DE3884627T2 - CONTROL SYSTEM FOR A VEHICLE WITH AUTOMATIC TRANSMISSION. - Google Patents

Description

The invention relates to a control system for a vehicle with automatic transmission, in which shifting takes place according to at least two different shift programs.

Control systems for vehicles with automatic transmissions, in which the gears can be changed either according to a "SPORT" program or a so-called "ECONOMY" program, are well known. In the SPORT program, the gears are changed for good acceleration. In the ECONOMY program, the gears are changed for better fuel consumption. The vehicle has a manually operated switch for switching from one program to the other, which is located, for example, on the instrument panel. The driver can select a specific driving program according to his or her wishes.

The system described has proven itself to a certain extent, but is inconvenient in that the driver has to operate the switch to change programs. In a vehicle with an automatic transmission, a minimum of intervention on the part of the driver is desirable.

The publication FR-A-26 02 724 describes a control system for a vehicle with an automatic transmission, in which the control system enables gearshifts according to either a SPORT program or an ECONOMY program. In this known control system, the driving style is determined by the speed of movement of the accelerator pedal, and the gearshift program of the automatic transmission is changed accordingly from "economical" to "sporty". If the driver moves the accelerator pedal quickly, the gearshift program of the automatic transmission can be changed.

The system according to the invention is thus characterized in that the program changes according to the movements of the accelerator pedal. A program change occurs when the movement in one direction exceeds a specified value, so that too frequent changes due to accidental adjustment of the accelerator pedal are avoided.

Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram of the functions of the control system;

Fig. 2 is a diagram showing circuits according to the rate of change of the accelerator pedal position;

Fig. 3 is a diagram showing circuits corresponding to a threshold position of the accelerator pedal;

Fig. 4 a diagram of the output adjustment of the gearshifts;

Fig. 5 is a diagram comparing the fuel consumption between a system according to the invention and standard control systems ECONOMY and SPORT; and

Fig. 6 is a bar chart showing the results of drivability tests comparing a control system according to the invention with a standard ECONOMY control system.

The components for implementing this invention can include an electronic control unit (ECU) (1) in standard design, for example the SMP module system from Siemens. The ECU can be connected to an independent standard transmission control unit (2) for controlling the transmission (3). The system according to the invention is particularly suitable for a vehicle with an EH transmission (3) and an E-petrol injection system (4), as shown in Fig. 1. In an EH transmission, gear shifts are carried out hydraulically in response to electrical signals from the transmission control unit (2). The E-petrol injection system replaces the mechanical coupling of the accelerator pedal with the throttle valve. This means that with E-petrol injection, electrical signals derived from movements of the accelerator pedal determine the opening of the throttle valve, which in turn influences the engine (5).

The transmission control system is simulated in the ECU (1). In the embodiment of the invention described here, the ECU simulates the standard "SPORT" transmission control system, as well as a "stationary drive" transmission control system, which will be discussed in more detail. This means that the vehicle can be driven according to a SPORT program or a stationary program, depending on which system simulation is in effect. The ECU supplies the switching commands for the gear changes and the torque converter to the transmission control unit, which in turn processes the commands and controls corresponding solenoid valves in the EH transmission. In addition, the independent transmission control unit performs safety functions and determines the timing.

The standard transmission control system SPORT and its electronic simulation are well known: they are designed to provide good driving dynamics, including optimum acceleration. The functional details of the SPORT program are not part of this invention and are therefore not described in detail here. The transmission control system for stationary driving is designed to achieve the lowest possible fuel consumption ensure, ie when the vehicle is in stationary operation, the ECU signals to the transmission control system (2) should initiate gear shifts coordinated with minimum fuel consumption.

In addition to data for simulating the transmission control system SPORT, the ECU also contains data for simulating the control system for stationary driving. The simulation of the transmission control system SPORT is referred to below as the "SPORT program" and the simulation of the control system for stationary driving is referred to as the "stationary driving program".

