Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reissue Patent
2000-06-30
2003-11-25
Nguyen, Hoang (Department: 3748)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C091S37600A
Reissue Patent
active
RE038327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a brake apparatus and, more particularly, to a brake apparatus having a brake pedal provided in a leg space of a vehicle to transfer a pressing force applied to the brake pedal to a master cylinder.
2. Description of the Related Art
A foot operated brake apparatus having a brake pedal for inputting a force by applying a foot press is disclosed in Japanese Laid-Open Patent Application No.6-211115. The brake apparatus disclosed therein has a function to prevent a displacement of a brake pedal when a force is applied from a frontal direction such as when the front of the vehicle is involved in an accident. In this brake apparatus, the brake pedal supported by a pedal support is connected to a master cylinder via a booster so that the master cylinder generates an appropriate hydraulic pressure in accordance with a pressing force applied to the brake pedal by an operator. The booster is provided for increasing the pressing force applied to the brake pedal. The booster and the brake support are mounted on a cowl provided above the brake pedal. More specifically, the brake support is fixed to the cowl by bolts fastened to slits formed in the cowl. The slits are elongated in a front-to-rear direction of the vehicle so that the brake support slides in the rear direction and causes downward movement of the brake pedal. This arrangement prevents transmission of a force exerted on the brake apparatus when the vehicle crushes in the front.
In this type of brake apparatus, a link mechanism is provided to transmit a force applied to the brake pedal to the master cylinder. The link mechanism comprises a brake pedal including a lever portion and a push rod as an input shaft of the master cylinder. More specifically, the brake pedal is supported by a pedal support directly under the cowl, and the push rod is connected in the middle of the lever portion of the brake. In this construction, a desired lever ratio required for the link mechanism can be easily achieved. Thus, a good brake feel can be obtained.
Accordingly, in the conventional brake apparatus, generally the pedal support is extended upwardly from a position of the booster to a dash panel. This is a reason for mounting the booster and the brake pedal on the cowl in the above-mentioned brake apparatus.
However, in the above-mentioned construction in which the brake pedal is supported under the cowl and the link mechanism is constituted by the brake pedal and the push rod, the booster must be spaced apart from the brake pedal in the front-to-rear direction of the vehicle.
When the brake apparatus is mounted on the vehicle, the position of the pedal is determined first in view of operability of the brake pedal. Positions of other component parts including the booster are determined by reference to the position of the brake pedal. Accordingly, the position of the booster is moved further toward the front of the vehicle as the distance between the booster and the brake pedal is increased. As a result, space between the booster and an engine positioned in front of the booster is reduced. This space is hereinafter referred to as a crush space. From this point of view, the above-mentioned conventional brake apparatus has a problem in that it is difficult to provide a sufficient crush space in front of the booster.
Generally, the booster is provided in a disk brake apparatus so as to increase a pressing force applied by a driver since a self servo effect cannot be obtained in the disk brake apparatus. In the booster of this type, a servo ratio is important. Japanese Laid-Open Utility Model Application No.4-35962 discloses a structure in which the servo ratio is changed during a brake applying operation.
FIG. 1
shows a booster disclosed in the above-mentioned document. As shown in
FIG. 1
, a power piston
108
is situated in a space formed between a front shell
100
and a rear shell
102
in a state where the power piston
108
is urged by a return spring
110
. The power piston
108
comprises a valve body
104
and a diaphragm plate
106
. A diaphragm
112
is provided on a back face of the diaphragm plate
106
so as to divide the space within the shells into a negative pressure chamber
114
and an atmospheric pressure chamber
116
.
An operating rod
118
, a plunger
120
, a reaction disk
122
and a push rod
124
are provided, in that order from the rear end, along the center axis of the power piston
108
. A predetermined gap is formed between the reaction disk and a pressing portion
120
A formed on a front end of the plunger
120
. An atmospheric pressure valve
120
B is formed on the rear end of the plunger
120
. A vacuum valve
130
A of a poppet valve
130
is pressed by a return spring
128
. An end of a negative pressure passage
132
is open in the vicinity of the vacuum valve
130
A of the poppet
130
. An atmospheric pressure passage
134
is formed in the vicinity of the atmospheric pressure valve
120
B of the plunger
120
.
Additionally, a reaction disk
122
comprises a first reaction disk
122
A and a second reaction disk
122
B. The first reaction disk
122
A has a convex shaped cross section and is positioned on the push rod
124
side. The second reaction disk
122
B has a ring shape and is positioned on the back side of the first reaction disk
122
A The hardness of the first reaction disk
122
A is lower than that of the second reaction disk
122
B.
In the above-mentioned structure, when a pressing force is applied to the brake pedal, a periphery of the second disk is pressed by a cylindrical portion
104
A of the valve body
104
. Thus, the first reaction disk
122
A having a lower hardness is deformed toward the plunger
120
, and contacts the pressing portion
120
A of the plunger
120
. Accordingly, a servo ratio at this stage is represented by tan &THgr;
1
as shown by a line A-B in the graph of FIG.
2
. When the pressing force applied to the brake pedal is increased, the second reaction disk
122
B also contacts the pressing portion
120
A of the plunger
120
. Thus, the servo ratio at this stage is represented by tan &THgr;
2
as shown by a line B-C in the graph of FIG.
2
. When the pressing force is further increased, the servo ratio is changed to a value represented by tan &THgr;
3
as shown by a continuing line C in the graph of FIG.
2
. Accordingly, in the above-mentioned structure, the servo ratio can be changed during operation of the booster.
However, in the above-mentioned structure, the characteristic (a booster characteristic) of the booster exhibits an upwardly closed convex characteristic curve. That is, the servo ratio is decreased as the pressing force is increased. Generally, a brake pad has the same characteristic and exhibits an upwardly closed convex characteristic curve. Thus, the braking characteristics (a pressing force versus deceleration characteristic) also exhibit an upwardly closed convex characteristic curve when the two characteristics are combined. This has a disadvantage in that brake pedal operation feel deteriorates.
Japanese Laid-Open Patent Application No5-185912 discloses a brake apparatus having a lever ratio changing mechanism provided between a brake pedal and an output member connected to a brake booster. The lever ratio changing mechanism changes a lever ratio of the entire brake pedal mechanism. More specifically, the lever ratio changing mechanism gradually increases the lever ratio as the brake pedal moves from an initial position to a start braking position, and gradually decreases the lever ratio as the brake pedal moves from the brake start position to the end of the brake pedal stroke.
Accordingly, when the brake pedal is on the way to the start braking position, that is, when the brake pedal is in an idling range (may be referred to as a first fill range), the lever ratio is small. Thus, the travel of the output member connected to the brake booster is large relative to travel of the brake pedal. This results in a completion of the first fill by a short stroke o
Isono Hiroshi
Kato Yoichi
Sakamoto Shigeru
Sekiya Yoshihide
Nguyen Hoang
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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