Abstract:
An aircraft control system includes a propeller governor in which a stepper motor is used to apply a compression force on a speeder spring, and a turbocharger in which a stepper motor is used to actuate a needle valve associated with a diaphragm cell. An electronic control unit may be used to control the stepper motor in the propeller governor and the stepper motor in the turbocharger. The integration of the propeller governor and the turbocharger into a single control system decreases the number of individual adjustments that must be performed manually by the pilot.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 60/226,579, which was filed on Aug. 21, 2000, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for controlling the turbo charging of an internal combustion engine, in particular an aircraft engine, as well as a method and apparatus for controlling an aircraft propeller. 
     BACKGROUND OF THE INVENTION 
     Aircraft are controlled by a throttle control lever, which adjusts a throttle valve in the aircraft engine, and a speed control lever, which adjusts the speed of rotation of the engine and the propeller. The speed control lever controls a propeller governor. The propeller governor in turn controls a propeller pitch control mechanism. Accordingly, the governor serves to operatively couple the speed control lever to the propeller pitch control mechanism. The pitch of the propeller determines the load on the engine. As the pitch increases, the load on the engine increases. Conversely, as the pitch decreases, the load on the engine decreases. 
     A disadvantage of this system is that the pilot must control both the throttle control lever and the speed control lever simultaneously. Obviously, the pilot may select less than optimum speed control settings for a given throttle setting. Excess wear and tear on the engine and poor fuel efficiency may result from these less than optimal settings. 
     The turbo charging of internal combustion engines is usually controlled through a waste gate. The waste gate is disposed in a by-pass duct that connects a turbine inlet directly with a turbine outlet. Exhaust gasses by-pass the turbine as they pass through the by-pass duct. The position of the waste gate determines the admission of exhaust gasses to the turbine. Thus, the waste gate functions in the same way as a valve. By increasing or decreasing the admission of exhaust gas to the turbine, it is possible to influence a compressor&#39;s output. The compressor is connected to the turbine through a turbocharger shaft. The charge pressure produced by the compressor is, therefore, determined by the position of the waste gate. 
     In many instances, but particularly in automotive applications, the waste gate is actuated by means of a diaphragm cell that comprises a membrane that is acted upon by gas pressure, a spring that acts against the pressure exerted by the gas, and an operating rod. The operating rod forms the connection between the diaphragm and the waste gate, so that the waste gate can be opened and closed. The air charge generated by the compressor is usually used as the pressure medium within the diaphragm cell. If the gas pressure in the diaphragm cell changes, then the diaphragm and the operating rod move to a position where the force exerted by the gas and the force exerted by the spring are in equilibrium. The spring is disposed in a chamber that is vented to the atmosphere. In this way, the waste gate may be moved into various positions as a function of the gas pressure. The gas pressure is usually adjusted by an electromagnetic timing valve. The greater the opening, the higher the gas pressure (and vice versa). The timing valve itself is controlled by the Engine Control Unit (ECU). 
     Although this method is effective for controlling automotive applications, it is extremely problematic for applications used on aircraft engines. Should the timing valve or its control system fail, the valve may be left either fully open or fully closed, depending on the type of valve involved. This may result in the waste gate being either fully opened or fully closed. This, in turn, may result in an abrupt drop in charge pressure that may result in a loss of power. Alternatively, this may result in an increase in charge pressure, with a corresponding risk of damage to the engine. Both situations are hazardous in aircraft engine applications. In principle, excess pressure can be dissipated through special “pop-off”, or alternatively, relief valves, although such valves are relatively costly. 
     In aircraft applications, hydraulic-mechanical control systems are normally used today in order to actuate the waste gate. In such cases, motor oil itself is usually used as the pressure medium, and this oil acts on a hydraulic actuating piston through a hydraulic-mechanical controller-logic system. The actuator piston is connected to the waste gate and thus adjusts it. However, the system is relatively costly. The relatively high weight of the system is also a disadvantage. In addition, there is no redundancy built into the system, i.e., there is no backup system that can perform system functions that may be lost in the event of a failure. A hydraulic-mechanical system is more stable than the previously described system using an electromagnetic timing valve, which controls a diaphragm cell. However, in the event of a system failure in a hydraulic-mechanical system, it cannot be excluded that under unfavourable conditions, charge pressure could tend towards an extreme value, and this eventuality is associated with the dangers discussed heretofore. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a simple, cost-effective propeller governor having improved characteristics. 
     It is another object of the invention to provide a simple, cost-effective turbocharger system having improved characteristics. 
     It is yet another object of the invention to provide an aircraft control system through which the operation of an aircraft can be greatly simplified. 
     It is yet another object of the invention to provide an aircraft control system through which the safe operation of an aircraft can be enhanced. 
     It is still another object of the invention to provide an aircraft control system through which an optimal setting for the aircraft propeller governor can be set automatically. 
