EP2118526A1

EP2118526A1 - Method for controlling a drive train of a motor vehicle

Info

Publication number: EP2118526A1
Application number: EP08717001A
Authority: EP
Inventors: Werner Wolfgang; Maik WÜRTHNER; Ingo Sauter
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2007-03-02
Filing date: 2008-02-21
Publication date: 2009-11-18
Also published as: WO2008107309A1; US8321102B2; CN101622476A; US20100324790A1; DE102007010295B4; JP2010520428A; DE102007010295A1; CN101622476B

Abstract

The invention relates to a method for controlling a drive train of a motor vehicle, which comprises a driving motor, an automatic transmission, and an automated clutch disposed in the power flux between the driving motor and the transmission. In order to achieve a low-wear and comfortable trailing throttle operation and a spontaneous transition to the traction mode, it is provided that further trailing throttle downshifts are prevented as soon as the driving speed (vF) of the motor vehicle has reached or dropped below (vF <= vGr) a previously defined limit speed (vGr) for trailing throttle downshifts, or the presently engaged gear (G) corresponds to a previously defined limit gear (GGr) for trailing throttle downshifts (Gi = GGr), and that after the limit speed (vGr) has no longer been met or after the limit gear (GGr) has been engaged, a transition into traction mode is prepared in that, as a function of the driving speed (vF) of the motor vehicle and/or the rotational motor speed (nM) of the driving motor a current target gear (Gz) and an associated shifting rotational speed (ns) of an adjustment gear change for the transition into the traction mode is determined.

Description

Method for controlling a drive train of a motor vehicle

The invention relates to a method for controlling a drive train of a motor vehicle, comprising a drive motor, an automated transmission and an arranged in the power flow between the drive motor and the transmission automated clutch, and in which the drive motor by means of an engine control unit and the transmission together with the clutch means a transmission control unit are controllable, and both control units via data and sensor lines with each other and at least with a speed sensor, an actuation sensor of an accelerator pedal and an actuation sensor of a brake pedal are connected, wherein in overrun at least as a function of the current vehicle speed and the current engine speed automatic push downshifts performed be made, and at the latest with the operation of the accelerator pedal a matching circuit for the transition to train operation.

Automated clutches and automated manual transmissions are increasingly being used in modern motor vehicles in the drivetrain, since this, on the one hand, achieves a reduction in fuel consumption and pollutant emissions and, on the other hand, an increase in the driving comfort of the relevant motor vehicles. The control of the clutch and the gearbox is usually carried out in each case via an electronic transmission control unit, the information of current driving and operating parameters of the motor vehicle, such as the engine speed and the engine load of the drive motor, the rotational speeds of the input shaft and the output shaft and the engaged gear of the gearbox, the Einrückungsgrad the clutch and the degrees of actuation of the accelerator pedal and the brake pedal are fed and processed there to control commands, which are used to carry out starting and switching operations to the gear selector of the gearbox, to the clutch the clutch and be passed to the engine control unit of the drive motor.

Corresponding drive trains are known, for example, from DE 197 23 393 A1, DE 199 52 623 A1, DE 101 21 389 C1, and DE 102 21 701 A1. In DE 197 23 393 A1, such a drive train and a control method of this drive train is described in which the clutch plate for engaging and disengaging the clutch and / or the gear plate for engaging and disengaging the gears of the gearbox are designed as electric motor. DE 199 52 623 A1 has a method for controlling a corresponding drive train to the object in which the engagement of the clutch is delayed until the speed of the drive motor is adjusted independently of the operation of the accelerator pedal to the speed of the input shaft of the gearbox. In another method for controlling such a drive train according to DE 101 21 389 C1, a load shock in the drive train caused by disengaging under load is avoided by disengaging the clutch by adjusting the engine torque of the drive motor, thus making disengaging more comfortable. In DE 102 21 701 A1 discloses a method for controlling a corresponding drive train is described with a hydraulic clutch actuator, according to the engagement of the clutch to terminate a sailing operation by a prior adjustment of the engine speed of the drive motor to the speed of the input shaft of the gearbox particularly fast and low-jerk is carried out.

