Abstract:
A circuit arrangement for aircraft engine regulators, for providing or generating a bipolar output direct current signal as a function of at least one pulse-width modulated input signal is disclosed. Said circuit arrangement comprises at least two driver stages, each driver stage being controllable by a pulse-width modulated input signal and wired up to preferably one step-down actuator stage in such a way that, for the control of a first driver stage, a first switching device of a step-down actuator stage controls a low-pass filter device of the step-down actuator stage, and for the control of a second driver stage, a second switching device of the step-down actuator stage controls the low-pass filter device of the step-down actuator stage.

Description:
BACKGROUND 
   The present invention relates to a circuit arrangement for aircraft engine controllers. 
   Digital controllers which have the ability to process complex control algorithms within the shortest period of time are increasingly used as aircraft engine controllers. The digital controllers increasingly replace controllers designed to use analog technology. Digital aircraft engine controllers are used, in particular, for controlling actuators to be operated with direct current; such an actuator may be a torque motor, for example. By using such a torque motor or a d.c.-operated actuator, the fuel supply to the aircraft engine may be influenced, for example. Further areas of application, in which torque motors or d.c.-operated actuators are used, are, for example, reversing the guide blades in an aircraft engine or adjusting nozzles in aircraft engines. As a rule, digital aircraft engine controllers provide a digital output signal, it being necessary for activating a d.c.-operated actuator using such a digital output signal to convert the digital output signal of the digital aircraft engine controller into a direct current signal. 
   According to the related art, the digital output signals are converted into a direct current signal by using expensive digital-to-analog converters or by using expensive single-bit converters and analog amplifier modules. The circuits known from the related art are thus altogether complex and expensive. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to create a novel circuit arrangement for aircraft engine controllers. 
   According to the present invention, a circuit arrangement for aircraft engine controllers may be used for providing or generating a bipolar direct current output signal as a function of at least one pulse-width modulated input signal. The circuit arrangement includes at least two driver stages, each driver stage being activatable by a pulse-width modulated input signal, and the or each driver stage being preferably connected to a step-down converter stage in such a way that when a first driver stage is activated by a pulse-width modulated input signal, a first switching element of a step-down converter stage activates a low-pass device of the step-down converter stage and that when a second driver stage is activated by a pulse-width modulated input signal, a second switching element of the step-down converter stage activates the low-pass device of the step-down converter stage. 
   With the aid of the present invention, a circuit arrangement for aircraft engine controllers is proposed for providing a direct current output signal as a function of at least one pulse-width modulated, digital input signal which functions without expensive digital-to-analog converters or expensive single-bit converters. The circuit according to the present invention allows the use of small, inexpensive output semiconductors. The circuit according to the present invention is characterized by small size, low weight, and high reliability. The present invention makes it possible to simply generate a variable, controllable, and bipolar direct current source. 
   Preferred refinements of the present invention arise from the subclaims and the following description. Exemplary embodiments, without being restricted thereto, are explained in greater detail on the basis of the drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  shows a block diagram of an aircraft engine controller including the circuit arrangement according to the present invention, and 
       FIG. 2  shows a detailed block diagram of the circuit arrangement according to the present invention. 
   

   The present invention is described in greater detail in the following with reference to  FIGS. 1 and 2 . 
   DETAILED DESCRIPTION 
     FIG. 1  shows a block diagram of an aircraft engine controller  10  for activating an actuator  11  to be operated using direct current. D.c.-operated actuator  11  is a torque motor in particular. As is apparent from  FIG. 1 , actuator  11  to be operated or activated represents an ohmic load and an inductive load, the ohmic resistance of actuator  11  being indicated in  FIG. 1  with R 0  and the inductivity of actuator  11  being indicated with L tq . 
   The function of the aircraft engine controller is to activate actuator  11  using a defined direct current signal I act . The actual control current is measured for this purpose and a corresponding measuring signal  12  is conveyed to a block  13 , block  13  representing a difference amplifier stage having a downstream analog-to-digital converter. Output signal  14  of block  13  is thus a digitized measuring signal which is compared in aircraft engine controller  10  with a digital setpoint signal  15 . Error signal ε (t), the difference between digitized measuring signal  14  and corresponding setpoint signal  15 , is conveyed to a digital current controller  16 . Digital current controller  16  is preferably designed as a PID controller (proportional-plus-integral-plus-derivative controller) and provides an output signal I lin , output signal I lin  being linearized in blocks  17  and  18  and converted into pulse-width modulated output signals D and D* of aircraft engine controller  10 . 
