Method for controlling a road vehicle to perform a static start

Abstract

A method for controlling a road vehicle (1) to perform a static start, the control method comprising the steps of: engaging a gear in a gearbox (7) while a corresponding clutch (16A) is open; gradually closing the clutch (16A) so that the clutch (16A) transmits a torque causing at least a pair of drive wheels (3) to rotate; determining a target slip ratio (S T ) of the drive wheels (3); periodically determining an actual slip ratio (S R ) of the drive wheels (3); and continuously adjusting the torque transmitted by the clutch (16A) during the closing of the clutch (16A) based on a difference between the target slip ratio (S T ) and the actual slip ratio (S R ) of the drive wheels (3).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000017522 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 of controlling a road vehicle to perform a standing start.

[0004] The invention is advantageously used 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 of which 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 shaft by a corresponding gear train, each defining a gear.

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

[0007] There is a function (known as "performance launch") which enables the driver to perform a very high-performance static launch. This function, also known as "performance launch", is activated by the driver when the road vehicle is stationary (e.g. by pressing a button) and requires the electronic control unit to autonomously control the internal combustion engine (i.e. the production of torque) and the drivetrain (i.e. the regulation of clutch closure during acceleration and the engagement of subsequent gears) so as to maximize longitudinal acceleration at all times. In particular, in order to activate the function known as "performance launch", the driver must press the brake pedal and the accelerator pedal simultaneously, and the static launch of the road vehicle begins when the brake pedal is released (the driver must keep the accelerator pedal fully depressed throughout the execution of the maneuver).

[0008] The most complex and delicate phase of a static start is certainly the regulation of clutch engagement, as the clutch needs to be engaged as quickly as possible without causing excessive drive wheel slip (moderate drive wheel slip is a positive because it maximizes torque transfer to the road).

[0009] The function known as "performance launch" currently requires predetermining the torque value to be transmitted to the ground during the clutch closing phase and gradually closing the clutch so that the clutch constantly transmits this predetermined torque value. However, this operating mode does not always ensure that the longitudinal acceleration is maximized at every moment, because the actual tire capacity to transmit torque to the ground is very variable, so that it cannot always be accurately predicted; for example, the same tire on the same road surface may provide different performances depending on the wear state of the tire, the temperature of the tire and the temperature of the road surface. Under certain unfavorable conditions, this operating mode transmits too much torque, thus determining excessive slip of the drive wheels (a significant performance degradation compared to the ideal performance), while under other more favorable conditions it transmits too little torque (and therefore does not achieve the ideal performance).

[0010] Patent DE19653855C1, patent application DE102005051145A1 and patent application DE102010014563A1 describe a method of controlling a road vehicle to perform a static launch, during which a clutch connecting an internal combustion engine to drive wheels is controlled to impart a specified slip to the drive wheels. Summary of the invention

[0011] The object of the present invention is to provide a method of controlling a road vehicle performing a static launch which does not suffer from the above-mentioned disadvantages and which is at the same time easy and economical to implement.

[0012] According to the present invention, a method for controlling a road vehicle to perform a static start is provided, the control method comprising the following steps:

[0013] engaging a gear in a gearbox of the road vehicle while a corresponding clutch of the road vehicle is open;

[0014] gradually closing the clutch so that the clutch transmits a torque that causes at least one pair of drive wheels of the road vehicle to rotate;

[0015] Determining a target slip ratio of the driving wheels;

[0016] periodically determining an actual slip ratio of the drive wheels; and

[0017] Based on the difference between the target slip ratio of the drive wheels and the actual slip ratio of the drive wheels, the torque transmitted by the clutch is continuously adjusted during clutch closure.

[0018] The control method is characterized in that the torque transmitted by the clutch is adjusted during the clutch closing period to achieve a target slip ratio of the drive wheels.

[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 of the invention, in which:

[0021] Figure 1 is a schematic plan view of a rear-wheel drive road vehicle provided with a powertrain having a dual-clutch servo-assisted gearbox and controlled according to the control method of the present invention;

[0022] Figure 2 yes Figure 1 A schematic diagram of the powertrain; and

[0023] Figure 3 is a block diagram of the control logic implemented in the control unit of the powertrain. DETAILED DESCRIPTION

[0024] exist Figure 1 In the figure, reference numeral 1 generally denotes a road vehicle, in particular a car, having two front driven (i.e. 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 gear train manner to a self-locking differential 9, from which a pair of half shafts 10 originate, each integral with the drive wheels 3.

[0025] The road vehicle 1 comprises a control unit 11 of an engine 4, which controls the engine 4, a control unit 12 of a powertrain 6, which controls the powertrain 6, and a bus line 13, which is made, for example, according to the CAN (Car Area Network) protocol, extends over 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 information sent via the bus line 13. Furthermore, the control unit 11 of the engine 4 and the control unit 12 of the powertrain 6 can be directly connected to each other via 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 delays 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 may be exchanged using the bus line 13.

