Patent Publication Number: US-6983894-B2

Title: Piezo-electrically actuated canister purge valve with a hydraulic amplifier

Description:
CROSS REFERENCE TO CO-PENDING APPLICATIONS 
   This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/356,999, filed 13 Feb. 2002, the disclosure of which is incorporated by reference herein in its entirety. 

   FIELD OF THE INVENTION 
   This invention relates generally to on-board emission control systems for internal combustion engine powered motor vehicles, e.g., evaporative emission control systems, and more particularly to an emission control valve, such as a canister purge valve for an evaporative emission control system. 
   A known on-board evaporative emission control system includes a vapor collection canister that collects fuel vapor emitted from a tank containing volatile liquid fuel for the engine, and a canister purge solenoid (CPS) valve for periodically purging collected vapor to an intake manifold of the engine. The CPS valve in the known evaporative system control system includes an electromagnetic solenoid that is under the control of a purge control signal generated by a microprocessor-based engine management system. 
   The purge control signal is believed to be a duty-cycle modulated square-pulse waveform having a relatively low operating frequency, e.g., in the 5 Hz to 20 Hz range, which is modulated between 0% and 100%. This means that for each cycle of the operating frequency, the electromagnetic solenoid is energized for a certain percentage of the time period of the cycle. During the energized, i.e., “on,” time of the duty cycle, an armature of the electromagnetic solenoid travels full stroke. During the de-energized, i.e., “off,” time of the duty cycle, the armature is returned to its normal position, e.g., under the bias of a spring engaging the armature. As the percentage of the duty cycle increases, the “on” time during which the electromagnetic solenoid is energized also increases, and therefore so does the purge flow through the valve. Conversely, the purge flow decreases as the percentage decreases. 
   However, known electromagnetic solenoids that move an armature in accordance with a duty-cycle modulated square-pulse wave suffer from a number of disadvantages, including slow response time and large overall size. 
   SUMMARY OF THE INVENTION 
   The present invention provides a canister purge valve for regulating a fuel vapor flow between a fuel vapor collection canister and an intake manifold of an intake manifold of an internal combustion engine. The canister purge valve includes a body having a passage extending between a first port and a second port, a seat defining a portion of the passage, a member movable with respect to the seat, and an actuator that moves the member. The first port of the body is adapted to be in fluid communication with the fuel vapor collection canister, and the second port of the body is adapted to be in fluid communication with the intake manifold of the internal combustion engine. The member moves generally along an axis between a first configuration that prohibits fuel vapor flow through the seat and a second configuration that permits fuel vapor flow through the seat. And the actuator includes a piezo-electric element that moves the member from the first configuration to the second configuration. 
   The present invention also provides an emission control system for an automobile, which has a fuel tank that supplies fuel to an internal combustion engine. The fuel tank holds a supply of volatile liquid fuel and fuel vapor in a headspace above the liquid fuel. The internal combustion engine combusts a combination of the fuel and air, which is drawn through an intake manifold of the internal combustion engine. The emission control system includes a fuel vapor collection canister and a purge valve. The fuel vapor collection canister includes a collection port and a discharge port. The collection port is in fluid communication with the headspace of the fuel tank. The purge valve includes an inlet that is in fluid communication with the discharge port of the fuel vapor, and includes an outlet that is in fluid communication with the intake manifold of the internal combustion engine. The purge valve further includes a body that has a passage that extends between the inlet and the outlet, a seat that defines a portion of the passage, a member that moves with respect to the seat, and an actuator. The member moves generally along an axis between a first configuration that prohibits fuel vapor flow through the seat and a second configuration that permits fuel vapor flow through the seat. The actuator includes a piezo-electric element that moves the member from the first configuration to the second configuration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention. 
       FIG. 1  is a schematic diagram of an evaporative emission control system including a canister purge valve according to a preferred embodiment. 
