Brake hydraulic pressure control apparatus

A brake hydraulic pressure control apparatus includes a reservoir, a brake hydraulic pressure supply device, a hydraulic pump, a plurality of wheel cylinders, a cut valve, a plurality of pressure-increasing solenoid valves, a plurality of pressure-decreasing solenoid valves, a discharge passage including a plurality of relief passages and a circulating passage, a controlling device bringing a brake hydraulic pressure to be applied to the wheel cylinders from the hydraulic pump by disconnecting the brake hydraulic pressure supply device from the wheel cylinders by the cut valve while the pressure-increasing solenoid valves are in an open state, and bringing the brake fluid within the wheel cylinders to be circulated to the reservoir via the discharge passage by operating the pressure-decreasing solenoid valves, and a pulsation transmission decreasing device provided at the discharge passage and decreasing a transmission of a pressure pulsation generated by at least one of the pressure-decreasing solenoid valves.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2009-199336, filed on Aug. 31, 2009, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a brake hydraulic pressure control apparatus.

BACKGROUND DISCUSSION

A known brake hydraulic pressure control apparatus controlling a hydraulic pressure of a wheel cylinder by means of a linear solenoid valve is disclosed in JP2005-162176A (which will be hereinafter referred to as Reference 1). The brake hydraulic pressure control apparatus disclosed in Reference 1 includes a master cylinder pressurizing a brake fluid within a reservoir by a brake pedal operation, cut valves arranged between the master cylinder and wheel cylinders, and a hydraulic pressure supply source including a hydraulic pump for applying a brake hydraulic pressure to the wheel cylinders. The brake hydraulic pressure control apparatus further includes pressure-increasing solenoid valves each formed by a linear solenoid valve and arranged between the hydraulic pressure supply source and the respective wheel cylinders. The wheel cylinders are connected to the reservoir via pressure-decreasing solenoid valves each formed by a linear solenoid valve.

In the brake hydraulic pressure control apparatus disclosed in Reference 1, when the brake pedal is operated in a state where the hydraulic pressure supply source is normally operated, the cut valves disconnect the master cylinder and the wheel cylinders from each other. The hydraulic pressure generated by the hydraulic pressure supply source is regulated and increased to a predetermined value by the pressure-increasing solenoid valves, and is applied to the wheel cylinders. In addition, the brake fluid at each of the wheel cylinders is discharged to the reservoir by operations of the pressure-decreasing solenoid valves so as to control the brake hydraulic pressure within the wheel cylinders in response to the operation of the brake pedal. The brake hydraulic pressure control apparatus disclosed in Reference 1 may include a buffer between the hydraulic pump and the reservoir so as to restrain an extreme decrease of an internal pressure of each of the pressure-decreasing solenoid valves caused by the pump operation. Such brake hydraulic pressure control apparatus is disclosed in JP2008-247354A (which will be hereinafter referred to as Reference 2).

According to the brake hydraulic pressure control apparatus disclosed in Reference 1, relief passages are connected to the respective pressure-decreasing solenoid valves. End portions of the relief passages are connected to a single circulating passage within a housing unit. The circulating passage is connected to the reservoir. The brake hydraulic pressure within each of the wheel cylinders is controlled or adjusted by the pressure-increasing solenoid valves and the pressure-decreasing solenoid valves formed by the linear solenoid valves. Such control is obtained by an adjustment of a valve opening of each of the solenoid valves that is achieved by means of a load balance between an electromagnetic force of a solenoid acting on a valve element, a pressure difference of the brake fluid, and a biasing force of biasing means. Specifically, according to each of the pressure-decreasing solenoid valves, because the valve element is brought to separate from a valve seat, the aforementioned load balance tends to deteriorate and an oscillation of the valve element (i.e., a self-oscillation) may occur. The self-oscillation that occurs at one of the pressure-decreasing solenoid valves causes pulsation of pressure at the relief passage to which the aforementioned pressure-decreasing solenoid valve is connected. The pressure pulsation that occurs at the aforementioned relief passage is transmitted to the other pressure-decreasing solenoid valves formed at the other relief passages. Accordingly, the load balance of the valve element in the other pressure-decreasing solenoid valve that receives the pressure pulsation may be deteriorated and the self-oscillation may occur, which leads to a cause of an operation noise (abnormal noise) of the brake hydraulic pressure control apparatus.

In addition, aeration in which air dissolved in the brake fluid turns to air bubbles in a valve chamber where the valve element is accommodated causes the self-oscillation of the valve element because of insufficient attenuation of the oscillation of the valve element. In such case, the self-oscillation generated at one of the pressure-decreasing solenoid valves is transmitted to the other pressure-decreasing solenoid valve(s), which leads to a cause of the operation noise of the brake hydraulic pressure control apparatus.

According to the brake hydraulic pressure control apparatus disclosed in Reference 1 where the cut valves disconnect the master cylinder from the wheel cylinders and the brake hydraulic pressure applied to the wheel cylinders from the hydraulic pump is controlled by the pressure-increasing solenoid valves and the pressure-decreasing solenoid valves formed by the linier solenoid valves, it is necessary to control the brake hydraulic pressure within each of the wheel cylinders without a generation of the operation noise upon brake operation under a normal driving condition of the vehicle. Thus, prevention of the operation noise upon operation of the brake hydraulic pressure control apparatus is an important issue in regards to the function of the brake hydraulic pressure control apparatus.

In order to decrease an occurrence of self-oscillation of the pressure-decreasing solenoid valve, the buffer is provided between the hydraulic pump and the reservoir so that the extreme decrease of the internal pressure of the pressure-decreasing solenoid valve caused by the pump operation is restrained as disclosed in Reference 2. However, the resulting structure is complicated, which leads to an increase of size and cost of the brake hydraulic pressure control apparatus.

A need thus exists for a brake hydraulic pressure control apparatus which is not susceptible to the drawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a brake hydraulic pressure control apparatus includes a reservoir storing a brake fluid at an inner portion connected to atmospheric air, a brake hydraulic pressure supply device connected to the reservoir and pressurizing the brake fluid that is supplied by the reservoir in response to an operation of a brake pedal, a hydraulic pump suctioning the brake fluid within the reservoir and discharging the brake fluid having a predetermined brake hydraulic pressure, a plurality of wheel cylinders provided at a plurality of wheels of a vehicle respectively and connected to the brake hydraulic pressure supply device, each of the plurality of wheel cylinders generating a braking force at each of the wheels by receiving the brake hydraulic pressure from the hydraulic pump, a cut valve provided between the brake hydraulic pressure supply device and the plurality of wheel cylinders and disconnecting the brake hydraulic pressure supply device from the plurality of wheel cylinders, a plurality of pressure-increasing solenoid valves provided between the hydraulic pump and the respective wheel cylinders, the plurality of pressure-increasing solenoid valves connecting and disconnecting the hydraulic pump relative to the respective wheel cylinders by opening and closing, a plurality of pressure-decreasing solenoid valves connected to the respective wheel cylinders and opening and closing, the pressure-decreasing solenoid valves being formed by linear solenoid valves respectively, a discharge passage including a plurality of relief passages of which first ends are connected to downstream sides of the pressure-decreasing solenoid valves respectively and a circulating passage connecting second ends of the plurality of relief passages to the reservoir, a controlling device controlling the brake fluid within the wheel cylinders to be a predetermined value in response to an operating level of the brake hydraulic pressure supply device in a case where the brake hydraulic pressure supply device is operated, the controlling device bringing the brake hydraulic pressure to be applied to the wheel cylinders from the hydraulic pump by disconnecting the brake hydraulic pressure supply device from the wheel cylinders by the cut valve while the pressure-increasing solenoid valves are each in an open state, and bringing the brake fluid within the wheel cylinders to be circulated to the reservoir via the discharge passage by operating the pressure-decreasing solenoid valves, and a pulsation transmission decreasing device provided at the discharge passage and decreasing a transmission of a pressure pulsation generated by at least one of the pressure-decreasing solenoid valves.

