Abstract:
The present invention provides an assembly for providing a variable output torque based upon a constant input force. The assembly includes an actuator for providing a constant input force and at least one link operatively coupled to the actuator and a pivot point such the constant input force is converted to the variable output torque.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 09/534,009 filed on Mar. 24, 2000 now U.S. Pat. No. 6,481,415; and claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/126,199, filed on Mar. 25, 1999, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates, in general, to mechanical linkages, and has applications in the fields of automotive, general mechanical, and civil engineering. In the field of automotive engineering, the present invention has particular applications in automotive power train engineering and engine throttles. 
     BACKGROUND OF THE INVENTION 
     A mechanical linkage having two ends can be used to transfer an input force at one end to an output force at the other end. In applications that require a varying force at the output end of a mechanical linkage, a varying force can be provided at the input end by a variable torque actuator or motor attached to the input end. However, variable torque motors are expensive and can be difficult to operate for providing the desired variable output force. Therefore, in applications that require a varying output force, there is a need for a mechanical linkage system that can provide a varying output force without the use of expensive variable torque motor. 
     In the field of automotive engineering, engine throttle control typically requires a variable torque motor operatively connected to a throttle valve in an automotive throttle. An automotive throttle for regulating the delivery of intake air to the manifold of an internal combustion engine generally comprises a throttle body with a butterfly valve rotatably mounted within its bore. The configuration of the throttle body and the butterfly valve have been identified as apparently giving rise to mechanical resistances when the valve is close to the bore of the throttle body (i.e. when the valve is nearly fully closed), the plane of the valve approaching perpendicularity relative to the longitudinal axis of the throttle body. The resistances are believed to be due to ice or other contamination that can form in the small clearance between the butterfly valve and the throttle body inside diameter when the valve is nearly fully closed. Furthermore, the pressure drop across the valve approaches its maximum value when the valve approaches the nearly closed position. Therefore, to overcome the above mentioned mechanical resistances of the butterfly valve in the nearly closed position, the butterfly valve can be operatively connected to a variable torque motor. The variable torque motor can be configured to provide a relatively greater amount of torque at the valve nearly closed position than the torque needed at a valve partially or fully opened positions. However, there still remains a need for a throttle control system that can operatively control the butterfly valve in an automotive throttle without the use of expensive variable torque motors. 
     SUMMARY OF THE INVENTION 
     The present invention offers a solution to the foregoing problems by providing an assembly for providing a variable output torque based upon a constant input force. The assembly includes an actuator for providing a constant input force and at least one link operatively coupled to the actuator and to a pivot point such the constant input force is converted to the variable output torque. 
     The present invention also provides an assembly for providing a variable output torque based upon a constant input force. The assembly comprises first and second links each having a first end pivotally mounted about a respective axis and each having a second end operatively coupled together an additional link, each of the first and second links having a different angular orientation relative to an imaginary line extending between the axes; and an actuator driving the first link pivotally about its axis at the constant input such that the second link is driven pivotally about its axis at the variable output. 
     The present invention also provides an assembly for controlling the position of a throttle valve rotating about a first axis between a first position and a second position. The assembly comprises a motor for moving an actuator between two positions; and at least one link coupling the actuator and to the valve and imparting to the valve a first torque when the valve is in the first position and a second torque when the valve is in the second position, the second torque being less than the first torque. 
     The present invention also provides a method for controlling the position of a throttle valve. The valve is pivotal about an axis of rotation. The method comprises applying a first torque with an actuator to the valve when the valve is in a first position; and applying a second torque with the actuator to the valve when the valve is in a second position. 
     The present invention also provides a method for determining the position of a valve in a throttle. The valve is driven by an electric motor and a relationship has been established between the current drawn by the motor and the position of the valve. The method comprises measuring the current drawn by the motor; and determining the position of the valve from an established relationship between the current drawn by the motor and the position of the valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain features of the invention. 
     FIG. 1 shows an embodiment of a mechanical linkage for providing a variable output torque based upon a constant input torque. 
     FIG. 2 shows an embodiment of an electronic throttle control assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the mechanical linkage assembly  100  according to the present invention includes a linear actuator  102 , pivoted about fixed pivot point  103  and operatively connected to a first end of link  104  at location  101 . Second end of link  104  is pivotally connected at second ends of links  106  and  108  at pivot point  107 . Link  106 , is also pivotally mounted at fixed pivot point  105 . First end of link  108  is pivotally connected to second end of link  112  at pivot point  109 . First end of link  112  is fixedly attached to link  111  at fixed pivot point  110 , thereby allowing simultaneous rotation of links  112  and  111  about fixed pivot point  110 . 
