U.S. patent application number 09/905919 was filed with the patent office on 2002-02-21 for wheel brake apparatus and method for operating it.
This patent application is currently assigned to Robert Bosch GmbH. Invention is credited to Blattert, Dieter, Schanzenbach, Matthias.
Application Number | 20020020591 09/905919 |
Document ID | / |
Family ID | 7649532 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020591 |
Kind Code |
A1 |
Schanzenbach, Matthias ; et
al. |
February 21, 2002 |
Wheel brake apparatus and method for operating it
Abstract
The invention relates to a wheel brake apparatus having an
electric motor, a rotation/translation conversion mechanism that
can be driven to rotate by the electric motor, a hydraulic working
piston that can be moved by the rotation/translation conversion
mechanism, and a brake lining piston that can be hydraulically
moved by the working piston. In order to permit an emergency
actuation of the wheel brake apparatus in the event of a leak in
the hydraulics, the invention proposes embodying the wheel brake
apparatus so that the brake lining piston can also be mechanically
moved by the working piston. This can be achieved by virtue of the
fact that the two pistons are disposed coaxially.
Inventors: |
Schanzenbach, Matthias;
(Eberstadt, DE) ; Blattert, Dieter;
(Kirchheim/neckar, DE) |
Correspondence
Address: |
RONALD E. GREIGG
GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Assignee: |
Robert Bosch GmbH
|
Family ID: |
7649532 |
Appl. No.: |
09/905919 |
Filed: |
July 17, 2001 |
Current U.S.
Class: |
188/158 |
Current CPC
Class: |
B60T 13/745 20130101;
F16D 2125/10 20130101; F16D 2066/005 20130101; F16D 2125/40
20130101; Y10S 303/03 20130101; F16D 2066/003 20130101; F16D 65/18
20130101; F16D 2127/06 20130101; F16D 2125/48 20130101 |
Class at
Publication: |
188/158 |
International
Class: |
B60L 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2000 |
DE |
1 00 35 220.0 |
Claims
We claim:
1. In a wheel brake apparatus that has an electric motor, a
rotation/translation conversion mechanism that can be driven to
rotate by the electric motor, a working piston that is movably
contained in a working cylinder and can be moved by the
rotation/translation conversion mechanism, and a brake lining
piston that is movably contained in a cylinder, wherein the working
cylinder and the cylinder of the brake lining piston are
operationally connected, the improvement wherein the
rotation/translation conversion mechanism (28) are operable to
provide a mechanical connection with the brake lining piston (12)
and as a result to thereby move the brake lining piston (12).
2. The wheel brake apparatus according to claim 1, wherein a
movable driven element (26) of the rotation/translation conversion
mechanism (28) can be moved into contact with the brake lining
piston (12).
3. The wheel brake apparatus according to claim 1, wherein the
working piston (16) can be moved into contact with the brake lining
piston (12).
4. The wheel brake apparatus according to claim 1, wherein a valve
(22) is connected to the working cylinder (18) and/or to the
cylinder (14) of the brake lining piston (12).
5. The wheel brake apparatus according to claim 4, wherein the
valve (22) is open in a normal position.
6. The wheel brake apparatus according to claim 1, wherein the
wheel brake apparatus (10) further comprises a pressure sensor (24)
connected to the working cylinder (18) and the cylinder (14) of the
brake lining piston (12).
7. The wheel brake apparatus according to claim 1, wherein the
wheel brake apparatus (10) has a rotation angle sensor which can
measure a rotation angle of a rotor of the electric motor (48) or
of the rotation/translation conversion mechanism (28).
8. The wheel brake apparatus according to claim 1, wherein the
wheel brake apparatus (10) has a path sensor which can measure a
displacement path of the driven element (26) of the
rotation/translation conversion mechanism (28).
9. The wheel brake apparatus according to claim 1, wherein the
rotation/translation conversion mechanism (28) is self
locking-free.
10. The wheel brake apparatus according to claim 9, wherein the
wheel brake apparatus (10) further comprises a brake (50) which can
lock in place a rotor of the electric motor (48) or of the
rotation/translation conversion mechanism (28).
11. The wheel brake apparatus according to claim 10, wherein the
brake (50) has a stable brake position.
