Patent Publication Number: US-2005128673-A1

Title: Solenoid drive circuit

Description:
BACKGROUND OF THE INVENTION  
      1. Technical Field of the Invention  
      The present invention relates to a solenoid drive circuit in which an energization controller that controls the energization/de-energization of a coil is provided either between a power source and the coil or between the coil and ground, and a diode, which allows electric current to flow toward the power source, that is connected between the power source and ground while bypassing the coil.  
      2. Related Art  
      A conventional solenoid drive circuit is known, such as, for example, the circuit disclosed in published Japanese translation No. 10-504259 of a PCT application.  
      In the conventional solenoid drive circuit, the diode is used to gradually reduce the electric current flowing through the coil when energization of the coil is stopped. Furthermore, in the conventional solenoid drive circuit, the diode also functions to prevent the occurrence of noise due to a valve body hitting a valve seat when a solenoid valve closes.  
      In the case of a solenoid valve employing a coil, a rapid switch over operation of the solenoid valve by de-energizing the coil is sometimes required. However, if the electric current flowing through the coil is gradually reduced by the diode, the rapid switch over operation of the solenoid valve is not possible.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to at least overcome the above-described deficiencies of the conventional solenoid drive circuit.  
      It is also an object of the present invention to provide a solenoid drive circuit that can easily switch over between a state in which the electric current flowing through a coil is gradually reduced and a state in which the electric current flowing through the coil is rapidly reduced.  
      In accordance with a preferred embodiment of the present invention, a solenoid drive circuit includes an energization control means which controls the energization/de-energization of a coil and which is provided either between a power source and the coil or between the coil and ground. A diode that allows electric current to flow toward the power source is connected between the power source and ground while bypassing the coil. The solenoid drive circuit also includes switch means provided either between the power source and the diode or between the diode and ground.  
      Because of the above-described structural arrangement, switching over the conduction/cutoff of the switch means facilitates switching between a state in which the diode is active and a state in which the diode is substantially inactive. Therefore, it is possible to easily switch over between a state in which the electric current flowing through a coil is gradually reduced and a state in which the electric current flowing through the coil is rapidly reduced by switching the switch means between conduction and cutoff. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      A structural arrangement and method for carrying out the present invention is described below by reference to a preferred embodiment of the present invention shown in the attached drawings, wherein:  
       FIG. 1  is a schematic diagram of a brake fluid pressure circuit of a passenger vehicle brake system;  
       FIG. 2  is a cross-sectional side view of a normally open solenoid valve used in the circuit shown in  FIG. 1 ;  
       FIG. 3  is a graph illustrating the change in attractive force between the fixed core and armature of the solenoid valve shown in  FIG. 2  with the change in stroke of a valve stem;  
       FIG. 4  is a schematic diagram showing the arrangement of a drive circuit of the normally open solenoid valve shown in  FIG. 1  in a controller according to a preferred embodiment of the present invention;  
       FIG. 5A  is a graph illustrating the gradual change in electric current passing through the coil when the switch means provides conduction between the diode and ground of the drive circuit shown in  FIG. 4 ; and  
       FIG. 5B  is a graph illustrating the rapid reduction in electric current passing through the coil when the switch means cuts off conduction between the diode and ground of the drive circuit shown in  FIG. 4 .  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1 , a tandem master cylinder M includes first and second output ports  1  and  2  that generate a brake fluid pressure according to the pressure applied to a brake pedal P by the foot of a vehicle driver. Fluid pressure control valve means VA and VB are provided between a first output fluid pressure path  3  connected to the first output port  1 , and a left front wheel brake BA and right rear wheel brake BB, respectively. Fluid pressure control valve means VC and VD are provided between a second output fluid pressure path  4  connected to the second output port  2 , and a right front wheel brake BC and left rear wheel brake BD, respectively.  