The present invention is now based on a pushing operation of a motor vehicle provided with such a drive train. In this phase of operation, the driver has released the accelerator pedal and optionally actuates the brake pedal below an actuation limit, from which an emergency braking would take place with an automatic opening of the clutch. The fuel supply or fuel injection at the drive motor of the vehicle is in Pushing operation completely switched off (fuel cut-off) or at least greatly reduced, so that there is a high drag torque of the drive motor, by which the motor vehicle is decelerated except by the driving resistance of the motor vehicle and possibly the braking torque of the service brake.

By the shift program of the transmission control unit automatic overrun decelerations are triggered and performed in overrun at least in response to the current vehicle speed and the current engine speed. Due to the ever smaller gear ratios increasing translation jumps occur each with an increasingly stronger shift shock and thus are always uncomfortable. Because of the decreasing speed, especially when operating the service brake, always further increasing delay also increases the switching sequence of the push downshifts, so that the clutch is barely closed and thus the braking effect by the drag torque of the drive motor finally goes to zero.

The high number of circuits and the high switching sequence are also disadvantageously associated with high wear of the clutch and the gear clutches of the gearbox. Furthermore, to make the transition from overrun to train operation, which can be triggered by the driver by the operation of the accelerator pedal, usually a matching circuit in the form of a downshift is required to the drive motor in conjunction with a connection or increase the fuel injection to a higher speed and to deliver a correspondingly high engine torque. Due to the decreasing driving speed increasing switching frequency of the target gear of the matching circuit often can not be determined fast enough, whereby the matching circuit is done with noticeable delay. Against this background, the present invention has the object to provide a method for controlling a drive train of the type mentioned, with a low-wearer and more comfortable overrun operation and a more spontaneous transition to the train operation is possible with a corresponding motor vehicle.

This object is achieved according to the features of the main claim by a method for controlling a drive train of a motor vehicle comprising a drive motor, an automated transmission and an arranged in the power flow between the drive motor and the transmission automated clutch, and in which the drive motor by means of a motor control unit and the manual transmission can be controlled together with the clutch by means of a transmission control unit, and both control units via data and sensor lines with each other and at least with a speed sensor, an actuation sensor of an accelerator pedal and an actuation sensor of a brake pedal are in communication, in overrun at least as a function of the current driving speed v _F and the current engine speed n _M automatic boost downshifts are performed, and at the latest with the actuation of the accelerator pedal x _F p> 0 Anpa Switching to the transition to train operation takes place.

In addition, it is provided in this method according to the invention that further push downshifts are prevented as soon as the vehicle speed v _{F of} the motor vehicle has reached or fallen below a predetermined limit speed v _Gr for downshifts (v _F <= v _Gr ) or the currently engaged gear Gi a predetermined limit _gear G _GΓ for pushing downshifts corresponds to Gj = G _Gr , and that after falling below the limit speed v _Gr or after the insertion of the limit gear G _Gr a transition to the train operation is prepared by depending on the vehicle speed v _{F of} the motor vehicle and / or the engine speed n _M the drive motor is determined in each case a current target gear G _z and an associated switching speed n _{s of} a matching circuit for the transition to the train operation.

Advantageous embodiments and further developments of the method according to the invention are the subject of the dependent claims.

In that no further coast downshifts longer be carried out from below the fixed for coast downshifts limit speed v _Gr or from the insertion of the set for coast downshifts boundary transition, eliminated the problems associated with high gear jumps coast downshifts between the smaller gears. Consequently, the associated load surges in the drive train or longer slip phases of the clutch are avoided. The overrun operation of the motor vehicle thus takes place more gentle and more comfortable. By early determination of a respective current target gear and an associated switching speed of a matching circuit for a transition to the train operation, the change from overrun to train operation with a corresponding operation of a driving control element, such as the brake or accelerator pedal, by the driver at any time spontaneously and with relative done quickly and with little impact controlled load change.

