Method and apparatus for controlling a rotatable shaft

Information

  • Patent Grant
  • 6302089
  • Patent Number
    6,302,089
  • Date Filed
    Thursday, May 20, 1999
    25 years ago
  • Date Issued
    Tuesday, October 16, 2001
    23 years ago
Abstract
A device for latching a rotatable shaft. A lever arm is coupled with the shaft and rotates the shaft between a first and second positions when the lever arm rotates between respective first and second positions. A latching device latches the lever arm, in response to receiving an activation signal, when the lever arm is in the first position. The latching device holds the lever arm in the first position. A biasing device is coupled with the lever arm and exerts a biasing force on the lever arm that biases the lever arm towards the second position.
Description




TECHNICAL FIELD




The present invention relates generally to rotatable shafts, and more specifically, to an apparatus for biasing a rotatable shaft.




BACKGROUND ART




Regulatory agencies such as the Environmental Protection Agency and the Engine Manufacturers Association require strict emission requirements for heavy-duty diesel engines. One method used to reduce emissions of engines is an Exhaust Gas Recirculation (“EGR”) system. The EGR system controls the amount of exhaust gas that is introduced into the engine's air intake system by a valve that adjusts the flow rate based on various engine operating parameters.




In addition to the normal operation of the EGR system, most EGR systems also have a fail-safe mode that drives the EGR valve either fully closed or fully open, depending on the design of the EGR system. Typically a spring is added to the EGR system to move the EGR valve when in fail-safe mode. The spring, however, is permanently affixed, and continuously exerts a biasing force on the EGR valve, i.e., during both normal and fail-safe operation. This places a large and unnecessary load on the actuator during normal operation. The additional load increases the likelihood of the actuator overheating, or requires a more powerful actuator than would otherwise be needed.




Further, because of the high powered actuators, conventional EGR systems typically use hydraulic or pneumatic powered actuators to adjust the position of the EGR valve. Both hydraulic and pneumatic systems are, however, susceptible to leaking.




SUMMARY OF THE INVENTION




The present invention provides a method and apparatus for latching a rotatable shaft. A lever arm is coupled with the shaft and rotates the shaft between a first and second positions when the lever arm rotates between respective first and second positions. A latching device restrains the lever arm in the first position in response to receiving an activation signal. A biasing device is coupled with the lever arm and exerts a biasing force on the lever arm that biases the lever arm towards the second position.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is an end view of an apparatus for latching a rotatable shaft according to one embodiment of the invention.





FIG. 2

is a block diagram and schematic of an actuator having the apparatus of

FIG. 1

according to one embodiment of the invention.





FIG. 3

is a functional block diagram of an engine having the actuator of

FIG. 2

according to one embodiment of the invention.











BEST MODE OF THE INVENTION





FIG. 1

is an end view of an apparatus


10


for latching a rotatable shaft


12


according to one embodiment of the invention. A drive hub


14


is disposed around a portion of the shaft


12


such that rotation of the drive hub


14


causes rotation of the shaft


12


. A biasing device, such as a cylindrical torque spring


16


is disposed around a portion of the drive hub


14


. Other types of biasing devices, including other types of springs may also be used, as appropriate. A lever arm


18


, such as an armature, containing a magnetic material is coupled with the spring


16


on one end, such as by a first drive pin


19


. The lever arm


18


may be entirely or only partly made of the magnetic material, or have a portion that is magnetic. The other end of the spring


16


is anchored by an anchoring device, such as an anchor pin


20


. The anchor pin


20


is typically coupled with a housing


22


or other fixed object. Other types of fastening may also be used to immobilize the end of the spring


16


, such as welding, for example. In that case, the anchoring device would be the weld itself. The lever arm


18


is also coupled with the drive hub


14


, such as by a second drive pin


23


, so that rotation of the drive hub


14


causes rotation of the lever arm


18


. A latching device, such as an electrically actuated hook (not shown) or an electromagnet


24


, is located a predetermined distance from the shaft


12


in the rotational path of the lever arm


18


.




In operation, the shaft


12


is rotated from a first position, such as the 9 o'clock position, to a second position, such as a 12 o'clock position, with the second position being a position that causes the lever arm


18


to come in direct physical contact with the electromagnet


24


. An actuator (not shown) or other appropriate device may be used to rotate the shaft


12


. The electromagnet


24


is energized by an activation signal, causing the magnetic material within the lever arm


18


to be attracted to the electromagnet


24


. Because the lever arm


18


is in direct contact with the electromagnet


24


, i.e., there is no air gap, the amount of power used by the electromagnet


24


may be relatively small. Alternately, a more powerful electromagnet


24


or higher current may be used to attract the lever arm


18


from a distance if the lever arm


18


does not come in direct contact with the electromagnet


24


due to normal rotation of the shaft


12


from the first to second positions.




