Automotive hydraulic braking system

An automotive hydraulic braking system includes a pivoted brake lever coupled to a master hydraulic cylinder assembly which in turn is coupled by a brake line to a plurality of hydraulically actuatable calipers. A mechanical brake pressure intensifier is provided in-line between the master cylinder and the calipers. Pedal travel is controlled according to a developed formula to approximate preestablished industry standards set for conventional vacuum-assisted hydraulic braking systems.

This invention relates to hydraulic braking systems for automobiles and 
particularly to those having a mechanical brake pressure intensifying 
device arranged in line between or included within the master cylinder and 
the brake calipers of the system. 
BACKGROUND OF THE INVENTION 
Multi-stage hydraulic pressure boosters for use in vehicular braking 
systems are relatively well known in the prior art. Such pressure 
boosters, or intensifiers, employ a system of concentric pistons to obtain 
a gradual boost in wheel cylinder pressure, providing a brake pedal feel 
comparable to that provided by vacuum-power assisted vehicular braking 
systems. Such prior art pressure intensifiers are illustrated in U.S. Pat. 
Nos. 3,101,282 and 3,010,238 to Jansson, and in U.S. Pat. Nos. 3,425,222; 
4,976,190; and 5,048,397 to Cooney. These references disclose a 
self-contained apparatus installed along the brake fluid line extending 
between the master cylinder or within the master cylinder housing and the 
wheel calipers of the vehicle. A cylindrical chamber surrounds two 
concentric pistons slidably disposed in the cylinder and urged by a 
compression spring toward a fluid inlet of the cylinder. A spring-loaded 
valve is disposed inside the inner piston and is held open by engagement 
with an abutment within the cylinder. 
Application of pressure to the brake pedal by a user displaces hydraulic 
fluid from the master cylinder into the intensifier which initially passes 
directly through the intensifier into the caliper urging the brake pads 
into engagement with the rotating disk or rotor, or; in the case of drum 
brakes, with the drum. Once the brake pads engage, the resistance to 
further movement increases the hydraulic pressure throughout the system 
and at the inlet of the intensifier sufficiently to cause the pistons to 
move against the spring force thereby closing the valve, preventing any 
further flow through of fluid through the intensifier. The ratio between 
the inlet and outlet side of the pistons of the intensifier are such as to 
deliver greater hydraulic pressure to the caliper than the pressure 
exerted on the intensifier by the master cylinder, hence providing the 
desired boosting or intensifying effect. 
SUMMARY OF THE INVENTION AND ADVANTAGES 
The present invention is a hydraulic braking system of an automotive 
vehicle which improves the prior art described above by providing a 
formula to control various parameters of the system within prescribed 
limits to govern the amount of brake pedal travel needed to attain a 
predetermined braking pressure. 
According to the invention, a brake pedal is mounted on support structure 
of the vehicle for pivotal travel (T.sub.p) in an arc about an axis and 
has a free end that is spaced from the axis by a pedal distance d.sub.p 
for displacement by the foot of the user along an arc of the axis. A 
linkage is coupled to the foot pedal at a location spaced from the axis by 
a displacement distance d.sub.1 less than the pedal distance d.sub.p 
defining a positive displacement ratio d.sub.p /d.sub.1 between the free 
end and the linkage. 
The system has at least one hydraulically actuatable brake caliper with 
displaceable brake pads for engaging and applying a braking force to an 
adjacent rotating friction element of the vehicle. The caliper has a 
piston bore adjacent the brake pads in which a piston is slideably 
supported defining an axial space between the piston and its bore into 
which hydraulic fluid may be introduced to displace and actuate the brake 
pads. The caliper space has a known volumetric capacity, V.sub.c, required 
to displace the piston a predetermined amount to achieve a predetermined 
braking force. 
The system also has a master cylinder that is mounted on the support 
structure of the vehicle adjacent the pedal and includes a housing having 
a piston bore therein with a fluid inlet at one end in communication with 
a source of hydraulic fluid and including a fluid outlet at an opposite 
end. Supported slideably within the master cylinder bore is a piston that 
is coupled to an opposite end of the linkage and is provided with a face 
of predetermined area, A.sub.m, for displacing hydraulic fluid out of the 
master cylinder through the outlet in response to displacement of the 
brake pedal. 