      The fluid pressure control valve means VA to VD include normally open solenoid valves  5 A to  5 D, respectively. The solenoid valves  5 A to  5 D correspond to the left front wheel brake BA, right rear wheel brake BB, right front wheel brake BC, and left rear wheel brake BD, respectively. Check valves  7 A to  7 D are connected in parallel to a corresponding normally open solenoid valve  5 A to  5 D. A normally closed solenoid valve  6 A to  6 D is provided for a corresponding wheel brake BA to BD.  
      The normally open solenoid valves  5 A and  5 B corresponding to the first output fluid pressure path  3  are disposed between the first output fluid pressure path  3 , and the left front wheel brake BA and right rear wheel brake BB. The normally closed solenoid valves  6 A and  6 B corresponding to the first output fluid pressure path  3  are disposed between a single first reservoir  8 A, the left front wheel brake BA, and the right rear wheel brake BB. Connected to the first reservoir  8 A, via a first suction valve  9 A, is the suction side of a first pump  10 A capable of drawing brake fluid from the first reservoir  8 A. The discharge side of the first pump  10 A is connected to the first output fluid pressure path  3  via a first discharge valve  11 A and a first damper  12 A.  
      The normally open solenoid valves  5 C and  5 D corresponding to the second output fluid pressure path  4  are disposed between the second output fluid pressure path  4 , and the right front wheel brake BC and left rear wheel brake BD. The normally closed solenoid valves  6 C and  6 D corresponding to the second output fluid pressure path  4  are disposed between a single second reservoir  8 B, the right front wheel brake BC, and the left rear wheel brake BD. Connected to the second reservoir  8 B, via a second suction valve  9 B, is the suction side of a second pump  10 B capable of drawing brake fluid from the second reservoir  8 B. The discharge side of the second pump  10 B is connected to the second output fluid pressure path  4  via a second discharge valve  11 B and a second damper  12 B.  
      Each check valve  7 A to  7 D is connected, in parallel, to a corresponding normally open solenoid valve  5 A to  5 D so as to allow the brake fluid to flow from the corresponding wheel brake BA to BD to the master cylinder M.  
      A controller C controls operation of the fluid pressure control valve means VA to VD. In other words, the controller C controls operation of the normally open solenoid valves  5 A to  5 D, the normally closed solenoid valves  6 A to  6 D, and the first and second pumps  10 A and  10 B.  
      During normal braking when there is no possibility of the wheels locking, the fluid pressure control valve means VA to VD are controlled by the controller C so as to provide communication between the master cylinder M and the wheel brakes BA to BD while blocking communication between the wheel brakes BA to BD and the reservoirs  8 A and  8 B. In other words, the normally closed solenoid valves  6 A to  6 D are each in a closed state since they are de-energized, and the normally open solenoid valves  5 A to  5 D are each in an open state since they are de-energized. As a result, the brake fluid pressure output from the first output port  1  of the master cylinder M is applied to the left front wheel brake BA via the normally open solenoid valve  5 A and to the right rear wheel brake BB via the normally open solenoid valve  5 B. Also, the brake fluid pressure output from the second output port  2  of the master cylinder M is applied to the right front wheel brake BC via the normally open solenoid valve  5 C and to the left rear wheel brake BD via the normally open solenoid valve  5 D.  
      When a wheel is about to lock during braking, among the fluid pressure control valve means VA to VD, the controller C controls the fluid pressure control valve means corresponding to the wheel that is about to lock so that communication between the master cylinder M and the wheel brake BA to BD is blocked and communication between the wheel brake BA to BD and the corresponding reservoir  8 A or  8 B is provided. In other words, among the normally open solenoid valves  5 A to  5 D, the normally open solenoid valve corresponding to the wheel that is about to lock is closed by energizing the corresponding normally open solenoid valve. Likewise, the normally closed solenoid valve  6 A to  6 D corresponding to the wheel that is about to lock is opened by energizing the corresponding normally closed solenoid valve. In this way, a part of the brake fluid pressure of the wheel that is about to lock is absorbed by the first reservoir  8 A or the second reservoir  8 B, thereby reducing the brake fluid pressure of the wheel that is about to lock.  
