Method and arrangement for controlling the position of an actuating element

The invention is directed to a method and an arrangement for controlling the position of an actuating element (1) which prevent damage to the actuating element by a collision with at least one stop (25, 30) and simultaneously ensure good dynamic characteristics. The position of the actuating element (1) tracks a desired value within a displacement range. The displacement range is limited for the actuating element (1) by at least one stop (25, 30). A check is made as to whether the distance between the desired value for the position of the actuating element (1) and the at least one stop (25, 30) drops below a pregiven value (S1). Only in this case is a change of the desired value limited.

BACKGROUND OF THE INVENTION

Methods are already known for controlling the position of an actuating element configured as a throttle flap, an exhaust-gas recirculation valve or as a charge movement flap. The position of the actuating element within a displacement range tracks a desired value and the displacement range is limited by at least one stop for the actuating element.

For the position of the actuating element, a digital control is utilized in a motor vehicle which is carried out by the engine control apparatus. For example, the two methods discussed below are used.

In a first method, a sufficiently high scanning rate must be ensured for the control of the position of the actuating element. Here, it must be prevented that the mechanical stops are not driven against in order to avoid damage to the actuating elements. For this purpose, the displacement range is limited with the aid of an offset. For the described systems having high scanning rates, the offset can, as a rule, be selected small because the design of the control can be so selected that only overshoots with low amplitudes occur.

In a second method, the digital control of the position of the actuating element is carried out at a scanning rate, which is less in comparison to the first method, in order to save on running time and the actuating element need not be moved with high dynamic. In this method, a desired value change limit is mostly used. In this way, overshoots are substantially suppressed.

SUMMARY OF THE INVENTION

Compared to the above, the method and arrangement of the invention for controlling the position of an actuating element afford the advantage that a check is made as to whether the distance between the desired value for the position of the actuating element and the at least one stop is less than a first pregiven value and, only in this case, is a change of the desired value limited. In this way, the desired value change limiting can be limited to the endangered range(s) wherein virtually no overshoots may occur or in which a specific displacement speed may not be exceeded when positioning the actuating element in order to prevent a movement against the at least one stop by the actuating elements and thereby prevent possible damage to the actuating element. It is true that overshoots can occur in the control of the actuating element but these overshoots do not take place in the above-mentioned endangered ranges and therefore do not lead to damage of the actuating element. By saving the desired value change limiting in non-endangered ranges in the above-described second method, a more rapid change of the desired value for the positioning of the actuating element is realized with a high dynamic and therefore the control of the position of the actuating element is accelerated.

Furthermore, with the desired value change limiting in the endangered regions, compared to the first-mentioned method, no offset between the at least one stop and the start of the displacement range is required or the offset can be minimized. This is especially advantageous for systems wherein a throughflow quantity is to be controlled by the position of an actuating element and wherein, for achieving a minimum throughflow quantity, the actuating element must be driven as close as possible to the at least one mechanical stop. This is, for example, an advantage for reducing the leakage air by means of an actuating element configured as a throttle flap in a vehicle. With the method of the invention and the arrangement of the invention, it is ensured that the actuating element is driven sufficiently slowly and so protects the component when driven in the direction toward the at least one mechanical stop.

It is especially advantageous that a limiting of the change of the desired value is lifted when the distance between the desired value for the position of the actuating element and the at least one stop becomes greater. In this way, the desired value change limiting can be disabled also in the above-mentioned endangered regions when the desired value for the positioning of the actuating element moves in the direction out of the particular endangered region because, in this case, one does not have to consider a collision of the actuating element with the at least one stop. In this way, a dynamic improvement for the change of the desired value and therefore an acceleration of the control of the positioning of the actuating element is realized also in the endangered region(s).

