Brake device for automobile

A push rod of a vacuum booster includes an inner rod section, a pipe-shaped outer rod section which is slidably fitted over an outer periphery of a rear portion of the inner rod section and connected to a brake pedal, and a buffer member made of a synthetic resin and fitted over the outer periphery of the inner rod section in front of the outer rod section. Usually, an end face of the outer rod section is retained in a position in which it abuts against a projection of the inner rod section. When an axial compressing force is applied to the push rod upon a collision of an automobile, the end face of the outer rod section slides forwards over and past the projection, while buckling the buffer member. Thus, the pushing-up of the brake pedal toward a vehicle compartment due to the retreating movement of a master cylinder is prevented, and the load applied to a driver's foot is alleviated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a brake device for an automobile for 
braking a wheel by brake hydraulic pressure. The brake hydraulic pressure 
is generated by a brake hydraulic pressure generating means due to 
depression of a brake pedal. 
2. Description of the Related Art 
A brake pedal of an automobile is supported on a dash board which rises 
from a floor panel of the vehicle. For this reason, when a shock generated 
upon a collision of the automobile causes the dash board to retreat toward 
a vehicle compartment along with the brake pedal, there is a possibility 
that a load may be applied to a driver's foot which is placed on the brake 
pedal. To alleviate the load applied to the driver's foot during a 
collision, a brake device is known from Japanese Patent Application 
Laid-open No. 6-211115, in which a pedal bracket for rotatably supporting 
an upper end of a brake pedal and a dash board are connected to each other 
so as to be separable due to a shock. Upon collision of the vehicle, the 
pedal bracket, which is separated from the dash board, is rotated forwards 
along with the brake pedal to alleviate the load applied to the driver's 
foot. 
The degree and magnitude of deformation of the dash board varies depending 
upon the extent of the collision. For this reason, in the known device, 
there is a possibility that the bracket may not reliably be separated from 
the dash board depending upon the extent of the collision. Hence, the 
brake pedal cannot be rotated forwards. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to reliably alleviate 
the load received by the driver's foot from the brake pedal upon a 
collision of the automobile. 
To achieve the above object, according to a first aspect and feature of the 
present invention, there is provided a brake device for an automobile, 
comprising a brake pedal operated by a driver and connected to a push rod 
of a brake hydraulic pressure generating means which generates a brake 
hydraulic pressure. The push rod includes an inner rod section, an outer 
rod section axially slidably supported on an outer periphery of the inner 
rod section, and a coupling means for integrally coupling both rods to 
each other. The coupling means is adapted to release the coupling to 
permit the sliding of the outer rod section when an axial compressing 
force, equal to or larger than a predetermined value, is applied between 
both rods. 
With the above arrangement, when the driver depresses the brake pedal to 
cause an axial compressing force which is smaller than a predetermined 
value to be applied between both rods, the rods are moved together to 
transmit the movement of the brake pedal to the brake hydraulic pressure 
generating means. When the brake hydraulic pressure generating means is 
retreated, due to the collision of the automobile, the axial compressing 
force equal to or larger than the predetermined value is applied between 
both rods. The coupling by the coupling means is then released to permit 
the rods to slide relative to each other. Thus, the forward stroke of the 
brake pedal is permitted to alleviate the load applied to the driver's 
foot. 
The term "predetermined value" means a value which is larger than an axial 
compressing force which is generated by the driver applying a normal 
depressing force to the brake pedal and which is smaller than an axial 
compressing force which is generated by the retreating movement of the 
brake hydraulic pressure generating means due to the collision of the 
automobile. 
In this case, an end face of the outer rod section may be put into contact 
with a projection formed on an outer periphery of the inner rod section. 
When the axial compressing force is applied between both rods, the outer 
rod section slides over and past the projection. With such a construction, 
the magnitude of the axial compressing force which permits the coupling by 
the coupling means to be canceled, can be regulated by changing the height 
and/or shape of the projection. Moreover, the load applied to the driver's 
foot can be effectively alleviated by a resisting force which is generated 
when the outer rod section slides over and past the projection. 