      When a constant brake fluid pressure is maintained, the controller C controls the fluid pressure control valve means VA to VD so that the wheel brakes BA to BD are cut off from the master cylinder M and the reservoirs  8 A and  8 B. In other words, the normally open solenoid valves  5 A to  5 D are closed by energizing them while simultaneously the normally closed solenoid valves  6 A to  6 D are closed by de-energizing them. When the brake fluid pressure is increased, the normally closed solenoid valves  6 A to  6 D are closed by de-energizing them, and at the same time, by controlling the electric current applied to the normally open solenoid valves  5 A to  5 D, the fluid pressure on the downstream side of the normally open solenoid valves  5 A to  5 D is linearly controlled according to the applied electric current.  
      The first and second pumps  10 A and  10 B are controlled by the controller C so as to operate when the above-mentioned anti-lock brake control is occurring, and the brake fluid in the first and second reservoirs  8 A and  8 B is returned to the master cylinder M side via the first and second pumps  10 A and  10 B. Returning the brake fluid in this way prevents any increase in the depression amount of the brake pedal P due to the brake fluid absorbed by the first and second reservoirs  8 A and  8 B. Moreover, since pulsations in the discharge pressure of the first and second pumps  10 A and  10 B can be absorbed by the first and second dampers  12 A and  12 B, the return of brake fluid does not interfere with the operational feel of the brake pedal P.  
      When anti-lock brake control is carried out in this way, on and off control of the normally closed solenoid valves  6 A to  6 D is carried out by the controller C. The normally open solenoid valves  5 A to  5 D are controlled by an intermediate value of electric current between on and off as well as by the on and off control. Among the normally open solenoid valves  5 A to  5 D which are arranged so as to change the fluid pressure on the wheel brake BA to BD side linearly according to the electric current applied at such an intermediate value, the arrangement of the normally open solenoid valve  5 A is explained below by reference to  FIG. 2 .  
      In  FIG. 2 , the normally open solenoid valve  5 A is formed from a solenoid part  14  that exerts an electromagnetic force and a valve part  15  driven by the solenoid part  14 . The valve part  15  is housed within a mounting hole  17  provided in a fixed support block  16  and opens on one face  16   a  of the support block  16 . The solenoid part  14  extends from the one face  16   a  of the support block  16 .  
      The valve part  15  includes a valve housing  18  formed from magnetic metal in the shape of a stepped cylinder. The valve housing  18  is fitted within the mounting hole  17  of the support block  16 . Fitted on the inner face of the mounting hole  17  toward the open end is a stop ring  19  which engages the valve housing  18  to prevent the valve housing  18  from detaching from the mounting hole  17 . Annular seals  20  and  21  are mounted on the outer face of the valve housing  18  in two positions spaced apart from each other in the axial direction. An annular chamber  22  is formed between the seals  20  and  21  and between the support block  16  and the valve housing  18 .  
      A cylindrical valve seat member  23  is press-fit and fixed within the valve housing  18 . Furthermore, slidably fit within the valve housing  18  is a non-magnetic valve stem  24 . An output chamber  25  is formed between a lower end of the valve stem  24  and the valve seat member  23 . Fixed to the lower end of the valve stem  24  is a spherical valve body  26  positionable on a valve seat  23   a  formed in the valve seat member  23  so as to face the output chamber  25 . Moreover, disposed between the lower end of the valve stem  24  and the valve seat member  23  is a return spring  27  which biases the valve stem  24 , that is, the valve body  26 , in a direction so as to unseat the valve body  26  from the valve seat member  23 .  