       FIG. 2  is a cross-section view of a canister purge valve according to a preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an evaporative emission control system  10 , such as for a motor vehicle (motor vehicle not shown), that comprises a vapor collection canister  12 , and a canister purge valve  14  according to the present disclosure. The valve  14  is connected in series between a fuel tank  16  and an intake manifold  18  of an internal combustion engine  20 . An engine management computer  22  that receives various input signals supplies a purge control output signal for operating valve  14 . 
   Referring to  FIG. 2 , the valve  14  comprises a body part  24  having an inlet port  25  and an outlet port  26 . Body part  24  is fabricated from suitable fuel-tolerant material, such as by injection molding. The two ports  25 , 26  can be embodied as nipples. Body part  24  provides for the mounting of the valve  14  at a suitable mounting location on an automotive vehicle, e.g., on the vapor collection canister  12 . The body part  24  includes a passage  27  extending between the inlet and outlet ports  25 ,  26 . A seat  28  defines a portion of the passage  27 . 
   Valve  14  further comprises a piezo-electric assembly  30  that is housed within body part  24 . The piezo-electric assembly  30  can include a single piezo-electric element or can include a plurality of stacked piezo-electric elements. The piezo-electric assembly  30  is actuated in response to an electric signal provided at terminals  32  by the engine management computer  22 . 
   Reference characters A—A designate an imaginary longitudinal axis of valve  14  with which piezo-electric assembly  30  and inlet port  25  are coaxial. The piezo-electric element(s) of the piezo-electric assembly  30  are arranged so as to expand or contract principally along the longitudinal axis A—A. Preferably, the application of an electric signal at the terminals  32  causes the piezo-electric element(s) to expand along the longitudinal axis A—A, and discontinuing the electric signal at the terminals  32  causes the piezo-electric element(s) to contract along the longitudinal axis A—A. 
   According to the illustrated embodiment, the piezo-electric assembly  30  contiguously engages a first piston  34 . The first piston  34  is slidingly received in a first bore  40  defined by the housing  24 . Preferably, the first bore  40  has an inside diameter D 1 . 
   The first bore  40  is in fluid communication with a second bore  50  defined by the housing  24 . Preferably, the second bore  50  has an inside diameter D 2 . A second piston  52  is slidingly received in the second bore  50 . 
   Preferably, the first and second pistons  34 , 52  are provided with fluid tight seals relative to the first and second bores  40 , 50 , respectively. As such, a predetermined volume of substantially incompressible hydraulic fluid  48  is captured in the space defined by the first and second pistons  34 , 52  and by the first and second bores  40 , 50 . 
   The second piston  52  is coupled to a pintle  54 . Preferably, the second piston  52  and the pintle  54  are integrally formed from a single, homogeneous material. The pintle  54  includes a sealing face  56  that is adapted to engage the seat  28  defined by the housing  24 . In a closed configuration of the canister purge valve  14 , the sealing face  56  of the pintle  54  contiguously and sealingly engages a sealing edge  60  of the seat  28 . The closed configuration of the canister purge valve  14  is shown in  FIG. 2 . 
   Preferably, a resilient member  70  provides a biasing force opposing the expansion force of the piezo-electric assembly  30 . The resilient member  70  is preferably a compression coil spring that extends between the housing  24  and the first piston  34 , and occupies a portion of the space in which the hydraulic fluid  48  is captured. Of course, other types of resilient members  70 , e.g., a wave spring, and other arrangements of the resilient member  70 , e.g., extending between the housing  24  and the pintle  54 , are also envisioned. 
   The inside diameter D 1  of the first bore  40  is larger than the inside diameter D 2  of the second bore  50  such that a relatively small displacement along the longitudinal axis A—A of the first piston  34  by the piezo-electric assembly  30  causes a relatively large displacement along the longitudinal axis A—A of the second piston  52 . Preferably, the piezo-electric assembly  30  is capable of expanding and contracting in the direction along the longitudinal axis A—A by an amount in a range of 0.01 to 0.035 millimeters. Inasmuch as the preferred range of movement of the pintle  54  along the longitudinal axis A—A is between 1.0 and 6.0 millimeters, the ratio of the inside diameters D 1 /D 2  is at least five, and is preferably approximately 25. Of course, different relative inside diameters D 1 , D 2  are envisioned for providing the appropriate degree of movement amplification between the displacement of the piezo-electric assembly  30  and the pintle  54 . 
   While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.