U.S. patent application number 16/624505 was filed with the patent office on 2020-06-04 for brake system.
The applicant listed for this patent is IPGATE AG. Invention is credited to Heinz LEIBER, Thomas LEIBER, Anton VAN ZANTEN.
Application Number | 20200172068 16/624505 |
Document ID | / |
Family ID | 59887205 |
Filed Date | 2020-06-04 |
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United States Patent
Application |
20200172068 |
Kind Code |
A1 |
LEIBER; Thomas ; et
al. |
June 4, 2020 |
BRAKE SYSTEM
Abstract
A brake system may include an actuation device, in particular a
brake pedal; a first piston-cylinder unit with two pistons, in
particular an auxiliary piston and a second piston, in order to
supply brake circuits with a pressure medium via a valve device,
wherein one of the pistons, in particular the auxiliary piston, can
be actuated by means of the actuation device; a second
piston-cylinder unit comprising an electric motor-powered drive, a
transmission, and at least one piston in order to supply pressure
medium to at least one of the brake circuits via a valve device;
and a motor pump unit with a valve device in order to supply
pressure medium to the brake circuits. The brake system may further
include a hydraulic travel simulator which is connected to a
pressure or working chamber of the first piston-cylinder unit.
Inventors: |
LEIBER; Thomas; (Rogoznica,
HR) ; LEIBER; Heinz; (Oberriexingen, DE) ; VAN
ZANTEN; Anton; (Ditzingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IPGATE AG |
Pfaffikon SZ |
|
CH |
|
|
Family ID: |
59887205 |
Appl. No.: |
16/624505 |
Filed: |
August 30, 2017 |
PCT Filed: |
August 30, 2017 |
PCT NO: |
PCT/EP2017/071738 |
371 Date: |
December 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T 17/221 20130101;
B60T 2270/10 20130101; B60T 8/4022 20130101; B60T 2270/402
20130101; B60T 13/662 20130101; B60T 13/16 20130101; B60T 13/58
20130101; B60T 2270/404 20130101; B60T 2270/403 20130101; B60T
2270/604 20130101; B60T 8/4036 20130101; B60T 8/4081 20130101; B60T
8/176 20130101; B60T 8/268 20130101; B60T 8/4018 20130101; B60T
13/745 20130101; B60T 2270/413 20130101 |
International
Class: |
B60T 8/40 20060101
B60T008/40; B60T 17/22 20060101 B60T017/22; B60T 13/58 20060101
B60T013/58; B60T 13/16 20060101 B60T013/16; B60T 13/66 20060101
B60T013/66; B60T 8/176 20060101 B60T008/176 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2017 |
DE |
102017113563.4 |
Claims
1.-26. (canceled)
27. A brake system, comprising: an actuating device, a first
piston-cylinder unit having a first piston and a second piston,
arranged to supply at least one first brake circuit and at least
one second brake circuit with pressure medium via a valve device,
wherein the first piston is enabled to be actuated by means of the
actuating device, wherein the first piston-cylinder unit comprises
a first pressure chamber or a first working chamber in which the
first piston is arranged and to which at least the second brake
circuit is connected, wherein the first piston-cylinder unit
comprises a second pressure chamber or a second working chamber, to
which at least the first brake circuit is connected, a second
piston-cylinder unit with an electromotive drive, a transmission
and at least one piston for supplying pressure medium to at least
one of the brake circuits via a valve device, a motor-pump unit,
with a valve device, arranged to supply pressure medium to the
first and second brake circuits, a hydraulic travel simulator
connected to one of the first or second pressure chambers or
working chambers of the first piston-cylinder unit, wherein a
pressure or working chamber of the second piston-cylinder unit is
connected to the first brake circuit via a hydraulic line and is
supplied with pressure via the first piston, and wherein the second
piston-cylinder unit is aligned parallel to the axis of the first
piston-cylinder unit.
28. The brake system according to claim 27, wherein the brake
system is designed for a subsequent conveying of volumes from a
storage container during the piston return stroke of the second
piston-cylinder unit via a suction valve, wherein the suction valve
and a breather hole of the second piston-cylinder unit are
connected to the storage container via a return line.
29. The brake system according to claim 27, wherein the first
piston-cylinder unit has a partition wall with a seal for a
penetrating plunger, for forming a third pressure chamber or a
third working chamber, in which a piston is arranged, which is
connected via a valve device to a brake circuit.
30. The brake system according to claim 29, wherein, in the event
of failure of the first brake circuit, the plunger transmits force
of the actuating device to the second piston and thus generates
pressure in the second brake circuit.
31. The brake system according to claim 30, wherein the plunger has
a smaller cross-sectional area than the first and second pistons of
the first piston-cylinder unit, by at least a factor of 5, and
contributes insignificantly to pressure build-up and serves for
pressure sensing in at least one of the brake circuits, and the
plunger further transmits a force to the actuating device and thus
generates a haptic feedback to the actuating device.
32. The brake system according to claim 27, further comprising a
control device arranged to enable a motor of the electromotive
drive of the second piston-cylinder unit and a motor of the
motor-pump unit to be used together or independently of one
another.
33. The brake system according to claim 27, wherein, in the event
of failure of the motor-pump unit, an ABS function is carried out
by a piston control of the second piston-cylinder unit together
with pressure regulating valves of the motor-pump unit.
34. The brake system according to claim 27, wherein the second
piston-cylinder unit is only effective in a specific pressure
range, and wherein the motor-pump unit is used for pressure
generation for a further, higher pressure range.
35. The brake system according to claim 27, wherein control of the
second piston-cylinder unit is carried out via travel of the
actuating device and control of pressure is carried out by means of
a corresponding brake booster characteristic, wherein instead of
the pressure, the motor current is used for regulating the second
piston-cylinder unit.
