Brake devices

A brake device has at least one wheel cylinder operable by the pressure of a working liquid. A reservoir stores the working liquid discharged from the at least one wheel cylinder during the operation of an anti-lock braking function. A pump serves to transfer the working liquid from the reservoir. An outlet valve is disposed on the discharge side of the pump. A master cylinder receives the working liquid delivered from the pump via the outlet valve. A pulsation reducing device is disposed on a downstream side of the outlet valve between the pump and the master cylinder. The pulsation reducing device controls the operation speed of the outlet valve in order to reduce possible pulsations produced in the working liquid discharged from the pump.

This application claims priority to Japanese patent application serial number 2003-330300, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to brake devices having a pump that serves to pump a working liquid previously discharged into a reservoir from the wheel cylinders and to deliver the working liquid to a master cylinder via a discharge valve associated with the pump.

2. Description of the Related Art

In general, brake devices have a master cylinder and a wheel cylinder(s). The master cylinder serves to pressurize a working liquid in response to the operation of a brake pedal so as to deliver hydraulic pressure via the working liquid to the wheel cylinder(s). The wheel cylinder(s) then functions to press the friction surfaces of brake pads against a brake disk as a result of the pressure of the working liquid.

Brake devices having an anti-lock function for preventing a wheel(s) from being locked up during braking (i.e., stopping rotation while the vehicle is still moving) are also known. These types of brake devices typically have an actuator that includes a reservoir and a pump. The reservoir serves to store the working liquid that is discharged from the wheel cylinder(s) when the pressure of the wheel cylinder(s) is to be reduced (thereby, eliminating or preventing the locking effect upon the wheel). The pump then serves to pump the working liquid stored within the reservoir in order to deliver the working liquid to the master cylinder. Conventionally, a reciprocating pump (e.g., a plunger pump) has been generally used as a pump for this type of brake device. Japanese Laid-Open Patent Publication No. 8-230642 and U.S. Pat. No. 6,000,764 teach such brake devices.

However, the working liquid discharged from the reciprocating pump naturally has pulsations in pressure. Such pulsations may cause vibrations of various pipelines, the master cylinder, etc., of the brake device, possibly producing unpleasant vibration sounds. In addition, vibrations may be transmitted to the vehicle body and create an uncomfortable feeling or sensation for passengers.

In order to reduce the effects of pulsations of the working liquid, there has been proposed to provide a damper chamber on the downstream side of the pump. However, in many cases it has been difficult to effectively suppress the pulsations only by the provision of the damper chamber.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to teach improved techniques for effectively reducing pulsations in the pressure of a working liquid discharged from a pump of a brake device.

According to one aspect of the present teachings, brake devices are taught that include at least one wheel cylinder operable by the pressure of a working liquid, a reservoir for storing the working liquid discharged from the at least one wheel cylinder, a pump for pumping the working liquid from the reservoir, an outlet valve disposed on a discharge side of the pump, and a master cylinder for receiving the working liquid delivered from the pump via the outlet valve. A pulsation reducing device is disposed on a downstream side of the outlet valve between the pump and the master cylinder. The pulsation reducing device controls the operation speed of the outlet valve in order to reduce possible pulsations produced in the working liquid discharged from the pump.

Therefore, possible pulsations in the working liquid discharged from the pump can be reliably reduced.

In another aspect of the present teachings, the pulsation reducing device controls the operation speed of the outlet valve only with respect to the movement of the outlet valve in an opening direction.

Therefore, the outlet valve may be prevented from being rapidly opened. In other words, the rate of increase in the pressure of the working liquid discharged from the pump via the outlet valve can be lowered. As a result, the peak value of possible pulsations of the discharged working liquid can be lowered, so that the amplitude distribution of the pulsations can be smoothed (i.e., the pulsations can be reduced). On the other hand, when the outlet valve is closed, the outlet valve may not be significantly prevented from moving in the closing direction. Therefore, the outlet valve may rapidly close to prevent the back flow of the working liquid toward the pump via the outlet valve.

In another aspect of the present teachings, the pulsation reducing device controls the operation speed of the outlet valve with respect to the movement of the outlet valve in both opening and closing directions. In addition, the force for suppressing the movement of the outlet valve in the opening direction is greater than the force for suppressing the movement of the outlet valve in the closing direction. In other words, the pulsation reducing device causes the movement of the outlet valve in the opening direction to be at a lower rate than the movement of the outlet valve in the closing direction.