Further, a buffer member may be supported between a stopper which is formed 
on an outer periphery of the inner rod section and the projection. Thus, 
an end face of the sliding outer rod section pushes the buffer member 
against the stopper to buckle the buffer member. With such a construction, 
it is possible to further effectively alleviate the load applied to the 
driver's foot by a resisting force resulting from buckling of the buffer 
member upon sliding of the outer rod section. 
To achieve the above object, according to a second aspect and feature of 
the present invention, there is provided a brake device for an automobile, 
comprising a brake pedal operated by a driver. The brake pedal is 
connected to a rear end of a push rod of a brake hydraulic pressure 
generating means which generates a brake hydraulic pressure. An axis of 
the push rod is disposed to be inclined with respect to a horizontal 
plane. When an axial compressing force, which is equal to or larger than a 
predetermined value, is applied to the push rod upon collision of the 
automobile, the push rod is flexed to permit the movement of the brake 
pedal in a forward direction of a vehicle body. 
With the above arrangement, when the driver depresses the brake pedal 
causing an axial compressing force, which is smaller than the 
predetermined value to be applied to the push rod, the push rod, without 
being flexed, transmits the movement of the brake pedal to the brake 
hydraulic pressure generating means. When the brake hydraulic pressure 
generating means is retreated due to the collision of the automobile, an 
axial compressing force, which is equal to or larger than the 
predetermined value, is applied to the push rod. The push rod is flexed by 
application of a flexing load to the push rod. Since the push rod is 
disposed to be inclined, a forward stroke of the brake pedal alleviates 
the load applied to the driver's foot. 
The term "predetermined value" means a value which is larger than an axial 
compressing force which is generated by the driver applying a normal 
depressing force to the brake pedal and which is smaller than an axial 
compressing force which is generated by the retreating movement of the 
brake hydraulic pressure generating means due to the collision of the 
automobile. 
The above and other objects, features and advantages of the invention will 
become apparent from the following description of the preferred 
embodiments taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described by way of particular 
embodiments with reference to the accompanying drawings. 
A first embodiment of the present invention will now be described with 
reference to FIGS. 1 to 4. 
As shown in FIGS. 1 and 2, a booster shell 1 of a vacuum booster VB, 
constituting a brake hydraulic pressure generating means, includes a pair 
of front and rear shell halves 1a and 1b with their opposed ends coupled 
to each other. A booster piston 3, having a diaphragm 2 coupled to its 
rear surface, is received in booster shell 1 for longitudinally 
reciprocating movement. The diaphragm 2 has an outer periphery fixed to 
coupled portions of the shell halves 1a and 1b, and has an inner periphery 
fixed to an outer periphery of a front portion of a piston boss 4. The 
inside of the booster shell 1 is divided by the booster piston 3 and the 
diaphragm 2 into a front-side vacuum chamber A which faces a front surface 
of the booster piston 3, and a rear-side working chamber B which faces a 
rear surface of the diaphragm 2. A rearward extending tube 5 is integrally 
formed at a central portion of a rear wall of the shell half 1b. An air 
inlet 6 is defined in a rear end of the rearward extending tube 5. The 
vacuum chamber A normally communicates with the inside of an intake 
manifold (not shown) of an internal combustion engine, which is a vacuum 
source. The booster piston 3 is biased rearwards by a return spring 7 
which is mounted between the booster piston 3 and the shell half 1a. 
The piston boss 4 includes a cylindrical portion 4a which is slidably 
supported in the rearward extending tube 5 with a seal member 9 interposed 
therebetween. A filter 11, which is deformable so as not to obstruct the 
operation of an input rod 10, is mounted in a rear area of the cylindrical 
portion 4a. The filter 11 purifies the air introduced through the air 
inlet 6. A valve piston 13 is connected to a tip end of the input rod 10 
which is connected to a brake pedal 12. The valve piston 13 is slidably 
supported at the center of the piston boss 4. A control valve 14 is 
provided in the cylindrical portion 4a of the piston boss 4. The control 
valve 14 is switchably operated in response to the relative movement of 
the valve piston 13 relative to the piston boss 4 by the 
advancing/retreating operation of the input rod 10. 