DETAILED DESCRIPTION

A first embodiment disclosed here will be explained with reference toFIG. 1. A brake hydraulic pressure control apparatus1is so-called a brake-by-wire type. The brake hydraulic pressure control apparatus1includes a master cylinder reservoir11serving as a reservoir and a master cylinder12serving as a brake hydraulic pressure supply device. The master cylinder reservoir11stores a brake fluid at an inner portion connected to atmospheric air. The master cylinder12is connected to the master cylinder reservoir11.

The master cylinder12pressurizes the brake fluid in the master cylinder reservoir11in response to an amount of depression of a brake pedal13so that the brake fluid at the same pressure value is discharged to both a primary port12aand a secondary port12b. A stroke sensor13ais attached to the brake pedal13so as to detect the amount of depression of the brake pedal13.

A stroke simulator22is connected to the secondary port12bof the master cylinder12via an on-off valve21. The on-off valve21is a normally closed electromagnetic valve and is able to disconnect the secondary port12band the stroke simulator22from each other. The stroke simulator22includes a cylinder22ain which a piston22bis movably accommodated. Then, a compression spring22cis disposed between an end surface of the piston22band the cylinder22a. The piston22bis fluid-tightly fitted to the cylinder22aso that a hydraulic chamber22dis defined within the cylinder22a. The hydraulic chamber22dis connected to the secondary port12bwhen the on-off valve21is in an open state.

In a case where the on-off valve21is in the open state, a brake hydraulic pressure generated at the secondary port12bis applied to the hydraulic chamber22dto thereby move the piston22bwithin the cylinder22awhile the compression spring22cis being deflected or compressed. Then, the depression amount of the brake pedal13and a reaction force against the brake pedal13appropriate for the generated brake hydraulic pressure at the secondary port12bare obtained.

A suction port of a hydraulic pump32of a hydraulic pressure supply source30is connected to an input port11aof the master cylinder reservoir11via an inlet port91cformed at an outer peripheral surface of a housing unit90(which will be explained later). The hydraulic pump32is driven by an electric motor31so as to suction the brake fluid within the master cylinder reservoir11and discharges the brake fluid having a predetermined brake hydraulic pressure. The hydraulic pressure supply source30also includes an accumulator33accumulating the brake hydraulic pressure obtained by the hydraulic pump32and a relief valve34that is able to return the brake fluid at a discharge side of the hydraulic pump32to the master cylinder reservoir11. The relief valve34is normally in a closed state. In a case where the pressure of the brake fluid discharged from the hydraulic pump32is equal to or greater than a predetermined value, the relief valve34is brought to the open state.

A front-left wheel cylinder WC1, a front-right wheel cylinder WC2, a rear-left wheel cylinder WC3, and a rear-right wheel cylinder WC4(which will be hereinafter collectively referred to as wheel cylinders WC1to WC4) are provided at a front-left wheel FL, a front-right wheel FR, a rear-left wheel RL, and a rear-right wheel RR (which will be hereinafter collectively referred to as wheels FL, FR, RL, and RR), respectively, of a vehicle. The wheel cylinder WC1provided at the front-left wheel FL is connected to the secondary port12bof the master cylinder12. The wheel cylinder WC2provided at the front-right wheel FR is connected to the primary port12aof the master cylinder12.

The wheel cylinders WC1to WC4are connected to the hydraulic pressure supply source30so that the brake hydraulic pressure is applied to the wheel cylinders WC1to WC4from the hydraulic pump32or the accumulator33of the hydraulic pressure supply source30. The wheel cylinders WC1to WC4then generate the braking force for the corresponding wheels FL, FR, RL, and RR.

A first cut valve41is provided between the wheel cylinder WC1and the secondary port12bof the master cylinder12. The first cut valve41is a normally open electromagnetic valve and is closed while operating. The first cut valve41disconnects the wheel cylinder WC1and the secondary port12bfrom each other. In addition, a second cut valve42is provided between the wheel cylinder WC2and the primary port12aof the master cylinder12. The second cut valve42is a normally open electromagnetic valve and is closed while operating. The second cut valve42disconnects the wheel cylinder WC2and the primary port23afrom each other. The first cut valve41and the second cut valve42serve as cut valves.

A first pressure-increasing solenoid valve43is provided between the wheel cylinder WC1and a discharge port of the hydraulic pump32of the hydraulic pressure supply source30. The first pressure-increasing solenoid valve43is a normally-closed linear solenoid valve and is brought to the open state and the closed state when operating. The first pressure-increasing solenoid valve43connects and disconnects the wheel cylinder WC1and the hydraulic pump32with each other. The first pressure-increasing solenoid valve43controls a drive current supplied to a solenoid that is provided at the first pressure-increasing solenoid valve43, to thereby control or adjust an amount of brake fluid supplied to the wheel cylinder WC1from the hydraulic pump32.

A second pressure-increasing solenoid valve44is provided between the wheel cylinder WC2and the hydraulic pump32. The second pressure-increasing solenoid valve44is also a normally-closed linear solenoid valve and is brought to the open state and the closed state when operating. The second pressure-increasing solenoid valve44connects and disconnects the wheel cylinder WC2and the hydraulic pump32with each other. The second pressure-increasing solenoid valve44controls the drive current supplied to a solenoid that is provided at the second pressure-increasing solenoid valve44to thereby control or adjust an amount of brake fluid supplied to the wheel cylinder WC2from the hydraulic pump32.

A third pressure-increasing solenoid valve45is provided between the wheel cylinder WC3and the hydraulic pump32. The third pressure-increasing solenoid valve45is also a normally-closed linear solenoid valve and is brought to the open state and the closed state when operating. The third pressure-increasing solenoid valve45connects and disconnects the wheel cylinder WC3and the hydraulic pump32with each other. The third pressure-increasing solenoid valve45controls the drive current supplied to a solenoid that is provided at the third pressure-increasing solenoid valve45to thereby control or adjust an amount of brake fluid supplied to the wheel cylinder WC3from the hydraulic pump32.

A fourth pressure-increasing solenoid valve46is provided between the wheel cylinder WC4and the hydraulic pump32. The fourth pressure-increasing solenoid valve46is also a normally-closed linear solenoid valve and is brought to the open state and the closed state when operating. The fourth pressure-increasing solenoid valve46connects and disconnects the wheel cylinder WC4and the hydraulic pump32with each other. The fourth pressure-increasing solenoid valve46controls the drive current supplied to a solenoid that is provided at the fourth pressure-increasing solenoid valve46to thereby control an amount of brake fluid supplied to the wheel cylinder WC4from the hydraulic pump32. The aforementioned first pressure-increasing solenoid valve43, the second pressure-increasing solenoid valve44, the third pressure-increasing solenoid valve45, and the fourth pressure-increasing solenoid valve46serve as pressure-increasing solenoid valves.

