U.S. patent application number 15/312292 was filed with the patent office on 2017-11-16 for actuating system for a vehicle brake and method of operating the actuating system.
The applicant listed for this patent is IPGATE AG. Invention is credited to Christian KOGLSPERGER, Heinz LEIBER, Valentin UNTERFRAUNER, Anton VAN ZANTEN.
Application Number | 20170327098 15/312292 |
Document ID | / |
Family ID | 58056059 |
Filed Date | 2017-11-16 |
United States Patent
Application |
20170327098 |
Kind Code |
A1 |
LEIBER; Heinz ; et
al. |
November 16, 2017 |
ACTUATING SYSTEM FOR A VEHICLE BRAKE AND METHOD OF OPERATING THE
ACTUATING SYSTEM
Abstract
The invention relates to an actuating system for a vehicle
brake, with an actuating arrangement, in particular a brake pedal,
at least one (first) piston-cylinder unit, which is connected via a
hydraulic line to the vehicle brake (braking circuit) in order to
supply the braking circuit with pressure medium and apply pressure
to the vehicle brake, and with a drive for the piston-cylinder
unit. According to the invention, pressure medium can be fed to the
braking circuit in controlled manner in both piston movement
directions, in particular the advance stroke and the return stroke,
by means of at least one, in particular stepped, piston (10) of the
piston-cylinder unit (10, 10a, 10b).
Inventors: |
LEIBER; Heinz;
(Oberriexingen, DE) ; UNTERFRAUNER; Valentin;
(Munchen, DE) ; KOGLSPERGER; Christian;
(Geretsried, DE) ; VAN ZANTEN; Anton; (Ditzingen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IPGATE AG |
Pfaffikon Sz |
|
CH |
|
|
Family ID: |
58056059 |
Appl. No.: |
15/312292 |
Filed: |
May 20, 2015 |
PCT Filed: |
May 20, 2015 |
PCT NO: |
PCT/EP2015/061105 |
371 Date: |
July 11, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T 7/042 20130101;
B60T 13/146 20130101; B60T 8/4031 20130101; B60T 8/4081 20130101;
B60T 8/344 20130101; B60T 8/4018 20130101; B60T 13/686 20130101;
B60T 13/745 20130101; B60T 8/341 20130101; B60T 8/4022
20130101 |
International
Class: |
B60T 8/40 20060101
B60T008/40; B60T 13/68 20060101 B60T013/68; B60T 8/40 20060101
B60T008/40; B60T 7/04 20060101 B60T007/04; B60T 8/34 20060101
B60T008/34; B60T 8/34 20060101 B60T008/34; B60T 13/74 20060101
B60T013/74; B60T 13/14 20060101 B60T013/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2014 |
DE |
10 2014 107 112.3 |
Jul 4, 2014 |
DE |
10 2014 109 384.4 |
Jul 9, 2014 |
DE |
10 2014 109 628.2 |
Claims
1-50. (canceled)
51. An actuating device for a vehicle brake, comprising: an
actuating arrangement, at least a first pressure source, comprising
a first piston-cylinder unit having a master cylinder, configured
to be actuated by means of the actuating arrangement, and a second
pressure source, comprising a second piston-cylinder unit with an
electromechanical drive, wherein the first and second pressure
sources are connected with at least one braking circuit via a
hydraulic line, in order to supply the at least one braking circuit
with pressure medium and to apply pressure to the vehicle brake,
and wherein the actuating device further comprises a valve
arrangement configured to regulate the brake pressure, wherein, by
means of the piston of the second piston-cylinder unit of the
second pressure source, wherein the piston of the second
piston-cylinder unit is a stepped piston, at least one braking
circuit is supplied with pressure medium in a controlled manner
during both forward and return piston strokes.
52. The actuating device according to claim 51, wherein no valves
are arranged in a line section between the first pressure source
and the valve arrangement.
53. The actuating device according to claim 51, wherein the first
piston-cylinder unit comprises one or two pistons.
54. The actuating device according to claim 51, wherein the second
piston-cylinder unit forms two or three pressure chambers.
55. The actuating device according to claim 51, further comprising
a third piston-cylinder unit, wherein a working chamber of the
third piston-cylinder unit is connected with at least one working
chamber of the second piston-cylinder unit, the first
piston-cylinder unit, or both the first and second piston-cylinder
units by means of a hydraulic line, in which a valve arrangement is
arranged.
56. The actuating device according claim 51, wherein a hydraulic
connecting line is disposed between a pressure chamber of the
second pressure source and a pressure chamber delimited by the rear
of the piston of the first piston-cylinder unit, wherein at least
one solenoid valve is disposed in the hydraulic connecting line and
is configured to control a piston of the first piston-cylinder
unit.
57. The actuating device according to claim 51, further comprising
a third piston-cylinder unit having a pressure chamber connected
via a hydraulic line with a travel simulator and via asolenoid
valve with at least one braking circuit.
58. The actuating device according to claim 55, wherein the third
piston-cylinder unit comprises a force-travel simulator.
59. The actuating device according to claim 55, wherein a pressure
chamber of the third piston-cylinder is connected via a hydraulic
connecting line and at least one solenoid valve with at least one
braking circuit.
60. The actuating device according to claim 51, further comprising
a hydraulic connecting line with a solenoid valve, wherein the
hydraulic connecting line with the solenoid valve is arranged
between a pressure chamber of a piston of the second
piston-cylinder unit and at least one braking circuit for
prefilling from the pressure chamber of the piston of the second
piston-cylinder unit.
61. The actuating device according to claim 51, wherein the
electromechanical drive comprises an electric motor, wherein the
electric motor is arranged parallel to and is configured to drive
the second piston-cylinder unit.
62. The actuating device according to claim 51, wherein, if the
vehicle is idle or at a standstill, hydraulic systems and lines or
pressure chambers are pressure-balanced in an equalisation
reservoir by means of open valves to a return line.
63. The actuating device according to claim 51, wherein, by means
of the first pressure source, through the design of seals
and/orvalve switching, a depression is developed for setting a
lining clearance.
64. A method of operating the actuating device according to claim
51, the method comprising: using a delivery volume of the second
pressure source for pressure-related correlation with a
pressure-volume curve of one or more individual wheel brakes for
diagnosis of leaks in the at least one braking circuit and, if
necessary, shutting down one or more braking circuits diagnosed as
having leaks, or for diagnosis of a presence of air in the at least
one braking circuit.
65. A method of operating the actuating device according to claim
51, that the method comprising: using a defined delivery volume of
the second pressure source, oriented towards a pressure-volume
curve of a respective wheel, for pressure build-up or pressure
reduction via a respective inlet valve or exhaust valve for
controlling the second pressure source.
66. The method according to claim 64, further comprising developing
a depression for setting a lining clearance, using the second
piston-cylinder unit.
67. An actuating system for a vehicle brake, comprising: an
actuating arrangement, at least a first pressure source, comprising
a first piston-cylinder unit having a master cylinder, configured
to be actuated by means of the actuating arrangement, a second
pressure source, comprising a second piston-cylinder unit, with an
electromechanical drive, wherein the first and second pressure
sources are connected via a respective hydraulic line with at least
one braking circuit, to supply the braking circuit with pressure
medium and to apply pressure to the vehicle brake, and a valve
arrangement configured to regulate brake pressure, wherein, by
means of the second piston-cylinder unit, during forward and return
piston strokes, at least one braking circuit is arranged to be
supplied with pressure medium in a controlled manner.
68. The actuating device according to claim 51, wherein, in at
least one hydraulic line from the first pressure sourceto the valve
arrangement, no valves are arranged.
69. An actuating system for a vehicle brake, comprising: an
actuating arrangement, at least a first pressure source, comprising
a first piston-cylinder unit having a master cylinder, configured
to be actuated by means of the actuating arrangement, a second
pressure source, comprising a second piston-cylinder unit, with an
electromechanical drive, wherein the first and second pressure
sources are connected via a respective hydraulic lines with at
least one braking circuit, to supply the braking circuit with
pressure medium and to apply pressure to the vehicle brake, and a
valve arrangement configured to regulate brake pressure, wherein,
between a pressure chamber of a double stroke piston of the second
pressure source and a pressure chamber delimited by a rear of the
piston of the first piston-cylinder unit of the first pressure
source, a hydraulic connecting line exists, in which at least one
solenoid valve configured to control various operating modes is
arranged.
70. The actuating device according to claim 51, wherein solenoid
valves are arranged in first and second hydraulic lines connecting
the first pressure source and second pressure source with the valve
arrangement, and wherein a pressure sensor is arranged in only one
of these first and second hydraulic lines or in a further hydraulic
line leading from the second piston-cylinder unit to the valve
arrangement.
71. The actuating device according to claim 51, further comprising
non-return valves or solenoid valves arranged in hydraulic lines
connecting together pressure chambers of the second piston-cylinder
unit, the non-return valves or solenoid valves being arranged for
controlling pressure medium inflow and outflow.
72. The actuating device according to claim 71, further comprising
a pressure relief valve disposed in a hydraulic line connecting the
hydraulic lines in which the non-return valves or solenoid valves
are arranged.
73. The actuating device according to claim 51, further comprising:
a third piston-cylinder unit, comprising a pressure chamber; a
hydraulic line connecting the pressure chamber of the third
piston-cylinder unit with at least one braking circuit; and a
solenoid valve arranged for feeding pressure medium into the at
least one braking circuit and disposed in the hydraulic line
connecting the pressure chamber of the third piston-cylinder unit
and the at least one braking circuit.
74. The actuating device according claim 51, further comprising a
spring arranged on one piston of the first piston-cylinder
unit.
75. The actuating device according to claim 51, further comprising
a third piston-cylinder unit, wherein a counterforce is applied
using a piston of the second piston-cylinder unit, in order to
reduce pressure in the third piston-cylinder unit.
76. The actuating device according to claim 51, wherein the first
piston-cylinder unit comprises a plunger rod piston and a floating
piston, wherein the plunger rod piston has only one seal, and
wherein the plunger rod piston and the floating piston are coupled
together by means of a spring housing of the plunger rod
piston.
77. The actuating device according to claim 76, further comprising
a diagnostic circuit for testing one or more seals associated with
one or more pistons.
78. The actuating device according to claim 51, further comprising
a third pressure source, comprising a third piston-cylinder unit,
disposed upstream of the first pressure source.
79. The actuating device according to claim 51, wherein the second
pressure source comprises a motorised pump with an associated
solenoid valve or non-return valve.
80. The actuating device according to claim 51, further comprising:
a third piston-cylinder unit; and a travel simulator arrangement
configured to interact with the third piston-cylinder unit.
81. A method of operating the actuating device according to claim
51, the method comprising: supplying pressure medium to a rear of a
piston of the first piston-cylinder unit of the actuating device
according to claim 51 by means of the second piston-cylinder unit
of the actuating device according to claim 51.
82. The method according to claim 81, further comprising developing
pressure in braking circuits without the use of isolation
valves.
83. The method according to claim 81, further comprising
controlling various operating modes using at least one solenoid
valve.
84. An actuating system for a vehicle brake, comprising: an
actuating arrangement, at least a first pressure source, comprising
a first piston-cylinder unit having a master cylinder, configured
to be actuated by means of the actuating arrangement, a second
pressure source, comprising a second piston-cylinder unit, with an
electromechanical drive, wherein the first and second pressure
sources are connected via a respective hydraulic lines with at
least one braking circuit, to supply the braking circuit with
pressure medium and to apply pressure to the vehicle brake, and a
valve arrangement configured to regulate brake pressure, wherein
the first piston-cylinder unit comprises just a single
pressure-developing piston.
85. The actuating device according to claim 51, wherein at least
one pressure chamber of the second piston-cylinder unit is
hydraulically connected with a pressure or working chamber formed
on a rear of a piston of the first piston-cylinder unit, via a
further valve arrangement.
86. The actuating system according claim 84, further comprising: a
third piston-cylinder unit; and a travel simulator, wherein the
third pressure source or piston-cylinder unit is configured to
supply the travel simulator with pressure medium and to supply at
least one braking circuit with pressure medium in case of a
pressure supply failure.
87. The actuating system according to claim 86, wherein the third
piston-cylinder unit comprises a cross bore, connected via a
hydraulic line with a reservoir.
88. The actuating system according to claim 84, wherein a working
chamber of the single pressure-developing piston is connected via a
cross bore, and via a solenoid valve or a throttle-non-return valve
arrangement with a reservoir.
89. The actuating system according to claim 84, wherein the
actuating arrangement is arranged to act on a spring or spring
combination of the single pressure-developing piston.
90. The actuating system according to claim 87, further comprising
a normally-open solenoid valve arranged in a hydraulic line from
the third piston-cylinder unit to the travel simulator and to the
at least one braking circuit.
91. The actuating system according to claim 87, further comprising
a normally-closed solenoid valve arranged in a hydraulic line from
the third piston-cylinder unit to the travel simulator and to the
reservoir.
92. A method of operating the actuating system according to claim
84, the method comprising: supplying pressure medium to the rear of
a piston of a first piston-cylinder unit of the actuating system of
claim 84, by means of the second piston-cylinder unit of the
actuating system according to claim 84.
93. The method according to claim 92, further comprising developing
pressure in braking circuits, by means of one or more of the
piston-cylinder units, without the use of isolation valves.
94. The method according to claim 92, further comprising
controlling various operating modes using at least one solenoid
valve.
95. The method according to claim 64, further comprising supply
pressure medium at the rear of a piston of the first
piston-cylinder unit, using the second piston-cylinder unit.
96. The method according to claim 94, further comprising developing
pressure in braking circuits by means of at least one of the
pressure sources, without the use of isolation valves.
97. The method according to claim 93, further comprising
controlling various operating modes using at least one solenoid
valve.
98. The method according to claim 92, further comprising using a
pressure source or third piston-cylinder unit to supply pressure
medium to a travel simulator and, in case of pressure supply
failure, to a braking circuit.
99. The method according to claim 92 further comprising performing
functional diagnostics, wherein a comparison is performed between a
volume delivery of the second piston-cylinder unit and a pressure
level achieved at the time of the diagnostics.
100. A method of operating a braking device, the braking device
having a first pressure source or piston-cylinder unit and a second
pressure source including a second piston cylinder unit, in the
form of a double stroke stepped piston, the method comprising:
controlling at least one braking circuit using the stepped piston
of the second piston-cylinder unit of the second pressure source
during both forward and return strokes of the double stroke stepped
piston.
Description
[0001] The invention relates to an actuating system for a vehicle
brake according to the preamble of claim 1 and a method of
operating the actuating system.
PRIOR ART
[0002] Braking systems are subject to increasing demands. This is
particularly the case in terms of reliability and a good fallback
level. If the brake booster fails, then for the internationally
prescribed foot force of 500 N, ideally a deceleration of more than
0.64 g should be achieved, which is considerably higher than the
minimum required by law of 0.24. An advantage of the high
achievable deceleration is also that a red warning lamp, which is
irritating for the driver, does not have to be activated.
[0003] These demands can be met by brake-by-wire systems with a
travel simulator. Here the master cylinder (HZ) or tandem master
cylinder (THZ) is designed for the fallback level if the braking
system fails. This is achieved by appropriate dimensioning with a
small diameter. This results in higher pressures for a
corresponding foot force. The necessary brake fluid volume for 0.64
g and corresponding pressure is relatively small compared to that
at maximum pressure with full vehicle deceleration and fading. A
THZ cannot fully deliver the necessary volume even with a longer
stroke. DE 102009043494 of the applicant proposes a solution for
this with a storage chamber, which at higher pressures feeds
corresponding volume into the braking circuit. DE 102010045617 A1
of the applicant also describes a further solution, in which by
means of suitable valve and THZ control, volume from the master
cylinder is fed from the reservoir into the braking circuit. In
vehicles with high volume uptake, e.g. SUVs and small vans, the
filling of the braking circuits when braking must necessarily take
place before the blocking pressure for high .mu. is required. Both
solutions place high demands on the tightness of the valves.
Furthermore, the additional filling of the braking circuits is
associated with an interruption in the pressure build-up and minor
braking losses.
[0004] DE 102011111369 of the applicant describes a system with an
additional piston, which delivers the necessary pressure medium
volume and has the advantage that it is operated by the motor
spindle and is not active in the fallback level, e.g. allows the
specified deceleration. The disadvantage here can be that in some
cases correspondingly high forces arise which place stress on the
spindle, the ball screw unit (KGT) and the bearings.
[0005] A further important consideration is the installed length.
In this regard, there are two different types of braking system
design, known as the "serial type" S and the "parallel type" P
(hereinafter also referred to as "S system" and "P system"). What
this means is that with the S system the main components (such as
for example in DE 102011111369) of the master cylinder THZ, motor
with ball screw unit KGT and auxiliary piston are arranged in a
single axis and with the P system (such as for example in DE 10
2012222897 A1), the master cylinder THZ is arranged in one axis and
a plunger for volume provision with motor is arranged in a
laterally displaced second axis.
[0006] The P systems require less installed length, but are more
complicated and less reliable than S systems. According to DE
102013111974.3 of the applicant a P system is implemented with a
double stroke piston and THZ, the installed length and valve
switching of which does not meet all requirements.
OBJECT OF THE INVENTION
[0007] The object of the invention is to provide a system with a
short installed length and great reliability.
ACHIEVEMENT OF THE OBJECT
[0008] The object is achieved according to the invention by the
features of claim 1.
[0009] Advantageous embodiments or designs of the invention are
contained in the further claims, to which reference is made
here.
ADVANTAGES OF THE INVENTION
[0010] With the solution according to the invention and its
embodiments or designs, an actuating system for a vehicle brake and
a method of operating the actuating system with reduced installed
length and improved reliability are provided. Such an actuating
system is also provided with a little constructional effort and
less pressure loads from extreme pedal forces.
[0011] In an advantageous embodiment, in the hydraulic line
sections between the working chambers of the first pressure source
or piston-cylinder unit (master cylinder) and the valve block VBL
containing the ABS/ESP control valves, unlike known systems no
switching or isolating valves are provided. Pressure regulation can
be advantageously performed with other means, in particular
existing switching valves (such as EA or VDK). Hydraulic line
sections leaving the working chambers of the second pressure source
or piston-cylinder unit are connected prior to the valve block VBL
with the line sections coming from the working chambers of the
first piston-cylinder unit. In the former in particular in each
case a non-return valve and a switching valve can be arranged.
[0012] From these line sections, which can be connected between the
non-return valves and the switching valves, a further hydraulic
line section can expediently be run to a working chamber formed on
the rear of a piston of the first pressure source or
piston-cylinder unit (master cylinder), in which in particular a
switching valve is arranged.
[0013] A further advantageous design provides that a working
chamber of a third pressure source or piston-cylinder unit
(auxiliary piston) by means of a hydraulic line, in which in
particular a valve device is arranged, is connected with at least
one working chamber of the second (DHK) and/or first pressure
source or piston-cylinder unit (master cylinder).
[0014] The invention or its embodiments/designs also provide
sufficient brake fluid volume with an additional prefill
function.
[0015] Further potential for improvement, in particular based on a
brake mechanism according to the applicant's patent application DE
102013111974.3 with partial P design and DE 102014102536.9 with
double stroke piston DHK and prefill function with S design (to
which reference is hereby made), is also realised.
[0016] The solutions described in applicant's applications DE
102013111974.3 and DE 102014102536.9 (the content of which is
included here by reference), or the main features of these, can
advantageously also be applied or transferred to the invention or
its embodiments/designs, such as for example fail-safe adaptive
travel simulator with auxiliary piston and feed function in the
fallback level, prefill function with its respective advantages
such as short installed length, minimized complexity, and low pedal
initial force, ideally comparable with the S design.
[0017] The system with serial (S) arrangement of THZ and Motor is
longer in design than the parallel (P) system, in which the THZ and
motor are arranged in separate axes. The P system, however, is more
complex with housings and valves. With the extensive functions and
dimensions described it is intended that the complexity of the P
system can be reduced and that the functions can be expanded.
[0018] By hydraulically connecting the double stroke piston DHK
with the secondary side of the plunger rod piston DK, a functioning
of the P system similar to that of the S system is brought about,
in which instead of the hydraulic pressure, the motor drive acts on
the plunger rod piston DK. This is associated with a number of
advantages, such as the pistons being loaded with real pressure and
also piston displacement, in particular by the plunger rod piston
DK, fault detection being easier and the ability to vary the volume
supply to the braking circuits by different valve arrangements.
Furthermore, at least one isolation valve can be dispensed with in
the connection of the double stroke piston DHK. Similarly, fewer
solenoid valves are required for the double stroke piston DHK and
the feed valve can be dispensed with.
[0019] The piston-cylinder unit or the double stroke piston can
also be replaced by a pressure source with continuous delivery,
e.g. an electromotor-driven high pressure pump.
[0020] The valves used to open the braking circuit for pressure
reduction are checked for tightness with each braking.
[0021] Furthermore, by alternate switching of the valves EA, a
pressure sensor can be dispensed with, since the volume delivery by
the double stroke piston DHK, in comparison with the
pressure-volume characteristic curve and pressure, identifies both
the volume intake and leakage or brake circuit failure.
[0022] The free travel proposed with the S design for installed
length reduction and advantages in recovery, in that the THZ motor
and double stroke piston DHK are not operated, can also be used in
the P version. This allows considerably reduced wear.
[0023] Further features and advantages of the invention or its
designs are indicated by the claims or the following description of
the figures, to which reference is made here.
DESCRIPTION OF THE FIGURES
[0024] These show as follows:
[0025] FIG. 1 a system in the P version with reduced
complexity;
[0026] FIG. 1a an additional spring arrangement in the floating
piston SK;
[0027] FIG. 2 a system as in FIG. 1 with simplified valve switching
of a double stroke piston DHK;
[0028] FIG. 2a a system with a high-pressure pump, instead of a
piston-cylinder unit;
[0029] FIG. 3 a system as in FIG. 1 with additional valves of the
tandem master cylinder to the reservoir;
[0030] FIG. 4 a system in the P design with parallel double stroke
pistons (DHK3) with three effective piston surfaces;
[0031] FIG. 5 a system in the P design simplified with parallel
double stroke pistons (DHK2) with two pistons;
[0032] FIG. 5a a system with simplified twin piston version;
[0033] FIG. 6 a system in P design with a motor arranged in
parallel with drive belts;
[0034] FIG. 7 a particularly simple implementation (minimal
version) of the system with additional installed length
reduction;
[0035] FIG. 7a a spring arrangement;
[0036] FIG. 7b spring characteristics; and
[0037] FIG. 7c a cross bore arrangement.
[0038] The system shown in FIG. 1 represents minimum complexity for
minimum function. With this P design, on a first axis A1 a (first)
piston-cylinder unit (master cylinder) with plunger rod piston (DK)
12a and floating piston (SK) 12 and a further (second)
piston-cylinder unit with a piston 16 (auxiliary piston) are
situated, and on a second axis A2, which is radially displaced with
respect to the first axis, a piston-cylinder unit with a double
stroke piston (DHK), a ball screw unit (KGT) with spindle 5 and a
drive motor 8 are situated. The piston-cylinder unit with auxiliary
piston can also be arranged on a parallel axis, as for example in
applicant's patent application DE 102011017436.2, in which the
pedal plunger is arranged on the central axis of the master
cylinder and two auxiliary pistons on axes displaced parallel
thereto. From working chambers of the first piston-cylinder unit
(master cylinder or THZ) hydraulic lines HL1 and HL2 (without
isolation valve) are connected via a valve block (VBL) with wheel
brakes (not shown). From working chambers 10a, 10b of the
piston-cylinder unit with double stroke piston (DHK) line sections,
in which non-return valves V3, V4 are arranged, and a common line
section, leading to two further hydraulic line sections, in which
(normally closed) switching valves EA are arranged, run to the
hydraulic lines HL1, HL2 or via the valve block VBL to the wheel
brakes. The working chambers 10a, 10b of the double stroke piston
are in other words hydraulically connected via said line sections
and valves EA with the working chambers of the first
piston-cylinder unit. From the common line section a further line
section branches off, which is connected to a working chamber 12c,
formed by the rear of the piston (DK) of the first piston-cylinder
unit.
[0039] From the working chambers 10a and 10b of the double stroke
piston, hydraulic lines also run (shown by dashes), in which
non-return valves are fitted, to a reservoir VB.
[0040] A travel simulator arrangement with a travel simulator WS
with pistons, non-return valves RV0, RV1 and UV, and an aperture D
and a solenoid valve WA is connected via a hydraulic line HL3 with
a working chamber of the piston-cylinder unit with auxiliary piston
16 and corresponds to the travel simulator described in applicant's
patent applications DE 102013111974.3 and DE 10 2104 102 536.9, to
which in this respect reference is made. The pressure relief valve
UV has two functions here: in normal functioning at high pedal
speed to reduce the throttle force and similarly in the fallback
level RFE, to allow the pedal force to be converted more quickly
into pressure. The travel simulator arrangement can expediently be
arranged parallel to the THZ or also in the valve block VBL.
[0041] The working spaces of the plunger rod piston DK and the
floating piston SK are connected via hydraulic line sections HL1
and HL2 with the valve block VBL, wherein in these line sections no
valves, in particular no switching valves, are arranged (unlike the
designs according to FIGS. 4 and 5. During pressure build-up
P.sub.auf by means of the double stroke piston DHK initially a
volume supply from the working chamber 10a of the double stroke
piston DHK into the working chamber 12c of the plunger rod piston,
e.g. to the rear of the plunger rod piston DK of the
piston-cylinder unit (THZ), is effected, so that the pistons DK and
SK develop or increase pressure in their pressure chambers or the
lines HL1, HL2. Unlike the design shown in FIG. 6, therefore, the
volume or pressure is directed from the piston-cylinder unit (THZ)
via the pressure control valves (not shown) in the valve block VBL
directly to the braking circuits (BK) or the wheel brakes. Pedal
travel sensors 2a, 2b determine the pressure in the braking
circuits BK, which is brought about via the drive of the double
stroke piston DHK and appropriate volume supply. The travel
simulator WS determines the pedal force characteristic. For a
travel of .DELTA.WS this travel simulator is activated, accounting
for approximately 40% of the entire travel of the pedal plunger.
The volume supply can in a first operating mode 1 be changed for
the corresponding travel in that by opening the two valves EA
volume directly from the working chamber of the double stroke
piston DHK reaches the hydraulic lines associated with the pistons
DK and SK. Here the pistons DK and SK remain in the position,
indicated by the travel of the DK piston or the spring forces of
the springs of the pistons DK and SK. By switching the valves EA
there is in practice the same pressure on both sides of the pistons
SK and DK, so that the plunger rod piston DK rests on the pedal
plunger (PS) 3, provided the springs are suitably coordinated. This
can be performed selectively with an additional spring, as for
example described in connection with FIG. 1a.
[0042] A progressive spring characteristic of the floating piston
SK, allows the plunger rod piston DK to stay in position for a
travel of .DELTA.WS and the floating piston SK to have a particular
distance to the plunger rod piston DK.
[0043] The positioning of the plunger rod piston DK on the pedal
plunger 3 is preferably used in the ABS function (operating mode
2). The ABS function can also be performed before the full travel
.DELTA.WS, since here the maximum brake pressure of, for example,
200 bar is applied. The ABS function can be performed at a low .mu.
of just 10 bar and a correspondingly low travel of the pedal
plunger 3. Here also, the plunger rod piston DK is intended to come
up against the pedal plunger 3. With further movement of the pedal
plunger 3 this causes additional counterforces due to friction and
spring forces and compressive force via the pedal plunger 3. This
is quite advantageous, because a small reaction by ABS against the
pedal 1 is desirable. This can be further reinforced and modulated
by varying the admission pressure Pvor by means of the double
stroke piston DHK.
[0044] The starting position of the floating piston SK with stroke
reserve is of major significance for the "worst case" failure of
the motor at low .mu. and subsequent positive .mu.-jump. Here the
floating piston SK can only deliver enough volume, if it has
sufficient stroke and is not already up against the end of the
housing. With the abovementioned coordination, the pistons SK and
DK deliver volume via the residual stroke, without the pistons DK
and SK clashing, whereupon disadvantageous asymmetric brake
pressures would arise.
[0045] For diagnosis of the position of the floating piston SK this
can be implemented with a sensor (not shown here).
[0046] The pressure build-up P.sub.auf takes place for as long as
the pedal travel sensors 2a/2b specify this to the motor
controller. If, for a high pressure level or volume, e.g. during
fading, the volume of the double stroke piston DHK in the advance
stroke via the pressure relief valve S1 is insufficient, then in
the return stroke a further volume boost takes place via valve
S2.
[0047] With this valve switching of the suction valves S1 and S2
with pressure relief valves V3 and V4 the double stroke piston DHK
is no longer able to perform additional functions such as
prefilling or pressure reduction P.sub.ab. These are described in
the following figures with additional valve complexity.
[0048] The eight valves necessary for pressure regulation (four
inlet valves EV and four exhaust valves AV) or alternatively four
switching valves SV in multiplex operation MUX are contained in the
valve block VBL.
[0049] With the ABS function the double stroke piston DHK works
continuously with advance stroke and return stroke, since the
volume drawn for the pressure reduction P.sub.ab via the exhaust
valves AV must be repeatedly requested. If a pressure reduction
P.sub.ab initiated by the pedal sensors 2a/2b takes place, then
this similarly takes place via the valves AV in the return stroke
R. This preferably takes place via only one valve AV, e.g. in the
DK circuit with open valves EA.
[0050] For reduced complexity, there is also only one pressure
sensor DG. It is possible to determine the pressure in both braking
circuits with just one pressure sensor, since the floating piston
12 equalises the pressure between the two braking circuits.
[0051] This takes place independently of the switching position of
the E/A valves. If a pressure build-up is performed by the double
stroke piston DHK via the E/A valves directly in the braking
circuits (e.g. during ABS) it is possible by alternating switching
of the valves EA of the double stroke piston DHK in each case to
boost only in the respective braking circuit, so that the braking
circuits are never directly connected with one another.
[0052] The functions of the double stroke piston DHK and the travel
simulator WS are also described in applicant's patent applications
DE 102010045617 A1, DE 102013110188.7, DE102014102536.9 and DE
102014107112.3, to which reference is hereby made in this
connection.
[0053] FIG. 1a shows a spring arrangement with an additional spring
on the floating piston SK. Here a spring housing 26 with floating
piston-spring F.sub.SK is shown, as is standard in tandem master
cylinders THZ. In addition, here a spring F.sub.X arranged between
the floating piston and spring housing acts, corresponding to the
starting spring force of the conventional spring of the floating
piston SK. It is known that this is designed such that as a result
the floating piston SK and plunger rod piston DK are reset and the
friction forces overcome. The spring of the plunger rod piston DK,
on the other hand, is constrained to a high force level. Thus, with
a correspondingly progressive spring design of the floating piston
SK, simultaneous closing, when there is a pressure build-up
P.sub.auf, by both pistons DK and SK of the cross bore 27 or the
cross bore not shown here of the plunger rod piston DK (shown in
FIG. 1a in the open position) can be achieved. With this
arrangement as well, this is the case by corresponding dimensioning
of F.sub.X, which has the same force as a conventional spring of
the floating piston SK. Normally, when there is a pressure build-up
P.sub.auf, the distance between the floating piston SK and plunger
rod piston DK is determined by the volume uptake of the braking
circuits, wherein the pressure forces overcome the spring forces.
In the abovementioned case, by parallel connection of the valves EA
an almost even pressure level results, so that the compressive
forces are not applied and the respectively acting spring and
friction forces determine the position of the pistons. In the case
described with the parallel connection of the valves EA it is
intended that the plunger rod piston DK rests on the pedal plunger
PS, which is possible by spring adjustment.
[0054] At high temperatures and with no rain (when, therefore,
normally no .mu.-jump is possible) operating mode 1 can be
activated, in which the parallel connection of valve EA does not
take place and the floating piston SK and if necessary also the
plunger rod piston DK are moved to the stroke end. This has the
advantage that the seals can in each case be checked over the full
stroke, such that "dormant failures" are impossible.
[0055] FIG. 2 shows the next configuration level with valves ESV in
line section HL4 and V.sub.DK in line section HL5, and with SV5 in
line section HL6, and correspondingly expanded functions.
[0056] The feeding-in ES of additional volume into the braking
circuits BK has major advantages at the fallback level RFE, since
the additional volume results in a higher pressure level or shorter
pedal travel. The feeding-in ES, however, requires that the valve
V.sub.DK is closed, so that a pressure equalisation, which occurs
when the valve EA is open, is prevented here. Thus, the feeding-in
via the valve EA is possible optionally in one braking circuit BK
or both together. Since during feeding-in, compressive forces from
auxiliary piston 16 and also plunger rod piston DK act on the pedal
1, the feeding-in ES is limited to pressures of, for example,
20-25% of the blocking pressure, e.g. 20-25 bar due to excessive
pedal forces. Following the feeding-in ES the valve ESV is closed
(operating mode 5). This is effective with 30-40% additional volume
in the fallback level RFE. Since the pressures in the fallback
level RFE are lower than is normally the case, the valve V.sub.DK
can have a correspondingly smaller design in the switchable
pressure range. This allows larger cross-sections or lower magnetic
forces, which is cost-relevant.
[0057] Since with the valve V.sub.DK closed, the plunger rod piston
DK is moved via the pedal plunger PS, the valve SV5 is necessary to
avoid a depression as the piston moves. With the pressure reduction
P.sub.ab the valve V.sub.DK is opened, and the volume reaches the
reservoir VB via the open valves ES and WA or similarly the
reservoir VB via the valves EA and AV.
[0058] Here a free travel LW between pedal plunger 3 and the
plunger rod piston DK can be employed, which in combination with
valve ESV provides advantages, namely no activation of the double
stroke piston DHK and of the motor for pressure build-up and
pressure reduction or no piston operation during recovery and a
reduction in installed length.
[0059] The plunger rod piston DK does not have a standard design
here as in a conventional THZ with two seals (the second seal
serves to avoid external oil leaks). In FIGS. 4 and 6, for example,
the plunger rod piston DK is combined with the double stroke piston
DHK as a 3-piston solution and advantageously has just one seal
with its pressure chamber. This design with just one seal D1 can
also be used here without combining with the double stroke piston
DHK and without stepped piston for the non-stepped cylindrical
plunger rod piston DK. A coupling of the spring housing 26 with the
floating piston SK is required here, however. This is necessary so
that during pressure build-up P.sub.auf the piston SK pulls the
piston DK normally through the cross bore 27 of the plunger rod
piston, since here the volume from the double stroke piston DHK
flows via the open cross bore 27 of the plunger rod piston DK into
the braking circuit associated with the piston DK and the
corresponding pressure acts on the braking circuit associated with
the piston SK. With further pressure build-up and the cross bore of
the plunger rod piston DK closed, the admission pressure acts on
the rear of the braking circuit associated with the piston DK and
continues to move the piston DK for further pressure build-up. This
is achieved in that in the first phase of the pressure build-up
P.sub.auf, the valve EA of the plunger rod piston DK is open until
through corresponding volume of the double stroke piston both cross
bores are closed, since here the pressure of the plunger rod piston
DK acts on the floating piston SK. Then the valve EADK is closed
again and the admission pressure Pvor acts on the plunger rod
piston DK for pressure build-up (operating mode 4)
[0060] During braking, a phase of constant pressure (e.g. no change
in pedal travel) often occurs in the travel simulator step 1
(pressure range <30 bar). This is used to diagnose the leak
tightness of all components, including the valves EA. Here valve
VDK and valve EA are closed, the motor position is unchanged, and
the valves ESV and WA are open, wherein if all components of the
braking circuits are leak tight, no pressure reduction should take
place. In particular, the valves EA are in practice tested during
each partial braking (80%) of all braking operations.
[0061] Advantages of the design according to FIG. 2 are: [0062] if
the plunger rod piston DK secondary seal fails, unlike in FIGS. 1
and 3 there is no failure of the brake booster BKV. In the event of
failure of the DK seal in FIG. 2, the brake booster BKV does not
fail either. The function of the seal must be checked at regular
intervals, which can take place when the vehicle is at a
standstill, for example; [0063] lower piston friction; [0064] lower
stressing of the sleeve gaskets, since the volume during pressure
build-up P.sub.auf opens the sleeve; [0065] a design with free
travel LW is possible, since the feeding-in volume at the auxiliary
piston reaches the pressure rod DK circuit directly via the cross
bore.
[0066] As is known, the braking system must also be designed for
maximum pedal forces that are 12 times greater than the pedal force
upon reaching the blocking pressure. This affects the pressure
loading of the auxiliary piston, the housing of the auxiliary
piston and valves ESV and WA. The existing valve switching offers a
simple solution to this. If this case arises and the valve WA
designed for a low pressure level, e.g. 200 bar, opens at this
pressure, then a pedal movement occurs, which is measured by the
pedal sensors 2a/2b. This leads to the closing of valve V.sub.DK.
The pedal plunger acts on the plunger rod piston DK, and a
depression occurs on the secondary side of the plunger rod piston
DK. The pressure of the plunger rod piston acts on the primary
side, and can be increased to 200 bar on the abovementioned signal.
Thus, the pedal force is equalised by two pistons rather than one,
leading to a significant reduction in pressure level for the
abovementioned components (operating mode 5).
[0067] In the event of failure of the travel simulator, e.g. due to
a leak, the functioning of the travel simulator WS normally fails,
e.g. the pedal force reaction is absent. The applicant's patent
applications DE 102014102536.9 and DE 102014107112.3 have already
created the possibility that with the travel simulator arrangement
shown with auxiliary piston 16 what is referred to as follow-up
brake boosting can be switched to, so that as with a conventional
vacuum-brake servo the pedal force contributes to the brake
booster, where longer pedal travel may have to be taken into
consideration.
[0068] A failure of the travel simulator is also possible with the
system according to FIG. 2. Following operation of the brake pedal,
in the first step only the return spring 18 acts on the pedal
force, e.g. the pressure reduction P.sub.ab takes place as
described by a corresponding motor controller via the pedal travel
sensors 2a/2b. The failure of the travel simulator WS is only
identified if the valve WA should close for a certain pedal travel.
If it does not do so, e.g. due to failed seals also, then this is
detected via the force-travel sensor KWS. The pressure build-up
P.sub.auf then takes place normally following the signal from the
pedal travel sensors 2a/2b. Here volume or pressure is also
triggered on the rear of the plunger rod piston DK and in parallel
to the prefilling of the braking circuits BK via the two valves EA,
i.e. all that is missing is the counterforce of the travel
simulator WS. A small counterforce acts on the pedal plunger. A
larger counterforce can be developed by closing the valve V.sub.DK.
As a result of depression, the full compressive force of the
plunger rod piston DK acts on the pedal plunger PS 3. By actuation
of the V.sub.DK valve by pulse width modulation PWM, with the help
of the force-travel measuring element KWS a counterforce can be
developed. Alternatively, the valves EA can be closed after
prefilling. Then the pedal force and motor controller act with
appropriate volume supply due to the brake boosting (operating mode
7). Here the brake boosting effect can be reduced if necessary. For
prefilling, in this valve arrangement with valves V3 and V4,
instead of an additional solenoid valve (see, for example, valve VF
in FIG. 3) a pressure relief valve UV2 can be used, which in
particular is arranged in a connecting line between the line
sections containing non-return valves V3, V4, wherein for example,
up to 30 bar prefilling with larger piston surface takes place and
then above 30 bar volume flows for pressure equalisation to the
rear of the double stroke piston DHK. Thus, up to 30 bar the large
piston area of the double stroke piston DHK acts and at >30 bar
as a result of the pressure equalisation a smaller effective
surface acts for volume supply.
[0069] For the application of the multiplex method (MUX)for
pressure modulation, for the pressure reduction function during
brake boosting operation a valve AVMUX is necessary. In this case,
with valves EA open, volume for pressure reduction can reach the
return flow, providing a pressure build-up for additional volume
with return stroke (RH) (fading) takes place via the double stroke
piston DHK. During normal braking, this valve AVMUX is
unnecessary.
[0070] A failure of the secondary seal of the floating piston must
also be considered. Essentially, normally (no failure) the
P.sub.vor acts on the plunger rod pistons DK and displaces the
pistons DK for pressure build-up in both braking circuits. In the
above case the volume would flow from the VDK via the cross bore of
the plunger rod piston DK and the failed seal. This can be
prevented by the following measures: [0071] the cross bores act as
chokes, so that the dynamic pressure before the plunger rod piston
DK moves the DK-piston; [0072] in the return line from the floating
piston SK to the reservoir VB a valve VVB is connected, which in
the event of failure closes or for each braking process closes
briefly until a corresponding stroke of the piston DK takes place
at which point the cross bore of the floating pistons SK is
securely closed; [0073] an additional spring on the plunger rod
piston DK at a distance from the pedal plunger PS. This is
preloaded with a force greater than the preloading of the SK
spring, so that the PS after a distance a moves the DK piston and
thus closes the cross bore at the plunger rod piston DK. Pvor then
acts and DK comes up against the floating piston SK for pressure
build-up in the floating piston SK and in the case of failure of
the DK braking circuit. The BKV operation is thus not
jeopardised.
[0074] In the absence of a failure, the additional spring is
inactive, since the DK piston is moved by the Pvor pressure, see
also operating mode.
[0075] FIG. 2a shows an alternative to the double stroke piston
DHK, with a pump driven by an electric motor. This can be a gear,
vane or piston pump. The motor can expediently be an EC motor. A
piston pump does not need an additional non-return valve, unlike a
sliding vane pump, since its operating states are at constant
pressure without volume delivery, so that here there is no return
flow. If for the brake booster BKV mode the pressure reduction is
not intended to take place via exhaust valves AV of the ABS
pressure regulator device VBL, this is performed via valve AVMUX.
With such a system, however, there is no prefilling VF and also no
multiplex operation(MUX), nor any pressure reduction as is possible
with a double stroke piston DHK with valve AS.
[0076] FIG. 3 shows a system with additional functions and valve
alternatives. The suction valve SV5 can be avoided by having a
3/2-V.sub.DK valve. In the normally open state of the double stroke
piston DHK and plunger rod piston DK the return flow is closed. In
the fallback level RFE, unlike in the switched state, the
connection between double stroke piston DHK and plunger rod piston
DK is isolated and that to the reservoir VB open.
[0077] The valve arrangement of the double stroke piston DHK with
valves AS and V.sub.F is known from the applicant's DE
102014107112.3, with the valves TV being left out. Here the valve
AS allows a pressure reduction with the open valves EA without
opening of the braking circuits BK by valve AV. The valve ESV is
closed and only open in fallback level 3 with a failure of the
vehicle electrical system, which is particularly effective with a
plunger rod piston DK according to FIG. 2.
[0078] All systems shown have in common that both the pedal travel
plunger 3 and the double stroke piston DHK can act on the plunger
rod piston DK with volume delivery and corresponding pressure. By
appropriate valve switching the following operating modes (BM) are
possible: [0079] 1. The pressure source or high-pressure pump or
the double stroke piston (Pvor) acts on the rear of the plunger rod
piston DK, the valves EA are closed both during the forward stroke
and if necessary also during the return stroke, the pedal plunger 3
has no contact with the plunger rod piston DK; [0080] 2. The
pressure source or high-pressure pump or the double stroke piston
(Poor) acts on the plunger rod piston and via valve EA directly in
the braking circuits BK, wherein for example in the ABS mode the
pedal plunger 3 is in contact with the plunger rod piston DK);
[0081] 3. The pedal plunger 3 acts in the fall-back level directly
on the plunger rod piston (applies to the system according to FIG.
1) (the operating modes 1-3 apply to a system according to FIGS. 1,
2 and 3); [0082] 4. Prefilling of the braking circuits BK or first
phase of the piston operation in the system according to FIG. 2,
valve EADK is briefly opened, the floating piston SK moves with the
plunger rod piston DK as a result of the coupling until both the
cross bores associated with the pistons are closed by corresponding
activation of the stroke of the double stroke piston or volume
and/or pressure measurement in the braking circuit associated with
the piston DK. DHK acts in plunger rod piston DK, the pedal plunger
3 is not in contact with the plunger rod piston DK; [0083] 5. The
pressure source or the double stroke piston DHK acts via valve EA
in the braking circuits; valve VDK is closed, e.g. during the
highest pedal force together with pedal plunger 3; [0084] 6. The
feeding-in of volume from the auxiliary piston acts in the
fall-back level RFE 2 (motor failure) and 2a (motor failure with
low .mu. with subsequent positive .mu.-jump) via valve EA in the
braking circuits BK; valve VDK is closed, valve ESV is open, during
free travel LW the pedal plunger 3 is only in contact with the
plunger rod piston after this free travel (applies to systems
according to FIGS. 2 and 3); [0085] 7. The pressure source or the
double stroke piston DHK acts via valve VDK together with the pedal
plunger on the plunger rod piston. The valve VDK controls the brake
power boosting if necessary via KWS. This arrangement acts as what
is known as a follow-up booster if the travel simulator WS fails;
[0086] 8. The pedal plunger acts on the plunger rod piston in the
fallback level with and without feeding-in for pressure
generation.
[0087] The advantages common to the systems according to FIGS. 1, 2
and 3 include: [0088] During normal braking (without considering
ABS) the SK and DK seals are loaded by >90% with directly acting
brake pressure, i.e. no "dormant failures" can occur here
(exception: DK seal in FIG. 2; wear of the seal is low, however,
due to the absence of loading by pressure and cross bore). In other
systems, only the slight pressure from the travel simulator WS acts
on the THZ, harbouring failures that are dormant until in the
fallback level a substantially higher pressure (by a factor of
approximately 2 to 3) acts. The effect is even more extreme if the
high pedal forces described occur. [0089] ABS causes a small pedal
reaction; [0090] Reduction in the installed length by parallel
arrangement of motor and THZ; [0091] The travel simulator WS with
auxiliary piston is highly reliable; [0092] With each pressure
build-up the tightness of the EA valves is tested, avoiding dormant
failures; [0093] If seals fail, the brake booster BKV does not
fail, which is important for a normal driver who, despite there
being a smaller master cylinder piston in travel simulator systems,
requires >4 times more pedal force for the same braking if the
brake booster BKV fails; [0094] With the small additional cost of a
V.sub.F valve a more rapid pressure build-up P.sub.auf is possible
by V.sub.F, resulting in a shorter braking distance; [0095] Since
isolation valves TV are not present or are absent, the system is
simpler and more reliable with a few knock-on effects as
described.
[0096] The cost of this is low compared with competing systems.
[0097] In the following the embodiments shown in FIGS. 4-6 are
described. In the embodiments, according to FIGS. 4 and 5 isolation
valves TV are arranged in the lines from the THZ to the valve block
VBL. Valves AS, VF and VDK are also provided.
[0098] FIG. 4 shows the P design, in which in the first axis a
piston-cylinder unit with a piston 16 (auxiliary piston), a further
piston-cylinder unit (THZ) with DK piston 12a and SK piston 12 are
located, and in the second axis, which in relation to the first
axis is laterally or radially displaced, a piston-cylinder unit
with a double stroke piston (DHK), a ball screw unit (KGT), with
spindle 5 and a drive motor 8 are located. From working chambers of
the further piston-cylinder unit (THZ), hydraulic lines, in which
the solenoid valves TV associated with the braking circuits are
connected, are connected via a valve block (VBL) with wheel brakes
(not shown). From working chambers of the piston-cylinder unit with
double stroke piston, hydraulic lines, in which the solenoid valves
EA associated with the braking circuits are arranged, similarly run
via the valve block VBL to the wheel brakes.
[0099] From the working chambers 10a and 10c of the double stroke
piston, hydraulic lines, in which non-return valves S1 and S2 are
connected, also run to reservoir VB.
[0100] A travel simulator WS with piston, non-return valves RV0,
RV1, aperture D and solenoid valves ESV, WA is connected via a
hydraulic line with aperture D or non-return valve RV0 with a
working chamber of the piston-cylinder unit with auxiliary piston
and corresponds to the travel simulator described in the
applicant's patent applications DE 102013111974.3 and DE 102014102
536.9, to which reference is made in this connection. A pressure
relief valve UV here has two functions: during normal functioning
at high pedal speed, to reduce the plunger force and similarly in
the fallback level RFE, to allow the driver to convert the pedal
force more rapidly into pressure. The travel simulator WS can
expediently be arranged parallel to the THZ or in the valve block
VBL.
[0101] During normal functioning, in the event of pedal operation
of the auxiliary pistons 16, a force-travel-simulator KWS (see
applicant's DE 102010045617.9) and pedal travel sensors 2a, 2b are
activated. These activate the motor 8, which via the spindle 5 with
KGT 7 via the piston plunger 4 drives the double stroke piston
(DHK3) 10 with three or (DHK2) with two pistons or effective piston
surfaces.
[0102] The volume delivery in the braking circuit is performed in
the S design and the P design by the double stroke piston DHK. The
volume delivered is determined by the effective piston surface and
the piston stroke. With the S design the delivery is performed
during the forward stroke directly into the braking circuit and
with the P design via the EA valves into the braking circuit.
During the return stroke, both with the S design and the P design,
the delivery is performed via the EA valves. If what is referred to
as prefilling VF takes place, then as a result of valve switching
the effective piston surface is greater. Depending on the different
demands on the S design and P design, the double stroke piston DHK
is configured with three (DHK3) and/or two (DHK2) effective piston
surfaces.
[0103] For the application in the S design, the double stroke
piston DHK must deliver the volume in the braking circuit for
pressure build-up during the forward stroke and similarly during
the return stroke. Since here the piston with seal D1 and D3 draws
volume from the braking circuit, the annular surface must be
suitably dimensioned. Furthermore, during prefilling it is intended
that the effective piston area is increased. Here, the volume from
the annular surface is pushed through under the unilaterally
operating sleeve gasket, with the advantage that this already takes
place in the area of the cross bore and thus relieves the
gasket.
[0104] In addition, a piston movement with the generation of a
depression in the brake calliper is desirable for setting the
lining clearance, to reduce the residual frictional moment and thus
the CO2. Here the seal D1 must be depression-proof. The result is a
double stroke piston DHK3 with three effective surfaces. This can
also be used in a P arrangement (e.g. according to FIG. 4).
[0105] One piston area of the double stroke piston DHK2 can be
reduced by giving up the underpressure delivery. Furthermore, with
the double stroke piston DHK, as shown in FIG. 5a and further
described below, the isolation valve can be dispensed with.
However, here the reduction in braking circuit BK pressure must
take place either via the ABS valves AV or an additional valve
AUX.
[0106] The volume delivery in the braking circuit correlates with
the volume increase as a function of the pressure for the
individual wheel circuits or the braking system as a whole. This is
referred to as the p-v curve. Therefore, the correlation can be
used for diagnosing the braking circuit (fill level, leakage, BK
failure). But also for the abovementioned pressure control for the
pressure build-up P.sub.auf and also the pressure reduction Pab.
Here a "partial multiplex" (Part-MUX) can be provided for, wherein
the multiplexing process is used only for the pressure build-up or
the pressure reduction, as described in more detail in the
applicant's patent application DE 102005055751, to which reference
is made in this connection.
[0107] The piston plunger preferably has an elastic configuration,
so that under the impact of the spindle a lower transverse force on
the double stroke piston(DHK) 10 is developed. The torque support
is not implemented here and corresponds to the torque support
described in the applicant's DE 102012103506, to which in this
respect reference is made. The functions of the double stroke
piston (DHK3) 10 with suction valves S1 and S2 with isolation valve
AS correspond to the functions described in the applicant's DE
102013111974. If the double stroke piston (DHK) 10 is operated via
the motor drive, then the brake fluid volume is delivered from the
pressure chamber 10b via the valves EA in the braking circuits DK
and SK. The valve AS remains open, and the valve VF is open. To
monitor the deaeration state of the braking circuits BK, the
delivery volume is checked using the pressure in the braking
circuits BK via pressure sensor DG. If it does not match the
pressure-volume curve, then an EA valve is closed alternately and
the further pressure build-up monitored. If a BK failure is
identified, the corresponding valve EA remains closed.
Simultaneously with the motor operation the isolation valves TV are
closed.
[0108] If at the end of the forward stroke of the double stroke
piston 10 DHK the desired pressure level has not yet been reached,
then the return stroke takes place as described in the applicant's
application DE 102013111974.3, during which the valve AS is closed
and the valve VF is open. If the VF function claimed in application
DE 102013111974.3 is required, then during the forward stroke the
valve AS and the valve VF are closed. If now the ABS function is
required, then for example the pressure regulation takes place
according to the prior art with inlet valves EV and exhaust valves
AV for pressure reduction (see valve block VB). Here the volume for
the pressure reduction reaches the reservoir VB via the return
lines R. To reduce the pressure difference at the valve EV it is
possible to set the pressure difference at EV for example at only
20% higher than the blocking pressure of what is referred to as the
high wheel. Due to the lower pressure difference, with the same
maximum pressure gradient the valve cross-section can be selected
to be greater, so that during rapid braking the dynamic pressure is
lower and what is referred to as the time-to-lock is shorter.
[0109] Alternatively, instead of four inlet valves EV and four
exhaust valves AV, the MUX pressure controller can be used with
four switching valves SV. One of the many advantages is accurate
pressure control, because the piston (DHK) sets the appropriate
volume in the wheel circuit. This method can also be used here
during pressure build-up P.sub.auf via valve EV.
[0110] During operation to move the brake pedal 12 the redundant
pedal travel sensors 2a and 2b are operated in a function to be
defined by the OEM, determined by the motor 8 and thus the pressure
build-up and the brake booster (BKV). Between the pedal plunger 3
and DK piston a small amount of free travel LW is built-in, so that
the pedal initial force is small. This is determined by the
restoring forces of the springs, friction in the guides, pedal
travel sensors and essentially by the friction of the seals, which
are pressure-dependent. This overall friction, acting on the pedal,
is conceptually very different. With the S system according to the
applicant's DE 102010045617.9 essentially only two seals and the
return springs act, and the master cylinder piston with springs
only in the fallback level RFE, since as a result of the control
signal of the pedal travel sensors in the brake booster (BKV)
operation the master cylinder pistons are moved by the pedal
plunger. In other systems, for example DE 102012205962, four seals
act. In FIG. 4 there are two actuation possibilities, a. and b.
[0111] a. Once it has passed through the free travel LW the pedal
plunger 3 comes up against the piston 12a and then further acts on
the master cylinder return spring 23a and in addition four seals,
since the spring 23 is preloaded. So, there is a total of six
seals. When the motor starts the valves TVDK and TVSK are closed
and an HLF valve opened for return R to the reservoir VB, so that
no additional compressive force acts on the piston 12a and pedal
plunger 3. Apart from the abovementioned friction the force-travel
curve determines just the travel simulator WS, which can also be
adaptive as described in the applicant's DE 102014102536.9. [0112]
b. Via the opened VDK valve, during the advance stroke of the
double stroke piston 10, depending on the motor controller, brake
fluid volume from the pressure chamber 10b (also from the pressure
chamber 10a via opened valves AS and VF) reaches a pressure chamber
12c delimited by the rear of the DK piston 12a, and thus this acts
like the abovementioned S design according to the applicant's DE
102010045617.9, since with the open valve AS only the volume of the
front piston contributes to the volume delivery, as also described
in the applicant's patent applications DE 102013111974.3 and DE
102014102536.9, to which reference is made here in this connection.
Thus, only the frictional force of two seals acts here on the pedal
initial force, wherein the pressure components of the small pedal
plunger diameter of <15% can be disregarded. In this phase,
initially both valves TV are open, advantageously the TVSK is
closed once the cross bore 12b of the piston 12a has been passed.
This can be identified indirectly via the movement of the DHK
piston 10 via the motor sensors. Following closing of TVSK, TVDK
remains open, the EADK is closed, and EASK is open, so that the
volume of the DHK once TVSK is closed reaches the braking circuit
SK. Thus, both BK are at approximately the same pressure level,
which at high pressures is no longer the case due to seal friction
in the DK piston 12a. For pressure equalisation, here the EADK can
be opened, and thus the pressure of the double stroke piston (DHK)
10 acts with the same pressure level in both braking circuits BK. A
possible braking circuit failure is diagnosed by one pressure
sensor DG in each braking circuit BK and the volume delivery of the
double stroke pistons DHK, which must correlate with the
pressure-volume curve of the braking circuit BK. If this is not the
case, then the volume supply via the respective valve EA is shut
down. If there is prefilling intended to balance out the lining
clearance or for a rapid increase in pressure, then the valves AS
and VF will be closed, so that a large effective piston area of the
double stroke piston DHK 10 can be fully operative. Here, with the
double stroke piston DHK3, a large piston area comprising the front
piston (pressure chamber 10b) and the annular piston (pressure
chamber 10a) acts, which via the piston displacement results in a
larger (for example, by a factor of 3) quantity delivered than just
with the front piston or its effective surface. With the double
stroke piston DHK2 the piston acts with the seal D2. During
prefilling, a pressure equalisation on the rear side of the piston
is prevented by locking the valve VF according to FIG. 5.
[0113] The actuation according to b. has many advantages. For
example, the seals of the master cylinder piston are always loaded
with real pressure. In systems in which the master cylinder piston
is jointly used for the travel simulator WS, only the WS pressure
acts here which is approximately only 30% of the brake pressure in
the braking circuit BK.
[0114] Furthermore, when the travel simulator (WS) actuation point
at approximately 40% of the pedal travel is achieved, the valve
TVDK is closed together with the WA valve of the travel simulator
WS, which is already closed in step 2 of the travel simulator WS.
This means that in step 1 of the flat curve the valve WA is open,
wherein only the return spring 18 and the seal friction at the
auxiliary piston 16 essentially act on the pedal force. In step 2
the valve WA is closed, i.e. the travel simulator piston with its
spring characteristic acts on the pedal.
[0115] It is known that the pressure in the travel simulator WS can
become very high, if a strong driver fully depresses the pedal.
Pressures of >300 bar can arise here, stressing the housing and
seals. This high pressure is measured with the pressure sensor DG,
since the high pedal force acts on the DK piston, if, for example
at high pressure of >200 bar the valve WA mechanically opens. In
this case the valve VDK can be closed and the valve ESV opened.
Thus, both the compressive forces of DK-piston 12a, and also of
auxiliary piston 16, act on the brake pedal. Thus, the compressive
loading is in the range of 200 bar when the valve WA opens. This
can be resolved by flow control of the normally open valve.
[0116] The pressure reduction in the brake booster (BKV) mode takes
place by a return movement of the double stroke piston 10 DHK by
additional pressure reduction via AV valves in the return R since
the additional volume of VF is not equalised in the return stroke
of the double stroke piston DHK.
[0117] In the following the fallback levels RFE are now
described.
[0118] RFE1 in the event of failure of the travel simulator WS, for
example due to a leak. In this case the counterforce is lacking,
since no pressure develops in the travel simulator WS. It is known
that this is identified by the force-travel simulator KWS as
described in the applicant's DE 102014102536, to which reference is
hereby made, when the progressive increase in force of the travel
simulator WS in step 2 after a defined pedal travel (see DE
102014102536) acts or fails. In this case the pedal plunger 3 comes
up against the DK piston 12, resulting in a change in pressure
measured by the force-travel simulator KWS. In this case the motor
actuation and volume control take place on the rear of the DK
piston 12a via the valve VDK as a function of the KWS signal. In
this case the brake booster BKV acts like a conventional brake
booster with pedal force support as a follow-up brake booster
(Fo-BKV). The advantage here, over the S design, is that with
follow-up brake boosting the same short pedal travel acts, but with
a somewhat discontinuous curve.
[0119] Optimisation of the sensitivity of the force-travel
simulator KWS would allow the travel simulator WS to be dispensed
with.
[0120] RFE 2 with motor failure at low .mu., DK piston at travel
simulator actuation point with high pedal force and subsequent
positive .mu.-jump. As previously explained in the applicant's DE
102013111974.3, to which reference is made here in this connection,
here volume is fed using auxiliary pistons via open valve ESV and
EADK into the braking circuit BK by DK piston.
[0121] RFE3 with motor and vehicle electrical system failure. The
valves ESV, VDK and WA are open here, the valves EADK, EASK are
closed. The pedal plunger acts on DK piston 12. The pressure is
developed conventionally via the pedal force.
[0122] It is also conceivable to construct the S design according
to DE 102014102536.9, to which reference is made here, such that
the motor is positioned in parallel and via a toothed belt drive,
e.g. according to DE 102011050587, acts on the ball screw unit
KGT.
[0123] FIG. 5 differs from FIG. 2 by the absence of valve HLF, in
that only actuation method b. is used, and a double stroke piston
(DHK2) 15 with two pistons. Furthermore, by dispensing with VF this
valve can be omitted. In FIG. 5 this valve is shown for the
function VF and is, however, unlike in FIG. 4 positioned between
valve AS and the double stroke piston 15.
[0124] This double stroke piston DHK2 or also DHK3 according to
FIG. 4 can also be used in a P design according to DE 10 2012 222
897 A1.
[0125] In hydraulic systems, it must be ensured that these are
pressure balanced when the vehicle is at a standstill. This is the
case with the system according to FIG. 4 and FIG. 5, since all
valves (AS, VF, VDK, ESV, WA) for the return flow and also the
cross bores of the master cylinder piston are open.
[0126] There are two advantages that differentiate double stroke
piston (DHK3) according to FIG. 4 with three pistons from the
double stroke piston (DHK 2) according to FIG. 5. The double stroke
piston DHK3 can develop a depression in the pressure chamber 10b,
if the Dl seal is depression-proof. This is an advantage when
setting the lining clearance of the brake pistons with depression
as described in the applicant's DE 10 2008 051 316.4, to which in
this respect reference is made here. The second advantage is the
reliability in the event of failure of the seals D1-D3. If one of
the three seals fails, then pressure can be developed in the
advance stroke, and the BKV function is maintained. Furthermore,
the failure is diagnosed. This is important for autonomous
driving/braking, since in the event of single faults the function
must be retained.
[0127] FIG. 5a, with the double stroke piston DHK, shows a
simplification of the 2-piston version. Here the isolation valve AS
is dispensed with, with two pressure relief valves V1 and V2 being
used. The plunger 4 acts via seal D3 directly on the piston. When
the return stroke is not used for further volume delivery in the
braking circuit, with the intention instead being pressure
reduction upon retraction of the brake pedal, this can take place
by opening the ABS-AV valve or by an additional AVX valve in the
double stroke piston DHK circuit.
[0128] FIG. 6 shows a vehicle brake or an actuating system for
this, with first, second and third piston-cylinder units arranged
one behind the other in a row.
[0129] In parallel, e.g. with a spatially displaced central axis,
in the area of the first piston-cylinder unit (double-stroke
piston) a drive with electric motor 8 is arranged, wherein the
propulsion takes place from the drive spindle to a surrounding nut
and from this to the spindle 5 of a ball screw unit 7 by means of a
toothed belt. The other elements of the actuator system correspond
extensively to those shown in FIGS. 4 and 5, so that a more
detailed description can be dispensed with here. A parallel
arrangement of the motor with belt drive can also be advantageous
apart from that in a P arrangement of the actuating system shown in
FIGS. 4 and 5.
[0130] FIG. 7 shows a particularly simple implementation of the
invention with considerable further reduction in installed length
in which the (second) piston-cylinder unit DHK (double stroke
piston) driven by the electric motor is implemented as in FIG. 2.
Here, however, the first piston cylinder unit DHK (master cylinder)
arranged in parallel to the driven piston-cylinder unit has only
one piston SK, the first working chamber of which, provided with a
spring F.sub.SK, is connected via a line HL1 and via the valve
block VBL with corresponding wheel brakes and forms a first braking
circuit. In other words, a further piston DK (as is present in the
implementation according to FIG. 2) is not provided here. A further
working chamber 12d formed on the rear of the floating piston SK of
the piston cylinder unit (master cylinder) is connected via a line
HL2 and the valve block VBL with corresponding wheel brakes and
forms a second braking circuit. The working chamber 12d expediently
has at an appropriate point a vent (not shown), for example by
means of a mechanical vent screw or a normally closed solenoid
valve. Here the first piston-cylinder unit (master cylinder) has a
stop A for the piston SK, which the piston SK can come up against
by means of the piston spring F.sub.SK. In this way, free travel a
between the piston SK and the pedal plunger 3 arranged on the
auxiliary piston 16 is set up. The gap or free travel a corresponds
here preferably to half the stroke of the pedal plunger 3, e.g.
36/2 mm. It can also be smaller, however, wherein the minimum
corresponds to the stroke until the stop of the travel simulator
WS. In the lines to the hydraulic lines or braking circuits HL1 or
HL2, with regard to braking circuit HL1, a normally closed valve
EA.sub.SK is used and with regard to braking circuit HL2, a
normally open valve EA.sub.DK is used. Since otherwise the
implementation according to FIG. 7 largely corresponds to that of
FIG. 2, reference thereto is also made, so that here a more
detailed description can be dispensed with and only the differences
concerning implementation and function are described.
[0131] A third piston-cylinder unit (auxiliary piston) is arranged
in series with the first piston-cylinder unit (master cylinder) and
has a plunger (pedal plunger 3) arranged on the auxiliary piston
16, the end of which can act on the piston SK.
[0132] The working chamber of the piston-cylinder unit (auxiliary
piston) is connected via a hydraulic line HL3, a travel simulator
arrangement and a hydraulic line HL4 with the braking circuits and
the second piston-cylinder unit DHK.
[0133] The travel simulator arrangement largely corresponds to that
shown in FIG. 2 wherein, however, in the implementation according
to FIG. 7 a normally closed valve WA is used.
[0134] When the double stroke piston DHK is operated here from the
working chamber 10a via valve EA, hydraulic fluid is delivered
directly into the associated braking circuit or the pressure
correspondingly raised.
[0135] In the fallback level RFE, by means of the auxiliary piston
16 from the working chamber of which, via line HL3, HL4 and the
normally open valve ESV, hydraulic fluid can be delivered into the
braking circuits or the pressure correspondingly raised, wherein
the valve WA is normally closed. In other words, here the auxiliary
piston 16 performs the function of the piston DK in the
implementation according to FIG. 2. Here the hydraulic fluid volume
from the working chamber of the auxiliary piston 16 reaches, via
the normally open valve EA.sub.DK and the normally open valve ESV,
the line HL2 or the corresponding braking circuit.
[0136] In the implementation according to FIG. 1 or 1a, a two-step
spring is provided on the floating piston SK. A corresponding
spring can also be provided in the implementation according to FIG.
7, and is shown enlarged in FIG. 7a. The spring power F.sub.SK of
this spring does not have to be highly progressive, since a plunger
rod piston DK and thus also in this simplest of implementations a
spring for this is not present here. The spring provided for on the
plunger rod piston in the implementation according to FIG. 1, is
unnecessary here or can be replaced by a combined spring
arrangement, which is supported on the pedal plunger 3, as shown in
FIG. 7a.
[0137] Alternatively, on the third piston-cylinder unit (auxiliary
piston 16) a cross bore SL can be provided. As a result, a pressure
equalisation advantageously takes place between the double stroke
piston DHK and the auxiliary piston 16 and furthermore a reliable
deaeration of the auxiliary piston. A pressure equalisation via the
cross bore SL can also be dispensed with. Here the volume expansion
of the travel simulator WS is absorbed and can, for example when
the vehicle starts up, be equalised by briefly opening the valve
EA.sub.SK or the valve AV via the return to the reservoir. Volume
equalisation can also take place by combining the valve RV1 with a
choke, allowing a small leakage flow, since the temporal change as
the temperature rises is small.
[0138] Since the piston DK is missing from the implementation
according to FIG. 7, the supply of additional volume by parallel
connection of the auxiliary piston and piston DK is not possible in
the implementation according to FIG. 7. All other functions of the
other embodiments shown in FIGS. 1-6 are possible with the
implementation according to FIG. 7, however, in particular:
follow-up brake boosting, reduction of the pressure level in the
auxiliary piston circuit by lowering the pressure level in the
braking circuit HL2 and full pressure level in the braking circuit
of the floating piston SK, diagnostics, prefilling, adaptive travel
simulation, no failure of the brake boosting if the braking
circuits HL1 and HL2 fail through diagnosis of the braking circuit
failure and blocking of the valve EA.
[0139] In the implementation according to FIG. 7 the pressure
build-up takes place upon braking from the working chamber 10a of
the second piston-cylinder unit (double stroke piston DHK) via the
valve EA.sub.DK in the braking circuit HL2 and via the working
chamber of the piston SK of the first piston-cylinder unit (master
cylinder) in the braking circuit HL1. Here the valve ESV is closed
and the valve WA is opened, depending on the working range of the
travel simulator WS. In step 1 of the travel simulator WS the valve
WA is open, wherein only the return spring 18 of the auxiliary
piston 16 determines the pedal force.
[0140] In the ABS mode, the valve ESV is closed and the valve may
similarly be closed, depending on the working range of the travel
simulator WS. Pressure medium is supplied to the braking circuits
HL1 and H12 from the working chamber 10a of the double stroke
pistons DHK, so that due to the open valves EA a pressure
equilibrium is present at the piston SK. The positions of the
piston SK are determined by the springs F.sub.SK and F1, as shown
and described in this respect in FIGS. 7a and 7b.
[0141] In the fallback level 1 (failure of the travel simulator
arrangement) the system operates as a follow-up brake booster. Once
the pedal has gone through its travel the pedal plunger 3 comes up
against the floating piston SK. In this area, the increase in pedal
force is relatively flat. In this area, however, a prefilling
already takes place via the valve UV2, so that once the pedal
plunger 3 comes up against the piston SK a smaller pedal travel is
necessary for the pressure increase. Once the pedal plunger 3 has
come up against the piston SK, the admission pressure of the double
stroke piston DHK is controlled via the valve EA.sub.DK by means of
the force-travel simulator KWS provided on the auxiliary piston 16
such that a desired pedal force or a desired brake pressure
develops in the braking circuits HL1 and HL2.
[0142] In the fallback level 2/2a the volume displaced from the
working chamber of the auxiliary piston 16 acts via valves ESV and
EA in the braking circuits HL1 and HL2, wherein an unsymmetrical
pressure build-up may result, depending on the position of the
piston SK. This can be avoided by a pressure equalisation via open
valves EA. Here the piston SK can be in the starting or end
position and the pedal plunger 3 coming up against the piston SK
then causes an unsymmetrical pressure level in the braking circuits
HL1 and HL2.
[0143] In the fallback level 3 the volume from the working chamber
of the auxiliary piston 16 acts fully on the braking circuit HL2
and the volume from the working chamber of the floating piston
correspondingly on the braking circuit HL1. In this way, the
auxiliary piston 16 acts like a plunger rod piston DK (e.g. the
implementation according to FIG. 2). The volume of auxiliary piston
16 fed in is reduced by the volume uptake of the travel simulator
WS (approx. 20%). This can be avoided if necessary by an isolation
valve (not shown) for the travel simulator WS. By suitable
dimensioning of the auxiliary piston 16 the delivery volume in the
fallback level RFE can be increased with a corresponding
dimensioning of the travel simulator piston and the travel
simulator springs.
[0144] By using an extended valve function as shown in FIG. 3 with
valves AS and VF and AV.sub.MUX, here also the various additional
functions described such as defined advance and return stroke,
pressure reduction in double stroke piston DHK, prefilling and
multiplexing (MUX), can be implemented with relatively little
additional cost. It is also possible to use the double stroke
piston with three pistons (or three effective piston surfaces)
according to FIG. 4, in order for example to achieve a specific
depression for controlling the lining clearance. In this system,
the double stroke piston DHK acts to develop pressure (and
modulation in the multiplex procedure MUX) in the braking circuits.
The auxiliary piston 16 acts together with the travel simulator
piston as a travel simulator and determines the pedal
characteristic. If the double stroke piston DHK or the motor fails
(fallback level), the auxiliary piston 16 steps in and acts like a
plunger rod piston DK and supplies one braking circuit directly or
via the piston SK, in which the volume or pressure of the auxiliary
piston 16 acts on the secondary side of the piston SK, both braking
circuits, with pressure medium. Due to this dual function of the
auxiliary piston 16 not only is there a reduction in costs, but
also an even simpler implementation of the many functions according
to the invention.
[0145] A pressure reduction from the braking circuits HL1 and HL2
takes place in a first step (as far as travel simulator step 1) via
the valve ESV and WA in the reservoir VB and from the second step
(travel simulator step 2) via the valves EA and IV from braking
circuit HL2 in the reservoir VB.
[0146] FIG. 7a shows in enlarged detail the piston SK with the
pedal plunger 3. The piston SK is fixed in its starting position
with springs. The intention here is that when the pedal plunger 3
is operated the piston SK is moved via the cross bore 27, so that
in this position in both braking circuit HL1 and HL2 pressure can
be fed in. This is achieved by the spring force F1 as Fx; see also
FIG. 7b. Following a stroke of .DELTA.S.sub.sk, during which the
poppet valve 27 is securely closed, the preloaded spring F then
acts. If now volume or pressure is fed from the double stroke
piston DHK into the pressure chamber 12d, then the piston SK moves
accordingly. If now the piston SK for the sake of sufficient volume
in the fallback levels is intended to be moved back into the
starting position .DELTA.S.sub.sk, then this takes place at the
same pressure on both sides of the piston SK due to the higher
spring force of the spring F.sub.SK. Due to the progressive design
of the spring, e.g. according to the curve F11 in FIG. 7b, this
position can be changed to another value .DELTA.S.sub.sk.
[0147] FIG. 7c shows an alternative to the valve V.sub.VB in the
connection of cross bore 27 of the piston SK to the reservoir VB.
This valve is needed so that in the rare event of the secondary
sleeve of the piston SK failing, the pressure supply from the
double stroke piston DHK does not fail as well. In this case the
double stroke piston DHK would be delivering volume in chamber 12a
without an increase in pressure if there is a major leak. This case
is identified by the diagnostics by comparing the volume delivery
with the pressure, leading to closure of the valve V. This can be
solved at low cost according to FIG. 7c, by using a choke D and a
suction valve in the connecting line. The cross-section of the
choke D is very small, since it is used only for volume
equalisation with increasing temperature, so that the volume from
the braking circuit HL1 can flow back into the reservoir VB. Due to
the choke, the volume delivery of the double stroke piston DHK is
significantly greater than the leakage volume, such that sufficient
pressure develops. The suction valve SV is used for deaerating the
braking circuit HL1. The valve EA.sub.DK has the task, in the event
of a leak in the braking circuit HL2, between chamber 12d and the
valve block VBL or in the double stroke piston DHK, of isolating
the braking circuit HL2 by closing EA. Since this can be excluded
from the design, the valve EA.sub.DK can also be dispensed with.
The pressure sensor DG can also be replaced by measurement of the
motor current, which behaves approximately proportionally to the
pressure. The valve EASK is necessary for pressure equilibrium
between the braking circuits HL1 and HL2 for the described piston
positioning of the piston SK and also in order, in the event of a
leak in the braking circuit HL1 as a whole, to isolate this.
[0148] With these simplifications, reliable diagnostics are of
major importance, to reliably detect leaks in time. This
essentially takes place by comparing the volume delivery of the
double stroke piston DHK with the pressure level reached, which is
determined directly by means of pressure sensor DG or indirectly by
means of motor current measurement. The volume and pressure are
compared here with the vehicle-specific pressure-volume curve. This
can take place in any operating mode with the due validity, i.e.
comparison with one or two braking circuits. In the event of
invalidity or a leak, a corresponding switching of valve or motor
takes place, usually an isolation of a braking circuit. The
corresponding braking circuits are then no longer supplied by the
piston-cylinder unit (double stroke piston). The volume of the
double stroke piston is measured, for example, via the motor or the
rotation angle of the rotor, which drives the spindle 5 and thus
the double stroke piston DHK.
LIST OF REFERENCE NUMERALS
[0149] 1 Brake pedal [0150] 2a Pedal travel sensors Master [0151]
2b Pedal travel sensors Slave [0152] 3 Pedal plunger [0153] 4
Piston plunger [0154] 5 Spindle [0155] 6 Motor sensor [0156] 7 KGT
[0157] 8 EC-motor [0158] 9 Bearing [0159] 10 Double stroke piston
(DHK3) [0160] 10a Working chamber (annular chamber) or pressure
chamber [0161] 10b Working chamber or pressure chamber [0162] 10c
working chamber or pressure chamber [0163] 11 Reservoir [0164] 12
SK piston [0165] 12a DK piston [0166] 12b Cross bore DK [0167] 12c
Working or pressure chamber [0168] 15 Double stroke piston (DHK2)
[0169] 16 Auxiliary piston [0170] 18 Pedal return spring [0171]
Master cylinder return spring [0172] 23a Master cylinder return
spring [0173] 24 Isolation valve [0174] 25 DHK housing [0175] 26
Spring housing [0176] 27 Cross bore [0177] A Stop [0178] D Choke
aperture [0179] S1 Suction valve 1 [0180] S2 Suction valve 2 [0181]
S5 Suction valve 5 [0182] V3 Pressure relief valve [0183] V4
Pressure relief valve [0184] V.sub.VB Solenoid valve [0185] R
Return to reservoir VB [0186] RV0 Non-return valve 0 [0187] RV1
Non-return valve 1 [0188] WS Travel simulator [0189] WA Solenoid
valve [0190] UV Pressure relief valve [0191] UV2 Prefill pressure
relief valve [0192] HiKo Auxiliary piston [0193] HL1 Hydraulic line
or braking circuit [0194] HL2 Hydraulic line or braking circuit
[0195] LW Free travel [0196] RFE Fallback level [0197] LS Clearance
[0198] KWS Force-travel sensor [0199] BK Braking circuit [0200] DG
Pressure sensor [0201] VF Prefilling [0202] BKV Brake servo [0203]
Fo-BKV Follow-up BKV [0204] VB Reservoir [0205] VBL Valve block
[0206] F.sub.SK Return spring SK [0207] F.sub.X Supplementary
spring [0208] AV Exhaust valve ABS [0209] EV Inlet valve ABS [0210]
P.sub.vor Admission pressure from DHK [0211] FoDK Supplementary
spring on piston DK [0212] VVB Valve to reservoir VB
* * * * *