Process and Device for Boost Control

The invention relates to a method and an arrangement for controlling the boost pressure on an internal combustion engine with a first and a second suction path, each having suction pressures which are controlled.

There is a known arrangement for boost control, having two pressure sensors which each measure the suction-path pressure in one of the two suction paths. These measured suction-path pressures are each compared with a desired value, and one of two means of controlling determines a duty factor for a bypass valve on each of the two supercharging turbines from the respective control deviation values.

With the known arrangement, therefore, there are different suction-path pressures when the two pressure sensors do not work in an identical way, which happens frequently.

The object on which the invention is based is to provide a method for boost control, by means of which the boost pressures in two suction paths can each be regulated to the same value with a high degree of accuracy. A further object on which the invention is based is to provide an arrangement for carrying out such a method.

The invention relates to a method for boost control in an internal combustion engine having a first and a second suction path with the suction pressures of each path being controlled. According to a first embodiment of the method, the boost pressure in the first suction path is measured and this boost pressure is regulated to a desired value. The differential pressure between the boost pressures in the first and second suction paths is measured and the boost pressure in the second suction path is regulated to the desired value by taking into account the boost pressure in the first suction path and the differential pressure.

In a second embodiment of the method of the invention, the boost pressures in the first and second suction paths are measured alternately by switching over the pressures to a single pressure sensor. The control value determined for one suction path is maintained, while the boost pressure for the other suction path is measured and controlled.

In the arrangement according to the invention, a pressure sensor is connected only to one suction path. Additionally, however, there is a differential-pressure sensor between the two suction paths. It is possible by means of this arrangement to carry out a method according to which the suction pressure in that suction path, to which the pressure sensor is connected, is controlled directly by means of the measured pressure signal, while the pressure in the other suction path is controlled by means of the pressure signal from the other suction path and the differential pressure. This arrangement and the associated method do not place high demands on the accuracy of the pressure sensor and of the differential-pressure sensor. It is merely necessary to ensure that, when the differential pressure is 0, the differential-pressure sensor indicates this differential pressure 0 correctly.

In another embodiment of the arrangement according to the invention, there is only a single pressure sensor which can be connected alternately to the two suction paths. Thus, since the same pressure sensor is used for pressure measurement in both suction paths, identical suction-path pressures can be set easily, irrespective of the accuracy of the pressure sensor. The method with the arrangement just mentioned works in such a way that, during the time when the pressure signal for one suction path is being measured, the pressure signal for the other suction path is maintained, so that it is available for the control.

The invention is explained in detail below by means of the embodiments illustrated by figures. Of these:

FIG. 1 shows an arrangement for boost control with a pressure sensor and a differential-pressure sensor; and

FIG. 2 shows an arrangement for boost control with a single pressure sensor which can be fitted alternately to two suction paths.

The boost-control arrangement according to FIG. 1 is used there on a V-engine with 8 cylinders which has two banks 10.1 and 10.2 of 4 cylinders each. A first supercharger 12.1 is arranged in the suction tract 11.1 of the first bank 10.1, while in the associated exhaust-gas tract 13.1 there is a first turbine 14.1 which is driven by the exhaust gas and which thereby drives the supercharger 12.1. The driving connection between the supercharger 12.1 and the turbine 14.1 is represented by a solid line. A first timing valve 16.1 drivable by means of the first timing control 17.1 is arranged in a bypass line 15.1 to the first turbine 14.1. The bypass throughflow rate and consequently the rotational speed of the turbine 14.1 and thereby, in turn, the boost pressure provided by the first supercharger 12.1 can be set by activating the timing valve 16.1.

Components corresponding to those on the first bank 10.1 are present on the second bank 10.2. Corresponding reference symbols bear the additional designation "0.2" instead of "0.1".

The arrangement for boost control has a pressure sensor 18, a differential-pressure sensor 19, a desired-value transmitter 20, a first means of control 21.1 and a second means of control 21.2. Moreover, an addition unit 22 as well as a first subtraction unit 23.1 and a second subtraction unit 23.2 are provided. The pressure sensor 18 is connected to the first suction tract 11.1, and the differential-pressure sensor 19 connects the first suction path 11.1 to the second suction path 11.2.

This arrangement functions as follows.

The signal emitted by the pressure sensor 18, namely a voltage signal UPS1, is supplied to the first subtraction unit 23.1. There, this signal is subtracted from a desired voltage UP.sub.-- des. The control deviation UPl is supplied to the first means of control 21.1 which emits in the usual way a timing signal to the first timing control 17.1 as a function of the control deviation.

