Patent Application
20060081077
The present invention relates to actuation of pintle-type valves; more particularly, to devices for positively actuating pintle valves in both the opening and the closing directions; and most particularly, to a pintle valve actuated by an electric motor and a rack and pinion gear transmission.
Pintle or poppet valves are well known. For example, it is known to provide a pintle valve between the exhaust manifold and the intake manifold of an internal combustion engine for recirculating a portion of the engine exhaust into the intake air stream. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve.
An EGR valve consists of two basic components, a valve assembly and an actuator. Typically, an actuator includes a position feedback sensor to monitor the degree of openness of the valve. Typical known actuators include linear solenoids, torque motors, stepper motors, and DC motors. The actuator, when coupled with an appropriate logic driver, moves the pintle shaft of the valve assembly to a desired position as commanded by a master engine control module (ECM). The position sensor provides feedback to the ECM on pintle shaft position so that the ECM can adjust the command to the actuator accordingly. When the engine is running, this closed loop control system operates continuously to regulate the correct amount of exhaust gas recirculation under all engine conditions.
Not all EGR valve performance is equal. Some important performance criteria for an EGR valve actuator are high force capability, to overcome carbon deposits on the pintle shaft; fast response to meet frequency-response modulated timing; low manufacturing cost, with few components and easy assembly; and adjustable actuation stroke, to allow an actuator to be used in a plurality of valve applications or sizes.
Solenoid actuators are low in cost but are also very low in force and generally may be driven in one direction only, relying on a spring for the opposite motion, which spring must be overcome by the solenoid, further reducing the available valve-opening force. Torque motors, although operable in both directions, are also force-limited, stroke-limited, and expensive. Stepper motors are response-time limited and force- limited.
DC motors that can meet the cost and size requirements for an EGR application do not have sufficient torque to generate the required amount of force directly and so typically are coupled to a transmission to gain mechanical advantage. With a proper prior art transmission, a DC motor actuator has the most force potential for an EGR valve but generally has the slowest response time of all prior art actuators.
What is needed is a DC motor as a valve actuator coupled with a gear transmission which overcomes many of the performance limitations of prior art actuators.
It is a principal object of the present invention to provide a high force potential for an EGR valve actuator at fast response time with low design, manufacturing, and assembly costs, having an easily adjustable actuation stroke, and being easily adaptable for combination with any of a plurality of pintle valve assemblies.
Briefly described, a rack and pinion transmission for a pintle valve in accordance with the invention includes a motor mounted to a body including a gear case. The motor shaft has a pinion gear that engages a large reduction gear having a hub gear. The hub gear is a planet gear for a planetary ring segment gear that pivots on a shaft and includes a pinion segment gear that engages a linear rack. The rack is attached to a valve pintle shaft, causing the valve to be opened and closed in response to rotation of the motor shaft. An actuator in accordance with the invention has low assembly costs, as the pintle shaft, a return spring, rack, and gears may all be assembled by slip fit. The gear case cover may be secured by machine.
An actuator in accordance with the invention is a high-force actuator having a fast time response and compact design by virtue of a rack and composite pinion and planetary gearing. Various types of rack position sensors may be adapted for use without requiring changes in the actuator. The stroke of the rack is readily adapted for use with various pintle valves having differing stroke requirements by simply varying the rotational angle through which the motor operates, or by changing the angular orientation of a composite gear during assembly.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
A first drawback of prior art actuator 10 is that link 93 places a side load on shaft 29 during actuation thereof, which can cause undesirable wear and premature failure. A second drawback is that the motion of shaft 29 is not linear with uniform rotation of gear 87.
Referring to
Referring to
Rack 140 is located within body 112 by a rack keeper 142 which is a feature of body 112. Rack 140 is also kept in position by a rack retainer 144 which is a flange on the side of pinion gear segment 138. Rack 140 is provided with a bulbous opening 146 for receiving a bulb end 148 on a shaft 150 for actuation thereof. For example, shaft 150 may be the pintle shaft of poppet valve 115, such as an EGR valve for an internal combustion engine 117. In the example shown, shaft 150 extends into gear case 120 via an opening 154. A bias return spring 158 urges valve 115 into a closed position and eliminates mechanical lash in the entire gear train.
Gear case 120 includes a cover plate 156 that is attached to housing 112 via bolts 160. Cover plate 156 includes an inner bore 162 for receiving and stabilizing the outer end 163 of first shaft 124.
Preferably, a stop pin 170 is provided within gear case 120 and extending inward from body 112. Pin 170 is positioned to interfere with travel of pie-shaped gear segment 131 and thus function as a lower limit of rack travel.
Preferably, an actuator 110 in accordance with the invention includes a position sensor 172 for determining the position of rack 140, and hence the open status of valve 115, at all times. The rack position is monitored by the engine control module (not shown) by receiving feedback from position sensor 172 mounted on body 112.
Preferably, sensor 172 includes an axially slidable probe 174, the position of which is sensed in known fashion within sensor 172. Probe 174 engages an upper surface 176 of rack 140.
In opening operation, when a positive voltage command is applied to motor 116, motor 116 turns gear 122 in a clockwise (CW) direction. Gear 122 then drives gear 126 and associated gear 128 in a counter-clockwise (CCW) direction. Gear 128 drives gear 131 in a CCW direction which also drives gear 138 in a CCW direction, causing rack 140 to be displaced downward (with respect to the orientation shown in
Closing operation is the reverse of opening.
In fail-safe closing, should motor 116 lose power, return spring 158, attached to shaft 150 by collar 166, will urge valve 115 into a closed position.
An actuator 110 in accordance with the invention entails desirably easy assembly and low assembly costs. Motor 116 may be assembled to body 112 by machine, and gear 122 is readily installed conventionally onto motor shaft 118. Fixed shafts 124,136 and stop pin 170 may be inserted into bores in body 112 by machine. No extraneous parts, such as screws or clips, are required to complete the assembly, nor is any welding. The pintle shaft, spring, rack, and gears are all assembled by slip fit. The gear case cover may be secured by machine.
An actuator 110 in accordance with the invention is a high-force actuator having a fast time response and compact design by virtue of a rack 140 and internal gearing between gears 128,130. Various types of sensors 172 may be adapted for use without requiring changes in the actuator. The stroke of the rack is readily adapted for use with various pintle valves having differing stroke requirements either by varying the rotational angle through which the motor operates or by varying the angle at which composite gear 131 is installed onto shaft 136.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
