Abstract:
An electric positional actuator that includes a default device for positioning the actuated device in a default position. The actuator includes an electric motor that controls the rotational position of a shaft through a gear system. When the shaft rotates, it moves a link-bar that actuates the actuated device. A rotational sensor coupled to a printed circuit board detects the position of the shaft, and provide a feedback signal of the shaft&#39;s position. The default device includes a spring wrapped around the shaft. When the link bar is rotated away from its default position, one leg of the spring remains in contact with a housing spring boss while the other leg of the spring is in contact with the link bar opposing the movement and trying to return the link-bar to the default position.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to an electric positional actuator and, more particularly, to an electric positional actuator employing a default positioning device for returning an actuated device to a desired default position in the event of actuator failure, where the actuator has particular application for controlling air flow through a turbocharger or a supercharger. 2. Discussion of the Related Art  
           [0003]    In a four-stroke internal combustion engine, the combustion air and fuel mixture typically enters the cylinders of the engine under atmospheric pressure. By pressurizing the combustion air before it enters a cylinder, more fuel can be mixed with the high-pressure air to obtain the desired air/fuel mixture, and thus, more power can be delivered for each stroke of the cylinder. A supercharger employs a compressor driven by the engine to increase the combustion air pressure. However, the power increase from the cylinders is partly lost due to the parasitic losses from driving the compressor by the engine. A turbocharger uses the exhaust gas pressure to drive a turbine. A compressor mounted on the same shaft as the turbine is rotated by the turbine, and is thereby used to increase the combustion air pressure. Thus, the compressor is not coupled to the engine, and the losses associated therewith are avoided.  
           [0004]    Control valves are employed in a supercharger and a turbocharger to control the flow of combustion air through the compressor. One design employs a series of vanes that control the back-pressure in the turbine of a turbocharger to control turbine speed. Other turbocharger or supercharger designs employ a valve flapper member that controls air flow through the turbine or compressor. A suitable actuator is used to position the valve member or the vanes in the desired location. It would be desirable to provide a default device within the actuator so that the valve member or vanes remain at a desirable position in the event of actuator failure so that the engine keeps running.  
           [0005]    U.S. Pat. No. 5,492,097 issued Feb. 20, 1996 to Byram et al. discloses a throttle body valve for regulating the flow of combustion air to an internal combustion engine. The valve includes a valve member selectively positionable between a minimum air flow position and a maximum air flow position in a combustion air passage extending through the valve. A default position is defined between the minimum and maximum air flow positions to allow the engine to operate if the actuator fails. A first end of a biasing member applies a force against the valve member towards the default position when the valve member is in the minimum air flow position, and a second end of the biasing member applies a force against the valve member towards the default position when the valve member is in the maximum air flow position.  
         SUMMARY OF THE INVENTION  
         [0006]    In accordance with the teachings of the present invention, an electric positional actuator is disclosed that includes a default actuation device for positioning the actuated device in a default position in the event of actuator failure. The actuator has particular application for controlling air flow in a turbocharger or supercharger, but can be used for controlling many other devices and systems. The actuator includes an electric motor that controls the rotational position of a shaft through a gear system. When the shaft rotates, it moves a link-bar that actuates the actuated device. The actuator further includes a printed circuit board having a microprocessor and related circuitry. External control signals cause the microprocessor to activate the motor to position the shaft at the desired location. A rotational sensor coupled to the circuit board detects the position of the shaft, and provides a feedback signal to the microprocessor of the shaft&#39;s position.  
           [0007]    The default device positions the shaft in a default position in the event of actuator failure. The default device includes a spring wrapped around the shaft. One end of the spring is positioned on one side of a lever arm coupled to the link-bar, and an opposite end of the spring is positioned on the other side of the lever arm. Therefore, the shaft rotates against the bias of the spring in both directions. If motor power is not applied to the shaft, then the spring holds the shaft in the default position.  