A further advantage is that the desired value is maintained when the distance between the desired value and the at least one stop reaches the first pregiven value as long as the distance between an actual value for the position of the actuating element and the at least one stop does not exceed the first pregiven value and the change-limited desired value is inputted after reaching or dropping below the first pregiven value by the distance of the actual value from the at least one stop. In this way, the advantage is realized that overshoots of the actual value for the position of the actuating element, because of the inertia of the actuating element, are reliably suppressed by the change limiting of the desired value for the position of the actuating element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

InFIG. 1, reference numeral35identifies an arrangement for controlling the position of an actuating element1. Means15are provided for bringing the position of the actuating element closer to a desired value within a displacement range. The means15can, for example, be configured as a controller which causes an actual value for the position of the actuating element1to track the desired value within the displacement range of the actuating element1. At least one stop for the actuating element1is provided which limits the displacement range of the actuating element. The actuating element1can be maximally driven up to the at least one stop. A displacement of the actuating element beyond the at least one stop is not possible. The at least one stop can, for example, be a mechanical stop.

InFIG. 4, an example of such an actuating element1is shown. The actuating element1can, for example, be a throttle flap, a charge movement flap, an exhaust-gas recirculation valve or the like in a vehicle. According toFIG. 4, a first stop25and a second stop30are shown by way of example. According to the example ofFIG. 4, the actuating element1is rotatably journalled about a center axis40.

In the following, it should be assumed by way of example that the actuating element1is a throttle flap in an intake manifold45of an internal combustion engine. The first stop25defines a lower stop and the second stop30defines an upper stop in the intake manifold45. The lower stop25is always driven to. The second, upper stop30is, as a rule, also always present but is mostly not driven to or the distance is very great.

In the block circuit diagram ofFIG. 1, the arrangement35further includes a detecting device50for detecting the actual value of the position of the actuating element1. The actual value, which is detected by the detecting device50, is supplied to the controller15as an input quantity. As additional input quantity, the desired value for the position of the actuating element1is supplied to the controller15. The position of the actuating element1is electronically adjusted in the displacement range of the actuating element1by an output signal of the controller15. The output signal of the controller15is formed in dependence upon the difference between the desired value and the actual value in such a manner that the position of the actuating element1tracks the desired value, for example, in the sense of a minimum control deviation. The desired value is supplied to the controller15via a switch55. The switch55is controlled by a control20. The desired value is supplied to the controller15via a desired value input60and the actual value is supplied via an actual-value input65. Via the switch55, the desired value input60can be connected either to an output of a filter5(for example, a lowpass) or to a desired value store70. The desired value store70can be connected to an engine control (not shown inFIG. 1). The engine control inputs the desired value for the position of the actuating element1and stores the same in the desired value store70. The desired value can be pregiven by the engine control, for example, in dependence upon a driver command torque.

In the following, it should, for example, be assumed that the filter5is a lowpass filter. A time constant is supplied to the lowpass5from a time-constant memory80. Furthermore, a limit value is supplied to the lowpass5from a limit value store75and the lowpass5can be initialized with the limit value. The initialization of the lowpass5takes place via a control signal from the control20. The limit value from the limit value store75is also supplied to the control20. The desired value from the desired value store70is supplied to the lowpass5as an input signal to be filtered as well as to the control20. Furthermore, a first pregiven value S1is supplied from the input value store85to the control20.

The operation of the arrangement ofFIG. 1is explained in the following with reference to the flowchart inFIG. 2and is by way of example.

After the start of the program and at program point100, the control20checks whether a control signal is outputted to the switch55for connecting the output of the lowpass5to the desired value input60of the controller15. If this is the case, then it is assumed in the control20that the output of the lowpass5is connected to the desired value input60via the switch55and therefore a desired value change limiting is active. In this case, there is a branching to program point105; otherwise, there is a branching to program point115. For an active desired value change limiting, the change of the desired value is limited by the filter action of the lowpass5and an overshoot of the actuating element is substantially avoided during the control.