     In furtherance of these objects, one aspect of the present invention is to provide a propeller governor that uses a stepper motor. The propeller governor is adjusted through the use of the stepper motor. 
     Another aspect of the present invention is to control the propeller governor through an electric control unit. 
     Yet another aspect of the present invention is to control the propeller governor through an electronic control unit in communication with a throttle valve. The propeller governor is adjusted in response to the position of the throttle value. 
     Yet another aspect of the present invention is to provide a turbocharger control system having a needle valve actuated by a stepper motor. The needle valve is configured to operatively actuate a diaphragm cell. The diaphragm cell actuates a waste gate. 
     Yet another aspect of the present invention is to provide a turbocharger control system having overboost protection. 
     Yet another aspect of the present invention is to provide an aircraft control system having a single electronic control unit through which a propeller governor and a turbocharger are controlled. 
     These and other aspects of the present invention will be made apparent by the description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Rreference will be made herein after to the accompanying drawings, which illustrate various embodiments of the present invention discussed herein below, wherein: 
     FIG. 1 is a cross-sectional side view of a propeller governor constructed in accordance with the teachings of the present invention; 
     FIG. 2 is a schematic view of a turbocharger control system constructed in accordance with the teachings of the present invention with several features of the turbocharger shown in cross-section; 
     FIG. 3 is a cross-sectional side view of a portion of the turbocharger control system illustrated in FIG. 2, showing a needle valve and a diaphragm cell; 
     FIG. 4 is an enlarged detail of the needle valve illustrated in FIG. 3; 
     FIG. 5 is side view schematic of a plenum used in association with the turbocharger control system illustrated in FIG. 2; 
     FIG. 6 is a schematic view of a diaphragm cell used in association with the turbocharger control system illustrated in FIG. 2, the diaphragm cell being shown in a first operational position; 
     FIG. 7 is a schematic view showing the diaphragm cell illustrated in FIG. 6 in a second operational position; and 
     FIG. 8 is a schematic view showing the operational control system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a preferred embodiment of the propeller governor  100  of the present invention. The propeller governor  100  includes a housing  102  within which a plunger valve  104  is moveably disposed. The plunger valve  104  is a hydraulic control valve through which the governor controls the oil pressure at a propeller pitch controller (not shown). The plunger valve  104  may also be referred to as a pilot valve. Unlike most of the features of the governor  100  illustrated in FIG. 1, the plunger valve  104  is almost entirely not shown in cross-section. The plunger valve includes an elongate body  105  that includes a plurality of generally cylindrical sections  106 - 112  connected to each other into a unitary body. A first section  106  includes a large diameter. A second section  107  includes a small diameter. A third section  108  includes a large diameter. A fourth section  109  includes a small diameter. A fifth section  110  includes a large diameter. A sixth section  111  includes a small diameter. A seventh section  112  includes a large diameter. A head  113  is connected to the elongate body seventh section  112 . The head includes a bottom surface  114  and a top surface  115 . A bearing assembly  116  separates the head bottom surface  114  from the head top surface  115 , and allows the top surface  115  to rotate relative to the bottom surface  114 . The plunger valve further includes a first orifice  117  disposed within the second cylindrical section  107 , and a second orifice  118  disposed within the sixth cylindrical section  111 . The first orifice  117  is in fluid communication with the second orifice  118  through a passage (not shown), which extends through the interior of the elongate body  105  of the plunger valve  104 . 
     A rotating flyweight mechanism  120  is also disposed within the housing  102 . The rotating flyweight mechanism includes an elongate body  122  which is rotationally mounted within the housing  102 . The elongate body  122  includes a first end  123  which is adapted to be driven rotationally by the engine through an appropriate means such as a gear, belt, or chain (not shown). Accordingly, the flyweight mechanism  120  is responsive to engine speed (rpm) at all times. A gear  124 , which extends from the elongate body, drives an oil pump comprising a toothed gear. Tooth  146  of the oil pump toothed gear is shown meshed with the gear  124 . A first port  125 , a second port  126 , and a third port  127  each extend through the elongate body. The first port  125  is in fluid communication with a first passage  128  extending through the housing  102 . The first passage  128  is in fluid communication with a sump (not shown). The second port  126  is in fluid communication with a second passage  129 . The second passage  129  is in fluid communication with the pump. The third port  127  is in fluid communication with a third passage  130 . The third passage  130  is in communication with the propeller pitch control mechanism. 
