WO2008132011A1 - Method for operating a drive train - Google Patents

Abstract

The invention relates to a method for operating an automotive drive train comprising at least one automatic transmission and one drive unit. According to said method, a starting gear and a starting speed are determined during starting of the motor vehicle, a starting process being triggered using the determined starting gear and the determined starting speed by closing a starting element, especially a starting clutch. The method according to the invention is characterized by the following steps: a) determining forces or torques on the vehicle side that have to be surmounted during starting as the tractive resistances; b) determining forces or torques on the engine side that reduce an engine torque made available by the drive unit, said torque being made available for starting; c) determining an acceleration for starting; d) calculating by using a formula a required engine torque for the starting process depending on the determined forces or torques on the motor vehicle side, depending on the determined forces or torques on the engine side, depending on the determined acceleration and depending on a ratio of the determined starting gear; e) determining, based on the calculated engine torque, an engine speed that is used as the starting speed.

Description

 Method for operating a drive train

The invention relates to a method for operating a drive train of a motor vehicle comprising at least one automatic transmission and one drive unit.

The main components of a drive train of a motor vehicle are a drive unit and a transmission. A gearbox converts torques and speeds and thus converts the tractive power of the drive unit. The present invention relates to a method for operating a drive train, which comprises at least one drive unit and an automatic transmission. For the purposes of the present invention, the term automatic transmission is understood to mean all transmissions with an automated gear change or an automatic gear change. Between the drive unit and the automatic transmission of a drive train is preferably designed as a starting clutch starting element is switched to trigger a startup of the motor vehicle, the starting element is automatically closed or automatically taking into account a previously determined starting gear and a previously determined starting speed.

DE 198 39 837 A1 and DE 198 39 838 A1 disclose methods by means of which a starting gear can be determined for a starting operation with the aid of an electronic control device.

From DE 102 02 520 A1 a method is known, with the aid of which a starting speed can be determined for a starting process, namely such that a predetermined starting characteristic curves on the basis of characteristics start-up speed during the startup based on a characteristic that the actual acceleration behavior of the motor vehicle is reflected, modified. On this basis, the present invention is based on the problem to provide a novel method for operating a drive train comprising at least one automatic transmission and a drive unit.

This problem is solved by a method according to claim 1. According to the invention, the method comprises at least the following steps: a) vehicle-side forces or moments are determined which must be overcome when starting as driving resistances; b) motor-side forces or moments are determined which reduce a motor torque provided by the drive unit, which provides the same for starting; c) an acceleration is determined for starting; d) Depending on the particular vehicle-side forces or moments, depending on the specific engine-side forces or moments, depending on the specific acceleration and depending on a translation of the determined starting gear a required engine torque for the starting process is calculated formula; e) on the basis of the calculated engine torque, an engine speed is determined, which is used as the starting speed.

With the present invention, a method for operating a drive train is proposed for the first time, in which for a starting process a required for the starting engine torque is calculated formula, namely on the basis of predetermined vehicle-side forces or moments, depending on predetermined engine-side forces or Moments, depending on a predetermined acceleration and depending on a translation of a determined starting gear. From this calculated, required for the starting engine torque, the starting speed for the starting process is determined. As a result, an optimal starting behavior of a motor vehicle is ensured while minimizing the load of the starting element. With the help of the method according to the invention dynamic influences such. B. a temperature-dependent reduction in engine performance, as well as influences of various vehicle configurations such. As axle ratios and tire radii, are taken into account in the determination of the starting speed for the starting process.

Preferred embodiments of the invention will become apparent from the dependent claims and the description below. Embodiments of the invention will be described, without being limited thereto, with reference to the drawings. Showing:

Fig. 1 is a diagram for illustrating the method according to the invention for operating a drive train of a motor vehicle.

The present invention relates to a method for operating a drive train of a motor vehicle, wherein such a drive train comprises at least one drive unit and an automatic transmission. The method according to the invention relates to the starting of the motor vehicle, the method according to the invention being described in detail below with reference to FIG. 1.

1 illustrates the method according to the invention for operating a drive train comprising a drive unit and an automatic transmission with the aid of a signal flow diagram, wherein the inventive method according to FIG. 1 is subdivided into a total of five steps or blocks.

In a first block or step 1 of the method according to the invention, forces or torques on the motor vehicle are determined which must be overcome when starting as driving resistances. When the vehicle-side forces or moments that must be overcome when starting as driving resistances, it is at least a vehicle-side rolling resistance and a vehicle-side gradient resistance force. An air resistance can be neglected when starting.