For the specific control of the overrun operation after falling below the limit speed or after the insertion of the limit gear and the on-demand transition to train operation, two variants of the method are provided according to the invention.

In a first variant of the method, it is provided that upon reaching the respective switching speed n _s in the currently determined target gear G _{z of} the respective matching circuit is switched, the clutch respectively only partially engaged and until the transition to train operation in the slip mode is kept (0 <x _κ <1, where x _{κ is} the degree of engagement of the clutch). Through such a gearing the target gear intended for a transition to train operation is already engaged, so that the transition to the traction mode can be carried out quickly and conveniently at any time by the complete engagement of the clutch and the control of the drive motor in the traction mode.

It is accepted that only a relatively small drag torque of the drive motor can be transmitted to the drive wheels via the slip operation of the clutch at a reasonable thermal load. Likewise, the switching frequency caused by the constant gear tracking adversely affects the life of the switching elements of the gearbox, such as speed clutches and gear shifter from. When a fault occurs in the transmission and clutch control, a passively closable clutch is automatically closed, whereas an actively closable clutch is optionally opened and must be closed in emergency operation via an energy storage and kept closed at least over a limited period, for. safely leaving a danger zone.

The transition to the train operation is preferably carried out such that the clutch fully engaged (x _κ = 1) and the fuel supply of the drive motor is switched on or increased as soon as a deflection of the accelerator pedal from the rest position (x _F p> 0), ie an actuation the accelerator pedal is sensed by the driver. The chronological course of the engagement of the clutch and the torque buildup of the drive motor takes place in a generally known manner as a function of the deflection of the accelerator pedal and optionally of the deflection speed of the accelerator pedal.

In a second variant of the method, it is provided that the gear Gj last engaged in overrun mode remains engaged until a deflection of the accelerator pedal from the rest position x _F p> 0, ie an actuation of the driving gear. Pedals is sensed by the driver, and that is then switched to the currently determined target gear G _{z of} the respective matching circuit, the clutch fully engaged (x "= 1) and the fuel supply of the drive motor is turned on or increased.

In this process variant, the drive clutch is permanently closed, so that a larger drag torque of the drive motor can be transferred to the drive wheels and the drive train is in a safe operating state when a fault occurs. Due to the reduced compared to the first method variant switching frequency, the switching elements of the gearbox, such as speed clutches and gear shifter, spared and thus increases the life of the gearbox. A disadvantage is taken into account that the transition to the train operation, a full matching circuit must be performed, which is associated with a delayed implementation of the transition to train operation.

An acceleration of the transition to the train operation is in this process variant, however, achievable that switched at a previous actuation of the service brake (x _B p> 0) in the current target gear of the respective matching circuit and the clutch is at least partially engaged when reaching the rest position is sensed by the brake pedal (x _BP = 0), ie the release of the brake pedal by the driver. In this way, there is a harmonious transition from the second method variant to the first method variant. Accordingly, from the release of the brake pedal as long as a gear track in the respective current target gear Gz the relevant matching circuit for the transition to train operation until the driver actuates the accelerator pedal (x _F p> 0) and thus the complete engagement of the clutch (x _κ = 1) and triggers the transition to train operation. One possible variation for this purpose is a one-time gear tracking circuit triggered by the release of the brake pedal.