12. The wheel brake apparatus according to claim 10, wherein the
brake (50) is a magnetic brake.
13. A method for operating a wheel brake apparatus of the type
having an electric motor, a rotation/translation conversion
mechanism that can be driven to rotate by the electric motor, a
working piston that is movably contained in a working cylinder and
can be moved by the rotation/translation conversion mechanism, and
a brake lining piston that is movably contained in a cylinder,
wherein the working cylinder and the cylinder of the brake lining
piston are operationally connected, the method comprising measuring
a hydraulic pressure in the working cylinder (18) and/or in the
cylinder (14) of the brake lining piston (12) and measuring a
displacement path of a movable driven element (26) of the
rotation/translation conversion mechanism (28), and comparing the
two measurement values to reference values associated with a
properly functioning wheel brake apparatus (10).
14. The method according to claim 13,wherein when the wheel brake
apparatus (10) is actuated, the hydraulic pressure in the working
cylinder (18) and/or in the cylinder (14) of the brake lining
piston (12) is measured and compared to a reference value.
15. The method according to claim 13, further comprising connecting
a valve (22) to the working cylinder (18) and/or the cylinder (14)
of the brake lining piston (12) and, when the wheel brake apparatus
(10) is not actuated, closing the valve (22) and monitoring the
hydraulic pressure in the working cylinder (18) and/or in the
cylinder (14) of the brake lining piston (12) for a pressure
increase.
16. The method according to claim 13, wherein when the wheel brake
apparatus (10) is actuated, the chronological progression of the
hydraulic pressure in the working cylinder (18) and/or in the
cylinder (14) of the brake lining piston (12) is monitored and a
displacement path of the driven element (26) of the
rotation/translation conversion mechanism (28) is measured up to a
break point in the pressure progression at the transition from a
virtually constant, low hydraulic pressure to a mounting hydraulic
pressure.
17. The method according to claim 13, wherein when the brake (50)
is released and the valve (22) is open, the electric motor (48) is
driven to rotate in a brake-applying direction, that the
chronological progression of the hydraulic pressure is measured,
and that the displacement path of the driven element (26) of the
rotation/translation conversion mechanism (28) is measured up to
the transition of the hydraulic pressure from an overpressure to a
negative pressure.
18. The method according to claim 13, wherein in order to actuate
the wheel brake apparatus (10), the brake (50) is released, the
valve (22) is closed, and the electric motor (48) is supplied with
current in a brake-applying direction.
19. The method according to claim 13, wherein in order to release
the wheel brake apparatus (10), the brake (50) is released and when
the valve (22) is closed, the electric motor (48) is supplied with
current in a reverse rotation direction.
20. The method according to claim 13, wherein, for an emergency
actuation of the wheel brake apparatus (10), the brake (50) is
released and when the valve (22) is open, the electric motor (48)
is supplied with current in a brake-applying direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a wheel brake apparatus and a
method for operating the wheel brake apparatus including an
electric motor and a rotation/translation conversion mechanism.
[0003] 2. Description of the Prior Art
[0004] A wheel brake apparatus of the type with which this
invention is concerned is disclosed by DE 195 29 664 A1. The known
wheel brake apparatus has an electric motor which can drive a
rotation/translation conversion mechanism. The rotation/translation
conversion mechanism of the known wheel brake apparatus is embodied
as a helical gear. The rotation/translation conversion mechanism
can move a hydraulically acting working piston in a working
cylinder. The working cylinder communicates with a cylinder in
which a brake lining piston is movably contained. The movement of
the working piston in the working cylinder moves the brake lining
piston in its cylinder and because the cylinder diameters are
different, a hydraulic path reduction and force increase can be
produced. The brake lining piston can press a frictional brake
lining against a brake body non-rotatably connected to a vehicle
wheel, for example a brake disk or brake drum, in order to produce
a brake force or a brake moment. The known wheel brake apparatus
combines an electromechanical drive mechanism with a hydraulic
drive mechanism.