A first pressure-decreasing solenoid valve47is connected to the wheel cylinder WC1via a first wheel cylinder passage61. The first pressure-decreasing solenoid valve47, a second pressure-decreasing solenoid valve48, a third pressure-decreasing solenoid valve49, and a fourth pressure-decreasing solenoid valve50, which will be explained later, serve as pressure-decreasing solenoid valves. One end of a first relief passage65is connected to a downstream side of the first pressure-decreasing solenoid valve47. The first relief passage65, a second relief passage66, a third relief passage67, and a fourth relief passage68, which will be explained later, serve as relief passages.

The other end of the first relief passage65is connected to a circulating passage69. The circulating passage69is connected to the input port11aof the master cylinder reservoir11. The aforementioned first relief passage65, the second relief passage66, the third relief passage67, the fourth relief passage68, and the circulating passage69collectively serve as a discharge passage.

A first check valve71is provided at the first relief passage65so as to allow the brake fluid to flow in a direction from the first pressure-decreasing solenoid valve47to the circulating passage69and to prohibit the brake fluid to flow in an opposite direction from the circulating passage69to the first pressure-decreasing solenoid valve47. The first check valve71according to the first embodiment includes a ball valve that is freely movable within a valve chamber (which will be explained later). The first check valve71is a one-way valve that is opened by the brake fluid flowing in the direction from the first pressure-decreasing solenoid valve47to the circulating passage69and that is closed by the brake fluid flowing in the direction from the circulating passage69to the first pressure-decreasing solenoid valve47. The first check valve71, a second check valve72, a third check valve73, and a fourth check valve74, which will be explained later, serve as a pulsation transmission decreasing device and check valves.

The aforementioned first pressure-decreasing solenoid valve47is a normally-closed linear solenoid valve. The first pressure-decreasing solenoid valve47is operated to open and close so as to connect and disconnect the wheel cylinder WC1and the circulating passage69with each other. The first pressure-decreasing solenoid valve47controls the drive current supplied to a solenoid to thereby adjust the amount of brake fluid discharged to the master cylinder reservoir11from the wheel cylinder WC1via the circulating passage69.

The second pressure-decreasing solenoid valve48is connected to the wheel cylinder WC2via a second wheel cylinder passage62. One end of the second relief passage66is connected to a downstream side of the second pressure-decreasing solenoid valve48. The other end of the second relief passage66is connected to the circulating passage69. Then, the second check valve72is provided at the second relief passage66so as to allow the brake fluid to flow in a direction from the second pressure-decreasing solenoid valve48to the circulating passage69and to prohibit the brake fluid to flow in an opposite direction from the circulating passage69to the second pressure-decreasing solenoid valve48. The second check valve72according to the first embodiment includes a ball valve that is freely movable within a valve chamber. The second check valve72is a one-way valve that is opened by the brake fluid flowing in the direction from the second pressure-decreasing solenoid valve48to the circulating passage69and that is closed by the brake fluid flowing in the direction from the circulating passage69to the second pressure-decreasing solenoid valve48.

The aforementioned second pressure-decreasing solenoid valve48is a normally-closed linear solenoid valve. The second pressure-decreasing solenoid valve48is operated to open and close so as to connect and disconnect the wheel cylinder WC2and the circulating passage69with each other. The second pressure-decreasing solenoid valve48controls the drive current supplied to a solenoid to thereby adjust the amount of brake fluid discharged to the master cylinder reservoir11from the wheel cylinder WC2via the circulating passage69.

The third pressure-decreasing solenoid valve49is connected to the wheel cylinder WC3via a third wheel cylinder passage63. One end of the third relief passage67is connected to a downstream side of the third pressure-decreasing solenoid valve49. The other end of the third relief passage67is connected to the circulating passage69. Then, the third check valve73is provided at the third relief passage67so as to allow the brake fluid to flow in a direction from the third pressure-decreasing solenoid valve49to the circulating passage69and to prohibit the brake fluid to flow in an opposite direction from the circulating passage69to the third pressure-decreasing solenoid valve49. The third check valve73according to the first embodiment includes a ball valve that is freely movable within a valve chamber. The third check valve73is a one-way valve that is opened by the brake fluid flowing in the direction from the third pressure-decreasing solenoid valve49to the circulating passage69and that is closed by the brake fluid flowing in the direction from the circulating passage69to the third pressure-decreasing solenoid valve49.

The aforementioned third pressure-decreasing solenoid valve49is a normally-open linear solenoid valve. The third pressure-decreasing solenoid valve49is operated to open and close so as to connect and disconnect the wheel cylinder WC3and the circulating passage69with each other. The third pressure-decreasing solenoid valve49controls the drive current supplied to a solenoid to thereby adjust the amount of brake fluid discharged to the master cylinder reservoir11from the wheel cylinder WC3via the circulating passage69.

The fourth pressure-decreasing solenoid valve50is connected to the wheel cylinder WC4via a fourth wheel cylinder passage64. One end of the fourth relief passage68is connected to a downstream side of the fourth pressure-decreasing solenoid valve50. The other end of the fourth relief passage68is connected to the circulating passage69. Then, the fourth check valve74is provided at the fourth relief passage68so as to allow the brake fluid to flow in a direction from the fourth pressure-decreasing solenoid valve50to the circulating passage69and to prohibit the brake fluid to flow in an opposite direction from the circulating passage69to the fourth pressure-decreasing solenoid valve50. The fourth check valve74according to the first embodiment includes a ball valve that is freely movable within a valve chamber. The fourth check valve74is a one-way valve that is opened by the brake fluid flowing in the direction from the fourth pressure-decreasing solenoid valve50to the circulating passage69and that is closed by the brake fluid flowing in the direction from the circulating passage69to the fourth pressure-decreasing solenoid valve50.

The aforementioned fourth pressure-decreasing solenoid valve50is a normally-open linear solenoid valve. The fourth pressure-decreasing solenoid valve50is operated to open and close so as to connect and disconnect the wheel cylinder WC4and the circulating passage69with each other. The fourth pressure-decreasing solenoid valve50controls the drive current supplied to a solenoid to thereby adjust the amount of brake fluid discharged to the master cylinder reservoir11from the wheel cylinder WC4via the circulating passage69.

Hereinafter, the first pressure-decreasing solenoid valve47, the second pressure-decreasing solenoid valve48, the third pressure-decreasing solenoid valve49, and the fourth pressure-decreasing solenoid valve50will be referred to as the pressure-decreasing solenoid valves47to50when being described collectively. In addition, the first wheel cylinder passage61, the second wheel cylinder passage62, the third wheel cylinder passage63, and the fourth wheel cylinder passage64will be referred to as the wheel cylinder passages61to64when being described collectively. Further, the first relief passage65, the second relief passage66, the third relief passage67, and the fourth relief passage68will be referred to as the relief passages65to68when being described collectively. Still further, the first check valve71, the second check valve72, the third check valve73, and the fourth check valve74will be referred to as the check valves71to74when being described collectively.