Therefore, the outlet valve may not operate as rapidly to open in comparison with the closing operation, so that the rate of increase of pressure of the working liquid discharged via the outlet valve is lowered. As a result, the peak value of possible pulsations of the discharged working liquid can be lowered, and the amplitude distribution of the pulsations can be smoothed (i.e., the pulsations can be reduced). On the other hand, when the outlet valve is closed, the outlet valve may rapidly close, because the suppressing force against the closing movement of the outlet valve produced by the pulsation reducing device is relatively small. Therefore, the outlet valve can rapidly close to prevent the back flow of the working liquid toward the pump via the outlet valve.

In another aspect of the present teachings, the pulsation reducing device includes a plunger disposed on the downstream side of the outlet valve and movable in response to the movement of the outlet valve, and a support member for movably receiving the plunger. A liquid control chamber is defined within a support hole on one side of the moving direction of the plunger (creating a cylindrical cavity bordered by the support member around the circumference and one axial end and bordered by the plunger on the other axial end). A flow control device serves to provide communication between the liquid control chamber and the outside of the support member. The flow control device also controls the flow rate of the working liquid flowing between the liquid control chamber and the outside of the support member so as to control the moving speed of the plunger.

Thus, the liquid control chamber is defined within the support hole that receives the plunger. The flow control device controls the flow rate of the working liquid flowing between the liquid chamber and the outside of the support member. For example, if the flow rate of the working liquid flowing out of the liquid control chamber is reduced, the plunger may be inhibited in moving toward the liquid control chamber. In other words, the flow control device may control the moving speed of the plunger so that the plunger can modify the opening or closing speed of the outlet valve.

In another aspect of the present teachings, the flow control device has a plurality of communication paths communicating between the liquid control chamber and the outside of the support member. The flow control device is operable to open and close at least one of the communication paths in response to the moving direction of the plunger.

For example, if the movement of the plunger toward the liquid control chamber closes one of the communication paths, the flow rate per unit time of the working liquid flowing out of the liquid chamber may be reduced. The movement of the plunger toward the liquid control chamber may then be restricted. Consequently, the plunger may function to lower the opening speed of the outlet valve.

In another aspect of the present teachings, brake devices are taught that include at least one brake cylinder operable by the pressure of a working liquid. For example, the brake cylinder may be a wheel cylinder for applying a braking force to a wheel of an automobile. A pump serves to deliver the working liquid to the at least one brake cylinder. An outlet valve that may be configured as a check valve is disposed on a discharge side of the pump. A pulsation reducing device is associated with the outlet valve and is operable to control the operating speed of the outlet valve in response to changes in pressure of the working liquid discharged from the pump.

Therefore, the pulsation reducing device may control the pressure of the working liquid discharged from the pump via the outlet valve in order to reduce or minimize the potential pulsations of the working liquid.

In another aspect of the present teachings, the pulsation reducing device serves to reduce the operating speed of the outlet valve as the pressure of the working liquid discharged from the pump increases (for example, when the pressure increase causes the outlet valve to move in the opening direction).

In another aspect of the present teachings, the outlet valve includes a valve member movable in an opening direction by the pressure of the working liquid discharged from the pump. The pulsation reducing device includes a movable member, a support member, a liquid control chamber, a communication device, and a flow control device. The movable member is disposed opposite the valve member along the opening direction of the valve member. The support member serves to support the movable member such that the movable member is slidably movable relative to the support member in a direction parallel to the moving direction of the valve member. The liquid control chamber is a substantially cylindrical cavity defined between the movable member and the support member. The communication device provides communication between the liquid control chamber and the outside of the support member. The flow control device controls the flow of the working liquid that flows through the communication device in response to the movement of the movable member relative to the support member.

In another aspect of the present teachings, the movable member is a plunger and the support member has a support hole defined within the support member in order to slidably receive the plunger. The liquid control chamber is a substantially cylindrical cavity defined by the plunger within the support hole. The plunger borders one axial end of the liquid control chamber on the side of the plunger opposite to the valve member. The support hole borders the circumference and the other axial end of the liquid control chamber. Preferably, the outlet valve is a ball and one end of the plunger opposing to the ball has a spherical concave surface corresponding to an outer peripheral surface of the ball, so that the ball contacts with the plunger via the spherical concave surface of the plunger.