[0026] 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 intervention of the transmission shaft 8; each clutch 16 is an oil bath clutch and is therefore pressure-controlled (i.e., the degree of opening / closing 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 opening / closing 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.

[0027] The dual-clutch servo-assisted transmission 7 has seven forward gears (1st gear I, 2nd gear II, 3rd gear III, 4th gear IV, 5th gear V, 6th gear VI and 7th 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 fixed to the main shaft 15 and a counter gear 19 fixed to the countershaft 17. In order for the dual-clutch servo-assisted transmission 7 to operate correctly, all odd-numbered gears (1st gear I, 3rd gear III, 5th gear V, 7th gear VII) are coupled to the same main shaft 15, while all even-numbered gears (2nd gear II, 4th gear IV and 6th gear VI) are coupled to another main shaft 15.

[0028] Each main gear 18 is connected to the corresponding main shaft 15 by a spline 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 installed 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 installed on the countershaft 17, disposed between two sub-gears 19, and designed to be operated to alternately fix the corresponding two sub-gears 19 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 fix one sub-gear 19 to the countershaft 17, or can move in the other direction to fix another sub-gear 19 to the countershaft 17.

[0029] 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 .

[0030] 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) 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) to request a downshift (i.e., to engage a new gear that is lower than and adjacent to the current gear).

[0031] When the road vehicle 1 is stationary, the driver can enable (e.g. by pressing a button) a function (technically known as “performance launch”) which allows a very high-performance static launch and requires the electronic control unit 12 of the drivetrain 6 to autonomously control the internal combustion engine 4 (i.e. determine the torque produced by the internal combustion engine 4) and to control the drivetrain 6 (i.e. regulate the closing of the clutch 16A during acceleration and the engagement of the subsequent gear) so as to maximize the longitudinal acceleration at all times. In particular, in order to enable the function known as “performance launch”, the driver must simultaneously depress the brake pedal 23 and the accelerator pedal 22, and the static launch of the road vehicle 1 begins when the brake pedal 23 is released (the driver must keep the accelerator pedal 22 fully depressed throughout the execution of the operation).

[0032] As long as the brake pedal 23 is depressed and the road vehicle 1 is visibly stationary, the control unit 12 of the drivetrain 6 causes the internal combustion engine 4 to run relatively slowly (about 2000-3000 rpm), engages the first gear I for starting a static launch, and slightly closes the clutch 16A (which engages an odd gear and therefore also engages the first gear I for starting a static launch) so as to transmit a non-zero minimum torque (e.g. in the range of 4 to 8 Nm) through the clutch 16A, thereby preloading the drivetrain 6 (i.e. restoring all mechanical play). As soon as the brake pedal 23 is released, the control unit 12 of the drivetrain 6 causes the rotation speed of the internal combustion engine 4 and the torque generated by the internal combustion engine 4 to increase, while gradually closing the clutch 16A so that the clutch 16A transmits a torque that causes the two drive wheels 3 to rotate.

[0033] In particular, according to Figure 3 The control unit 12 of the powertrain 6 periodically determines the target slip ratio S of the drive wheel 3. T , periodically determine the actual slip rate S of the drive wheel 3 during the static start R , then based on the target slip ratio S of the drive wheel 3 TThe actual slip ratio S of the driving wheel 3 R The difference between the torque transmitted by the clutch 16A during the closing of the clutch 16A is continuously adjusted (changed) by the difference between the torque transmitted by the clutch 16A during the closing of the clutch 16A. Preferably, the control unit 12 of the powertrain 6 predetermines (i.e., before starting the static start) an initial value of the torque transmitted by the clutch 16A during the closing of the clutch 16A, and then adjusts (changes) the torque transmitted by the clutch 16A during the closing of the clutch 16A starting from the predetermined initial value.

[0034] In other words, the control unit 12 of the powertrain 6 adjusts the torque transmitted by the clutch 16A during the closing of the clutch 16A to achieve the target slip ratio S of the drive wheels 3. T , that is, the driving wheel 3 always has the target slip ratio S T .

[0035] Obviously, if a subsequent gear is engaged during a relatively long static launch (eg second gear II, which like all even gears is controlled by clutch 16B), the control unit 12 of the driveline 6 regulates the torque transmitted by clutch 16B during the closing of clutch 16B.

[0036] according to Figure 3 In the preferred embodiment shown, the control unit 12 of the powertrain 6 implements feedback control to adjust the torque transmitted by the clutch 16A during the closing of the clutch 16A; in the feedback control, the control error ε S Equal to the target slip ratio S of driving wheel 3 T The actual slip ratio S of the driving wheel 3 R In particular, the feedback control requires the use of a subtractor block 26, which calculates the target slip ratio S of the drive wheel 3. T The actual slip ratio S of the driving wheel 3 R The difference between the control error ε S , and it is also necessary to use a PID controller 27, which receives as input the control error ε S and provides a control signal T corresponding to the actual torque transmitted by the clutch 16A at each moment. C as the output value.