     A rotating flyweight assembly  131  is disposed on the second end of the flyweight mechanism  120 . The rotating flyweight assembly includes flyweights  132 ,  138 . The flyweight assembly  131 , and, thus the flyweights  132 ,  138  are rotated by the engine through the first end of the flyweight mechanism  120 . Accordingly, the rotational speed of the flyweights  132 ,  138  is responsive to engine speed (rpm) at all times. The flyweights  132 ,  138  include an L-shaped body. The flyweights  132 ,  138  pivot about pivot points  134 ,  140 . The flyweights  132 ,  138  pivot outwardly as the centrifugal forces acting upon them increase, and pivot inwardly as the centrifugal forces acting upon them decrease. The flyweights  132 ,  138  include toe portions  136 ,  142  which contact the head bottom surface  114  to pull on the plunger valve  104  as the flyweights  132 ,  138  pivot outwardly. As the flyweights  132 ,  138  pull on the plunger valve  104 , the plunger valve  104  is pulled, and thus moves relative to the housing  102  (to the left in FIG.  1 ). The flyweight assembly  131  further includes a base  144  on which pivot points  134 ,  140  are disposed. 
     A first annular gap  147  separates the plunger valve elongate body second section  107  from the elongate body  122  of the flyweight mechanism  120 . A second annular gap  148  separates the plunger valve elongate body fourth section  109  from the elongate body  122  of the flyweight mechanism  120 . A third annular gap  149  separates the plunger valve elongate body sixth section  111  from the elongate body  122  of the flyweight mechanism  120 . The annular gaps  147 ,  148 , and  149  comprise passages through which oil may pass. 
     A speeder spring  150  is disposed within the housing  102 . The speeder spring  150  includes a first end  152  in contact with the head top surface  115  and a second end  154  in contact with a speeder spring cap  160  which is disposed around the speeder spring second end  154 . The speeder spring  150  applies a compression force which pushes on the plunger valve  104 . This compression force opposes the pulling force applied by the flyweights  132 ,  138 . 
     The propeller governor  100  further includes a linear stepper motor  170  operatively adapted to apply a predetermined adjustable compression force on the speeder spring  150 . The linear stepper motor  170  includes a shaft  172  which moves in a linear direction. In this preferred embodiment, the stepper motor  170  includes a first set of windings  170 A and a second set of windings  170 B. In this preferred embodiment, the stepper motor  170  is operatively actuated by an ECU. Each winding  170 A and  170 B of the stepper motor would be connected to the ECU through a separate lane. The two lanes would be galvanically isolated. The ECU is shown in greater detail in FIG.  2 . The operation of the ECU will be described in greater detail in reference to FIG.  2  and FIG.  8 . 
     A pivoting lever mechanism  180  comprises a lever arm  181  having a first end  182 , a second end  184 , and a pivot  186  disposed between the first end  182  and the second end  184 . The pivoting lever mechanism  180  translates the movement of the stepper motor shaft  172  to the speeder spring  150 . To do this, lever arm first end  182  is coupled to the stepper motor shaft  172  and the lever arm second end  184  is coupled to the speeder spring  150  through a pivot  188  disposed on the cap  160 . 
     A compression spring  190  is disposed around the speeder spring  150 . The compression spring  190  is disposed between the plunger valve  104  and the housing  102 . The compression spring  190  serves to assist the stepper motor  170  in maintaining the position of the speeder spring  150 . 
     There are three positions of the plunger valve  104  which correspond to three positions of the rotating flyweights  132 ,  138 . These three positions are described below. 
     In a first steady state position shown in FIG. 1, the flyweights  132 ,  138  are in a neutral position, neither pivoted inwardly, nor pivoted outwardly. In this plunger valve  104  position, the passage  130 , which connects the plunger valve to the propeller pitch controller is closed due to the position of the plunger valve  104  relative to the housing  102 . Specifically, the plunger valve fifth section  110  is aligned with the port  127 . Oil is, thus prohibited from moving from the oil pump via the passage  129 , and into the passage  130 . As the passage is closed, oil is also prohibited from moving through the passage  130  from the propeller pitch controller to the sump through passage  128 . Accordingly, the propeller pitch control mechanism makes no adjustment to the pitch of the propeller blades, as oil is prevented from passing either to or from the propeller pitch controller through the passage  130 . 
     In a second plunger valve  104  position (not shown), which occurs during an over-speed condition, the engine rpm and propeller speed are greater than a desired value, for example, a value determined by the ECU. As a result, the centrifugal forces acting on the rotating flyweights  132 ,  138  exceeds the force applied by the speeder spring  150  which opposes the centrifugal force of the rotating flyweights  132 ,  138 . Consequently the centrifugal force acting on the flyweights  132 ,  138  causes the flyweights  132 ,  138  to pivot outwardly. The plunger valve  104  is pulled relative to the housing  102  by the outwardly pivoting flyweights  132 ,  138 . In this plunger valve  104  position, the annular gap  148  is aligned with the ports  126  and  127 . Oil is consequently allowed to pass from the oil pump to the propeller pitch controller. Specifically, oil passes from the oil pump through the second passage  129 , through the second port  126 , and into the annular gap  148 . From the annular gap  148 , the oil passes through the third port  127  into the third passage  130  which is in fluid communication with the propeller pitch controller. The oil pressure at the propeller pitch control mechanism increases resulting in a higher pitch of the propeller blades. The higher pitch of the propeller blades increases the load on the aircraft engine. Accordingly, the engine speed decreases, resulting in a decrease in the rotational speed of the rotating flyweights  132 ,  138 . Obviously, as the rotational speed of the flyweights  132 ,  138  decreases, the centrifugal forces acting on the flyweights  132 ,  138  also decrease. The compression force of the speeder spring  150 , is then able to overcome the centrifugal force acting on the flyweights  132 ,  138 , and the speeder spring  150  pushes the plunger valve  104  back to the steady state position. The ports  121 , 123  through which oil traveled are closed as the plunger valve is returned to the steady state position. 