In another aspect of the present teachings, the brake devices further includes a biasing device that biases the plunger in the closing direction of the valve member.

In another aspect of the present teachings, the communication device includes a first communication path defined by the plunger and an inner wall of the support hole. The first communication path has a first end communicating with the liquid control chamber and a second end communicating with the outside of the support member. The flow control device serves to control the flow of the working liquid through the first communication path.

In another aspect of the present teachings, the flow control device includes a control member disposed axially movably within a first recess. The first recess is formed in an outer surface of the plunger. The first recess has a first end and a second end along the axial direction of the plunger. The first end communicates with the liquid control chamber and the second end communicates with the outside of the support member. The first communication path includes a first flow channel defined between the control member and an inner wall of the first recess. The control member is operable to open and close the first flow channel in response to the axial position of the control member relative to the first recess.

In another aspect of the present teachings, the communication device further includes a second communication path. The second communication path includes a second flow channel defined between the control member and an inner wall of the support hole.

In another aspect of the present teachings, the control member is a ring having a thickness in the axial direction of the plunger. The first recess is an annular recess having a width in the axial direction of the plunger. The thickness of the ring is smaller than the width of the annular recess. The first flow channel includes first and second clearances defined on both sides of the ring along the axial direction and a third clearance defined between an inner peripheral surface of the ring and an inner recess wall of the annular recess opposing thereto. The ring closes one of the first and second clearances on the side of the valve member when the plunger moves in the opening direction of the valve member.

In another aspect of the present teachings, the support hole has an open first end opening into the outside of the support member and a closed second end positioned on the side opposing the plunger. The liquid control chamber is defined between the plunger and the closed second end of the support hole.

In another aspect of the present teachings, the support hole has a first end and a second end, each opening to the outside of the support member. The first end is disposed on the side of the valve member and the second end is disposed on the side opposite to the valve member, so that the liquid control chamber is defined between the plunger and the second end of the support hole. The second end of the support hole defines the first flow channel. The flow control device includes a second valve member disposed within the liquid control chamber. The second valve member is operable to open and close the second end of the support hole in response to the pressure within the liquid control chamber.

In another aspect of the present teachings, the communication device further includes a second communication path defined between the plunger and the inner wall of the support hole. The second communication path always communicates between the liquid control chamber and the outside of the support member via the first end of the support hole.

In another aspect of the present teachings, a valve seat is formed within the second end of the support hole, and the second valve member is a ball that is adapted seat against the valve seat in order to close the second end of the support hole.

DETAILED DESCRIPTION OF THE INVENTION

First Representative Embodiment

A first representative embodiment of the present invention will now be described with reference toFIGS. 1 to 6. As shown inFIG. 1, a brake device1according to the first representative embodiment generally includes a brake pedal14, a master cylinder13, and a plurality of wheel cylinders or brake cylinders10(only one wheel cylinder10is shown in the drawings). The brake device1also includes solenoid valves15and16for each wheel cylinder10, a reservoir11, a pump2, and a damper chamber30, that together constitute an actuator for performing an anti-lock braking function. In this first representative embodiment, the brake device1is designed for use with a vehicle, in particular an automobile.

The master cylinder13serves to pressurize a working liquid (brake fluid) in response to a pressing force applied to the brake pedal14. The pressurized working liquid is delivered to each wheel cylinder10via a pipeline P1, the solenoid valve15, and a pipeline P2.

The wheel cylinders10are operable to press friction materials against respective brake disks (not shown) due to the hydraulic pressure of the working liquid, so that the rotation of wheels (not shown) can be inhibited or suppressed. In general, the brake device1has two or four wheel cylinders10that are all connected in parallel with each other to the master cylinder13. Each wheel cylinder10is connected to the reservoir11via the solenoid valve16and a pipeline P3. When any of the wheels begins to lock up during braking, a control unit (not shown) may output signals to close the solenoid valve15and to open the solenoid valve16of the corresponding wheel cylinder10. The working liquid is discharged from the appropriate wheel cylinder10to reduce the hydraulic pressure of the working liquid within the wheel cylinder10. As a result, the locked wheel can be released from a locked condition. The working liquid discharged from the wheel cylinder10is delivered to the reservoir11via the pipeline P3so as to be stored within the reservoir11. The reservoir11is connected to the pump2via a conduit P4.