In order to allow a stronger deceleration by means of the service brake (emergency braking) within the overrun mode, it is expedient that the clutch completely disengaged, if necessary, switched to the current target gear of the relevant matching circuit and the fuel supply of the drive motor is turned on or increased as soon as the overrun a predetermined Auslenkungsgrenzwertes by the brake pedal (x _F p> x _FP _ _GΓ) and / or a predetermined braking pressure threshold value of the service brake (per> PBI _GI-) is detected by sensors. Alternatively or additionally, this can also take place as soon as the response of an antilock braking system (ABS) is triggered by corresponding sensor signals from wheel speed sensors. By fully opening the clutch, the drag torque of the drive motor is removed from the drive wheels, thus allowing for better metering of brake force via the brake pedal and full functionality of an ABS system. Unless this already happens anyway, speed-dependent switching to the target gear of a matching circuit for a transition to train operation, wherein the target gear at vehicle standstill or at very low driving speed is a starting gear. By switching on or increasing the fuel supply of the previously driven by the transmitted drag torque drive motor is kept running, thus preventing dying of the drive motor.

In this sense, it is also advantageous if the clutch completely disengaged, if necessary, switched to a starting gear and the fuel supply of the drive motor is switched on or increased as soon as the undershooting of a predetermined minimum speed of the motor vehicle (v _F <v _M i _n ) and / or a predetermined minimum speed of the drive motor (n _M <n _M in) is detected by sensors. To clarify the invention, the description is accompanied by a drawing with exemplary embodiments. In this shows:

1 is a flowchart of a first variant of the control method according to the invention and

2 shows a flow chart of a second variant of the control method according to the invention.

In a first variant of the method according to FIG. 1 will be within the control procedure of a push operation, preferably after performing a push downshift or a thrust upshift, checked in step S1, is whether the current vehicle speed v _F of the vehicle reaches a predetermined limit speed v _Gr for coast downshifts or below (v _F <= v _Gr ) - If this is not the case, the system returns to the beginning of the thrust control. If the condition according to step S1 is met, in step S2 the target gear G _{z of} a matching circuit for a transition to train operation suitable for the current driving situation is determined, and in step S3 the shift rotational speed n _s assigned to this gear is determined to trigger the respective matching circuit.

Subsequently, it is checked in step S4 whether the current driving speed v _F has fallen below a predetermined minimum speed v _M in and thus the motor vehicle is traveling at a low driving speed or is at a standstill. If this condition is met, the previously determined target gear G _{z is} engaged in steps S6 to S8, but to avoid stalling of the drive motor, the clutch is completely disengaged, which corresponds to a degree of engagement x _{κ of} the clutch of zero (x _κ = 0), and the fuel supply to the drive motor is switched on or, if this was not previously switched off completely, increased accordingly. The same is also done if, in step S5, an overrun considered emergency braking occurs a predetermined deflection _{limit value} X _BP _ _{GΓ is detected} on the brake pedal (x _B p> XBP_GΓ) -

If, on the other hand, neither of the two conditions of S4 and S5 is fulfilled, it is checked in step S9 whether the current engine speed n _{M has} reached or fallen below the shift speed n s previously determined in step _S 3. If this is true, in step S10 in the target gear Gz the matching circuit is switched, the clutch but after step S1 1 initially only partially engaged (0 <x "<1) to continue to drag torque of the drive motor for the deceleration of the motor vehicle use.

Thereafter, in step S12, which is also carried out at not yet reached or undershot switching speed n _s , at undershot minimum speed v _M in, and at exceeded limit position x _B p_Gr of the brake pedal, checked whether an operation of the accelerator pedal is present (X _FP > 0 ). If this is the case, in step 13, if this has not been done before, the target gear G _{z of} the matching circuit is switched, and subsequently in step S14 the clutch is completely engaged, which corresponds to an engagement degree X _{K of} the clutch of one (x "= 1), and the fuel supply to the drive motor according to the accelerator pedal displacement x _F p increases or, if this was previously completely switched off, turned on and then increased accordingly.

Then is transferred to the control of the train operation or at low driving speed in the starting control. However, as long as the accelerator pedal is not actuated (x _F p = 0), branched back to step S1, so that is switched at a deceleration of the motor vehicle below the limit speed v _Gr continuously in the respective current target gear G _{z of} the respective matching circuit, and the clutch is kept in slip mode (0 <x _κ <1), provided a sufficiently high driving speed (v _F > = v _M m) and a moderate operation of the service brake (x _B p <= XBP_GΓ) are present.

