Abstract:
A spool valve includes a groove defined in the spool and a notch. A line  A  is drawn to extend through a communication zone a provided upon communication of the notch which is disposed at a distal end of the line A and defined in a step of a spool with an input port to form a 69° angle with respect to an L-axis. Fluid flowing into the groove through the communication zone a upon communication of the notch with the input port, does not collide with other portions of the spool before colliding with a bottom of the groove. Therefore, the flow of the fluid along the L-axis causes a flow force applied to the spool to be suppressed resulting in a decreased load on an actuator. The notch makes it is possible to ensure the stable operation of a spool valve, while preventing the self-induced vibration of the spool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a spool valve having notches provided in a step between a land and a groove in a spool. 
     2. Description of the Related Art 
     Such a spool valve is known from Japanese Utility Model Registration Nos. 2568961 and 2580463. 
     FIGS. 9 and 10 show the structure of a conventional pressure-controlling spool valve having a proximal end toward a direct drive-type linear solenoid  26  and a distal end away from the solenoid. An input port  13 , an output port  14 , a drain port  15  and a feedback port  16  are open along an axis, L, into a valve bore  12  which is circular in cross section and defined in a valve housing  11 . A spool  17  is slidably received in the valve bore  12  in the valve housing  11  and includes a first land  18 , a second land  19 , a third land  20 , a spring seat  21  extending from a distal end of the third land  20 , a first groove  22  defined between the first land  18  and the second land  19 , a second groove  23  defined between the first land  18  and the third land  20 , and a solenoid connection  24  extending from a proximal end of the second land  19 . The spool  17  is biased proximally by a valve spring  25  disposed between an end of the valve bore  12  and the spring seat  21  to coaxially abut against a distal end of an output rod  27  of the direct drive-type linear solenoid  26  for directly operating the spool  17 . 
     The first groove  22  in the spool  17  is connected to a proximal end of the first land  18  through a first step  28 . The first step  28  is perpendicular to the L-axis and axially disposed from the second land  19  through a second step  29  perpendicular to the L-axis. A predetermined number of (e.g., four) notches  30  are defined in the first step  28  by chamfers inclined at 30° with respect to the L-axis. When the spool  17  is in a position as shown in FIG. 9, the input port  13  is in communication with the output port  14  through the first groove  22 . When the spool  17  is moved proximally, to cut off the communication between the input port  13  and the first groove  22 , the output port  14  is brought into communication with the drain port  15  through the first groove  22 . A feedback pressure is applied to an oil chamber  31  provided distally of the third land  20  through the feedback port  16 . An oil chamber  32  defined between the first land  18  and the third land  20  communicates with the spool  17  through an oil bore  33  defined to connect the first groove  22  and the second groove  23  to each other. 
     In the spool valve having the above-described arrangement, when the linear solenoid  26  is excited to drive the output rod  27  distally, thereby urging the proximal end of the spool  17  against a repulsive force of the valve spring  25 , the input port  13  is put into communication with the output port  14  through the first groove  22 , such that the hydraulic pressure in the input port  13  is reduced depending on the opening degree thereof and delivered from the output port  14 . In this case, the amount of pressure changed in the output port  14  relative to the amount of change in position of the spool  17  can be decreased to inhibit a self-induced vibration of the spool  17 . 
     In the above prior art, the oil supplied from the input port  13  is passed through the notches  30  into the first groove  22 . The oil flows within the first groove  22  in the direction of the L-axis to collide with the second step  29 , thereby producing a flow force Fo for biasing the spool  17  proximally. The flow force Fo acts to oppose a distal drive force Fs generated by the linear solenoid  26 , causing the smooth operation of the linear solenoid  26  is obstructed. As a result, it is difficult to conduct a subtle hydraulic pressure control. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to ensure that the notches are defined in the spool to suppress the generation of a flow force, thereby stabilizing the operation of the spool valve, while preventing the generation of vibration. 
     To achieve the above object, according to a first aspect and feature of the present invention, there is provided a spool valve comprising a valve housing having a valve bore, an input port and an output port axially spaced within the valve housing and opening into the valve bore. A spool is received in the valve bore for sliding movement in the axial direction. A first land and a second land are formed on the spool and spaced along the axis. A groove is defined in the spool and connected to the first and second lands through first and second steps. A notch is formed by a cutout portion from the first step. Also, an actuator drives the spool in the axial direction, so that the spool is driven by the actuator to put the input port into communication with the groove. When the input port is put into communication with the groove, a fluid flowing into the groove through the input port is discharged from the output port through the groove. The notch in the spool is formed so that a line, which extends through a communication zone provided upon communication of the notch with the input port, and which forms a free flow-in angle with respect to the axial direction, first intersects a bottom of the groove. 