For the stationary driving program, the ECU stores reference maps that result in the most fuel-efficient gear for each gear shift and each operating point (affects throttle valve position and engine speed) of the engine. The corresponding data can be calculated from the specific constant consumption Be = f(Nmot,We) and the throttle valve position Dk = f(Nmot,We) for the respective engine. Where:

Be = specific consumption of the engine

DK = throttle position

Nmot = engine speed

We = Specific power of the engine.

The above-mentioned characteristics are determined during engine tests and can be provided by the manufacturer. They make it possible to plot the throttle position against the output speed, and the most fuel-efficient gear can then be entered for each gear change and each possible operating point. The most fuel-efficient gears are calculated based on the fuel consumption advantage, ie gear calculation is carried out in such a way that the fuel consumption advantage exceeds a minimum value when changing gears. By setting a fuel consumption advantage, it is ensured that too frequent, unpleasant gear changing does not occur. For the specific vehicle with which the invention was tested, a satisfactory fuel consumption advantage of 2% was determined. In the case of engine performance that cannot be achieved in the next higher gear, gear changing only takes place at speeds below the maximum engine speed. A further limiting condition for gear changes is that the new engine speed must be within certain limits. For the test vehicle, the limiting conditions for the new engine speed were set at > 1000 rpm and < 5500 rpm.

The reference maps can be reduced to simpler shift curves, since there is only a single boundary line between the initial gear and the new gear. (This does not necessarily apply to other engine types).

Thus, a total of six maps are generated, one for each gear shift, i.e. 1/2, 2/3, 3/4, 4/3, 3/2 and 2/1.

In the test vehicle, it was found that controlling the gear shifts according to consumption-optimized shift curves of the type above results in generally favorable shifting behavior. In the high driving speed range, however, the 4/3, 3/2, 2/1 shift characteristic results in an "earlier" shift characteristic in the ECONOMY program. This is partly due to enrichment of the engine mixture towards full load with poorer specific fuel consumption at high loads. Occasionally, downshifting from fourth gear to third gear at high speeds may be more economical. Another reason for the greater number of 3/4 and 4/3 shifts is related to the change in the control program according to accelerator pedal movements, as will be explained below. Since the driver's movements of the accelerator pedal are greater at higher speeds (the vehicle accelerates less when the accelerator pedal is moved), 4/3 shifts occur more frequently when changing to the SPORT program than when changing back to the ECONOMY program when the accelerator pedal is released.

Downshifts from fourth gear to third gear may be desirable in terms of fuel consumption, but are not desirable at high driving speeds. Each gear change is associated with a shift shock, and too frequent gear changes are unpleasant for the driver. In the preferred embodiment of the invention, it is assumed that the described downshift is unacceptable at high driving speeds for reasons of comfort and that instead of the "optimum consumption" shift criterion, a compromise must be achieved between driving comfort and fuel consumption.

For this reason and in order to be able to better assess the driver's wishes (see below), the consumption-optimized shift curves for the stationary driving program are approximated to the shift curves for the well-known ECONOMY transmission control system for gear shifts from third to fourth gear and from fourth to third gear.

Thus, switching from the stationary drive program to the SPORT program due to adjustments of the accelerator pedal in fourth gear does not occur. A manual "override" switch may be desirable for switching from the stationary drive program to the SPORT program in fourth gear in the event that the driver wishes to downshift.

According to the invention, switching from one control program to another takes place in accordance with the movements of the accelerator pedal. From how the driver operates the accelerator pedal, it can be determined whether he wants acceleration, constant driving or deceleration. In the embodiments of the invention described below, it is only necessary to determine which acceleration the driver wants. The ECU thus receives electrical signals about the position of the accelerator pedal, as shown in Fig. 1, and derives the required driving program from these signals.