[0037] Generally speaking, since a small amount of tire slip allows the torque transmitted from the tire to the road to be maximized, the target slip ratio S of the drive wheel 3 is T In the range of 0.1 to 0.2 (but can also be slightly different).

[0038] According to a preferred but non-binding embodiment, the control unit 12 of the powertrain 6 determines the level of grip of the road surface on which the road vehicle 1 is located and determines, based on the level of grip of the road surface, an initial value of the torque transmitted by the clutch 16A during the closing of the clutch 16A. In general, information about the level of grip is available via the bus line 13, since it is estimated (in a known manner) and shared by the brake control unit.

[0039] According to a preferred but non-binding embodiment, the control unit 12 of the powertrain 6 periodically determines the target slip ratio S based on the grip level of the road surface. T (It may vary continuously as the road vehicle 1 moves and therefore as the road surface on which the road vehicle 1 is located changes.) According to a possible embodiment, a map (usually obtained experimentally) is stored in the control unit 12 of the powertrain 6, which provides a target slip ratio S of the drive wheels 3 based on the grip level of the road surface. T Obviously, the parameters of the map are set according to the type of tires mounted on the drive wheels 3. As a result, the grip level of the road surface can be used to determine the initial value of the torque transmitted by the clutch 16A during the closing of the clutch 16A and to determine the target slip ratio S T .

[0040] According to an alternative embodiment, the target slip ratio S of the drive wheels 3 is T Remains constant for the entire static start process and is predetermined before the static start begins.

[0041] According to a possible embodiment, the control unit 12 of the drive train 6 stores in the memory box 28 the final value T of the overall influence of the PID controller 27 at the end of the previous stationary start. H , then by means of the adder block 29 the final value T of the overall influence of the PID controller 27 at the end of the previous static start H and the control signal T generated by the PID controller 27 during the subsequent static start C By adding the final value T H With the control signal T C The corrected control signal T F is used to control the clutch 16A. In other words, by influencing the closed loop (ie, the control signal T generated by the PID controller 27) C ) and the open-loop effect (i.e., the final value T of the overall effect of the PID controller 27 at the end of the previous static start H ) is added to obtain the corrected control signal T FIn this way, after a first (previous) static start has been made, the actual corrections required during the first (previous) static start can be learned in order to initiate a second (subsequent) static start from a starting point requiring less corrections. Obviously, during the first static start, the final value T H is zero.

[0042] It should be noted that since the clutch 16 is controlled based on the (oil) pressure, the corrected control signal T is converted to F Convert to corresponding pressure value.

[0043] According to a preferred embodiment, the final value T of the overall influence of the PID controller 27 at the end of the previous static start is H Only before the road vehicle 1 is turned off is considered; that is, the road vehicle 1 is turned off so that the final value T H According to various embodiments, the final value T is reset (to zero) only after a specified time (e.g., twenty minutes) has passed since the previous static start. H Reset (to zero).

[0044] According to a different embodiment, the control unit 12 of the driveline 6 stores the average value of the torque transmitted by the clutch 16A during the closing of the clutch 16A of the previous static start and assumes that the initial value of the torque of the new start is equal to this average value of the torque transmitted by the clutch 16A during the closing of the clutch 16A of the previous static start. In this case, again, the average value of the torque transmitted by the clutch 16A during the closing of the clutch 16A of the previous static start is taken into account only before the road vehicle 1 is turned off (or within a specified time from the previous static start).

[0045] according to Figure 3 , a calculator block 30 is provided, which calculates the actual slip ratio S of the driving wheel 3 by the following equation R :

[0046] S R =(ω3-ω2) / ω2

[0047] ω2: rotational speed corresponding to the longitudinal speed of the road vehicle 1;

[0048] ω3: rotation speed of driving wheel 3;

[0049] S R : The actual slip rate of driving wheel 3.

[0050] In particular, the rotational speed ω2 corresponding to the longitudinal speed of the road vehicle 1 is equal to the rotational speed ω2 of the pair of non-driven wheels 2 .

[0051] 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 modifications.

[0052] The above control methods have different advantages.

[0053] First, the control method enables the driver to always obtain the maximum acceleration during a static start without considering the actual surrounding conditions (such as road surface temperature, tire temperature, tire wear state), because it can always adapt to the surrounding environment in an ideal and fast manner, based on the target slip ratio S of the drive wheel 3. T and the actual slip ratio S of the driving wheel 3 R The difference between φ and φ is used to continuously adjust the torque transmitted by clutch 16A during the period when clutch 16A is closed.

