WO2002036384A1

WO2002036384A1 - Control system for an automatic gearbox of a motor vehicle

Info

Publication number: WO2002036384A1
Application number: PCT/EP2000/010458
Authority: WO
Inventors: Markus Henneken; Friedemann Jauch; Kai-Uwe Herbster; Franz-Josef Schuler; Thomas Mauz
Original assignee: Zf Friedrichshafen Ag
Priority date: 1999-10-23
Filing date: 2000-10-24
Publication date: 2002-05-10
Also published as: DE19951107A1

Abstract

The invention relates to a control system for an automatic gearbox of a motor vehicle in the event of reduced engine torque. The automatic gearbox is driven by an internal combustion engine which can be influenced by an accelerator pedal, and a signal (HDK) which is proportional to a pedal position is transmitted to an electronic gearbox control system (EGS) in which gear shifting programmes (SKL, SKL red) having gear shifting parameters are stored. The reduced engine torque is taken into account in the selection of the gear shifting programme in such a way that, in a quasi-stationary state and during at least approximately complete load operation, an engine torque reduction factor (k MOM red) is determined, constituting an influencing variable for the selection of the gear shifting programme (SKL, SKL red). The invention also relates to an electronic gearbox control system (EGS) for carrying out the control process.

Description

Control of an automatic transmission of a motor vehicle

The invention relates to a control of an automatic transmission of a motor vehicle with a reduction of an engine torque according to the kind defined in claim 1. Furthermore, the invention relates to an electronic transmission control for carrying out this control.

Modern automatic transmissions work with an electronic transmission control (EGS), by means of which criteria relevant to customer and safety can be fulfilled. The electronic transmission control processes signals from the transmission, engine and vehicle. The transmission-side signals include, for example, a transmission input speed, an output speed and the transmission temperature, while the motor-side signals include an engine speed, an engine torque, a throttle valve position and an engine temperature. A kickdown signal, a position signal about a selected shift position, a shift program signal, a brake light signal or signals from other vehicle systems can be present on the vehicle side. From the input signals and stored data, such as shift characteristics for gears, tuning parameters for pressure calculation, engine intervention and time levels, as well as controller and diagnostic parameters, the electronic transmission control uses appropriate program modules to calculate the correct gear and optimal pressure curves for gearshifts.

Such an electronic transmission control is known, for example, from the publication "ATZ Automobiltechnische Zeitschrift" 94 (1992), for certain Driving situations special shift programs for situation-dependent gear selection are provided.

An important influencing variable for determining a current operating point of the vehicle in conventional transmission controls is the driving performance or tractive force as a selectable influencing variable for the driver within the scope of the engine performance. The most important influencing factor of the driver is the accelerator pedal position, by which a driver's request for more, the same or less power or acceleration is expressed.

The engine operating state is usually detected by the engine torque, which is not measured directly, but is usually determined from stored maps by the engine speed and an actuator position.

From the German publication H.J. Forester, "Automatic vehicle transmission", Springer Verlag 1991,

Pages 326 ff., Various shift programs are known, whereby the problem of shifting oscillations is also described _, which can arise, for example, at the engine speed limit at full throttle if the driving resistance line just crosses the speed limit of a gear. In this case, the vehicle accelerates in lower gear until the transmission shifts up at the speed limit. Since the driving performance in the upper gear is not sufficient, the vehicle decelerates again until it reaches the downshift line, at which a downshift is carried out with subsequent acceleration. This process, also known as "shift hunting", is repeated continuously, which is perceived by the driver as annoying. Furthermore, this has the disadvantage that the transmission is stressed unnecessarily without increasing the driving performance.

In order to avoid such pendulum shifts, it is proposed to use forward programs in which it is no longer possible to shift up into upper gears. Such a forward program is selected by the driver or automatically, the acceleration being determined and the programmed upshift being prevented if the acceleration is very low at full load.

With the known controls, however, an oscillation circuit with a reduction in the engine torque due to external factors, such as e.g. an extremely low air pressure or a very high outside temperature. It has been shown in practice that when driving at an altitude of, for example, over 3000 m a.s.l. the performance of the internal combustion engine is significantly reduced due to the reduced oxygen content of the air even when the throttle valve is fully open. The engine torque thus decreases continuously with falling air pressure and constant speed and pedal position.

