DE19805458B4 - Start-up control for CVT transmissions - Google Patents

Abstract

Method for starting control of a motor vehicle with an electronically controlled starting clutch and CVT transmission, whereby a clutch torque is controlled, characterized in that an individual transmission drive speed is determined for the end of the starting control at each start, at which the control of the clutch torque is ended by the starting control, that the individual transmission input speed is determined for a predetermined transmission ratio in the CVT transmission, that until the individual transmission input speed is reached for the end of the starting control, the clutch torque is regulated in such a way that an engine speed is set according to a predetermined function, namely the engine speed increases monotonically.

Description

The invention relates to a method for starting control of a motor vehicle according to the features of the preamble of claim 1.

In such start-up regulations a variety of conditions are to be observed. For example, a minimum speed should not be undershot.

Furthermore, the speed that occurs at stalled vehicle and full load (stall speed) should be at the speed at which the engine gives its maximum torque. At this speed, the traction is maximum and the energy converted to heat at the clutch is minimal for this traction. A higher engine power at speeds beyond that is only converted into heat in the clutch. The traction no longer increases here.

Another condition to note is that the stall speed for mean accelerator pedal angles should be a function of this accelerator pedal angle.

Furthermore, it is important in turbo engines that the engine speed is controlled so that the boost pressure is built up as quickly as possible.

Finally, the transition between the start-up and the translation should be clearly defined and imperceptible to the driver.

In the EP 0 207 228 B1 a control system for an oil pressure controlled continuously variable transmission is described in which the transmission ratio is controlled by regulating the oil pressure via an electromagnetic control valve such that in particular a function of a difference between a desired transmission ratio and an actual transmission ratio, a predetermined translation Change rate sets.

From the DE 42 32 233 A1 For example, a control apparatus and method for a continuously variable transmission (CVT) is known which is used as a vehicular transmission and is operated by oil pressure. A controller controls the available oil pressure in various control modes. If the control unit detects a driver's approach, it initially maintains a holding mode until a speed of the engine has reached such a value that sufficient oil pressure is ensured. Only then does it switch to a startup mode. The clutch pressure is set in the start mode to an appropriate level to prevent blowby of the engine and to provide engine torque sufficient to produce jolt-free movement of the vehicle. However, no provision is made for a defined transition from start mode to drive mode. Furthermore, the speed curve lacks sufficient dynamics and it encounters an undesirable, atypical for a CVT gear stage behavior especially in the transition from the start mode to the drive mode.

From the DE 38 29 262 C2 a control for a continuously variable belt transmission is known in which a first control circuit for starting and a second control circuit is active after starting. The first control circuit outputs a control signal for temporarily reducing the drive pulley width of the transmission when it is determined that the vehicle is starting. Thereafter, the first control loop adjusts a belt pressing force in the transmission such that no slippage occurs between the belt and the drive pulley. Finally, the second control loop is changed immediately as soon as a speed greater than zero is determined at a predetermined step of the control program. Thus, there is also a hard transition from the starting control to the control after starting, without taking into account the current operating conditions. This again leads to a jerky, gradual transition.

From the DE 37 31 259 A1 a device for controlling an automatic motor vehicle coupling for heavy duty vehicles is known. Here, the closing of the clutch takes place when starting immediately with a dependent on the position of the accelerator pedal basic engagement. The Grundeinrückgeschwindigkeit is adapted to the different starting resistances via corrections during the entire engagement process, in particular several correction factors are determined or used here, which ensure that the increase in the engine speed is reduced before reaching the synchronization point to an at least partially constant course.

From the DE 41 35 969 A1 For example, a method for controlling a friction clutch of a vehicle with a continuously variable transmission is known. Here, the friction clutch is brought into a slipping state and set a first period of time as a function of the temperature of a hydraulic oil. When the first time period has elapsed during startup, the clutch is forcibly brought from the slipping state to a fully engaged state. This prevents an excessive increase in oil temperature and annealing of the coupling.

From the DE 40 40 11 850 A1 a method for controlling a friction between an engine and a transmission friction clutch is known, wherein for the starting process, a control engagement point of the clutch is determined in response to an angle measurement and / or torque measurement carried out in the drive train. Again, the engine speed is reduced when starting after a sharp increase and then runs until the adjustment to the transmission input shaft speed then substantially constant or is further reduced.

A start-up control with control of the rotational speed as a function of time is disadvantageous insofar as the starting behavior of the vehicle changes by changing the driving resistance and the vehicle weight, but these changes are disregarded by the start-up control.

The present invention has for its object to provide an improved start-up control of the type mentioned above, wherein the above-mentioned hot pursuit are overcome and the control is carried out taking into account the continuous translation selection.

