U.S. patent application number 10/739489 was filed with the patent office on 2005-06-23 for compression release brake system.
Invention is credited to Afjeh, Homa, Ellison, Mark S., Pipis, John S. JR..
Application Number | 20050133003 10/739489 |
Document ID | / |
Family ID | 34634524 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133003 |
Kind Code |
A1 |
Afjeh, Homa ; et
al. |
June 23, 2005 |
COMPRESSION RELEASE BRAKE SYSTEM
Abstract
A compression release brake system 10 includes a hydraulic
apparatus 12 for controllably opening at least one exhaust valve 14
of at least one cylinder 16 of an engine in response to motion of a
cam actuator 12. The system 10 includes a master piston assembly 40
having a master piston 42 engageable with the cam actuator 12. The
master piston 42 includes a compressible piston pin 56. A slave
piston assembly 44 is hydraulically linked to the master piston
assembly 40 and includes a slave piston 46 engageable with the at
least one exhaust valve 14.
Inventors: |
Afjeh, Homa; (Peoria,
IL) ; Ellison, Mark S.; (Pontiac, IL) ; Pipis,
John S. JR.; (Washington, IL) |
Correspondence
Address: |
CATERPILLAR INC.
100 N.E. ADAMS STREET
PATENT DEPT.
PEORIA
IL
616296490
|
Family ID: |
34634524 |
Appl. No.: |
10/739489 |
Filed: |
December 18, 2003 |
Current U.S.
Class: |
123/321 |
Current CPC
Class: |
F01L 1/181 20130101;
F01L 1/146 20130101; F01L 9/10 20210101; F01L 13/065 20130101; F01L
9/14 20210101; F01L 2305/00 20200501; F01L 2001/34446 20130101 |
Class at
Publication: |
123/321 |
International
Class: |
F01L 013/06 |
Claims
What is claimed is:
1. A compression release brake system having a hydraulic apparatus
for controllably opening at least one exhaust valve of at least one
cylinder of an engine in response to motion of a cam actuator,
comprising: a master piston assembly having a master piston
engageable with said cam actuator, said master piston including a
compressible piston pin; and a slave piston assembly hydraulically
linked to said master piston assembly and having a slave piston
engageable with said at least one exhaust valve.
2. A compression release brake system, as set forth in claim 1,
including a travel-limiting piston assembly positioned to
controllably limit linear movement of said master piston within
said master piston assembly to a predetermined amount.
3. A compression release brake system, as set forth in claim 2,
wherein said compressible piston pin is adapted to absorb motion
induced by said cam actuator which exceeds that necessary to move
said master piston said predetermined amount.
4. A compression release brake system, as set forth in claim 3,
including a brake control valve controllably connectable to a
hydraulic fluid supply, a hydraulic fluid drain, and to each of
said master, slave, and travel-limiting piston assemblies, said
brake control valve being moveable between a power position at
which said master, slave, and travel-limiting piston assemblies are
connected to said hydraulic fluid drain, and a brake position at
which said master, slave, and travel-limiting piston assemblies are
connected to said hydraulic fluid supply.
5. A compression release brake system, as set forth in claim 3,
wherein said master piston assembly includes: a piston housing
having a bore, said master piston being slidably disposed in said
piston housing bore; said compressible piston pin having a
compressible portion, a solid portion, and a bore extending through
said compressible portion into said solid portion; and a guide pin
slidably disposed in said piston pin bore and having an end portion
engageable with said cam actuator and being adapted to controllably
move said master piston within said piston housing bore in response
to motion of said cam actuator.
6. A compression release brake system, as set forth in claim 5,
wherein said master piston includes a pin receiving portion, and
said master piston assembly further includes a piston spring
arranged between said piston housing and said piston pin solid
portion and adapted to urge said piston pin solid portion into
abutting arrangement with said piston body pin receiving
portion.
7. A method for limiting travel of at least one exhaust valve of at
least one cylinder of an engine during a compression release brake
event, said engine having a cam actuator, a master piston assembly
having a master piston, said master piston including a compressible
piston pin and a guide pin, said guide pin being engageable with
said cam actuator, a slave piston assembly hydraulically linked to
said master piston assembly and having a slave piston engageable
with said at least one exhaust valve, and a travel-limiting piston
assembly having a travel-limiting piston positioned to controllably
limit movement of said master piston, comprising the steps of:
moving said travel-limiting piston to a position sufficient to
limit movement of said master piston to a predetermined amount;
moving said master piston said predetermined amount in response to
said cam actuator acting upon said guide pin, and responsively
opening said at least one exhaust valve a predetermined amount; and
compressing said compressible piston pin in response to further
action of said cam actuator upon said guide pin beyond that
required to move said master piston said predetermined
distance.