In a second variant of the method according to FIG. 2, instead of falling below a limit speed v _Gr in step S1, it is checked whether a previously defined limit gear G _{Gr has been set} for push downshifts in the preceding push-down shift (G _i = G G) - if this is not the case, is branched back to the beginning of the thrust control. If the condition is met, the target gear G _{z of} a matching circuit for a transition to train operation suitable for the current driving situation is determined in step S 2, and the shift rotational speed n _s assigned to this gear is determined for triggering the respective matching circuit in step _S 3.

Then it is checked in step S4 whether the current engine speed n _M has fallen below a predetermined minimum speed n _M in and thus threatens to die off the drive motor. If this condition is satisfied, the previously determined target gear G _{z is} inserted in steps S6 to S8, however, to avoid a dying of the drive motor, the clutch completely disengaged (X _K = 0) and the fuel supply to the drive motor is turned on or, if so previously not completely switched off, increased accordingly. The same also takes place if, in step S5, a exceeding of a predefined brake pressure limit value Pßr_Gr of the service brake considered as emergency braking is determined (per> PBI-_GI -) -

If, on the other hand, neither of the two conditions of S4 and S5 is fulfilled, it is checked in step S9 whether there is no actuation of the brake pedal (X _BP = 0). If this is the case, it is checked in the following step S10 whether the current engine speed n _{M has} reached or fallen below the previously determined switching speed n _s . If this is true, in step S1 1 in the target gear G _{z of} the matching circuit is switched, the clutch thereby after step S12 but initially only partially engaged (0 <x "<1) to continue on To use drag torque of the drive motor for the deceleration of the motor vehicle. However, if the brake pedal is still actuated (x _B p> 0), the circuit fails in the target gear Gz of the matching circuit and the partial engagement of the clutch first.

In all cases, it is subsequently checked in step S13 whether an actuation of the accelerator pedal is present (X _FP > 0). If this is the case, in step 14, if this has not been done before, is switched to the target gear G _{z of} the connection circuit, and subsequently in step S15, the clutch fully engaged (x _κ = 1) and the fuel supply to Drive motor corresponding to the accelerator pedal deflection x _F p increases or, if this was previously completely switched off, turned on and then increased accordingly. Then is transferred to the control of the train operation or at low driving speed in the starting control.

However, as long as the accelerator pedal is not actuated (x _F p = 0), branches back to step S1, so that when the motor vehicle decelerates below the limit speed v _Gr a circuit in the target gear Gz the matching circuit is avoided as long as the engine speed n _M does not fall below the minimum speed n _M m (n _M > = n _M in), as the brake pressure p _{Br of} the service brake does not exceed the brake pressure limit p _Br _Gr (p _Br <= P _BI -_ _GI -) as the brake pedal is actuated becomes (x _BP > 0) and as the accelerator pedal is not actuated (X _FP = 0).

In other words, in the second variant of the method after engaging the limit gear G _Gr or, which is equivalent, after falling below the limit speed v _Gr within the specified operating limits before actuation of the accelerator pedal only in the previously determined target gear G _{z of} the matching circuit switched when the driver releases the brake pedal when the service brake is applied or if he does not use the service brake during this phase. This will be compared to the first Process variant of FIG. 1 frequent switching operations and longer slippage phases of the clutch avoided. Both variants of the method each lead to a relatively low-wear and comfortable overrun operation and allow a spontaneous transition to train operation.