[0054] Furthermore, the control method described above is easy and economical to implement, since only limited memory space and low computing power are required to execute the method.

[0055] Reference numerals list

[0056] 1 Road vehicles

[0057] 2 Front wheels

[0058] 3 Rear wheels

[0059] 4 Engine

[0060] 5 Drive shaft

[0061] 6 Powertrain

[0062] 7 Gearbox

[0063] 8 Drive shaft

[0064] 9 Differential

[0065] 10 Half shaft

[0066] 11 Engine control unit

[0067] 12 Powertrain control unit

[0068] 13 Bus lines

[0069] 14 Sync Cable

[0070] 15 Spindle

[0071] 16 Clutch

[0072] 17 Countershaft

[0073] 18 Main gear

[0074] 19 Secondary gear

[0075] 20 Synchronizer

[0076] 21 Steering Wheel

[0077] 22 Accelerator pedal

[0078] 23 Brake pedal

[0079] 24 Upshift paddle shifters

[0080] 25 Downshift paddle shifters

[0081] 26 Subtractor Frame

[0082] 27 PID Controller

[0083] 28 Memory box

[0084] 29 Adder Box

[0085] 30 Calculator Box

[0086] ω2 Speed

[0087] ω3 Speed

[0088] S R Actual slip rate

[0089] S T Target slip rate

[0090] ε S Control error

[0091] T C Control Signal

[0092] T H Final Value

[0093] T F Corrected control signal

Claims

1. A control method for controlling a road vehicle (1) to perform a first static start, the control method comprising the following steps: engaging a gear in a gearbox (7) of the road vehicle (1) while a corresponding clutch (16A) of the road vehicle (1) is open; gradually closing the clutch (16A) so that the clutch (16A) transmits a torque causing at least one pair of drive wheels (3) of the road vehicle (1) to rotate; Determine the target slip ratio (S) of the driving wheel (3) T ); The actual slip ratio (S R );as well as Based on the target slip ratio (S) of the driving wheel (3) T ) and the actual slip rate (S R ), continuously regulating the torque transmitted by the clutch (16A) during the period when the clutch (16A) is closed; During the closing period of the clutch (16A), the torque transmitted by the clutch (16A) is adjusted by feedback control to achieve the target slip ratio (S) of the drive wheel (3). T ), where the control error (ε S ) is the target slip ratio (S) of the driving wheel (3) T ) and the actual slip rate (S R ); and The torque transmitted by the clutch (16A) during the closing of the clutch (16A) is regulated by a PID controller (27) which receives a control error (ε S ) as input value; The control method is characterized in that it further comprises the following steps: The final value (T H ) for storage; and The final value (T) of the overall influence of the PID controller (27) at the end of the first static start H ) and a control signal (T) generated by a PID controller (27) during a second static start after the first static start C ) added.

2. The control method according to claim 1, characterized in that: The final value (T H ).

3. The control method according to claim 1, characterized in that: The control method further comprises the following steps: storing an average value of the torque transmitted by the clutch (16A) during the period in which the clutch (16A) is closed during the first stationary launch; and It is assumed that the initial value of the torque in the second static start after the first static start is equal to the average value of the torque transmitted by the clutch (16A) during the closing of the clutch (16A) during the first static start.

4. The control method according to claim 3, characterized in that: The mean value of the torque transmitted by the clutch (16A) during the closing of the clutch (16A) is taken into account only during the first stationary launch before the road vehicle (1) is switched off.

5. The control method according to claim 1, characterized in that: The control method further comprises the following steps: Determine the rotation speed (ω3) of the driving wheel (3); determining a rotation speed (ω2) corresponding to a longitudinal speed of the road vehicle (1); and The actual slip ratio (S) of the driving wheel (3) is calculated by the following equation: R ): S R =(ω3-ω2) / ω2, where ω2 is the rotational speed corresponding to the longitudinal speed of the road vehicle (1), ω3 is the rotational speed of the drive wheel (3), S R is the actual slip rate of the driving wheel (3).

6. The control method according to claim 5, characterized in that: The rotation speed (ω2) corresponding to the longitudinal speed of the road vehicle (1) is equal to the rotation speed (ω2) of the pair of non-driven wheels (2).

7. The control method according to claim 1, characterized in that: The control method further comprises the following steps: Determining a grip level of a road surface on which a road vehicle (1) is located; storing an initial value of the torque transmitted by the clutch (16A) during closing of the clutch (16A) based on the grip level of the road surface; and The target slip ratio (S) of the driving wheel (3) is periodically determined based on the grip level of the road surface. T ).

8. The control method according to claim 1, characterized in that: The target slip ratio (S) of the driving wheel (3) T ) is in the range of 0.1 to 0.2.

Images