      A filter  29  mounted in the valve housing  18  is disposed between the valve seat member  23  and a fluid pressure path  28  provided in the support block  16  so as to communicate with the first output fluid pressure path  3 . Furthermore, another filter  30  is mounted around the outer surface of the valve housing  18  in a region so as to face or oppose the annular chamber  22 . A passage  31  disposed in the valve housing  18  provides communication between the output chamber  25  and the annular chamber  22  via the filter  30 . The annular chamber  22  communicates with the wheel brake BA through a fluid pressure path  32  provided in the support block  16 . Moreover, disposed in the valve housing  18  between the valve seat member  23  and the filter  29  is the check valve  7 A that opens when the pressure of the fluid pressure path  28  becomes lower than that of the annular chamber  22 , thus returning the brake fluid of the annular chamber  22  to the fluid pressure path  28  side.  
      The solenoid part  14  includes a fixed core  35  with an armature  36  coaxially connected to the upper end of the valve stem  24  of the valve part  15  and facing the fixed core  35 . A guide tube  37  guides the movement of the armature  36  toward and away from the fixed core  35 . A bobbin  38  surrounds the guide tube  37 . A coil  39  is wound around the bobbin  38  with a magnetic path frame  40  surrounding the coil  39 . Also, a coil spring  41  is disposed between the magnetic path frame  40  and the bobbin  38 .  
      The fixed core  35  has a cylindrical shape and is coaxially connected, in an integral manner, to the center of a first end of the valve housing  18 . The guide tube  37  is formed from a non-magnetic material, such as, for example only, stainless steel, in a thin, bottomed cylindrical shape with a hemispherical closed end. Fitted into the open end of the guide tube  37  is an extremity of the fixed core  35 , wherein the open end of the guide tube  37  is secured to the fixed core  35  by, for example, welding. When the valve housing  18  is mounted in the mounting hole  17 , the guide tube  37  extends from the face  16   a  of the support block  16 .  
      The bobbin  38  is formed from a synthetic resin so as to have a center hole  38   a  through which the guide tube  37  runs, and the coil  39  is wound around the bobbin  38 .  
      The magnetic path frame  40  includes a magnetic path tube  42  surrounding the bobbin  38  and coil  39 . Joined by caulking to one end of the magnetic path tube  42  is a ring-shaped magnetic path plate  43  that is in contact with the bobbin  38  so that the closed end of the guide tube  37  extends from the center of the plate  43 .  
      Integral with the other end of the magnetic path frame  42  is a ring-shaped contact plate  42   a  that contacts the first end of the valve housing  18  around the fixed core  35 . The base part of the fixed core  35  mates with the inner circumference of the contact plate  42   a . One end of the coil spring  41  contacts the contact plate  42   a  while the other end of the coil spring contacts the bobbin  38 .  
      Housed within the guide tube  37  is the armature  36  which is movable toward and away from the fixed core  35 . The upper end of the valve stem  24  which movably runs through the fixed core  35  is in coaxial contact with the armature  36 . Since the valve stem  24  is biased by the spring force of the return spring  27  in a direction so as to unseat the valve body  26  from the valve seat member  23 , and the upper end of the valve stem  24  is in constant contact with the armature  36 , the valve stem  24 , that is, the valve body  26 , moves in the axial direction in response to the axial movement of the armature  36 .  
      When there is no magnetic force to attract the armature  36  toward the fixed core  35 , the armature  36  is moved back by the spring force of the return spring  27  to a position where it is received by the closed end of the guide tube  37 . In this position, the valve body  26  is unseated from the valve seat member  23 , and the normally open solenoid valve  5 A is open. When the armature  36  is magnetically attracted toward the fixed core  35  until the valve body  26  is seated on the valve seat member  23 , the normally open solenoid valve  5 A is closed.  
      The resultant of the fluid pressure force due to the fluid pressure of the output chamber  25  and the spring force of the return spring  27  acts on the lower end of the valve stem  24 , and a magnetic attraction force that attracts the armature  36  toward the fixed core  35  acts on the upper end of the valve stem  24 . As a result, the valve stem  24  undergoes a stroke motion so that the resultant of the fluid pressure force and the spring force balances the magnetic attraction force. Controlling the amount of electric current applied to the coil  39  by, for example, duty control of the controller C so that the amount is at an intermediate value between the on and off values, changes the magnetic attraction force that attracts the armature  36  toward the fixed core  35 .  