A brake pressure intensifier device has a fluid cylinder provided with a 
fluid inlet communicating with the outlet of the master cylinder for 
receiving the hydraulic fluid displaced from the master cylinder into the 
intensifier and a fluid outlet communicating with the brake caliper space 
for conveying hydraulic fluid under pressure from the intensifier to the 
space. The intensifier has a first piston that is supported slideably 
within the cylinder and a second piston supported telescopically within 
the first piston. A flow passage extends axially through the pistons to 
provide open fluid communication between the inlet and outlet of the 
cylinder. The flow passage has a valve seat that communicates with an 
adjacent valve member supported within the cylinder and is urged by a 
valve spring acting between the valve member and the second piston toward 
biased sealing engagement with the valve seat. A piston spring acts 
between the cylinder and the second piston urging the valve member into 
engagement with an adjacent abutment opposite the valve spring and thereby 
forcing the valve member out of engagement with the valve seat in 
opposition to the spring force of the valve spring. This initially opens 
the flow passage and allows a predetermined volume of hydraulic fluid 
displaced by the master cylinder to pass through the intensifier into the 
space of the caliper in response to displacement of the brake pedal 
causing in turn a corresponding displacement of the brake pads into 
engagement with the rotating friction element and thereafter producing 
increased hydraulic pressure at the inlet of the intensifier sufficient to 
overcome the piston spring causing the second piston and valve member to 
be displaced out of engagement with the abutment to close the flow passage 
preventing further flow of hydraulic fluid through the flow passage and 
defining a remaining volume requirement of hydraulic fluid, V.sub.I to be 
supplied to the caliper space by the intensifier in order to achieve the 
predetermined braking pressure. The second piston has forward and rearward 
end face areas A.sub.f, A.sub.r defining a positive output-to-input 
pressure intensification ratio, A.sub.f /A.sub.r when the flow passage is 
closed, and wherein the amount of pedal travel, (T.sub.p) of the brake 
pedal required to achieve the predetermined braking force is controlled by 
the formula: 
EQU T.sub.p =[(V.sub.c -V.sub.I)A.sub.f /A.sub.r +V.sub.I ]d.sub.p /(d.sub.l 
A.sub.m) 
A hydraulic brake system designed according to the above formula produces 
pedal travel within acceptable industry standards set for a conventional 
vacuum-assisted hydraulic braking systems.

DETAILED DESCRIPTION 
Referring to FIG. 1, the braking system is shown generally at 10 and 
includes a brake pedal 12 pivotally attached about a pivot axis 14 to 
support structure 16 of an automotive vehicle. The brake pedal 12 extends 
from the pivot axis 14 to a free end 18 fitted with a foot pad. The free 
end 18 is spaced a predetermined pedal distance d.sub.p from the axis 14 
and moveable about an arc of the axis 14 from the unactuated position 
shown in FIG. 1 along path A toward an actuated position. Return spring 20 
acts in tension between the brake pedal 12 and the support structure 16 to 
urge the brake pedal 12 toward the unactuated position into engagement 
with a fixed stop member 21 of the structure 16. 
A linkage in the preferred form of a push rod 22 has one end pivoted at 24 
to the foot pedal 12 in spaced relation to the pivot axis 14 at a 
displacement distance d.sub.l relatively closer to the pivot axis 14 than 
the free end 18, defining a positive displacement ratio, d.sub.p /d.sub.l, 
between the free end 18 and the linkage 22 in known manner to provide a 
mechanical advantage to the displacement of the linkage 22 in relation to 
the free end 18. 
A master cylinder assembly 26 is mounted on the support structure 16 of the 
vehicle adjacent the brake lever 12 and includes a hydraulic fluid F 
reservoir 28 disposed above and in fluid communication with an inlet 30 
provided at one end of a cylinder 32 of the master cylinder device 26. A 
fluid outlet 34 is provided at an opposite end of the cylinder 32. A 
piston 36 is supported slideably within the cylinder 32 presenting a face 
having a predetermined contact area, A.sub.M, for displacing the hydraulic 
fluid F out of the cylinder 30 when the piston 36 is slid along the 
cylinder 32 toward the outlet 34. 
The push rod linkage 22 is coupled at its opposite end to the piston 36 so 
that as an operator applies pressure to the brake pedal 12, the piston 36 
is caused to move within the cylinder 32 toward the outlet 34 thereby 
displacing hydraulic fluid out of the cylinder 32 through the outlet 34. A 
return spring 38 is disposed within the cylinder 32 and acts against the 
piston 36 to bias the piston 36 toward the unactuated position shown in 
FIG. 1. 
