Method and device for operating a drive device, and drive device

Abstract

A method for operating a drive device of a motor vehicle, having an internal combustion engine and at least one switchable mechanism. The mechanism can be switched to change an operating state influencing a fuel consumption and switching causes an increased fuel consumption. It is proposed that a torque and a rotational speed of the internal combustion engine are predicted depending on a current operating situation, that a dwell time of the mechanism in a switching state is predicted depending on the torque and the rotational speed, and that the mechanism for changing the operating state is actuated depending on the dwell time.

Claims

1. A method for operating a drive device of a motor vehicle, having an internal combustion engine and at least one switchable mechanism, the at least one switchable mechanism comprising at least one of a shift transmission having several transmission stages and a valve stroke adjustment device of a variable valve train of the internal combustion engine, wherein the mechanism can be switched to change an operating state influencing a fuel consumption, and a process of switching the at least one switchable mechanism causes an increased fuel consumption, wherein a torque and a rotational speed of the internal combustion engine are predicted depending on a current operating situation, and a predicted dwell time of the mechanism in a switching state is determined depending on the torque and the rotational speed, wherein the current operating situation includes: a driver type identification based on a gas pedal position, a brake pedal position, and a steering wheel angle; a current travel route based on a navigation system determining one or more of hills, slopes, stops or speed-reducing restricted zones; and traffic information along the current travel route from a traffic control system, wherein a minimum dwell time is determined based on a probable fuel consumption which is predicted based on the current operating situation, and compared to the increased fuel consumption caused by the process of switching the at least one switchable mechanism, and if the predicted dwell time is longer than the minimum dwell time, the mechanism for changing the operating state is actuated.

2. The method as claimed in claim 1, wherein an ignition angle and/or a fuel supply of the internal combustion engine is/are varied upon switching in such a way that a driving torque of the drive device remains the same or almost the same during the switching.

3. The method as claimed in claim 1, wherein the mechanism is actuated depending on a dwell time-dependent fuel consumption.

4. The method as claimed in claim 1, wherein the probable fuel consumption is determined depending on an operating range of the internal combustion engine.

5. The method as claimed in claim 1, wherein the probable fuel consumption is determined depending on the determined rotational speed and the determined torque.

6. A device for operating a drive device of a motor vehicle, comprising: an internal combustion engine and at least one switchable mechanism, wherein the mechanism can be switched to change an operating state influencing a fuel consumption and a process of switching the at least one switchable mechanism causes an increased fuel consumption, wherein a specially designed control unit, which, when used as intended, carries out the method as claimed in claim 1.

7. A drive device for a motor vehicle, comprising: an internal combustion engine having at least one switchable mechanism and a device as claimed in claim 6, wherein the at least one switchable mechanism can be switched to change an operating state influencing a fuel consumption and a process of switching the at least one switchable mechanism causes an increased fuel consumption.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention shall be explained more closely with the aid of the drawing. Shown therein are:

(2) FIG. 1 a motor vehicle in a simplified top view;

(3) FIG. 2 a flow chart for the operation of the motor vehicle;

(4) FIG. 3 a diagram for predicting wheel power;

(5) FIG. 4 a diagram of torque vs. rotational speed; and

(6) FIG. 5 a switching diagram.

DETAILED DESCRIPTION

(7) FIG. 1 shows, in a simplified top view, a motor vehicle 1 having a drive device 2 that comprises an internal combustion engine 3, which is connected by an actuatable clutch 4 to an automatic shift transmission 5, which has several different transmission stages, the shift transmission 5 being operatively connected at the driven end to drive wheels 6 of the motor vehicle 1. The clutch 4 is associated with an actuator mechanism 7, which can be actuated to engage or disengage the clutch 4. For the actuating, a control unit 8 is present, which actuates the internal combustion engine 3 and the actuator mechanism 7. Furthermore, the control unit 8 is connected to a rotational speed sensor 9, which is associated with a driven shaft of the internal combustion engine 3, as well as to a navigation system 10, a traffic information system 11, and a driver type identification device 12. The internal combustion engine 3 advantageously has a variable valve train, comprising an actuatable valve stroke adjustment mechanism 13, by means of which the valve strokes and/or valve opening or closing times can be varied.