36. The brake system according to claim 27, wherein a
pressure-volume characteristic is used for controlling the second
piston-cylinder unit and for diagnosis, wherein the brake system is
designed to detect a failure of one of the brake circuits by
comparing pressure-volume characteristics, wherein the
pressure-volume characteristic is stored in a characteristic map at
intervals as part of a diagnostic cycle.
37. The brake system according to claim 27, wherein the first
piston and the second piston of the first piston-cylinder unit have
different diameters.
38. The brake system according to claim 27, further comprising a
two-box, wherein a first module of the two-box is connected to a
12V battery or 12V voltage network and a second module of the
two-box is connected to a DC/DC converter or other on-board network
with a higher voltage than 12V.
39. The brake system according to claim 38, wherein both of the
first and second modules of the two-box are each connected
redundantly both to the 12V battery or voltage network and to the
DC/DC converter or other on-board network with a higher voltage
than 12V.
40. The brake system according to claim 27, wherein four-wheel
blending takes place for a recuperation control, wherein a pressure
control takes place via a piston with open valves of the valve
device of the motor-pump unit, and/or wherein the transmission
comprises a trapezoidal spindle with self-locking, having a
self-locking action in the event of failure of the electromotive
drive.
41. The brake system according to claim 27, wherein a plug
connection for the brake system is arranged below a storage
container and is directed inwards towards a center of the brake
system in order to enable a lateral removal of an associated
plug.
42. The brake system according to claim 27, wherein the second
piston of the first piston-cylinder unit has, in addition to a
passage in form of a breather hole which is provided with two
seals, a further passage which is provided with a further seal, and
which is connected via a throttle to a line leading to a storage
container.
Description
[0001] The invention relates to a brake system according to the
preamble of claim 1.
DESCRIPTION OF THE PRIOR ART
[0002] The trend towards vehicles with autonomous driving (AD)
places high demands on the brake system in terms of fault tolerance
on the one hand and redundant functions, e.g. for brake pressure
generation, power supply and computer functions (ECU) on the other.
So-called one-box and two-box systems are favored. The latter
consist of an electric brake booster (BKV), a so-called e-booster,
and an ESP system (Electronic Stability Control System). This
makes, for example, the generation of brake pressure via electric
motor and electronic control unit (ECU) redundant for e-boosters
and return pumps with electric motor and ECU.
[0003] The known solutions have relatively long overall lengths and
a high weight.
[0004] In WO2011/098178 (hereinafter referred to as variant A or as
a follow-up booster or e-booster), such a solution is described
with a coaxial drive in which an electric motor acts via a gear and
piston on the HZ piston (=main cylinder piston). The BKV control is
effected via an electrical element and reaction disc as a so-called
follow-up booster, the pedal travel is a function of the brake
pressure and the volume absorption of the brake system, which
requires long pedal travel in the event of fading or brake circuit
failure.
[0005] WO2009/065709 (hereinafter referred to as variant B, or as a
follow-up booster or e-booster) also shows an e-booster as a
follower BKV. Here the BKV control takes place via pedal travel and
pressure. A separate pressure supply with electric motor and
plunger acts via the amplifier piston on the HZ piston.
[0006] WO2012/019802 (hereinafter variant C) shows an arrangement
similar to WO2011/098178 with coaxial drive in which an electric
motor acts on the HZ piston via a gear and piston. An additional
piston cylinder unit is used here, which acts on a travel simulator
piston (WS). The pedal travel is thus independent of e.g. fading
and brake circuit failure. However, the complexity and the
construction length are high.
[0007] DE 10 2009 033 499 (hereinafter also referred to as variant
D) shows a brake booster (BKV) with additional ESP unit with
hydraulic actuation of the booster piston and external pressure
supply. This arrangement with four or five pistons and six solenoid
valves (MV) is complex and unfavorable in length. The
non-hydraulically acting travel simulator (WS) is located within
the piston-cylinder unit upstream of the main cylinder and cannot
be damped or switched via a solenoid valve (MV).
[0008] All above mentioned solutions have a redundant brake booster
(BKV) function, because in case of failure of the BKV motor the ESP
unit with pump similar to the assistance functions with vacuum BKV
guarantees the brake function in autonomous driving mode.
[0009] In the event of failure of the ESP motor, ABS shall function
via the possibility of pressure modulation by the BKV motor as
described in WO2010/088920 of the applicant. However, this only
allows a common pressure control for all four wheels, which does
not result in an optimal braking distance.
[0010] All previously known one-box systems have a so-called travel
simulator (especially for brake-by-wire) because of the advanced
pedal travel characteristics.
OBJECT OF THE INVENTION
[0011] Based on the prior art, it is the object of the present
invention to provide an improved brake system.
[0012] In particular, the invention is based on the object of
creating a brake system for use in autonomous driving operation
(hereinafter AD) and/or electric vehicles/hybrid vehicles with
increasingly strong recuperation power (energy recovery by braking
via generator/or drive motor in generator operation). Preferably,
the weight is reduced and/or the dimensions of the system are
reduced and/or the reliability is increased.
[0013] Preferably, a cost-effective brake system for autonomous
driving is to be created, which fulfils all required redundancies
as well as very high safety requirements.
Solution According to the Invention
[0014] This object is solved according to the invention with the
features of patent claim 1.
[0015] Among other things, the improvement is characterized in that
the design of the brake booster has very few simple components with
low tolerance requirements (e.g. valves only in open/closed
operation) and is therefore cost-effective, very short and narrow
in design and enables a constant pedal travel characteristic,
especially with strong recuperation.