If it is determined that the driver wants to accelerate, the gears are shifted according to the standard SPORT program, and otherwise, i.e. if the driver wants the "stationary driving program", the gears are shifted according to the "consumption-optimized" shifting characteristics described above. In the SPORT program, only gears 1 to 3 are used, as the best acceleration is achieved in these gears. In the "consumption-optimized" program, the gears are shifted between all gears 1 to 4.

It should be noted here that the "stationary driving program" is a driving program in which the vehicle is driven predominantly at a constant speed, on average, but which also allows slight acceleration for distance corrections in traffic.

In a specific embodiment of the invention, which is shown in Fig. 2, the speed of movement of the accelerator pedal when the vehicle is moving is used to determine whether the driver wants to accelerate. It is assumed that if the driver wants to accelerate, he moves the pedal faster than if the stationary driving program is desired. If a specified pedal movement speed PEDGRENZ/t is exceeded, the stationary driving program is immediately ended, and the gears are then changed according to the shift characteristic curves for the SPORT program. Fig. 2 shows the accelerator pedal position as a function of time for a typical journey. At diagram point A, the speed of movement of the accelerator pedal exceeds the limit value PEDGRENZ/t and the stationary driving program is ended.

If the accelerator pedal is fully released and the engine is idling while the vehicle is being driven in the stationary driving program, the driver's acceleration request is not determined from the movement speed of the accelerator pedal for a certain period of time immediately after the idling state, but rather the pedal position is compared for a time tLL (see Fig. 2) with a value PEDLL, which is made up of a base value PEDKONST and a movement value PEDGRENZ. If the accelerator pedal position exceeds the value PEDLL, the stationary drive program ends and the system switches to the SPORT program. The PEDKONST value depends on the driving speed; it corresponds to the pedal position for a constant driving speed previously selected by the driver. As an example, we assume that the vehicle is being driven at a constant speed and the road gradient allows driving at a constant speed without accelerator. If the driver then quickly presses the accelerator pedal back to the previous position, it is assumed that he wants to maintain the stationary driving program; if, on the other hand, the new pedal position exceeds the previous pedal position by the PEDGRENZ value or more within the time tLL, it is assumed that acceleration is desired. After the time period tLL has elapsed, the speed of movement of the accelerator pedal is again used to determine the driver's desired acceleration. Thus, at point B, the SPORT program is selected again, but during the first time period tLL the control system does not switch to the SPORT program (see Fig. 2).

The driving speed is also measured, and at speeds below 13 km/h, for example, the SPORT program is always selected for good starting acceleration.

It should be clear that the speed at which the driver presses the accelerator pedal depends on the actual road conditions. If the driving programs are changed solely based on the speed of the accelerator pedal, slow adjustments of the accelerator pedal up to almost full throttle do not result in a change from the stationary driving program to the SPORT program. This is acceptable if the vehicle acceleration during a pedal adjustment remains low (eg when driving uphill) because the driver simply accelerates more to keep the speed constant. On a flat road, however, slow adjustments of the accelerator pedal mean a corresponding (intentional) acceleration. In the preferred embodiment of the invention, the acceleration of the vehicle is thus measured, as well as the speed of movement of the accelerator pedal, in order to better assess the driver's wishes. In the event of intentional acceleration, the system switches to the SPORT program and upshifts due to high engine speed are avoided.

In the case of FULL THROTTLE and KICKDOWN, the stationary driving program is always terminated immediately. In the described embodiment of the invention, the system switches from the stationary driving program to the SPORT program when the accelerator pedal is adjusted negatively. As Fig. 1 shows, the stationary driving program is only used again when a negative pedal adjustment by a specified value PEDNEG occurs and a delay time tACCEL has elapsed after this change, during which the pedal was not depressed again. The control system has therefore switched from the SPORT program to the stationary driving program at diagram point C in Fig. 2.