(8) With the aid of FIG. 2, which shows an operating strategy for operating the motor vehicle 1 or the drive device 2 in the form of a flow chart, the operation of the drive device 2 shall now be explained, which is optimized in relation to fuel consumption of the internal combustion engine 3. Thanks to the advantageous method, a dwell time of the valve stroke adjustment mechanism 13 and/or the shift transmission 5 is predicted, each of which represents a mechanism that can be switched in order to change an operating time influencing fuel consumption and the switching causes an increased fuel consumption. In this case, a dwell time of the shift transmission 5 is to be understood to be the period of time during which an engaged transmission stage of the shift transmission 5 is maintained, or the period of time that elapses until a transmission stage of the shift transmission 5 is changed. The shift transmission is an automatic shift transmission, which is actuated by the control unit 8 in order to engage a desired transmission stage. A dwell time of the valve stroke adjustment mechanism 13 is understood to be, accordingly, the period of time during which an engaged valve stroke and established valve opening and closing times are constant or maintained. Both the switching of the shift transmission 5 and the switching of the valve stroke adjustment mechanism 13 result in an increased fuel consumption, as already mentioned above.

(9) The operating strategy is designed to perform the changing of a transmission stage 5 or a valve stroke in a way that is optimized for fuel consumption. The most important parameters for determining the target state of the shift transmission 5 are the torque and the rotational speed of the internal combustion engine 3. In order to calculate the dwell time of the shift transmission in a state of such a drive device 2, these two parameters are predicted as quasi-continuous functions of time for the immediate future. Together with the switching thresholds of the shift transmission 5, it is thus possible to calculate the dwell time through the rotational speed and the load.

(10) For this purpose, it is provided that first a wheel drive torque of the driving wheels 6 is predicted in a step S1. FIG. 3 shows, for this purpose, a drive wheel torque MR or, alternatively, a wheel power of the motor vehicle 1 or the drive device 2, plotted in a diagram as a function of the time t. The wheel power is known up to the time to and is based on measured values lying in the past. As of the time to, i.e., lying in the future, the drive wheel torque is unknown and therefore shown by broken line in FIG. 3. In order to predict the course of the wheel torque, the data of the navigation system 10, the traffic information system 11, and the driver type identification device 12 is utilized.

(11) For this, in a step S1a, first a driver type identification is made by means of the driver type identification mechanism 12. The driver type identification device 12 derives the most probable behavior of the driver in the future up to the time of the prediction (to) from the behavior of the current driver of the motor vehicle 1. In particular, in this case, a distinction is made between a sporty driver, an economy-conscious driver, and an average driver. The driver type identification is an independent subroutine that is carried out on the basis of information of a gas pedal position, a brake pedal position, a steering wheel angle, a ratio of target speed to actual speed, or the like, in order to characterize the current driver of the motor vehicle 1, so that an optimized prediction of the behavior of the driver in the future is possible. It is also conceivable to determine the driver type on the basis of driver identification features. As driver identification features, for example, it is possible to identify the face of the driver by means of an optical face recognition, or identify the driver by the ignition key used by him.

(12) In a step S1b, furthermore, data regarding the current travel route of the motor vehicle 1 is ascertained with the aid of the navigation system 10. With the aid of the navigation data, the travel route of the motor vehicle can be predicted with relatively good certainty for the immediate future. In particular, a distinction is made between a target destination mode and a free driving mode. In the target destination mode, the driver indicates a travel destination, so that the navigation system can calculate a travel route to reach this travel destination. In this state, it may be assumed that the driver will follow the pre-calculated travel route, so that the predicted travel route corresponds to the actual travel route with very high probability. In the free driving mode, the driver steers the motor vehicle 1 without active navigation, i.e., without indicating a travel destination. Depending on the current road type and a current road size, however, the data of the navigation system provides an indication as to the most likely travel route, which is then used in the present case as the basis for the further calculation. Given a knowledge of the travel route, it is possible, in particular, to identify hills, slopes, stops or speed-restricted zones and to take these into account when predicting the drive wheel torque.

(13) In a step S1c, moreover, the data of the traffic information system 11 is evaluated by the control unit 8 in order to ascertain the current traffic congestion and/or predict the traffic congestion on the travel route, since often the vehicle speed and thus the drive wheel torque is not determined by the travel route alone, but also by the traffic congestion or the current traffic situation. The traffic congestion identification is an independent subroutine in the present case, making a pronouncement as to the current traffic congestion on the basis of target speed versus actual speed, the speed profile, and vehicle sensors such as distance sensors, ultrasound sensors, crash sensors and pre-crash sensors. Furthermore, data from a traffic information service is also preferably used, which transmits current traffic data, for example, by radio or wirelessly. Thus, for example, the traffic data of a radio transmitter, which is also being considered at the present time by the navigation system, is used to determine the traffic congestion and especially to predict the traffic congestion.