A hydraulic sensor81is provided at a conduit connecting the secondary port12bof the master cylinder12and the first cut valve41. The hydraulic sensor81detects a pressure value of the brake fluid discharged from the secondary port12b. In the same way, a hydraulic sensor82provided at a conduit connecting the primary port12aof the master cylinder12and the second cut valve42detects a pressure value of the brake fluid discharged from the primary port12a. A hydraulic sensor83provided at a conduit connecting the discharge port of the hydraulic pump32and the pressure-increasing solenoid valves43to46detects a pressure value of the brake fluid discharged from the hydraulic pump32or the accumulator33. Hydraulic sensors84,85,86, and87provided at the wheel cylinder passages61to64, respectively, detect pressure values of the brake fluid at the wheel cylinders WC1to WC4, respectively.

The housing unit90illustrated inFIG. 1is made of aluminum alloy, or the like. The hydraulic pressure supply source30, the cut valves41,42, the pressure-increasing solenoid valves43to46, the pressure-decreasing solenoid valves47to50, the check valves71to74, and the like are assembled within the housing unit90while constituting the brake hydraulic pressure control apparatus1. Then, conduits connecting the aforementioned components with each other are formed within the housing unit90. At this time, the hydraulic pressure supply source30may be separately formed from the housing unit90.

The circulating passage69is connected to the relief passages65to68within the housing unit90. The circulating passage69extends through an inner portion of the housing unit90and projects therefrom so as to be connected to the input port11aof the master cylinder reservoir11outside of the housing unit90. In practice, a first drain port91a, formed at the outer peripheral surface of the housing unit90, and the input port11aare connected by a brake hose made of synthetic rubber, a metallic brake tube, or the like.

The stroke sensor13a, the on-off valve21, the electric motor31, the cut valves41,42, the pressure-increasing solenoid valves43to46, the pressure-decreasing solenoid valves47to50, and the hydraulic sensors81to87are electrically connected to a controller EC serving as controlling means. A vehicle speed sensor detecting a speed of the vehicle, a wheel speed sensor detecting the speed of each of the wheels FL, FR, RL, and RR, a steering sensor detecting a steering angle of the vehicle, a shift switch detecting a shift position of a transmission of the vehicle, an acceleration sensor detecting an acceleration opening of the vehicle, a yaw rate sensor detecting a yaw rate of the vehicle, and the like are also connected to the controller EC.

Next, an operation control method of the brake hydraulic pressure control apparatus1will be explained below. In a case where a driver of the vehicle operates the brake pedal13under a normal operation of the hydraulic pressure supply source30, the controller EC controls the cut valves41and42to be in the closed state so as to disconnect the secondary port12bof the master cylinder12from the wheel cylinder WC1provided at the front-left wheel FL, and the primary port12aof the master cylinder12from the wheel cylinder WC2provided at the front-right wheel FR. At the same time, the controller EC controls the on-off valve21to be in the open state so as to connect the secondary port12bof the master cylinder12to the stroke simulator22.

In the aforementioned state, the controller EC drives the hydraulic pump32and controls the pressure-increasing solenoid valves43to46to open, thereby supplying the brake fluid from the hydraulic pump32to the wheel cylinders WC1to WC4. In addition, the controller EC controls the pressure-decreasing solenoid valves47to50to open so that the brake fluid supplied to the wheel cylinders WC1to WC4is discharged to the master cylinder reservoir11via the wheel cylinder passages61to64, the pressure-decreasing solenoid valves47to50, the relief passages65to68, the check valves71to74, and the circulating passage69. As a result, the brake fluid at the wheel cylinders WC1to WC4is reduced.

The controller EC controls the brake hydraulic pressure within each of the wheel cylinders WC1to WC4to a predetermined value based on the depression amount of the brake pedal13detected by the stroke sensor13aand the pressure value detected by each of the hydraulic sensors81to87so that the braking force is generated at each of the wheels FL, FR, RL and RR depending on the depression amount of the brake pedal (i.e., a normal brake control).

As mentioned above, the pressure-increasing solenoid valves43to46and the pressure-decreasing solenoid valves47to50are formed by the linear solenoid valves. For example, the adjustment of the drive current supplied to each of the pressure-increasing solenoid valves43to46and the pressure-decreasing solenoid valves47to50by a duty control achieves a control of the amount of brake fluid supplied to the wheel cylinders WC1to WC4from the hydraulic pressure supply source30and the amount of brake fluid discharged to the master cylinder reservoir11from the wheel cylinders WC1to WC4. A pressure-increasing gradient and a pressure-decreasing gradient of each of the wheel cylinders WC1to WC4are adjustable accordingly.

On the other hand, in a case where the brake pedal13is operated under a condition where the hydraulic pressure supply source30malfunctions and therefore it is impossible to apply the brake hydraulic pressure to each of the wheel cylinders WC1to WC4, the controller EC controls the cut valves41and42to be maintained in the open state so that the secondary port12bof the master cylinder12is connected to the wheel cylinder WC1provided at the front-left wheel FL while the primary port12aof the master cylinder12is connected to the wheel cylinder WC2provided at the front-right wheel FR. In addition, the controller EC controls the on-off valve21to be in the closed state so as to disconnect the secondary port12bof the master cylinder2from the stroke simulator22. Therefore, the brake hydraulic pressure generated at the master cylinder12is applied to the wheel cylinder WC1provided at the front-left wheel FL and to the wheel cylinder WC2provided at the front-right wheel FR via the cut valves41and42from the secondary port12band the primary port12a, respectively.

When a locked state (wheel lock-up) of either one of the wheels FL, FR, RL, and RR is detected by the wheel speed sensor, and the like in a state where the hydraulic pressure supply source30is normally operated and therefore the brake hydraulic pressure is applied to each of the wheel cylinders WC1to WC4, the controller EC controls and operates the pressure-increasing solenoid valves43to46and the pressure-decreasing solenoid valves47to50. As a result, the brake hydraulic pressure at each of the wheel cylinders WC1to WC4is controlled to avoid the locked state of either one of the wheels FL, FR, RL, and RR (i.e., an anti-skid (ABS) control).

When a spin state of either the wheel FL or FR is detected by the vehicle speed sensor and the like upon an acceleration of the wheels FL and FR serving as driving wheels in a state where the brake pedal13is not operated, the controller EC controls and operates the pressure-increasing solenoid valves43,44and the pressure-decreasing solenoid valves47,48. As a result, the brake hydraulic pressure at each of the wheel cylinders WC1and WC2is controlled to avoid the spin state of either the wheel FL or FR (i.e., a traction control (TRC)).

When an unstable state of the vehicle is detected by the yaw rate sensor, and the like, the controller EC controls and operates the pressure-increasing solenoid valves43to46and the pressure-decreasing solenoid valves47to50. As a result, the brake hydraulic pressure at each of the wheel cylinders WC1to WC4is controlled to avoid the unstable state of the vehicle (i.e., a vehicle stability control or an electronic stability control (ESC)).

