U.S. patent application number 09/873102 was filed with the patent office on 2002-10-31 for parking brake for drum type brakes with electronic lining wear sensor and adjuster.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Riddiford, Bryan Peter, Shaw, Schuyler Scott.
Application Number | 20020157907 09/873102 |
Document ID | / |
Family ID | 25360973 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157907 |
Kind Code |
A1 |
Shaw, Schuyler Scott ; et
al. |
October 31, 2002 |
PARKING BRAKE FOR DRUM TYPE BRAKES WITH ELECTRONIC LINING WEAR
SENSOR AND ADJUSTER
Abstract
A parking brake assembly for an automotive drum brake is
provided. The parking brake assembly replaces a conventional
mechanical strut with an electronic strut actuator subassembly that
provides for parking brake engagement and disengagement, sensing of
brake lining wear and adjustment of brake shoe-to-drum
clearance.
Inventors: |
Shaw, Schuyler Scott;
(Dayton, OH) ; Riddiford, Bryan Peter; (Dayton,
OH) |
Correspondence
Address: |
ROBERT M. SIGLER
DELPHI TECHNOLOGIES, INC.
Legal Staff
P.O. Box 5052, Mail Code: 480-414-420
Troy
MI
48007-5052
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
TROY
MI
48007-5052
|
Family ID: |
25360973 |
Appl. No.: |
09/873102 |
Filed: |
April 26, 2001 |
Current U.S.
Class: |
188/79.51 ;
188/1.11R |
Current CPC
Class: |
F16D 2066/003 20130101;
F16D 65/563 20130101; F16D 2065/386 20130101; F16D 2066/006
20130101 |
Class at
Publication: |
188/79.51 ;
188/1.11R |
International
Class: |
F16D 051/00 |
Claims
1. An electrically actuated strut actuator subassembly for an
electro-hydraulically applied parking brake in an automotive drum
brake for use in engaging or disengaging a parking brake, sensing
brake lining wear and adjusting brake shoe-to-drum clearance that
has a backing plate, brake shoes that are supported on said backing
plate, a brake drum disposed about said brake shoes, a hydraulic
wheel cylinder mounted to said backing plate, return springs
connecting said brake shoes at upper portions and lower portions
and a strut actuator subassembly located parallel to said wheel
cylinder and mounted between webs in slots that interconnects said
upper portions between ends, wherein said strut actuator
subassembly comprises, a strut tube having female threads and
tapering to a fork at another end, a power screw having male
threads and a rod portion at one end, a connector fork having a
female portion at one end suitable for receiving said rod portion
of said power screw and a fork at another end, a low power electric
motor having a driveshaft at one end, and a position encoder, that
are all in a common axial relationship with one another and wherein
said strut tube and said power screw are connected by said female
and male threads and said rod portion of said power screw is
connected to said connector fork at said female portion to define
the transverse structure of said strut actuator subassembly, and
further wherein said electric motor and said position encoder are
connected to one another and located within the interior of said
strut tube and said electric motor is further connected to said
power screw by said driveshaft, so that upon actuation of said
electric motor, said driveshaft turns said power screw that
advances said connector fork in one direction and said strut tube
in an opposing direction along the axis of connection to engage or
disengage said brake shoes with said brake drum for activating or
deactivating said parking brake, sensing brake lining wear, or
adjusting brake shoe-to-drum clearance.
2. The strut actuator subassembly of claim 1 wherein said position
encoder comprises a controller for adjusting said brake
shoe-to-drum clearance.
3. The strut actuator subassembly of claim 2 wherein said position
encoder further comprises means to determine a worn lining
condition.
4. The strut actuator subassembly of claim 1 wherein upon parking
brake activation, said electric motor turns said driveshaft and
said power screw advancing said connector fork and said strut tube
in opposing directions along said axis outwardly to engage said
brake shoes with said brake drum.
5. The strut actuator subassembly of claim 1 wherein upon parking
brake deactivation, said electric motor turns said driveshaft
retracting said power screw and said strut tube in opposing
directions along said axis inwardly to disengage said brake shoes
from said brake drum.
6. The strut actuator subassembly of claim 1 wherein said electric
motor periodically turns said driveshaft and said power screw and
moves said connector fork and said strut tube in opposing
directions along said axis to touch and retract said brake shoes
with said brake drum for sensing of said brake lining wear.
7. The strut actuator subassembly of claim 6 wherein said brake
shoes are retracted from said brake drum to a predetermined
distance to adjust said brake shoe-to-drum clearance.