In a second block or step 2 of the method according to the invention, engine-side forces or moments are determined which reduce an engine torque provided by the drive unit, which provides the same for starting. This is at least a friction torque on the engine side and a loss moment on the engine-side ancillary units or secondary consumers on the engine side.

On the basis of the vehicle-side rolling resistance force, the vehicle-side gradient resistance force, the engine-side friction torque and the torque loss of the engine-side ancillaries, an engine torque can be calculated, which is sufficient to hold a motor vehicle at a standstill, which, however, still allows no access.

In a third block or step 3 of the method according to the invention, an acceleration for starting the motor vehicle is additionally determined. This is the desired or desired acceleration for the starting process.

According to a first variant, the acceleration for starting can be specified directly in dependence on an accelerator pedal operation, a vehicle mass, a driving resistance and a drive train ratio in block 3, wherein the powertrain ratio of a wheel radius, a translation of the driven axle and the translation of the particular starting gear is dependent , Alternatively, it is possible to calculate in block 3, the acceleration for starting assuming a uniformly accelerated movement of the motor vehicle based on a closing time of the starting clutch to the slip-free transmission. The calculation of the acceleration for starting on the basis of the closing time of the starting clutch to the slip-free transmission takes place with the following formula:

2 * π * _rRAD * n _MOT

¹ GES 'AT F AHR

where a _{KFZ is} the acceleration to start, where i _GES is the driveline ratio, where r _{RAD is} the wheel radius, where n _{MOT is} the engine speed, and where t ^^ is the closing time of the launch clutch to slip-free transmission.

In a subsequent block or step 4 of the method according to the invention is carried out depending on the determined in block 1 vehicle-side forces or moments, depending on the determined in block 2 engine side forces or moments, depending on the acceleration determined in block 3 and dependent from a translation of the starting gear a formulaic calculation of the motor torque required for the starting process.

The motor torque required for the starting process is calculated using the following formula:

[VΛ '/ ¹ f MOT - ^l M ^yl REIB - ^l M ^yl MOT, PTO II * ^GES * 7' / 7GES = ^L F ROLL + ^{τ 1} F RISK 4 ^τ - p ^e * "m ¹ vehicle * / ^u j motor vehicle

'WHEEL wherein M _M0T is the required motor torque, wherein M _REIB is the motorsei- term friction torque, wherein M _{M0T PT0} is the loss torque motor side auxiliary units, where F _R0LL is the vehicle-side rolling resistance force, F _FALL is the vehicle-side slope resistance, wherein a _car acceleration to Startup is where i _GES is the driveline ratio, where _{n is} the wheel radius, where η _{GES is} powertrain efficiency, where m is the _{motor vehicle} 's mass, and e is a driveline dependent size. The following formula-related relationship applies for the drive train ratio dependent variable e:

_ 1 i ^J RAD ^{τ 1 τ 1} OUTPUT SHAFT ^J GES ^J MOT MKFZ ^r RAD

where J ₁ ^ _{0 is} the mass moment of inertia of the wheel, where i _{ACUSE is} the axle ratio, where J _{ABTRIEB is} the mass moment of inertia of the output, where i _{GES is} the powertrain ratio, where J _{M0T is} the mass moment of inertia of the motor, where m is the _{motor vehicle} mass is, and where ^ _{n is} the wheel radius.

In block 4, the formula calculated engine torque for the starting process by a maximum allowable engine torque, which is specified by an accelerator pedal operation can be limited.

Following the formula-based calculation of the engine torque required for the starting process, in a block or step 5 of the method according to the invention, the engine torque is determined on the basis of the calculated engine torque, which is used as the starting speed for the starting operation. In this case, the procedure is such that the smallest possible engine speed is determined from the calculated engine torque by means of an engine characteristic curve or an engine characteristic field, at which the calculated engine torque is available. The starting speed is chosen as low as possible in order to keep a load and thus wear of the starting clutch as low as possible.

The map or the characteristic curve of the engine or drive unit can be stored statically. Preferably, however, the engine characteristic curve or the engine map, based on which the starting speed is determined, is continuously provided by the drive unit. If in the map or in the characteristic of the engine or drive unit dynamic effects such. As temperature influences or turbocharger pressures are not taken into account, the same can be taken into account directly or by other variables transmitted by a motor control.

The determined in block 5 engine speed is used as the starting speed. The control of the engine speed can be done via a transmission internal controller or an internal motor controller. Then, when the engine speed control via an internal-transmission controller, a motor intervention can be done via a torque setting. Then, however, when the engine speed control is done via an engine-internal controller, a speed is specified as the engine intervention, namely the determined in step 5 engine speed.