OBJECT AND SUMMARY OF THE INVENTION
[0005] In the wheel brake apparatus according to the invention, the
rotation/translation conversion mechanism can be brought into a
mechanical connection with the brake lining piston and as a result,
the brake lining piston can be moved. This has the advantage that a
parking brake function of the wheel brake apparatus can be produced
which is independent of the hydraulics. A brake force built up in
the parking brake function remains unchanged for a long time since
the brake force is built up in an exclusively mechanical fashion
and as a result, leakage losses in the hydraulics are prevented
from reducing the brake force. Another advantage of the wheel brake
apparatus according to the invention is its ability to be actuated
in an exclusively mechanical fashion, for example in the event of a
leak in the hydraulics of the wheel brake apparatus. This permits a
mechanical emergency braking operation in the event of a
malfunction in the hydraulics. In comparison to an exclusively
electromechanical wheel brake apparatus, the wheel brake apparatus
according to the invention has the advantage that it can easily be
embodied with two or more brake lining pistons and can thus be
inexpensively designed, for example in the form of a fixed yoke
brake device.
[0006] According to one embodiment, a movable element of the
rotation/translation conversion mechanism can be moved into contact
with the brake lining piston and in this manner, the brake lining
piston can be mechanically moved in order to press the frictional
brake lining against the brake body. The movable element can be a
spindle of a rotation/translation conversion mechanism embodied as
a helical gear.
[0007] Another possibility for mechanically moving the brake lining
piston is to provide the working piston so that it can be moved
into contact with the brake lining piston.
[0008] In a preferred embodiment of the invention, the wheel brake
apparatus has a valve that can be opened and closed, which is
connected to the working cylinder and to the cylinder of the brake
lining piston. When the valve is open, a hydraulic operational
connection between the working piston and the brake lining piston
is disengaged and the brake lining piston can be moved mechanically
with the rotation/translation conversion mechanism. Moreover,
opening the valve makes possible for the wheel brake apparatus to
be released in the event of a malfunction in its electromechanical
drive mechanism. The valve is preferably open in a normal
position.
[0009] According to one modification, the wheel brake apparatus of
the invention has a pressure sensor for measuring the hydraulic
pressure. The pressure sensor can be used, for example, to
determine a brake force of the wheel brake apparatus since the
brake force is at least approximately proportional to the hydraulic
pressure.
[0010] According to a further embodiment, the wheel brake apparatus
according to the invention has a rotation angle sensor for the
rotor of the electric motor or the rotation/translation conversion
mechanism. The rotation angle sensor can measure a rotation angle
of the rotor of the electric motor or of a rotating part of the
rotation/translation conversion mechanism, in complete rotations
and/or in fractions of a rotation. Since the rotation angle is
proportional to a displacement path of the rotation/translation
conversion mechanism, a displacement path of the
rotation/translation conversion mechanism can therefore be
determined.
[0011] The correlation of the rotation angle measured with the
rotation angle sensor and the hydraulic pressure measured with the
pressure sensor permits the proper functioning of the wheel brake
apparatus to be monitored. When the wheel brake apparatus is
functioning properly, these two values maintain a particular
proportion to each other in every operating state of the wheel
brake apparatus. During operation of the wheel brake apparatus
according to the invention, if the proportion of the two values to
each other diverges significantly from their proportion during
proper operation wheel brake apparatus, then this indicates a
malfunction.
[0012] Instead of the rotation angle sensor, the wheel brake
apparatus can also have a path sensor for the displacement path of
the rotation/translation conversion mechanism.
[0013] According to another modification, the rotation/translation
conversion mechanism of the wheel brake apparatus according to the
invention is embodied as self locking-free so that when the
electric motor is without current, a pressing force of the
frictional brake lining against the brake body decreases to a
negligible value. As a result, it is possible for the wheel brake
apparatus to be released in the event of a failure of the power
supply of the electric motor.
[0014] For the parking brake function, in order to maintain a brake
force without current once the brake force has been exerted, a
brake is provided with which the rotor of the electric motor or the
rotation/translation conversion mechanism can be locked in
place.
BRIEF DESCRIPTION OF THE DRAWING
[0015] The invention will be better understood and further objects
and advantages thereof will become more apparent from the ensuing
detailed description of preferred embodiments taken in conjunction
with the drawing, which shows a partially simplified schematic
representation of an axial section through a wheel brake apparatus
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The wheel brake apparatus 10 according to the invention
shown in the drawing has a brake lining piston 12, which is movably
contained in a cylinder 14. The brake lining piston 12 can press a
frictional brake lining, which is not shown and is in contact with
the brake lining piston 12, against a brake body, likewise not
shown, for example a brake disk, in order to produce a brake moment
or a brake force in an intrinsically known manner.
