U.S. patent application number 11/903632 was filed with the patent office on 2008-01-24 for brake system for a motor vehicle.
Invention is credited to Wilfried Giering, Erwin Michels, Benedikt Ohlig.
Application Number | 20080018171 11/903632 |
Document ID | / |
Family ID | 33304949 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080018171 |
Kind Code |
A1 |
Ohlig; Benedikt ; et
al. |
January 24, 2008 |
Brake system for a motor vehicle
Abstract
A brake system for a motor vehicle includes a master brake
cylinder in which a primary piston for generating a brake pressure
in a hydraulic brake circuit can be displaced according to
actuation of a brake pedal. It is possible to displace the primary
piston under the effect of a hydraulic servo pressure circuit in
the master brake cylinder. The hydraulic servo pressure circuit
includes a pressure source for generating the servo pressure and a
pressure accumulator for maintaining a minimum servo pressure in
the servo pressure circuit, wherein the discharge line is
constructed with a non-return valve which only allows discharge of
hydraulic fluid from the pressure accumulator into the servo
pressure circuit. A pressure sensor for detecting the hydraulic
pressure prevailing in the pressure accumulator is associated with
the pressure accumulator.
Inventors: |
Ohlig; Benedikt; (Vallendar,
DE) ; Giering; Wilfried; (Mendig, DE) ;
Michels; Erwin; (Kail, DE) |
Correspondence
Address: |
MACMILLAN, SOBANSKI & TODD, LLC
ONE MARITIME PLAZA - FOURTH FLOOR
720 WATER STREET
TOLEDO
OH
43604
US
|
Family ID: |
33304949 |
Appl. No.: |
11/903632 |
Filed: |
September 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11255621 |
Oct 21, 2005 |
7296861 |
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11903632 |
Sep 24, 2007 |
|
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PCT/EP04/03652 |
Apr 6, 2004 |
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11255621 |
Oct 21, 2005 |
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Current U.S.
Class: |
303/10 ;
303/116.1; 303/15 |
Current CPC
Class: |
B60T 13/68 20130101;
B60T 13/148 20130101; Y10S 303/11 20130101; B60T 8/4054 20130101;
B60T 8/4077 20130101; B60T 8/405 20130101; B60T 13/142 20130101;
B60T 8/441 20130101 |
Class at
Publication: |
303/010 ;
303/116.1; 303/015 |
International
Class: |
B60T 13/68 20060101
B60T013/68; B60T 13/122 20060101 B60T013/122; B60T 13/14 20060101
B60T013/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2003 |
DE |
103 18 850.9 |
Claims
1. Brake system for a motor vehicle comprising a master brake
cylinder in which a primary piston for generating a brake pressure
in a hydraulic brake circuit can be displaced according to
actuation of a brake pedal, it being possible to displace the
primary piston under the effect of a hydraulic servo pressure
circuit in the master brake cylinder and the hydraulic servo
pressure circuit comprising a pressure source for generating the
servo pressure and a pressure accumulator for maintaining a minimum
servo pressure in the servo pressure circuit, wherein the discharge
line is constructed with a non-return valve which only allows
discharge of hydraulic fluid from the pressure accumulator into the
servo pressure circuit, and wherein a pressure sensor for detecting
the hydraulic pressure prevailing in the pressure accumulator is
associated with the pressure accumulator.
2. Brake system according to claim 1, wherein the servo pressure
circuit comprises a manifold valve, in particular a two-way
solenoid valve, that is actively controllably interconnected
between the master brake cylinder and the pressure source and the
pressure accumulator.
3. Brake system according to claim 2, wherein the servo pressure
circuit comprises a further manifold valve, in particular a two-way
solenoid valve, that is actively controllably interconnected
between the master brake cylinder and a hydraulic fluid
reservoir.
4. Brake system according to claim 1, wherein the servo pressure
circuit comprises a bypass channel that can be activated as a
function of pressure and is connected downstream of the pressure
source.
5. Brake system according to claim 1, further comprising a
controller for evaluating detected hydraulic pressures and for
controlling actively controllable components.
6. Brake system according to claim 1, wherein the primary piston is
mechanically decoupled from the brake pedal.
7. Brake system for a motor vehicle comprising a master brake
cylinder, wherein a primary piston for generating a brake pressure
in a hydraulic brake circuit can be displaced according to
actuation of a brake pedal, it being possible to displace the
primary piston under the effect of a hydraulic servo pressure
circuit in the master brake cylinder, and the hydraulic servo
pressure circuit comprising a pressure source for generating the
servo pressure, and a pressure accumulator for maintaining a
minimum servo pressure in the servo pressure circuit, the pressure
accumulator being fluidically connected by a supply line to the
servo pressure circuit, and the supply line comprising a fluid
supply controller for controlling the supply of hydraulic fluid to
the pressure accumulator as a function of the servo pressure
prevailing in the servo pressure circuit, characterised in that the
fluid supply controller comprises an actively controllable manifold
valve, in particular a two-way solenoid valve.
8. Brake system according to claim 7, wherein a pressure sensor is
arranged in the servo pressure circuit for detecting the servo
pressure.
9. Brake system according to claim 7, wherein the manifold valve is
controllable according to the servo pressure detected by the
pressure sensor.
10. Brake system according to claim 7, wherein the pressure source
comprises a motor-driven pump.