     With the above arrangement, when the notch is put into communication with the input port, the fluid flowing into the groove through the communication zone does not collide with other portions of the spool, before colliding with the bottom of the groove. Therefore, the flow of the fluid in the axial direction, which causes the flow force applied to the spool, is suppressed and the load on the actuator is decreased. Thus, it is possible to decrease the flow force applied to the spool to achieve the stable operation of the spool valve, while preventing the self-induced vibration of the spool as a result of the notch cut out from the first step. 
     According to a second aspect and feature of the present invention, the free flow-in angle is 69°, which corresponds to a maximum free flow-in angle. Hence, even if the free flow-in angle becomes equal to 69°, corresponding to the maximum free flow-in angle in accordance with the shape of the notch and the opening degree of the input port, the flow force applied to the spool can be suppressed so as to be small. 
     According to a third aspect and feature of the present invention, the notch is formed in a direction perpendicular to the axis. The notch can be made by an end mill, resulting in enhanced workability. 
     According to a fourth aspect and feature of the present invention, there is provided a spool valve comprising a valve housing having a valve bore, an input port and an output port defined in the valve housing and spaced along an axis and opening into the valve bore. A spool is received in the valve bore for sliding movement in the axial direction. A first land and a second land are formed on the spool and spaced along the axis. A groove is defined in the spool and connected to the first and second lands through first and second steps, respectively. A notch is formed as a cutout portion from the first step, and an actuator for driving the spool in the axial direction, puts the input port into communication with the groove, so that a fluid flowing into the groove through the input port is discharged from the output port through the groove. A concave curved face is formed on a bottom of the groove. The notch in the spool is formed so that a line, which extends through a communication zone provided upon communication of the notch with the input port and which forms a free flow-in angle of a jet formed by the notch, points to a portion of the curved face displaced from a smallest-diameter portion toward the first step. 
     With the above arrangement, a fluid flowing into the groove upon communication of the notch in the spool with the input port, before colliding with the bottom of the groove, does not collide with other portions of the spool. Therefore, the momentum of the fluid causing a flow force applied to the spool can be suppressed to decrease the load on the actuator. Particularly, a portion, against which the fluid flowing into the groove through the communication zone first collides, is that portion of the concave curved face formed in the groove, which is displaced from the smallest-diameter portion toward the first step. Therefore, the fluid is guided to the curved face, where the fluid is then turned smoothly and radially outwards. Hence, the flow force can be effectively be further decreased. Thus, the flow force applied to the spool can be decreased to ensure the stable operation of the spool valve, while preventing the self-induced vibration of the spool because of the notch in the first step. 
     According to a fifth aspect and feature of the present invention, the portion of the curved face displaced from the smallest-diameter portion toward the second step points toward the output port. Hence, the fluid can be guided smoothly to the output port, so that the flow force can be further decreased. 
     According to a sixth aspect and feature of the present invention, the free flow-in angle is 69°, which corresponds to a maximum free flow-in angle. Hence, even if the free flow-in angle becomes equal to 69° corresponding to the maximum free flow-in angle in accordance with the shape of the notch and the opening degree of the input port, the flow force applied to the spool can be suppressed so as to be small. 
     According to a seventh aspect and feature of the present invention, the notch is formed in a direction perpendicular to the axis. Hence, the notch can be made by an end mill, resulting in enhanced workability. 
     According to an eighth aspect and feature of the present invention, the notch comprises a face extending contiguously from the communication zone to the curved face. Hence, the fluid flowing into the groove through the communication zone can be guided to the output port with the momentum thereof suppressed to the minimum, so that the flow force applied to the spool can be further decreased. 
     A linear solenoid  26  in each of embodiments corresponds to the actuator of the present invention, and a first groove  22  in each of the embodiments corresponds to the groove of the present invention. 
     The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to  3  show a first embodiment of the present invention, wherein 
     FIG. 1 is a vertical sectional view of a spool valve; 
     FIG. 2 is a perspective view of a spool; 
     FIG. 3 is a view for explaining a flow-in angle; 
     FIGS. 4 and 5 show a second embodiment of the present invention, wherein 
     FIG. 4 is a vertical sectional view of a spool valve; 
     FIG. 5 is a perspective view of a spool; 
     FIG. 6 is a vertical sectional view of a spool valve according to a third embodiment of the present invention; 
     FIGS. 7 and 8 show effects of the embodiments, wherein 
     FIG. 7 is a graph showing variations in pressure loss with respect to the flow rate of a fluid; 
     FIG. 8 is a graph showing the risings in clutch hydraulic pressure with respect to the time lapsed from the start of supplying of electric current to a linear solenoid; 
     FIGS. 9 to  11 B show the prior art, wherein 
     FIG. 9 is a vertical sectional view of a spool valve; 
     FIG. 10 is a perspective view of a spool; and 
     FIGS. 11A and 11B are views each showing the shape of a notch in the conventional spool valve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will now be described with reference to FIGS. 1 to  3 . 
