Drive control device and method for controlling a motor vehicle drivetrain

Abstract

Drive control device for a motor vehicle powertrain comprising a drive motor (1) with an electronic engine control unit (6) and an automatic transmission (2) with a torque converter (3), with a gear-associated clutch (5) and with an electronic transmission control unit (7) in which a creep reduction function is implemented, wherein the creep reduction is activated at or near a standstill of the vehicle by engaging the gear-associated clutch (5) or brake in the automatic transmission (2) in such a way as to reduce or eliminate the power transmission in the vehicle's powertrain, wherein the transmission control unit (7) is configured such that, during the deactivation of an activated creep reduction when the accelerator pedal and brake are substantially not actuated, a correspondingly configured function module (8) can be activated.by which the occurrence of defined disturbance vibrations is checked and by which, after the detection of the defined disturbance vibrations, the creep reduction remains fundamentally deactivated, whereby the disturbance vibrations are defined in such a way that a component tolerance-related defective gearbox is detected.

Description

[0001] The invention relates to a drive control device and a method for controlling a motor vehicle drive train with the function of creep reduction.

[0002] For the technical background, reference is made to, for example, the patent documents DE 44 46 077 C2, DE 10 2009 030 605 A1, DE 692 24 696 T2, DE 10 2011 014 570A1, DE 10 2012 209 755 A1 and DE 10 2013 016 762 A1.

[0003] Such a method is also known, for example, from DE 44 46077 C2. This method relates in particular to automatic transmissions that are connected to the internal combustion engine of the motor vehicle via a torque converter. The torque converter has a pump on the engine side and a turbine on the transmission side. The pump is coupled to the internal combustion engine in such a way that its speed corresponds to the speed of the internal combustion engine. When the motor vehicle is stationary, the pump drives the turbine on the transmission side at a speed corresponding to the idling speed of the internal combustion engine in such a way that, without a creep reduction function, the motor vehicle would creep. When the vehicle's braking system is actuated, a value proportional to the brake pressure is detected, and the creep reduction is controlled depending on this detected value.In the method known from this, not only is it determined whether the vehicle brake system is being applied, but also how strongly. This prevents the creep reduction from oscillating on and off when the vehicle brake system is only intermittently applied with low pressure, from which it can be concluded that the vehicle is actually being driven to creep, e.g., in a traffic jam. However, if a significant brake pressure is detected, preferably within a predetermined time window, the driver's desire to actually bring the vehicle to a standstill is recognized, and this desire is accommodated by activating the creep reduction.

[0004] Creep reduction or creep prevention is achieved by reducing the pressure in one of the clutches responsible for the currently preselected gear (starting gear).

[0005] A creep prevention system, also known as stationary decoupling, is also known from DE 10 2009 030 605 A1. DE 10 2009 030 605 A1 deals specifically with the transition from stationary decoupling to resuming driving. The focus here is on the controlled closing of the starting clutch, which is partially or fully open for creep prevention or stationary decoupling, depending on the dynamics of the driver's input. This also involves a corresponding adjustment of the engine torque control.

[0006] The object of the invention is to improve a method of the type mentioned at the outset in such a way that vibrations which are perceived as uncomfortable are avoided when the stationary decoupling or creep reduction is switched off.

[0007] This problem is solved by the features of the independent patent claims. Advantageous developments of the invention are the subject matter of the dependent patent claims.

[0008] The drive control device according to the invention for a motor vehicle drive train consists of a drive engine with an electronic engine control unit and an automatic transmission with an electronic transmission control unit in which a creep reduction function is implemented. The creep reduction function is activated when the vehicle is at or near a standstill by placing a clutch or brake in the automatic transmission into slip engagement or in the open position in such a way that traction in the vehicle's drive train is reduced or eliminated.