The outlet 34 of the master cylinder device 26 is fluidly coupled to at 
least one, and preferably a plurality, of hydraulically actuatable brake 
calipers 40 via a brake line 42. FIG. 1 illustrates that there are four 
such calipers 40 however, for purposes of simplicity, only one is shown in 
detail, with it being understood that the remaining calipers 40 (shown in 
block form) may be of the same or equivalent construction and operation as 
that to be described below. 
The calipers 40 may comprise any of a number of well known types such as a 
drum or disc brake system in which the calipers 40 each include a cast 
body 44 supporting a pair of brake pad elements 46 displaceable toward and 
away from one another to engage and release, respectively, an adjacent 
rotating friction element 48, such as a drum or rotor to control braking. 
Those skilled in the art will readily appreciate that the invention will 
work equally well with drum brakes, automatic braking systems (ABS), and 
the like. 
Each caliper body 44 is formed with a piston bore 50 having an open end 52 
adjacent the brake pad elements 46 and a closed end 54 spaced from the 
open end 52. A piston 56 is supported slideably within the bore 50 having 
a front face 58 adjacent the brake pad elements 46 and a back face 60 
adjacent the closed end 54 of the bore 50 defining an axial space or gap 
62 therebetween. The space 62 has a hydraulic fluid inlet opening 63 
coupled to the brake line 42 to receive hydraulic fluid under pressure 
into the space 62 in order to displace the piston 56 from an unactuated 
position shown in FIG. 1 in which the brake pads 46 are spaced out of 
engagement with the rotating element 48, to an actuated position, 
illustrated in FIG. 3, in which the brake pads 46 have been displaced by 
the piston 56 into engagement with the rotating element 48 and further 
urged by the piston 56 against the rotating element 48 to achieve a 
predetermined braking force (e.g., 1000 PSI) of the calipers 40. 
The calipers 40 have a characteristic combined volumetric capacity of the 
spaces, V.sub.c, known to be required to produce the desired predetermined 
braking force. In other words, a certain combined volume V.sub.c of the 
hydraulic fluid F must be introduced into the spaces 62 of the calipers 40 
to move the pistons 56 and hence the brake pad elements 46 from the 
unactuated position of FIG. 1 to the fully actuated position of FIG. 3 in 
order to attain the desired braking force. In FIG. 3, the right most 
phantom line indicates the unactuated position of the piston back face 60 
as shown in FIG. 1. 
A hydraulic brake pressure intensifier device 64 is arranged in-line 
between the master cylinder assembly 26 and the brake calipers 40 or may 
be incorporated into the master cylinder as a unit. The intensifier 64 is 
preferably of the type disclosed in the aforementioned U.S. Pat. Nos. 
4,976,190 and 5,048,397, incorporated herein by reference. In view of the 
detailed disclosures provided by these patents, only a brief description 
of the intensifier 64 will be provided below. 
The intensifier 64 includes a fluid cylinder 66 having a fluid inlet 68 at 
an inlet end coupled to a section of the brake line 42a extending between 
the outlet 34 of the master cylinder 26 and the inlet 68 of the 
intensifier 64 for receiving the hydraulic fluid displaced from a master 
cylinder 28 into the cylinder 66 of the intensifier 64, and including an 
outlet 70 at an opposite outlet end of the cylinder 66 communicating with 
each of the caliper spaces 62 through a second section 42b of the brake 
line for conveying hydraulic fluid under pressure into the space 62 of 
each caliper 40. 
As described more fully in the aforementioned incorporated patents, the 
intensifier 62 includes a first outer piston 72 slideably supported within 
the cylinder 66 and a second inner piston 74 also disposed in the cylinder 
in sliding, telescoping engagement within the first piston 72. A flow 
passage 76 extends axially through the pistons 74 and 76 to provide open 
fluid communication between the inlet 68 and outlet 70 of the cylinder 66. 
A valve member 78 is disposed in the flow passage 76 within a pocket 80 of 
the second piston 74 in adjacent relationship to a valve seat 82 of the 
flow passage 76. A valve spring 84 is disposed in the pocket 80 and acts 
in compression between the valve member 78 and a spring seat 86 of the 
second piston 74 to urge the valve member 78 with predetermined force 
toward sealing engagement with the valve seat 82, such that when seated, 
hydraulic fluid is prevented from flowing through the passage 76. 