At program point115, the desired value change limiting is not active and the switch55is driven by the control20in such a manner that the switch directly connects the desired value store70to the desired value input60. At program point115, the control20determines a first distance between the desired value for the position of the actuating element1and the first stop25and a second distance between the desired value for the position of the actuating element1and the second stop30. Based on the point symmetry to the center axis40of the arrangement shown inFIG. 4, it should be assumed by way of example in the following that the first distance and the second distance are essentially the same so that, in the following, the description is with respect to only a single distance.

At program point115, the control20checks whether the distance is less in magnitude than the first pregiven value S1. If this is the case, then there is a branching to program point120; otherwise, there is a movement out of the program. At program point120, the control20causes a drive of the switch55in such a manner that the switch connects the output of the lowpass5to the desired value input60. Furthermore, the control20triggers the initialization of the lowpass5with the limit value from the limit value store75. Here, the limit value defines a position of the actuating element1which is spaced from the corresponding stop (25,30) by the first pregiven value S1. For a switchover of the switch55for connecting the output of the lowpass5to the desired value input60, the limit value from the limit value store75is supplied as a desired value to the desired value input60with an approximately simultaneous initialization of the lowpass5. Thereafter, the output95of the lowpass5is made to approach the desired value from the desired value store70, which is applied to the filter input90of the lowpass5, via lowpass filtering with the time constant from the time constant store80and is supplied via the switch55to the desired value input60of the controller15. Thereafter, there is a movement out of the program.

In this way, the desired value change limiting is limited by means of the lowpass5to the regions whereat the distance between the desired value from the desired value store70and the particular stop (25,30) is less than the first pregiven value S1. For a suitable selection of the first pregiven value S1, the desired value change limiting can thereby be limited to a region close to the stop so that, in this region, overshoots in the control of the position of the actuating element1can be substantially avoided. In this way, a driving to the stops (25,30) by the actuating element1and therefore damage to the actuating element1is prevented. In contrast, outside of the region close to the stop and fixed by the first pregiven value S1, the desired value can be pregiven without a desired value change limiting and therefore without dynamic loss and the control of the position of the actuating element1accelerated. With the desired value change limiting, which is carried out in the above region close to the stop, an offset in this region between the particular stop (25,30) and the beginning of the displacement range is unnecessary or such offset can be reduced to a minimum because, as described, the occurrence of overshoots in this region is substantially avoided in the tracking of the actuating element1.

At program point105, the control20checks whether the distance between the desired value from the desired value store70and the particular stop (25,30) becomes greater than the previously determined distance. If this is the case, then there is a branching to program point110; otherwise, there is a movement out of the program.

At program point110, the control20causes a switchover of the switch55in such a manner that the desired value store70is directly connected to the desired value input60of the controller15and the desired value change limiting by the lowpass5is thereby disabled or deactivated. In this way, the desired value change limiting, which is carried out in the described region close to the stop, can again be disabled when the desired value for the position of the actuating element1moves away from the particular stop (25,30) and therefore a collision of the actuating element with the stops (25,30) is not a danger. The desired value change limiting is disabled even when the desired value, which moves away from the particular stop (25,30), is still disposed in the region, which is close to the stop and defined by the first pregiven value S1; that is, the distance of the desired value from the particular stop (25,30) is less in magnitude than the pregiven value S1. In this way, a dynamic improvement for the desired value can be achieved also in the region close to the stop and therefore an acceleration of the control of the position of the actuating element1can be achieved when a drive of the actuating element1to the stops (25,30) can be precluded.

After the end of the program, the program can be run through as often as desired.

According toFIG. 1, the desired value change limiting is realized based on the lowpass5. The invention is, however, not limited to a lowpass for realizing the desired value change limiting function. Rather, any desired desired value change limiting functions can be used.

