Patent Publication Number: US-7591448-B2

Title: Hydraulic control valve system

Description:
This application is a continuation-in-part application of application Ser. No. 11/604,432 filed Nov. 27, 2006, the entirety of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a valve system for controlling a hydraulic drive system. 
   Hydraulic drive systems are used in many mechanical load applications, for example in construction equipment, farming equipment, fork lifts, cranes and other hydraulically driven work systems. Hydraulic pistons driving an associated mechanical organ are controlled by valves controlling the flow of hydraulic fluid through a pump line and a return line, in order to fill or to empty the hydraulic piston. The degree of opening and closing of the pump line, respectively return line control valves, determines the rate of displacement and position of the associated mechanical load member. It is therefore important to ensure accuracy in the opening and closing of the control valves and to reduce sensitivity of the control valve opening to pressure in the hydraulic system. 
   In certain conventional systems, hydraulic valves are controlled by means of electro-magnetic actuators combined with a hydraulic amplifier to provide the required force to displace and to hold the valve rod. It is however difficult with such control systems to obtain precise and rigid control of the valves. Another known means of controlling valves is by way of an actuator comprising an electrical motor driving the valve control rod, as described in DE 19 948 379 or U.S. Pat. No. 4,650,159. 
   The use of a stepping motor to actuate a valve rod is advantageous in view of the high rigidity it confers to the hydraulic valve control system as well as enabling high precision in the opening and closing of the valves through control of the stepping motor. A major disadvantage of such systems is however the size of the stepping motor and the limited number of hydraulic valves that may be arranged in a juxtaposed manner. In DE 19 948 379 for example, the hydraulic block has four pairs of control valves mounted in a juxtaposed manner, each control valve being actuated by an electrical stepping motor connected to the valve rod via a link arm, each of the motors being arranged in a different orientation. In this configuration, additional valves cannot be added to the valve block and the different arrangements of the various electrical motors increases manufacturing and assembly costs. 
   SUMMARY OF THE INVENTION 
   In view of the aforegoing, it is an object of the invention to provide a hydraulic control valve system with a plurality of juxtaposed valves that is compact, economical to manufacture and assemble, and that provides precise and rigid control of the opening and closing of the hydraulic valves. 
   It is a further object of this invention to provide a hydraulic control valve system that may be easily expanded to include more control valves in a juxtaposed manner in a compact block. 
   Objects of this invention have been achieved by providing a hydraulic control valve system comprising a hydraulic valve block with a plurality of control valve segments arranged in a juxtaposed manner, each control valve segment comprising a first line, for example a pump line, a second line, for example a return line, and a displaceable valve rod adapted to open and close the first line, respectively close and open the second line to varying degrees depending on a position of the valve rod, the valve system further comprising a plurality of actuators arranged in a juxtaposed manner, one actuator for each valve segment, each actuator comprising an electrical motor connected to a respective said valve rod through a coupling mechanism, each motor having a rotor and a stator having a plurality of coils positioned around the rotor, approximate mid points of the coils defining a virtual circle around the rotor, whereby a ratio DS/HS of a diameter DS of the virtual circle defined by mid-points of the coils of the stator divided by an overall height HS of the coils in a direction parallel to an axis of rotation of the rotor is greater than 1.6. 
   Advantageously, the actuator has width equal or smaller than each hydraulic valve segment such that a plurality of identical actuators can be assembled in a juxtaposed manner to actuate a plurality of respective hydraulic valves in a compact valve block while benefiting from the positional rigidity and control accuracy of the electrical motor. 
   The coupling mechanism of the actuator may advantageously comprise a rack and pinion, the rack fixed directly to or forming an extension of the valve rod. 
