Abstract:
A hydraulic valve with a position sensor is described. According to various implementations, the valve has a cage with a set of radial holes, a spool assembly slideable within the cage, and a sensor, which may be a Hall effect sensor, that reacts to the movement of the spool assembly. In other implementations, the spool comprises one or more of the following: a spool, a pin that is mechanically coupled to the spool, a dampener, which may be a spring, having a first and a second end, the first end being in contact with the pin and the second end being in contact with the spool.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Application No. 60/285,808, filed Apr. 23, 2001. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates generally to hydraulic valves, and, more particularly, to hydraulic valves in which the position of a movable spool or poppet can be detected.  
         BACKGROUND  
         [0003]    Hydraulic valves are used to regulate the flow and pressure of hydraulic fluid in a variety of types of devices, ranging from construction equipment like bulldozers and power shovels to jet aircraft. Many hydraulic valves use a spool or poppet that changes position within the valve to control the amount of hydraulic fluid passing through the valve per unit of time. One challenge in using such valves is determining the current position of the spool or poppet at any given time. Since the spool or poppet is typically located inside the valve and is not visible, the information can be difficult to obtain.  
         SUMMARY  
         [0004]    In accordance with the foregoing, the invention is generally directed to a hydraulic valve with a position sensor. According to various embodiment of the invention, the valve has a cage with a set of radial holes, a spool assembly slideable within the cage, and a sensor, which may be a Hall effect sensor, that provides an electrical signal based on the position of the spool assembly. In more specific embodiments, the spool assembly comprises one or more of the following: a spool, a pin having an enlarged portion and mechanically coupled to the spool and a biasing means, which may be a spring, having a first and a second end, the first end being in contact with the pin and the second end being in contact with the spool.  
           [0005]    In other embodiments of the invention, the spool assembly comprises a generally cylindrical guide aligned with the spool and in contact with an end surface of the spool, the guide having a longitudinal hole and at least a portion of the pin being disposed within the longitudinal hole. The spool assembly may also comprise a biasing means disposed within the longitudinal hole, a first end of the biasing means being in contact with the portion of the pin that is disposed within the longitudinal hole and a second end of the biasing means extending out from the longitudinal hole and in contact with the spool. In more specific embodiments, the longitudinal hole of the guide may have a first and a second section, the first section being smaller in diameter than the second section, a circular step of the guide being defined between the first and second sections, wherein, during operation of the valve, the circular step limits the movement of the enlarged portion of the pin to prevent the pin from exiting the longitudinal hole of the guide.  
           [0006]    In yet other embodiments of the invention, the valve comprises a spool having a longitudinal blind hold at one end, a portion of a guide being disposed within the longitudinal blind hole, wherein the guide has a collar that is disposed outside of the longitudinal blind hole and is in contact with an end of the spool. The valve may further comprise a plug disposed at an end of the valve, a sensor held stationary by the plug, and a spring annularly disposed around the guide, wherein a first end of the spring abuts the plug and a second end of the spring abuts the annular collar of the guide, wherein the spring pushes the guide and the spool away from the plug.  
           [0007]    According to still other embodiments of the invention, a safety system for a hydraulic device, comprises a hydraulic valve that, by itself, comprises: a cage having a set of radial holes for allowing the passage of fluid; a spool slideable within the cage to allow or block the flow of fluid through the set of radial holes, the spool having at least a first position and a second position; a pin coupled to the spool; and a sensor disposed adjacent to the pin, wherein when the spool moves from the first position to the second position, the pin moves relative to the sensor, thereby causing a change in a magnetic field near the sensor, wherein the sensor reacts to the change by generating an electrical signal. The safety system may further comprise a safety circuit electrically connected to the sensor, wherein the safety circuit allows or prevents a user from activating the hydraulic device based on the electrical signal generated by the sensor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    While the appended claims set forth the features of the invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings, of which:  
         [0009]    [0009]FIG. 1 is a cross-sectional view of a hydraulic valve according to an embodiment of the present invention shown in a neutral position;  
         [0010]    [0010]FIG. 1 a  is an enlarged view of section A of the valve of FIG. 1;  
         [0011]    [0011]FIG. 1 b  is an enlarged fragmentary view showing an area near a target pin and a sensor of the hydraulic valve of FIG. 1;  
         [0012]    [0012]FIG. 1 c  is a cross-sectional view along line B-B of the hydraulic valve of FIG. 1;  
         [0013]    [0013]FIG. 2 is a cross-sectional view of the hydraulic valve of the present invention shown in a shifted position;  
         [0014]    [0014]FIG. 2 a  is an enlarged view of section A of the valve of FIG. 2; and  
