Method and Arrangement for Detecting and Loosening Jammed Actuators

The invention relates to a method and an arrangement for detecting and loosening jammed actuators.

Such actuators have long been known, see for example U.S. Pat. No. 3,964,457 or U.S. Pat. Nos. 4,313,408 and 4,419,973. A specific embodiment of such an actuator drive, such as for example the duplex-winding rotary ,actuator, is described in British Patent 1,602,507. Idling control systems with a further actuator in a bypass channel, carrying auxiliary air, to the throttle flap for internal combustion engines are described, for example, in published British patent application 2,007,878 or U.S. Pat. No. 4,356,802. In such electromechanical actuators having a continuous characteristic, soiling or the formation of ice can, however, cause an increased hysteresis or else a jamming of the actuator to occur. So, in the past, designs for such actuators were devised which, in the case of a de-energized servo motor or in the case of a failure of the servo motor, moved the actuator with the aid of a spring into a defined throttling cross section which sufficed to supply the internal combustion engine with a quantity of air sufficient for the particular situation. Such a configuration is described in U.S. Pat. No. 4,494,517.

In contrast, the method and arrangement according to the invention for detecting and loosening jammed actuators has the advantage that the jamming of an actuator is detected and, by introducing the measures according to the invention, the actuator can in many cases be loosened again and an overshooting is avoided upon sudden overcoming of the resistance. It should be noted in this case, that depending on the type of the existing actuator, and in combination with a processor control of the drive system, no or only few additional components are necessary.

The invention will now be described with reference to the drawings wherein:

FIG. 1 is a schematic showing an arrangement of the invention which includes an actuator drive for driving an actuator in the form of a throttle flap to adjust the airflow to the engine and control means connected to the actuator drive; and

FIG. 2 is a schematic showing a duplex-winding rotary actuator drive and a spring for displacing the actuator into a specific rest position when the actuator is in the undriven condition.

FIG. 1 shows the elements by which the invention is to be explained. The actuator (throttle flap) is identified here by 10. The associated drive 20 and the actual-value signalling device 30 are fastened on the same axis of rotation. Downstream of the actual-value signalling device 30 is an electronic actual-value acquisition 50. From there, the actual value is supplied to the safety and control logic 60 according to the invention and to the position control 70. Furthermore, the safety and control logic 60 according to the invention can intervene in the position control. Downstream of the position control 70 is an output stage 40, which drives the actuator drive 20. The actuator desired value 80 is also supplied to the safety and control logic 60 and the position control 70. Furthermore, a fault signalling device 61 is connected to the control logic 60 and a specific operating state (for example starting case) can also be signalled to the control logic 60 by a separate input 62. In order to detect a jamming of the actuator, the difference between the actual value of the actuating variable and the given desired value of the actuating variable can be used. As soon as the difference exceeds a certain threshold, a jamming of the actuator is assumed. Furthermore, by summing up of the difference values in a certain time-slot pattern (integrating) a measure of the jamming of the actuator can be obtained. Furthermore, the jamming detection can be switched off if, for example, a device is present which is to sense the mechanical end stops, or if one of the mechanical end stops is to be approached, for example at the instant of starting. Such jams in the case of electromechanical actuators may be caused, for example, by soiling or the formation of ice.

Such electromechanical actuators are often driven by pulse signals of fixed frequency and variable pulse duration (pulse duty factor) in order to effect a continuous displacement. The frequency is selected such that the actuating variable, due to the mechanical inertia, is adjusted to be sufficiently smoothed. The small mechanical movements occurring are intended and serve to reduce the hysteresis of the actuator by avoiding static friction. The following methods are suitable as a measure for releasing jammed actuators:

(1) The control signal is constantly increased or decreased in a certain time-slot pattern, depending on the direction of the deviation of desired value and actual value. At the same time, when a threshold value of the difference between desired value signal and actual value signal is exceeded, the desired signal is no longer increased, in order to achieve a defined swing of the actuator to the current desired value without overshooting when release of the actuator is detected.

(2a) The frequency of the control signal (pulse signal) is reduced for a certain period of time to such an extent that it is around the resonant frequency of the actuator. A jamming can be released by the large changes in torque which occur. The pulse duty factor remains the same as at normal frequency in order that the average value of the actuating variable is also maintained after release. Thereafter, a transition back to normal pulse frequency is made.

(2b) With electric drives which can be operated actively in two directions, the drive is not only switched on and off at low frequency but is reversely driven.

The inertia (time constant) of the controlled system influenced by the actuating variable must be great, in relation to the low control frequency for the actuator, in order to obtain sufficiently small controlled variable amplitudes. This is generally the case with internal combustion engines.

In the figure of the exemplary embodiment, a drive is shown, which can be moved in two directions. For this reason, the output stage of the position control 70 is a bridge circuit 40. An equivalent effect can, however, also be achieved for the duplex-winding rotary actuator drive 13 having separate windings 13A and 13B as shown in FIG. 2 as well as for other drives. According to another feature of the invention, the actuator 10 can be adjusted into a rest position by a spring 14 when the actuator is in the undriven condition. Reference numeral 15 indicates an opening stop. A further advantageous embodiment of the invention is to be seen in that a fault message is sent to the driver if there is an isolated or repeated occurrence of jamming.

The exemplary embodiment described above is in no way to be understood as restrictive. Besides various already existing drive systems for actuators and the associated drive circuits possibly to be modified purely mechanical solutions for such a shaking drive are also conceivable. For example, in a purely mechanical drive, a shaking mechanism similar to a percussion drill could be activated by a slip clutch. Electromechanical solutions with an automatic interrupter (Wagner's hammer) are also conceivable. Furthermore, the invention can be applied both to a main throttle flap and to an actuator in a bypass line.