8. A travel-limited master piston assembly for a compression
release brake system, comprising: a piston housing having a bore; a
master piston slidably disposed in said piston housing bore; a
compressible piston pin having a compressible portion, a solid
portion, and a bore extending through said compressible portion
into said solid portion; a guide pin slidably disposed in said
piston pin bore and adapted to controllably move said master piston
within said piston housing bore; and a travel-limiting piston
assembly positioned to controllably limit the range of slidable
linear movement of said master piston within said piston housing
bore in response to engagement of said compression release brake
system.
9. A travel-limited master piston assembly for a compression
release brake system, as set forth in claim 8, wherein said master
piston includes a pin receiving portion a piston, and said master
piston assembly includes a piston spring arranged between said
piston housing and said piston pin solid portion and adapted to
urge said piston pin solid portion into abutting arrangement with
said piston body pin receiving portion.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to a system and
method for opening at least one valve associated with a cylinder of
an engine and, more particularly, to a system and method for
controllably limiting the amount of lift or displacement of an
engine valve during a valve opening event.
BACKGROUND
[0002] Engines, such as internal combustion engines, commonly
utilize intake and exhaust valves associated with engine cylinders.
In a normal running mode, intake valves may be opened to admit a
fuel and air mixture into the combustion chamber of a cylinder, and
exhaust valves may be opened to permit combustion byproducts to be
exhausted from the cylinder.
[0003] It is also known to operate engines in a compression release
braking mode, in which one or more engine cylinders are temporarily
used to consume energy by compressing air. The energy required to
compress air in the one or more engine cylinders produces a braking
effect. This is accomplished by controllably opening a cylinder
valve, for example, an exhaust valve, at a time when the engine has
consumed energy compressing air in the cylinder, thus preventing
recovery of the expended energy.
[0004] One common method for controllably opening an engine valve
during a braking event is to use a rotating cam, for example, an
injector cam, associated with the engine to provide the mechanical
energy necessary to open the valve. The cam may be linked to the
valve by a hydro/mechanical linkage including master and slave
pistons and cylinders, such that rotation of the cam is translated
into valve motion. One problem with this method is that the profile
of the engine cam may not provide the optimum amount of valve
displacement or lift. This is a particular problem in the braking
mode of engine operation, because the engine cylinder valve is
typically opened during the time that the cylinder piston is at or
near top dead center. Consequently, if the valve extends too far
into the cylinder it can make contact with the piston causing
damage to the engine.
[0005] One approach to controlling the amount of valve displacement
when using a fixed cam profile to indirectly actuate an engine
valve is to employ some form of lost-motion linkage between the cam
actuator and the engine valve. Such a linkage is designed to absorb
motion caused by the fixed cam profile that exceeds the amount
necessary to provide a desired valve displacement.
[0006] Many of the lost-motion devices employed in the past for
this purpose incorporate some form of hydraulic arrangement, such
that the force transmitted from the cam actuator to the engine
valve is dissipated or absorbed hydraulically during at least a
portion of the cam profile excursion. Such devices are sometimes
referred to as hydraulic clippers, because they clip or limit
excessive valve travel. For example, U.S. Pat. No. 6,415,752
illustrates a lost-motion system that includes a hydraulic
accumulator that controllably absorbs hydraulic fluid in excess of
that required to cause a desired engine valve displacement.
[0007] Known lost-motion devices used for the above described
purpose tend to be complex and expensive, and often employ special
and precise hydraulic fluid porting. This can lead to system
failures and unreliable operation. The present invention is
directed to overcoming one or more of the problems as set forth
above.
SUMMARY OF THE INVENTION
[0008] In one aspect of the present invention, a compression
release brake system includes a hydraulic apparatus for
controllably opening at least one exhaust valve of at least one
cylinder of an engine in response to motion of a cam actuator. The
system includes a master piston assembly having a master piston
engageable with the cam actuator. The master piston includes a
compressible piston pin. A slave piston assembly is hydraulically
linked to the master piston assembly and includes a slave piston
engageable with the at least one exhaust valve.
[0009] In a second aspect of the present invention, a method for
limiting travel of at least one exhaust valve of at least one
cylinder of an engine during a compression release brake event is
disclosed. The engine may include a cam actuator and a master
piston assembly having a master piston. The master piston includes
a compressible piston pin that is engageable with the cam actuator.
