downshift in a drive train provided with a servo-assisted transmission.SOLUTION: A method includes the steps of: detecting a condition of slowing down of a road vehicle and simultaneously detecting a driver's request for multiple downshift; continuously executing a plurality of downshifts in an autonomous manner while slowing down the road vehicle regardless of further operations of the driver; a step for determining a duration of a shift time interval (Δt); and executing each downshift following a first downshift when the shift time interval (Δt) has exactly elapsed since the previous downshift.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This patent application claims priority to Italian Patent Application No. 102019000017507, 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 to perform multiple downshifts in a drivetrain having a servo-assisted transmission.

[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] There is a feature (called "sequential downshift") that allows the driver to gear down multiple times while braking (actually at the end of braking) to engage the lowest possible gear (depending on the maximum RPM of the internal combustion engine) at the end of braking to have the maximum possible acceleration upon restart. This feature, known as "sequential downshift", is activated by the driver during braking (i.e., when the brake pedal is depressed) by pressing a downshift paddle shifter for an extended period of time (i.e., for a time exceeding a certain time threshold), which is usually pressed only for a short moment to request one single downshift (i.e., engagement of a new gear lower than the current gear).

[0007] In other words, the driver may rely on an upshift paddle shifter, which is pressed briefly to request one single upshift (i.e., engagement of a new gear higher than and adjacent to the current gear) and a downshift paddle shifter, which is pressed briefly to request one single downshift (i.e., engagement of a new gear lower than and adjacent to the current gear), to control the dual-clutch servo-assisted transmission. During braking (obviously a long brake), the driver may press the downshift paddle shifter continuously while depressing the brake pedal to activate a feature called "sequential downshift" that automatically gears down multiple times during braking so that the lowest possible gear is engaged at the end of braking (i.e., when the brake pedal is released).

[0008] The feature, known as "sequential downshift," is typically used when sprinting around the track, at the end of a straight stretch where the driver chooses to invoke the feature to handle the ideal gear selection while concentrating on preparing for the next curve.

[0009] A function called "sequential downshift" currently involves setting a series of thresholds for the rotational speed of the internal combustion engine, and therefore automatically shifting gears whenever the rotational speed of the internal combustion engine reaches a corresponding rotational speed threshold. However, the software that generates the series of rotational speed thresholds for the internal combustion engine requires lengthy and complex tuning, and furthermore, the operating mode of the function known as "sequential downshift", although effective, is usually not appreciated by drivers, who tend to find it "unnatural" (i.e., contrary to the driver's expectations).

[0010] Some examples of implementations of a feature called "sequential downshift" are described in patent applications WO2013153309 and EP2921746. Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a method for controlling a road vehicle to perform multiple downshifts in a drivetrain equipped with a servo-assisted transmission, said method not suffering from the above-mentioned drawbacks and at the same time being easy and economical to implement. [Means for solving the problem]

[0012] According to the present invention there is provided a method of controlling a road vehicle to perform multiple downshifts in a drivetrain having a servo assisted transmission as claimed in the accompanying claims.

[0013] 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]

[0014] 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. [Diagram 3] 4 shows the time variations in the rotational speeds of two clutches and the drive shaft during multiple downshifts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] When the road vehicle 1 is decelerating (due to the driver's action on the brake pedal 23) and the driver keeps the downshift paddle shifter 25 pressed for a long time (i.e., for a time exceeding a certain time threshold), which is usually pressed for a short moment to request one single downshift, the control unit 12 of the drivetrain 6 activates a function (called "sequential downshift") that allows the driver to downshift multiple times while braking in order to engage the lowest possible gear (depending on the maximum rpm of the internal combustion engine 4) at the end of braking in order to have the maximum possible acceleration at the restart (which is actually done at the end of braking). This function, known as "sequential downshift", determines the automatic execution (i.e., without driver interaction) of multiple downshifts in succession until the deceleration of the road vehicle 1 is interrupted (i.e., until the driver stops pressing the brake pedal 23).

[0023] In other words, the driver may rely on the upshift paddle shifter 24, which is pressed briefly to request one single upshift (i.e., engagement of a new gear higher than and adjacent to the current gear) and the downshift paddle shifter 25, which is pressed briefly to request one single downshift (i.e., engagement of a new gear lower than and adjacent to the current gear) to control the dual clutch servo assisted transmission 7. During braking (obviously a long brake), the driver may press the downshift paddle shifter 25 continuously while depressing the brake pedal 23 to activate a function called "sequential downshift" that automatically gears down multiple times during braking so that the lowest possible gear is engaged at the end of braking (i.e., when the brake pedal 23 is released).