   The electrical motor may advantageously be a stepping motor, the stator comprising a plurality of coils positioned around radially extending arms of the stator. The stator preferably comprises at least six coils, preferably eight. In view of obtaining high accuracy and rigidity when displacing the valve rod, the motor preferably has a large number of steps per revolution, preferably more than 100, for example around 200 steps. The large number of steps is also particularly advantageous in providing a very low positional hysteresis when changing drive direction. In the embodiment shown, the rotor has around 50 teeth. 
   Further objects and advantageous features of the invention will be apparent from the claims and the following detailed description and figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a view of a hydraulic control valve system according to this invention; 
       FIG. 1   b  is a view in the direction of arrow  1   b  of  FIG. 1 ; 
       FIG. 1   c  is a view in the direction of arrow  1   c  of  FIG. 1   b;    
       FIG. 2   a  is a longitudinal cross-sectional view through one of the segments shown in  FIGS. 1   a - 1   c;    
       FIG. 2   b  is a cross-sectional view through line  2   b - 2   b  of  FIG. 2   a;    
       FIG. 3   a  is a cross-sectional view similar to  FIG. 2   a , except that it shows a variant of the electrical actuator; 
       FIG. 3   b  is a cross-sectional view through line  3   b - 3   b  of  FIG. 3   a;    
       FIG. 4   a  is a cross-sectional view similar to  FIG. 2   a  except that it shows yet another variant of an electrical actuator; 
       FIG. 4   b  is a cross-sectional view through line  4   b - 4   b  of  FIG. 4   a;    
       FIG. 5   a  is a cross-sectional view of part of a variant of the hydraulic control valve system of  FIG. 2   a ; and 
       FIG. 5   b  is a cross-sectional view through line  5   b - 5   b  of  FIG. 5   a.    
   

   DETAILED DESCRIPTION 
   Referring to the figures, a hydraulic control valve system  2  comprises a plurality of juxtaposed hydraulic control valve segments  4 , each segment comprising a hydraulic valve device  6  and an actuator  8 ,  8 ′,  8 ″,  8 ′″. The hydraulic valve devices of the control valve segments may be provided as separate components assembled together to form a single block or alternatively may be made out of a single block or out of a number of components assembled together as a single block. 
   Each hydraulic valve device comprises a body portion  10  within which are provided channels  12 ,  14 ,  16 ,  17 ,  19  through which hydraulic fluid flows. The channels include a first channel  12  and a second channel  14  that are intended to be connected to hydraulic lines leading to a hydraulic piston for driving a mechanical load. The channels further include input channels  17 ,  19  intended to be connected to a hydraulic pump system that provides the hydraulic pressure, and an evacuation channel  16  for return of hydraulic fluid. The first and second channels  12 ,  14  may be connected respectively to a first line (such as a pump line) and a second line (such as a return line). The hydraulic valve further comprises a valve rod  22  slidably mounted in a valve rod cavity  28  that communicates with the channels  12 ,  14 ,  16 ,  17 ,  19 . The valve rod is movable in linear direction T along a valve rod axis  13 . The valve rod has reduced cross-section portions  24 ,  26  to interconnect or to disconnect the first line, respectively second line, with the input channels  17 ,  19  so as to open and close the first line  12  or the second line  14 , for forward or reverse movement of the hydraulic piston connected thereto. 
   The translational position of the valve rod in the cavity determines how much the valves are opened or closed which in turn varies the pressure and flow of hydraulic fluid to or from the hydraulic drive system connected to the valve. It is therefore important to have an accurate displacement and positioning of the valve rod, as well as a high rigidity in holding and stabilizing the valve rod in any given position. This accurate positioning and rigid holding of the valve rod is provided by the actuator  8 ,  8 ′,  8 ″,  8 ′″ mounted on an actuator mounting face  21   a  of the hydraulic valve body  10  through which extends an extremity  23  of the valve rod  22 . 