In the second embodiment of the invention, which is shown in Fig. 3, the driver's acceleration request is determined from the travel of the accelerator pedal. If the accelerator pedal is operated beyond a certain threshold, the stationary driving program is terminated and the system switches to the SPORT program. The threshold value sets consists of a speed-dependent accelerator pedal value PEDKONST for constant driving speed and a pedal shift value PEDOFFSET for the driver to switch to the SPORT program. This means that the stationary driving program is ended when the driver drives the vehicle at a constant speed and the pedal travel PEDKONST (or within a certain tolerance range around this value) and then presses the pedal by the additional travel PEDOFFSET. The PEDOFFSET value can be fixed or speed-dependent, since the pedal adjustment by the driver can depend on the driving speed. In Fig. 3, the stationary driving program ends at point A. Just as with the previously described embodiment of the invention, the stationary driving program is also immediately ended when full throttle is applied or kickdown occurs. Return to the stationary driving program only occurs when the actual accelerator pedal travel subsequently falls below the threshold value (reduced by a hysteresis value PEDHYST to avoid too frequent changes between the driving programs), ie the driver releases the accelerator pedal. The stationary driving program starts again at point B in Fig. 3. (The value PEDHYST can be fixed or speed-dependent).

The program change strategy in this embodiment of the invention can be modified so that at speeds above 130 km/h, due to a high accelerator pedal threshold value, an acceleration request is only signaled when the full throttle position is reached. The system is set up so that full power is achieved in fourth gear at a pedal value of 70%, by raising the accelerator pedal/throttle valve characteristic curve accordingly. The aim is to modify the stationary driving program in order to reduce the subjective feeling of sluggish acceleration in fourth gear. A steeper accelerator pedal/throttle valve characteristic curve is used for fourth gear than for gears 1 to 3.

The characteristic curve in fourth gear is given by the following equation:

The pedal value at which the throttle valve reaches the full load position is specified using the constant K. In this case, it was selected as 70%. This means that at the pedal value of 70%, the throttle valve is set to full power and a less abrupt change in power occurs when switching 3/4 or 4/3.

The power before and after a gear change should be the same for good drivability. The torque characteristics of the engine should therefore be set via the throttle valve inversely proportional to the engine speeds before and after a gear change, taking into account the throttle valve characteristic curves We = f(Dk, Nmot).

The different accelerator pedal/throttle valve characteristic curves for gears 3 and 4, as mentioned above, make only a limited contribution to the power adjustment during gear shifts 3/4 and 4/3. The precise adjustment of the power When changing gears via the throttle valve, operating points are created that are not necessarily on the accelerator pedal/throttle valve characteristic curves for gears 3 and 4. To prevent the throttle valve and accelerator pedal from drifting apart after several gear changes, the seconds between the actual accelerator pedal point and idling or full load (relative to the accelerator pedal) are calculated for new accelerator pedal/throttle valve characteristic curves after each power adjustment and accelerator pedal adjustment. This means that each accelerator pedal adjustment brings the vehicle closer to the original characteristic curve.

This behavior is shown in Fig. 4, which refers to a downshift from fourth to third gear. The power adjustment results in operating points that lie next to the characteristic curves (shown as solid lines). Movements of the accelerator pedal result in an iterative approximation to the original characteristic curve.

Systems according to the invention have been tested with an automatic vehicle with EH transmission and electric fuel injection, as described above. Various measurements were carried out with the test vehicle to evaluate the systems. The results of these tests are described below and will demonstrate the advantages of the invention.

Consumption measurements for the CVS test (urban driving) and the highway test were carried out on a roller dynamometer. The CVS test simulates the conditions of normal city driving, while the highway test simulates the driving conditions on normal highways. The CVS test involved three measurements with different sequences for each of the various transmission control programs in the warm operating phase (ht). In the highway test, only two measurements were taken in each case. When measuring consumption according to the exhaust emissions on the test bench, consumption was also measured according to the injection time determined by the transmission control system. The consumption values for constant driving speed were also determined at speeds of up to 140 km/h on a highway.