     Referring to FIGS. 1 and 2, a spool valve according to a first embodiment of the present invention is of a similar structure as the conventional spool valve described with reference to FIGS. 9 and 10, except that the shape of a notch  34  is different from that of the notch in the conventional spool valve. Therefore, the duplicated description is omitted by designating components or portions corresponding to those in the first embodiment by like reference characters, and thus, the point of difference between the first embodiment and the conventional spool valve, i.e., the structure of the notch  34  will be mainly described. 
     A predetermined number of (e.g., four) notches  34  formed in a first step  28  connecting a first land  18  and a first groove  22  of a spool  17  to each other are each comprised of a partially columnar cutout portion extending in a direction perpendicular to an axis, L. The notches are connected at their opposite ends to an outer peripheral surface of the first land  18  and an outer peripheral surface of the first groove  22 . In this way, the notches  34  are formed in a direction perpendicular to the L-axis and can be made by an end mill, resulting in enhanced workability. 
     An angle at which oil flows into the first groove  22  upon opening of an input port  13  is called a flow-in angle φ. The flow-in angle φ provided when the oil flows in parallel to the L-axis is 0°, and the flow-in angle φ provided when the oil flows perpendicularly to the L-axis is 90°. As shown in FIG. 3, the flow-in angle φ provided when a first step  28  has no notch and an input port  13 , are formed at an angle of 90° with respect to the L-axis is called a free flow-in angle φf. The free flow-in angle φf is increased up to a maximum value (φf=69°) with an increase in opening degree of the input port  13 . In general, the flow-in angle φ provided when the notches  34  are formed in the first step  28  is smaller than the free flow-in angle φf provided when there are no notches provided. Therefore, the flow-in angle φ provided when the notches  34  are formed in the first step  28  cannot exceed 69°. The flow-in angle φ is disclosed in “Hydraulic Pressure Control” written by Toshio Takenaka and Eizo Kamata (issued from Maruzen, Colo.). 
     Returning to FIG. 1, when a line  A  is drawn extending through a communicating zone a provided upon communication between the input port  13  and the first groove  22  toward the L-axis at an angle of 69° (which is the maximum value of the free flow-in angle) with respect to the L-axis, the shape of the notch  34  is determined so that the line A first intersects a bottom of the first groove  22 , but does not intersect other portions of the spool  17 . If the notches  34  are located opposite the flow-in angle φ in the above manner, the flow-in angle φ provided upon opening of the input port  13  is, at the most, smaller than 69°. The oil flowing into the first groove  22  through the input port  13  in the form of a jet can reach the bottom of the first groove  22  without being obstructed by the notches  34 . The jet reaching the bottom of the first groove  22  has a reduced flow speed, and therefore, even if the jet is deflected along the L-axis to flow along the bottom of the first groove  22  and collide with a second step  29 , a generated flow force Fo is suppressed, ensuring the smooth operation of a linear solenoid  26 . 
     In contrast, in the prior art shown in FIG. 11A, the angle of each of the notches  30  is 30° or 45° and the notches protrude toward a proximal side of the line A. For this reason, the jet flowing into the first groove  22  upon opening of the input port  13  is guided to the notches  30  and forcibly deflected proximally along the L-axis and forcefully collides with the second step  29  to produce a large flow force Fo. In the prior art shown in FIG. 11B, the angle of the tip end of the notch  30  is a right angle and the notch  30  is located toward a distal end of the line A, but the step  30   a  of the notch  30  extending in the direction of the L-axis extends in the direction of the proximal side of the line A. For this reason, the jet flowing into the first groove  22  upon opening of the input port  13  is guided to the step  30   a  of the notch  30  and forcibly deflected proximally along the L-axis. At this time, the vigorousness of the jet deflected proximally is also increased to produce a large flow force Fo, because the distance between the step  30   a  of the notch  30  and the input port  13  is small. 
     A second embodiment of the present invention will be described below with reference to FIGS. 4 and 5. 
     A spool valve according to the second embodiment is of a structure similar to that in the first embodiment, except for a difference in that a concave curved face  35  is formed in a first groove  22  of a spool  17  of the spool valve. Therefore, a point of difference, i.e., the shape of the curved face  35  will be mainly described below. 