This object is achieved by the features of claim 1.

For this purpose, it is provided that at each start for the end of the Anfahrregelung an individual transmission input speed is determined, in which the control of the clutch torque is terminated by the Anfahrregelung.

This has the advantage that the approach or the starting control is terminated shortly after the start of the gear ratio adjustment in the CVT gearbox in the direction of overdrive.

In a particularly advantageous embodiment, an engine speed is used as the desired value for the control of the clutch torque.

For optimum adaptation to the vehicle, the individual transmission input speed is determined for a predetermined gear ratio in the CVT transmission.

In order to complete the start-up control exactly and individually for different start-up situations at the time of the start of the gear ratio adjustment, the engine speed curve is selected such that when the predetermined individual gear drive speed is reached, the startup control is terminated and only the gear ratio control determines the engine speed.

Advantageously, while the engine speed between the beginning of the approach and start end as a function of input or output shaft speed is specified as the desired speed.

For example, this function is a linear function.

In one embodiment, from a map of a desired input shaft speed as a function of load and output shaft speed, the individual transmission input speed is determined by selecting a current load state characteristic and determining its intersection with a straight line for a predetermined gear ratio, which corresponds to the point of intersection in the map Drive shaft speed is selected as the individual gear drive speed. This has the advantage that at the end of the Anfahrregelung the target speed corresponds exactly to the speed without slip in the clutch and so a soft and direct transition from the approach to the normal driving takes place.

Expediently, the intersection point is calculated in such a way that with a binary search, adjacent interpolation points of the load curve in the characteristic field are searched for, and the intersection point is calculated therefrom by interpolation.

In a particularly preferred embodiment, the intersections are calculated during the application and stored in a new map.

For a flexible adaptation to different driving requirements different maps are suitably vorwählbar for different starting requirements.

For example, a sport adjustment characteristic field is selected for a quick start and an ECO adjustment characteristic field for an energy-saving startup.

Advantageously, the different load curves of the respective characteristic map are selected via a deflection angle of the accelerator pedal.

Further features, advantages and advantageous embodiments of the invention will become apparent from the dependent claims, and from the following description of the invention with reference to the accompanying drawings. These show in

1 a graphical representation of various desired speed curves as a function of time,

2 a first Verstellkennfeld for economic (ECO) operation,

3 a second Verstellkennfeld for a speedy (SPORT-) operation, and

4 a stall speed characteristic.

Taking into account the conditions for a start-up control mentioned initially, a starting nominal speed curve follows according to the curve 10 from 1 , At t = t0, the driver accelerates, ie he actuates an accelerator pedal by a predetermined angle alpha. This deflection AlphaDkl is in 1 with a curve 12 shown. At the latest at t = t1, the vehicle is rolled. The engine speed is controlled by a corresponding adjustment of the clutch torque to a constant value. At t = t2, the slip in the clutch is reduced and the approach is completed.

However, such a journey has insufficient dynamics and is not accepted by a driver because of a gradual, not the nature of a CVT transmission speed curve corresponding.

There is therefore a Anfahrsoll speed curve according to curve 14 or 16 selected. Here the engine speed is raised when the vehicle is accelerating and the approach is ended only at t = t3. This results in a much more dynamic behavior of the vehicle when approaching. In addition, the driver's approach appears more comfortable, since the engine speed increases continuously when approaching and does not remain constant for a long time.

It is selected during the journey, ie in particular between t0 and t3, the course of the engine target speed as a function of the drive or the output shaft speed. The approach is terminated in an advantageous manner shortly after the beginning of the translation adjustment in the direction of overdrive.

For this purpose, at any time of the journey, for example, from a Verstellkennfeld, known at which speed the adjustment of the translation begins. At this speed, the start-up control is ended, expediently at the time t3, the engine target speed corresponds to the engine speed with the clutch engaged without slippage in order to prevent a sudden jump in the engine speed. Up to there advantageously increases the course of the speed when accelerating the vehicle in a substantially monotonous.

The engine target speed at time t3 is determined, for example, as follows: In a control program for the CVT transmission, the input shaft speed is stored in a map as a function of load and output shaft speed. Such a map is in the 2 and 3 to see. For different vehicle conditions, "Eco" for economical driving ( 2 ) or sport for drafty driving ( 3 ), is additionally interpolated between several maps in a suitable manner. The transmission control program determines a drive shaft speed for the current load, vehicle condition, and vehicle speed. This size serves as a reference for the translation control.

From these maps, the relationship between the input and output shaft speed can be determined at any time. This makes it possible for the current vehicle state to predict at which input or output shaft speed a certain ratio is adjusted.