Measurements have been carried out for the following transmission control programs:

a) Standard transmission control program “SPORT”;

b) Transmission standard control program “ECONOMY”;

c) Switching between the "SPORT" gearshift characteristics and the consumption-optimized gearshift characteristics according to the speed of movement of the accelerator pedal;

d) Switching between the "SPORT" gearshift characteristics and the consumption-optimized gearshift characteristics according to the accelerator pedal threshold;

e) Driving with consumption-optimised gearshift characteristics.

The results of the mentioned tests are shown in the following tables: Consumption measurements for CVS test (ht phase) in l/100 km) MEASUREMENT SPORT ECONOMY ACCELERATOR PEDAL SPEED ACCELERATOR PEDAL THRESHOLD OPTIMISATION CURVE Exhaust Ti Average Consumption measurements during highway test (in l/100 km) MEASUREMENT SPORT ECONOMY ACCELERATOR PEDAL THRESHOLD Exhaust Ti Average Consumption measurements on the motorway (average speed 130 km/h) SPORT ECONOMY ACCELERATOR PEDAL THRESHOLD

The results are summarized graphically in the tables above in Fig. 5. Measurements of fuel consumption with an inventive SPORT/"consumption-optimized" system and changes between the programs according to the "accelerator pedal position threshold" switching strategy are shown with a solid line. The curve with long dashed lines represents measurements with the well-known ECONOMY standard program, the curve with short dashed lines measurements with the well-known SPORT standard program. The bar diagrams superimposed in Fig. 5 show the average fuel consumption measurements for the CVS test, the highway test and the motorway test.

From the tables above and the diagram in Fig. 5 it is clear that the Sport/"consumption-optimized" control system gives consumption values comparable to those in the standard ECONOMY program, but on the other hand allows gear changes according to the SPORT program when acceleration is required.

The results of the drivability tests show that the system according to the invention does not lead to any deterioration in the vehicle dynamics.

A key switch was installed on the automatic gear selector lever to assess the drivability of the vehicle when controlled by a system according to the invention, recording the test driver's assessment. The key switch enabled a mark to be placed each time a gear change was made that was unnecessary in the driver's opinion, and each time the driver considered an additional gear change necessary. Accordingly, The test drivers were asked to operate the switch every time they made an "unnecessary" gear change, and also whenever they felt that an additional gear change should have been made.

The test drives were carried out with six drivers on the same stretch of highway at speeds over 100 km/h. At such speeds, average acceleration means shifting down from fourth gear to third gear.

The test drives were carried out and evaluated using various transmission control programs, including the ECONOMY standard program for comparison purposes. When evaluating the results, a distinction was made between correct gear shifts, additional required gear shifts and superfluous gear shifts. The sum of the superfluous and correct gear shifts is the total number of gear shifts carried out during a test drive.

The results of the drivability tests are shown in the bar chart of Fig. 6, on which the sum of the correct and additional required shifts is standardized.

It is clear that the "driveability" of the systems with program changes according to an accelerator pedal threshold and accelerator pedal speed is comparable, but both systems represent a great advance over the ECONOMY standard program.

When evaluating the position of the marks set for the change rate of the pedal position, it was determined that when changing programs, the limit value for the accelerator pedal speed should be adjustable for different drivers in order to achieve the best possible driver acceptance. In the test vehicle, rotary knobs were provided for changing the limit value PEDLIMIT or the hysteresis value PEDHYST. In the optimal, practical version, all three values PEDHYST, PEDLIMIT and PEDOFFSET should be tailored to the respective driver. Certain means for adjusting these parameters in a practical system may therefore be desirable. These means can be manually adjustable knobs, but the control system can also determine and set suitable values independently according to the accelerator pedal movements.

It was found that switching from one program to another via the accelerator pedal threshold was not problematic for different drivers with constant setting values, since the control movements by the different drivers differed less than the increases in the speed of the accelerator pedal.

Shifting gears according to an accelerator pedal threshold and the full-load requirement, as mentioned above, has the advantage that at speeds above 130 km/h the regulating movement or the torque reserve for the stationary driving program is larger and is shifted less frequently, but on the other hand the reaction to an acceleration request requires a pedal movement of up to 70% of the accelerator pedal travel.