FIG. 3shows a further example for the above. InFIG. 3, a course10of a pregiven displacement speed (v) is shown over the distance (s) between the desired value and the particular stop (25,30). In the example ofFIG. 3, the course10climbs from the distance s=0 up to the first pregiven value s=S1linearly from the displacement speed v=0 up to a first pregiven displacement speed v=V1. This means that the displacement speed (v) for which the desired value goes linearly to zero with decreasing distance to the particular stop (25,30) so that the desired value with decreasing distance to the particular stop (25,30) should be changed less so that overshoots in the tracking of the actuating element1are ever more strongly suppressed. A nonlinear course may be selected in lieu of the linear course10for the pregiven displacement speed shown inFIG. 3. This nonlinear course starting with the distance s=0 at the displacement speed v=0 and increasing for increasing distances (s) can be at least greater than zero. The linear trace10for the pregiven displacement speed shown inFIG. 3can, for example, be a ramp function. The displacement speed (v) is exemplary inFIG. 3for a change of the desired value in the direction of the particular stop (25,30) because, as described, a desired value change limiting can be omitted in the reverse direction. The displacement speed (v) according toFIG. 3is pregiven maximally also only up to the distance s=S1because, for greater distances, the desired value change limiting should be deactivated in accordance with the invention. The limiting of the change of the desired value by the pregiven displacement speed can be carried out starting from the embodiment ofFIG. 1in lieu of the lowpass function described there. In this case, a supply of the time constants and the limit value is not required. Overshoots need therefore not be absolutely avoided because one has sufficient distance to the particular stop (25,30). Because of the ramp, the control is then so slowed that no overshoots occur. The drive of the switch55by the control20takes place, for example, in the manner described according to the flowchart ofFIG. 2. An additional initialization of the desired value limiting function with pregiven displacement speed by the control20in the region close to a stop is not required because the limiting action is initiated with the switchover of switch55for connecting the output of the desired value change limiting function to the desired value input60. The block inFIG. 1, which is identified by reference numeral5, can therefore, in general, define any desired desired value change limiting function including the input90and the output95. In accordance with the example described here, the block5can be configured as a lowpass or as a desired value change limiting function having pregiven displacement speed.

The invention was described with respect to the example of an actuating element and two stops (25,30). The invention is also applicable in a corresponding manner for an actuating element and only one stop or more than two stops. Accordingly, only one region close to the stop or more than two regions close to stops have to be considered in a corresponding manner.

InFIG. 5a, the course of the distance A of the desired value for the position of the actuating element1from the first stop25is shown by a broken line in the diagram and is identified by reference numeral205. The distance A between the position of the actuating element1and the first stop25is plotted as a function of time (t). Here, the ordinate is the distance and the abscissa is the time. At time point t=0, the desired value is at the second stop30. From time point t=0, the distance A of the desired value decreases to the first stop25up to the first pregiven value S1. After reaching the first pregiven value S1, the distance then decreases between the desired value and the first stop25in its change limited by an ever lesser slope and approaches zero.

InFIG. 5a, the distance between the actual value for the position of the actuating element1and the first stop25is furthermore shown by a dotted line and is identified by reference numeral200. Due to the control of the position of the actuating element1, the course of the distance between the actual value and the first stop25follows the course of the distance between the desired value and the first stop25with a certain time delay. Because of the inertia of the actuating element1, the change limiting of the desired value is likewise carried out by the actual value with a time delay so that, at first, an overshoot of the distance between the actual value and the first stop25occurs when the change of the desired value is limited as shown inFIG. 5a. Such an overshoot is to be absolutely avoided in order to prevent damage to the actuating element1and to the first stop25. For this reason, inFIG. 5, the desired value for the position of the actuating element1is maintained as soon as the distance between the desired value and the first stop25reaches the first pregiven value S1starting from higher values. InFIG. 5b, the same reference numerals are used for the same elements as inFIG. 5a. A further approaching of the desired value for the position of the actuating element1to the first stop25takes place only at the time point at which the distance between the actual value and the first stop25likewise reaches the first pregiven value S1starting from higher values. From this time point on, the desired value is brought to the first stop25change limited (that is, with an ever decreasing slope) so that the actual value can follow the desired value without significant time delay in the above-mentioned control and overshoots of the actual value for the position of the actuating element1are avoided.