The situation is similar in driving situations with a very high outside temperature, as is the case, for example, when driving through the desert. Here, too, an engine torque reduction can be determined at the same engine speed and pedal position, the engine torque reduction increases with increasing outside temperature.

Since the shift characteristics of the shift programs are usually based on the throttle valve angle, a downshift characteristic is achieved with reduced engine output, which leads to a downshift, whereupon a shorter translation with vehicle acceleration takes place until the upshift characteristic is reached. In addition, when the engine torque is reduced, the driver often tries to compensate for the missing engine torque by increasing the engine speed by increasing the pedal position. If, for example, the engine torque is reduced from 100% to 70% due to low air pressure or high outside temperature, then the constant vehicle speed of 150 km / h, for example, cannot be maintained even when driving on a flat surface. As a result, the vehicle slows down, and the driver usually accelerates and downshifts. The vehicle then accelerates again to 150 km / h, the driver releasing the accelerator after reaching the desired speed and thereby triggering an upshift and subsequent deceleration of the vehicle. This process of pendulum switching is repeated as often as required.

It is an object of the present invention to provide a control system for an automatic transmission for a motor vehicle, with which oscillating circuits due to a reduction in engine torque in an approximately statically determined state, in particular as a result of factors external to the vehicle, such as air pressure and outside temperature, are avoided. According to the invention, this object is achieved with a control according to claim 1 and an electronic transmission control (EGS) for carrying it out.

The control according to the invention with the determination of the engine torque reduction in a quasi-steady state and with at least approximately full load operation and the selection of the shift program dependent on the engine torque reduction offers the advantage that pendulum shifts can be avoided with a shift program selection adapted to the driving situation. With the control according to the invention, factors external to the vehicle, such as a low air pressure or a high outside temperature, can advantageously be detected, for which an increase in the

Switching frequency can be prevented by suitable adaptation.

In this way, both the service life of the transmission, which is reduced in the control according to the invention, and the driving comfort for the driver are significantly improved.

Further advantages and developments of the invention result from the subclaims and from the exemplary embodiments described in principle below with reference to the drawing.

It shows: Fig.l is a flowchart of an automatic transmission control according to the invention;

2 shows a flowchart of a further embodiment of the control according to the invention with an alternative determination of the engine torque reduction factor compared to the embodiment according to FIG. 1; and

3 shows a schematic diagram with a full-load characteristic and a partial-load characteristic of an engine map.

Referring to FIGS. 1 and 2, a flow chart of a control of an automatic transmission for a motor vehicle is shown in a highly simplified manner, which is implemented as a program module in a symbolically indicated electronic transmission control EGS. The electronic transmission control EGS is supplied with a signal HDK proportional to a pedal position, an engine speed NMO and an engine torque MMO, a pedal position gradient HDK_G, an engine speed gradient NMO_G and an engine torque gradient MMO_G being determined from the continuously incoming signals. These values are fed to the program module for controlling the automatic transmission, the controls described here taking into account motor torque reduction in a particular manner when selecting shift programs SKL, SKL_red, which are each stored in the electronic transmission control EGS with a shift map. A switching program SKL or SKL_red is selected, which prevents pendulum switching under special driving conditions such as extremely low air pressure, such as prevails at altitudes above 3000 udM, or at very high outside temperature C_AT, which can occur, for example, when driving through the desert.

Characteristic of such special driving conditions is a quasi-steady state, which is recognized via the gradient of the motor torque MMO_G or the gradient of the pedal position HDK_G. To determine whether there is a relatively statically determined state, a first distinction function Fl checks whether the pedal position gradient HDK_G, the engine torque gradients MMO_G and / or the engine speed gradient NMO_G is less than a respectively predetermined limit value GW_HDK_G, GW_MMO_G or GW_NMO_G. If this condition is not met, the program branches back to the beginning of the program module. If a quasi-steady state is recognized, the input values of the engine torque MMO, the engine speed NMO and the pedal position HDK are recorded in a further function F2.