         [0015]    [0015]FIG. 2 b  is an enlarged fragmentary view showing an area near a target pin and a sensor of the hydraulic valve of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring to FIG. 1, a hydraulic valve  2  includes an adaptor  4  and cage  6  connected to each other by engagement between a threaded portion  7  of the cage  6  and a threaded portion  9  of the adaptor  4 , and a spool assembly slidable within a bore  10  of the cage  6 . The spool assembly comprises a spool  8 ; a guide  14 ; a biasing means, shown as being implemented as a spring  33 ; and a target pin  34 . The spool  8  has a longitudinal blind hole  12  with a guide  14  installed therein. The adaptor  4  has a longitudinal threaded through hole  11  with a plug  16  installed therein. The plug  16  has a threaded portion  17  that threadably engages the adaptor  4  in the longitudinal threaded through hole  15 . The plug  16  is made from a non-magnetic material, preferably a stainless steel, and has a longitudinal threaded blind hole  18  that threadably engages a sensor  20 . The sensor  20  comprises a sensing member  22 , which is preferably a Hall Effect sensor. A lock nut  24  threadably engages the sensor  20  to lock the sensor  20  in a fixed position within the plug  16 . The guide  14  has a collar  15  and a two-section longitudinal coaxial hole with a first section  26  being smaller than a second section  28  to provide a circular step  30 . A target pin  32 , made from a magnetic material, passes through the first section  26  and the second section  28  of the longitudinal hole of the guide  14  with an enlarged portion  34  of the target pin  32  being prevented from exiting out of the second section  28  of the longitudinal coaxial hole by the step  30 , and being pushed toward the step  30  by a biasing means, which is shown in FIG. 1 as being implemented as a spring  33  accommodated within the second section  28  of the longitudinal hole of the guide  14  between the enlarged portion  34  of the target pin  32  and the end of the longitudinal blind hole  12  of the spool  8 . The spool  8  has a circular groove  36  to accommodate a circular ring  38  limiting movement of the spool  8  in one direction. A bias means, which is shown in FIG. 1 as being implemented as a spring  40 , is installed between the guide  14  and the plug  16 . The plug  16  has a longitudinal blind hole  42  with a portion of the target pin  32  being accommodated therein. The hole  42  has a small diameter relative to a threaded portion  17  of the plug  16 , so that even with a small thickness “T” of a wall between the longitudinal threaded blind hole  18  of the plug  16  and the longitudinal blind hole  42  of the plug  16  (see FIG. 3), preferably about 0.05 in, the fluid pressure inside the adaptor  4  would not create a sufficient stress in the material of the wall of the plug  16  to break it.  
         [0017]    The cage  6  has a first set of radial holes  44 , a second set of radial holes  46  and a third set of radial holes  48 , with each set of radial holes defining a separate valve port. One end of the bore  10  of the cage  6  defines a valve port  52  used to apply a so-called pilot pressure to shift the spool  8  relative to the cage  6 . The cage  6  has a longitudinal groove  53  (also shown in FIG. 1 c ) passing through the threaded portion  7  of the cage  6  to provide communication between the inside of the adaptor  4  and the first set of radial holes  44  of the cage  6 . When the valve  2  is in its neutral position (i.e. the spool  8  is in a neutral position), there is a gap “G” between the end of the longitudinal blind hole  42  of the plug  16  and the target pin  32  and the first set of radial holes  44  communicates with the second set of radial holes  46 .  
         [0018]    During operation of the valve  2 , when a pressure is applied at the port  52 , the spool assembly is pushed away from the port  52 . Specifically, the spool  8  moves away from the port  52 , thereby pushing the spring  33  and the target pin  32  toward the sensing member  22 . As the target pin  32  moves, the gap “G” decreases and a magnetic field near said sensing member  22  changes, thereby triggering the sensing member  22 . When the sensing member  22  triggers, it generates, depending on the implementation of the sensor  20 , either an electrical logical signal “1” (a so-called sourcing output signal), or an electrical logical signal “0” (a so-called sinking output signal). As the spool  8  continues to move further, the target pin  32  eventually stops against the end surface of the longitudinal hole  42  of the plug  16 . As the spool  8  continues to move away from the port  52 , it pushes the guide  14  and the spring  33 , causing the springs  33  and  40  to compress. Since the target pin  32  is stopped against the end surface of the longitudinal hole  42 , the distance between the target pin  32  and the sensing member  22  does not change and, thus, the sensing member  22  continues to be in its triggered state.  
         [0019]    Referring to FIGS. 1 a  and  1   b,  the sensitivity with which the position of the spool  8  can be detected generally depends on several factors, including the characteristics of the sensing member  22 , the size of the gap “G,” and the size of the full stroke “S.” While there are many possible values for “S” and “G,” setting the maximum size of “G” equal to about 0.03 in and setting “S” equal to about 0.386 in is known to be suitable. If, for example, the maximum size of the gap “G” (i.e. when the target pin  32  is farthest away from the sensing member  22 ) is selected to be very small, such as about 0.03 in, the sensing member  22  will be triggered and will provide an electrical output signal even when the spool  8  moves a small distance (less than 0.030 in) away from the neutral position. In contrast, if the maximum size of the gap “G” is set so as to be nearly equal to the size of the full stroke “S,” then the sensing member  22  will only provide an output signal when the second set of radial holes  46  fully communicates with the third set of radial holes  48 .  
         [0020]    Referring again to FIG. 1, an example of an application in which the valve  2  may be used will now be described. In this example, the valve  2  is a component of a safety system for a hydraulic device. The sensor  20  is electrically connected by a line  55 , which may be a cable or a wire, to a safety circuit  54  of the hydraulic device  56 . Furthermore, the logic of the safety circuit  54  is configured so that the hydraulic device  56  is prevented from being activated or performing a certain function unless the valve  2  is determined by the safety circuit  54  to be in a specified position, such as a neutral or a shifted position. The safety circuit determines the position of the valve based on the logical output signal provided by the sensing member  20 .  
         [0021]    The foregoing detailed description has been for the purpose of illustration only. Thus, a number of modifications and changes may be made without departing from the spirit and scope of the invention. Furthermore, it will be appreciated that the invention is not restricted in its applicability to the two-position, four way, screw-in, spool type valve shown in the figures, but that it is applicable to all other valves in which detecting the spool or poppet position would be useful.