The structure of the control valve 14 will be described below. The control 
valve 14 includes a) a valve member 15 made of a rubber, b) an annular 
first valve seat 16.sub.1 which is formed within the piston boss 4, so 
that the valve member 15 can seat on the valve seat 16.sub.1, and c) a 
second valve seat 16.sub.2 which is formed angularly at a rear end of the 
valve piston 13 and surrounded by the first valve seat 16.sub.1, so that 
the valve member 15 can seat on the valve seat 16.sub.2. The valve member 
15 is formed cylindrically and fixed at its rear end to a valve member 
retaining tube 18 which is fitted to an inner periphery of the cylindrical 
portion 4a of the piston boss 4. The valve member 15 has a front end 
portion formed at an increased wall thickness so as to be able to seat on 
the first valve seat 16.sub.1 and the second valve seat 16.sub.2. The 
valve member 15 is biased toward the first and second valve seats 16.sub.1 
and 16.sub.2 by a valve spring 19 which is mounted between the valve 
member 15 and the input rod 10. The input rod 10 is biased in a retreating 
direction by a return spring 8 which is mounted between the input rod 10 
and the valve member retaining tuber 18. 
The outside of the first valve seat 16.sub.1 communicates with the vacuum 
chamber A through a through-hole 20 provided in the piston boss 4. 
Intermediate portions of the first and second valve seats 16.sub.1 and 
16.sub.2 communicate with the working chamber B through another 
through-hole 21 which is provided in the piston boss 4. The inside of the 
second valve seat 16.sub.2 communicates with the air inlet 6 through the 
inside of the valve member 15. 
In such a control valve 14, when the valve member 15 is seating on the 
first and second valve seats 16.sub.1 and 16.sub.2, the communication 
between the vacuum chamber A and the working chamber B is cut off, and the 
communication between both chambers A and B and the air inlet 6 is also 
cut off. Thus, the control valve 14 is in a neutral state. When the valve 
piston 13 is advanced from the neutral state relative to the piston boss 
4, the second seat 16.sub.2 is moved away from the valve member 15, 
thereby causing the working chamber B to communicate with the air inlet 6 
through the through-hole 21. When the valve piston 13 is retreated 
relative to the piston boss 4, the valve member 15 is moved away from the 
first valve seat 16.sub.1, thereby causing the vacuum chamber A and the 
working chamber B to communicate with each other through the through-holes 
20 and 21. 
The piston boss 4 is provided with a forward extending output rod 22 which 
is connected to a master cylinder M which constitutes the brake hydraulic 
pressure generating means. The vacuum booster B is fixed to a dash board 
24, which defines a front portion of a vehicle compartment, by a rod 23 
extending longitudinally through the booster shell 1. The master cylinder 
M is commonly fastened to the booster shell 1. An outer periphery of the 
rod 23 is covered with a boot 2a, which is integrally provided on the 
diaphragm 2, so that the vacuum chamber A and the working chamber B do not 
communicate with each other. 
The structure of the push rod 10 will be described below. The push rod 10 
comprises a) an inner rod section 25 accommodated within the rearward 
extending tube 5, b) a pipe-shaped outer rod section 26 which is slidably 
fitted over an outer periphery of a rear portion of the inner rod section 
25 which protrudes from the rearward extending tube 5, c) a buffer member 
27 made of a synthetic resin which is fitted over the outer periphery of 
the inner rod 25 in front of the outer rod section 26, and d) a coupling 
means 28 which is adapted 1) to normally integrally couple both the rod 
sections 25 and 26 and 2) to permit the sliding movement of the outer rod 
section 26 relative to the inner rod 25, when an axial compressing force, 
which is equal to or larger than a predetermined value, is applied to 
between both the rod sections 25 and 26. 
