Patent Application
20080275612
The invention concerns a shift control method for an automated motor vehicle transmission, which is connected on its input side to a drive engine by an engine clutch made as an automated friction clutch. The engine is an internal combustion engine provided with controllable fuel injection, such that during a gearshift, between a gear under load and a target gear, before the loaded gear is disengaged the torque of the drive engine is adjusted to an idling torque by a modification of the amount of fuel injected and, after the target gear has been engaged, to a load torque by a converse modification of the injection amount.
Automated transmissions are increasingly used in motor vehicles for both passenger cars and commercial vehicles, while having relatively low weight, compact dimensions and high transmission efficiency, owing to their automated shift operations, they offer a high level of operating comfort and reduce the fuel consumption of the motor vehicle concerned. A range of automated transmissions for commercial vehicles is described in ATZ9/2004 from page 772 onwards under the title “The ZF-AS-Tronic Family”.
In a modern drive train provided with an automated transmission, the engine clutch and the drive engine are connected by control means to the transmission so that, during a shift operation, besides the automated disengagement and engagement of the engine clutch during the gear change, the torque and speed of the drive engine are also adapted by appropriate control means, as a rule both being reduced. A number of possibilities are available for doing this, depending on the structural features of the drive engine and the specific sequence during the shift process.
In DE 197 15 850 A1, it is known to reduce the torque and speed during a shift operation in an automated transmission by at least partially closing an exhaust gas throttle valve, by delaying the ignition time, by reducing the delivery power of a fuel pump or the quantity injected by injection valves and/or by at least partially closing an intake throttle valve.
In DE 199 04 129 C1, it is proposed that during a shift operation of this type the torque reduction of the drive engine, before the engine clutch is disengaged should be used to make the transmission load free from the disengagement of the loaded gear. In contrast, DE 102 43 277 A1 describes a shift control method for an automated transmission in which a shift process takes place with the engine clutch engaged and a mechanical engine brake is used for synchronization of the target gear.
In the present case the starting point is an integrally controllable drive train of the type described above in which, during a shift operation, before the gear under load is disengaged, the torque of the drive engine is adjusted to an idling torque in essence by modifying the amount of fuel injected, i.e., for a traction shift reduced by decreasing the amount injected and for a thrust shift increased by increasing the amount injected and in which, once the target gear has been engaged, the torque of the drive engine is readjusted to the required load torque by a converse modification of the amount injected, i.e., for a traction shift increased by increasing the amount injected and for a thrust shift reduced by decreasing the amount injected.
The shift operation concerned can be carried out both with a disengaged and an engaged engine clutch. The drive train is freed from load during the shift process in the first case, essentially by disengaging the engine clutch and, in the second case, (in the absence of other auxiliary means) by setting a corresponding idling torque.
Such a control method of the shift operation, by virtue of the amount of fuel injected, is preferably used with motor vehicles having diesel engines, in particular commercial vehicles, but it can also be used with motor vehicles having gas engines, in particular when the latter comprise direct gasoline injection. For controlling the amount injected, until now the amount injected appropriate for the idling torque has been taken as a constant value, but in certain operating situations such as a traction upshift while driving uphill with a heavy load, this can lead to unfavorable shifting behavior in relation to shift duration, clutch wear and shift comfort.
Against this background, the purpose of the present invention is to propose a shift control method for an automated transmission of the type mentioned to begin with, which is better adapted to the operating situation at the time.
This objective is achieved such that, at the beginning of the shift operation, at least one operating parameter that characterizes the current operating condition of the motor vehicle and/or a shift parameter that characterizes the shift operation envisaged is detected and evaluated. The drive engine injection amount associated with the idling torque is adapted variably to the operating condition of the motor vehicle and/or to the shift operation in accordance with the result of the evaluation.
By adjusting the injection amount associated with the idling torque according to the invention, the torque and speed of the drive engine are increased or reduced, depending on the control direction, and are thereby adapted to the operating condition of the motor vehicle at the time and/or to the shift operation itself envisaged, whereby the shift operation is either accelerated or can take place with less wear and more comfortably.
The current operating condition of the motor vehicle is determined inter alia by the driving resistance at the time, which can expediently be determined in order to adapt the injection amount of the drive engine associated with the idling torque in relation to an average driving resistance, in the case of higher driving resistance by increasing, and in the case of a lower driving resistance by reducing the amount.
During steady-state driving the driving resistance is a combination of rolling resistance, air resistance and road inclination resistance. The rolling resistance increases in proportion to the weight of the vehicle, the air resistance increases proportionally to the square of the driving speed and the inclination resistance proportionally to vehicle weight and road inclination. Thus, the laden weight of the motor vehicle can be determined by a load sensor and from this and the known unladen weight the rolling resistance can be calculated.