   The actuator comprises a housing  30 , an electrical motor mounted in the housing coupled to the valve rod  22  via a coupling mechanism  33 . The motor comprises a stator  32 ,  32 ′,  32 ″,  32 ′″ rigidly fixed to the housing  30 , and a rotor  36 ,  36 ′,  36 ″,  36 ′″ rotatably mounted via bearings  41  to the stator or housing. The axis R ( FIG. 2   b ) of the rotation of the rotor extends in an axial direction A, orthogonal to the valve rod axis  13  and a major plane generally defined by the valve rod  22  and first and second hydraulic channels  12 , 14 . 
   The coupling mechanism  33  comprises a rotor gear  38  rigidly fixed to the rotor engaging a reduction gear  25  having a large gear wheel  37  and a pinion  39  rotatably mounted on an axis  43  fixed to the housing. Instead of the reduction gear, it is also possible to have a transmission belt around the rotor gear  38  and the pinion  39 . The reduction gear pinion  39  engages a toothed rack  40  that is coupled to, and in line with, the extremity  23  of the valve rod  22 . Alternatively, the toothed rack may be integrally formed with the valve rod. Other coupling mechanisms known in the art that transform a rotation movement of the rotor into a linear translational movement of the valve rod may also be used without departing from the scope of this invention. 
   The toothed rack  40  is supported and guided by a roller  27  bearing against a face  29  of the toothed rack opposite the pinion  39 . 
   The actuator housing  30  has a generally parallelepiped shape bounded by opposed major faces  53   a ,  53   b  and narrow minor faces  53   c ,  53   d ,  53   e ,  53   f , one of which is a mounting face. The housing comprises a base part  35   a , preferably of a cast non-magnetic metal alloy and a cover part  35   b . The base part comprises a cavity  52  for lodging the stator  32  of the motor, and cavities  55   a ,  55   b ,  55   c  for lodging the rotor bearing  41  and the axes  43   a ,  45   a  of the reduction gear  25  and the support roller  27  respectively. The cover part  35   b  may also be provided with corresponding cavities  54   a ,  54   b  for lodging the corresponding rotor bearing  41  and reduction gear axis  43  in a compact manner while advantageously allowing axial assembly of the motor and coupling mechanism with the housing parts  35   a ,  35   b.    
   The narrow mounting face  53   c  of the actuator housing  30 , for mounting against the mounting face  21   a  of the hydraulic valve body, comprises a passage  56  for the valve rod  22  coupled with the toothed rack  40 , the passage  56  being formed by a tubular extension  57  adapted to be received in a corresponding cavity  58  in the hydraulic valve body portion  10 . The tubular extension  57  enables the actuator to be accurately positioned with respect to the hydraulic valve body portion  10  and moreover guides and positions the valve rod extremity  23  accurately into the actuator. 
   Electrical connectors  59 ,  59 ′ extend out of the housing  30  on a narrow minor face  53   e  (see  FIG. 2   a ) on the side where the hydraulic first and second channels  12  to  14  are connected, or on the narrow minor face  53   d  opposite the mounting face  53   c  (see  FIG. 5   a ). 
   The stator of the electrical motor comprises a plurality of coils  42  mounted on a magnetic circuit structure with radially and inwardly extending stator arms  34 , preferably formed from stacked laminated sheets of ferro-magnetic material, for generating a varying magnetic field that drives the rotor. 
   In the embodiment shown in  FIGS. 2   a ,  2   b , and  5   a ,  5   b , the motor is a stepping motor. The rotor comprises a permanent magnet  44  in the shape of a disc sandwiched between a pair of magnetic flux conducting discs  46 , for example discs made of stacked laminated ferro-magnetic material. The stator preferably comprises at least six coils  42  arranged around the circumference of the rotor, mounted on the radially extending stator arms  34 . 
   In view of obtaining high accuracy and rigidity when displacing the valve rod, the stepping motor preferably has a large number of steps per revolution, preferably more than 100, for example around 200 steps. The large number of steps is also particularly advantageous in providing a very low positional hysteresis when changing drive direction, and a high resolution. Both the rotor and the stator of the stepping motor preferably have a large number of teeth  47 , preferably more than 40. The stator of the stepping motor embodiment preferably has at least six coils, but preferably eight or more. 