A spherical portion 25a is formed at a front end of the inner rod section 
25 and is oscillatably coupled to the valve piston 13. A collar-shaped 
stopper 25b, an annular projection 25c and a guide portion 25d are formed 
to the rear of the spherical portion 25a. The guide portion 25d supports 
the outer rod section 26 for sliding movement. The cylindrical buffer 
member 27, having a slit 27a in its side, is supported between the stopper 
25b and the projection 25c of the inner rod section 25. When the buffer 
member 27 is mounted on the inner rod section 25, the buffer member 27 can 
be allowed to run over the projection 25c by widening the slit 27a. The 
outer rod section 26, which is inserted on to the guide portion 25d of the 
inner rod section 25 from the rear, is retained in a location in which the 
front end face 26a thereof abuts against the projection 25c of the inner 
rod section 25. The outer rod section 26 is integrally formed at its rear 
end with a connecting portion 26b to which the brake pedal 12 is 
connected. The guide portion 25d and the projection 25c of the inner rod 
section 25 and the end face 26a of the outer rod section 26 constitute the 
coupling means 28. 
The operation of the embodiment will be described below. 
When a depressing force is applied to the brake pedal 12 to brake the 
vehicle, and the input rod 10 and the valve piston 13 coupled to the input 
rod 10 are advanced, the booster piston 3 is not initially moved. Hence, 
the second valve seat 16.sub.2 of the valve piston 13 is moved away from 
the valve member 15 of the control valve 14. This causes the working 
chamber B to communicate with the air inlet 6 through the through-hole 21 
to the atmosphere. The booster piston 3 is advanced by a difference in 
pressure generated between the vacuum chamber A and the working chamber B, 
thereby enabling the master cylinder M to be operated through the output 
rod 22. When the depressing force on the brake pedal 12 is released, the 
input rod 10 is first retreated along with the valve piston 13 by a 
resilient force of the return spring 8. The second valve seat 16.sub.2 
seats on the valve member 15, while causing the valve member 15 to leave 
the first valve seat 16.sub.1. As a result, the vacuum chamber A and the 
working chamber B communicate with each other through the through-hole 20, 
so that the difference in pressure between both chambers is decreased. 
Thus, the booster piston 3 is retreated by the resilient force of the 
return spring 7 to cancel the operation of the master cylinder M. 
When a normal depressing force is being applied to the brake pedal 12 by a 
driver's braking operation, the axial compressing force, which is applied 
forward to the outer rod section 26, is transmitted from the end face 26a 
of the outer rod section 26 via the projection 25c to the inner rod 
section 25. When the master cylinder M has been retreated toward the 
vehicle compartment along with the dash board 24 upon a collision of the 
automobile, an axial compressing force, which is larger than the normal 
depressing force, is applied to the push rod 10, if the driver's foot is 
on the brake pedal 12. As shown in FIGS. 4A and 4B, if the axial 
compressing force exceeds a predetermined value, the outer rod section 26 
slides forward with respect to the inner rod section 25 by the end face 
26a of the outer rod section 26 running over the projection 25c of the 
inner rod section 25. As a result, the pushing-up of the brake pedal 12 
toward the vehicle compartment by the retreating movement of the master 
cylinder M is prevented, and the load applied to the foot of the driver is 
alleviated. It should be noted that the axial compressing force permitting 
the end face 26a of the outer rod section 26 to overrun the projection 25c 
can be regulated to any value by changing the height and/or shape of the 
projection 25c. 
When the outer rod section 26 slides forward with respect to the inner rod 
section 25, the outer rod section 26, having run onto the projection 25c, 
is deformed so that its diameter is increased. The buffer member 27, which 
is clamped between the end face 26a of the outer rod section 26 and the 
stopper 25b of the inner rod section 25, is squashed. Thus, a shock 
generated during forward sliding of the inner rod section 26 can be 
buffered to further effectively alleviate the load applied to the driver's 
foot. 
A second embodiment of the present invention will now be described with 
reference to FIGS. 5 to 8. 