[0016] Advantageous embodiments or designs of the invention are
contained in the further claims, the drawing and the figure
description to which reference is made here.
[0017] With the solution according to the invention and its
embodiments and designs, a brake system is created which has a very
short construction as well as an advantageous pedal
characteristic.
[0018] In particular, a two-box system is created according to the
invention, having an electric brake booster which is connected to a
standard ESP unit via two hydraulic lines (hereinafter referred to
as X-Boost and ESP/ABS unit, together referred to as two-box
system), wherein the brake booster has a pedal characteristic which
is independent of the volume absorption of the brake system and the
degree of recuperation.
[0019] Furthermore, the invention achieves a compact design of the
brake booster with a low box volume, which is very short and narrow
and has many redundancies, e.g. for pressure generation, electrical
supply, failure of the pump motor of the ESP unit and also includes
an ABS function with reduced performance in the event of failure of
the ESP unit. In emergency operation without ESP, the ABS function
should include at least one individual regulation axle-by-axle to
improve the braking distance ("select-low" pressure
regulation).
[0020] The installation spaces in the unit compartment are becoming
smaller and smaller, thus the dimensions of the brake unit should
be as small as possible, especially in terms of width and length.
This compact design is possible on the one hand by decoupling the
main cylinder (HZ) piston from the motor drive and on the other
hand by a special short main cylinder (HZ) according to
WO2016/023994 of the applicant, which is referred to here with
parallel arranged pressure supply (hereinafter pressure supply or
DV) consisting of electric motor with piston drive.
[0021] The pressure supply (DV) is only effective up to the wheel
locking limit of 80 to 100 bar. For higher pressures (e.g. for
driver assistance functions), the pump of the ESP unit is switched
on. This can therefore be realized with the solution according to
the invention in comparison to variant A of the prior art described
above, since the ESP pump function has no influence on the pedal
feel, since the brake pedal is decoupled.
[0022] In the pedal characteristic, a retroactive effect from
volume absorption, e.g. in the event of brake circuit failure,
should be excluded. On the other hand, it should be possible to
generate a desired pedal feedback, e.g. a small pedal movement when
using the ABS function, optionally also intermittently. Faults,
e.g. brake circuit failure, can also be indicated by moving the
pedal parallel to the warning lamp.
[0023] Various solutions are conceivable for the pedal travel
simulator. In the entire pressure range (150 to 200 bar) the pedal
travel simulator should deliver a good pedal travel characteristic,
e.g. up to 30 bar with a flat characteristic curve and then
progressively increasing without influence whether the X-Boost or
the ESP unit delivers the pressure. In the embodiment of the
e-booster as a follow-up booster (variant A according to the prior
art), the pedal force characteristic curve changes significantly
during the transition from e-booster to ESP and requires a lot of
software effort for the PWM operation of the valves necessary for
this. This is not the case with the solution according to the
invention, since the operation of the ESP pump has no influence on
the pedal characteristics, since the pedal is decoupled via the
travel simulator.
[0024] To reduce the construction volume, the return spring (18)
can be used in the flat part of the pedal travel characteristic
curve, so that the volume in the piston travel simulator is smaller
and only corresponds to the progressive part of the characteristic
curve, as also shown in WO2013/072198 of the applicant, to which
reference is made here.
[0025] Another possibility for the realization of a pedal travel
simulator is a THZ (=tandem main brake cylinder) with plunger
without piston travel simulator as described or illustrated in
WO2016/023994 of the applicant, to which reference is made here in
this respect. Here, the control pressure to the BKV, which depends
on the pedal travel, acts on the plunger and thus generates the
pedal feedback effect.
[0026] Depending on the pedal position, pressure is transmitted
from the piston of the pressure supply to the SK piston of the main
brake cylinder (T)HZ, which creates the brake pressure. The
pressure supply consists of an electric motor which drives the
piston via a spindle. Both a ball screw drive (KGT) and a
trapezoidal spindle with nut can be used as transmissions. The
latter is cheaper and quiet, but has a lower efficiency and is
self-locking. The latter has the advantage that in the event of a
failure in the pressure supply DV, e.g. of the engine, the piston
remains in the position so that there is no increase in volume in
the brake circuit under the influence of brake pressure.
[0027] For the ball screw drive (KGT), an additional shut-off valve
must be used for this failure. The aspiration of the liquid from
the storage container (VB) takes place via a suction valve or via
the piston sleeve seal with a breather hole, as in a main cylinder
(HZ).
[0028] Access to the piston travel simulator can be closed with a
solenoid valve (WA), as in the event of a pressure supply failure
(DV) the pedal force acts on the main cylinder (HZ) and thus
generates brake pressure in the so-called fallback level (RFE).
Without the valve (WA), the pedal travel in the fallback level
(RFE) would be extended by the volume absorption of the piston
travel simulator (WS).
[0029] Since the interconnection of X-Boost and ESP unit provides
two redundant systems for pressure generation with redundant power
supply, the fallback level (RFE) is only effective during towing,
actually only for deep loading, e.g. in the event that the
transmission of the vehicle may be blocked. These facts allow
greater degrees of freedom in system and piston design, e.g. saving
a WA solenoid valve.
[0030] X-Boost and ESP unit have separate power supplies in one
embodiment, e.g. ESP is connected to a 12V battery and X-Boost is
connected to a DC/DC converter of a multi-voltage vehicle
electrical system. Alternatively, both X-Boost and ESP unit can be
connected to both 12V battery and DC/DC converter. Thus both
modules of the brake system of the two-box have a redundant power
supply in each case.
[0031] Some of the solutions according to the invention have even
more advantages over the prior art variant A: [0032] I. If the
brake circuit fails, there is no pedal through fall; [0033] II. If
the ESP motor fails, the pressure can also be controlled axle by
axle, which enables a considerable reduction in braking distance;
[0034] III. Many driver assistance functions can be implemented in
X-Boost and can be implemented with greater precision than in the
ESP unit; and/or [0035] IV. Recuperation control is easier, quieter
and more accurate by control via the DV than via inlet and outlet
valves and the pump of the ESP unit.
[0036] Pedal through fall I) can thus be avoided, since a leak in
the system has no effect on the pedal feeling, since the travel
simulator is decoupled. In contrast to the solution according to
the invention, a leak in the system has a direct effect on the
pedal feeling in variants A and B, for example, so that in the
worst case the pedal travel is suddenly extended and the change
cannot be controlled by the driver and leads to accidents.
[0037] The individual pressure regulation II) of axles is made
possible by the solution according to the invention because in the
event of failure of the ESP motor, the electric motor of the
pressure supply DV of the X-Boost takes over the pressure
regulation and the pressure regulation has no influence on the
pedal. This means that there are considerably more degrees of
freedom than with follow-up booster solutions (variants A and B).
For this purpose, the pressure control of the invention via the
piston travel and motor current in accordance with (DE 10 2005
018649 of the applicant) and pressure gradient regulation (DE 10
2005 055751 of the applicant), to which reference is made here in
this respect, is used for a high-precision pressure control which
cannot be achieved with pulse width modulation (PWM) control of
valves of the ESP unit.
[0038] The system decoupling (pedal of the system) is also of great
importance for the implementation of III) driver assistance
functions, as described in more detail below.
[0039] Recuperation control (IV) is becoming increasingly important
due to the increasing hybridization and spread of electric
vehicles. The brake pressure is varied depending on the possible
generator braking effect and the total braking effect required from
the driver. This is called brake pressure blending.
[0040] The recuperation control (IV) for one of the solutions
according to the invention is carried out exclusively via the
piston travel control of the pressure supply DV, e.g. in four-wheel
blending. Depending on the deceleration effect of the generator of
the vehicle or the drive motor of an electric vehicle operated in
generator mode, a corresponding braking pressure is set by
adjusting the piston so that the sum of the hydraulic braking force
and the braking effect by the drive motor results in the desired
total deceleration force.
[0041] This is possible in a completely variable manner, as the
pressure position of the pressure supply DV of the X-Boost has no
effect on the pedal feel. This has considerable advantages,
especially compared to the variants A and B of the prior art, where
the coupling between the pedal and the HZ volume means that the
storage chambers of the ESP unit have to be emptied in order to
achieve a reduced deceleration while maintaining the same pedal
feel. This requires an intervention in ESP and a very complex
control of the outlet valves of the ESP unit. In addition, with
some of the solutions according to the invention, different ESP
variants for different brake circuit distribution (diagonal and
parallel/brake circuits axle by axle, rear and front drives) can be
avoided, since control takes place exclusively via the piston,
independent of the brake circuit distribution and the drive type.
In particular, the following advantages of the X-Boost also result
from the recuperation. Some of the solution approaches according to
the invention offer the following advantages in the pedal feel
compared to the prior art: [0042] No change in pedal feel due to
blending [0043] No change in pedal feel due to changes in the brake
system (e.g. changes in brake release clearance, changes in PV
characteristic curve)
[0044] Blending offers the following advantages in summary: [0045]
Precise adjustment of brake pressures, even with rapid changes in
generator torque=>Simple point braking; [0046] No perceptible
noises, e.g. from switching valves in the ESP unit; [0047] Blending
in the entire vehicle deceleration range; [0048] Much simpler
software for blending than conventional e-boosters; [0049] Brake
force distribution can be displayed at will, up to the wheel lock
limit. ESP interventions for vehicle stabilization, especially on
slippery and uneven road surfaces, and interruptions of the
recuperation process with complex switching from recuperation to
purely hydraulic braking and vice versa, can thus be avoided;
[0050] Changes to the wheel brakes (e.g. pressure-volume
characteristics or p-V characteristics) on the non-driven axle have
no influence on the hydraulic braking; [0051] No additional
components required to hold hydraulic fluid (e.g. no "smart
actuator"); [0052] No harder return spring required for pedal
(important for P.sub.max in RFE); and/or [0053] Changes in the PV
characteristic curve of the brake system are diagnosed.
[0054] In known systems according to variant A with follow-up
booster, the pedal travel is a function of the volume take-up. To
prevent the pedal travel from becoming large during normal
operation, it is necessary to adjust the dimensions of the main
cylinder HZ for different vehicle types with different piston
diameters. In the event of a system failure in the fallback level
RFE, this leads to high pedal forces with the same pedal travel in
brake systems with greater volume absorption. In accordance with
the requirements of ECE-13H, a vehicle deceleration of at least
0.24-0.3 g is required for a maximum foot force of 500 N.
[0055] Some of the solutions according to the invention allow the
use of a small auxiliary piston diameter in comparison to the SK
piston and thus higher brake pressures in the fallback level RFE at
500 N foot force. In addition, the volume in the brake circuits can
be further increased with brake fading in that DV continues to
convey. This additional volume must be able to be transferred from
the SK piston into the floating circuit, either by a larger
diameter of the SK piston than the auxiliary piston or by a larger
travel of the SK piston.
[0056] The BKV is controlled in one embodiment in accordance with
DE 10 2005 018649 and DE 10 2005 055751 of the applicant, to which
reference is made here, via the piston of the pressure supply DV by
applying a pressure in the brake circuit via a BKV characteristic
curve as a function of the pedal travel. The pressure is measured
in the ESP unit and provided by the pressure supply DV via a
corresponding piston travel. If the pressure sensor fails, this
pressure signal is not available. The pressure sensor failure is
detected by the pressure supply DV via evaluation of the pressure
volume characteristic curve (p-V characteristic curve). Here the
corresponding pressure value is missing for the piston travel.
[0057] The current measurement of the DV motor can also be used
here as a replacement for the pressure measurement. In general, it
is also conceivable to use only current measurement. For the
corresponding accuracy for pressure build-up and reduction, the
hysteresis must be included in the characteristic curve of the
pressure supply DV (piston travel and pressure or current
alternatively) by the friction forces in the drive, optionally with
correction values, e.g. by correlation of the current with the
vehicle deceleration.
DESCRIPTION OF THE DRAWINGS
[0058] Further features and advantages of the invention result from
the following description of embodiment examples of the invention
and their design.
[0059] The drawings show as follows:
[0060] FIG. 1: Complete X-Boost system with ESP;
[0061] FIG. 1a: THZ main cylinder with pressure supply DV and
piston travel simulator KS;
[0062] FIG. 1b: An exemplary detail design of the first
piston-cylinder unit;
[0063] FIG. 2: Pedal characteristics;
[0064] FIG. 3: Main components of the system.
[0065] FIG. 1 shows a schematic diagram of the brake system with an
actuating device, in particular brake pedal 1, a first
piston-cylinder unit THZ, which can be actuated by means of the
actuating device, a second piston-cylinder unit with an
electromotive drive and a transmission (hereinafter also X-Boost or
booster) and an ABS/ESP unit. The ABS/ESP unit is known with the
main components pump P with motor M, valves HSV1 and HSV2, USV1 and
USV2, inlet and outlet valves EV and AV assigned to the wheel
brakes, and storage chamber (SpK). This system is described in many
publications and patent applications. It is already on the market
as an e-booster and is mainly used in electric and hybrid vehicles,
because here the brake system is controlled in conjunction with the
braking torque of the generator, i.e. recuperation. As is well
known, both the e-booster and the ESP elements can play a role
here, especially in the pedal characteristics. Another field of
application is vehicles with autonomous driving. The focus here is
on error safety and redundancy of the functions, such as pressure
supply and ABS function. The main difference in system design is
the new X-Boost concept. This consists of a special main cylinder
HZ with travel simulator WS and pressure supply DV, which is
arranged parallel or perpendicular to the main cylinder HZ in order
to achieve a short overall length, see also FIG. 3.
[0066] The main cylinder HZ essentially consists of an auxiliary
piston (HiKo) 16 and a floating piston (SK piston) 12 with return
spring 12a. The auxiliary piston 16 is connected to a plunger 16a,
which acts through a partition wall 14 with seal into the pressure
chamber 12d. A distance of approx. 50% of the travel of the
auxiliary piston (HiKo) 16 is between the end of the plunger and
the SK piston. The plunger 16a has a significantly smaller
cross-sectional area than the pistons of the first piston-cylinder
unit (>factor 5 smaller) and contributes insignificantly to
pressure build-up and pressure sensing in the brake circuit and
transmits this force to the brake pedal, thus generating a haptic
feedback to the brake pedal, especially during ABS operation and/or
fading.
[0067] Normally, a valve FV is closed at the start of braking and
the auxiliary piston HiKo acts on the travel simulator WS, whose
function and variants are described later. The auxiliary piston
HiKo has two functions: for normal operation and for a fallback
level in the event of a failure of the pressure supply DV. In the
first case, normal operation, it feeds the travel simulator WS with
the valve FV closed, and the pedal travel is the input signal for
the pressure supply DV. At the fallback level, when the pressure
supply DV fails, it also feeds the travel simulator WS when the
valve FV is closed, but the pedal travel is now the input signal
for the ESP booster.
[0068] When brake pedal 1 is actuated with pedal plunger 3,
redundant pedal travel sensors 2a/2b are activated simultaneously.
These can additionally be decoupled via an elastic member KWS, as
described in DE 11 2011 103274 of the applicant, to which reference
is made here in this respect. Advantages are on the one hand
detection when the auxiliary piston (HiKo) 16 is blocked, and on
the other hand the differential travel of the sensors when the
auxiliary piston (HiKo) 16 is blocked provides a control signal for
auxiliary braking. The elastic member can also be part of the
spring characteristic of the WS travel simulator. The auxiliary
piston (HiKo) 16 has a normal breather hole of a THZ piston which
is connected to the storage container VB. It is well known that a
brake circuit fails if the primary seal fails. This can be avoided
by using a check valve RV which is used for venting and a throttle
in the connection line to VB. The throttle is dimensioned with a
small flow rate so that the pedal characteristic is not
significantly changed (3 mm pedal travel in 10 s) if the seal fails
and can still be diagnosed. The same arrangement can also be used
for the floating piston (SK) 12 (not shown), which makes the
failure of both seals uncritical. Alternatively, a normally open
solenoid valve can also be used in the feedback line, which closes
after pedal actuation or diagnosis. This applies to both pistons of
the HZ (auxiliary piston HiKo and the second piston SK).
[0069] The travel simulator WS can be designed in different ways.
The illustrated design corresponds to the prior art, which is
described in various patent applications, consisting of a WS piston
with spring combinations, which as a function of the pedal travel
provide the pedal travel characteristics. The valve RV is used for
the fast pressure reduction P.sub.ab from the travel simulator WS,
if the pedal is released very fast, and the throttle D for the
desired throttled pressure build-up P.sub.auf with the
corresponding pedal characteristics. In addition, the travel
simulator WS can be switched off via the valve WA. This is
necessary for non-redundant systems in the fallback level (RFE) so
that the intake volume of the travel simulator WS does not affect
the delivery volume of the auxiliary piston HiKo to the brake
circuit BK1 and pressure chamber 12d. With this system (FIG. 1) the
ESP acts redundantly in case of failure of the X-Boost, where the
ESP pump sucks volume from the storage container via the main
cylinder THZ and the pressure supply DV. The valve WA can therefore
be dispensed with. Another version is described in FIG. 1a. The
auxiliary piston (HiKo) 16 with pedal plunger 16a is moved to the
initial position by the pedal return spring 18 after brake
actuation.