           [0008]    Additional objects, advantages and features of the present invention will become apparent to those skilled in the art from the following discussion and the accompanying drawings and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of an electric positional actuator, according to the invention, coupled to a turbocharger;  
         [0010]    [0010]FIG. 2 is a front perspective view of the actuator shown in FIG. 1 separated from the turbocharger;  
         [0011]    [0011]FIG. 3 is a back perspective view of the actuator shown in FIG. 2;  
         [0012]    [0012]FIG. 4 is a cut-away perspective view of the actuator shown in FIG. 2;  
         [0013]    [0013]FIG. 5 is a perspective view of a default positioning spring, according to the invention, for positioning the actuator output shaft to a desired position in the event of actuator failure;  
         [0014]    [0014]FIG. 6 is a cut-away, cross-sectional view of the actuator of the invention showing the ends of the default spring relative to a spring boss in the default position; and  
         [0015]    [0015]FIG. 7 is a cut-away, cross-sectional view of the actuator of the invention showing one end of the default spring separated from the spring boss. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]    The following discussion of the embodiments of the invention directed to an electric positional actuator is merely exemplary in nature, and is in no way intended to limit the invention or it&#39;s applications or uses. Particularly, the actuator of the invention is described herein as being used to control air flow in a turbocharger or a supercharger. However, as will be appreciated by those skilled in the art, the actuator of the invention has application for actuating many other types of actuated devices.  
         [0017]    [0017]FIG. 1 is a perspective view of a turbocharger  10  including a turbine  12 , a compressor  22  and an electric positional actuator  14 , according to an embodiment of the present invention. The turbocharger  10  is intended to represent any turbocharger known in the art that includes a valve (not shown) for controlling the flow of air through the turbocharger  10 . One end of a link-bar  16  is coupled to an output shaft  18  of the actuator  14  and the other end of the link-bar  16  is coupled to one end of a linkage  20 . The other end of the linkage  20  is coupled to the valve. Rotation of the shaft  18  imparts linear actuation to the link-bar  16  to move the linkage  20  and control the position of the valve within the turbocharger  10 . Actuation of the shaft  18  will be described in more detail below.  
         [0018]    [0018]FIG. 2 is a front perspective view, FIG. 3 is a back perspective view and FIG. 4 is a cut-away perspective view of the actuator  14  separated from the turbocharger  10 . The actuator  14  includes an outer housing  24  made of a cast metal in this embodiment. An electric DC motor  26  is mounted within the housing  24 , and includes a rotor rotatable therein. The motor  26  can be any motor of the proper size and output torque suitable for the purposes described herein. A shaft (not shown) rotated by the motor rotor is coupled to a motor shaft gear  28 . The shaft gear  28  meshes with a first idler gear  30 , and the first idler gear  30  meshes a second idler gear  32 . The second idler gear  32  meshes with a shaft gear  34  rigidly mounted to one end of the shaft  18 , as shown. The gears  28 ,  30 ,  32  and  34  transmit the rotational energy from the motor  26  to the shaft  18  and provide increased torque. The gears  28 ,  30 ,  32  and  34  provide a flexible gear ratio between the motor  26  and the shaft  18  to achieve various torque and response characteristics. The gear-train flexibility can include a dual or single idler gear system dependent on requirements.  
         [0019]    When the motor  26  rotates, the shaft  18  rotates through the gears  28 ,  30 ,  32  and  34 . The direction that the motor  26  rotates determines the direction that the shaft  18  rotates. Therefore, when the motor  26  rotates, the shaft  18  imparts a linear motion to the link-bar  16  in the appropriate direction, which moves a link-pin  36  coupled to the linkage  20 , thus moving the valve.  
         [0020]    The shaft  18  is rotatable on a pair of bearings  44  and  46 . In this embodiment, the bearings  44  and  46  are ball bearings. However, as will be appreciated by those skilled in the art, other types of bearings, such as needle bearings, suitable for the purposes described herein can be used. In an alternate embodiment, the bearings  44  and  46  can be suitable bushings. The bearings  44  and  46  are press fit into a common housing  24 . This provides and maintains the alignment of the shaft  18 . Mounting bores  50  extend through the housing  24  to accept bolts (not shown) that secure the actuator  14  to the turbocharger, or other suitable location.  