[0024] The feature, known as "sequential downshift," is typically used when sprinting around the track, at the end of a straight stretch where the driver chooses to invoke the feature to handle the ideal gear selection while concentrating on preparing for the next curve.

[0025] The control unit 12 of the drivetrain 6 detects the state of deceleration of the road vehicle 1 (e.g., by determining the degree of depression of the brake pedal 23 by detecting the pressure of the brake fluid in the hydraulic circuit of the brake system) and at the same time detects the driver's request for multiple downshifts (when the driver keeps the downshift paddle shifter 25 pressed for an extended period of time), and thus, if both aforementioned conditions occur, the control unit 12 of the drivetrain 6 autonomously performs multiple downshifts in succession while the road vehicle 1 is decelerating, regardless of further driver actions. In particular, the control unit 12 of the drivetrain 6 determines the duration of one single shift time interval Δt common to all of the multiple downshifts (i.e., said single shift time interval Δt is applied in the same way for all downshifts of the multiple downshifts) and performs each downshift following the first downshift exactly when said shift time interval Δt has elapsed since the previous downshift.

[0026] According to a preferred embodiment, the control unit 12 of the drivetrain 6 performs the first downshift at the same time T1 (shown in FIG. 3 ) when the driver's request for a multiple downshift is detected, and performs all other downshifts (following the first downshift) exactly each time the shift time interval Δt has elapsed since the previous downshift, in this way all downshifts are equidistantly spaced from one another in time by the same shift time interval Δt (always constant, i.e. always the same), i.e. the duration of the shift time interval Δt always remains constant for all downshifts performed one after the other.

[0027] Obviously, the control unit 12 of the drivetrain 6 decides to downshift when the deceleration state of the road vehicle 1 ends, i.e. when the driver ends braking by releasing the brake pedal 23.

[0028] The downshift is performed at a rotation speed ω of the internal combustion engine 4. E When there is a risk of causing an excessive increase in the rotation speed ω E the control unit 12 of the drive train 6 delays the downshift, i.e., if necessary, delays the downshift when the rotation speed ω of the internal combustion engine 4 exceeds the permitted maximum speed. E It should be noted that the downshift is delayed until the downshift can be performed without causing an undue increase in torque.

[0029] According to a preferred embodiment, the control unit 12 of the drive train 6 determines the rotational speed ω of the internal combustion engine 4 at the time T1 at which a driver's request for a multiple downshift is detected. E Based on this, the duration of the shift time interval Δt is determined based on the gear that is engaged in the dual clutch servo assisted transmission 7 at the time T1 when the driver's request for multiple downshifts is detected, and / or based on the degree of depression of the brake pedal 23 at the time T1 when the driver's request for multiple downshifts is detected.

[0030] According to a possible embodiment, the control unit 12 of the drive train 6 stores in its memory the rotational speed ω E based on the gear that is engaged in the dual clutch servo assisted transmission 7 and based on the depression of the brake pedal 23.

[0031] As an example, the duration of the shift time interval Δt may be 3-4 tenths of a second for high depression of the brake pedal 23 and 10-12 tenths of a second for low depression of the brake pedal 23 .

[0032] According to a preferred but non-binding embodiment, the control unit 12 of the drivetrain 6 determines the value of a comfort index (known as "CMFidx") at the time T1 when the driver's request for multiple downshifts is detected, and the control unit 12 of the drivetrain 6 accordingly adjusts the execution speed of the downshift based on the value of the comfort index, i.e., if the comfort index indicates that the driver cares about comfort, the downshift is executed more slowly (smoothly), thus causing less longitudinal oscillations, whereas if the comfort index indicates that the driver does not care about comfort, the downshift is executed more quickly (abruptly), thus causing more longitudinal oscillations. For example, the control unit 12 of the drivetrain 6 may determine the value of the comfort index based on the position of a driver-controlled selector (also known as a "hand lever") to indicate the type of desired driving style.

[0033] FIG. 3 shows an example of multiple downshifts during (extended) braking.

[0034] At time T1, the driver (who has already depressed the brake pedal 23) presses the downshift paddle shifter 25 and keeps it pressed for an extended period of time, so that at time T1, the control unit 12 of the drivetrain 6 first (starting from the time T1, the rotation speed ω E is the rotation speed ω of the clutch 16B B from the rotational speed ω of clutch 16A A t) and calculate the duration of the shift time interval Δt.