[0017] In order to move the brake lining piston 12, the wheel brake
apparatus 10 has a working piston 16, which is movably contained in
a working cylinder 18. The working piston 16 is disposed coaxial to
the brake lining piston 12; it has a smaller diameter than the
brake lining piston 12. The working cylinder 18 and the cylinder 14
of the brake lining piston 12 are hydraulic cylinders which are
operationally connected to each other. In the exemplary embodiment
shown, the working cylinder 18 and the cylinder 14 of the brake
lining piston 12 are of one piece with each other; the working
cylinder 18 coaxially adjoins the cylinder 14 of the brake lining
piston 12. The working cylinder 18 is connected to a brake fluid
storage tank 20 which is operationally connected to the working
cylinder 18 and therefore also the cylinder 14 of the brake lining
piston 12 by means of a solenoid valve 22. The solenoid valve is
embodied as a 2/2-way solenoid valve that is open in its
currentless normal position. In addition, a pressure sensor 24 is
connected to the working cylinder 18 and can measure a hydraulic
pressure in the working cylinder 18 and the cylinder 14 of the
brake lining piston 12.
[0018] The working piston 16 is a one-piece component of a spindle
26 of a helical gear 28. The helical gear 28 constitutes a
rotation/translation conversion mechanism, or screw link actuator.
Instead of the helical gear 28, another kind of
rotation/translation conversion mechanism can also be used, for
example a recirculating ball transmission or a planetary roller
screw drive (not shown). For rotational securing, the spindle 26
has a slide key or spring 30, which rests in an axially parallel
groove 32 of the spindle 26 and in an axially parallel groove 34 in
a housing 36 of the wheel brake apparatus 10.
[0019] In order to axially move the spindle 26 together with a
working piston 16 that is of one piece with it, the helical gear 28
has a nut 38 which engages with the spindle 26. The nut 38 is
rotatably supported in the housing 36 by an angular roller bearing
40 and is supported axially against the housing 36 by this angular
roller bearing 40. The screw link actuator 28 is self locking-free,
i.e. axial pressure in the spindle 26 can set the nut 38 into
rotation and move the spindle 26 axially.
[0020] The nut 38 of the helical gear 28 is of one piece with a
gear 42, which meshes with a smaller diameter gear 44. The two
gears 42, 44 constitute a toothed wheel-work. The smaller gear 44
is non-rotatably connected to a motor shaft 46 of an electric motor
48. The electric motor 48 has an integrated rotation angle sensor,
not visible in the drawing, for its motor shaft 46. A magnetically
actuatable brake is flange-mounted to the electric motor 48 and
will be referred to below as a magnetic brake 50. The magnetic
brake 50 has a stable brake position in which it fixes the motor
shaft 46 in place. In order to release the magnetic brake 50, it is
supplied with current. The magnetic brake 50 can be designed as
bistable, i.e. it remains without current both in the braked
position and in a released position and is supplied with current
only for switching between the braked position and the released
position and vice versa. Magnetic brakes of this kind are
intrinsically known to the specialist in a number of embodiments,
both in a monostable and bistable design, and therefore the
construction of the magnetic brake 50 requires no further
discussion at this point.
[0021] The toothed wheel-work 42, 44 is a mechanical reduction
gear; a moment transmission from the electric motor 48 to the nut
38 of the helical gear 28 occurs here. Because of the smaller
diameter of the working piston 16, a hydraulic reduction of the
displacement path and an increase of the force of the working
piston 16 against the brake lining piston 12 also take place.
[0022] Function of the Wheel Brake Apparatus
[0023] In order to actuate the wheel brake apparatus 10, the
magnetic brake 50 is released, the solenoid valve 22 is closed, and
the electric motor 48 is supplied with current in a brake-applying
direction. The toothed wheel-work 42, 44 sets the nut 38 of the
helical gear 28 into rotation and moves the spindle 26, together
with the working piston 16 that is of one piece with it, toward the
brake lining piston 12. The working piston 16 displaces brake fluid
from the working cylinder 18 into the cylinder 14 of the brake
lining piston 12 and therefore moves the brake lining piston 12.