As shown inFIG. 1, the pump2is configured as a reciprocating pump, in particular a plunger pump. The pump2has a pumping member (pump plunger)20, a flow path P5, and an outlet valve21. When operated, the pump2draws the working liquid from the reservoir11and discharges the working liquid into the damper chamber30via the flow path P5and the outlet valve21. As shown inFIG. 1, the pump2and the damper chamber30are disposed within a housing3. The reservoir11also is disposed within the housing3.

The outlet valve21, serving as a check valve, is configured as a ball positioned on the downstream side of a valve seat22disposed at the outlet end of the flow path P5. The flow path P5may be closed when the outlet valve21seats against the valve seat22. On the other hand, the flow path P5may be open when the outlet valve21is moved away from the valve seat22. The outlet valve21is disposed within the damper chamber30. A pulsation reducing device12also is disposed within the damper chamber30.

The pulsation reducing device12serves to control the opening and closing speed of the outlet valve21in order to reduce possible pulsations in pressure of the working liquid discharged from the pump2. As shown inFIG. 1, the pulsation reducing device12includes a plunger4and a support member5.

As shown inFIG. 2, the plunger4has a substantially cylindrical configuration and has an annular recess42formed in the outer peripheral surface of the plunger4. A ring7is fitted into the annular recess42. The plunger4is inserted into a support hole50formed in the support member5and is slidably movable within the support hole50in an axial direction (the vertical direction as viewed inFIG. 2). A valve support portion41is formed at the lower end of the plunger4and defines a substantially hemispherical concave surface corresponding to the configuration of the outlet valve21. The valve support portion41can provide a location for stably supporting the outlet valve21. For example, scraping, cutting, or otherwise machining the lower end of the plunger4may form the hemispherical concave surface of the valve support portion41. Therefore, when the outlet valve21moves upward (i.e., in an open direction), the outlet valve21is positioned on the valve support portion41and forces the plunger4to move upward.

As shown inFIG. 1, the support member5has a substantially cylindrical configuration and has an outer diameter that is substantially the same as the inner diameter of the damper chamber30. The support member5is inserted into the damper chamber30in order to separate the damper chamber30into a first chamber30aand a second chamber30b.In addition to the support hole50for receiving the plunger4, a communication passage51is formed in the support member5. The communication passage51serves to provide communication between the first chamber30aand the second chamber30b.

As shown inFIG. 2, the support hole50is configured as a bottomed hole. Thus, the support hole50has an opening50aon the side of the first chamber30aand has a closed bottom50bon the side of the second chamber30b.The plunger4is inserted into the support hole50via the opening50a,so that a liquid control chamber63is defined on the insertion side (the upper side as viewed inFIG. 2) of the plunger4. In other words, the liquid control chamber63is defined within the support hole50by an end surface of the plunger4on the insertion side, the bottom50bof the support hole50, and the inner circumferential surface of the support hole50.

A biasing member6is disposed within the liquid control chamber63in order to bias the plunger4in a direction toward the outlet valve21(the downward direction as viewed inFIG. 2). In this representative embodiment, the biasing member6is configured as a coil spring.

As shown inFIG. 2, the pulsation reducing device12includes a flow control device that is constituted by a first communication path60and a second communication path61which provide communication between the liquid control chamber63and the outside of the support member5(i.e., the first chamber30a). As will be described in more detail, the first communication path60is opened and closed in response to the moving direction of the plunger4. More specifically, the first communication path60is opened and closed when the plunger4respectively moves downward and upward.

Thus, the flow control device may control the flow rate per unit of time of the working liquid that flows between the liquid control chamber63and the outside of the support member5. The flow control device will be hereinafter explained in more detail.

As shown inFIG. 2, the first and second communication paths,60and61, are defined between the outer peripheral surface of the plunger4and the inner wall of the support hole50. The first communication path60is configured to extend through the interior of the ring7and the second communication path61is configured to extend through the exterior of the ring7. More specifically, the first communication path60is constituted by path parts60d,60a,60b,60c, and60e, arranged in this sequence from the upstream side of the plunger4(i.e., starting at the opening50a). On the other hand, the second communication path61is constituted by path parts60d,61a, and60e, arranged in this sequence also from the upstream side of the plunger4. The path parts60dand60eare common pat parts for the first and second communication paths60and61and are formed due to the difference between the outer diameter of the plunger4and the inner diameter of the support hole50. As shown inFIG. 2, the path parts60a,60b, and60c, are defined between the inner surface of the annular recess42and the ring7.