An abutment, in the preferred form of a pin 88, projects axially into the 
flow passage 76 from the inlet end of the cylinder 66 presenting a free 
end adjacent the side of the valve member 78 opposite the valve spring 84. 
A piston spring 90 is disposed within the cylinder 66 and acts between the 
second piston 74 and the outlet end of the cylinder 66 to bias the second 
piston 74 and the valve member 78 as a unit toward the inlet end of the 
cylinder 66 with a counteracting force exceeding that provided by the 
valve spring 84 to urge the valve member 78 against the abutment 88 and 
out of engagement with the valve seat 82, to initially open the flow 
passage 76. The open condition of the flow passage 76 allows a 
predetermined volume of the hydraulic fluid F to pass through the 
intensifier 64 when a user depresses the free end 18 of the foot pedal 12 
in the direction of arrow A (FIG. 1), thereby displacing the piston 32 of 
the master cylinder 26 and forcing hydraulic fluid F out of the master 
cylinder 26, through the intensifier 64, and into the spaces 62 of the 
calipers 40, causing the caliper pistons 56 and brake pads 46 to be 
displaced from the initial unactuated position shown in FIG. 1, toward and 
into initial engagement with the rotating element 48, as illustrated in 
FIG. 2. 
Once having engaged the rotating element 48, it takes an additional 
remaining volume requirement hydraulic fluid, V.sub.I, (shown exaggerated 
in FIG. 3 where the left most phantom line indicates the piston back face 
60 in FIG. 2) that must be provided to the calipers 40 in order to urge 
the brake pad elements 46 with greater intensity against the rotating 
element 48 to achieve the predetermined braking force (illustrated by a 
comparison of FIGS. 2 and 3). Forcing the brake pad elements 46 further 
against the rotating element 48 causes an increase in hydraulic fluid 
pressure to develop throughout the system and at the inlet 68 of the 
intensifier 64 which in turn exerts a force on the inlet side of the 
pistons 72 and 74 that exceeds the counteracting force of the piston 
spring 90 and causes the second piston 74 and the valve member 78 to be 
displaced as a unit out of engagement with the abutment 88. The valve 
spring 84 thereafter urges the valve member 78 into sealing engagement 
with the valve seat 82 causing the flow passage 76 to become closed 
preventing any further flow of hydraulic fluid through the flow passage 
76. Thus, when the valve member 82 seats to close the flow passage 76, the 
calipers 40 are in the engaged condition (FIG. 2 position) and require the 
remaining additional known remaining quantity of hydraulic fluid V to 
achieve the predetermined braking force (FIG. 3 position). 
As explained fully in the aforementioned incorporated patents, the purpose 
of the intensifier 64 is to controllably or smoothly increase or boost the 
line pressure of the hydraulic fluid that exits the intensifier 64 through 
the outlet 70 in comparison to the relatively lower pressure of the 
hydraulic fluid entering the intensifier at outlet 68. The intensifier 64 
is able to produce the pressure boost by providing the inner second piston 
74 at its inlet side with a forward end face 94 having a forward end face 
area A.sub.f and a rearward end face 98 having a rearward end face area 
A.sub.r at its outlet side defining a positive output-to-input pressure 
intensification ration A.sub.f /A.sub.r. In this way, the output pressure 
delivered by the intensifier 64 is relatively greater than the input 
pressure to the intensifier 64 from the master cylinder 26. 
It has been found that the amount of displacement or pedal travel, T.sub.p, 
of the free end 18 of the pedal 12 in the direction of arrow A necessary 
to achieve the predetermined braking force at the calipers 40 can be 
controlled according to the formula: 
EQU T.sub.p =[(V.sub.c -V.sub.I)A.sub.f /A.sub.r +V.sub.I ]d.sub.p /(d.sub.l 
A.sub.m) 
and is optimized when A.sub.f /A.sub.r is between 1.5 and 3.0 and when 
A.sub.m is between 0.196 and 7,096. Such a hydraulic braking system 
constructed according to the above formula results in pedal travel values 
T.sub.p that are comparable to acceptable industry standards established 
for conventional hydraulic braking systems not employing a mechanical 
hydraulic brake pressure intensifier. 
The disclosed embodiment is representative of a presently preferred form of 
the invention, but is intended to be illustrative rather than definitive 
thereof. The invention is defined in the claims.