This produces a force transmission from the working piston 16 to
the brake lining piston 12 in the proportion of their two
diameters. In an intrinsically known manner, the brake lining
piston 12 presses the frictional brake lining, not shown, against
the brake body, not shown, and therefore exerts a brake moment or a
brake force on the brake body.
[0024] In order to reduce the brake force and to restore the wheel
brake apparatus 10, the electric motor 48 is supplied with current
in a reverse rotation direction, as a result of which the toothed
wheel-work 42, 44 and the helical gear 28 move the working piston
16 and therefore also the brake lining piston 12 back. The
hydraulic pressure in the working cylinder 18 and in the cylinder
14 of the brake lining piston 12 is measured by the pressure sensor
24. Since the hydraulic pressure is proportional to a force with
which the brake lining piston 12 presses the frictional brake
lining against the brake body, the pressing force of the frictional
brake lining against the brake body and therefore the brake force
of the wheel brake apparatus 10 can be determined from the
hydraulic pressure measured by the pressure sensor and can be
regulated in relation to a reference value.
[0025] Parking Brake Function, Emergency Brake Function
[0026] In order to be used as a parking brake, when the magnetic
brake 50 is released, the electric motor 48 is supplied with
current and the working piston 16 is moved in the above-described
manner until it strikes against the brake lining piston 12. The
solenoid valve 22 thus remains open so that brake fluid displaced
by the working piston 16 flows out into the brake fluid storage
tank 20. With the working piston 16 resting against the brake
lining piston 12, the brake lining piston 12 is moved further until
the frictional brake lining, not shown, rests against the brake
body. Through a continued supply of current to the electric motor
48, the working piston 16 resting against the brake lining piston
12 presses the frictional brake lining against the brake body and
thus produces a brake force. The magnetic brake 50 is brought into
its braking position and locks the motor shaft 46 in place. The
supply of current to the electric motor 48 can be stopped; the
magnetic brake 50 uses the toothed wheel-work 42, 44 to keep the
nut 38 of the helical gear 28 from rotating and therefore also
locks the spindle 26 and the working piston 16 in place. The brake
force exerted due to the supply of current to the electric motor 48
is retained when the electric motor 48 is without current. The
brake force is exerted and maintained mechanically through the
contact of the working piston 16 against the brake lining piston
12, without the hydraulic action of the brake fluid, so that once
applied, the brake force is not reduced by possible leakage
losses.
[0027] An emergency brake function is possible in the same way as
the parking brake function. If the hydraulic transmission of the
movement of the working piston 16 to the brake lining piston 12
fails, for example due to the lack of brake fluid or due to
leakage, the working piston 16 can be moved into contact with the
brake lining piston 12 and the brake lining piston 12 can be
mechanically displaced by means of the working piston 16 resting
against it.
[0028] Function Monitoring
[0029] The hydraulic pressure measured with the pressure sensor 24
and the rotation angle of the motor shaft 46 measured by the
integrated rotation angle sensor of the electric motor 48 retain a
particular relationship to each other in every operating state of
the wheel brake apparatus 10. The term rotation angle is understood
to mean a number of complete rotations and/or a fraction of a
rotation. For example, when the solenoid valve 22 is closed, if the
electric motor 48 is supplied with current in order to build up a
brake force and therefore its motor shaft 46 is set into rotation,
then the working piston 16 and the brake lining piston 12 are thus
displaced. Only a slight amount of hydraulic pressure builds up
before the frictional brake lining comes into contact with the
brake body. As soon as the frictional brake lining comes into
contact with the brake body, the hydraulic pressure increases with
further rotation of the motor shaft 46. This dependence of the
hydraulic pressure on the rotation angle of the motor shaft 46 is
used to monitor the function of the wheel brake apparatus 10. To
that end, the actually prevailing hydraulic pressure and the
rotation angle of the motor shaft 46 are measured and compared to
reference values associated with a properly functioning wheel brake
apparatus 10. If the measured values diverge from the reference
values by more than a fixed, permissible tolerance, this indicates
a malfunction of the wheel brake apparatus 10. This function
monitoring can also take place when a motor vehicle equipped with
the wheel brake apparatus 10 according to the invention is not
running. The function monitoring of the wheel brake apparatus 10
can, for example, be automatically executed when the engine of the
vehicle is started, before driving begins.