[0070] The pressure supply or DV is required for the BKV function.
This consists of an EC motor 8, which moves a piston 10 via a
spindle 7 and nut and delivers pressure medium into the brake
circuit BK1 and the pressure chamber 12d. The dimensioning of the
volume is derived from the BKV control, which controls a pressure
from pedal travel 2a/2b via the BKV characteristic curve, which is
measured by the pressure transducer DG in ESP. Alternatively, the
motor current, measured via a shunt, can be used instead of the
pressure. To improve the accuracy of the pressure control via the
current measurement, this requires the recording of the friction
losses in P.sub.auf and P.sub.ab in a characteristic map,
optionally additionally improved by correction factors, e.g. by
comparison with the vehicle deceleration. This is particularly
important if the spindle drive is not a ball screw drive KGT, but a
trapezoidal spindle with a plastic nut, for example.
[0071] In the starting position, the piston 10 has a breather hole
27 as in the main cylinder THZ. The volume can be sucked in via the
sleeves or via a suction valve (SV) 28, which requires a lower
vacuum to open and is temperature-independent.
[0072] If a trapezoidal spindle is used, the pistons remain in the
position in which the motor drive no longer acts due to the
self-locking of the pistons.
[0073] The dimensioning of the pressure supply DV can be staggered
so that the full travel of the DV piston corresponds to the volume
consumption of brake circuit BK2 or the travel of the SK piston 2.
The SK piston can be designed larger in diameter and also in travel
for larger volume intakes. The pressure supply DV, on the other
hand, can be designed accordingly or smaller in volume (piston and
travel) by making the missing volume possible by replenishing with
piston return travel via the SV suction valve. For this a normally
closed solenoid valve PD1 is required, which is not shown in FIG. 1
(see FIG. 1a). For full volume compensation in the event of
pressure reduction P.sub.ab, the piston must be moved to its
initial position with the breather hole open. The suction valve 28
and the breather hole 27 are connected to the return line to the
VB. All components of the pressure supply DV are combined in one
housing 25.
[0074] The pressure build-up P.sub.auf and pressure reduction
P.sub.ab in brake circuit BK1 and brake circuit BK2 is achieved via
the BKV control and pedal travel sensors, and the piston of the DV
moves accordingly. Normally, the X-Boost pumps volume into the
brake circuit BK up to the blocking limit 80-120 bar. At higher
pressures, the ESP pump is switched on and generates a pressure
build-up to approx. 200 bar with correspondingly lower output and
thus slower than the pressure build-up with the X-Boost. This is
permissible because the pressure build-up up to 200 bar is only
relevant for fading cases and does not have to take place as
quickly as the pressure build-up up to the blocking limit (e.g. for
the implementation of emergency brake functions). The ESP pump is
thus set to 200 bar, the X-Boost to 80-120 bar.
[0075] If the pressure supply DV fails during a braking process,
the DV piston is pushed back under pressure in brake circuit BK1 so
that the brake pressure can be completely reduced. If a
self-locking gear is used for the DV piston (trapezoidal spindle
with plastic nut), such a pressure reduction is not possible. In
this case, a normally closed solenoid valve AV is provided in brake
circuit BK1 with connection to the storage container (not shown) or
in connection from the breather hole of the Hiko to the storage
container VB.
[0076] In the event of failure of both electronic control or
regulating units (ECU) of X-Boost and ESP, which occurs very
seldom, volume is conveyed in the fallback level RFE by the
auxiliary piston (HiKo) 16 to the brake circuit BK1 and to the main
cylinder HZ on the rear side of the SK piston through the opened
valve FV and the brake pressure is increased, wherein the brake
pressure in the main cylinder HZ displaces the SK piston and the
pressure in brake circuit BK2 increases. To prevent this volume
from escaping through the opened breather hole of the DV, a
normally closed solenoid valve PD1 is provided (not shown in FIG.
1, see FIG. 1a).
[0077] Function in Case of Brake Circuit (BK) Failure
[0078] The failure of a brake circuit is detected by the pressure
supply DV by comparing the p-V characteristic curve of the brake
system, which is stored in a characteristic map at certain
intervals as part of a diagnostic cycle.
[0079] If, for example, the piston travel/volume is greater than
the standard value, there is correspondingly air in the brake
circuit BK or a leak. This can be identified via the p-V
characteristic curve. In the event of a leak, the leak can be
identified by closing the four valves EV one after the other,
provided this is located outside the units, e.g. in the wheel
cylinder. If this is the case, for example, in brake circuit BK1,
the valves EV of brake circuit BK1 are closed. The pressure supply
DV then acts via the SK piston into the brake circuit BK2
(corresponding description of the diagnostic logic in the patent
applications DE 10 2015 106 089.2 and 10 2016 112 971.2, to which
reference is made here in this respect). If this does not work, the
pressure supply DV fails, and so does the brake booster BKV. In
this case, the ESP pump acts as brake booster BKV in brake circuit
BK2.
[0080] Failure of brake circuit BK2 does not result in failure of
pressure supply DV, as the floating piston SK represents an
important safety gate with separation of brake circuits BK1 and
BK2.
[0081] In both cases, the pedal characteristics remain the same and
there is no pedal through fall.