         [0021]    A printed circuit board (PCB)  56  is mounted to the housing  24  proximate the gears  28 - 34 , as shown. The PCB  56  includes a microprocessor and related circuitry (not shown) for controlling the operation of the actuator  14 , as discussed herein. An electrical connector  58  is coupled to the housing  24 , and allows external control and power signals to be electrically coupled to the PCB  56  and the microprocessor. The connector  58  is mounted directly to the housing  24  to eliminate unwanted stress on the PCB  56 . A suitable electrical connector (not shown) is electrically coupled to the connector  58  and to a control circuit (not shown), such as a vehicle controller, to control the actuator  14 . In alternate embodiments, the microprocessor does need to be mounted in the housing  24 , but could be at any suitable location.  
         [0022]    A rotational sensor  60  is provided to detect the position of the shaft  18 . The sensor  60  and associated sensor circuitry are electrical components mounted to the PCB  56 . In this embodiment, the sensor  60  is a magnetic Hall Effect sensor employing magnets  62 . However, as will be appreciated by those skilled in the art, other types of sensors, such as inductors, potentiometers, etc., can be employed for this purpose. The sensor  60  provides feedback for improving actuator performance. The sensor  60  allows the microprocessor to learn the systems hard stop positions, and reduce the speed at which the actuator  14  approaches the stops. Further, the sensor  60  allows the optimum actuator position to be determined, and provide redundant feedback of the obtained position to verify proper system operation. In other words, the sensor  60  gives the actual rotational position of the shaft  18 , and this position is compared to the desired position by the microprocessor.  
         [0023]    According to the invention, the actuator  14  employs a default positioning device  66  that puts the actuator  14  in a desired default or fail-safe position in the event of a system or an actuator failure. Therefore, the vehicle, or other actuated device, is able to function if the actuator  14  becomes inoperable. FIG. 5 is a perspective view of the default positioning device  66  separated from the actuator  14 . The device  66  includes a lever arm  68  rigidly mounted to the link-bar  16 , or part of the link bar  16 , and a spring  72  formed around a spring bushing  74 . The spring bushing  74  acts to reduce friction. The spring  72  is a helical spring in this embodiment, and has a certain spring bias for the purposes described herein. Other designs may employ other types of spring elements within the scope of the present invention. The spring  72  includes a first end  76  positioned against one side of the lever arm  68 , and a second end  78  positioned against an opposite side of the lever arm  68 , as shown. FIGS. 6 and 7 are cut-away, cross-sectional views of the actuator  14  showing the ends  76  and  78  of the spring  72  positioned on opposite sides of a housing spring boss  80 .  
         [0024]    When the shaft  18  is in the position shown in FIG. 5, the spring  72  is under minimal bias, and the shaft  18  is in the default position. The width of the arm  68  and the housing spring boss  80  are the same so that there is little or no torque applied to the shaft  18  at the default position. Torsional forces increase as misalignment between the arm  68  and the spring boss  80  increases. This default position is selected so that the linkage  20  positions the flow valve in the turbocharger  10  at the desired location for proper vehicle operation if the actuator  14  fails. If the shaft  18  rotates in one direction from the default position, one of the ends  76  or  78  applies a force against the arm  68  when the opposing leg  76  or  78  of the spring  72  is in contact with the spring boss  80  so that the spring  72  is under tension. The motor force is enough to rotate the shaft  18  against the spring bias to the desired position, but the spring bias moves the shaft  18  back to the default position when the motor force is not present. If the shaft  18  rotates in the other direction from the default position, the other of the ends  76  or  78  applies a force against the arm  68  when the opposing leg  76  or  78  of the spring  72  is in contact with the spring boss  80  so that the spring  72  is under tension. The circumferential orientation of the lever arm  68  relative to the shaft  18  can be adjusted in various designs to allow the default position to be at any angular position within the normal travel of the actuator  14 . The default position of the actuator  14  can prevent over-speeding of the turbocharger  10 , or allow the operation of the engine at some reduced power level should the actuator  14  fail. The design can provide default positioning anywhere within the normal travel of the actuator  14 .  
         [0025]    The foregoing discussion describes merely exemplary embodiments of the present invention. One skilled in the art would readily recognize that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.