REFERENCE CHARACTERS

G _gr border crossing

Gi Currently engaged gear

G _z Target gear n _M Motor speed of the drive motor n _M i _n Minimum speed of the drive motor n _s Switching speed

Pe _r brake pressure of the service brake

Pßr_Gr Brake pressure limit of the service brake

S1-S16 method steps v _F driving speed of the motor vehicle v _Gr limit speed

VMin Minimum speed of the motor vehicle x _B p Brake pedal travel, deflection of the brake pedal

Xßp_Gr deflection limit value of the brake pedal x _F p accelerator pedal travel, deflection of the accelerator pedal

X _K's indentation of the clutch

Claims

Patent claims

A method for controlling a drive train of a motor vehicle, comprising a drive motor, an automated transmission and arranged in the power flow between the drive motor and the transmission automated clutch, and in which the drive motor by means of an engine control unit and the transmission together with the clutch by means of a transmission control unit are controllable, and both control units via data and sensor lines with each other and at least with a speed sensor, an actuation sensor of an accelerator pedal and an actuation sensor of a brake pedal are in communication, wherein in overrun at least in dependence on the current vehicle speed (V _F ) and the current engine speed ( n _M ) automatic downshifts are performed, and in which at the latest with the actuation of the accelerator pedal (x _F p> 0) a matching circuit for the transition to the train operation takes place, characterized gekenn shows that further overruns are prevented as soon as the vehicle speed (v _F ) has reached or fallen below a preset limit speed (v _Gr ) for downshifts (v _F <= v _Gr ) or the currently engaged gear (Gj) is preset Threshold gear (G _Gr ) for pushing downshifts corresponds to (Gj = G _Gr ), and that after falling below the limit speed (v _Gr ) or after the _{engagement of} the limit _gear (G _GΓ ) a transition to the train operation is prepared by depending on the driving speed (V _F ) of the motor vehicle and / or of the engine speed (n _M ) of the drive motor in each case a current target gear (G _z ) and an associated switching speed (ris) a matching circuit is determined to transition to train operation.

2. The method according to claim 1, characterized in that when reaching the respective switching speed (n _s ) in the currently determined target gear (Gz) of the respective matching circuit is switched, the clutch respectively only partially engaged and until the transition to the train operation in the slip mode is held (O <x «<1).

3. The method according to claim 2, characterized in that the clutch fully engaged (x _κ = 1) and the fuel supply of the drive motor is switched on or increased as soon as a deflection of the accelerator pedal from the rest position (X _FP > 0) is detected by sensors.

4. The method according to claim 1, characterized in that the last engaged in overrun gear (Gi) remains inserted until a deflection of the accelerator pedal from the rest position (X _FP > 0) is sensory detected, and then in the currently determined target gear (Gz) of the respective matching circuit is switched, the clutch fully engaged (X _K = 1) and the fuel supply of the drive motor is turned on or increased.

5. The method according to claim 4, characterized in that in a previous actuation of the service brake (x _B p> 0) switched to the current target gear of the respective matching circuit and the clutch is at least partially engaged when reaching the rest position by the brake pedal (x _B p = 0) is sensory detected.

6. The method according to at least one of claims 1 to 5, characterized in that the clutch completely disengaged, if necessary, switched to the current target gear of the respective matching circuit and the fuel supply of the drive motor is switched on or increased as soon as the exceeding of a predetermined deflection limit by the brake pedal (x _B p> X _BP _ _GΓ) and / or a predetermined braking pressure threshold value of the service brake (p _Br> P _BI -_ _GI -) is detected by sensors.

7. The method according to at least one of claims 1 to 6, characterized in that the clutch completely disengaged, if necessary, switched to the current target gear of the respective matching circuit and the fuel supply of the drive motor is turned on or increased, as soon as by appropriate sensor signals from Raddrehzahlsensoren the response of an anti-lock braking system (ABS) is triggered.

8. The method according to at least one of claims 1 to 7, characterized in that the clutch completely disengaged, if necessary, switched to a starting gear and the fuel supply of the drive motor is switched on or increased as soon as the undershooting of a predetermined minimum speed of the motor vehicle (v _F < v _M in) and / or a predetermined minimum speed of the drive motor (n _M <n _M i _n ) is detected by sensors.