11. Brake system according to claim 7, wherein the servo pressure
circuit comprises a non-return valve connected downstream of the
pressure source.
12. Brake system according to claim 7, wherein the servo pressure
circuit comprises a manifold valve, in particular a two-way
solenoid valve, that is actively controllably interconnected
between the master brake cylinder and the pressure source and the
pressure accumulator.
13. Brake system according to claim 12, wherein the servo pressure
circuit comprises a further manifold valve, in particular a two-way
solenoid valve, that is actively controllably interconnected
between the master brake cylinder and a hydraulic fluid
reservoir.
14. Brake system according to claim 7, wherein the servo pressure
circuit comprises a bypass channel that can be activated as a
function of pressure and is connected downstream of the pressure
source.
15. Brake system according to claim 7, wherein a pressure sensor
for detecting the hydraulic pressure prevailing in the pressure
accumulator is associated with the pressure accumulator.
16. Brake system according to claim 7, further comprising a
controller for evaluating detected hydraulic pressures and for
controlling actively controllable components.
17. Brake system according to claim 7, wherein the primary piston
is mechanically decoupled from the brake pedal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional patent application of U.S.
patent application Ser. No. 11/255,621, filed Oct. 21, 2005, which
was a continuation of International Application No.
PCT/EP2004/003652 filed Apr. 6, 2004 which claimed priority to
German Patent Application No. 103 18 850.9 filed Apr. 25, 2003, the
disclosures of all three applications are incorporated herein by
reference.
BACKGROUND
[0002] Various embodiments of a brake system for a motor vehicle
are described herein. In particular, the embodiments described
herein relate to an improved brake system for a motor vehicle. In
one embodiment, the brake system for a motor vehicle comprises a
master brake cylinder in which a primary piston for generating a
brake pressure in a hydraulic brake circuit can be displaced
according to actuation of a brake pedal, it being possible to
displace the primary piston under the effect of a hydraulic servo
pressure circuit in the master brake cylinder and the hydraulic
servo pressure circuit comprising a pressure source for generating
the servo pressure and a pressure accumulator for maintaining a
minimum servo pressure.
[0003] Brake systems of this type are known from the prior art.
Thus DE 195 42 656 A1, and corresponding U.S. Pat. No. 6,290,307
B1, both of which are incorporated by reference herein, for example
discloses a brake system for a motor vehicle in which actuation of
a brake pedal is detected by sensors. A servo pressure circuit is
controlled by a control unit with the aid of the detected pedal
actuation. A pressure source is provided in this servo pressure
circuit and generates a servo pressure in the hydraulic servo
pressure circuit. The pressurised hydraulic fluid is supplied by
means of a manifold valve to the master brake cylinder. More
precisely, the primary piston that can be displaced inside the
master brake cylinder by means of the servo pressure for generating
a brake pressure is also pressurised with a servo force, resulting
from the servo pressure, in addition to the pedal actuation force.
As a result, the primary piston can be effectively displaced inside
the master brake cylinder without the entire force required for
generating the brake force having to be applied by the brake
pedal.
[0004] In order to be able to provide a sufficiently high servo
pressure at any instant during operation, the servo pressure
circuit of DE 195 42 656 A1 provides a pressure accumulator
connected downstream of the pressure source. This pressure
accumulator is directly coupled to the servo pressure circuit.
Whenever the pressure source of the servo pressure circuit is
active hydraulic fluid is conveyed from the servo pressure circuit
into the pressure accumulator and stored therein. However, this has
the effect that in a state in which there is a relatively low
hydraulic pressure in the servo pressure circuit and in which the
full power of the pressure source would be inherently required for
generating a brake pressure inside the master brake cylinder for
displacing the primary piston, a certain portion of the hydraulic
fluid conveyed by the pressure source will also always be conveyed
into the pressure accumulator owing to the fluidic connection of
the pressure accumulator and pressure source. The efficiency and
the response characteristic of the brake system suffers as a
consequence, in particular as not all of the hydraulic fluid
required for actuating the primary piston is conveyed from the
servo pressure circuit into the master brake cylinder.
SUMMARY
[0005] The present application describes various embodiments of a
brake system for a motor vehicle. In one embodiment, a brake system
is provided for which at the outset of operation the servo pressure
circuit operates in a manner suitable to the situation and with
increased effectiveness.
[0006] Such increased effectiveness is achieved by a brake system
for a motor vehicle comprising a master brake cylinder in which a
primary piston for generating a brake pressure in a hydraulic brake
circuit can be displaced according to actuation of a brake pedal,
it being possible to displace the primary piston under the effect
of a hydraulic servo pressure circuit in the master brake cylinder
and the hydraulic servo pressure circuit comprising a pressure
source for generating the servo pressure and a pressure accumulator
for maintaining a minimum servo pressure. The pressure accumulator
of the servo pressure circuit can be supplied with hydraulic fluid
as a function of the servo pressure prevailing in the servo
pressure circuit.