To further illustrate the invention, two examples with summary data for the switching strategies follow.

Summary of switching strategies

(OPTIM.ON = "stationary driving program")

example 1 Shifting according to accelerator pedal speed

1) Initial state: OPTIM.OFF, previously negative pedal adjustment

OPTIM.ON: (dNAB(t)/dt < NABGRAND) .....a

AND (dPED(t)/dt < PEDLIMIT) .....b

AND ((FP AND KD) = OFF) .....c

AND (SPEED > 13 km/h) .....d

AND (tACCEL > 13 s)

The delay time tACCEL is provided when conditions a, b, c and d are met.

2) Initial state: OPTIM.ON

OPTIM.OFF: Condition a OR b OR c OR d is not fulfilled.

3) Initial state: OPTIM.ON, after idle

OPTIM.ON: (tLL < 0.75 s)

AND (PED(t) < PEDCONST + PEDLIMIT)

The delay time tLL is counted from the end of idle time ; for tLL > 0.75 s, 1

4) Initial state: Change OPTIM.ON/OPTIM.OFF

OPTIM.OFF: PED(t) > PEDMAX(OPTIM.OFF)-PEDNEG

Constants: NABGRENZ 250/min/s

PEDLIMIT 100 (10% of PEDmax for 3)

(66% of FP/s for 1)

PEDNEG 40 (4% of PEDmax)

tACCEPT 3 s

tLL 0.75 s

PEDKONST = f(speed, 4th gear)

Sampling time 50 ms

Example 2 Shifting according to accelerator pedal threshold

1) Initial state: OPTIM.OFF

OPTIM.ON: (PED(t) < PEDKONST+PEDOFFSETT+PEDHYST)

AND (FP AND KD) = OFF)

AND (v > 13 km/h)

2) Initial state: OPTIM.ON

OPTIM.OFF: (PED(t) > PEDCONST + PEDOFFSET)

OR (FP OR KD) = ON)

OR (v < 13 km/h)

Constants: PEDOFFSET 200 (20% of PEDmax)

PEDHYST 70 (7% of PEDmax)

PEDKONST = f(v, 4th gear)

(Note: FP = full load (full throttle)

KD = Kickdown)

Other strategies for switching from one program to another are possible within the scope of the invention, for example, a speed-dependent limit value for the movement speed of the accelerator pedal could be used. With the strategy based on the accelerator pedal threshold, a pedal displacement value dependent on the driving speed would be possible.

Claims (3)

1. Control system for a vehicle with automatic transmission (3), in which the gear shifts are carried out according to at least two different shift programs, whereby in the first shift program gear shifts are carried out mainly for optimal fuel consumption, while in the second shift program gear shifting is carried out mainly for best acceleration, so that changes from one shift program to the other occur according to movements of the accelerator pedal, characterized in that a change from the second shift program to the first shift program occurs in response to a movement of the accelerator pedal in the negative direction by a defined value (PEDNEG) if the pedal is subsequently not moved in the positive direction at more than a defined speed (PEDGRENZ/t) during a defined time (tBESCHL) after the negative movement of the accelerator pedal. 2. Control system according to claim 1, characterized in that the change from one switching program to the other takes place when the accelerator pedal is moved below a fixed position. 3. Control system for a vehicle with automatic transmission (3), in which the gear shifts are carried out according to at least two different shift programs, wherein in the first shift program shifts are carried out mainly for optimum fuel consumption, while in the second shift program shifts are carried out mainly for optimum acceleration, so that changing from one shift program on the other hand, in response to movements of the accelerator pedal, characterized in that a change from the first switching program to the second switching program takes place in response to a movement of the accelerator pedal in a positive direction by a predetermined value (PEDOFFSET), the predetermined value being dependent on the driving speed, and if the accelerator pedal has then exceeded a predetermined position.