A slave piston assembly is hydraulically linked to the master
piston assembly and has a slave piston engageable with the at least
one exhaust valve. A travel-limiting piston assembly has a
travel-limiting piston positioned to controllably limit movement of
the master piston. The method includes the steps of moving the
travel-limiting piston to a position sufficient to limit movement
of the master piston to a predetermined amount. The master piston
is moved the predetermined amount in response to the cam actuator,
and the at least one exhaust valve is responsively opened a
predetermined amount. The compressible piston pin is compressed in
response to further action of the cam actuator beyond that required
to move the master piston the predetermined distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic representation of an embodiment of the
present invention configured for compression release braking
operation;
[0011] FIG. 2 is a schematic representation of an embodiment of the
present invention configured for powered operation; and
[0012] FIG. 3 is a cross-section of a travel-limiting master piston
assembly in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION
[0013] Referring first to FIGS. 1 and 2, a compression release
brake system 10 includes a hydraulic apparatus 12 for controllably
opening at least one exhaust valve 14 of at least one cylinder 16
of an engine (not shown) in response to motion of a cam actuator
18. The cam actuator 18 may be a rotating cam such as an injector
cam 20 that is normally used to activate one or more fuel
injectors, and may include a cam follower 22 and rocker arm arm 24
arranged to translate the rotary motion of the cam 20 into a linear
driving motion, as is well known in the engine art. The engine
valve 14 may include a similar cam driver 26 having an associated
cam 28, cam follower 30, and rocker arm 32. The rocker arm 32
normally reciprocates according to the profile of the cam 28, in
turn periodically opening the engine valve 14 by transferring
motion to a push rod 34. A valve closing spring 36 acts to close
the engine valve 14 when it is not held open by the rocker arm
32.
[0014] A master piston assembly 40 has a master piston 42
engageable with the cam actuator 18 through the cam follower 22 and
rocker arm 24 arrangement. A slave piston assembly 44 is
hydraulically coupled to the master piston assembly 40 and includes
a slave piston 46 engageable with the at least one exhaust valve 14
through the associated rocker arm 32 and push rod 34. A
travel-limiting piston assembly 48 is positioned relative to the
master piston assembly 40 to controllably limit linear movement of
the master piston 42 within the master piston assembly 40 to a
predetermined amount.
[0015] The master, slave, and travel-limiting piston assemblies 40,
44, 48 are shown in more detail in FIG. 3. The master piston
assembly 40 includes a piston housing 50 having a bore 52. The
master piston 42 is slidably disposed in the piston housing bore 52
and cooperates with the piston housing 50 to form a master
hydraulic reservoir 54. In the illustrated embodiment, a
compressible piston pin 56 has a compressible portion 58, a solid
portion 60, and a bore 62 extending through the compressible
portion 58 into the solid portion 60. A guide pin 64 is slidably
disposed in the piston pin bore 62, and has an end portion 66
engageable with the rocker arm 24 of the cam actuator 18. The end
portion 66 may be connected to an end of the master pin
compressible portion 58 with a shear pin 65, and may include a
swivelable foot 67 adapted to maintain alignment between the guide
pin 64 and the rocker arm 24. The guide pin 64 is adapted to
controllably move the master piston 42 within the piston housing
bore 52 in response to motion of the cam actuator 18. The master
piston 42 also may include a pin receiving portion 68, and a piston
spring 70 arranged between the piston housing 50 and the piston pin
solid portion 60. The piston spring 70 is arranged to urge the
piston pin solid portion 60 into abutting arrangement with the
master piston pin receiving portion 68, and to further urge the
master piston 42 in the direction of the master hydraulic reservoir
54.
[0016] The slave piston 46 of the slave piston assembly 44 is
slidably disposed in a slave piston housing bore 72 to form a slave
hydraulic reservoir 76. A slave piston spring 78 is arranged to
urge the slave piston 46 in the direction of the slave hydraulic
reservoir 76. The master and slave hydraulic reservoirs 54, 76 are
connected to one another by a hydraulic line 80.
[0017] The travel-limiting piston assembly 48 includes a
travel-limiting piston 82 that is slidably disposed in a
travel-limiting piston housing bore 84 to form a travel-limiting
hydraulic reservoir 88. The travel-limiting piston assembly 48 may
be mounted integral with the master piston assembly 40, and the end
of the travel-limiting piston 82 opposite the travel-limiting
hydraulic reservoir 88 may controllably extend a predetermined
distance into the master hydraulic reservoir 54 in a manner
sufficient to contact the master piston 22. The predetermined
distance may be established by a travel-limiting piston stop 90 as
shown. This distance may be made adjustable by, for example,
providing means for adjusting this stop or for moving the
travel-limiting piston assembly 48 relative to the master piston
assembly 40.
[0018] A brake control valve 92 is controllably connectable to a
pressurized hydraulic fluid supply 94, a hydraulic fluid drain 96,
and to each of the master, slave, and travel-limiting hydraulic
reservoirs 54, 76, 88. The brake control valve 92 is movable
between a power position as shown in FIG. 2, at which the master,
slave, and travel-limiting piston reservoirs 54, 76, 88 are
connected through the brake control valve 92 to the hydraulic fluid
drain 96, and a brake position, as shown in FIG. 1, at which the
master and slave hydraulic reservoirs 54, 76 are connected to the
hydraulic fluid supply 94 through a first check valve 98, and the
travel-limiting hydraulic reservoir 88 is connected to the
hydraulic fluid supply 94 through the first check valve 98 and
through a second check valve 99.