[0035] At time T2 (which is exactly the shift time interval Δt away from time T1), the control unit 12 of the drive train 6 executes a second downshift autonomously (i.e. without further commands from the driver) (starting from time T2, the rotational speed ω E is the rotation speed ω of the clutch 16A A from the rotational speed ω of clutch 16B B (Note that the

[0036] At time T3 (which is exactly the shift time interval Δt away from time T2), the control unit 12 of the drive train 6 executes a third downshift autonomously (i.e. without further commands from the driver) (starting from time T3, the rotational speed ω E is the rotation speed ω of the clutch 16B B from the rotational speed ω of clutch 16A A (Note that the

[0037] At time T4 (which is exactly the shift time interval Δt away from time T3), the control unit 12 of the drive train 6 executes a fourth downshift autonomously (i.e. without further commands from the driver) (starting from time T4, the rotational speed ω E is the rotation speed ω of the clutch 16A A from the rotational speed ω of clutch 16B B (Note that the

[0038] At time T5 (which is less than the shift time interval Δt away from time T4 and therefore too early for a downshift that does not actually occur), the driver releases the brake pedal 23 (i.e., ending the braking phase) and thus the control unit 12 of the drivetrain 6 ends the multiple downshifts as the deceleration state of the road vehicle 1 ends.

[0039] 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.

[0040] The embodiments described herein can for this reason be combined with one another without exceeding the scope of protection of the invention.

[0041] The above described control method has several advantages.

[0042] First of all, the above described control method makes it possible to significantly reduce and simplify the adjustment steps, since the laws giving the duration of the shift time intervals Δt can be determined and set in a relatively easy and quick manner.

[0043] Furthermore, the above described control method controls the dual clutch servo assisted transmission 7 in a manner that is commonly accepted by drivers who consider them to be "natural" (i.e., corresponds to the driver's expectations).

[0044] Finally, the above described control method is simple and economical to implement since its implementation requires limited storage space and low computational power. [Explanation of symbols]

[0045] 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 ω A Rotational speed ω B Rotational speed At T1 At T2 At T3 At T4 At T5 Δt time interval

Claims

1. A method for controlling a road vehicle (1) to perform multiple downshifts in a drivetrain having a servo-assisted transmission (7), comprising: detecting a state of deceleration of the road vehicle (1) and at the same time detecting a driver request for multiple downshifts; autonomously performing multiple downshifts in succession while the road vehicle (1) is decelerating, regardless of further driver input; In a control method comprising: determining a duration of a single shift time interval (Δt) common to all of the plurality of downshifts; executing each downshift following an initial downshift exactly the shift time interval (Δt) since the previous downshift; Further comprising: The rotation speed (ω) of the internal combustion engine (4) connected to the drive train (6) Ｅ a downshift is delayed if the downshift would cause an excessive increase in torque.

2. The first downshift occurs at the same time that a driver request for multiple downshifts is detected (T １ The control method according to claim 1 , wherein the control method is performed on the

3. The duration of the shift time interval (Δt) is determined based on the time at which a driver request for a multiple downshift is detected (T １ ) the rotation speed (ω Ｅ The control method according to claim 1 or 2, wherein the control is determined based on the

4. The duration of the shift time interval (Δt) is determined based on the time at which a driver request for a multiple downshift is detected (T １ 4. The method according to claim 1, wherein the first gear is meshed with the servo-assisted transmission (7).

5. The duration of the shift time interval (Δt) is determined based on the time at which a driver request for a multiple downshift is detected (T １ 5. The control method according to claim 1, wherein the brake pedal depression is determined based on a degree of depression of the brake pedal (23) at the brake pedal depression position.

6. 6. The method of claim 1, wherein the duration of the shift time interval (Δt) remains constant for all downshifts of the plurality of downshifts.

7. 7. The method according to any one of claims 1 to 6, wherein the downshifts end when a deceleration state of the road vehicle (1) ends.

8. 8. Method according to any one of the preceding claims, wherein the deceleration state of the road vehicle (1) is detected by determining the depression of a brake pedal (23).

9. 9. The method of claim 1, wherein a driver request for multiple downshifts is detected when the driver continues to press the down paddle shifter (25) for an extended period of time.

10. The time when a driver's request for multiple downshifts is detected (T １ ) determining a comfort index value; adjusting a downshift execution speed based on the comfort index; The control method according to claim 1 , further comprising:

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