[0009] According to the invention, the transmission control unit or a functional module within the transmission control unit is designed or programmed in such a way that, during the deactivation of an activated creep reduction function, the occurrence of defined disturbing vibrations is checked when the accelerator pedal and the brake are essentially not applied. After the defined disturbing vibrations are detected, the creep reduction remains fundamentally deactivated. The disturbing vibrations are defined in such a way that they identify a defective transmission due to component tolerances. Thus, fundamental deactivation could be necessary and implemented for the entire transmission service life.Preferably, however, a renewed test for the presence of these disturbing vibrations is carried out regularly, for example after a specified period of time or after a specified number of kilometers driven after the detection of the defined disturbing vibrations, since empirical studies have shown that healing can occur via running-in effects of the transmission mechanics.

[0010] The defined disturbing vibrations are preferably detected by evaluating the vehicle's longitudinal acceleration or a variable analogous to the vehicle's longitudinal acceleration (e.g., wheel torque). This involves checking whether vibration amplitudes of the vehicle's longitudinal acceleration are greater than a specified minimum amplitude and / or whether the vibrations of the vehicle's longitudinal acceleration exhibit a specified frequency spectrum. These disturbing vibrations are counted. If the number of disturbing vibrations is at least greater than one (preferably also greater than two), creep reduction is and remains deactivated - with certain exceptions. Exceptions may include the re-evaluation of defined disturbing vibrations after a specified number of kilometers driven or if the transmission temperature is lower than a specified temperature threshold at which, based on experience, the defined disturbing vibrations do not occur at all.

[0011] The invention detects, in particular, interference vibrations caused by component tolerances and subsequently prevents them by appropriate control measures.

[0012] The creep reduction / creep prevention function can be reactivated due to a possible improvement in the component tolerances of the detected defective gearbox due to running-in effects after a mileage-dependent retest.

[0013] The invention is based on the following findings: It has been empirically established that tolerances in automatic transmissions, particularly in an unbraked vehicle and at comparatively low loads (especially at zero load) as well as at higher transmission temperatures during the exit from creep prevention (i.e. when the open clutch is closed), cause a so-called "shuddering", i.e. an uncomfortable oscillation or jerking, to occur.

[0014] The invention is intended to activate creep prevention only when this shuddering does not occur, for example at low transmission temperatures and / or with sufficient braking force and / or with sufficient load, or when the shuddering problem is to be checked again.

[0015] The drawing shows an embodiment of the invention. Fig. 1 the essential components of the device according to the invention and Fig. 2 the mode of operation of the method according to the invention by means of a correspondingly programmed function module in the transmission control unit.

[0016] In Fig. 1, a drive motor, for example, an internal combustion engine 1, is connected to an automatic transmission 2 via a torque converter 3. The pump P of the torque converter 3 is driven by the internal combustion engine 1. When the internal combustion engine 1 is switched on, the pump P delivers oil flow via the stator L of the torque converter 3 to the blades of the turbine T. The turbine T of the torque converter 3 is connected in a rotationally fixed manner to the input train of the transmission 2. Block 4 schematically indicates additional clutches and gear sets of the transmission 2.

[0017] The internal combustion engine 1 is generally controlled by an electronic engine control unit 6. The automatic transmission 2 is generally controlled by an electronic transmission control unit 7. The engine control unit 6 and the transmission control unit 7 are connected to one another, for example, via a CAN data bus. The engine control unit 6 transmits, for example, via this data connection to the transmission control unit 7 the position of the accelerator pedal by means of an accelerator pedal angle signal FP (as a sensor signal corresponding to the engine load or the engine torque) and the engine speed n_M. The transmission control unit 7 additionally receives as input signals, for example, the vehicle speed v, the vehicle longitudinal acceleration a, the brake pressure p of the vehicle brake triggered by the driver, and the transmission temperature T. The transmission control unit 7 contains a function module 8, in particular in the form of a corresponding software program, for carrying out the method according to the invention.