In order to ensure that driving is in an accelerator pedal position in which a full-load torque is present, which is already assumed in gasoline engines at approximately 70% of the full-load standard torque, a further differentiation function F3 checks whether the pedal position value HDK, which here corresponds to a throttle valve angle, is greater than an associated minimum pedal position value GW HDK for the quasi-stationary state. If this condition is not met, a branch is made back to the beginning of the program module, otherwise an engine torque reduction factor k_M0M_red is subsequently determined, which serves as an influencing variable for the selection of the switching program.

The control according to FIG. 1 shows an adaptive determination of the engine torque reduction factor k_MOM_red with the aid of engine load characteristics of an engine map, such as the load characteristics shown in a very simplified form in FIG. 3.

3 shows a full load characteristic curve KL_MOT_l of the engine under standard conditions with an outside air pressure p_MO of 1023 mbar and an outside air temperature of 20 ° C. With a partial load characteristic curve KL_MOT_0.7 a state is represented which corresponds to 70% of the engine torque under standard conditions. The characteristic curves KL_MOT_l and KL_MOT_0.7 are comparison variables in order to compare the quasi-stationary actual state with a target state.

Operating points which result from the current engine torque MMO and the current engine speed NMO are assigned a value of the engine torque reduction factor k_MOM_red. Operating points which lie on the full load characteristic KL_MOT_l or above are assigned an engine torque reduction factor k_MOM_red with the value "1.0". Operating points which are below the full load characteristic KL_MOT_l but on or above the partial load characteristic KL_MOT_0.7 are given an engine torque reduction factor k MOM red with the value "0.7". For operating points, which are below the partial load characteristic KL_MOT_0.7, the torque reduction factor k_M0M_red is set to a value "0.6".

In Fig. 1 this is. Procedure with a differentiation function F4 shown, in which it is first checked whether the current value of the motor torque MMO is greater than or equal to the values of the full load characteristic KL_MOT_l. If this is the case, the engine torque reduction factor k_MOM_red is set to "1.0" in a subsequent processing function F5, otherwise it is initially set to the value "0.7" in a further processing function F6. A distinction function F7 then checks whether the current operating point is below the partial load characteristic KL_MOT_0.7, the torque reduction factor k_MOM_red being set to the value “0.6” in a subsequent processing function F8 if the result of the query is positive.

In the embodiment according to FIG. 2, the engine torque reduction factor k_MOM_red is not determined adaptively according to the functions F4 to F8 in FIG. 1, but alternatively as a function of measured input variables such as the outside air temperature C_AT and / or the outside air pressure p_MO from an applicable map KF (p_MO , C_AT) determines what is shown in FIG. 2 with a processing function F9.

During initialization, ie when the engine is started, the torque reduction factor k MOM red becomes "1.0" set. The motor torque reduction factor k_MOM_red is then recalculated each time the program is run.

As can be seen in FIG. 1 and FIG. 2, the current result of the engine torque reduction factor k_MOM_red is filtered in a function F10, with long-term filtering, for example with a first-order low-pass filter, being provided in the present embodiments. If the filtered engine torque reduction factor has an approximate value of 0.7, an extreme condition is recognized either with low air pressure or high outside temperature and a switching program with corresponding switching characteristics is sought.

The SKL_MOD switching programs are each with a

Parameter proves which are each assigned to a driving state with a certain driving resistance, in the present case the road inclination. To determine whether it is possible to remain in the current shift program or to switch to a shift program SKL_red that is adapted to the extreme driving situation, a correction factor MOD_red, which is assigned to the determined engine torque reduction factor k_MOM_red, is first determined.

In this case, for filtered engine torque reduction factors greater than 0.85, a correction factor MOD_red is equal to "1", for filtered engine torque reduction factors between 0.73 and 0.85 a correction factor MOD_red is equal to "2", and for filtered engine torque reduction factors between 0 , 65 and 0.73 a correction factor M0D_red with the value "3" is provided, the limits, which change between two values of the correction factor MOD_red are subject to hysteresis. The assignment can of course be determined differently.