      Tapered opposing faces  35   a  and  36   a  of the fixed core  35  and the armature  36  each have a diameter that increases in a direction away from the output chamber  25 .  
      The tapered shape of the opposing faces  35   a  and  36   a  of the fixed core  35  and the armature  36  permits the change in the opposite distance, that is, the distance in a direction perpendicular to the tapered faces, between the fixed core  35  and the armature  36  to be small relative to the travel distance of the axial stroke of the armature  36 , so that the change in the attractive force generated between the opposing faces  35   a  and  36   a  is smaller than the change in the axial stroke of the armature  36 . The actual attractive force in the axial direction is the component of the attractive force generated between the opposing faces  35   a  and  36   a . Accordingly, the sharper the angle of the tapered faces, the smaller the change in axial attractive force relative to the change in attractive force between the opposing faces  35   a  and  36   a.    
      As shown by the solid lines in  FIG. 3 , the attractive force between the fixed core  35  and the armature  36  is substantially flat or constant in a working range between the fully closed state and the fully open state of the valve part  15 . On the other hand, when the opposing faces  35   a  and  36   a  of the fixed core  35  and the armature  36  are flat and perpendicular relative to the axial direction, since the opposing distance between the fixed core  35  and the armature  36  varies proportional to the axial stroke of the valve stem  24 , the attractive force between the fixed core  35  and the armature  36  varies or is not constant in the working range, as shown by the broken lines in  FIG. 3 .  
      The controller C includes a drive circuit, shown in  FIG. 4 , that drives the normally open solenoid valve  5 A. The drive circuit includes energization control means  46  provided between a power source  45  and the coil  39  to control the energization/de-energization of the coil  39 . A diode  47  is connected between the power source  45  and ground while bypassing the coil  39 . Switch means  48  is provided between the diode  47  and ground.  
      The energization control means  46  includes a PNP transistor  51  having an emitter connected to the power source  45 . Resistors  52  and  53  and an NPN transistor  54  are connected in series between the power source  45  and ground. Resistors  56  and  57  are connected in series between a control signal input terminal  55  and ground. The junction between the resistors  52  and  53  is connected to the base of the PNP transistor  51 , and the junction between the resistors  56  and  57  is connected to the base of the NPN transistor  54 .  
      The NPN transistor  55  conducts in response to a high level control signal being input into the control signal input terminal  55 , which results in the PNP transistor  51  conducting.  
      The coil  39  is connected to the collector of the PNP transistor  51  and grounded via a resistor  58 . The diode  47  is connected to the collector of the PNP transistor  51  to allow electric current to flow toward the power source  45 .  
      The switch means  48  includes a PNP transistor  59  having an emitter connected to the diode  47 . Resistors  60  and  61  and an NPN transistor  62  are connected in series between the diode  47  and ground. Resistors  64  and  65  are connected in series between a control signal input terminal  63  and ground. The junction between the resistors  60  and  61  is connected to the base of the PNP transistor  59 , and the junction between the resistors  64  and  65  is connected to the base of the NPN transistor  62 .  
      The NPN transistor  62  conducts in response to a high level control signal being input into the control signal input terminal  63 , which results in the PNP transistor  59  conducting.  
      An amplifier  66  is connected across opposite ends of the resistor  58  and the output of the amplifier  66  is output from a terminal  67 . The output from the terminal  67  is used for feedback control of the energizing electric current provided to the coil  39 .  
      In the drive circuit, the diode  47  gradually reduces the electric current flowing through the coil  39  when energization of the coil  39  is stopped. Although the diode  47  exhibits this function when the switch means  48  provides conduction between the diode  47  and ground, the diode  47  does not exhibit this function when the switch means  48  cuts off conduction between the diode  47  and ground.  