     In the concave curved face  35  formed on a bottom of the first groove  22 , a smallest-diameter portion b is located at an intermediate portion along the L-axis. A curved face portion extending distally along the L-axis from the smallest-diameter portion b terminates at a location corresponding to a first step  28 . A curved face portion extending proximally along the L-axis from the smallest-diameter portion b terminates at a location short of a second step  29 . 
     When a line A is drawn extending through a communicating zone a provided upon communication of the input port  13  with the first groove  22  toward the L-axis at an angle of 69° (which is the maximum value of the free flow-in angle φf) with respect to the axis L, the shape of the notch  34  is determined, so that the line A first intersects a portion (displaced from the first step  28  toward the smallest-diameter portion b) of the curved face  35  formed on the bottom of the first groove  22 , but does not intersect other portions of the spool  17 . If notches  34  are located on a distal end of the line A in the above manner, the flow-in angle φ provided upon the opening of the input port  13  is, at most, smaller than 69°, the oil flowing into the first groove  22  through the input port  13  in the form of a jet can reach the bottom of the first groove  22  without being obstructed by the notches  34 . The jet reaching the bottom of the first groove  22  has a reduced flow speed and therefore, even if the jet is deflected along the L-axis to flow along the bottom of the first groove  22 , and collide with the second step  29 , a generated flow force Fo is suppressed to a small level, ensuring the smooth operation of a linear solenoid  26 . 
     Moreover, the line A points the portion of the curved face  35  of the first groove  22  displaced from the smallest-diameter portion b toward the first step  28 . As such, the jet first collides against the portion of the curved face  35  of the first groove  22  displaced from the smallest-diameter portion b toward the first step  28 , and is guided radially inwards then gradually turned radially outwards. Thereafter, the jet is guided smoothly toward an output port  14  by a portion of the curved face  35  of the first groove  22  displaced from the smallest-diameter portion b toward the second step  29 . 
     A third embodiment of the present invention will be described below with reference to FIG.  6 . 
     The third embodiment is different from the second embodiment in respect of the shape of a notch  34 . The notch  34  in the second embodiment is formed in the direction perpendicular to the L-axis and, in contrast, the notch  34  in the third embodiment is formed obliquely with respect to the L-axis. The notch  34  extends from a communication zone a between the input port  13  and the first groove  22 , and is linearly connected to a distal end of the curved face  35  without a step. The other construction is similar to that in the second embodiment. 
     According to the present embodiment, a fluid flowing into the groove  22  through the communication zone a is guided smoothly along the notch  34  to the curved face  35 . Therefore, the fluid can be guided to the output port  14  with a reduction in momentum of the fluid suppressed to be a minimum, thereby further reducing the flow force Fo applied to the spool  17 . 
     The effect of the present invention will be described with reference to FIGS. 7 and 8. 
     A graph in FIG. 7 shows the relationship between the flow rate of the oil flowing into the first groove  22  through the input port  13  and the oil pressure in the output port  14  in each of the first and second embodiments and the prior art (shown in FIG. 11A in which θ=30° and θ=45°). The pressure loss is largest in the prior art in which θ=30° and smallest in the prior art in which θ=45° and also in the first and second embodiments. Specifically, the pressure loss is smallest in the second embodiment. 
     A graph in FIG. 8 shows the relationship between the rising of the clutch hydraulic pressure and the time lapsed from the start of supplying of electric current to the linear solenoid  26  in each of the first and second embodiments and the prior art (shown in FIG.  11 A and in which θ=30° and θ=45°). The rising of the clutch hydraulic pressure is earliest in the second embodiment and then latest in the order of the first embodiment and the prior art in which θ=45° and the prior art in which θ=30°, specifically the rising of the clutch hydraulic pressure is latest in the prior art in which θ=30°. 
     As described above, according to the first and second embodiments of the present invention, the flow force Fo can be effectively reduced and therefore, it is possible to prevent an extra load from being applied to the linear solenoid  26  and alleviate the pressure loss and overcome a reduction in responsiveness of the pressure control. In particular, the present invention is advantageous when a direct drive-type linear solenoid  26  is employed as an actuator and previous difficulties in generating large drive force Fs due to a small size of a coil can be eliminated. 
     According to the third embodiment, a further enhancement in performance more than that in the second embodiment is expected in view of a further reduction in flow force Fo. 
     The shape of the notch  34  is not limited to that disclosed in the embodiments and may be changed as desired. The spool valve according to the present invention is applicable to any valve other than the hydraulic pressure control valve. If the communication zone a and the distal end of the curved face  35  are connected smoothly by a curved line in place of the straight line in the third embodiment, further effectiveness can be achieved. 
     Although the embodiments of the present invention have been described in detail, it will be understood that the present invention is not limited to the above-described embodiments, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims.