Information
-
Patent Grant
-
6253730
-
Patent Number
6,253,730
-
Date Filed
Friday, January 14, 200024 years ago
-
Date Issued
Tuesday, July 3, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Nixon Peabody LLP
- Leedom, Jr.; Charles M.
- Brackett; Tim L.
-
CPC
-
US Classifications
Field of Search
US
- 123 9015
- 123 321
- 123 322
-
International Classifications
-
Abstract
An engine compression braking system having an integral rocker lever and reset valve utilizes a single rocker lever to operate an engine in both normal power and braking modes while effectively closing an exhaust valve to define a braking mode exhaust valve opening event prior to a primary opening event. The system includes a reset valve mounted on the rocker arm a spaced distance from an actuator piston to relieve fluid pressure from a high pressure circuit after an initial opening of the exhaust valve. A reset contact element is mounted on a stationary engine component for engagement by the reset valve during movement of the rocker lever to cause opening of the reset valve and relief of the pressure. In one embodiment, a bias chamber and bias chamber supply circuit are provided to permit low pressure braking fluid to be continuously supplied to an actuator supply circuit.
Description
TECHNICAL FIELD
This invention relates to compression braking systems for internal combustion engines for selectively operating an engine in either a power mode or a braking mode, i.e. compression braking. More specifically, this invention relates to a simple, effective compression braking system capable of minimizing the size and weight of the associated engine while providing optimal predictable compression braking.
BACKGROUND OF THE INVENTION
For many internal combustion engine applications, such as for powering heavy trucks, it is desirable to operate the engine in a braking mode. This approach involves converting the engine into a compressor by cutting off the fuel flow and opening the exhaust valve for each cylinder near the end of the compression stroke.
An early technique for accomplishing the braking effect is disclosed in U.S. Pat. No. 3,220,392 to Cummins, wherein a slave hydraulic piston located over an exhaust valve opens the exhaust valve near the end of the compression stroke of an engine piston with which the exhaust valve is associated. To place the engine into braking mode, three-way solenoids are energized which cause pressurized lubricating oil to flow through a control valve, creating a hydraulic link between a master piston and a slave piston. The master piston is displaced inward by an engine element (such as a fuel injector actuating mechanism) periodically in timed relationship with the compression stroke of the engine which in turn actuates a slave piston through hydraulic force to open the exhaust valves. The compression brake system as originally disclosed in the '392 patent has evolved in many aspects, including improvements in the control valves (see U.S. Pat. Nos. 5,386,809 to Reedy et al. and U.S. Pat. No. 4,996,957 to Meistrick) and the piston actuation assembly (see U.S. Pat. No. 4,475,500 to Bostelman). A typical modern compression braking system found in the prior art is shown in U.S. Pat. No. 4,423,712 to Mayne et al. where the exhaust valves are normally operated during the engine's power mode by an exhaust rocker lever. To operate the engine in a braking mode, a control valve separates the braking system into a high pressure circuit and a low pressure circuit using a check valve which prevents flow of high pressure fluid back into the low pressure supply circuit, thereby allowing the formation of a hydraulic link in the high pressure circuit. A three-way solenoid valve, positioned upstream of the control valve, controls the flow of low pressure fluid to the control valve, and thus, controls the beginning and end of the braking mode.
The system disclosed in Mayne el al. also includes a reset valve which operates to cause the slave piston to retract after an initial opening of the exhaust valve during braking. As a result, the exhaust valve is closed prior to the end of the expansion stroke and before the hydraulic pressure drops due to a return motion of the master piston. This design advantageously avoids shock or asymmetric loading of the crosshead by the exhaust rocker arm at the start of the main opening event of the exhaust valve following the initial opening event. However, the reset valve is formed in the slave cylinder for contact, and thus tripping, by the slave piston. Thus, the reset valve relies on the movement of the slave piston relative to the piston housing. Also, the reset valve is closed when the engine is operating in a power mode thereby undesirably creating a small volume in the slave piston which is not connected to the low pressure drain. As a result, air pockets may form in this volume disrupting slave piston or reset valve motion thereby possibly adversely affecting the predictability of the braking event.
U.S. Pat. No. 5,680,841 to Hu discloses an electro-hydraulic engine valve control system for permitting engine braking operation which includes a slave piston mounted in a bore formed in a rocker lever, a control oil circuit formed in the rocker lever and rocker shaft and a check valve positioned in the oil control circuit between the slave piston and a central oil passage formed in the rocker shaft. The system also includes an electronically controlled valve and an accumulator positioned along the oil control circuit. However, this system uses a cam profile which causes the exhaust valve to completely close between the initial opening of the exhaust valve and the primary opening of the exhaust valve during braking. This invention also requires the electronic control solenoid valve to open and close every engine cycle in both power and braking modes. Also, this design appears to undesirably require a solenoid for each cylinder.
Therefore, there is a need for an improved engine compression braking system having an integral rocker lever and reset valve capable of effectively avoiding asymmetric loading of a valve crosshead while providing accurate and predictable compression braking.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to overcome the deficiencies of the prior art and to provide an engine compression braking system capable of utilizing an integral rocker lever and reset valve to achieve optimum compression braking.
Another object of the present invention is to provide an engine compression braking system which incorporates a slave piston into the rocker lever along with a reset valve while eliminating other components of conventional systems, such as a control valve, master piston, adjusting screw and brake housing.
A further object of the present invention is to provide an engine braking system at a reduced cost while also minimizing weight and size.
Yet another object of the present invention is to provide an engine braking system including an integrated rocker lever and slave piston and a cam having a profile which avoids reverse pivoting of the rocker lever between an initial opening of the exhaust valve during braking and a main opening event.
It is yet another object of the present invention to provide an engine compression braking system including a rocker lever and a reset valve integrated into the rocker lever which is capable of effectively causing the return of an exhaust valve to a closed position without the reverse pivot of the rocker arm.
A still further object of the present invention is to provide an integrated rocker lever and reset valve wherein the reset valve is positioned to be operated by contact with an adjacent engine component.
Yet another object of the present invention is to provide an engine braking system including an integrated rocker lever and slave piston wherein the slave piston is positioned in a bore continuously connected to a braking fluid supply when the engine brake is off and the engine is operating in a normal power mode.
These and other objects are achieved by providing a braking system for an internal combustion engine having at least one engine piston reciprocally mounted within a cylinder for cyclical successive compression and expansion strokes and at least one exhaust valve operable to open near the end of an expansion stroke of the engine piston when the engine is operated in a power mode and operable to open in a timed relationship to the engine piston compression stroke when the engine is operated in a braking mode. The braking system includes a rocker lever pivotally mounted adjacent the exhaust valve for opening the exhaust valve and a braking fluid circuit formed in the rocker lever and including a low pressure circuit and a high pressure circuit. The braking system further includes a control valve positioned along the braking fluid circuit and operable in a first position to cause engine operation in the power mode and a second position to cause engine operation in the braking mode. The braking system further includes an actuator piston bore formed in the rocker lever in communication with the high pressure circuit and an actuator piston slidably mounted in the actuator piston bore. In addition, the braking system includes a reset valve mounted on the rocker lever a spaced distance from the actuator piston so as to be free from contact with the actuator piston. The reset valve is operable to relieve fluid pressure from the high pressure circuit during operation in the braking mode. The reset valve may be movable between an open position permitting communication between the high pressure circuit and the low pressure circuit and a closed position blocking communication between the high pressure circuit and the low pressure circuit. The movement of the rocker lever in the present invention causes movement of the reset valve into the open position.
The braking system may further include a reset contact element mounted on the engine adjacent the rocker lever in position for contact by the reset valve during movement of the rocker lever to move the reset valve into an open position. The contact element is mounted for adjustment to vary a distance between the reset contact element and the reset valve. The reset valve includes a valve head positioned for abutment against a valve seat and a reset pin positioned in abutment against the valve head. The valve head may include a ball and the reset pin may be positioned for contact with the reset contact element. The reset valve may include a reset plunger positioned to contact the reset contact element wherein the reset pin extends between the valve head and the reset plunger. Further, a bias chamber may be included for receiving the reset plunger wherein fluid pressure in the bias chamber generates pressure forces on the reset plunger to move the reset plunger toward the reset contact element to cause movement of the reset valve into a closed position.