      In other words, when the switch means  48  provides conduction between the diode  47  and ground, the electric current passing through the coil  39  gradually decreases when energization the coil  39  is stopped, as shown in  FIG. 5A . When the switch means  48  cuts off conduction between the diode  47  and ground, the electric current passing through the coil  39  rapidly reduces when energization of the coil  39  is stopped, as shown in  FIG. 5B .  
      The other normally open solenoid valves  5 B,  5 C, and  5 D have the same arrangement as that of the normally open solenoid valve  5 A.  
      Next, the operation of the preferred embodiment is explained. In the normally open solenoid valves  5 A to  5 D disposed between the master cylinder M and the corresponding wheel brake BA to BD, the opposing faces  35   a  and  36   a  of the fixed core  35  and the armature  36  are formed to be tapered in shape, and the amount of electric current applied to the coil  39  is controlled by the controller C so as to be on or off, or at an intermediate value between the on and off values.  
      In the normally open solenoid valves  5 A to  5 D, since the attractive force between the fixed core  35  and the armature  36  may be freely changed and, moreover, the opposing faces  35   a  and  36   a  of the fixed core  35  and the armature  36  are tapered, the change in the opposing distance between the fixed core  35  and the armature  36  is small compared with the amount of axial stroke of the armature  36 , and the attractive force between the fixed core  35  and the armature  36  is substantially flat or constant in the working range, as shown in  FIG. 3 .  
      The valve stem  24  therefore operates so that the force acting on the lower end of the valve stem  24  based on the fluid pressure of the output chamber  25 , that is, the output fluid pressure of the normally open solenoid valves  5 A to  5 D, balances the attractive force acting on the armature  36 . Accordingly, the brake fluid pressure is linearly controlled by the normally open solenoid valves  5 A to  5 D, and the fluid pressure on the wheel brakes BA to BD side is linearly changed. It is thus possible to improve the operational feeling of the brake pedal P by preventing kick-back from occurring in the master cylinder M.  
      The normally closed solenoid valves  6 A to  6 D disposed between the reservoirs  8 A and  8 B and the wheel brakes BA to BD are controlled so as to be on or off. The normally closed solenoid valves  6 A to  6 D are closed to reliably prevent leakage of the brake fluid when the fluid pressure is linearly controlled by the normally open solenoid valves  5 A to  5 D. Thus, the precision of brake pressure control of the wheel brakes BA to BD is enhanced.  
      Furthermore, since the normally open solenoid valves  5 A to  5 D are formed to be linear by slightly modifying a conventional on/off normally open solenoid valve, the dimensions do not increase, thus avoiding any increase in the dimensions of the fluid pressure control valve means VA to VD.  
      The drive circuit of the controller C for driving the normally open solenoid valves  5 A to  5 D includes the energization control means  46  provided between the power source  45  and the coil  39  so as to control the energization/de-energization of the coil  39 . The diode  47  is connected between the power source  45  and ground while bypassing the coil  39 . The switch means  48  is provided between the diode  47  and ground. Switching over the switch means  48  between conduction and cutoff results in the switching over between a state in which the diode  47  is active and a state in which the diode  47  is substantially inactivated.  
      It is therefore possible to easily switch over between a state in which the electric current flowing through the coil  39  is gradually reduced and a state in which the electric current flowing through the coil  39  is rapidly reduced by switching over the switch means  48  between conduction and cutoff. As a result, both a smooth control in which the fluid pressure of the wheel brake BA to BD is linearly controlled by controlling the amount of electric current applied to the coil  39  at an intermediate value between the on and off values, and a rapid control to shift between the on state (valve closed) and the off state (valve open) can be achieved.  
      An embodiment of the present invention has been described in detail above, but the present invention is not limited to this embodiment and can be modified in a variety of ways without departing from the spirit and scope of the invention described in the claims.  
      For example, although in the preferred embodiment, the energization control means  46  is provided between the power source  45  and the coil  39 , the energization control means  46  may be provided between the coil  39  and ground. Also, the switch means  48  may be provided between the power source  45  and the diode  47 .