[0007] In such a brake system, the pressure accumulator is supplied
with hydraulic fluid contained in the servo pressure circuit or
conveyed by the pressure source only if current operation of the
entire brake system also allows it. Such a mode of supply takes
place, for example, if no braking is currently being carried out
which requires loading of the primary piston inside the master
brake cylinder with hydraulic fluid flowing in from the servo
pressure circuit. In such a situation the pressure source can be
used to "load" the pressure accumulator, in other words to produce
a pressure level therein which can subsequently be used in a later
operating state to equalise pressure fluctuations. If, however,
braking is initiated by actuation of the brake pedal, the
possibility of supplying the pressure accumulator with hydraulic
fluid originating from the pressure source is limited or even
prevented, so hydraulic fluid conveyed by the pressure source can
be supplied substantially completely to the master brake cylinder.
As a result the primary piston inside the master brake cylinder can
be quickly and effectively displaced for generating a brake
pressure. The embodiments described and illustrated herein thus
defy the drawbacks of the brake system according to DE 195 42 656
A1 discussed at the outset and allows operation of the various
components of the servo pressure circuit in a manner suitable to
the situation.
[0008] To allow selective supplying of the pressure accumulator as
a function of the current operating state of the brake system and
still allow reliable discharge of hydraulic fluid from the pressure
accumulator to equalise pressure fluctuations it is provided in one
embodiment of the brake system that the pressure accumulator is
fluidically connected by a supply line and/or a discharge line to
the servo pressure circuit. As a result of the construction of the
brake system with two at least partially separate lines for
supplying the pressure accumulator with hydraulic fluid and for
discharging hydraulic fluid from the pressure accumulator it is
possible to reliably achieve situation-dependent control of the
pressure accumulator. However, it is also possible to provide only
one line which can be used both for supplying the pressure
accumulator with hydraulic fluid and for discharging hydraulic
fluid from the pressure accumulator.
[0009] The supply line comprises a fluid supply controller for
controlling the supply of hydraulic fluid to the pressure
accumulator as a function of the servo pressure prevailing in the
servo pressure circuit. A fluid supply controller of this type can
be constructed so as to be passively or actively controllable.
Thus, it is possible that the fluid supply controller comprises a
pressure-limiting valve. The pressure-limiting valve can, for
example, only open if a specific minimum pressure is achieved or
exceeded. This means that the pressure source in the servo pressure
circuit has adjusted a sufficiently high hydraulic pressure by
means of which reliable operation of the brake system, in
particular reliable displacement of the primary piston inside the
master brake cylinder, is possible in the event of actuation of the
brake pedal. If this state is attained, the pressure-limiting valve
opens and the pressure accumulator can be filled, in other words
"loaded," with the hydraulic fluid conveyed by the pressure source.
A corresponding pressure level is adjusted in the pressure
accumulator in the process.
[0010] In another embodiment of the brake system, the fluid supply
controller comprises a throttle element. The use of a throttle
element for the fluid supply controller in the supply line also
allows function-dependent control of the pressure accumulator. The
throttle element thus allows supplying of the pressure accumulator
with hydraulic fluid conveyed by the pressure source only in the
event of high hydraulic pressures. In other words, the throttle
element, as a flow divider, to a certain extent also means that the
hydraulic fluid conveyed by the pressure source is supplied to the
master brake cylinder with higher priority and only on attaining a
specific minimum pressure is a certain portion of the hydraulic
fluid conveyed by the pressure source also conveyed to the pressure
accumulator.
[0011] The pressure-limiting valve and the throttle element may be
connected in series. A combination of this type of
pressure-limiting valve and throttle valve in the supply line
allows the quantity of hydraulic fluid supplied to the pressure
accumulator and the pressure level that has built up therein to be
limited as a result of the throttling effect of the throttle
element, even in the event of the minimum pressure, preset by the
pressure-limiting valve, for opening the pressure-limiting valve
and for supplying the pressure accumulator being exceeded.
[0012] A pressure sensor or a plurality of pressure sensors may be
provided at various points for monitoring the servo pressure
prevailing in the servo pressure circuit. In this connection,
another embodiment of the brake system provides that the fluid
supply controller comprises an actively controllable manifold
valve, in particular a two-way solenoid valve. The actively
controllable manifold valve can be controlled with the aid of the
data captured by the pressure sensor. For example this actively
controllable manifold valve can, on reaching a specific minimum
pressure, be transferred from its closed state into its open state
and be closed again after exceeding a specific minimum pressure in
the servo pressure circuit. It is also possible to construct the
pressure-limiting valve or the throttle element, both discussed
above, so as to be actively controllable. Thus for example the
pressure-limiting valve can also be controllable in such a way that
the minimum pressure thereof that determines the operating state is
changed as a function of the operating situation of the brake
system. When using an actively controllable throttle element the
throttling setting thereof can be changed as a function of the
servo pressure currently prevailing in the servo pressure
circuit.
[0013] In another embodiment, the discharge line is constructed
with a non-return valve. To avoid undesirable hydraulic fluid flows
via the discharge line the non-return valve can be used between the
pressure accumulator and the hydraulic line of the servo pressure
circuit connecting the pressure source to the master brake cylinder
in such a way that it only allows discharge of hydraulic fluid from
the pressure accumulator into the servo pressure circuit. The
non-return valve can, for example, also be replaced by an actively
controllable component.