     In a third plunger valve  104  position (not shown), which occurs during an under-speed condition, the engine rpm and propeller speed are less than a desired value, for example, a value determined by the ECU. As a result, the centrifugal forces acting on the rotating flyweights  132 ,  138  are exceeded by the force applied by the speeder spring  150  which opposes the centrifugal force acting on the rotating flyweights  132 ,  138 . Consequently the compression force of the speeder spring  150  causes the flyweights  132 ,  138  to pivot inwardly. The plunger valve  104  is moved relative to the housing  102  by the speeder spring  150 . In this plunger valve  104  position, annular gap  149  aligns with port  127  allowing pressurized oil from the propeller pitch control mechanism to travel from the passage  130  through the port  127  into the annular gap  149 . The oil in the annular gap  149  then passes through the orifice  118  into plunger valve passage (not shown). The oil passes through the plunger valve passage, through the orifice  117 , and into the port  125 . From the port  125 , the oil passes into the passage  128 , through which the oil is returned to the sump. The oil pressure at the propeller pitch control mechanism decreases resulting in a lower pitch of the propeller blades. The lower pitch of the propeller blades decreases the load on the aircraft engine. Accordingly, the engine speed increases, resulting in an increase in the rotational speed of the rotating flyweights  132 ,  138 . Obviously, as the rotational speed of the flyweights  132 ,  138  increases, the centrifugal forces acting on the flyweights  132 ,  138  also increase. The compression force of the speeder spring  150  is overcome by the centrifugal force acting on the flyweights  132 ,  138 , and the flyweights  132 ,  138  pull the plunger valve  104  back to the steady state position. The passage  130  through which oil traveled is closed as the plunger valve is returned to the steady state position. 
     To decrease the rotational speed of the propeller, the ECU communicates a signal to the stepper motor  170 , which results in the operation of the stepper motor. The stepper motor shaft  172  is moved a distance corresponding to the signal so that the compression force on the speeder spring  150  is decreased. The decreased compression force applied by the speeder spring  150  on the plunger valve  104  allows the centrifugal forces acting on the flyweights  132 ,  138  to cause the flyweights to pivot outwardly and to pull the plunger valve relative to the housing  102 . In this plunger valve  104  position, oil travels from the pump to the propeller pitch control mechanism in the manner previously described. The oil pressure at the propeller pitch control mechanism increases resulting in a higher pitch of the propeller blades. The higher pitch of the propeller blades increases the load on the aircraft engine. Accordingly, the engine speed decreases, resulting in a decrease in the rotational speed of the rotating flyweights  132 ,  138 . As the rotational speed of the flyweights  132 ,  138  decreases, the centrifugal forces acting on the flyweights  132 ,  138  also decrease. The compression force of the speeder spring  150  overcomes the centrifugal force acting on the flyweights  132 ,  138 , and the speeder spring  150  pushes the plunger valve  104  back to the steady state position. 
     To increase the rotational speed of the propeller, the ECU communicates a signal to the stepper motor  170 , which results in the operation of the stepper motor. The stepper motor shaft  172  is moved so that the compression force on the speeder spring  150  is increased. The increased compression force applied by the speeder spring  150  on the plunger valve  104  moves the plunger valve  104  relative to the housing  102 . The flyweights  132 ,  138  pivot inwardly as a result of the plunger valve  104  moving inwardly. In this plunger valve  104  position, oil passes from the propeller pitch controller back to the sump in the manner previously described. The oil pressure at the propeller pitch control mechanism decreases resulting in a lower pitch of the propeller blades. The lower pitch of the propeller blades decreases the load on the aircraft engine. Accordingly, the engine speed increases, resulting in an increase in the rotational speed of the rotating flyweights  132 ,  138 . As the rotational speed of the flyweights  132 ,  138  increases, the centrifugal forces acting on the flyweights  132 ,  138  also increase. The compression force of the speeder spring  150  is overcome by the centrifugal force of the flyweights  132 ,  138 , and the flyweights  132 ,  138  pull the plunger valve  104  back to the steady state position. 
     The propeller governor  100  described above is an increase pitch plunger valve type governor. This name of course, refers to the fact that the propeller pitch control mechanism, with which the governor operates, requires higher oil pressure to increase pitch. 