During the operation of the brake hydraulic pressure control apparatus1controlled by the controller EC in the aforementioned manner, valve elements of the pressure-decreasing solenoid valves47to50respectively are frequently operated to open and close. At this time, each of the valve elements is unbalanced and self-oscillation occurs thereat. The self-oscillation that occurs at one of the pressure-decreasing solenoid valves47to50generates pulsation of pressure at the relief passages65to68where the pressure-decreasing solenoid valves47to50are formed. However, the check valves71to74provided at the respective relief passages65to68prevent such pulsation of pressure. Accordingly, the pulsation of pressure caused by one of the pressure-decreasing solenoid valves47to50is prevented from being transmitted to the other pressure-decreasing solenoid valves47to50.

The present embodiment includes the check valves71to74serving as the pulsation transmission decreasing devices at the respective relief passages65to68so as to decrease the transmission of pressure pulsation that occurs at the pressure-decreasing solenoid valves47to50. Such simple structure prevents the transmission of pressure pulsation caused by the self-oscillation that occurs at one of the pressure-decreasing solenoid valves47to50to the other pressure-decreasing solenoid valves47to50. As a result, the occurrence of self-oscillation at the multiple pressure-decreasing solenoid valves is prevented to thereby decrease the generation of operation noise.

In addition, the pressure-decreasing solenoid valves47to50are constituted by the linear solenoid valves. Thus, the amount of brake fluid flowing from each of the wheel cylinders WC1to WC4to the master cylinder reservoir11is controlled and the self-oscillation that occurs at each of the pressure-decreasing solenoid valves47to50is reduced by means of the check valves71to74. The hydraulic pressure of the wheel cylinders WC1to WC4is therefore accurately controlled.

A second embodiment will be explained with reference toFIG. 2. A brake hydraulic pressure control apparatus1A according to the second embodiment is also a brake-by-wire type. The brake hydraulic pressure control apparatus1A of the second embodiment differs from the brake hydraulic pressure control apparatus1of the first embodiment in that the brake hydraulic pressure control apparatus1A includes orifices71a,72a,73a, and74aserving as throttle conduits and provided at the relief passages65to68so as to be in parallel to the respective check valves71to74.

In a case where air bleeding is performed on the brake hydraulic pressure control apparatus1A, including a filing of the brake fluid after air bleeding, the air is first removed from the master cylinder reservoir11by a usage of a vacuum pump. Then, while each of the valves is in the open state, the brake fluid is injected from the master cylinder reservoir11.

In the case of filling the brake fluid, the brake fluid injected from the master cylinder reservoir11is sent to the wheel cylinder WC1provided at the front-left wheel FL and the wheel cylinder WC2provided at the front-right wheel FR via the master cylinder12and the cut valves41and42. In addition, the brake fluid injected from the master cylinder reservoir11is sent to the wheel cylinder WC3provided at the rear-left wheel RL, the wheel cylinder WC4provided at the rear-right wheel RR, and the pressure-decreasing solenoid valves47to50via the hydraulic pressure supply source30and the pressure-increasing solenoid valves43to46.

Further, the brake fluid injected from the master cylinder reservoir11flows through the circulating passage69and the orifices71ato74aprovided at the respective relief passages65to68so that the brake fluid is also sent to the pressure-decreasing solenoid valves47to50in a direction opposite from the direction mentioned above. Cross-sectional areas (i.e., conduit areas) of the respective orifices71ato74aare defined in such a manner that the pulsation of pressure is prevented from being transmitted via the orifices71ato74aby restricting the brake fluid from flowing freely. Specifically, the cross-sectional areas of the respective orifices71ato74aare defined to be smaller than those of the relief passages65to68.

According to the second embodiment, the orifices71ato74aare provided at the respective relief passages65to68so as to be in parallel to the check valves71to74. Thus, when the brake fluid is injected from the master cylinder reservoir11upon the air bleeding of the brake hydraulic pressure control apparatus1A, the brake fluid from the circulating passage69flows through the orifices71ato74a. The filling of the brake fluid is never interfered by the check valves71to74. Accordingly, the air bleeding of the brake hydraulic pressure control apparatus1A is performed for a short period of time.

Next, a third embodiment will be explained with reference toFIGS. 3 to 7. A brake hydraulic pressure control apparatus1B according to the third embodiment is also a brake-by-wire type. The brake hydraulic pressure control apparatus1B differs from the brake hydraulic pressure control apparatus1A in that a first check valve75, a second check valve76, a third check valve77, and a fourth check valve78, all of which serve as the pulsation transmission decreasing devices and the check valves and all of which are provided at the relief passages65to68, each have a predetermined valve opening pressure greater than zero in a direction towards the circulating passage69from the pressure-decreasing solenoid valves47to50.

In addition, orifices75a,76a,77a, and78aare provided at the relief passages65to68respectively so as to be in parallel to the first to fourth check valves75to78. The first check valve75, the second check valve76, the third check valve77, and the fourth check valve78will be hereinafter referred to as the check valves75to78when being described collectively. In the same way, the orifices75a,76a,77a, and78awill be hereinafter referred to as the orifices75ato78awhen being described collectively.

In the same way as the second embodiment, the orifices75ato78aare provided to restrict the brake fluid from flowing freely. Specifically, cross-sectional areas of the respective orifices75ato78aprovided in parallel to the check valves75to78are defined in such a manner that the pulsation of pressure is prevented from being transmitted via the orifices75ato78aand are smaller than cross-sectional areas of the relief passages65to68.

FIG. 4is a cross-sectional view of the first pressure-decreasing solenoid valve47integrally provided with the first check valve75and the orifice75aand mounted on the housing unit90according to the brake hydraulic pressure control apparatus1B. In the following, an upper direction inFIG. 4will be explained as an upper direction of the first pressure-decreasing solenoid valve47. However, such direction is irrelevant to the actual direction of the first pressure-decreasing solenoid valve47.

In the first pressure-decreasing solenoid valve47, a solenoid101that generates an electromagnetic force when receiving an electric power is assembled on an outer periphery of a sleeve105. A fixing member103is arranged at an inner radial side of the solenoid101. Then, a joint106made by a nonmagnetic member is disposed between a lower end surface of the fixing member103and an upper end surface of the sleeve105.

A plunger107is accommodated within an inner bore105aof the sleeve105so as to be movable in an up and down direction as shown inFIG. 4. A void surrounded by a lower surface of the fixing member103, the inner bore105a, and an upper surface of a valve sheet109, which will be explained later, serves as a valve chamber. A spring bore103ais formed at the fixing member103so as to open at the lower surface thereof.

A coil spring108serving as a valve element pressing device is disposed between an inner peripheral surface of the spring bore103aand a plunger body107aso as to expand and contract in up and down direction inFIG. 4. An upper end of the coil spring108makes contact with a top surface of the spring bore103awhile a lower end of the coil spring108makes contact with a shoulder portion107cof the plunger107. Accordingly, the plunger107is constantly biased by the coil spring108in a vertically lower direction inFIG. 4.

A valve element107eis concentrically mounted at a lower end of the plunger body107a. At least a lower surface of the valve element107eis formed into a spherical shape. A valve seat109having substantially a cylindrical shape is press-fitted to the inner bore105aof the sleeve105from a lower end thereof. A pressure-decreasing port109cserving as an oil port is formed at the valve seat109so as to open downward inFIG. 4. The pressure-decreasing port109cis connected to a plunger chamber111, which will be explained later, via a seat portion109b.