Description
TECHNICAL FIELD
[0001] This invention relates to a leading/trailing type drum brake
assembly in which the parking brake lever, adjuster strut and
associated components are replaced with a single electronic
subassembly that controls the parking brake, senses brake lining
wear and adjusts the brake shoe-to-drum clearance to account for
lining wear. The parking brake assembly includes a strut actuator
subassembly that comprises a strut tube, an electric motor, a
position encoder, a power screw and a connector fork.
BACKGROUND OF THE INVENTION
[0002] Vehicle brakes are used to slow the vehicle and also to
maintain the vehicle in a parked position. Drum brakes are a common
type of vehicle brake. Drum brake assemblies utilize opposing
arcuate brake shoes that are movable away from one another into
engagement with an inner surface of a drum to slow the vehicle.
Typically, a hydraulic wheel cylinder forces the brake shoes into
engagement with the drum. The same brake shoes may also be used to
maintain the vehicle in a parked position. For example, drum brake
assemblies have employed a separate mechanical linkage, or parking
brake lever, that is actuated by a cable to maintain the brake
shoes in engagement with the drum. Such mechanical parking brakes
have presented various problems that have been partially addressed
by the use of electric parking brake mechanisms.
[0003] Some electric parking brake mechanisms have eliminated the
parking brake lever and completely redesigned the drum brake
assembly to incorporate an electric parking brake mechanism. These
mechanisms have required high torque motors and a gearbox to
generate sufficient force to apply the brakes, adding significant
cost to the drum brake assembly. These high torque motors tend to
be relatively large and cannot simply replace components presently
included in brake drum assemblies, but instead require substantial
redesign of the brake assembly package. Furthermore, high torque
motors utilize a significant amount of power that is undesirable in
modem vehicles.
[0004] Presently available electric brake systems have the further
disadvantage that they rely on conventional brake adjustment
mechanisms. Such conventional adjustment systems are mechanical and
only operate when the wheels are moving in a reverse direction. In
addition, neither known electric brake systems nor conventional
brake systems provide real-time sensing of brake lining wear and
determination of a worn brake lining condition.
[0005] Therefore, an electric parking brake assembly is needed that
requires relatively little power to apply, that may be easily
retrofitted into a conventional drum brake assembly, and that
provides real-time adjustment of the brake shoe-to-drum clearance
and sensing of brake lining wear.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to an electrically and
hydraulically (hereinafter referred to as "electro-hydraulic")
actuated electronic parking brake assembly for a leading/trailing
type automotive drum brake. The parking brake assembly includes a
strut actuator subassembly that replaces conventional components
including the parking brake lever, adjuster strut and associated
parts, used in a standard drum brake. The strut actuator
subassembly is easily incorporated into a conventional brake
assembly and comprises a strut tube, an electric motor having a
driveshaft, a position encoder, a power screw and a connector fork.
Due to the design of the strut actuator subassembly, a low power
(and low torque) motor can be used.
[0007] The brake assembly of the present invention includes a
backing plate having primary and secondary shoe hold-down pin and
spring assemblies with primary and secondary brake shoes. Each of
the brake shoes has a portion in spaced relation from one another.
A drum is disposed about the brake shoes. A wheel cylinder is
supported by the backing plate and is arranged between the portions
of the brake shoes for forcing the portions away from one another
to engage the brake shoes with the drum in a brake position. A
strut actuator subassembly, located adjacent to the wheel cylinder,
interconnects the brake shoes proximate to the portions. The strut
actuator subassembly comprises a strut tube, a power screw, a
connector fork, an electric motor with a driveshaft and a position
encoder. The strut tube has one open end having female threads
along a portion of the interior and an opposing end that tapers to
a two-pronged fork. The power screw has male threads along a
portion of its length and an unthreaded rod portion at one end. The
connector fork has an annular female receiver portion at one end
suitable for receiving the rod portion of the power screw and a
two-pronged fork at the other end. The electric motor and position
encoder are located within the strut tube, and the electric motor
is axially connected with the power screw via the driveshaft. The
strut tube and the power screw connect at their respective female
and male threaded ends. The power screw, at its rod end, connects
to the female end of the connector fork. The forked end of the
strut tube and the connector fork connect with slots in portions of
each web of opposing brake shoes thereby securing the strut
actuator subassembly between the opposing brake shoes. The strut
tube, electric motor with driveshaft, position encoder, power screw
and connector fork are in axial relationship with one another and
when connected define the transverse structure of the strut
actuator subassembly.