     In operation, when a linear upward force is imparted on link  104  by linear actuator  102 , a clockwise torque is imparted on link  106  about fixed pivot point  105 . Similarly, a clockwise torque is imparted through link  108  onto links  111  and  112  about fixed pivot point  110 . As link  104  travels upward by means of the linear actuator  102 , it can be seen that because of the fixed locations of pivot points  103 ,  105  and  110 , linear actuator  102  will pivot clockwise about fixed pivot point  103 . Additionally, as link  104  travels upward, the overall translation of pivot point  107  to position  116  relative to its original location at position  115  is initially greater in the vertical direction than in the horizontal direction. Therefore, the magnitude of the torque at fixed pivot point  110  is greater when pivot point  107  is at position  115  than that at position  116 . For translation from position  116  to position  117 , the magnitude of the torque at fixed pivot point  110  is greater when pivot point  107  is at position  116  than that at position  117 . Therefore, by providing a linear actuator  104  operatively mounted to two out-of-phase links  106  and  112 , a constant input torque about fixed pivot point  105  is transformed into a variable output torque about fixed pivot point  110 , without the use of a variable force actuator or a variable torque motor. It should be noted that an angular actuator could be used in place of the linear actuator  102 . Similarly a constant torque motor with a rotary shaft could also be used in place of the linear actuator  102  as will be described in detail below. 
     Referring to FIG. 2, the throttle control assembly  200  according to the present invention includes an electronic torque motor having a shaft with centerline A, and a pivot point  201  offset from and rotating about the centerline A, which torque motor is secured adjacent to a throttle. The throttle includes a butterfly valve  205 , which rotates about a centerline B. A fixed crank  210 , having a pivot point  215 , is coupled to butterfly valve  205 . A link  220  of fixed length connects pivot point  215  with pivot point  201 . Pivot point  201  is offset from the centerline A of the motor and is fixed to an actuator  225  of the motor. 
     The range of motion of the electronic throttle control assembly  200  includes three positions of interest. With the pivot point  201  in position  1 , the electronic throttle control assembly  200  is in a “limp home position.” In this position, in which the assembly  200  will reside when no electrical current is applied to the torque motor, the throttle is partially open, providing a fast idle engine speed only. When the pivot point  201  is moved to position  2 , a “hot idle position”, the assembly  200  rotates the butterfly valve  205  to provide the minimum airflow through the throttle. When the assembly  200  is moved to position  3 , it drives butterfly valve  205  to a vertical position (parallel with the longitudinal axis of the throttle body), such that the assembly  200  and the throttle are in a “wide open throttle position”. 
     The assembly  200  according to the present invention provides an “over-center” link arrangement, which provides a very high force (torque) to the butterfly valve  205  at the point where the valve is close to the bore of the throttle body. Maximum torque is required at this point to overcome ice/contamination, which can form between the small clearance between the butterfly valve  205  and throttle body inside diameter when the assembly  200  is in this position. Also, when the butterfly valve  205  approaches the fully closed position, the pressure drop across it approaches a maximum, resulting in a high force on the butterfly valve  205  and the shaft. 
     In addition to the over-center link according to the present invention providing high torque when required, the over-center link also allows the available torque to diminish as it becomes less necessary. Specifically, when butterfly valve  205  is in the wide open throttle position, minimal contact is possible between the butterfly valve  205  and the inside diameter of the throttle body. Also, as the butterfly valve  205  approaches the wide open throttle position  3 , the pressure drop across the valve approaches zero, under which condition the forces acting on the mechanism of butterfly valve  205  are minimal. 
     An additional inventive feature of the assembly  200  according to the present invention provides a valuable redundant means of determining the position of the throttle, supplemental to the information provided directly by the throttle position sensor (not shown). Specifically, there is an accurate correlation between the electrical current draw by the torque motor and the signal output of a position sensor (not shown) typically attached to the throttle shaft. Thus the torque motor current can be measured, recorded and continuously updated in the engine control module (not shown) and compared with the shaft position sensor output to detect the failure of either means of measuring position. This inventive feature is not limited to application in the context of the illustrated embodiment, not even to torque motors, but rather is applicable to electronically controlled throttles generally. 
     While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and their equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.