   The present invention relates to a circuit  19  in order to provide a corresponding direct current control signal I act  from digital pulse-width modulated output signals D and D* provided by aircraft engine controller  10  for activating actuator  11 . As is apparent from  FIG. 1 , pulse-width modulated output signals D, D* of aircraft engine controller  10  are conveyed as input signals to circuit  19  according to the present invention. Circuit  19  according to the present invention outputs a direct current signal I act  as an output signal. 
   Control circuit  19  according to the present invention is shown in greater detail in  FIG. 2 . In the preferred exemplary embodiment of  FIG. 2 , circuit  19  according to the present invention includes two driver stages  20  and  21 . Both driver stages  20  and  21  are connected to a step-down converter stage  22 . As is apparent from  FIG. 2 , each of the two driver stages  20  and  21  is activatable with a pulse-width modulated input signal D or D*; step-down converter stage  22  outputs the intended direct current signal I act . 
   First driver stage  20  includes a transistor Q 1  according to  FIG. 2 ; a pulse-width modulated input signal D may be applied to a base B Q1  of transistor Q 1  via a resistor R 1 . A capacitor C 1  is connected in parallel to resistor R 1 . Another resistor R 2  is connected between base B Q1  and emitter E Q1  of transistor Q 1  of first driver stage  20 . According to  FIG. 2 , additional resistors R 4 , R 5 , R 6 , and R 7  are connected to collector C Q1  of transistor Q 1  of first driver stage  20 , the additional resistors being connected to a capacitor C 2  according to  FIG. 2 . Transistor Q 1  of first driver stage  20  is designed as an NPN transistor. 
   Second driver stage  21  also includes a transistor Q 2 . Pulse-width modulated signal D* may be applied to base B Q2  of transistor Q 2  of second driver stage  21  via resistors R 8  and R 9 . A capacitor C 3  is connected in parallel to resistor R 9 . Moreover, additional resistors R 10  and R 11  are connected in parallel to resistor R 9 . Resistors R 10  and R 11  are also connected to emitter E Q2  of transistor Q 2  of second driver stage  21 . Additional resistors R 12 , R 13 , R 14 , R 15  and another capacitor C 4  are connected to collector C Q2  of transistor Q 2  of second driver stage  21  according to  FIG. 2 . The exact wiring of these modules is apparent in  FIG. 2 . Transistor Q 2  of second driver stage  21  is designed as a PNP transistor. As is apparent from  FIG. 2 , a supply voltage U AUX  for second driver stage  21 , which preferably corresponds to the supply voltage of the microprocessor of digital aircraft engine controller  10 , is applied to emitter E Q2  of transistor Q 2 . 
   It should be pointed out here that in the event that a positive direct current output signal I act  is to be provided, pulse-width modulated input signal D acts upon first driver stage  20 ; a constant or permanent high-level signal, however, acts upon second driver stage  21 . If a negative current output signal I act  is to be provided, pulse-width modulated input signal D* acts upon second driver stage  21 ; in contrast, a constant or permanent low-level signal acts upon first driver stage  20 . If a zero current is to be provided as the output signal of circuit  19 , the low-level signal constantly or permanently acts upon first driver stage  20  and the high-level signal constantly or permanently acts upon second driver stage  21 . 
   As is apparent from  FIG. 2 , step-down converter stage  22  includes a low-pass filter  23  which in turn includes an inductor L TP  and a capacitor C TP . Inductor L TP  of low-pass filter  23  operates in what is known as pulsating operation. In addition to low-pass filter  23 , step-down converter stage  22  includes two switching elements. 
