Method and device for controlling an internal combustion engine with a variable compression ratio

Abstract

In a method for operating an internal combustion engine a compression ratio is set to a setpoint compression ratio by means of an adjustment device, wherein in a normal operating mode of the internal combustion engine the setpoint compression ratio is determined as a function of an, operating variable of the internal combustion engine. The internal combustion engine is at least temporarily operated in a predictive operating mode in which the setpoint compression ratio is determined on the basis of an anticipated estimated operating variable which is estimated on the basis of the instantaneous gradient of the operating variable over time.

Claims

1. A method of operating an internal combustion engine, comprising: with an adjustment device setting a compression ratio to a setpoint compression ratio, wherein in a normal operating mode of the internal combustion engine the setpoint compression ratio is determined as a function of an operating variable of the internal combustion engine; and operating the internal combustion engine at least temporarily in a predictive operating mode, in which the setpoint compression ratio is determined as a function of an expected estimated operating variable, said expected estimated operating variable being estimated as a function of an actual gradient of the operating variable of the internal combustion engine over time.

2. The method of claim 1, wherein the predictive operating mode is initiated when a gradient of an operating element variable over time and/or the gradient of the operating variable over time exceeds a threshold value.

3. The method, of claim 1, wherein an actual load torque of the internal combustion engine is used as the operating variable.

4. The method of claim 1, wherein the estimated operating variable is estimated regularly during performance of the predictive operating mode.

5. The method of claim 1, further comprising determining a derivative of the gradient of the operating variable and terminating the predictive operating mode when the derivative falls below or exceeds a threshold value.

6. The method of claim 2, further comprising terminating the predictive operating mode when the gradient of the operating element variable and/or the gradient of the operating variable fall below the threshold value.

7. The method of claim 1, wherein an optimal ignition angle is selected in the predictive operating mode.

8. The method of claim 2, wherein a setting of the operating element is used as operating element variable.

9. The method of claim 2, wherein an acceleration pedal, a brake pedal or a clutch is used as the operating element.

10. An Internal combustion engine comprising: an adjustment device to adjust a compression ratio to a setpoint compression ratio, wherein the internal combustion engine is configured to determine in a normal operating mode the setpoint compression ratio as a function of an operating variable of the internal combustion engine, and wherein the internal combustion engine is configured to be operated at least temporarily in a predictive operating mode in which the setpoint compression ratio is determined as a function of an expected estimated setpoint operating variable, which is estimated as a function of an actual gradient of the operating variable over time.

Description

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS

(1) In the following, the invention is described on the basis of the exemplary embodiments shown in the drawing without limiting the invention. It is shown in:

(2) FIG. 1 a diagram in which an operating element variable, a load torque of an internal combustion engine, a setpoint compression ratio as well as an actual compression ratio over time are shown, and

(3) FIG. 2 a process diagram of a method to operate a internal combustion engine with a variable compression ratio.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) FIG. 1 shows a diagram in which different variables are plotted over the time t. A course 1 shows the course of an operating element variable, wherein the operating element variable reflects the position of an operating element of a motor vehicle, namely for example an acceleration pedal. It can be seen that a driver of the motor vehicle changes the position of the acceleration pedal at the time point t.sub.0 to achieve or compensate a higher load torque of the internal combustion engine of the motor vehicle. The change of the position of the acceleration pedal is completed a the time point t.sub.2. Up to the time point t.sub.3 the position remains constant. Subsequently the driver again changes the position again up to the time point t.sub.5 in order to adjust or compensate a smaller load torque of the internal combustion engine. The course of the load torque is shown by course 2. It can be seen that the load torque lags behind the operating element variable.

(5) The internal combustion engine includes an adjustment device by which the compression ratio can be adjusted in the cylinders of the internal combustion engine. The compression ratio represents the ratio of the cylinder volume prior to a compression to the cylinder volume after a compression. To adjust the compression ratio, a setpoint compression ratio is set at the internal combustion engine or the adjustment device. The course of this setpoint compression ratio is indicated by course 3. It can be seen that the setpoint compression ratio changes during a change of the load torque of the internal combustion engine, which is used as operating variable, based on a maximum value until reaching a minimum value.