[0082] ABS Function in the Event of Pump/Motor Failure in ESP.
[0083] When the ABS pressure reduction signal P.sub.ab occurs, the
DV control corrects the brake pressure to prevent the wheels from
locking. A corresponding pressure reduction P.sub.ab in both brake
circuits is necessary to prevent a wheel from one of the two brake
circuits from locking. However, this does not mean an optimal
braking effect. However, this can be improved.
[0084] For example, during wheel locking with corresponding
pressure reduction P.sub.ab in one brake circuit, the other brake
circuit cannot experience pressure reduction P.sub.ab by closing
the valve USVs. This can be optimized with individual wheel
regulation by modifying the valves EV without parallel check valve
RV as described in the patent application DE 11 2009 004636 (E112)
(to which reference is made here).
[0085] FIG. 1a shows the main cylinder (HZ) arrangement of FIG. 1
with changes in the travel simulator WS valve circuit. The travel
simulator WS has the normally closed WA valve as bypass valve.
According to FIG. 2, the piston-WS has the task, according to the
pedal characteristic, of taking up a volume with a corresponding
counterforce (pressure) on the auxiliary piston (Hiko) 16, which
causes costs and size. The pedal and WS characteristics are flat in
the lower pressure range. It makes sense to use the return spring
18 here, which accounts for approx. 40% of the volume of the WS,
and the WS piston becomes smaller accordingly. The valve WA is
opened at the start of braking. As a result, after a certain pedal
travel at the end of range A (see FIG. 2), the valve WA is closed
so that the more progressive part B+C is switched on.
[0086] The pressure supply DV here has an additional normally
closed solenoid valve PD1. This is necessary if the DV piston is
pushed back under pressure in the fallback level RFE and the
corresponding volume is lost in brake circuits BK1 and BK2.
Although this can be compensated by the large volume of the
auxiliary piston HiKo, this has a negative effect on the pedal
characteristics. When the DV piston returns to its initial
position, the breather hole opens and brake fluid drains into the
storage container. In the fallback level RFE, the valve PD1 is
closed. The valve PD1 can be opened again during ESP interventions
or ESP boost.
[0087] In area A (FIG. 2) it cannot be detected during braking
whether the valve WA has a leakage. For this reason, regular
diagnostics are provided, e.g. at the end of braking, when the
pressure supply DV pressurizes the space of the auxiliary piston
through the open valves PD1 and FV. The valve will not leak if the
pressure does not decrease when the DV piston is in a constant
position.
[0088] If the ECU of the X-Booster fails during braking, then the
ESP-Booster has to take over the function of the brake booster BKV.
For this purpose, the ESP must be able to draw volume from the VB
storage container and return it to the VB storage container at the
end of braking. In case of ECU failure, however, the valve PD1 is
closed, so that the connection between ESP and storage container VB
is interrupted by the breather hole of the pressure supply DV. With
redundant power supply of the ECU, this failure will occur very
rarely. If the ESP booster is nevertheless required, a normally
closed solenoid valve (not shown) can be provided between brake
circuit BK1 and storage container VB (valve AV, see description of
FIG. 1).
[0089] In one embodiment example, a seal D4 is arranged in the
cylinder of the floating piston SK 12.
[0090] FIG. 1b shows a further embodiment example of the cylinder,
in which a further seal D4r is provided for the floating piston SK
12 as redundancy to the seal D4. If this seal fails, the brake
circuit BK1 and the pressure supply DV will fail. In this case, the
ESP unit takes over the task of pressure supply, i.e. pressure
amplification. This can be avoided by the further seal D4r whose
connection to the storage container is provided with a throttle as
with the auxiliary piston (HiKo) 16. A failure of this seal does
not result in a failure of the brake circuit BK1 or the pressure
supply DV with the low leakage flow through the throttle. In
addition, a diagnosis is possible with this arrangement
advantageously.
[0091] FIG. 2 shows the pedal characteristics over the pedal travel
S.sub.p. In area A, the force increase with curve 1 is relatively
flat up to approx. 30 bar brake pressure, which corresponds to
approx. 85% of all braking operations. This process can also be
carried out via the pedal return spring. Then the more progressive
part B acts up to the blocking limit, followed by the range of
higher pressures, e.g. for fading. Here the driver should also feel
that there has been a change in the brake system.
[0092] Curve 1 corresponds to the X-Boost with travel simulator WS.
Without WS, i.e. with follow-up booster, curve 2 results where the
pedal travel depends on the venting state or fading. Accordingly,
there is a scattering (not shown) to 2a, which is even more extreme
in the event of brake circuit (BK) failure. With the conventional
e-booster the BKV is switched from e-booster to ESP booster at x.
This changes the pedal characteristics. Without influencing the BKV
control, at the same pressure and pedal force, the pedal with the
main cylinder (HZ) piston would deliver further volume to the ESP
pump until the pressure in the wheel cylinders has reached its
target values and the volume is returned to the main cylinder HZ by
overflowing the valves USVs.
[0093] A changed pedal characteristic with a larger pedal travel is
achieved by reducing the amplification factor of the X-Boost, which
results in the outlined scatter band. Additionally, the valves HSV1
and HSV2 can be modulated.
[0094] Here the X-Boost according to the invention with travel
simulator WS behaves like curve A with corresponding progressive
force increase as a function of the pedal travel.
[0095] Pedal Feedback at ABS
[0096] With the ABS function the pre-pressure supplied by the DV
changes constantly. This can be felt as a small force change on the
plunger 16a and thus on the connected pedal plunger 3, which is
demanded by many brake specialists. This can be changed at the
beginning of the ABS or intermittently during deceleration by
briefly increasing the inlet pressure.