[0008] In operation of an electro-hydraulic apply parking brake of
the present invention, the strut actuator subassembly serves as a
parking brake latch. Hydraulic pressure is applied by the
electro-hydraulic actuator to the wheel cylinder to advance the
brake shoes against the drum. As the brake is applied
hydraulically, the electric motor of the strut actuator subassembly
is energized. The strut actuator subassembly turns the power screw
to advance the connector fork and strut tube out against the
hydraulically extended brake shoes. Due to the design of the power
screw, it can only be driven in positive direction. Accordingly,
when the hydraulic pressure to the wheel cylinder is released along
with the power to the electric motor, the brake shoes become locked
to against the drum. The parking brake is released by the
application of a hydraulic pressure sufficient to remove the axial
load on the power screw, the connector fork and the strut tube. The
electric motor then re-energizes, reverses and retracts the power
screw and strut tube away from the shoes allowing them to return to
their predetermined disengaged position when the hydraulic pressure
is removed. The connector fork returns along with the return of the
brake shoes by action of the return springs.
[0009] The present invention also advantageously provides regular
and precise brake adjustment and sensing of braking lining wear.
During operation, the electric motor is periodically energized,
such as during the ignition start cycle, causing the power screw to
turn which advances the brake shoes out until they touch the drum.
The motor then reverses for a predetermined number of counts of the
position encoder to obtain the desired shoe-to-drum clearance. This
provides regular and precise brake adjustment. The position encoder
also concurrently determines the distance that the shoe has
traveled and compares it with the original brake lining position to
provide a reasonable estimate of a worn out lining condition. Upon
such indication of wear, the position encoder sends out a signal to
notify the operator of the worn lining condition.
[0010] Accordingly, the above invention provides an electric
parking brake mechanism that provides regular and precise brake
adjustment and lining wear indication. The mechanism requires
relatively little power to operate and may be easily incorporated,
such as by retrofit, into a conventional drum brake assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other advantages of the present invention can be understood
by reference to the following detailed description when considered
in connection with the accompanying drawing wherein:
[0012] FIG. 1 is a front elevation view of a drum brake assembly of
the present invention.
[0013] FIG. 2 is an exposed planar view of the strut actuator
subassembly, located at section 2-2 of FIG. 1, showing details of
the components.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] A drum brake assembly 10 for a vehicle is shown in FIG. 1.
The assembly 10 includes a backing plate 12 having primary 14 and
secondary 16 shoe hold down pin-and-spring assemblies with primary
18 and secondary 20 brake shoes supported respectively thereon. A
drum 21 is disposed about the brake shoes 18, 20. Each of the brake
shoes 18, 20 include brake shoe webs 22 that support friction
linings 24 adjacent drum 21. Each of webs 22 has a portion 30 in
spaced relation from the other that extends to a second portion 32.
Preferably, an anchor block 36 is arranged between brake shoes 18,
20 to support the second portions 32 in spaced relationship to one
another.
[0015] A wheel cylinder 40 is supported by backing plate 12 and is
arranged between portions 30 of brake shoes 18, 20. Wheel cylinder
40 includes pistons on either end, as is well known, that move in
opposite directions to force the portions 30 away from one another
to engage brake shoes 18, 20 with drum 21 when in a brake position.
Hydraulic fluid is forced into a chamber between the pistons by a
hydraulic brake actuator. Portions 30 have ears 42 that are
received in indentations in the pistons (not shown). As portions 30
are forced away from one another, brake shoes 18, 20 pivot outward
about pin-and-spring assemblies 14, 16.
[0016] A strut actuator subassembly 48, located at section 2-2, is
connected to slots 52, 53 in webs 22 interconnecting brake shoes
18, 20 at ends 50, 51 adjacent wheel cylinder 40 and proximate the
portions 30. Opposing ends 50, 51 of the strut actuator subassembly
48 engage webs 22 to hold the portions 30 in spaced relation. Ends
50, 51 also serve to secure strut actuator subassembly 48 between
brake shoes 18, 20 within brake assembly 10. Upper and lower return
springs 46, 47 interconnect the portions 30 and second portions 32
for retracting brakes shoes 18, 20 from drum 21 against strut
actuator subassembly 48 and anchor block 36. In this manner, anchor
block 36 and strut actuator subassembly 48 together determine the
spacing of brake shoes 18, 20 from drum 21. As linings 24 wear,
brake shoes 18, 20 must be moved closer to drum 21 to maintain
desirable brake application characteristics, such as consistent
brake pedal travel and brake response time. To this end, strut
actuator subassembly 48 serves as a lining wear sensor and a brake
shoe-to-drum clearance adjuster to accommodate for wear in brake
shoes 18, 20.