[0018] To engage a currently preselected gear, the transmission control unit 7 closes a clutch assigned to this gear, here for example clutch 5 of a starting gear, in order to transmit the torque acting via the input train to the output train of the transmission 2. When the motor vehicle is stationary, the speed of the output rod n_A is 0. However, if the internal combustion engine is running at idle speed (n_M = n_LL) when the motor vehicle is stationary, torque is transmitted to the turbine T via the pump P of the torque converter 3, which, however, cannot be used to drive the motor vehicle when the motor vehicle is braked and the clutch 5 is closed. This power loss of the internal combustion engine 1 leads to unnecessary fuel consumption. In known methods, this problem is solved while the motor vehicle is stationary, ien_A = 0, clutch 5 is fully or almost fully opened, so that no or only minimal torque is transmitted to the output train of transmission 2 (creep prevention or creep reduction). In particular, fully opening clutch 5 for creep reduction or creep prevention does optimize fuel consumption reduction, but can impair comfort when deactivating creep reduction and during the transition to the starting process, or reduce the starting response.

[0019] In principle, creep reduction is switched on, for example, when the vehicle speed v is zero and / or when the brake pressure p triggered by the driver is greater than a first predefined threshold. Creep reduction is preferably switched off when the detected braking pressure p is less than a second predefined threshold. The second predefined threshold can also be the same as the first predefined threshold. In this way, creep reduction is switched off when the brake is released, so that creep reduction is already switched off by the time the accelerator pedal is depressed, thus enabling comfortable but responsive pulling away. With automatic parking brake functions, creep reduction can be switched off when the accelerator pedal is depressed.

[0020] To optimize fuel consumption reduction, it is advantageous to fully open the clutch for the currently selected gear, as this prevents torque from being transferred to the transmission output, thus eliminating the additional load on the engine (creep prevention). However, if the clutch is fully opened, the clutch clearance must be overcome at the beginning of the engagement process when the creep prevention is deactivated in order to then engage the clutch plates.

[0021] During the speed synchronization phase, i.e. the time period in which the multi-plate clutch reduces slip (slip time), an uncomfortable oscillation (also called shudder) can occur.

[0022] By means of the functional module 8 according to the invention, which is based on Fig. 2, according to the exemplary embodiment presented here, during the deactivation of an activated creep reduction from time t0 with the accelerator pedal essentially not actuated - e.g., here, accelerator pedal angle FP=0 or FP<10% - and with the brake essentially not actuated - e.g., here, brake pressure p>-100 Nm - the occurrence of defined disturbing oscillations during the course of the vehicle's longitudinal acceleration a is checked. After the defined disturbing oscillations have been detected, the creep reduction remains deactivated. Fig. 2, this creep reduction prohibition is schematically indicated by a prohibition signal V changing from 0 to 1 at time t1.

[0023] The creep reduction remains deactivated in principle if the number Z of oscillations S1, S2, S3 and S4 whose amplitudes are greater than a minimum amplitude A and whose frequency spectrum simultaneously corresponds to a corresponding comparison spectrum (e.g. the occurrence of a 2nd order) is at least greater than one (here Z=2).

[0024] The general deactivation of creep reduction can be switched off for a new evaluation of defined disturbing vibrations after a specified number of kilometers driven, e.g. after 350, 750, 1300, 3000 and 12000 [km].

[0025] The general deactivation of creep reduction can be interrupted in exceptional cases if the transmission temperature T is lower than a specified temperature threshold (e.g., 55°C). This threshold must also be determined empirically in such a way that shuddering generally does not occur.

[0026] It was also discovered that shuddering does not occur at higher loads or at an engine torque corresponding to an accelerator pedal angle FP above a threshold of approximately 10%. The invention is therefore particularly relevant for so-called zero-load exits or exits from creep reduction at FP <10%. In a broader sense, an essentially non-actuated accelerator pedal therefore means, for example, an accelerator pedal actuation angle FP below 10% or the presence of a correspondingly low engine torque or a correspondingly low load.

[0027] It was also found that shuddering does not occur when the vehicle is braked. A substantially non-actuated brake means, for example, a non-actuated brake pedal, a pilot pressure below a comparatively low threshold, or a brake pressure p in the wheel brakes below a certain threshold; e.g., p>-100 Nm.