The approach or starting control is terminated, for example, at a gear ratio of Ü = 8, so a translation just below the underdrive ratio, so that the approach is terminated shortly after Verstellbeginn the CVT transmission. In the 2 and 3 straight lines are drawn for this translation and designated Ü = 8. From the intersection of the translation line with the valid for a given load drive shaft speed can be read at what point a translation of here z. B. Ü = 8 is set. This case is in 2 exemplary for two accelerator pedal angle λDkl = 56% and λDkl = 100% drawn. Thus, the further the driver pushes the accelerator pedal when starting, the longer the phase of the clutch torque control of the starting control with slippage and the faster and more sporty drives the vehicle. This also corresponds to the expectation of the driver who wants to drive quickly and quickly when the accelerator pedal is depressed.

The calculation of the intersection of the curves is carried out, for example, such that with a method of binary search in a few fonts, the vertices of the corresponding characteristic adjacent to the intersection are searched and the intersection is calculated therefrom by interpolation. Alternatively, this calculation can also be performed offline during the application and the results stored in a new map.

The determined point determines the drive shaft or output shaft speed at which the approach or the start-up control should be completed. This is in 1 the time t3. The course of the engine target speed between the beginning of the approach and the start end can be specified as a function of input or output shaft speed. Any functions are conceivable. This is in 1 with different curves 14 and 16 indicated.

wobei

n_mot_soll

Solldrehzahl

n_mot_stall

Motordrehzahl bei stehendem Fahrzeug (vgl. 4)

n_an_anf_ende

Antriebssolldrehzahl für Anfahrende (vgl. 2, n_an im Schnittpunkt)

n_ab_anf_ende

Abtriebssolldrehzahl für Anfahrende (vgl. 2, n_ab im Schnittpunkt

For the simple linear case z. B .:

in which

n_mot_nom

Target speed

n_mot_stall

Engine speed when the vehicle is stationary (cf. 4 )

n_an_anf_ende

Nominal drive speed for start-up end (cf. 2 , n_an at the intersection)

n_ab_anf_ende

Target output speed for start-up end (cf. 2 , n_ab at the intersection

The setpoint speed serves as the setpoint for the approach controller. The controller controls the clutch torque, which has an influence on the engine speed. Thus the control loop is closed.

LIST OF REFERENCE NUMBERS

10

Anfahrsolldrehzahlverlauf

12

Curve of accelerator pedal deflection AlphaDkl

14

Anfahrsolldrehzahlverlauf

16

Anfahrsolldrehzahlverlauf

Claims (12)

Method for starting control of a motor vehicle with electronically controlled starting clutch and CVT transmission, wherein a clutch torque is controlled, characterized in that at each start for the end of the Anfahrregelung an individual transmission input speed is determined, in which the control of the clutch torque is terminated by the start-up control, that the individual Gear drive speed for a predetermined gear ratio in the CVT transmission is determined that until reaching the individual transmission input speed for the end of the start-up control, the clutch torque is controlled such that an engine speed is set according to a predetermined function, namely, the engine speed increases monotonically. A method according to claim 1, characterized in that an engine speed is used as a setpoint for the control of the clutch torque. Method according to one of the preceding claims, characterized in that on reaching the predetermined individual transmission drive speed, the approach is terminated. Method according to one of claims 1 to 3, characterized in that the predetermined function is a linearly increasing function. Method according to one of claims 1 to 4, characterized in that the engine speed between the beginning of the approach and start end is specified as a function of input or output shaft speed as the target speed. Method according to one of the preceding claims, characterized in that from a characteristic field of a drive shaft target speed as a function of load and output shaft speed, the individual transmission input speed is determined by selecting a load characteristic for the current load condition and determines their intersection with a straight line for a predetermined ratio of the transmission is chosen, wherein the intersection point in the map associated drive shaft speed is selected as the individual transmission input speed. A method according to claim 6, characterized in that the calculation of the intersection point is such that are searched with a binary search to the intersection adjacent interpolation points of the load curve in the characteristic field and the intersection is calculated therefrom by interpolation. Method according to one of claims 6 and 7, characterized in that the intersections are calculated during the application and stored in a new map. Method according to one of claims 6 to 8, characterized in that different maps are preselected for different starting requirements. Method according to one of claims 6 to 9, characterized in that a sport adjustment characteristic is selected for a quick start. Method according to one of claims 6 to 10, characterized in that for an energy-saving start an ECO adjustment map is selected. Method according to one of claims 8 to 11, characterized in that the different load curves of the respective characteristic field are selected via a deflection angle of the accelerator pedal.

Images