[0014] In another embodiment, the pressure source comprises a
motor-driven pump. It may also be provided that the servo pressure
circuit comprises a non-return valve connected downstream of the
pressure source. The non-return valve is oriented such that it
allows conveying of hydraulic fluid from the pressure source into
the servo pressure circuit, in particular in the direction of the
master brake cylinder, whereas it prevents flowing back of
hydraulic fluid to the pressure source. Consequently it can be
ensured that the servo pressure that has built up in the servo
pressure circuit does not reduce in the direction of the pressure
source in the event of power fluctuations in the pressure source.
In particular, the non-return valve can prevent the servo pressure
emanating from the pressure accumulator and exerted on the servo
pressure circuit from discharging in the direction of the pressure
source but in the direction of the master brake cylinder.
[0015] As described above, the servo pressure circuit is used to
displace the primary piston inside the master brake cylinder to
generate a brake pressure in the brake circuit. For the event that
the servo pressure circuit fails, for example because the pressure
source fails, it should, however, be ensured that the primary
piston can also be displaced in some other way, for example by a
direct mechanical coupling to the brake pedal. In such a case the
situations where the actuating force acting on the primary piston
simultaneously also leads to recirculation of hydraulic fluid
inside the servo pressure circuit or actuation of the primary
piston is obstructed owing to the occurrence of above-atmospheric
pressure or a vacuum in the servo pressure circuit should be
avoided. For this reason, and for general shielding of the master
brake cylinder and servo pressure circuit, another embodiment of
the brake system provides that the servo pressure circuit comprises
an actively controllable manifold valve, in particular a two-way
solenoid valve, interconnected between the master brake cylinder
and the pressure source and the pressure accumulator. The servo
pressure circuit can be decoupled from the master brake cylinder by
means of the actively controllable manifold valve and undesirable
interactions can be ruled out. This actively controllable manifold
valve can also be generally used for controlling the servo pressure
acting on the primary piston. It may also be used to actively fill
the pressure accumulator. Thus it is possible, for example, to
close the actively controllable manifold valve after a braking
operation has ended and to continue to operate the pump over a
predetermined period. As a result, above-atmospheric pressure is
generated in the portion of the servo pressure circuit that is
close to the pump and shut by the actively controllable manifold
valve, it being possible to use the pressure to supply the pressure
accumulator with hydraulic fluid. If at the end of braking the
servo pressure in the servo pressure circuit was already
sufficiently high to supply the pressure accumulator, the pump can
also be switched off as early as at the end of braking and the
servo pressure prevailing in the servo pressure circuit can
initially be used for supplying the pressure accumulator before
this is reduced in some other way, for example in the direction of
a hydraulic fluid reservoir.
[0016] The servo pressure circuit may comprise a further actively
controllable manifold valve, in particular a two-way solenoid
valve, interconnected between the master brake cylinder and the
hydraulic fluid reservoir. As a result it is possible to connect
the master brake cylinder to the hydraulic fluid reservoir and thus
to reduce servo pressure in the servo pressure circuit after a
braking operation has ended. A further manifold valve of this type
may also ensure that no above-atmospheric pressure or vacuum builds
up in the servo pressure circuit and obstructs or even blocks the
primary piston displacement in the event of a mechanical actuation
of the primary piston caused by an emergency.
[0017] The case was discussed above where pressure is no longer
properly generated in the servo pressure circuit, for example owing
to a failure of the pressure source. It is equally possible for the
servo pressure circuit to supply excessive servo pressure which
could possibly lead to an overreaction of the brake system. To
prevent a scenario of this type a development, one embodiment of
the brake system provides that the servo pressure circuit comprises
a bypass channel that can be activated as a function of pressure
and is connected downstream of the pressure source. The bypass
channel can be opened or closed as a function of the prevailing
servo pressure and thus hydraulic fluid can be removed from the
servo pressure circuit in the event of excessive servo pressure.
During normal operation, i.e. if the servo pressure inside the
servo pressure circuit is below a predetermined maximum value, the
bypass channel is blocked.
[0018] In another embodiment of the brake system, a pressure sensor
for detecting the hydraulic pressure prevailing in the pressure
accumulator is associated with the pressure accumulator. As already
generally stated above with respect to the servo pressure circuit,
a separate pressure sensor can, in particular, also be associated
with the pressure accumulator. The instantaneous "loading state" of
the pressure accumulator can therefore be ascertained and evaluated
with the aid of the pressure prevailing in the accumulator, for
example to the extent that in the event of a specific minimum
pressure not being attained inside the pressure accumulator and
with the pressure source power simultaneously being available an
active fluid supply control element is opened and hydraulic fluid
is supplied to the pressure accumulator for increasing the
accumulator pressure.
[0019] Reference should be made to the fact that a low-pressure
accumulator is preferably used as the pressure accumulator, the
maximum accumulator pressure of which is limited. While a
low-pressure accumulator of this type is suitable only for
temporarily bridging a pressure drop, for example owing to starting
delays in the motor drive of the pressure source, it does have the
advantages that it is inexpensively available, requires only a
small installation space and is usually sufficient during
operation. The main load of the pressure generation generally falls
to the pressure source anyway. With respect to the use of a
low-pressure accumulator, a pressure sensor associated therewith
satisfies the further task of also detecting attainment of a
maximum pressure, whereupon an additional hydraulic fluid is to be
supplied to the pressure accumulator in order to prevent damage or
destruction to the low-pressure accumulator. Obviously the maximum
pressure value to be detected by the pressure sensor should be
selected with sufficient security with respect to a pressure value
at which damage can actually occur to the pressure accumulator.