As shown in FIG. 5, an upper dash board 35 extends substantially 
horizontally and a lower dash board 36 extends substantially downwards 
from the upper dash board 35. The upper and lower dash board 35 and 36 are 
provided in a front portion of a vehicle compartment of an automobile. A 
vacuum booster VB, having a master cylinder M integrally mounted thereon, 
is supported on the lower dash board 36. The master cylinder M and the 
vacuum booster VB constitute a brake hydraulic pressure generating means 
of the present invention. 
A brake pedal 12 is rotatably supported through a pin 38 at its upper end 
on a pedal bracket 37. The pedal bracket 37 connects the upper dash board 
35 and the lower dash board 36 to each other. A push rod 10, which extends 
rearwards from the vacuum booster VB, is supported at its rear end on an 
intermediate portion of the brake pedal 12 through a pin 39. An axis L of 
the push rod 10 is inclined, so that a rear portion of the axis L is at a 
lower level than a horizontal plane P. 
Although the push rod 10 of the vacuum booster VB in the first embodiment 
shown in FIG. 1 has been separated into the inner and outer rod sections 
25 and 26, with the buffer member 27 mounted between both the rods 25 and 
26, the push rod 10 of the vacuum booster VB in the second embodiment 
shown in FIG. 6 is formed from a simple rod. The other structures of the 
vacuum booster VB are common in the first and second embodiments. 
The operation of the second embodiment will be described below. The basic 
operation of the vacuum booster VB in the second embodiment is the same as 
in the first embodiment and hence, duplicated description is omitted. 
When the driver applies a depression force to the brake pedal 12, an axial 
compressing force is applied to the push rod 10. However, the push rod 10 
has a strength such that it is not flexed by the depression force. 
However, when the lower dash board 36 and the pedal bracket 37 are 
deformed upon collision of the automobile as shown in FIG. 7, the master 
cylinder M is retreated toward the vehicle compartment along with the 
lower dash board 36. An axial compressing force, which is larger than the 
normal depressing force, is applied to the push rod 10, if the driver's 
foot is on the brake pedal. At this time, the vacuum booster VB is 
retreated substantially horizontally along the horizontal plane P. 
However, a flexing load is applied to the push rod 10, which protrudes 
rearwards from the vacuum booster VB, to flex (or deform) the push rod 10 
downwards since the axis L of the push rod 10 is inclined toward the 
vertical with respect to a horizontal plane. As a result, the brake pedal 
12 is rotated forward, whereby the pushing-up of the brake pedal 12 toward 
the vehicle compartment by the retreating movement of the master cylinder 
M is prevented, and the load applied to the driver's foot is alleviated. 
A broken line in FIG. 8 shows how the load received by the driver's foot is 
varied with respect to the stroke of the brake pedal 12, when a 
dis-flexible push rod 10 having a higher strength is used. In this case, 
it can be seen that when the stroke of the brake pedal reaches a limit 
position, the load rises suddenly. On the other hand, a solid line in FIG. 
8 shows a variation in load in the present embodiment, wherein when the 
load is increased to a point a, a further increase in load can be avoided 
by the flexing of the push rod 10. 
The present invention has been applied to the push rod 10 of the vacuum 
booster VB in the first and second embodiments, but in a brake device 
having no vacuum booster VB, the present invention can be applied to a 
push rod of a master cylinder M. In addition, the inner rod section 25 has 
been disposed on the front side and the outer rod section 26 has been 
disposed on the rear side in the first embodiment, but the positional 
relationship between the inner and outer rod sections can be reversed. The 
stopper 25b and the projection 25c of the inner rod section 25 are not 
necessarily annular and can be formed from a step and a plurality of small 
projections disposed circumferentially. If a brittle portion is previously 
formed at a portion of the push rod 10 in the second embodiment, the push 
rod 10 can be further reliably flexed upon a collision of the automobile. 
Although the embodiments of the present invention have been described in 
detail, it will be understood that the present invention is not limited to 
the above-described embodiments, and various modifications in design may 
be made without departing from the spirit and scope of the present 
invention defined in claims.