     There is, however, a second type of governor that is referred to as a decrease pitch plunger valve type governor. As this name suggests a governor of this type operates with a propeller pitch control mechanism for which a decrease in pitch occurs in response to higher oil pressure at the propeller pitch control mechanism. In a governor of this type, the plunger valve in the overspeed condition is lifted by the flyweights to a position where the oil in the propeller pitch control mechanism can return to the sump through the plunger valve. The decrease in oil pressure at the propeller pitch controller results in an increase in the pitch of the propeller blades. Similarly, the plunger valve in the underspeed condition is pushed by the speeder spring to a position where oil from the pump travels through the plunger valve to the propeller pitch control mechanism. The increase in oil pressure at the propeller pitch control mechanism results in the decrease in the pitch of the propeller blades. It is, therefore, understood that the features of the propeller governor illustrated in FIG. 1, and which have been described heretofore, could have also been used in a decrease pitch plunger valve type governor. 
     The propeller governor  100  illustrated in FIG. 1 is preferably operated by an ECU. As will be described in reference to FIG. 8, the propeller governor  100  can be integrated into a control system along with other aircraft engine components. 
     Although a preferred embodiment of the propeller governor  100  has been described herein, it is understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention. In addition many modifications may be made to adapt a particular situation, component, or material to the teachings of the present invention without departing from its teachings as claimed. 
     For example, the preferred embodiment of the propeller governor  100  illustrated in FIG. 1, shows the linear stepper motor  170  applying a compression force on the speeder spring through the lever mechanism  180 . It is understood that the stepper motor  170  could have been mounted directly in line with the axis of the plunger valve  104  such that the stepper motor shaft  172  would apply pressure directly on the speeder spring cap  160 . Also possible would be the use of other forms of known transmission mechanisms to form the connection between a stepper motor and the speeder spring. Such examples include a rotary speed adjusting control lever and adjusting worm that is known in the art. Such a governor could utilize a linear stepper motor as has been previously described, or could utilize a stepper motor having a rotary output. A suitable transmission for converting the rotary motion to a linear motion would be necessitated in this example. Such transmissions are known in the art. 
     Additionally, in the preferred embodiment of the propeller governor illustrated in FIG. 1, the stepper motor  170  is redundancy based, i.e., it has two electrically separated windings  170 A and  170 B, that are actuated by the ECU through two largely independent lanes (not shown). If one lane fails, the other lane fulfils all the control functions. Flight safety can be greatly increased as a result of this. However, it is understood that a stepper motor that is not redundancy based could also have been used. 
     FIG. 2 shows the elements of the turbocharger control system  200  in a schematic view. The turbocharger control system  200  includes an exhaust duct  212 , a turbine  214  disposed within the exhaust duct  212 , an exhaust by-pass duct  216 , and a waste gate  218  disposed within the by-pass duct  216 . A shaft  220  attaches the turbine  214  to a compressor  224 . The compressor  224  blows air into the air duct  228 , through which pressurised air having a charge pressure P k  passes to a plenum (not shown). Air passes into the compressor  224  through an air inlet  226 . A charge pressure P k  duct  230  extends from the air duct  228  to a needle valve mechanism  250 . The needle valve mechanism  250  includes a valve needle (shown in FIGS.  3  and  4 ). The valve needle is operated by a stepper motor  260 . The needle valve mechanism  250  includes an atmosphere passage  252 , the pressure within which is at atmospheric pressure P u , and a diaphragm cell passage  254 . A diaphragm cell  280  is in communication with the needle valve mechanism  250  through the diaphragm cell passage  254 . The diaphragm cell  280  includes a housing  282 , and a diaphragm  284  which separates the housing  282  into an air chamber  286  and a coil spring chamber  288 , which is vented to the atmosphere. The pressure within the air chamber  286  is P m . A coil spring  290  is disposed within the coil spring chamber  288 . A coil spring cap  292  or piston separates the coil spring  290  from the diaphragm  284 , and provides support for the diaphragm  284 . An operating rod  294  forms the connection between the diaphragm  284  and the waste gate  218 , so that the waste gate  218  can be opened and closed. 
     FIG. 3 shows the components of the needle valve mechanism  250  and the diaphragm cell  280 . The needle valve mechanism  250  is shown having a stepper motor  260 . A shaft  264  extends from the stepper motor  260 . A double-conical or double-tapered valve needle  266  having opposing conical ends is secured at the end of the shaft  264  at a position opposite the stepper motor  260 . The valve needle  266  is disposed within a bore  265 . The valve needle  266  is disposed for linear movement within the bore  265  along the longitudinal axis of the shaft  264 . 