The plunger107is constantly pressed downward inFIG. 4relative to the fixing member103by the biasing force of the coil spring108. Thus, the valve element107eformed at the lower end of the plunger107engages with the seat portion109bof the valve seat109so as to disconnect a communication between the pressure-decreasing port109cand the plunger chamber111. Further, a filter110is attached to a lower end of the valve seat109.

According to the aforementioned structure, the plunger chamber111is defined by the inner bore105aof the sleeve105, a lower surface of the plunger body107a, and the upper surface of the valve seat109. In addition, a deflection chamber112is defined between the lower surface of the fixing member103and an upper surface of the plunger body107a. In order to allow the flowing of the brake fluid between the plunger chamber111and the deflection chamber112in association with the movement of the plunger107in the up and down direction as shown inFIG. 4, multiple connection grooves107fare formed to penetrate through the plunger body107ain the up and down direction. The plunger chamber111and the deflection chamber112collectively serve as the valve chamber.

A pair of discharge ports105bserving as relief ports are formed at the sleeve105so as to open at the outer periphery thereof. The pair of discharge ports105bis provided to connect the plunger chamber111to the outside of the sleeve105. In addition, the first check valve75illustrated inFIG. 3is formed at a position on the outer periphery of the sleeve105so as to cover the pair of discharge ports105b. Further, a cylindrical-shaped filter113is attached to a radially outer side of the first check valve75so as to cover the pair of discharge ports105b.

As illustrated inFIG. 4, a large diameter insertion bore92and a small diameter insertion bore93are formed at the housing unit90into which each of the pressure-decreasing solenoid valves47to50is inserted. The outer periphery of the sleeve105is press-fitted to the large diameter insertion bore92and the small diameter insertion bore93so that the first pressure-decreasing solenoid valve47is mounted on the housing unit90.

An outlet conduit94constituting a portion of the first relief passage65is formed, opening at an inner peripheral surface of the large diameter insertion bore92. An inlet conduit95constituting a portion of the first wheel cylinder passage61is formed, opening at a bottom surface of the small diameter insertion bore93. The outer periphery of the sleeve105and both of the larger diameter insertion bore92and the small diameter insertion bore93are fluid-tightly fitted to each other. Accordingly, the inlet conduit95is connected to the outlet conduit94via the pressure-decreasing port109c, a valve portion constituted by the valve element107eand the seat portion109b, the plunger chamber111and the discharge ports105b.

In the aforementioned first pressure-decreasing solenoid valve47, the plunger107is constantly pressed downward inFIG. 4by the biasing force of the coil spring108. Thus, in a case where the solenoid101is not supplied with the electric power, the valve element107eof the plunger107that is pressed by the coil spring108engages with the seat portion109b, thereby disconnecting a communication between the plunger chamber111and the pressure-decreasing port109c.

The solenoid101generates the electromagnetic force when being powered to thereby bias the plunger107in the upper direction inFIG. 4against the pressing force of the coil spring108. Thus, the engagement of the valve element107eof the plunger107with the seat portion109bis released to thereby connect the plunger chamber111to the pressure-decreasing port109c. The solenoid101generates the electromagnetic force depending on the drive current value supplied to the solenoid101. Therefore, a lifting amount of the valve element107erelative to the seat portion109bis variable by a change of power supply to the solenoid101. The control of the drive current value supplied to the solenoid101achieves the adjustment of the amount of brake fluid flowing to the plunger chamber111from the pressure-decreasing port10cand further the control of the brake hydraulic pressure at the inlet conduit95.

That is, the first pressure-decreasing solenoid valve47is operated depending on a load balance between the electromagnetic force, generated by the solenoid101and acting on the plunger107, the pressure difference of the brake fluid, and the biasing force of the coil spring108. As a result, the brake hydraulic pressure is adjusted at the wheel cylinder WC1. The operation of the first pressure-decreasing solenoid valve47in the aforementioned manner achieves the smooth pressure reduction of the brake hydraulic pressure at the wheel cylinder WC1in a case of the brake operation under a normal driving condition of the vehicle, without a generation of the operation noise.

FIG. 5is a perspective view of a valve member751that constitutes the first check valve75.FIG. 6is a cross-sectional view of the valve member751attached to the outer periphery of the sleeve105. The valve member751serving as a biasing member is formed into an arc shape obtained by a strip-shaped metallic spring member having flexibility and is formed into substantially a C-shape. The valve member751includes a predetermined curvature so as to be assembled on the outer periphery of the sleeve105. Both ends of the valve member751include engagement portions751a, respectively, so as to project in the radially inward direction of the sleeve105. The two engagement portions751aare positioned to face each other relative to a center of a imaginary perfect circle having the same curvature of that of the valve member751.

Each of the engagement portions751aincludes an outer diameter and a depth so as to be received within a tapered opening portion105cof the discharge port105bformed at the sleeve105. Because the engagement portions751aare received within the respective opening portions105c, the positioning of the valve member751at the outer periphery of the sleeve105is determined as illustrated inFIG. 6. Both ends of the valve member751attached to the outer periphery of the sleeve105are normally in contact with the outer periphery of the sleeve105so as to cover the respective discharge ports105b. The valve member751may be formed by a wire rod having elasticity instead of the strip-shaped spring member. Alternatively, the valve member751may be formed by spring steel or synthetic resin material. The orifice75a, which will be explained later, may be formed at only one of the engagement portions751a.

In a case where the brake hydraulic pressure equal to or greater than a predetermined value (i.e., greater than zero) is generated at the plunger chamber111, the brake hydraulic pressure is applied to the valve member751via the discharge ports105b. The end portions of the valve member751are deflected so that the valve member751expands in a radially outward direction of the sleeve105. As a result, the end portions of the valve member751are separated from the outer periphery of the sleeve105, thereby opening the first check valve75and opening the discharge ports105btowards the outlet conduit94. The valve opening pressure of the first check valve75is specified to be an appropriate value greater than zero by a change of deformation rigidity of the valve member751.

In a case where the hydraulic pressure is applied from the outlet conduit94, the end portions of the valve member751are prevented from being separated from the outer periphery of the sleeve105, thereby maintaining the first check valve75in the closed state. Thus, even when the pulsation of pressure acts towards the first pressure-decreasing solenoid valve47from the circulating passage69, the pulsation of pressure is interfered by the first check valve75and is prevented from being transmitted to the plunger chamber111or the deflection chamber112. The plunger107is never vibrated or oscillated accordingly. The orifice75ais formed in a penetrating manner at a top surface of each of the engagement portions751aof the valve member751positioned in a most radially inner direction of the sleeve105. Accordingly, even when the first check valve75is closed, each of the discharge ports105band the outlet conduit94is connected to each other by the orifice75aas illustrated inFIG. 6.

As mentioned above, the first pressure-decreasing solenoid valve47integrally formed with the first check valve75includes the orifice75abut still dynamically retains (i.e., while the first pressure-decreasing solenoid valve47is operating) a residual pressure equal to or greater than the aforementioned predetermined value (i.e., the predetermined pressure value). In the same way as the first pressure-decreasing solenoid valve47explained in the above, the normally-closed second pressure-decreasing solenoid valve48is also integrally formed with the second check valve76and the orifice76aand has the same structure as that of the first pressure-decreasing solenoid valve47.

InFIG. 7, structures of the normally-open third pressure-decreasing solenoid valve49and the fourth pressure-decreasing solenoid valve50bear the same numeral references as those of the first pressure-decreasing solenoid valve47illustrated inFIG. 4. Only differences of the third and fourth pressure-decreasing solenoid valves49and50from the first pressure-decreasing solenoid valve47will be explained below. In the third pressure-decreasing solenoid valve49, the plunger107is constantly pressed upward inFIG. 7by a biasing force of a coil spring208serving as the valve element pressing device. Thus, in a case where the solenoid101is not supplied with the electric power, the valve element107eof the plunger107that is pressed by the coil spring208is separated from the seat portion109bso that the plunger chamber111and the pressure-decreasing port109care connected to each other.

The solenoid101generates the electromagnetic force when being powered so as to press the plunger107downward inFIG. 7against the biasing force of the coil spring208. Then, the valve element107eis seated on the seat portion109bso as to disconnect the plunger chamber111from the pressure-decreasing port109c. The solenoid101generates the electromagnetic force depending on the drive current value supplied to the solenoid101. Thus, the control of the drive current achieves the control of the brake hydraulic pressure applied to the third wheel cylinder WC3connected to the inlet passage95.

According to the third embodiment, each of the check valves75to78includes the predetermined valve opening pressure greater than zero in a direction towards the circulating passage69from each of the pressure-decreasing solenoid valves47to50. While the pressure-decreasing solenoid valves47to50are operating, a predetermined hydraulic pressure is generated at the plunger chamber111and the deflection chamber112of each of the pressure-decreasing solenoid valves47to50so as to prevent a generation of air bubbles caused by aeration within the plunger chamber111and the deflection chamber112and to damp oscillations of the valve element107e. As a result, the self-oscillation of each of the pressure-decreasing solenoid valves47to50is reduced to thereby prevent an occurrence of the operation noise of the brake hydraulic pressure control apparatus1B.

In addition, the wheel cylinder WC3provided at the rear-left wheel RL and the wheel cylinder WC4provided at the rear-right wheel RR are constantly connected to the master cylinder reservoir11by means of the orifices77aand78a. Thus, the brake hydraulic pressure at each of the wheel cylinders WC3and WC4is zero in a state where the brake hydraulic pressure control apparatus1B is not operated, thereby preventing dragging of the wheels RL and RR caused by the residual pressure at the wheel cylinders WC3and WC4.

Each of the check valves75to78includes the valve member751formed by an arc-shaped elastic member having flexibility. The end portions of the valve member751cover the discharge ports105b. Each of the orifices75ato78aformed at the end portions of the valve member751causes the plunger chamber111and each of the relief passages65to68to communicate with each other. The valve member751where the orifices75ato78aare formed is simply attached to the outer periphery of the sleeve105to thereby integrally form each of the check valves75to78with each of the pressure-decreasing solenoid valves47to50. The small-sized and low cost brake hydraulic pressure control apparatus1B may be achieved accordingly.

A brake hydraulic pressure control apparatus1C according to a fourth embodiment will be explained with reference toFIG. 8. The brake hydraulic pressure control apparatus1C differs from the brake hydraulic pressure control apparatus1of the first embodiment in that the check valves71to74are not provided at the relief passages65to68, and the first relief passage65where the first pressure-decreasing solenoid valve47is provided extends from the first pressure-decreasing solenoid valve47through the inner portion of the housing unit90and runs to outside thereof so as to be connected to the circulating passage69as illustrated inFIG. 8. At this time, the first relief passage65may be directly connected to the master cylinder reservoir11.

As illustrated inFIG. 8, the circulating passage69extends through the inner portion of the housing unit90in the same way as that of the first embodiment and then runs to outside thereof from the first drain port91aso as to be connected to the input port11aof the master cylinder reservoir11. The second, third and fourth relief passages66,67, and68where the second, third, and fourth pressure-decreasing solenoid valves47,48, and49are formed respectively are connected to the circulating passage69within the housing unit90.

The first relief passage65extends through the inner portion of the housing unit90from the first pressure-decreasing solenoid valve47, and then runs to outside of the housing unit90from a second drain port91bformed at the outer peripheral surface of the housing unit90so as to be connected to the circulating passage69outside of the housing unit90. Thus, according to the fourth embodiment, the second drain port91band the inlet port91cformed at the outer periphery of the housing unit90and connected to the suction port of the hydraulic pump32are connected to each other outside of the housing unit90. At this time, a connection point between the first relief passage65and the circulating passage69formed at the outside of the housing unit90is desirably provided closer to the master cylinder reservoir11in view of reducing transmission of pressure pulsation caused by the self-oscillation of the first pressure-decreasing solenoid valve47.

In the brake hydraulic pressure control apparatus1C illustrated inFIG. 8, only the first relief passage65where the first pressure-decreasing solenoid valve47is formed is connected to the circulating passage69outside of the housing unit90. Alternatively, in addition to the first relief passage65, or instead of the first relief passage65, at least one of the relief passages66to68may be connected to the circulating passage69outside of the housing unit90. Further alternatively, all of the relief passages65to68may be individually connected to the circulating passage69or to the master cylinder reservoir11outside of the housing unit90. Further alternatively, one of or plurality of the relief passages65to68may be directly connected to the master cylinder11outside of the housing unit90instead of being connected to the circulating passage69.

According to the fourth embodiment, the first relief passage65extends from the first pressure-decreasing solenoid valve47within the housing unit90and runs to outside thereof so as to be connected to the circulating passage69. Thus, the connection point between the first relief passage65and the circulating passage69is away from the pressure-decreasing solenoid valves48to50provided at the other relief passages66to68. As a result, the pulsation of pressure from the first pressure-decreasing solenoid valve47to the other pressure-decreasing solenoid valves48to50is damped, thereby decreasing the transmission of pressure pulsation caused by the self-oscillation of the first pressure-decreasing solenoid valve47. The occurrence of operation noise of the brake hydraulic pressure control apparatus is reduced accordingly.

The first to fourth embodiments are not limited to have the aforementioned structures and may be modified or changed appropriately. For example, the brake hydraulic pressure control apparatus according to any one of the embodiments is applicable to a front-wheel-drive vehicle, a rear-wheel-drive vehicle, and four-wheel-drive vehicle, without being restricted by a driving system of the vehicle.

In addition, the brake hydraulic pressure control apparatus according to any one of the embodiments is not only applicable to a braking system performing all of the anti-skid control, the traction control, and the vehicle stability control in addition to the normal brake control but also applicable to the braking system performing one of or some of the aforementioned controls. The master cylinder reservoir11may be integrally formed with the master cylinder12as illustrated inFIG. 1, or formed separately from the master cylinder12and connected thereto by means of a hose, or the like.

According to the aforementioned brake hydraulic pressure control apparatus1,1A,1B,1C, the check valves71to74,75to78(the pulsation transmission decreasing device) are provided at the relief passages65to68respectively for decreasing the transmission of pressure pulsation that occurs at least one of the pressure-decreasing solenoid valves47to50. Thus, such simple structure enables a prevention of the self-oscillation that occurs at one of the pressure-decreasing solenoid valves47to50from being transmitted to the other pressure-decreasing solenoid valve(s)47to50. The amplification caused by a mutual interference of the self-oscillation between the pressure-decreasing solenoid valves47to50is reduced, thereby decreasing a generation of an operation noise of the brake hydraulic pressure control apparatus1,1A,1B,1C.

The pulsation transmission decreasing device includes the check valves71to74,75to78provided at the relief passages65to68respectively. The check valves71to74,75to78allow the brake fluid to flow in a direction from the pressure-decreasing solenoid valves47to50to the circulating passage69and prohibit the brake fluid to flow in a direction from the circulating passage69to the pressure-decreasing solenoid valves47to50.

According to the aforementioned brake hydraulic pressure control apparatus1,1A,1B, the check valves71to74,75to78prevent the transmission of pressure pulsation that occurs at the one of the pressure-decreasing solenoid valves47to50to the other pressure-decreasing solenoid valve(s)47to50. Therefore, such simple structure achieves a reduction of the operation noise.

The orifices71ato74a,75ato78arestricting the flow of the brake fluid are provided at the relief passages65to68respectively in parallel to the respective check valves71to74,75to78.

Because the orifices71ato74a,75ato78aare provided at the respective relief passages65to68so as to be in parallel to the check valves71to74,75to78, the brake fluid passes and flows through the orifices71ato74a,75ato78aat the relief passages65to68via the circulating passage69in a case where the brake fluid is injected from the reservoir11of the master cylinder12upon air bleeding of the brake hydraulic pressure control apparatus1A,1B. The check valves71to74,75to78never interfere with the filling of the brake fluid. Therefore, the air bleeding of the brake hydraulic pressure control apparatus1A,1B is achieved for a short period of time. At this time, a conduit area of each of the orifices71ato74a,75ato78aprovided in parallel to each of the check valves71to74,75to78is defined in such a manner that the pulsation of pressure is prevented from being transmitted via the orifices71ato74a,75ato78aby restricting the brake fluid from flowing freely.

The check valves75to78each include a predetermined valve opening pressure greater than zero in a direction from each of the pressure-decreasing solenoid valves47to50to the circulating passage69.

Accordingly, a predetermined hydraulic pressure is generated within the valve chamber of each of the pressure-decreasing solenoid valves47to50while each of the pressure-decreasing solenoid valves47to50is operating. Then, for example, a generation of air bubbles caused by aeration is restrained so as to damp oscillations of the valve element107eof each of the pressure-decreasing solenoid valves47to50. As a result, the self-oscillation of the valve element107eis decreased to prevent the operation noise of the brake hydraulic pressure control apparatus1B. In addition, the wheel cylinders WC1to WC4and the reservoir11are connected to each other by means of the orifices75ato78a. Thus, dragging of the wheels FL, FR, RL, and RR caused by a residual pressure at the wheel cylinders WC1to WC4may be prevented.

Each of the pressure-decreasing solenoid valves47to50includes the valve chamber (the plunger chamber111and deflection chamber112) connected to the relief port105bthat is connected to one of the relief passages65to68and the oil port109cthat is connected to one of the wheel cylinders WC1to WC4, the relief port105band the oil port109copening to an outside of the pressure-decreasing solenoid valve47,48,49,50, the valve seat109bbeing formed at a connecting portion of the valve chamber (the plunger chamber111and deflection chamber112) to the oil port109c, the valve element107emovably accommodated within the valve chamber (the plunger chamber111and deflection chamber112) and disconnecting the valve chamber (the plunger chamber111and deflection chamber112) and the oil port109cby making contact with the valve seat109b, the coil spring108,208biasing the valve element107ein a direction approaching the valve seat109bor separating from the valve seat109b, and the solenoid101generating an electromagnetic force by being supplied with an electric power and biasing the valve element107ein a direction against a pressing force of the coil spring108,208. Each of the check valves75to78is formed by an arc-shaped biasing member having flexibility and the orifice75a,76a,77a,78ais formed at least one end portion of the biasing member, the biasing member being attached to an outer periphery of the pressure-decreasing solenoid valve47,48,49,50so that the one end portion of the biasing member covers the relief port105bwhile the orifice75a,76a,77a,78acauses the valve chamber (the plunger chamber111and deflection chamber112) to be connected to the relief passage65,66,67,68. When the brake hydraulic pressure equal to or greater than a predetermined value is generated within the valve chamber (the plunger chamber111and deflection chamber112), the one end is deflected in a radially outward direction of the pressure-decreasing solenoid valve47,48,49,50to open the relief port105btowards the relief passage65,66,67,68.

The biasing member (the check valve) is simply attached to the outer periphery of each of the pressure-solenoid valves47to50to thereby integrally form each of the check valves75to48having the valve opening pressure with each of the pressure-decreasing solenoid valves47to50. The brake hydraulic pressure control apparatus1B is achieved at a low cost.

The brake hydraulic pressure control apparatus1C further includes a housing unit90in which at least the pressure-increasing solenoid valves43to46, the pressure-decreasing solenoid valves47to50, and the cut valves41and42are formed. The pulsation transmission decreasing device is configured in such a manner that the circulating passage69extends through an inner portion of the housing unit90and runs to outside thereof to be connected to the reservoir11, and at least one of the relief passages65to68extends through the inner portion of the housing unit90from at least one of the pressure-decreasing solenoid valves47to50and runs to outside thereof to be connected to either the circulating passage69or the reservoir11.

The connecting point between one of the relief passages65to68and the circulating passage69or between one of the relief passages65to68and the reservoir11is away from the pressure-decreasing solenoid valves47to50provided at the other relief passages65to68. Thus, the pressure pulsation from at least one of the pressure-decreasing solenoid valves47to50to the other pressure-decreasing solenoid valve(s)47to50is damped by one of the relief passages65to68that is connected to the circulating passage69or the reservoir11outside the housing unit90. Thus, the transmission of pressure caused by the self-oscillation is reduced, thereby decreasing the occurrence of the operation noise.

The brake hydraulic pressure control apparatus1C further includes a housing unit90in which at least the pressure-increasing solenoid valves43to46, the pressure-decreasing solenoid valves47to50, and the cut valves41and42are formed. The pulsation transmission decreasing device is configured in such a manner that all of the relief passages65to68extend through an inner portion of the housing unit90from downstream sides of the pressure-decreasing solenoid valves47to50and run to outside of the housing unit90to be connected to either the circulating passage69or the reservoir11.

The connecting points between all the relief passages65to68and the circulating passage69or between all the relief passages65to68and the reservoir11are away from all the pressure-decreasing solenoid valves47to50provided at the respective relief passages65to68. Thus, the pressure pulsation from one of the pressure-decreasing solenoid valves47to50to the other pressure-decreasing solenoid valve(s)47to50is damped by the relief passages65to68that are connected to the circulating passage69or the reservoir11outside the housing unit90. Thus, the transmission of pressure caused by the self-oscillation is reduced at all of the relief passages65to68, thereby decreasing the occurrence of the operation noise.