Patent Application
20050104443
1. Field of the Invention
The present invention relates to a master cylinder for use in a hydraulic brake apparatus of a vehicle, and more particularly to a master cylinder with a braking stroke simulator operated in response to operation of a manually operated braking member.
2. Description of the Related Arts
Heretofore, there is known various hydraulic brake apparatuses each having a master cylinder with a braking stroke simulator. Among them, such an apparatus as discussed below has been disclosed in Japanese Patent Laid-open publication No. 11-59349. According to the apparatus, when a pressure control device including a pressure source is normal, the hydraulic pressure generated by the pressure source is controlled by the pressure control device in response to operation of a manually operated braking member to be supplied into wheel brake cylinders, with the communication between the master cylinder and the wheel brake cylinder being blocked. When the pressure control device has come to be abnormal, the master cylinder is communicated with the wheel brake cylinder, to discharge the hydraulic pressure into the wheel brake cylinder in response to operational force of the manually operated braking member.
In general, the stroke simulator is adapted to provide the manually operated braking member with a stroke in response to the braking operation force, when the pressure control device is normal, i.e., when the communication between the master cylinder and the wheel brake cylinder has been blocked. And, according to the hydraulic brake apparatus as disclosed in the Japanese Patent Laid-open publication, the stroke simulator is disposed between the manually operated braking member and a master piston. In view of the fact that it is required to provide a large stroke of a brake pedal in response to a stroke of the stroke simulator, when the pressure control device is abnormal, i.e., when the hydraulic pressure is supplied from the master cylinder to the wheel brake cylinder, there is provided cut-off means for blocking the communication between a simulator chamber and an atmospheric pressure chamber in response to movement of the master piston. As for the cut-off means, there are provided a sleeve partially in contact with an inner surface of a cylinder body, and a seal member fixed to the master piston, whereby the stroke of the stroke simulator may be restricted, when the hydraulic pressure is supplied from the master cylinder to the wheel brake cylinder.
According to the hydraulic brake apparatus as disclosed in the Japanese Patent Laid-open publication, however, if the pressure control device became abnormal, for example, and the manually operated braking member was released rapidly from a state where the master piston was advanced to be in a braking operation, only a simulator piston could be retracted in advance. In this case, the master piston may not be retracted, with the simulator chamber completely closed. According to the apparatus as disclosed in the Japanese Patent Laid-open publication, therefore, a port has been provided on the simulator piston to communicate the simulator chamber with another atmospheric pressure chamber at its rear end position, which costs much.
Accordingly, it is an object of the present invention to provide a master cylinder having a braking stroke simulator used for a component of a hydraulic brake apparatus for a vehicle, which is capable of restricting a stroke of a manually operated braking member when the hydraulic pressure is supplied from a master pressure chamber to wheel brake cylinders, and opening the master pressure chamber when the braking operation is released.
In order to accomplish the above and other objects, the master cylinder is provided with a piston member which is slidably accommodated in a cylinder bore of a cylinder housing for defining a master pressure chamber in front of the piston member, and a stroke simulator which has a simulator piston for defining a simulator chamber in front of the simulator piston and moving back and forth in response to operation of a manually operated braking member, to communicate the master pressure chamber with an atmospheric pressure chamber when the piston member is placed in an initial position thereof, and block the communication between the master pressure chamber and the atmospheric pressure chamber when the piston member is advanced from the initial position thereof by a first stroke or more, and which has an elastic member for applying a stroke of the simulator piston in response to braking operation force of the manually operated braking member. The stroke simulator is adapted to transmit the braking operation force of the manually operated braking member to the piston member, through the simulator piston and the elastic member. Furthermore, a communication control device is provided for communicating the simulator chamber with the atmospheric pressure chamber when the piston member is placed in an initial position thereof, and blocking the communication between the simulator chamber and the atmospheric pressure chamber when the piston member is advanced from the initial position thereof by a second stroke, which is set to be greater than the first stroke, or more. And, a restriction device is provided for restricting the simulator piston to be retracted up to a position thereof which is placed relative to the piston member when the manually operated braking member is inoperative.