Claims

[1] Drive control device for a motor vehicle drive train, comprising a drive engine (1) with an electronic engine control unit (6) and an automatic transmission (2) with a torque converter (3), with a clutch (5) assigned to a gear, and with an electronic transmission control unit (7) in which a creep reduction function is implemented, wherein the creep reduction is activated at or near a standstill of the vehicle by bringing the clutch (5) or brake assigned to a gear in the automatic transmission (2) into slip engagement or into the open position in such a way that a frictional connection in the drive train of the vehicle is reduced or eliminated, wherein the transmission control unit (7) is designed such that, during the deactivation of an activated creep reduction function, a correspondingly designed functional module (8) can be activated when the accelerator pedal is essentially not actuated and the brake is essentially not actuated.by which the occurrence of defined disturbing vibrations is checked and by which, after the detection of the defined disturbing vibrations, the creep reduction remains deactivated in principle, whereby the disturbing vibrations are defined in such a way that they detect a defective gearbox due to component tolerances. [2] Drive control device according to claim 1, characterized by that the basic deactivation can be carried out for the entire service life of the gearbox, with regular re-checks for the presence of these disturbing vibrations. [3] Drive control device according to one of the preceding claims, characterized bythat by appropriate design of the functional module (8) the vehicle longitudinal acceleration (a) can be evaluated with regard to the detection of disturbing vibrations whose amplitudes are greater than a predetermined minimum amplitude and / or which have a predetermined frequency spectrum, and by means of which the disturbing vibrations can be counted. [4] Drive control device according to one of the preceding claims, characterized by that the creep reduction remains deactivated by appropriate design of the functional module (8) if the number (Z) of the detected defined interference vibrations is at least greater than one. [5] Drive control device according to one of the preceding claims, characterized bythat the basic deactivation of the creep reduction can be switched off by appropriate design of the function module (8) for a new evaluation of defined disturbing vibrations after a predetermined number of kilometers driven. [6] Drive control device according to one of the preceding claims, characterized by that, by appropriate design of the functional module (8), the basic deactivation of the creep reduction is exceptionally interrupted and / or the evaluation of the disturbing vibrations is not carried out if the gearbox temperature (T) is lower than a predetermined temperature threshold value (55°C). [7] Method for controlling a motor vehicle drive train comprising a drive engine (1) with an electronic engine control unit (6) and an automatic transmission (2) with a torque converter (3), with a clutch (5) assigned to a gear and with an electronic transmission control unit (7) in which a creep reduction function is implemented, wherein the creep reduction is activated at or near a standstill of the vehicle by bringing the clutch (5) or brake assigned to a gear in the automatic transmission (2) into slip engagement or into the open position in such a way that a frictional connection in the drive train of the vehicle is reduced or eliminated,wherein the transmission control unit (7) checks for the occurrence of defined disturbing vibrations during the deactivation of an activated creep reduction with the accelerator pedal essentially not actuated and the brake essentially not actuated, and after the defined disturbing vibrations have been detected, the creep reduction remains fundamentally deactivated, wherein the disturbing vibrations are defined in such a way that they detect a defective transmission due to component tolerances. [8] Method according to the preceding claim, characterized by that the basic deactivation is carried out for the entire lifetime of the gearbox, with regular re-checks for the presence of these disturbing vibrations. [9] Method according to one of claims 7 or 8, characterized bythat the longitudinal acceleration of the vehicle (a) is evaluated with a view to detecting disturbing vibrations whose amplitudes are greater than a predetermined minimum amplitude (A) and / or which have a predetermined frequency spectrum, and that the disturbing vibrations defined and detected in this way are counted. [10] Method according to one of claims 7, 8 or 9, characterized by that the creep reduction remains deactivated in principle if the number (Z) of disturbing oscillations is at least greater than one. [11] Method according to one of claims 7, 8, 9 or 10, characterized by that the basic deactivation of creep reduction for a new evaluation of defined disturbing vibrations is switched off after a specified number of kilometers driven. [12] Method according to one of claims 7, 8, 9, 10 or 11, characterized bythat the general deactivation of creep reduction is exceptionally interrupted and / or the evaluation of the disturbing vibrations is not carried out if the gearbox temperature (T) is lower than a specified temperature threshold (55°C).

Images