More specifically, the path part60a(hereinafter also referred to as “first path part60a”) is defined between the lower end surface71of the ring7and the lower wall42bof the annular recess42. To facilitate this end, the height (thickness) of the ring7is determined so as to be smaller than the width of the annular recess42.

As shown inFIG. 4, a plurality of recesses70(four recesses70are provided in this representative embodiment) is formed in the inner circumferential wall of the ring7and extends through the thickness of the ring7. The path parts60b(hereinafter also referred to as “second path parts60b”) are defined between the recesses70and the inner recess wall42aof the annular recess42.

Further, as shown inFIG. 3, a plurality of recesses42d(four recesses42dare provided in this representative embodiment) are formed in an upper wall surface42cof the annular recess42and extend in radial directions. The path parts60c(hereinafter also referred to as “third path parts60c”) are formed by the recesses42das shown inFIG. 2.

Furthermore, as shown inFIG. 4, a cut-out recess7ais formed in the outer peripheral surface of the ring7and extends throughout the thickness of the ring7. The path part61ais defined between the cut-out recess7aand the inner wall of the support hole50.

The operation of the pulsation reducing device12will now be described with reference toFIGS. 5 and 6. When the pump2is operated to discharge the working liquid, the outlet valve21is forced to move away from the valve seat22as shown inFIG. 5. The outlet valve21then forces the plunger4to move upward, so that the lower wall42bof the annular recess42closely contacts with the lower end surface71of the ring7. As a result, the path part60ais closed, and therefore, the first communication path60is closed.

As the outlet valve21further moves upward, the plunger4moves together with the ring7into the liquid control chamber63. Therefore, the working liquid within the liquid control chamber63is pressurized so as to gradually flow out of the support member5only via the second communication path61, because the first communication path60is closed in this state.

Thus, in this orientation, the working liquid is permitted to flow out of the liquid control chamber63only through the second communication path61. Therefore, the flow rate per unit of time of the working liquid flowing from the liquid control chamber63to the outside of the support member5is relatively small. Because of this reason, there is a relatively slow moving speed of the plunger4in the upward direction.

When the pressure of the working liquid discharged from the pump2decreases, the biasing force of the biasing member6may force the plunger4to move downward, as shown inFIG. 6. Initially, the working liquid may flow into the liquid control chamber63via the second communication path61. As the plunger4continues to move further downward, the lower wall42bof the annular recess42may move away from the lower end surface71of the ring7. As a result, the path part60ais opened, and therefore, the first communication path60is opened. Consequently, the working liquid may flow into the liquid control chamber63through both of the first and second communication paths,60and61.

The flow rate per unit time of the working liquid flowing into the liquid control chamber63may increase when the first communication path60is opened in addition to the second communication path61. Therefore, the moving speed of the plunger4in the downward direction may increase in response to the increase of the flow rate of the working liquid that flows into the liquid control chamber63.

As the plunger4continues to move further downward, the upper wall42cof the annular recess42of the plunger4may contact with the upper end surface72of the ring7. The plunger4then moves together with the ring7in the downward direction. The outlet valve21may be pressed downward by the plunger4and may either move together with the plunger4or move away from the plunger4so as to precede the plunger4.

If the outlet valve21moves together with the plunger4, the moving speed of the outlet valve21coincides with the moving speed of the plunger4. Therefore, in the same manner as the moving speed of the plunger4, the moving speed of the outlet valve21may be controlled by the flow rate of the working liquid flowing into the liquid control chamber63. Because the moving speed of the plunger4in the downward direction (i.e., the closing direction of the outlet valve21) is higher than the moving speed of the plunger4in the upward direction (i.e., the opening direction of the outlet valve21), the outlet valve21can be more rapidly closed.

On the other hand, if the outlet valve21moves so as to precede the plunger4, the movement of the outlet valve21may be primarily influenced by the pressure of the working liquid and may not be influenced or retarded by the pulsation reducing device12. Therefore, the outlet valve21can be more rapidly closed than the rate of the plunger4would have otherwise allowed.

When the outlet valve21is opened, the working liquid discharged from the pump2flows into the first chamber30a,resulting in an increase in the pressure within the first chamber30a.The pressurized working liquid then flows into the second chamber30bvia the communication passage51. The pressurized working liquid further flows into the master cylinder13via a flow path P6and a pipeline P7.