Preferably, the piston member includes a master piston which is slidably received in the cylinder bore for defining the master pressure chamber in front of the master piston, and the master piston has a recess which is formed to be opened rearward of the master piston, and in which the elastic member and the simulator piston are accommodated.
The restriction device as described above may include a blocking member fixed on a rear end portion of the recess of the master piston to prevent the simulator piston from being moved rearward beyond the blocking member. The blocking member may be a ring member which is formed in C-shape, and which is fitted into an annular groove formed on an inner peripheral surface of the rear end portion of the recess of the master piston. The blocking member may be an annular plug which is screwed into the rear end portion of the recess of the master piston, or an annular stopper which is pressed into the rear end portion of the recess of the master piston. Or, the blocking member may be a caulking portion which is formed on the rear end portion of the recess of the master piston.
In the master cylinder with the braking stroke simulator, the piston member may include a master piston which is slidably received in the cylinder bore for defining the master pressure chamber in front of the master piston, and an auxiliary piston which is placed to be in contact with a rear end face of the master piston, and which is formed with a recess being opened rearward of the auxiliary piston, to accommodate therein the elastic member and the simulator piston. The communication control device is adapted to block the communication between the simulator chamber and the atmospheric pressure chamber when the auxiliary piston is advanced from the initial position thereof by the second stroke or more, and the restriction device is adapted to restrict the simulator piston to be retracted up to a position thereof which is placed relative to the auxiliary piston when the manually operated braking member is inoperative.
The restriction device as described above may include a blocking member fixed on a rear end portion of the recess of the auxiliary piston to prevent the simulator piston from being moved rearward beyond the blocking member. The blocking member may be a ring member which is formed in C-shape, and which is fitted into an annular groove formed on an inner peripheral surface of the rear end portion of the recess of the auxiliary piston. The blocking member may be an annular plug which is screwed into the rear end portion of the recess of the auxiliary piston, or an annular stopper which is pressed into the rear end portion of the recess of the auxiliary piston. Or, the blocking member may be a caulking portion which is formed on the rear end portion of the recess of the auxiliary piston.
The above stated object and following description will become readily apparent with reference to the accompanying drawings, wherein like reference numerals denote like elements, and in which:
Referring to
As for the master piston MP, there are formed at its front end a recess M1 opening forward, and formed at its rear end a recess opening rearward, in the latter of which a cylinder bore is formed to provide a stepped bore of a small diameter bore M2 and a large diameter bore M3. On the inner surface of the large diameter bore M3 near the open end thereof, an annular groove MG is formed for holding a C-ring CR as described later. On the side wall of the master piston MP, there are formed a port P3 opening into the recess M1, and a port P4 opening into the small diameter bore M2. A land portion L1 is formed around the outer peripheral surface of a middle portion of the master piston MP, and a land portion L2 is formed around the outer surface of its rear portion, with annular grooves formed on their outer peripheral surfaces, to hold therein annular seal members S2 and S3 having cup-like cross sections, respectively.