If the correction factor MOD_red is determined in a function F1, its value is accepted in a subsequent function F12 as a parameter of a modified switching program SKL_red. In a subsequent function F13, this parameter is compared with the parameter of the current switching program SKL, in the present embodiment the switching program for a driving state "steep gradient" the parameter "0", for a driving state "slight gradient" the parameter "1", for a driving state "level" the parameter "2", for a driving state "slight incline" the parameter "3", and for a driving state "steep incline" the parameter "4".

If it is determined in function F13 that the parameter of the current switching program SKL is greater than that of the modified switching program SKL_red, a processing function F14 outputs that the previous switching program SKL is retained. However, if it is determined in the differentiation function F13 that the characteristic of the modified switching program SKL_red is greater than that of the previous switching program SKL, the modified switching program SKL_red is activated in a processing function F15.

In the present control system, the air pressure is extremely low and accordingly low

Motor torque reduction factor of, for example, "0.7" Correction factor M0D_red with the value "3" is assumed as the parameter of an alternative shift program SKL_red, which corresponds to a mountain driving program for a slight incline. If the current shift program SKL has a parameter 2, which stands for the driving state "plane", the engine power is reduced changed to the mountain driving program due to the low air pressure, which, for example with a 4-speed automatic transmission, means that the upshift characteristic between 3rd and 4th gear is no longer attainable, which is why a change to 4th Gear is no longer possible.

With an even lower outside air pressure p_MO or a higher outside temperature C_AT and consequently an even smaller engine torque reduction factor, which, for example, results in a correction factor MOD_red with the value "4", a mountain driving program associated with the parameter "4" for the driving state "steep incline" "changed, which has the consequence in a 4-speed automatic transmission that the 3rd gear is no longer selectable.

It is precisely these effects that are desirable when driving with a sharply falling air pressure and / or very high outside temperatures, since this prevents pendulum switching. reference numeral

C_AT outside temperature

EGS electronic transmission control Fl function for determining a quasi-steady state F2 function for holding current values

F3 function for determining a full load operation F4 differentiation function for determining the

Motor torque reduction factor F5 processing function for determining the

Engine torque reduction factor F6 Processing function for determining the engine torque reduction factor

F7 distinctive function to determine the

Motor torque reduction factor F8 processing function for determining the

Motor torque reduction factor F9 processing function for determining the

Motor torque reduction factor F10 Function for filtering the motor torque reduction factor Fll Function for selecting a correction factor MOD_red

F12 processing function to select one

Circuit program F13 differentiation function for selecting a

Circuit program F14 processing function for selecting a

switching program F15 processing function to select one

switching program

GW_HDK Limit pedal position gradient

GW_HDK_G Minimum limit value of the pedal position gradient for quasi-steady state

GW_MMO limit value motor torque

GW_MMO_G Limit value motor torque gradient

GW_NMO Limit engine speed

GW_NMO_G Limit value engine speed gradient HDK pedal position, throttle valve angle

HDK_G pedal position gradient, throttle valve angle gradient k_MOM_red engine torque reduction factor

KF map KL_MOT_0.7 partial load characteristic (70% full load) of the engine, depending on the engine speed

KL_MOT_l full load characteristic of the engine, depending on the engine speed,

MMO motor torque M0D_red correction factor

NMO engine speed p_MO outside air pressure

SKL switching program

SKL_red corrected switching program

Claims

Patent claims

1. Control of an automatic transmission of a motor vehicle with a reduction of an engine torque, the automatic transmission being driven by an internal combustion engine which can be influenced by an accelerator pedal and a signal (HDK) proportional to a pedal position being supplied to an electronic transmission control (EGS) in the shift programs (SKL , SKL_red) are stored with a shift map, and the engine torque reduction is taken into account in the shift program selection in such a way that an engine torque reduction factor (k_MOM_red) is determined in a quasi-steady state and at least approximately full load operation, which factor influences the selection of the shift program (SKL, SKL_red) is.