   A first switching element is formed by a transistor T 1  and a diode D 1 , the first switching element made up of transistor T 1  and diode D 1  cooperating with first driver stage  20 . A second switching element of step-down converter stage  22  is formed by a transistor T 2  and a diode D 2 , transistor T 2  and diode D 2  of this second switching element cooperating with second driver stage  21 . If pulse-width modulated signal D acts upon first driver stage  20  and a permanent high-level signal acts upon second driver stage  21  for providing a positive current output signal, then the first switching element made up of transistor T 1  and diode D 1  activates low-pass filter  23  of step-down converter stage  22 . If, however, pulse-width modulated signal D* acts upon second driver stage  21  and a permanent low-level signal acts upon first driver stage  20  for providing a negative direct current output signal, then the second switching element made up of transistor T 2  and diode D 2  activates low pass filter  23  of step-down converter stage  22 . 
   As is apparent from  FIG. 2 , transistor T 1  of the first switching element is designed as a PNP transistor, resistors R 5  and R 6  of first driver stage  20  and a positive supply voltage terminal +U S  for circuit  19  being connected to emitter E T1  of PNP transistor T 1 . In contrast, transistor T 2  of the second switching element of step-down converter stage  22  is designed as an NPN transistor, resistors R 13  and R 14  of second driver stage  21  and negative supply voltage terminal −U s  being connected to emitter E T2  of NPN transistor T 2 . Collector C T1  of PNP transistor T 1  of the first switching element and collector C T2  of NPN transistor T 2  of the second switching element are connected to one another. Moreover, inductor L TP  of low-pass filter  23  is connected to collectors C T1  and C T2  of these two transistors T 1  and T 2 . 
   Diode D 1  cooperates with PNP transistor T 1  of the first switching element of step-down converter stage  22 . Diode D 1  is connected to NPN transistor T 2  in such a way that anode A D1  of diode D 1  is connected to emitter E T2  of transistor T 2  and cathode K D1  of diode D 1  is connected to collector C 12  of transistor T 2 . Diode D 2  cooperates with NPN transistor T 2  of the second switching element, diode D 2  being connected, according to  FIG. 2 , to transistor T 1  of the second switching element in such a way that cathode K D2  of diode D 2  is connected to emitter E T1  of PNP transistor T 1  and anode A D2  of diode D 2  is connected to collector C T1  of transistor T 1 . Since the two diodes D 1  and D 2  are connected to one another in such a way that cathode K D1  of diode D 1  is connected to anode A D2  of diode D 2 , cathode K D1  of diode D 1  is furthermore connected to collector C T1  of PNP transistor T 1  and anode A D2  of diode D 2  is connected to collector C T2  of NPN transistor T 2 . 
   Circuit arrangement  19  according to the present invention thus includes two driver stages  20  and  21  which cooperate with a step-down converter stage  22 . Step-down converter stage  22  includes one switching element for each driver stage  20  and  21 , each of the two switching elements preferably being formed by a transistor T 1  and T 2  and diodes D 1  and D 2  which cooperate with transistors T 1  and T 2 . Depending on the activation of driver stages  20  and  21  using pulse-width modulated signals D and D*, either the first switching element made up of transistor T 1  and diode D 1  cooperating with first driver stage  20  or the second switching element made up of transistor T 2  and diode D 2  of step-down converter stage  22  cooperating with second driver stage  21  acts upon a low-pass filter  23  of step-down converter stage  22 . 
   If, for example, pulse-width modulated signal D acts upon first driver stage  20  and a permanent high-level signal acts upon second driver stage  21  for providing a positive direct current output signal I act , then the switching element formed by transistor T 1  and diode D 1  and cooperating with first driver stage  20  acts upon low-pass filter  23  of step-down converter stage  22 . The second switching element including transistor T 2  and diode D 2  plays a secondary role in this case. If, in this case, pulse-width modulated signal D has a high level, then transistor T 1  of the first switching element of step-down converter stage  22  is conductive and an appropriate current flows toward low-pass filter  23 . If, however, pulse-width modulated signal D has a low level then transistor T 1  of the first switching element is closed and impedance current I TP  in low-pass filter  23  commutates from transistor T 1  of step-down converter stage  22  to diode D 1  of step-down converter stage  22 . An appropriate operating mode of circuit  19  according to the present invention results when a permanent low-level signal acts upon first driver stage  20  and pulse-width modulated signal D* acts upon second driver stage  21  for providing a negative direct current output signal.