To that extent, the functioning of the arrangement illustrated in no way differs from the arrangement known from the state of the art.

In the arrangement according to the state of the art, the boost control for the second bank works in a completely identical way to the boost control for the first bank, that is, there is also a second pressure sensor connected to the second suction path. However, this is not true for the arrangement illustrated. In particular, a voltage measured by a second pressure sensor is not supplied to the second subtraction unit 23.2, but instead the subtraction unit 23.2 receives a signal which corresponds to the sum of the pressure signal UPS1 from the pressure sensor 18 and of the differential-pressure signal U.DELTA.P from the differential-pressure sensor 19. The sum of these two signals is formed in the addition unit 22. The differential-pressure sensor 19 is connected in such a way that, when the pressure in the second suction path 11.2 is higher than in the first suction path 11.1, it emits a signal with a sign corresponding to the sign of the signal UPS1 from the pressure sensor 18. Otherwise, the control of the boost pressure for the second bank 10.2 takes place exactly according to the above-described control for the first bank 10.1. The difference, therefore, is only that the actual values for the control are formed differently.

For the calibration of the arrangement, it is merely necessary to ensure that the differential-pressure sensor 19 emits a signal of the value 0 at the pressure difference 0. Moreover, the demands of accuracy placed on the pressure sensor 18 and the differential-pressure sensor 19 are not high, since it is only important to set the same pressure in each of the two suction paths 11.1 and 11.2, this being guaranteed when the differential-pressure sensor 19 then transmits the value 0.

An arrangement is explained with reference to FIG. 2 which can be produced even more cost-effectively than the arrangement according to FIG. 1, specifically because only a single pressure sensor 18 is used instead of a pressure sensor 18 and a differential-pressure sensor 19. In the arrangement according to FIG. 2, not only the differential-pressure sensor 19, but also the addition unit 22 is omitted. Instead, there are as additional functional parts a change-over valve 24 and a clock generator 25 which activates a first sensing/holding circuit 26.1, a second sensing/holding circuit 26.2, a signal switch 27 and a valve change-over switch 28. All the other functional parts correspond exactly to those of the arrangement according to FIG. 1.

The change-over valve 24 has two switch positions. In the first switch position shown, it connects the first suction path 11.1 to the pressure sensor 18. Correspondingly, in its second position, it connects the second suction path 11.2 to the pressure sensor 18. The valve can be changed over pneumatically between the two positions, this taking place by means of the valve switch 28 according to the timing predetermined by the timing generator 25. In the example, the timing frequency is 10 Hz. Whenever the pressure sensor 18 has just been connected to the first suction path 11.1, the signal switch 27 switches the output signal USP1 from the pressure sensor 18 to the first sensing/holding circuit 26.1 in response to the timing signal from the timing generator 25. From the first sensing/holding circuit 26.1, output signal USP1 arrives at the first subtraction unit 23.1. There, a difference is formed again to obtain a desired value UP.sub.-- des which is emitted by the desired-value transmitter 20 as a function of the values of the engine speed n and a load-dependent parameter L, for example the throttle-flap angle. The further control cycle takes place in the way described above with reference to FIG. 1.

In contrast, if the pressure sensor 18 was connected to the second suction path 11.2 by means of the timing signal from the timing generator 25, the signal switch 27 correspondingly switches the output signal USP2 from the pressure sensor 18 to the second sensing/holding circuit 26.2 and from there to the second subtraction unit 23.2. What was said above applies accordingly to the further control.

In practice, as many of the functional groups described as possible are implemented by the functioning of a microcomputer. These are particularly the desired-value transmitter 20 which is then designed, for example, as a memory, the two means of control 21.1 and 21.2, the subtraction units 23.1 and 23.2, the addition unit 22 and the sensing/holding circuits 26.1 and 26.2. The sensing/holding functions do not necessarily have to be at the illustrated point along the signal path. They can also perform their function, for example, at the outputs of the means of control. A microcomputer senses, for example, the pressure sensor 18 at predetermined time intervals whenever the latter has just been switched to one of the two suction paths. The measured value is used to calculate a new actuating value for the associated control circuit. The actuating value in the other control circuit is maintained and emitted to the associated timing control until a new actuating value is calculated for this control circuit too.

The above-described functional cycles correspond to preferred embodiments. However, the functional cycles described in detail are not essential to the invention, but it is crucial that the pressure control in the two suction paths should not be carried out by means of two separate pressure sensors, but either by means of a pressure sensor and a differential-pressure sensor or by means of a single pressure sensor which is switched alternately to the two suction paths.