[0020] As already illustrated above, the brake system may be
constructed with a large number of active components and pressure
sensors. In this connection, one embodiment of the brake system
provides a controller for evaluating detected hydraulic pressures
and for evaluating actively controllable components. The controller
can, for example, be formed by an electronic data processing system
present in a motor vehicle anyway. It can, however, also be formed
by a separate data processing system with a separate processor.
[0021] In the above description, it was generally illustrated that
the brake system operates according to actuation of the brake
pedal. This can mean that, on the one hand, the actuating force
exerted on a brake pedal is mechanically transmitted to the primary
piston and that actuation of the primary piston is assisted by the
servo pressure circuit. In other words the pedal actuating force
can be detected and accordingly intensified by the servo pressure
circuit. As an alterative to this it is also possible, during
normal operation, to completely mechanically decouple the primary
piston and its movement from brake pedal actuation. This means that
pedal actuation is accordingly no longer transmitted directly to
the primary piston, rather the energy causing it dissipates. The
primary piston is displaced in such a configuration of the brake
system exclusively during normal operation, under the effect of the
servo pressure circuit. As a result, during normal operation the
servo pressure circuit alone is responsible for displacement of the
primary piston. For emergency operation, in which, for example, a
component of the servo pressure circuit fails, a mechanical
coupling of brake pedal and primary piston may be provided and be
produced, for example, after bridging a movement pedal.
[0022] In another embodiment of the brake system for a motor
vehicle, the brake system comprises a master brake cylinder, in
particular of the above-described type, in which, according to
actuation of a brake pedal, but mechanically decoupled therefrom, a
primary piston can be displaced for generating a brake pressure in
a hydraulic brake circuit, it being possible to displace the
primary piston under the effect of a hydraulic servo pressure
circuit in the master brake cylinder and the hydraulic servo
pressure circuit comprising a pressure source for generating the
servo pressure. The servo pressure circuit may comprise a bypass
channel that can be activated as a function of pressure and is
connected upstream of the master brake cylinder.
[0023] Other advantages of the brake system for a motor vehicle
will become apparent to those skilled in the art from the following
detailed description, when read in light of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a schematic general diagram of a first
embodiment of a brake system;
[0025] FIG. 2 shows a schematic general diagram according to FIG. 1
of a second embodiment of a brake system;
[0026] FIG. 3 shows a schematic general diagram according to FIGS.
1 and 2 of a third embodiment of a brake system;
[0027] FIG. 4 shows a schematic general diagram according to FIGS.
1 to 3 of a fourth embodiment of a brake system; and
[0028] FIG. 5 shows a schematic general diagram according to FIGS.
1 to 4 of a fifth embodiment of a brake system.
DETAILED DESCRIPTION
[0029] FIG. 1 shows a first embodiment of a brake system which is
designated generally at 10. The brake system comprises a servo
pressure circuit 12 and a brake cylinder subassembly 14.
[0030] The brake cylinder subassembly 14 comprises a master brake
cylinder 16 in which a primary piston 18 is displaceably guided. A
secondary piston 20 is also displaceably guided in the master brake
cylinder 16 and mechanically coupled to the primary piston 18 by a
spring arrangement. The primary piston 18, with the master brake
cylinder 16 and the secondary piston 20, encloses a primary
pressure chamber 22. The secondary piston 20, with the master brake
cylinder 16, encloses a secondary pressure chamber 24. The primary
pressure chamber 22 and the secondary pressure chamber 24 are
fluidically coupled by respective supply channels to a hydraulic
fluid accumulator 26 for supplying hydraulic fluid in the rest
state shown in FIG. 1. The primary pressure chamber 22 and the
secondary pressure chamber 24 are also fluidically coupled to a
brake system 28 which, in a manner known per se, can bring about
deceleration of the wheels of a motor vehicle.
[0031] The brake cylinder subassembly 14 also comprises a pedal
simulation device 30. In detail, the pedal simulation device 30
comprises a force input member 32 mechanically coupled to a brake
pedal and which is workingly connected to a working piston 34. The
working piston 34 can be displaced in a piston chamber 36, it
limiting working chambers on either side inside the piston chamber
36. A gas contained in the working chambers on either side of the
working piston 34 is displaced from one working chamber through a
throttle 38 (as shown in FIG. 1) into the respective other working
chamber by a displacement of the working piston 34 inside the
piston chamber 36 and, as a result, due to the effect of the
throttle 38 a resistance to a movement of the force input member 32
is generated. A resistance which results from a simulation spring
arrangement 40 acts on the force input member 32 in addition to the
pneumatically generated resistance. This simulation spring
arrangement 40 is constructed in multiple stages, i.e. it comprises
a spring with low spring hardness and a spring with increased
spring hardness which can be reduced by steps, i.e. compressed with
a progressive spring characteristic.
[0032] Any pedal actuation, i.e. any displacement of the force
input member 32, is detected by a position sensor 42, the position
sensor 42 emitting a position signal to an electronic control unit
44, with the aid of which the existence of a pedal actuation can be
ascertained.
[0033] The brake system 10 according to FIG. 1 is designed in such
a way that a pedal actuation, and a displacement of the force input
member 32 resulting therefrom, is not mechanically transmitted to
the primary piston 18, rather the energy applied during the pedal
actuation is dissipated in the brake system 10. To carry out
braking, hydraulic pressure is generated in an actuating pressure
chamber 46 by means of the servo pressure circuit 12, which
pressure displaces the primary piston 18, and consequently the
secondary piston 20, and as a result provides for a pressure build
up in the primary pressure chamber 22 and in the secondary pressure
chamber 24. The primary piston 18 is thus completely mechanically
decoupled from the force input member 32 during normal operation of
the brake system 10.
[0034] The construction of the servo pressure circuit 12 is to be
described hereinafter. The servo pressure circuit 12 is supplied
with hydraulic fluid from the hydraulic fluid reservoir 26. This is
conveyed from the hydraulic fluid reservoir 26 via a supply line 48
by a pump 50 which is driven by a motor 52. The pump 50 is
fluidically coupled by a hydraulic fluid supply line 54 to the
actuating pressure chamber 46. A branch 56, which is connected in
parallel with the pump 50 and which comprises a pressure-limiting
valve 58, is provided in the hydraulic fluid supply line 54 so as
to issue from the pump 50. A non-return valve 60 is accordingly
integrated into the hydraulic fluid supply line 54 and allows fluid
to flow from the pump 50 into the actuating pressure chamber 46,
but blocks a flow of fluid in the opposite direction. A discharge
line 62 comprising a non-return valve 64 subsequently opens into
the hydraulic fluid supply line 54. The non-return valve 64 is
oriented in such a way that it blocks a flow of fluid from the
hydraulic fluid supply line 54 into the discharge line 62 but
allows fluid to flow in the opposite direction. A pressure
accumulator 66 is coupled to the discharge line 62. The pressure
accumulator 66 is constructed as a low-pressure accumulator and is
configured in such a way that hydraulic fluid can be stored therein
up to a specific maximum pressure. The pressure accumulator is
constructed in an inherently conventional manner and is coupled at
its side remote from the non-return valve 64 to a backflow line 68.
The pressure accumulator 66 also comprises a spring element 70
which is used for pressure accumulation.
[0035] A supply line 72 subsequently branches from the hydraulic
fluid supply line and is likewise provided with a pressure-limiting
valve 74. The supply line 72 is hydraulically coupled to the
pressure accumulator 66.
[0036] Starting from the branching of the supply line 72, a two-way
valve 76 that can be actively controlled by the electronic control
unit 44 is arranged in the further course of the hydraulic fluid
supply line 54. This, as shown in FIG. 1, can be switched into a
closed state and into an open state. Finally, a further bypass
channel 78, which likewise comprises a two-way valve 80 that can be
controlled by the electronic control unit 44, adjoins the further
course of the hydraulic fluid supply line 54. A further pressure
sensor 82, which detects the servo pressure currently prevailing in
the hydraulic fluid line 54 and forwards it to the electronic
control unit 44 in the form of a corresponding signal, is arranged
in the further course of and on the hydraulic fluid supply line
54.
[0037] The servo pressure circuit 12 functions as follows. The
motor 52, which motively drives the pump 50, is controlled
according to the control of the electronic control unit 44. The
pump conveys hydraulic fluid from the hydraulic fluid reservoir 26
into the hydraulic fluid supply line 54. The actuating pressure
chamber 46 is supplied with hydraulic fluid by the hydraulic fluid
supply line 54, so a pressure builds up in this chamber, if
required, which pressure, in the event of actuation of the brake
pedal and displacement of the force input member 32, leads, without
mechanical coupling of force input member 32 and primary piston 18,
to the primary piston 18 being displaced to the left in FIG. 1
under the effect of the hydraulic pressure that has built up in the
actuating chamber 46. As a result, a hydraulic pressure builds up
in the primary pressure chamber 22 and, with displacement of the
secondary piston 20, in the secondary pressure chamber 24.
[0038] With sufficiently high servo pressure in the hydraulic fluid
supply line 54, the pressure-limiting valve 74 opens in the supply
line 72, so hydraulic fluid can flow into the pressure accumulator
66 via the supply line 72. If, however, the servo pressure
prevailing in the hydraulic fluid supply line 54 exceeds a maximum
value, the pressure-limiting valve 58 opens and short-circuits the
entire portion of the servo pressure circuit 12 adjoining the
branch 56. As a result, overburdening of the servo pressure circuit
12 may be prevented. If, on the other hand, the servo pressure
prevailing in the hydraulic fluid supply line 54 sinks below a
specific minimum value, and if the pressure accumulator 66 is
sufficiently "loaded," the pressure accumulator 66 can, if
required, temporarily equalise a drop in pressure. Such a drop in
pressure can, for example, come about because an actuation of the
brake pedal (not shown) switches the two-way valve 46 over from its
closed position shown in FIG. 1 into an open state and servo
pressure is thus supplied from the servo pressure circuit 12 to the
actuating pressure chamber 56. However, owing to a starting delay
of the motor 52 the pump 50 cannot build up servo pressure in the
servo pressure circuit 12 quickly enough, so a pressure drop
briefly occurs. This is equalised by the pressure accumulator 66.
The two-way valve 76, controlled by the electronic control unit 44
according to the signal obtained by the position sensor 42 and
further signals, for example from the pressure sensor 82, thus acts
as an activating element for activation of the servo pressure
circuit 12. The two-way valve 80 also acts as a pressure relief
valve for the hydraulic fluid supply line 54. It is switched into
its open position shown in FIG. 1, for example, if there is no
brake actuation and thus a build up of pressure is not necessary in
the actuating pressure chamber 46 either. As a result, it may also
allow pressure equalisation between the master brake cylinder and
the reservoir 26. This is significant in particular with respect to
a possible defect in the servo pressure circuit 12 during which the
primary piston 32 can be mechanically moved. Opening the two-way
valve 80 prevents such a mechanical movement of the primary piston
32 from being obstructed by above-atmospheric pressure or a vacuum
occurring in the servo pressure circuit 12 as a result. As soon as,
during normal operation with a completely functional servo pressure
circuit 12, a brake actuation is detected by the position sensor 42
the two-way valve 80 is switched into its closed position so
hydraulic fluid can be supplied by the hydraulic fluid line 54 to
the actuating pressure chamber 46.
[0039] A fundamental aspect of the embodiments of the brake system
described herein lies in the fluidic connection of the pressure
accumulator 66 in the servo pressure circuit 12. In the solution
shown in FIG. 1, it is possible for the pressure accumulator 66 to
be supplied with hydraulic fluid if there is a sufficiently high
servo pressure in the servo pressure circuit 12, i.e. if the pump
50 conveys enough hydraulic fluid from the hydraulic fluid
accumulator 26. The pressure accumulator 66, if it is appropriately
loaded, can equalise pressure fluctuations inside the servo
pressure circuit 12. This is necessary for example if pressure
cannot be built up sufficiently quickly in the servo pressure
circuit 12 owing to abrupt braking and owing to a starting delay in
the unit comprising pump 50 and motor drive 52.
[0040] For supplying the pressure accumulator there is also the
possibility that the two-way valve 76 is closed after a braking
operation has ended and the pump 50 continues to be operated over a
predetermined period. As a result hydraulic pressure, which can be
used to load the pressure accumulator 66, builds up in the portion
of the hydraulic fluid supply line 54 between the pump 50 and the
two-way valve 76. In the event that the servo pressure is already
sufficiently high once the braking operation has ended, in order to
load the pressure accumulator 66 the pump 50 can also be directly
switched off once the braking operation has ended and when the
two-way valve 80 is closed and the two-way valve 76 is open the
pressure accumulator 66 can be loaded.
[0041] FIG. 2 shows a second embodiment of the brake system. To
provide a simpler description and to avoid repetitions only the
differences from the first embodiment according to FIG. 1 shall be
described. The same reference numerals as in the description of the
first embodiment according to FIG. 1 will be used for identical or
identically-acting components, but will be preceded by the number
"1."
[0042] The only difference between the embodiment according to FIG.
1 and the second embodiment according to FIG. 2 lies in the fact
that, in the supply line 172, the pressure-limiting valve 74
provided in FIG. 1 was been replaced in FIG. 2 by a throttle
element 186. The throttle element 186 fulfills the function of
limiting a supply of hydraulic fluid via the supply line 172 to the
pressure accumulator 166 as a function of pressure. The throttle
element 186 is used as a volume flow divider, the larger portion of
the volume flow conveyed by the pump 150 flowing through the
hydraulic fluid supply line 154 from the pump 150 into the
actuating pressure chamber 146 and only a small portion is supplied
via the throttle element 186 and the supply line 172 to the
pressure accumulator 166. However, in the event of high servo
pressure inside the hydraulic fluid supply line 154 a sufficiently
high quantity of hydraulic fluid is supplied via the throttle
element 186 and the supply line 172 to the pressure accumulator 166
and the latter loaded thereby. A gas contained in the working
chambers on either side of the working piston 134 is displaced from
one working chamber through a throttle 138 (as shown in FIG. 2)
into the respective other working chamber by a displacement of the
working piston 134 inside the piston chamber 136.
[0043] The remaining mode of operation of the brake system 110
corresponds to the mode of operation of the brake system 10 from
FIG. 1 and illustrated in detail.
[0044] FIG. 3 shows a third embodiment of a brake system. Again
only the differences from the embodiments according to FIG. 1 and 2
will be described to avoid repetitions. For this purpose, use will
again be made of the reference numerals from the preceding
description of the embodiments according to FIG. 1 and 2 for
identically-acting and identical components, the reference numerals
being preceded by the number "2."
[0045] The embodiment according to FIG. 3 shows a combination of
the two embodiments according to FIG. 1 and 2. Firstly the
pressure-limiting valve 274 and following it the throttle element
286 are connected in series into the supply line 272. As a result
it is possible to throttle the hydraulic flow via the throttle
element 286 even in the event of sufficiently high servo pressure
inside the servo pressure circuit 212 at which the
pressure-limiting valve 274 opens for supplying the pressure
accumulator 266. As a result the quantity of hydraulic fluid
supplied to the pressure accumulator 266 and the hydraulic pressure
that has built up therein can be reduced, even in the event of
sufficiently high hydraulic pressure, as the throttle element 286
again acts as a volume flow divider. With this solution it is
possible, in any pressure region, as long as it lies below the
maximum pressure value determining the function of the
pressure-limiting valve 258, to moderately supply the pressure
accumulator 266. A construction of this type is recommended in
particular when using a low-pressure accumulator 266 which is to
be-protected from being supplied with excessive hydraulic pressure.
A gas contained in the working chambers on either side of the
working piston 234 is displaced from one working chamber through a
throttle 238 (as shown in FIG. 3) into the respective other working
chamber by a displacement of the working piston 234 inside the
piston chamber 236.
[0046] Apart from that the brake system 210 according to FIG. 3
functions as described above with reference to FIG. 1 with respect
to the first embodiment.
[0047] FIG. 4 shows a fourth embodiment of the brake system. Again
only the differences from the preceding embodiments according to
FIG. 1 to 3 are to be described. The same reference numerals, as
were used in the description of FIG. 1 to 3, will again be used for
this description for identical or identically-acting components but
will be preceded by the number "3."
[0048] In the fourth embodiment according to FIG. 4, a two-way
valve 388, which can be controlled by the electronic control unit
344, is fitted into the supply line 372 leading from the hydraulic
fluid supply line 354 to the pressure accumulator 366. The supply
line 372 also comprises a pressure sensor 390 between the pressure
accumulator 366 and the two-way valve 388. The hydraulic pressure
prevailing in the pressure accumulator 366 can be detected by means
of the pressure sensor 390. If this hydraulic pressure falls below
a predetermined minimum value and the pump 350 supplies a
sufficiently high servo pressure in the servo pressure circuit 312
the two-way valve 388 is switched from its closed position shown in
FIG. 4 into the open position. The hydraulic fluid can thus flow
unhindered from the hydraulic fluid supply line 354 into the
pressure accumulator 366 and thus load the pressure accumulator
366. The change in the pressure level in the pressure accumulator
366 during this loading process is monitored by the pressure sensor
390 and the electronic control unit 344. As soon as a desired level
or a maximum permitted pressure level is attained in the pressure
accumulator 366 the pressure sensor 390 detects this and emits a
corresponding signal to the electronic control unit 344. The unit
then controls the two-way valve 388 so the latter returns to its
closed position shown in FIG. 4 and thus the fluidic connection via
the supply line 372 to the hydraulic fluid supply line 354 is
broken. The pressure accumulator 366 may thus be purposefully
loaded as a function of pressure by active switching of the two-way
valve 388 with the embodiment according to FIG. 4. A gas contained
in the working chambers on either side of the working piston 334 is
displaced from one working chamber through a throttle 338 (as shown
in FIG. 4) into the respective other working chamber by a
displacement of the working piston 334 inside the piston chamber
336.
[0049] Apart from that the brake system according to FIG. 4
functions as described above with respect to FIG. 1 to 3 with
regard to embodiments 1 to 3.
[0050] It should also be noted that, owing to the effect of the
two-way valve 388, the discharge line 362 can be omitted in a
development (not shown) of the embodiment according to FIG. 4. The
pressure accumulator 366 is supplied and emptied via the line 372
in this case.
[0051] FIG. 5 shows a fifth embodiment of the brake system. Again
only the differences from the above-described embodiments according
to FIG. 1 to 4 are to be described. The same reference numerals as
above for the description of FIG. 1 to 4 will be used for
identically-acting and identical components, but they will be
preceded by the number "4."
[0052] In the fifth embodiment according to FIG. 5, the servo
pressure circuit 412 is illustrated in a highly simplified manner
compared with the above-described embodiments. The circuit includes
only a pressure source comprising pump 450 and motor 452 and which
can be short-circuited by the branch 456 and the pressure-limiting
valve 458 located therein. The non-return valve 460 is also
provided as is the bypass channel 478 with the two-way valve 480
integrated therein and controllable by the electronic control unit
444.
[0053] In this embodiment of the brake system, the pump 450 and the
motor 452 are constructed in such a way that on activation by a
brake pedal actuation, they can react sufficiently quickly without
starting delay and thus a servo pressure can build up sufficiently
quickly inside the servo pressure circuit 412, which pressure then
provides for a displacement of the primary piston 418 in the
actuating pressure chamber 446. Such a fast-reacting construction
of the pressure source, comprising pump 450 and motor drive 452
allows a much simplified construction of the servo pressure
circuit. A gas contained in the working chambers on either side of
the working piston 434 is displaced from one working chamber
through a throttle 438 (as shown in FIG. 5) into the respective
other working chamber by a displacement of the working piston 434
inside the piston chamber 436.
[0054] The embodiment of a brake system described herein show a
simple and reliable possibility for providing a master brake
cylinder with a servo pressure according to a brake pedal
actuation.
[0055] Reference should be made to the fact that the embodiments of
a brake system described herein have been described in connection
with a brake system in which, during normal operation, complete
mechanical decoupling is provided between primary piston and force
input member. It is, however, equally possible to use the brake
systems described herein in which there is no such mechanical
decoupling between force input member (and thus the brake pedal)
and primary piston and the servo pressure only acts in a supportive
manner to displace the primary piston directly moved by actuation
of the brake pedal.
[0056] In accordance with the provisions of the patent statutes,
the principle and mode of operation of the brake system for a motor
vehicle have been explained and illustrated in its various
embodiments. However, it must be understood that the brake system
for a motor vehicle described herein may be practiced otherwise
than as specifically explained and illustrated without departing
from its spirit or scope.
* * * * *