[0097] If the reaction is more noticeable, the FV valve can open
and the control pressure of the DV acts directly on the auxiliary
piston HiKo.
[0098] Recuperation with Travel Simulator WS
[0099] The pedal characteristic is determined by the travel
simulator WS. Here, brake management with generator determines the
proportion of generator braking torque (electrical braking torque)
and braking pressure (hydraulic braking torque) for the required
vehicle deceleration. Both quantities can be changed at will during
deceleration. The calculation of the brake pressure during
recuperation is preferably based on wheel force. The required total
braking force (target braking force) on the wheels is determined
from the pedal travel. If the target braking force can be applied
electrically, then the hydraulic braking force is 0 N (braking
pressure in the wheel cylinders 0 bar). If the target braking force
exceeds the maximum possible electrical braking force, the
difference between the target braking force and the electrical
braking force is the hydraulic target braking force. The hydraulic
target braking force is realized by the pressure supply DV by
pressure generation in the wheel cylinders. For this purpose, the
individual Cp values of the wheel brakes are used to calculate the
target brake pressure, wherein the Cp value of a wheel brake
represents the ratio of brake force to brake pressure. The target
pressure is generated by a corresponding movement of the DV piston,
wherein the pressure sensor of the ESP is used for the feedback of
the piston movement. In this way, the pressure supply DV can set
the target pressure both during pressure build-up and during
pressure reduction. Due to the precise position control of the DV
piston, the pressure setting is very accurate. The pressure control
with the DV is also very quiet because no valves for P.sub.auf and
P.sub.ab have to be actuated. Noise-causing valve and pump
actuations of the ESP unit are not required. Furthermore, this
recuperation control can be used uniformly for front, rear and
all-wheel drive vehicles and X and II brake circuit splitting. The
pedal characteristic remains unchanged.
[0100] Driver Assistance Functions
[0101] There are many driver assistance functions that require
automatic brake intervention, such as: [0102] ACC (Adaptive Cruise
Control) in which the desired vehicle deceleration is set by active
braking intervention. [0103] AWB (Automatic Warning Brake) where a
braking impulse should wake the driver who has fallen asleep.
[0104] BDW (Brake Disc Wiping) where a very low brake pressure in
the wheel cylinders should wipe the water film off the brake discs
during rain so that the maximum braking effect is achieved
immediately during subsequent braking.
[0105] With these assistance functions, the pressure supply DV can
generate the necessary brake pressure in the wheel cylinders. The
target brake pressure is specified by the various driver assistance
systems. With the ACC the target brake pressure is variable and
depends on the required vehicle deceleration, whereas with the BDW
the target pressure has a small value (e.g. 1-3 bar). As with
recuperation, the brake pressure is generated by a corresponding
movement of the DV piston, wherein the pressure sensor of the ESP
is also used here for the feedback of the piston movement. As with
recuperation, the brake pressure setting is very accurate thanks to
precise position control of the DV piston. The pressure control
with the pressure supply DV is also very quiet in the driver
assistance systems.
[0106] The figure description in FIG. 2, in particular, shows the
decisive advantages of the invention in addition to the overall
length.
[0107] FIG. 3 shows the main components of the X-Boost in a spatial
representation: [0108] Pedal plunger 3 [0109] Mounting flange BF on
the front wall [0110] First piston-cylinder unit or main cylinder
HZ with pedal interface [0111] Motor 8 with housing pressure supply
I (DV) 25, arranged advantageously parallel to the main cylinder
(can also be aligned perpendicular to the axle of the HZ) [0112]
Hydraulic control and regulating unit HCU [0113] Electronic control
and regulating unit ECU [0114] Storage container VB [0115] The plug
connector ST is located below the storage container VB and above HZ
and HCU and faces inwards towards the center of the unit to allow
the associated connector to be pulled out sideways.
[0116] It follows from the above description that further
modifications of the brake system according to the invention are
possible by means of measures described in detail, which also
belong to the claimed scope of the invention.
LIST OF REFERENCE NUMERALS
[0117] 1 Brake pedal
[0118] 2a Master pedal travel sensors
[0119] 2b Slave pedal travel sensors
[0120] 3 Pedal plunger
[0121] 7 Spindle (KGT), trapezoidal spindle
[0122] 8 EC motor
[0123] 10 Piston (DV)
[0124] 11 Pressure chamber or working chamber of the DV
[0125] 12 SK piston
[0126] 12a Return spring SK piston
[0127] 12d Pressure chamber or working chamber on floating piston
SK (rear)
[0128] 14 Partition wall
[0129] 16 Auxiliary piston
[0130] 16a Tappet
[0131] 18 Pedal return spring
[0132] 25 DV housing
[0133] 27 Breather hole
[0134] 28 Suction valve
[0135] 28a Return spring
[0136] 28c Valve disc
[0137] 28b T-plunger of the valve disc
[0138] 30 Armature
[0139] 31 Coil
[0140] 32 Solenoid
[0141] BF Mounting flange for end wall
[0142] D Orifice for throttling
[0143] RV Check valve at the breather hole of the auxiliary
piston
[0144] R Return to storage container VB
[0145] KWS Force-displacement sensor
[0146] WA (Normally closed) solenoid valve
[0147] TTL Time to lock
[0148] BK Brake circuit
[0149] DG Pressure transducer
[0150] VF (Normally open) solenoid valve
[0151] VB Storage container
[0152] AV Outlet valve ABS
[0153] EV Inlet valve ABS
[0154] R Return line to storage container VB
[0155] ST Plug connector
[0156] WS Travel simulator
[0157] HZ Main cylinder
[0158] PD1 Normally closed solenoid valve to DV working chamber
* * * * *