     FIG. 3 also shows a preferred configuration of the diaphragm  284 , coil spring cap  292  and the housing  282 . The housing  282  is made in two parts. One part houses the coil spring  290 , the coil spring cap  292 , which is also known as the piston, and the operating arm  294 , as well as the stepper motor  260 . The other part contains the air chamber  286  as well as the bore  265 , within which the valve needle  266  is disposed. 
     In use, the charge pressure P k  is controlled by the waste gate  218 . Depending on the position of the waste gate  218 , a larger or smaller proportion of the flow of exhaust gas will be diverted from the by-pass duct  216  to the turbine  214 . Accordingly, the compressor output is controlled through the waste gate  218  so that different charge pressures P k  can be achieved. The waste gate  218  is adjusted by means of the diaphragm cell  280 . The diaphragm  284  is acted upon by gas pressure P m , and by the spring pressure exerted by spring  290  that acts opposite to the gas pressure P m . Changes to the gas pressure P m  result in a corresponding positional changes of the operating rod  294 . If the gas pressure P m  in the diaphragm cell  280  changes, then the diaphragm  284  and the operating rod  294  move to the point that the force exerted by the gas and the force exerted by the spring are once again in equilibrium. In this way, the waste gate  218  can be moved into various positions as a function of the gas pressure P m . The gas pressure P m  is controlled by the needle valve  250  that is actuated by a linear stepper motor  260 . 
     The operation of the valve needle will be described in reference to FIG. 4 which shows the valve needle  266  in greater detail. Reference also will be made to FIGS. 2 and 3. There are three positions of the needle valve  250 . In a first position, shown in FIG. 4, the valve needle  266  closes the charge pressure P k  duct  230 . Specifically, conical end  270  closes, the opening  255  to thus close off the duct  230 . The opening  253  to the atmosphere passage  252  is fully open and communicates with the diaphragm cell passage  254 . Air is thus removed from the diaphragm cell air chamber  286 . The diaphragm  284  is acted upon by atmospheric pressure (P m =P u ) allowing the return spring  290  to close the waste gate  218 . The charge pressure P k  of the turbocharger increases. 
     In a second position (shown previously in FIG.  3 ), the valve needle  266  closes off the atmosphere passage  252  through the conical end  268  closing the opening  253 . The charge pressure P k  duct  230  is fully open. Accordingly, the full charge pressure P k  acts on the diaphragm  284  (P m =P k ), causing the diaphragm and, thus, the waste gate to move. The waste gate is opened completely, providing the compressor pressure is high enough. 
     In a third position (not shown), the valve needle  266  is between the extreme positions described in the first and second positions. Accordingly, the diaphragm cell passage  254  communicates with the charge pressure P K  duct  230  and with the atmosphere passage  252 . The valve needle  266  thus functions as a pressure splitter. The following relationship describes the gas pressure P M  in the diaphragm cell: P k &gt;P m &gt;P u . Accordingly, the waste gate is moved by the diaphragm cell to a position between the fully open and fully closed positions. It is, of course, possible to adjust the gas pressures P m  to any pressure between the compressor pressure (charge pressure) P k  and atmospheric pressure P u . Accordingly, it is possible to achieve any position of the waste gate  218  between fully open and fully closed. 
     Returning to FIG. 2, a preferred embodiment of the stepper motor is shown. Stepper motor  260  is a double stepper motor, and, as such, comprises a stator with two electrically separate systems of windings  260 A and  260 B. Each system of windings comprises a winding or coil. The first system of windings are the primary windings of the motor  260 A. The second system of windings  260 B are a secondary system of windings. The windings are arranged around a common magnetic rotor. The connection to the valve needle may be formed by a spindle that is supported in the rotor through a spindle thread, and which would be attached rigidly to the valve needle at its other end. The spindle thread in this example would convert the rotary motion of the rotor into the linear motion of the valve needle. 
     Returning to FIG. 2, the two electrically separated winding systems are controlled from an ECU  298  through two largely independent lanes  298 A and  298 B. Each lane is essentially a fully operational ECU. Each lane is also galvanically isolated from other lanes. In other words, metallic connections between lanes are limited or omitted entirely. Thus, the system is redundancy-based. Should one control lane fail, the other lane takes over all the control functions, thereby significantly increasing flight safety. Even if there is a total failure of the valve-control system (failure of both control lanes or failure of the stepper motor  260 ), the system will still provide a very high degree of safety. In such a case, the last position of the valve (prior to the failure) is maintained. This is in contrast to the situation with respect to electromagnetic timing valves. Accordingly, abrupt changes in the charge pressure, together with the concomitant dangers (degraded performance, engine damage, etc.) can be avoided. 
     It should also be noted that more than two lanes can be used. If, for example, two lanes fail simultaneously, a third lane could assume the control functions performed by the two lanes that have failed. It is immediately apparent that security can be enhanced to any desired degree by adding extra lanes, although the associated costs will increase by an equal degree. It is understood that the lanes would preferably be galvanically isolated. In other words, there would be no metallic connection between the lanes. Finally, it is understood that the ECU and stepper motor arrangement described herein in reference to FIG. 2, also represents the preferable arrangement for the ECU and stepper motor used within the propeller governor control system that was described in reference to FIG.  1 . 