   The ratio DS/HS of the average diameter DS of a virtual circle defined by the approximate centers of the stator coils, with respect to the overall height HS of the coils, is advantageously greater than 1.6 and preferably 1.7 or more. The ratio DR/HR of the outer diameter DR of the rotor with respect to the overall axial height HR of the rotor discs, the axial height being measured in the direction of the axis of rotation R, is preferably greater than 2.5 and preferably 3 or more. 
   In the variant of  FIGS. 5   a ,  5   b , the ratio DS/HS is approximately 1.7 whereas in the variant of the  FIGS. 2   a ,  2   b  the ratio DS/HS is approximately equal to 2.2. 
   The aforementioned ratios enable the actuator to have the same thickness H or less than the width of conventional hydraulic valve segments, which are typically around 40 mm wide, while providing the required torque and stability for displacing the valve rod under typical pressures found in valve control systems for agricultural equipments, fork lifts, construction equipment and the like. The electrical actuators may thus be assembled in an identical and juxtaposed manner to any plurality of hydraulic valve segments of a hydraulic valve block. 
   In the embodiment shown in  FIGS. 3   a  and  3   b , the motor of the electrical actuator is a brushless DC motor comprising a ferro-magnetic stator  32 ′ with a plurality of radially and inwardly directed stator arms or poles  34 ′. The coils  42 ′ are mounted in a spaced apart manner around the periphery of the rotor on certain of the poles  34 ′. The rotor  36 ′ comprises an annular permanent magnet  44 ′ that has a plurality of adjacent alternately polarized segments. 
   The brushless DC motor generates a lower torque than the stepping motor variant illustrated in  FIGS. 2   a ,  2   b , but the rotor  36 ′ rotates at a higher speed such that the gear down ratio of the gear system acting on the rack  40  is greater than the gearing down ratio of the coupling mechanism of the stepping motor actuator. In view of the higher gearing down, reversibility of the hydraulic system (in the situation where the electric motor is switched-off) is not as good as with the stepping motor. Certain applications however do not require reversibility in the case of a power failure or for other reasons, and in certain applications reversibility may on the contrary not be desired. 
   Referring now to  FIGS. 4   a  and  4   b , another embodiment is shown in which the electrical actuator comprises a variable reluctance motor comprising a ferro-magnetic stator  32 ″ having a plurality of radially and inwardly directed stator arms or poles  34 ″ around which coils  42 ″ are mounted. In the case of a variable reluctance motor, the rotor  36 ″ comprises a ferro-magnetic body with a plurality of radially and outwardly directed poles  48 , there being less rotor poles than stator poles. The stator coils generate a varying magnetic field that generates the equivalent of a rotating magnetic field attracting the rotor poles  48 . In view of the fact that the variable reluctance motor does not generate any magnetic resistance when the electrical supply is switched off, the motor has a high reversibility and may therefore advantageously be used in applications where reversibility is desired. 
   The overall height L of the actuator (i.e. the distance between the minor faces  53   e  and  53   f ) may advantageously be approximately equal to the height of the hydraulic valve body, such that the opposite minor faces  53   e ,  53   f  of the actuator do not extend substantially beyond corresponding faces  21   b ,  21   c  of the hydraulic valve body. In the variant of  FIGS. 5   a ,  5   b , the electrical connector  59 ′, for connection of an external power supply and drive unit to the motor, projects from the minor face  53   d , opposite the mounting face  53   c , allowing easy and convenient access to the connectors. 
   Advantageously, the electrical motor actuators, which provide positional rigidity and control accuracy, have thicknesses equal or smaller than each hydraulic valve segment such that a plurality of identical actuators can be assembled in a juxtaposed manner to actuate a plurality of respective hydraulic valves, thus forming a compact yet performant hydraulic valve block system.