[0017] Referring to FIG. 2, strut actuator subassembly 48 comprises
a strut tube 54 that is open at one end having female threads and
tapers to a fork at opposite end 50. Strut actuator assembly 48
further comprises an electric motor 56 with a driveshaft 57, a
position encoder 58, a power screw 60 having male threads along a
portion of its length and a unthreaded rod portion at one end, and
a connector fork 62 having a female end suitable to receive the rod
portion of the power screw and a fork at end 51. As shown in FIG.
1, electric motor 56 and position encoder 58 are located within
strut tube 54. The electric motor 56 is axially connected via
driveshaft 57 to power screw 60. Power screw 60 connects via its
rod portion to connector fork 62 that connects at end 51 with slot
53, and strut tube 54 connects with its fork at end 50 with slot
52. In operation, the electric motor 56 turns driveshaft 57 to
rotate power screw 60. Power screw 60 advances connector fork 62
and strut tube 54 in opposing directions. When electric motor 56 is
operating in the positive direction, power screw 60 (with connector
fork 62) and strut tube 54 move outwardly to engage brake shoes 18,
20 with drum 21. This outward movement provides for parking brake
engagement, sensing of brake lining wear and determination of the
shoe-to-drum distance. When the motor is operating in the reverse
direction, power screw 60 and strut tube 54 move inwardly allowing
the brake shoes 18, 20 to retract from drum 21 and return to their
disengaged position. This inward movement provides for parking
brake disengagement and adjustment of the brakes to a pre-selected
brake shoe-to-drum clearance.
[0018] The electric parking brake of the present invention is
actuated in response to a parking brake signal received from an
electro-hydraulic parking brake mechanism (not shown). Hydraulic
pressure is applied by an electro-hydraulic actuator (also not
shown) to the wheel cylinder 40 that advances brake shoes 18, 20
against the drum 21. The electro-hydraulic actuator concurrently
sends a signal to the strut actuator subassembly 48 to energize
electric motor 56. Electric motor 56 turns driveshaft 57 in the
positive direction moving power screw 60 (with connector fork 62)
and strut tube 54 outwardly to engage the brake shoes 18, 20 with
the drum 21. Because the power screw 60 cannot be driven backwards,
when the hydraulic pressure to wheel cylinder 40 is released with
the power to the electric motor 56, the brake shoes 18, 20 become
locked against the drum 21. The parking brake is released when the
electro-hydraulic actuator is re-initiated by application of a
hydraulic pressure that is sufficient to remove the axial load on
the power screw 60, connector fork 62 and the strut tube 54. The
electric motor 56 is concurrently re-energized, reverses the
direction of driveshaft 57 and retracts power screw 60 and strut
tube 54, allowing brake shoes 18, 20 to return to a disengaged
position.
[0019] Brake lining wear sensing and adjustment are also controlled
by the strut actuator subassembly 48. Upon brake installation,
position encoder 58 records the original position of the brake
shoes according to the pre-selected brake-to-drum clearance. Then,
during operation, the electric motor 56 is periodically energized,
such as during the ignition start cycle, causing the power screw 60
(with connector fork 62) and the strut tube 54 to move outwardly
and advance the brake shoes 18, 20 out until they touch the drum
21. The electric motor 56 then reverses for a predetermined number
of counts according to position encoder 58 to obtain the desired
shoe-to-drum clearance. The position encoder 58 concurrently
determines the distance that brake shoes 18, 20 have traveled and
compares it with the original set-point position. The position
encoder 58 outputs a signal to notify the operator of a worn brake
lining condition when a predefined point is reached.
[0020] In the present invention, electric motor 56 is preferably a
low power, low torque motor since it need only generate enough
force to move the weight of the brake shoes 18, 20 against the
resistance of return spring 46 to touch drum 21.
[0021] The invention has been described in an illustrative manner,
and it is to be understood that the terminology that has been used
is intended to be in the nature of words of description rather than
of limitation. Obviously, many modifications and variations of the
present invention are possible in light of the above teachings. It
is, therefore, to be understood that within the scope of the
appended claims the invention may be practiced otherwise than as
specifically described.
* * * * *