     FIG. 5 is a side view of a plenum  300  used in the turbocharger control system illustrated previously in FIG. 2. A throttle valve  302  is also shown within the air duct  228 . Air passages  304 ,  306  and  308  extend from the plenum  300  to respective engine cylinders. A control mechanism or lever, as are known in the art, would be connected to the throttle valve  302 . The control mechanism could also be the ECU. 
     Finally, FIGS. 6 and 7 show an additional feature of the turbocharger control system illustrated in FIG. 2, which is an overboost control. For reasons of safety, this device is desirable should the turbine control system fail, and the pressure P P  in the plenum  300  and the associated engine output were to reach unacceptably high values. In principle, it would be possible to bleed off the excess pressure through a pop off valve arranged directly on the plenum  300 . Because of the high gas throughput that is required, however, such valves would have to be very large. If such a valve were to be electrically operated, it would be necessary to provide a very significant source of power. The overboost control provided by the present invention overcomes these disadvantages. 
     FIG. 6 is a schematic view showing the features of a diaphragm cell  320 , which operates as a plenum valve mechanism to provide overboost control. Diaphragm cell  320  is arranged on an opening  310  in the plenum  300 . Diaphragm cell  320  comprises a diaphragm  322 , a valve plate  324 , a spring  330 , and a choke  334 . The spring  330  presses the valve plate  324  against the opening  310  in the plenum  300  and thereby closes it off. In order to minimize any leakage, a seal  326  is interposed between the valve plate  324  and the opening  310  in the plenum  300 . The choke  334  in the valve plate connects the gas space in the plenum  300  with the gas space in the diaphragm cell  320 . It would also be possible to install an external choke  340  in an external line  342  (indicated by dashed lines) in place of the choke  334 . An air bleed line  344  through which the air can escape from the diaphragm cell is connected to the diaphragm cell. The air-bleed line  344  can be opened and closed by an electrically switched valve (e.g., a solenoid valve)  346  actuated by the ECU  298 . A pressure sensor, and temperature sensor (represented by P p , T p ) continuously measure the pressure, and temperature in the plenum. These measurements would be communicated to the ECU through known means. 
     During normal operation, as shown in FIG. 6, the valve  346  and thus the air-bleed line  344  are closed. Accordingly the pressure P P  in the plenum  300  and in the diaphragm cell  320  are equalized through the choke  334  or  340 . The forces that are acting on the valve plate  324  as a result of the gas pressure cancel each other out, so that the only unequalized force acting on the plate  324  is applied by the spring  330 . The spring force causes the valve plate  324  to seal the opening  310  in the plenum  300 . 
     FIG. 7 shows the diaphragm cell  320  in a second operational mode where the pressure in the plenum  300  exceeds a predetermined threshold value and the ECU  298  has opened the valve  346 . Pressurized gas is shown escaping from the diaphragm cell  320  to the atmosphere out the air bleed line  344 . Consequently, the pressure within the diaphragm cell  320  drops. As a consequence, the force exerted by the gas in the plenum  300  against the closing force of the spring  330  builds up, which forces the valve plate  324  off the plenum opening, allowing excess charge pressure to escape to the atmosphere. The pressure in the diaphragm cell  320  can be set within very wide limits by periodic actuation of the valve  346  (timing valve), because the cross section of the opening of the valve  346  is greater than the clear opening of the choke  334  or  340 . In this way, it has been made possible to vary the threshold value for the charge pressure in a very simple manner. 
     FIG. 8 is a schematic view of the control loop of the present invention. Referring to FIGS. 2-8, the control loop for the turbo charger control system is as follows. 
     In a first control loop for the turbo charger control system, the pressure P p , and the temperature T P  in the plenum  300  are measured through known sensors communicating with the ECU. From the measured values P p ,T P , the density of the air ρ p  within the plenum is calculated by the ECU. Additionally, the throttle valve position is also measured by a known throttle valve position sensor. The throttle valve position is communicated to the ECU. The ECU, through a process known as mapping computes the desired density ρ p(desired)  for the throttle valve position. The desired density ρ p(desired)  is compared to the actual density as calculated by the measured values P p ,T P . An actuating variable that is determined from the control differential (actual value−desired value) is computed by a control algorithm. From this actuating variable the ECU calculates the adjustment required at the stepper motor  260 , and the controller output necessary to produce the adjustment required. The controller output of the ECU is communicated to the stepper motor. 