As described above, according to the brake device1of the first representative embodiment, the pulsation reducing device12is provided on the downstream side of the outlet valve21of the pump2(as shown inFIG. 1). The location of the pulsation reducing device12is in order to control the opening and closing speed of the outlet valve21, so as to reduce the pulsations in pressure of the working liquid discharged from the pump2via the outlet valve21.

As described previously, when the outlet valve21is opening (as shown inFIG. 5) the pressure reducing device12suppresses the movement of the outlet valve21in the opening direction. The outlet valve21is not able to quickly open and the rate of increase in pressure of the working liquid discharged via the outlet valve21is low. As a result, the peak value of the pulsations of the discharged working liquid may also be low. Therefore, the distribution of amplitude in pressure of the pulsations may be smoother. In other words, the pulsations may be reduced in intensity.

In order to close the outlet valve21, the outlet valve21may either move away from the plunger4so as to precede the plunger4(i.e., the outlet valve21may travel in the closing direction at a faster rate than the plunger4) or the outlet valve21may move together with the plunger4as shown inFIG. 6. In the case of the situation that the outlet valve21moves apart from the plunger4so as to precede the plunger4, the movement of the outlet valve21is not restricted by the pulsation reducing device12. Therefore, the outlet valve21can quickly close. In the case of the situation that the outlet valve21moves together with the plunger4, the outlet valve21may still quickly close because the restriction force applied to the plunger4by the rest of the pulsation reducing device12is small. Therefore, in either case, the outlet valve21can close relatively quickly to prevent the back flow of the working liquid toward the pumping member20.

Further, the pulsation reducing device12includes the liquid control chamber63(shown inFIG. 2). The flow control device controls the flow rate of the working liquid flowing between the liquid control chamber63and the outside of the support member5. Thus, as the flow rate of the working liquid that is discharged from the liquid control chamber63is decreased, there is an increase in the resistance against the movement of the plunger4into the liquid control chamber63. The flow control device can therefore control the moving speed of the plunger4. Consequently, the flow control device can control the opening and closing speed of the outlet valve21via the plunger4.

Further, as shown inFIG. 2, the liquid control chamber63communicates with the outside of the support member5via the first and second communication paths,60and61. The first communication path60can be opened and closed in response to the moving direction of the plunger4. More specifically, the first communication path60is closed when the plunger4moves towards the liquid control chamber63, and opened when the plunger4moves away from the liquid control chamber63. Therefore, the flow rate per unit of time of the working liquid discharged from the liquid control chamber63may be reduced in order to resist against the movement of the plunger4towards the liquid control chamber63. The result is that the plunger4can lower the opening speed of the outlet valve21.

Second Representative Embodiment

A brake device according to a second representative embodiment will now be described with reference toFIGS. 7 to 11. The brake device according to the second representative embodiment differs from the brake device of the first representative embodiment in that a pulsation reducing device17(shown inFIG. 7) is incorporated in place of the pulsation reducing device12(shown inFIG. 2). In all other respects, the brake device according to the second representative embodiment is the same as the brake device of the first representative embodiment. Therefore, inFIGS. 7 to 11, the same reference numerals are affixed to the same or similar members previously described in the first representative embodiment. The second representative embodiment will only be described with respect to the construction that is different from the first representative embodiment.

Referring toFIG. 7, the pulsation reducing device17includes the plunger4and the support member5. A support hole52is formed in the support member5and extends throughout the thickness of the support member5. The support hole52has a lower opening52aand an upper opening52b.In addition, the support hole52has a tapered portion52cthat has a gradually decreasing diameter towards the upper opening52b.Consequently, the upper opening52bhas a diameter smaller than the diameter of the lower opening52a.

A valve device53, a biasing member6, and the plunger4are inserted into the support hole52in this order from the lower opening52a.

Therefore, a liquid control chamber80is defined between the plunger4and the valve device53. A first communication path81is defined on the upper side of the liquid control chamber80to provide communication between the liquid control chamber80and the second chamber30b.The valve device53is disposed within the first communication path81.

The valve device53includes a valve member54and an inner valve seat member55. The valve member54is configured as a ball. The inner valve seat member55serves to prevent the valve member54from moving in a direction toward the liquid control chamber80. The valve member54has a diameter greater than the diameter of the upper opening52b.The valve member54can close the upper opening52b,and thereby close the first communication path81when the valve member54moves upward.