With a speed sensor, usually present in the form of a rotation speed sensor arranged on the transmission output shaft, the driving speed can be determined and from it the air resistance calculated. The road inclination can be measured by an inclination sensor and from it, together with the previously determined driving speed, the inclination resistance can be calculated. When adapting the injection quantity associated with the idling torque to the driving resistance, for example a traction upshift, while driving uphill under heavy load takes place more rapidly than while driving along a flat stretch with a low load.
However, the current operating condition of the motor vehicle is also determined by the operating status of the drive engine. For example, in the case of combustion engines with a turbocharger, it is important for the speed of the drive engine not to decrease too much during the shift operation, otherwise the load build-up, due to the necessary acceleration of the exhaust gas turbine and hence the shift operation as a whole, takes a particularly long time. It is, therefore, expedient to determine the acceleration capacity of the drive engine at the beginning of the shift operation and, in relation to an average acceleration capacity, to decrease the injection quantity of the drive engine associated with the idling torque if the acceleration capacity is greater or to increase it if the acceleration capacity is smaller. The acceleration capacity of the drive engine can be calculated from the speed of the drive engine at the time, the current charge pressure of the drive engine and the torque of the drive engine at the time, the corresponding values are determined by sensors or read out of the engine control unit.
The power demand by the driver can also be regarded as a further operating parameter. It is, therefore, expedient to determine the power demand by the driver and, in relation to an average power demand, to increase the injection quantity of the drive engine if the power demand is greater or decrease it if the power demand is smaller.
The driver's power demand can be detected or deduced from the position of the accelerator pedal which can be determined by a path sensor, from the actuation of a kick-down switch when the accelerator pedal is fully depressed and, correspondingly, when the power demand is negative from the actuation of the service brakes that can be determined by virtue of a brake pedal switch.
Independent of any direct operation by the driver, an interrogation can distinguish which driving program is active as between an economical or a sporty setting or a summer or winter setting and the optimum injection quantity can be set appropriately for this.
Likewise, a shift operation is influenced substantially by transmission- and shift-specific shift parameters. Accordingly, the injection quantity associated with the idling torque is expediently also modified as a function of the transmission ratio change of the shift process envisaged, depending on the load direction during the shift process, and depending on the shift direction of the shift process.
In each case, the ratio change is determined by design and can usually be read out from an electronic memory. The injection quantity of the drive engine, associated with the idling torque relative to an average ratio change, is increased if the ratio change is larger and reduced if the ratio change is smaller such that, in either case, a shift operation of approximately the same length can be achieved.
Superimposed over this, to assist the load build-up, the injection quantity of the drive engine associated with the idling torque should be increased during a traction shift and reduced during a thrust shift and to assist the speed adaptation, reduced during an upshift and increased during a downshift.
The invention will now be described, by way of example, with reference to the accompanying drawings in which:
The sole FIGURE shows the variations of the regulating path of the engine clutch, the injection quantity of the drive engine and the torque of the drive engine during a traction shift in a time diagram.
In this time diagram, for the end of a shift process with the engine clutch disengaged considered as an example, a variation of a regulating path SK of the engine clutch, a variation of an injection amount αME and a variation of a torque MM of the drive engine controlled by the injection amount αME of the drive engine are shown as a function of time t.
At time point t0, the target gear is engaged and the injection amount αME is, in a normal case, reduced to a value α0a associated with an idling torque M0a. Consequently, the torque MM of the drive engine is close to zero at the value M0a. The engine clutch is in a disengaged or fully open position s0. At time point t1, the load build-up of the drive engine is started by a ramp-shaped increase of the injection amount αME from the value α0a to a value α1, which is reached at a time t2a. Correspondingly, between t1 and t2a, the torque MM increases in coordination with the engagement of the engine clutch (clutch path SK increases from position s0 to position s1) from the value M0a to a value M1. Thus, the shift operation takes up the interval t2a−t1.
If this interval t2a−t1 is too long, because of unfavorable operating conditions, then according to the invention the reduced injection amount αME of the drive engine is increased at the beginning of a shift operation to a value α0b, whereby the torque MM of the drive engine too is increased slightly to a value M0b. As a result, with the same gradient of the injection amount αME, the target value α1 during load build-up is reached earlier, namely at a time point t2b. In this case, since the engine clutch follows the load build-up of the drive engine during the shift process, the clutch path SK also reaches the engaged position s1 at time point t2b. Thus, the load build-up of the drive engine and the engagement process of the engine clutch now take place during a shorter interval t2b−t1, so the entire shift process is faster.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 057 809.8 | Dec 2005 | DE | national |
This application is a national stage completion of PCT/EP2006/011043 filed Nov. 17, 2006, which claims priority from German Application Serial No. 10 2005 057 809.8 filed Dec. 3, 2005.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/011043 | 11/17/2006 | WO | 00 | 6/2/2008 |