Preferably, movement of the reset valve into a closed position creates a hydraulic link in the high pressure circuit causing opening of the exhaust valve upon movement of the rocker lever to define a braking mode exhaust valve opening event. The low pressure circuit is connected to a low pressure braking fluid supply. The low pressure circuit may include an actuator supply circuit and a bias chamber supply circuit for delivering braking fluid to the bias chamber. The reset valve functions to control the flow through the actuator supply circuit. In this case, the control valve is movable into a first position to connect the bias chamber supply circuit to a low pressure drain and a second position to connect the bias chamber supply circuit to a low pressure braking fluid supply.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A
is a diagrammatic illustration of the integrated rocker lever, slave piston and reset valve associated with the compression braking system of the present invention;
FIG. 1B
is a cross sectional view of a portion of the integrated rocker lever and reset valve during the brake lift portion of the cam of
FIG. 1A
to define the braking mode exhaust valve opening event;
FIG. 1C
is a cross sectional view of the integrated rocker lever and reset valve immediately after tripping of the reset valve;
FIG. 1D
is a cross sectional view of the rocker lever and reset valve of the present invention during the dwell portion of the cam of
FIG. 1A
occurring between the braking mode exhaust valve opening event and a main exhaust valve opening event;
FIG. 1E
is a cross sectional view of the integrated rocker lever and reset valve of the present invention during the main lift portion of the cam of
FIG. 1A
;
FIG. 1F
is an illustration of the compression braking system of the present invention including a cross sectional view of the integrated rocker lever and reset valve during retraction of the rocker lever from the crosshead;
FIG. 2
is a graph of the cam lift versus crank degrees for a typical braking event showing the various stages of the cam lift and valve motion;
FIG. 3A
is a cutaway, exploded cross sectional view of the reset valve of the present invention illustrating the reset ball geometry to control the exhaust valve seating velocity;
FIG. 3B
is a graph of the cross sectional flow area through the reset ball valve versus ball lift;
FIG. 4
is a diagrammatic illustration of a second embodiment of the compression braking system of the present invention;
FIG. 5A
is an alternative embodiment of the reset valve for the compression braking system of
FIG. 4
;
FIG. 5B
is an end view of the cylindrical reset valve head of the embodiment of
FIG. 5A
;
FIG. 6
is an alternative embodiment of the reset valve for use in the engine compression braking system of
FIG. 4
;
FIG. 7
is an alternative embodiment of the reset valve of the present invention for use in the engine compression braking system of
FIG. 4
; and
FIGS. 8A and 8B
illustrate yet another embodiment of the reset valve of the present invention for use in the engine compression braking system of FIG.
4
.
DETAILED DESCRIPTION OF THE INVENTION
Referring to
FIG. 1A
, there is shown one embodiment of the compression braking system of the present invention, indicated generally at
10
, for operating an internal combustion engine as a compressor when the engine is placed in a braking mode. In particular,
FIG. 1A
discloses a rocker lever
12
that operates to reciprocally displace one or more exhaust valves
14
during a normal power mode and a braking mode of operation. For example, in the preferred embodiment, in the power mode, rocker lever
12
displaces both exhaust valves
14
into the engine cylinder (not shown) during, for instance, the exhaust cycle of a four-cycle operation of the engine in order to exhaust combusted gas from the engine cylinder. When it becomes necessary or desirable to operate the engine in a braking mode, rocker lever
12
functions to displace only one exhaust valve
16
into the engine cylinder at the appropriate time during the engine cycle, e.g. near the end of the compression stroke of the engine piston (not shown), to exhaust the compressed gas from the cylinder. Exhaust valves
14
are mounted on a crosshead
18
positioned for abutment by rocker lever
12
via a contacting element such as a friction reducing swivel pad
20
mounted on one end of rocker lever
12
. Exhaust valve
16
is mounted for downward movement into the engine cylinder independent of crosshead
18
and the other exhaust valve to permit single exhaust valve displacement in the braking mode. Exhaust valve springs
22
are used to bias exhaust valves
14
into the closed position.
Braking system
10
also includes a cam
24
mounted for timed rotation during the engine cycle. A cam roller
26
, mounted on one end of rocker lever
12
via a roller pin
28
, is positioned in biased abutment against the cam surface of cam
24
. Rocker lever
12
is mounted for pivotal movement on a support shaft
30
fixedly mounted in the overhead portion of the engine. Cam
24
includes an inner base portion
32
whereupon rocker lever
12
is pivoted in a clockwise direction around support shaft
30
into a retracted position causing separation of rocker lever
12
and crosshead
18
by a predetermined lash L. While cam roller
26
is positioned on inner base portion
32
, exhaust valves
14
are in the closed position. Cam
24
also includes a brake lift portion
34
which pivots rocker lever
12
in the counterclockwise direction around support shaft
30
to cause opening of exhaust valve
16
when the engine is operating in the braking mode as discussed more fully hereinbelow. Cam
24
further includes a dwell portion
36
which maintains rocker lever
12
in a predetermined pivoted position while avoiding reverse pivoting prior to a main exhaust valve opening event. Cam
24
also includes a main lift portion
38
following dwell portion
36
which functions to further pivot rocker lever
12
in a counterclockwise direction to cause the opening of both exhaust valves
14
during a main exhaust valve opening event as discussed more fully hereinbelow. It should be noted that cam
24
could be operatively connected to rocker lever
12
by a push rod or other drive train structure positioned between cam
24
and rocker lever
12
in a conventional manner.