The simulator piston SP has a large diameter piston portion SP1 to be slidably accommodated in the large diameter bore M3, and a small diameter axial portion SP2 extending rearward from the former. On the outer peripheral surface of the piston portion SP1, there is formed an annular groove for holding therein an annular seal member S4 having a cup-like cross section. The axial portion SP2 is connected to a brake pedal BP served as the manually operated braking member. The seal members S1 and S2 act as a check valve, respectively, to block the flow of brake fluid from the opened side of cup-like cross section to the closed side thereof, and allow the flow of brake fluid from the closed side to the opened side, so that the seal member S2 allows the flow of brake fluid from the front side (left side in
Next will be explained the parts as described above, according to an example of a sequence of steps for assembling them, and a device for restricting the retraction according to the present embodiment. At the outset, a compression spring E2 served as an elastic member for the simulator is received into the small diameter bore M2 and large diameter bore M3 of the master piston MP. Then, the simulator piston SP with the seal member S4 mounted thereon is fluid-tightly and slidably received into the large diameter bore M3 to define a simulator chamber C4 in front of the piston portion SP1. With the piston portion SP1 accommodated in the large diameter bore M3, fitted into the annular groove MG of the master piston MP is the C-ring CR, which acts as a blocking member served as a device for restricting the retraction according to the present invention, and which is formed in C-shape as shown in
Next, the seal member S1 is fitted into the annular groove G1 of the housing HS, and a compression spring E1 served as a return spring is received in the recess B1 of the housing HS and the recess M1 of the master piston MP, and then the master piston MP is fitted into the small diameter bore B2 and large diameter bore B3. Consequently, the master piston MP is fluid-tightly and slidably accommodated in the small diameter bore B2 and large diameter bore B3, through the seal members S1 and S3, respectively. Thus, with the master piston MP accommodated in the small diameter bore B2 and large diameter bore B3 of the housing HS, screwed into the open end portion B4 of the housing HS is a nut-like stopper NH with threaded grooves formed on its outer peripheral surface, which prevents the master piston MP from being moved rearward against the biasing force of the compression spring E1, to act as the annular blocking member.
With those parts assembled as described above, the master pressure chamber C1 is defined in front of the master piston MP in the master cylinder MC, to be communicated with the wheel brake cylinder WC through the port P1 (via an electromagnetic switching valve NO as described hereinafter). An atmospheric pressure chamber C2 is formed between the seal members S1 and S2 held on the inner peripheral surface of the housing HS, and an annular chamber C3 is formed between the seal members S2 and S3, so that the atmospheric pressure chamber C2 is so constituted to be always communicated with an atmospheric pressure reservoir RS (hereinafter, simply referred to as a reservoir RS) through the port P2. When the master piston MP is placed in its initial position as shown in
The master cylinder with the braking stroke simulator as described above is provided to constitute a hydraulic brake apparatus for a vehicle as shown in
According to the present embodiment, the pressure source PG includes an electric motor M controlled by an electronic control unit ECU, and a hydraulic pressure pump HP, which is driven by the electric motor M, and whose inlet is connected to the reservoir RS, and whose outlet is connected to an accumulator AC. According to the present embodiment, a pressure sensor Sps is connected to the outlet, and the detected pressure is monitored by the electronic control unit ECU. On the basis of the monitored result, the motor M is controlled by the electronic control unit ECU to keep the hydraulic pressure in the accumulator AC between predetermined upper and lower limits. The accumulator AC is connected to a hydraulic passage between the switching valve NO and the wheel brake cylinder WC, through a first linear solenoid valve SV1 of a normally closed type, to regulate the hydraulic pressure discharged from the pressure source PG and supply it to the wheel brake cylinder WC. Also, the reservoir RS is connected to the hydraulic passage between the switching valve NO and wheel brake cylinder WC, through a second linear solenoid valve SV2 of a normally closed type, to reduce the pressure in the wheel brake cylinder WC and regulate it. Accordingly, a pressure control device PC is formed by the pressure source PG, first and second linear solenoid valves SV1 and SV2, electronic control unit ECU, and sensors as described hereinafter.
According to the present embodiment, a pressure sensor Smc is disposed in a hydraulic passage between the master cylinder MC and the switching valve NO, and a pressure sensor Swc is disposed in a hydraulic passage between the switching valve NO and the wheel brake cylinder WC. On the brake pedal BP, a stroke sensor BS is operatively connected to detect its stroke. The signals detected by the sensors as described above are fed to the electronic control unit ECU. Thus, the hydraulic braking pressure discharged from the master cylinder MC, the hydraulic braking pressure in the wheel brake cylinder WC and the stroke of the brake pedal BP are monitored by those sensors. Furthermore, in order to achieve those controls including an anti-skid control or the like, sensors SN such as wheel speed sensors, acceleration sensor or the like have been provided, so that the signals detected by them are fed to the electronic control unit ECU.