     In a simpler, second version of the control loop, the pressure P p  in the plenum  300  is measured through a sensor communicating with the ECU. Additionally, the throttle valve position is also measured by a known throttle valve position sensor. The throttle valve position is communicated to the ECU. The ECU through mapping computes the desired pressure P p(desired)  for the throttle valve position. An actuating variable that is determined from the control differential (actual value−desired value) is computed by a control algorithm. From this actuating variable the ECU calculates the adjustment required at the stepper motor  260 , and the controller output necessary to produce the adjustment required. The controller output of the ECU is communicated to the stepper motor. 
     In keeping with the ECU  298  that operates according to the redundancy principle, the position of the throttle valve  302 , acquired by a throttle-valve position sensor (not shown) is typically duplicated (or replicated several times) in order to ensure the required degree of redundancy in the system. The same applies to the pressure sensor and temperature sensor (not shown) that is used to determine the pressure P P , and temperature T p  in the plenum  300 . 
     An important feature of the control loop is its stable behaviour as a regulator, which is explained in greater detail below on the basis of examples. 
     It is assumed that the throttle valve  302  is largely closed. If the throttle valve  302  is now opened abruptly, on the basis of the mapping the ECU  298  will call for a higher charge-air density ρ P  in the plenum  300  or for a higher pressure P P  in the plenum  300 . The charge pressure P K  at the compressor  224  will drop very rapidly because of the abrupt opening of the throttle valve  302 . However, as can be seen in FIG.  2  and FIG. 3, this drop in pressure also causes a corresponding and simultaneous drop in the gas pressure P m  in the diaphragm cell  280  (assuming a constant position of the needle valve  250 ), so that the force exerted by the spring  290  against the pressure of the gas P m  causes the waste gate  218  to close. Because of this closing of the waste gate  218 , an increased amount of gas is admitted to the turbine so that the turbocharger output pressure P k  increases. This ultimately leads to the desired increase in the charge-air density ρ p  in the plenum  300 . Analogously stable behaviour is achieved when the throttle valve  302  is closed abruptly. 
     This tendency to self-regulation also occurs when the aircraft changes altitude, i.e., when the pressure of the air outside the aircraft changes. If, for example, the turbo control system fails at a cruising altitude (e.g., 3000 meters), the controlled condition that was last set up will initially remain unchanged due to the way the waste gate  218  is controlled by the diaphragm cell  280 , needle valve  250 , and stepper motor  260 , as has been described above. If the altitude at which the aircraft is flying is then changed, the charge pressure P k  and thus the engine output remain more or less constant since, as the altitude increases, the pressure P m  in the diaphragm cell  280  will decrease in proportion to the drop in the pressure P u  of the air outside the aircraft. This results in the waste gate  218  being closed, and a corresponding increase in the compressor output. Analogous albeit opposite behaviour will occur when the altitude is decreased or when the pressure P u  of the air outside the aircraft increases. 
     The control loop for the propeller governor  100  is shown in FIG. 8 operates as follows. 
     The controlled variable is the propeller speed (not shown), the actual value of which is measured by a double (redundancy-based) speed sensor. This actual value is compared to the desired speed value in the ECU  298 . The desired value is determined by mapping, as in the case of the turbo control system, which is to say that a specific desired speed value is associated with every position of the throttle valve. A controller output that is determined from the control differential (actual value−desired value) is computed within the ECU by a control algorithm, and this is applied to the stepper motor  170 . Thus, there are two control loops, one is the hydraulic-mechanical control loop through which the governor controls the propeller pitch control mechanism, the other is the electrical control loop of the ECU  298 , through which the ECU  298  controls the governor. The electrical control loop relieves the pilot of having to constantly monitor the speed of the propeller. 
     In principle, different algorithms can be used as the control algorithm. Such algorithms include both linear algorithms (e.g., PID controller) as well as non-linear ones. Particularly advantageous for the present control task (propeller and turbo control) are controller systems that are based on fuzzy-logic architecture, which are comparatively robust and immune to changes in the controlled system, and, in which human “operator knowledge” can be incorporated. 
     In summary, one important advantage of the present invention is that to a very large extent the pilot is relieved of control tasks, so that flying comfort is greatly enhanced. The pilot now has to operate only one control lever, namely the throttle control  360 , which may be linked directly to the throttle valve  302 . Using mapping, the ECU  298  determines the desired value for the propeller speed and the charge-air density ρ p  or the charge pressure P p  in the plenum  300  and the actual value is automatically brought up to this desired value by the control processes. In principle, various strategies can be applied in order to generate the mapping. In particular, strategies that are oriented towards the maximum of the total efficiency (engine efficiency×propeller efficiency) are generally preferred. But, it is also possible to take influential factors that affect the aircraft into account. For example, the drag generated by the aircraft as a function of the aircraft&#39;s indicated air speed, and/or the aircraft&#39;s stall speed could be invoked. 
     Although at least one preferred embodiment of the invention has been described herein, it is understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention. In addition many modifications may be made to adapt a particular situation, component, or material to the teachings of the present invention without departing from its teachings as claimed.