As already mentioned, the motor torque calculated in block 4 is preferably limited by the maximum permissible engine torque, which is predetermined by the accelerator pedal actuation. This may be the case that the predetermined by the accelerator pedal engine torque is not sufficient to accelerate the motor vehicle. In this case, then the starting clutch remains open for a long period of time, whereby the same, however, in particular on slopes of a higher load and thus a higher wear is exposed. This can be counteracted by taking into account a minimum torque or an offset for the engine torque calculated in block 4 during the starting operation as a function of a predetermined minimum acceleration or a maximum sliding time of the starting clutch. Alternatively, it is also possible to specify via the accelerator pedal actuation no maximum permissible engine torque, but rather an acceleration or a clutch slip time.

As already stated, the lowest engine speed at which the calculated engine torque is available is determined in block 5 from the engine torque calculated in block 4 by means of an engine map or an engine characteristic curve. This engine speed is used as the starting speed. For reasons of comfort, z. B. due to a deteriorating engine run-round or a deteriorating acoustics, it is possible that this minimum engine speed can not be used as the starting speed. In this case, then a higher engine speed is selected as the starting speed.

Furthermore, it can be provided that in block 5, the starting speed is limited to a maximum value, namely a maximum starting speed. This may be necessary because the quantities used for the engine torque calculation in block 4 and the engine speed determination in block 5 may be faulty.

The method according to the invention can be used both in pure starting operations and in maneuvering operations. It is in the nature of maneuvering that for shunting operations the acceleration determined in block 3 is less than in the case of pure starting operations. REFERENCE CHARACTERS

1 block

2 block

3 block

4 block

5 block

Claims

claims 1. A method for operating a at least one automatic transmission and a drive unit comprising a drive train of a motor vehicle, wherein for starting the motor vehicle, a starting gear and a starting speed are determined, and wherein with the particular starting gear and with the certain starting speed a starting operation by closing a starting element, in particular one Starting clutch is triggered, with at least the following steps: a) vehicle-side forces or moments are determined, which must be overcome when starting as driving resistances; b) motor-side forces or moments are determined which reduce a motor torque provided by the drive unit, which provides the same for starting; c) an acceleration is determined for starting; d) Depending on the particular vehicle-side forces or moments, depending on the specific engine-side forces or moments, depending on the specific acceleration and depending on a translation of the determined starting gear a required engine torque for the starting process is calculated formula; e) on the basis of the calculated engine torque, an engine speed is determined, which is used as the starting speed. 2. The method according to claim 1, characterized in that in step a) at least one vehicle-side rolling resistance force and a vehicle-side gradient resistance force are determined. 3. The method according to claim 1 or 2, characterized in that in step b) at least one motor-side friction torque and a loss torque motor-side ancillaries are determined. 4. The method according to any one of claims 1 to 3, characterized in that in step c) the acceleration for starting based on an accelerator pedal actuation, a motor vehicle mass, a driving resistance and a drive train ratio is determined. 5. The method according to any one of claims 1 to 3, characterized in that in step c) the acceleration for starting on the basis of a closing time of the starting clutch is calculated formulas to the slip-free transmission. 6. The method according to any one of claims 1 to 5, characterized in that in step d) the engine torque required for the starting process with the formula - ^L M ^rl REIB - ^l M ^rl MOT, PTO II * ^GES * 7 '/ 7GES = ¹ F ROLL + ^{τ L} F RISK 4 ^τ - p ^e * "m ¹ Cars * n ^U Cars RAD is calculated, where M _M0T is the required motor torque, wherein M _REIB is the motor-side friction torque, wherein M _M0TPT0 motorseiti- the loss torque ger auxiliary units, where F _R0LL is the vehicle-side rolling resistance force, F _FALL is the vehicle-side slope resistance, where a _{KFZ is} the acceleration for starting, where i _GES the Antriebsstrangüberset¬ is pollution, where r is the wheel radius _RAD, wherein η _GES is the drive-train efficiency, where m is the mass of the _automotive vehicle, and wherein e is a drivetrain ratio-dependent size. 7. The method according to claim 6, characterized in that the calculated engine torque is limited by a maximum permissible engine torque, which is predetermined by an accelerator pedal operation. 8. The method according to any one of claims 1 to 7, characterized in that in step e) on the basis of the calculated engine torque via an engine map or a motor characteristic curve, the engine speed used as the starting speed is determined.