[0019] In a preferred embodiment, the compressible piston pin 56
compressible portion 58 may be implemented as a machined helical
spring. Such machined springs are commercially available from
Helical Products Company, Inc. However, other structural
arrangements that result in a compressible piston pin may be
substituted for the preferred machined spring without deviating
from the scope of the present invention. For example, the piston
pin 56 could be implemented in two or more discreet pieces
incorporating a solid portion with a more conventional coil spring.
It is also foreseeable that the solid portion could be dispensed
with and the entire compressible pin could be implemented in the
form of a machined or coil spring. Thus, it is intended that the
present invention be construed to cover these and other
modifications that come within the scope of the appended claims and
their legal equivalents.
Industrial Applicability
[0020] During powered operation of an engine incorporating the
present invention, the brake control valve 92 is electrically
shifted to the power position described in FIG. 2. In this mode,
the hydraulic reservoirs 54, 76, 88 of the master piston assembly
40, the slave piston assembly 44, and the travel-limiting piston
assembly 48 are all connected through the control valve 92 to the
hydraulic fluid drain or sump 96. Consequently, the master and
slave return springs 70, 78 associated with the respective piston
assemblies 40, 44 force the respective pistons 42, 46 to retract,
and the master and slave pistons 42, 46 are removed from engagement
with the cam actuator 18 and exhaust valve 14, respectively.
[0021] The master piston spring 70 and master piston 42 also act on
the travel-limiting piston 82 causing it to reset to a retracted
position. Hydraulic fluid in the master, slave, and travel-limiting
hydraulic reservoirs 54, 76, 88 is returned through the control
valve 92 to the hydraulic fluid drain 96. Consequently, the exhaust
valve 14 is not influenced by the hydraulic apparatus 12 and the
engine operates in a conventional manner.
[0022] During braking operation of the engine, the control valve 92
is shifted to the braking position as depicted in FIG. 1. Hydraulic
fluid is supplied under pressure from the hydraulic fluid supply 94
through the check valves 98, 99 to the master hydraulic reservoir
54, the slave hydraulic reservoir 76, and the travel-limiting
hydraulic reservoir 88. In turn, the master piston 42, compressible
piston pin 56, and guide pin 64 are engaged through the rocker arm
24 and cam follower 22 with the cam 20 of the cam actuator 18.
Likewise, the slave piston 46 is engaged with the exhaust valve 14
through the rocker arm 32 and push rod linkage 34. Finally, the
travel-limiting piston 82 is extended to its predetermined position
and is hydraulically locked by the second check valve 99. With the
hydraulic reservoirs 54, 76, 88 filled and hydraulically locked by
the check valves 98, 99, the guide pin 64 and responsively the
compressible piston pin 56 and master piston 42 will attempt to
follow the motion induced by rotation of the cam actuator 18.
[0023] As the master piston 42 moves upward in the piston housing
bore 52, hydraulic fluid in the master hydraulic reservoir 54 is
displaced through the hydraulic line 80 to the slave hydraulic
reservoir 76. This forces the slave piston 46 to extend and the
exhaust valve 14 to open. However, once the master piston 42 makes
contact with the travel-limiting piston 82, further linear movement
of the master piston 42 within the piston housing bore 52 is
blocked and further extension of the slave piston 46 cannot occur.
Consequently, the amount of exhaust valve 14 displacement or lift
is limited in accordance with the preset travel-limiting piston
assembly 48.
[0024] However, the cam actuator 18 continues to exert upward force
on the guide pin 64 and the compressible piston pin 56, causing the
piston pin compressible portion 58 to compress. The guide pin 64 is
free to continue to move within the piston pin bore 62 as
compression occurs, so the additional motion imparted by the cam
actuator 18 is absorbed by the compressible piston pin 56. As the
cam actuator 18 continues to revolve and the direction of linear
motion is reversed, the piston pin compressible portion 58 again
extends to follow the cam 20 profile. Once fully extended,
continued rotation of the cam actuator 18 permits the exhaust valve
closing spring 36 to close the exhaust valve 14, forcing hydraulic
fluid out of the slave hydraulic reservoir 76 and back into the
master hydraulic reservoir 54. The cycle continues until the
control valve 92 is returned to the engine power position depicted
in FIG. 2.
[0025] The above described embodiments of the invention discuss a
simple system for controllably actuating a single valve associated
with one cylinder of an engine. However, the described system can
be readily multiplied in a straightforward manner to include
multiple valves in multiple engine cylinders, as would be typically
employed for compression release braking without departing from the
scope of the present invention. Likewise, other modifications of
the described embodiment may be made by one skilled in the art
without deviating from the scope of the appended claims and legal
equivalents.
* * * * *