[0030] A heating of the brake fluid during braking can be
determined in the following way: if the brake fluid in the working
cylinder 18 and in the cylinder 14 of the brake lining piston 12
heats up due to frictional heat during a braking maneuver, then the
brake fluid expands. The hydraulic pressure is higher than the
known hydraulic pressure which would prevail at the same rotation
angle of the motor shaft 46 with cold brake fluid. The increased
hydraulic pressure permits the temperature increase to be detected
or also calculated. As a result, a warning can be given well before
a critical temperature of the hydraulic fluid is reached.
[0031] Even when driving while not using the brakes, the brake
fluid can be checked for heating. This can be the case when there
is insufficient air play or an absence thereof, i.e. when the
frictional brake lining continuously rests against the brake body
due to a mechanical malfunction. In order to test for such a
temperature increase of the brake fluid when the wheel brake
apparatus 10 is not being actuated, the solenoid valve 22 is closed
and the hydraulic pressure is measured by the pressure sensor 24.
If the brake fluid heats up, then the brake fluid expands and the
hydraulic pressure increases.
[0032] Determination of the Air Play
[0033] The air play determination takes place during the
above-described actuation of the wheel brake apparatus 10 through
the monitoring of the hydraulic pressure by means of the pressure
sensor 24. Until the frictional brake lining contacts the brake
body, an increase in the hydraulic pressure is slight and the
hydraulic pressure remains virtually constant. As soon as the
frictional brake lining rests against the brake body, the hydraulic
pressure increases. The number of rotations of the motor shaft 46
can be used to determine the displacement path of the brake lining
piston 12 and therefore the air play up until the pressure
increase, i.e. until the frictional brake lining comes into contact
with the brake body. If the air play is too great, for example due
to a wear on the brake lining, then it is adjusted by virtue of the
fact that the motor shaft 46 is turned back less during the release
of the wheel brake apparatus 10 than it was turned in the
brake-applying direction when the wheel brake apparatus 10 was
applied.
[0034] The distance of the working piston 16 from the brake lining
piston 12 can be determined in the following manner: by supplying
current to the electric motor 48 while the solenoid valve 22 is
open, the working piston 16 is moved toward the brake lining piston
12. The working piston 16 thus displaces brake fluid from the
working cylinder 18, as a result of which the hydraulic pressure
increases slightly. As soon as the working piston 16 strikes
against the brake lining piston 12 and moves it, the larger
diameter brake lining piston 12 aspirates brake fluid into the
working cylinder 18 and the cylinder 14 of the brake lining piston
12, the hydraulic pressure drops to a negative pressure. The number
of rotations of the motor shaft 46 until the drop in the hydraulic
pressure when the working piston 16 strikes against the brake
lining piston 12 can be used to determine the displacement path
that the working piston 16 has traveled and thereby the starting
distance between the working piston 16 and the brake lining piston
12 and can be adjusted when the working piston 16 is reset.
[0035] Releasing in the Event of a Malfunction
[0036] In the event of a malfunction, the wheel brake apparatus 10
can be released in two ways. On the one hand, when the wheel brake
apparatus 10 is being actuated, the solenoid valve 22 can be opened
and as a result, the wheel brake apparatus 10 can be released even
in the event of a jammed helical gear 28, for example. If the
working piston 16 is resting against the brake lining piston 12,
then the second possibility for releasing the wheel brake apparatus
10 lies in releasing the magnetic brake 50. When the wheel brake
apparatus 10 is being actuated and the magnetic brake 50 is
released, the brake lining piston 12 moves the working piston 16
and the spindle 26 of the self locking-free screw link actuator 28
back until the brake force exerted by the frictional brake lining
on the brake body has decreased to a residual brake force.
[0037] The foregoing relates to a preferred exemplary embodiment of
the invention, it being understood that other variants and
embodiments thereof are possible within the spirit and scope of the
invention, the latter being defined by the appended claims.
* * * * *