The movement of the shaft


12


loads the spring


16


, biasing the lever arm


18


back towards the first position (9 o'clock). When the electromagnet


24


is de-energized, the spring


16


moves the lever arm


18


back towards the first position. The movement of the lever arm


18


rotates the drive hub


14


, causing the shaft


12


to rotate back to the first position.




Significantly, the electromagnetic force exerted by the electromagnet


24


on the lever arm


18


is greater than the biasing force of the spring


16


on the lever arm


18


. Thus, when the electromagnet


24


is energized, the lever arm


18


remains in physical contact with the electromagnet


24


.




In an embodiment using the electrically actuated hook (not shown), the lever arm need not have any magnetic material within it. Instead, the hook may rotate into the rotational path of the lever arm


18


, catching the lever arm


18


.




In one embodiment, the shaft


12


may rotate without a corresponding rotation of the drive hub


14


. This can be accomplished, for example, by exerting a rotational force on the shaft


12


that is greater than a frictional force between the drive hub


14


and the shaft


12


, but less than the electromagnetic force acting on the lever arm


18


. Thus, when the lever arm


18


is coupled with the electromagnet


23


, the lever arm


18


would remain attached to the energized electromagnet


24


, and the drive hub


14


would be coupled with the lever arm


18


, but the shaft


12


would spin within the drive hub


14


.




Similarly, in another embodiment the drive hub


14


is fixedly attached to the shaft


12


, but the drive hub


14


may spin while the lever arm


18


remains in a fixed position, such as attached to the electromagnet


24


. This may be accomplished by any of a variety of ways known to those skilled in the art.




In one embodiment, the lever arm


18


may be directly coupled to the shaft


12


, without the presence of the drive hub


14


. Typically the lever arm


18


is friction mounted to the shaft so that the rotation of the lever arm


18


causes rotation of the shaft


12


, but the rotation of the shaft


12


need not cause rotation of the lever arm


18


(see discussion immediately above).





FIG. 2

is a block diagram and schematic of an actuator


50


having the apparatus


10


according to one embodiment of the invention. The actuator


50


includes a motor


52


, such as a DC motor, coupled with the shaft


12


. In operation, the motor


52


may drive the shaft


12


between the first position and the second position, and typically any position therebetween. The apparatus


10


functions as discussed above, and will not be repeated. In one embodiment, the motor


52


is back driveable, so that the biasing force exerted by the spring


16


will cause the shaft


12


to rotate back towards the first position (away from the electromagnet


24


).




Further, because the spring


16


is held by the electromagnet


24


, via the lever arm


18


, the preload (i.e., biasing) normally applied to the shaft


12


by the spring


16


in conventional actuators is not present. Thus, a smaller, i.e., less powerful, motor


52


may be used to rotate the shaft


12


than in conventional actuators. This reduction in load may also contribute to a reduction in heating of the motor


52


, because it is driving a smaller load. In addition, the actuator


50


may be entirely electrically powered and driven. Therefore, hydraulic or pneumatic systems are not needed. This avoids the problem of leaking with these systems.




In another embodiment, the frictional forces within the actuator


50


are sufficiently high so as to prevent the back driving of the motor


52


by the spring


16


. A clutch


54


is disposed between the motor


52


and the shaft


12


, such that upon a receipt of a predetermined control signal by the clutch


54


, the clutch disengages the shaft


12


from the rest of the actuator


50


, allowing for the spring


16


to bias the shaft


12


towards the first position. Typically the clutch


54


is engaged when the electromagnet


24


is energized and disengaged when the electromagnet


24


is not energized. This may be accomplished by placing the clutch


54


in series with the electromagnet


24


, such that the clutch


54


also receives the activation signal that energizes the electromagnet


24


. Thus, the clutch


54


receives a signal indicative of the state of the electromagnet


24


. Any of a variety of appropriate ways known to those skilled in the art may be used to cause the clutch


54


to engage and disengage as a function of the activation signal.