(6) However, because the adjustment device is used to adjust the compression ratio, only has a limited actuating speed, the actual compression ratio lags behind the setpoint compression ratio. The course of the actual compression ratio is shown by a course 4. A delay also exists between a first change of the setpoint compression ratio and a first change of the actual compression ratio. While the setpoint compression ratio already changes from the time point t.sub.0, this is only the case for the actual compression ratio from the time point t.sub.1. This also analogously applies to the reduction of the operating element variable from the time point t.sub.3, for which the change of the actual compression ratio only takes place from the time point t.sub.4.

(7) The diagram shows that the actual compression ratio follows relatively quickly. This is achieved in that the internal combustion engine can be operated in different operating modes. In a normal operating mode the setpoint compression ratio is to be determined as a function of an operating variable of the internal combustion engine, wherein the load torque can be taken into account as operating variable. In a predictive operating mode on the other hand, the setpoint compression ratio is to be determined as a function of an expected estimated operating variable, wherein this estimated operating variable is estimated on the basis of the actual gradient of the operating variable over time. The setpoint compression ratio is therefore not set to the actual operating point of the internal combustion engine, but to a prospective expected operating point. In this way, the actual compression ratio can be adjusted to an optimal compression ratio considerably faster than in normal operating mode, which ensures a fuel-efficient operation of the internal combustion engine.

(8) FIG. 2 shows a process diagram that illustrates the process for the predictive operating mode. The process starts at a starting point 5. In a step 6 it is examined whether the gradient of an operating element variable, in the described embodiment the adjustment of the acceleration pedal, is different from zero. When this is the case, it is examined in a step 7, whether the gradient is higher than a threshold value. Thereby, an absolute value is used for the gradient so that when the setting is changed toward a decrease of the load torque and when the setting is changed toward an increase of the load torque a change from the normal operating mode to the predictive operating mode is made.

(9) When the condition is actually satisfied, i.e., when the gradient is higher than the threshold, the gradient of the operating variable, for example the gradient of the actual load torque of the internal combustion engine, is determined in a step 8. From this gradient, the estimated operating variable is determined in step 9 and from the estimated operating variable the setpoint compression ratio. The setpoint compression ratio is determined for a time point that lies within a determined period of time in the future. The operations 8 and 9 are therefore performed at a time point t, which is indicated by box 10.

(10) Subsequently, in an operation 11, the derivation of the gradient of the operating variable is determined, in particular the second derivative of the load torque of the internal combustion engine. To accomplish this calculation, at least two values for the gradient of the operating variable are necessary. For instance, the operation 11, as indicated by bezel 12, is performed at a time point t following the time point t+t. After operation 11, it is examined in an operation 12 whether the derivation is lower than a threshold value. When this is the case, the predictive operating mode is terminated in an operation 14 and the normal operating mode is performed again because a prediction is not necessary when the derivation has a small value. If, however, the derivation of the gradient of the operating variable is higher than the threshold value, the estimated operating variable and with this the setpoint compression ratio is updated with the now actual gradient of the operating variable at the point of time t+t in operation 15.

(11) The setpoint compression ratio is determined in the predictive operating mode analogous to the procedure in the normal operating, mode, wherein instead of the operating variable, the estimated operating variable is taken into account as a basis. The determination can for example be performed by means of a mathematical relation, a table or a characteristic diagram, wherein the operating variable is used as input variable in the normal operating mode and the estimated operating variable in the predictive operating mode. Subsequently, the setpoint compression mode is used as output variable. With such a procedure, a rapid adjustment of the actual compression ratio to the setpoint operating ratio can be achieved in the predictive operating mode. Thereby, an otherwise necessary adaptation of the ignition angle during the adjustment of the compression ratio by the adjustment device can be mostly or even completely avoided, so that in overall fuel consumption and pollutant emissions are significantly reduced.