Hereinafter, explained is operation of the hydraulic brake apparatus having the master cylinder MC with the braking stroke simulator SM as constituted above. At the outset, when the pressure control device PC is normal, the switching valve NO is energized to be placed in its closed position, so that the communication between the master cylinder MC and the wheel brake cylinder WC is blocked, and the hydraulic pressure discharged from the master cylinder MC is supplied to the wheel brake cylinder WC in response to operation of the brake pedal BP, on the basis of the value detected by the stroke sensor BS and the pressure sensor Smc. That is, the electric current fed to the first and second linear solenoid valves SV1 and SV2 is controlled respectively, so that the wheel cylinder pressure detected by the pressure sensor Swc equals to a desired wheel cylinder pressure. Consequently, the hydraulic pressure controlled by the pressure control device PC in response to operation of the brake pedal BP is supplied to the wheel brake cylinder WC.
In the case where the pressure control device PC is normal as described above, according to the master cylinder MC, the master piston MP is not advanced substantially from such a position that the communication between the master pressure chamber C1 and the atmospheric pressure chamber C2 is blocked, i.e., the position advanced from the initial position of the master piston MP by the first stroke (D1). Therefore, the simulator chamber C4 is communicated with the atmospheric pressure chamber C2 and finally with the reservoir RS, through the clearance CL between the seal member S2 and the annular groove G2 formed in the housing HS, so that the simulator chamber C4 is under the atmospheric pressure. Accordingly, if the braking operation force applied to the simulator piston SP becomes equal to or greater than a compressive force for mounting the compression spring E2 in the stroke simulator SM, the compression spring E2 is compressed to provide the stroke of the simulator piston SP in response to the braking operation force. As a result, the stroke of the brake pedal BP is provided in response to the braking operation force.
On the contrary, in the case where the pressure control device PC including the pressure source PG and the like comes to be abnormal, the switching valve NO is de-energized (turned off) to be placed in its open position, so that the master cylinder MC and the wheel brake cylinder WC are communicated with each other, as shown in
In this case, even in such a state that the communication between the simulator chamber C4 and the atmospheric pressure chamber C2 is blocked, with the master piston MP being advanced, if the pressure control device PC comes to be abnormal during the operation of the brake pedal BP, i.e., when the stroke simulator SM is being stroked, the stroke simulator SM will be immediately retracted to its initial position by releasing the brake pedal BP to communicate the simulator chamber C4 with the atmospheric pressure chamber C2 through the seal member S2 with its function as a check valve. In other words, the position of the simulator piston SP relative to the position of the master piston MP is placed to be in its initial position. Therefore, a so-called dead stroke could be prevented effectively, even if the brake pedal BP was operated more. Also, even if the brake pedal BP was rapidly released from such a state that the communication between the simulator chamber C4 and the atmospheric pressure chamber C2 was blocked, the simulator piston SP could only be moved rearward up to the position where it would contact the C-ring CR. In other words, as the retracting operation of the simulator piston SP is restricted by the C-ring CR at the rearmost position of the simulator piston SP to be determined relative to the master piston MP when the brake pedal BP has not been depressed, the master piston MP will not be prevented from being moved rearward. Therefore, the master piston MP could be moved rearward until its rear end will contact the stopper NH, so that the master pressure chamber C1 could be definitely opened to communicate with the reservoir RS.
Next, another embodiment of the present invention is explained referring to
According to the embodiment as shown in
It should be apparent to one skilled in the art that the above-described embodiments are merely illustrative of but one of the many possible specific embodiments of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and scope of the invention as defined in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-386663 | Nov 2003 | JP | national |
This application claims priority under 35 U.S.C. Sec. 119 to No. 2003-386663 filed in Japan on Nov. 17, 2003, the entire content of which is herein incorporated by reference.