In one embodiment a gearbox


56


is disposed between the motor


52


and the shaft


12


. The gearbox


56


is coupled with the motor


52


on one end, typically to a first output shaft


57


of the motor


52


, and on the other end the gearbox is coupled with the shaft


12


. Alternately, a clutch


54


, as described above, may be coupled between the gearbox


56


and the shaft


12


. The gearbox


56


is operable to rotate the shaft


12


as a function of the rotational characteristics of the first output shaft


57


. Typically the gearbox


56


will rotate the shaft


12


at a different speed and torque than the first output shaft


57


.




In one embodiment, a rotary position sensor


58


is coupled with the shaft


12


to detect the position of the shaft


12


. The sensor


58


transmits a position signal indicative of the position of the shaft


12


. The sensor


58


may be used with any of a variety of electronic controllers (not shown) to create closed loop automatic control of the position of the shaft


12


. Alternately, the sensor


58


may be coupled with a portion of the motor


52


, gearbox


56


, clutch


54


, or drive hub


14


that is indicative of the position of the shaft


12


, and transmit a position signal that is a function of the position of that portion of the motor


52


, gearbox


56


, clutch


54


, or drive hub


14


. The position of the shaft


12


may then be determined from the position signal by ways known to those skilled in the art, e.g., using gear ratios. The position signal may be used as part of a closed loop control system (not shown) for automatically controlling the position of the shaft


12


by ways known to those skilled in the art.





FIG. 3

is a functional block diagram of an engine


70


having the actuator


50


according to one embodiment of the invention. The engine


70


includes an engine block assembly


72


having a variety of components known to those skilled in the art, such as a combustion chamber


74


, a piston


76


, a piston rod


78


, a fuel injector (not shown), intake and exhaust valves (not shown), a device for operating the valves (not shown), a device for lubricating the engine (not shown), and other devices. An air intake path


82


provides air to the combustion chamber


74


. The fuel injector injects fuel into the combustion chamber


74


and the combustion of the air/fuel mixture creates a first force that drives the piston


76


and piston rod


78


down, rotating the drive shaft


80


. The drive shaft


80


converts the (downward) first force to a second (rotational) force. The drive shaft may also include a variety of devices for further modifications and conversions of the rotational force known to those skilled in the art, such as a transmission (not shown), for example. After combustion, the air from the combustion chamber


74


is vented by an exhaust air path


84


by ways known to those skilled in the art.




An exhaust gas recirculation valve


86


is coupled between the intake and exhaust air paths


82


,


84


and is operable to divert a portion of the air from the exhaust air path


84


to the intake air path


82


by ways known to those skilled in the art. The shaft


12


of the actuator


50


, described above, is coupled with the exhaust gas recirculation valve


86


and is operable to rotate the exhaust gas recirculation valve


86


between the first and second positions: typically fully closed and fully open, although the exhaust gas recirculation valve


86


may also rotate to an infinite number of positions between fully closed and open. The actuator


50


functions as described above, and will not be repeated.




Significantly, in a fail-safe mode the activation signal is not transmitted to the latching device (i.e., the electromagnet


24


or electrically actuated hook (not shown)). Thus, the spring


16


biases the shaft


12


, and therefore the exhaust gas recirculation valve


86


, towards a predetermined position, such as a fail-safe position.




From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited to the specific embodiments described herein, but instead may include other embodiments and equivalents as may fall within the scoper of the appended claims.