(14) From the data thus collected, in step S1, the wheel torque or the wheel power of the drive device 2 is predicted for the immediate future, as already mentioned above.

(15) From the predicted drive wheel torque, in a following step S2, a rotational speed and a torque of the internal combustion engine 3 is predicted for the immediate future. The predicted rotational speed and the predicted torque result from the drive wheel torque and may be calculated by a computation as the rotational speed or the torque that is necessary or advantageous for achieving the predicted drive wheel torque.

(16) Furthermore, a gear stage prediction is also performed in a step S3 to determine or predict the rotational speed and torque.

(17) FIG. 4 shows the predicted torque Ma plotted in a diagram against the predicted rotational speed n, resulting particularly from the predicted travel route and/or the predicted traffic congestion and the identified driver type. The torque/rotational speed curve can be understood as a trajectory in the plane subtended by rotational speed and torque (characteristic rotational speed/load curve). The trajectory is parameterized by the time t. For the gear stage prediction, in step S3 one or more switching thresholds U are plotted in the diagram of FIG. 4. A switching is the intersection of the switching threshold U with the characteristic torque/rotational speed curve. The switching thresholds are determined in advance in this case in known manner and stored in the characteristic field. Then, from the value of the parameter time t of the trajectory, one obtains the time point of the switching, i.e., the time point at which the transmission stage of the shift transmission 5 will be changed. In this way, the dwell time of the shift transmission 5 in the currently engaged transmission stage is known or predicted in step S3, since the period of time until the intersection or until the switching corresponds to the sought-after dwell time.

(18) The gear stage prediction as shown in FIG. 5 can be derived from the known data. FIG. 5 shows different transmission stages G1, G2 and G3 of the shift transmission G5, which were plotted, for example, against the time t. As also in FIG. 3, the switchings between the transmission stages in the past are known and therefore the characteristic curve is depicted as a solid line. Starting from the current time to, however, the switching is predicted and the characteristic curve in its further course is therefore drawn as a broken line. As can be seen in FIG. 5, one may therefore also predict several gear changes or changes in the transmission stage in the near future. The ascertained dwell time is preferably compared to a minimum dwell time. In this case, the minimum dwell time is determined in step S4 depending on a current fuel consumption and the probable fuel consumption or the fuel consumption that is predetermined on the basis of the predicted data and the increased fuel consumption needed for the switching of the transmission stage. The minimum dwell time is thereby determined such that, upon reaching the minimum dwell time, a consequent switching of the transmission stage of the shift transmission 5 does not result in an increased fuel consumption, or, if the dwell time in a state of the drive device 2 is so long that the increased fuel consumption for the switching of the transmission stage is more than compensated for by the savings between two switchings. Thus, if the ascertained dwell time is longer than the minimum dwell time, the transmission stage is then switched in a step S5; otherwise the shift transmission 5 remains in the engaged transmission stage.

(19) As described with regard to the shift transmission 5, alternatively or additionally, the valve stroke adjustment mechanism 13 and the dwell time thereof is also taken into account. In this case, each time the switching is carried out so that it is torque-neutral. Thus, if the shift transmission 5 or the valve stroke adjustment mechanism 13 is switched, measures are taken to ensure that the drive torque of the drive device 2 remains unchanged or the same as long the driver's intent is unchanged. For this purpose, the fuel supply and/or an ignition angle of the internal combustion engine will be changed, for example. In particular, this produces an increased fuel consumption, which is taken into account when determining the dwell time or a time point for the switching, as described above.

(20) Thus, with the described method, one ensures that a switching of the shift transmission 5 or the valve stroke adjustment mechanism 13 only occurs if there is a valid expectation that the dwell time in the state after the switching is long enough in order to economize on fuel. Thanks to this advantageous method, furthermore, it is found that switching events occur less often for the driver or other passengers of the motor vehicle 1 and the ride comfort is enhanced in this way.

(21) The described method may be implemented likewise also in other mechanisms whose switching state influences the fuel consumption of the drive device. Such other mechanism may be, for example, a mechanism for the ignition angle adjustment or an actuator for influencing a flow pathway or a flow geometry.