2. Control according to claim 1, characterized in that a quasi-steady state is detected when a pedal position gradient (HDK_G) and / or a motor torque gradient (MMO_G) and / or a

Motor speed gradient (NMO_G) is less than a predetermined limit value (GW_HDK_G, GW_ MM0_G, GW_NMO_G).

3. Control according to claim 1 or 2, characterized in that to determine the engine torque reduction factor (k_M0M_red) an actual engine torque value (MMO) with a full-load characteristic (KL_M0T_1) and at least one partial-load characteristic (KL_MOT_0.7) of an engine map is compared, whereby a) the engine torque reduction factor (k_MOM_red) is equal to one of the full load characteristic (KL MOT 1) ordered value is set if the actual engine torque (MMO) is greater than or equal to the values of the full load characteristic (KL_MOT_l), b) the engine torque reduction factor (k_MOM_red) is set to a value assigned to the partial load characteristic (KL_MOT_0.7) if the engine torque - Actual value (MMO) is smaller than the values of the full-load characteristic (KL_MOT_l) and larger / equal than the values of the partial-load characteristic (KL_MOT_0.7), and c) the engine torque reduction factor (k_MOM_red) is set to a further, smaller value if the Actual motor torque (MMO) is smaller than the values of the partial load characteristic (KL_MOT_0.7).

4. Control according to claim 3, characterized in that the full-load characteristic curve (KL_MOT_l) of the engine map is assigned an engine torque reduction factor (k_MOM_red) with the value "1".

5. Control according to claim 3 or 4, characterized in that the engine torque values of the partial load characteristic curve (KL_MOT__0.7) of the engine map correspond to 70% of the engine torque values of the full load characteristic curve (KL_MOT_l), the partial load characteristic curve (KL_MOT_0.7) being an engine torque reduction factor (k_MOM_red is assigned the value "0.7".

6. Control according to one of claims 3 to 5, characterized in that the engine torque reduction factor (k MOM red) is set to a value "0.6" becomes when the actual engine torque value is smaller than the values of the partial load characteristic (KL_MOT_0.7).

7. Control according to claim 1 or 2, characterized in that the engine torque reduction factor (k_MOM__red) is determined as a function of a measured input variable from an applicable map (KF (p_MO, C_AT)).

8. Control according to claim 7, characterized in that the input variable is an outside air pressure (p_MO).

9. Control according to claim 7 or 8, characterized in that the input variable is an outside temperature (C_AT).

10. Control according to one of claims 1 to 9, characterized in that the determined engine torque reduction factor (k_MOM_red) is filtered.

11. Control according to one of claims 1 to 10, characterized in that the switching programs (SKL, SKL_red) are each assigned a parameter and are selected as a function of the engine torque reduction factor (k_MOM_red) such that by means of a correction factor assigned to the engine torque reduction factor (k_MOM_red) ( MOD_red) a parameter for a switching program (SKL_red) is determined, which is compared with the parameter of the current switching program (SKL).

12. Control according to claim 11, characterized in that the switching program (SKL_red) charged with the correction factor (MOD_red) is selected if its characteristic is greater than the characteristic of the current switching program (SKL).

13. Control according to claim 11 or 12, characterized in that the switching programs (SKL, SKL__red) and their parameters are each assigned to a driving state with a specific driving resistance, in particular a specific road inclination.

14. Control according to one of claims 1 to 13, g e k e n n z e i c h n e t by their use for

Detection of a driving condition with low outside air pressure (p_MO), especially when driving at an altitude of more than 3,000 m a.s.l. and / or with high outside temperature (C__AT), especially in desert climates.

15. Control according to claim 14, characterized in that a driving state with a low outside air pressure (p_MO) and / or with a high outside temperature (C_AT) is detected when the engine torque reduction factor (k_MOM_red) has a value of at least approximately “0.7 "is determined.

16. Control according to claim 14 or 15, characterized in that in a driving state with low outside air pressure (p_MO) and / or with high Au- temperature (C_AT) a switching program for mountain travel is activated.

17. Electronic transmission control (EGS) for an automatic transmission of a motor vehicle with a program module for performing the control according to one of claims 1 to 16.