Claims
  • 1. An actuator for rotating a drive shaft, comprising:a housing; a motor disposed within the housing and coupled with the drive shaft, the motor operable to receive a drive signal and to rotate the drive shaft between a first and second positions in response to receiving the drive signal; and an apparatus for latching the drive shaft, comprising: a lever arm coupled with the drive shaft and operable to rotate the drive shaft between a first and second positions when the lever arm rotates between respective first and second positions; a biasing device coupled with the lever arm, the biasing device operable to bias the lever arm towards the second position; and a latching device operable to be coupled with the lever arm and to restrain the lever arm in the first position in response to receiving an activation signal.
  • 2. The apparatus of claim 1 wherein the lever arm comprises an armature and includes a magnetic material, and the latching device comprises an electromagnet.
  • 3. The apparatus of claim 1 wherein the biasing device is operable to exert a biasing force on the lever arm, and the latching device is operable to exert a restraining force on the lever arm, the biasing force on the lever arm being less than the restraining force on the lever arm.
  • 4. The apparatus of claim 1 wherein the lever arm is operable to remain in the second position when the drive shaft rotates from the second position towards the first position when the latching device is restraining the lever arm.
  • 5. The actuator of claim 1 wherein the motor includes a first output shaft, and further comprising a gearbox coupled between the first output shaft and the drive shaft, the gearbox operable to rotate the drive shaft as a function of the rotation of the first output shaft, the rotation of the drive shaft having a speed and torque different than a speed and torque of the first output shaft.
  • 6. The actuator of claim 1 wherein the motor includes a first output shaft, and further comprising a clutch disposed between the motor and the drive shaft, the clutch operable to disengage the drive shaft from the first output shaft in response to receiving a predetermined control signal.
  • 7. The apparatus of claim 4 wherein the biasing device comprises a spring.
  • 8. The apparatus of claim 7 wherein the spring comprises a cylindrical torque spring disposed around the drive shaft.
  • 9. The apparatus of claim 8 wherein the torque spring includes a first and second tangs, and further comprising an anchoring device coupled with the first tang of the torque spring, the anchoring device operable to bias the first tang to a predetermined position, and the second tang being coupled with the lever arm.
  • 10. The apparatus of claim 9 wherein the anchoring device is coupled with the housing.
  • 11. The apparatus of claim 1 wherein the anchoring device comprises an anchor pin.
  • 12. The apparatus of claim 1 wherein the second position of the lever arm comprises a position wherein the lever arm is in physical contact with the electromagnet.
  • 13. The apparatus of claim 1, further comprising a drive hub coupled between the shaft and the biasing device, the drive hub being disposed around the drive shaft.
  • 14. The apparatus of claim 1, further comprising a rotary position sensor disposed within the housing and coupled with the shaft, the rotary position sensor operable to detect a position of the shaft and to transmit a position signal as a function of the position of the shaft.
  • 15. An engine, comprising:an engine block assembly having a combustion chamber and operable to generate a first force; a drive train coupled with the engine block assembly to receive the first force and to generate a second force as a function of the first force; an intake air path coupled with the combustion chamber, the intake air path operable to provide air to the combustion chamber; an exhaust air path coupled with the combustion chamber, the exhaust air path operable to vent air from the combustion chamber; an exhaust gas recirculation valve coupled with the intake and exhaust air paths, the exhaust gas recirculation valve having a control shaft and operable to divert a portion of air from the exhaust air path into the intake air path in response to the control shaft being in a predetermined position, the magnitude of the portion being a function of the position of the control shaft; and an actuator coupled with the control shaft and operable to rotate the control shaft, comprising: a housing; a motor disposed within the housing and coupled with the control shaft, the motor operable to receive a control signal and to rotate the control shaft between a first and second positions in response to receiving the control signal; and an apparatus for latching the control shaft, comprising: a lever arm coupled with the control shaft and operable to rotate the control shaft between a first and second positions when the lever arm rotates between respective first and second positions; a biasing device coupled with the lever arm, the biasing device operable to bias the lever arm towards the second position; and a latching device operable to be coupled with the lever arm and to restrain the lever arm in the first position in response to receiving an activation signal.
  • 16. The apparatus of claim 15 wherein the lever arm comprises an armature and includes a magnetic material, and the latching device comprises an electromagnet.
  • 17. The apparatus of claim 15 wherein the biasing device is operable to exert a biasing force on the lever arm, and the latching device is operable to exert a restraining force on the lever arm, the biasing force on the lever arm being less than the restraining force on the lever arm.
  • 18. The apparatus of claim 15 wherein the lever arm is operable to remain in the second position when the control shaft rotates from the second position towards the first position when the latching device is restraining the lever arm.
  • 19. The actuator of claim 15 wherein the motor includes a first output shaft, and further comprising a clutch disposed between the motor and the control shaft, the clutch operable to disengage the control shaft from the first output shaft in response to receiving a predetermined control signal.
  • 20. The apparatus of claim 15 wherein the biasing device comprises a cylindrical torque spring disposed around the control shaft.
  • 21. The apparatus of claim 15 wherein the second position of the lever arm comprises a position wherein the lever arm is in physical contact with the restraining device.
  • 22. The apparatus of claim 15, further comprising a drive hub coupled between the control shaft and the biasing device, the drive hub being disposed around the control shaft.
  • 23. The apparatus of claim 15, further comprising a rotary position sensor disposed within the housing and coupled with the control shaft, the rotary position sensor operable to detect a position of the control shaft and to transmit a position signal as a function of the position of the control shaft.
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