As shown inFIG. 8, the inner valve seat member55has a substantially annular configuration and has an outer peripheral edge55aand an inner peripheral edge55b.The inner peripheral edge55bhas a diameter smaller than the diameter of the valve member54. In addition, a plurality of radial cutout portions55care formed in the inner valve seat member55and extend radially from the inner peripheral edge55btoward the outer peripheral edge55a.Therefore, when the valve member54has been moved toward the lower opening52aand contacts the inner peripheral edge55bof the inner valve seat member55, the working liquid may still flow through the inner valve seat member55via the cutout portions55c.

The biasing member6, configured as a coil spring as described in connection with the first representative embodiment, is interposed between the plunger4and the inner valve seat member55. The biasing member6biases the plunger4in the downward direction (as viewed inFIG. 7).

A ring8is fitted into the annular recess42of the plunger4. As shown inFIG. 11, a cutout portion8ais formed in the outer peripheral surface of the ring8. As shown inFIG. 7, the cutout portion8aextends throughout the thickness of the ring8, so that a flow channel82bis defined between the ring8and the inner circumferential wall of the support hole52.

In addition, flow channels82aand82care defined by the clearance between the outer peripheral surface of the plunger4and the inner wall of the support hole52. Therefore, a second communication path82is formed by the flow channels82a,82b,and82c,to provide communication between the liquid control chamber80and the first chamber30a.As a result, the liquid control chamber80communicates with chambers outside of the support member5via the first and second communication paths81and82.

The operation of the pulsation reducing device17will now be described with reference toFIGS. 9 and 10. When the working liquid is discharged from the pump2, the outlet valve21moves upward to force the plunger4upward, as shown inFIG. 9. The increasing liquid pressure within the liquid control chamber80causes the valve member54to move upward. As a result, the first communication path81is closed. Therefore, the working liquid only flows out of the liquid control chamber80through the second communication path82, which communicates with the first chamber30a,restricting the movement of the plunger4. Consequently, the movement of the outlet valve21in the opening direction is restricted by the pulsation reducing device17. In other words, the moving speed of the valve21in the opening direction is reduced.

On the other hand, when the pressure of the working liquid discharged from the pump2is decreased, the plunger4may be moved downward by the biasing force of the biasing member6. Then, the pressure is lowered within the liquid control chamber80and the valve member54moves downward to open the first communication path81. The working liquid flows into the liquid control chamber80via both the first and second communication paths81and82. In this way, the downward moving speed of the plunger4is controlled by the pulsation reducing device17. In other words, the plunger4quickly moves to force the outlet valve21in the closing direction. As noted in connection with the first representative embodiment, the outlet valve21may move together with the plunger4or may move away from the plunger4to precede the plunger4in the closing direction.

(Possible Alternative Arrangements of First and Second Representative Embodiments)

(1) Although the plunger is inserted into the support hole formed in the support member in the first and second representative embodiments, this arrangement may be inverted such that the support member is inserted into the plunger. For example, the support member may have a projection extending toward the plunger and the support hole is formed in an upper portion of the plunger in order to receive the projection. A liquid control chamber and a flow control device configured in the same manner as the liquid control chamber and the flow control device of the first representative embodiment (or the second representative embodiment), may be respectively disposed between the projection and the support hole.
(2) In the first and second representative embodiments, the flow control device has two communication paths communicating between the liquid control chamber and the outside of the support member, and one of the flow communication paths is adapted to be opened and closed. However, the number of the communication paths is not limited to two. Thus, three or more communication paths may be provided and any one or more than one of the communication paths may be adapted to be opened and closed.
(3) In the first and second representative embodiments, the plunger4and the outlet valve21are formed as separate members from each other. However, the plunger and the outlet valve may be integrally formed with each other.
(4) In the first representative embodiment, the recesses70formed in the ring7define the second path parts (path parts60b). However, the second path parts may be defined by recesses that are formed in the inner recess wall42aof the annular recess42of the plunger4. In addition, the number of the second paths may not be limited.
(5) In the second representative embodiment, the third path parts (path parts60c) are defined by the recesses42dformed in the upper wall42cof the annular recess42of the plunger4. However, recesses formed in the upper end surface72of the ring7may define the third path parts. In addition, the number of the third paths may not be limited.