Importantly, braking system
10
further includes a braking fluid circuit
40
formed at least partially within rocker lever
12
, an actuator piston
42
mounted on rocker lever
12
adjacent exhaust valve
16
, and a control valve
44
for controlling the flow of braking fluid through braking fluid circuit
40
so as to selectively place the particular engine cylinder or the entire engine in a braking mode. Braking fluid circuit
40
includes a high pressure circuit
46
, a low pressure circuit
48
and a drain circuit
50
. High pressure circuit
46
includes an actuator piston bore
52
for slidably receiving actuator piston
42
. A bias spring
54
, positioned in actuator piston bore
52
, biases actuator piston
42
outwardly toward exhaust valve
16
. As discussed more fully hereinbelow, braking system
10
also includes a reset valve
56
positioned between high pressure circuit
46
and low pressure circuit
48
to control the flow of braking fluid between high pressure circuit
46
and low pressure circuit
48
so as to control the movement of exhaust valve
16
during the braking mode. Low pressure circuit
48
includes transverse and axial passages
58
formed in support shaft
30
and transfer passages
60
extending from passages
58
to communicate with control valve
44
. Transfer passages
60
are preferably formed in a shaft support (not shown) positioned to support support shaft
30
. Braking control valve
44
is preferably a compact, three-way solenoid valve which functions to selectively control the beginning and end of the braking mode. During the normal power mode of engine operation, control valve
44
is de-energized to connect low pressure circuit
48
to drain circuit
50
. When engine braking is desired, control valve
44
is energized to connect low pressure circuit
48
to a braking fluid supply line
62
connected to a supply of braking fluid, i.e. engine lubricating oil. Control valve
44
therefore remains energized during the braking mode. A braking fluid accumulator
64
may be provided along braking fluid supply line
62
to ensure a sufficient quantity, and a steady flow, of braking fluid through the low pressure and high pressure circuits
48
,
46
. Control valve
44
is controlled by an engine control module (not shown) which provides signals to valve
44
to cause energization and de-energization of the associated actuator, i.e. solenoid. Also, preferably, control valve
44
and accumulator
64
are mounted on a shaft support (not shown) supporting support shaft
30
.
Referring to
FIG. 1A
, reset valve
56
includes a valve head
70
biased into a closed position by a bias spring
72
to prevent flow between high pressure circuit
46
and low pressure circuit
48
. In the present embodiment, valve head
70
is a ball-type valve. Reset valve
56
also includes a reset pin
74
slidably mounted in a bore formed on the low pressure circuit side of valve
56
immediately adjacent the valve seat for abutment by valve head
70
. Thus, reset pin
74
is positioned to contact and move valve head
70
against the force of bias spring
72
as discussed more fully hereinbelow. A reset contact element
76
is mounted on an engine component, for example a pedestal
54
, immediately adjacent a lower end of reset pin
74
. Reset contact element
76
is positioned a predetermined spaced distance from reset pin
74
when cam roller
26
is positioned on the inner base portion
32
of cam
24
prior to actuation of exhaust valves
14
. During the initial pivoting movement of rocker lever
12
caused by brake lift portion
34
of cam
24
, reset pin
74
will contact reset contact element
76
causing reset pin
74
to move upwardly as shown in
FIG. 1A
thereby moving valve head
70
off its seat from a closed position into an open position resulting in the closing of exhaust valve
16
. It should be noted that the lash L between element
20
and crosshead
18
is set to be larger than the predetermined distance D between reset contact element
76
and reset pin
74
. Reset contact element
76
is preferably adjustably mounted by, for example, a threaded bolt and nut arrangement.
The operation, and the structural and functional advantages, of the braking system
10
of the present invention may best be understood by the following detailed description of each stage of operation as shown in
FIGS. 1A-1F
and FIG.
2
. The various cam lift positions and valve motion positions of each of the
FIGS. 1A-1F
are illustrated in FIG.
2
. During normal engine operation in a power mode, control valve
44
is de-energized blocking flow from braking fluid supply line
62
while connecting transfer passages
60
to drain circuit
50
. During the normal power mode of operation, high pressure circuit
46
is not filled with braking fluid. As cam
24
rotates, although brake lift portion
34
causes rocker lever
12
to pivot, actuator piston
42
merely moves inwardly into actuator piston bore
52
without opening exhaust valve
16
. However, main lift portion
38
then causes rocker lever
12
to pivot further resulting in element
20
contacting crosshead
18
and moving crosshead
18
downwardly so as to open exhaust valves
14
to defme a normal power mode exhaust valve opening event. When braking is desired, the engine ECU (not shown) signals energization of control valve
44
which closes drain circuit
50
and fluidically connects transfer passages
60
to braking fluid supply line
62
. Low pressure braking fluid flows through low pressure circuit
48
, including transfer passages
60
and passages
58
and into high pressure circuit
46
by forcing valve head
70
open against the bias force of spring
72
. Thus, actuator piston bore
52
is filled with low pressure braking fluid and reset valve
56
immediately closes to the position shown in FIG.
1
A. It should be noted that control valve
44
only needs to energize when braking is desired and therefore control valve
44
does not energize and de-energize every engine cycle. During rotation of cam
24
as brake lift portion
34
is encountered by cam roller
26
, rocker lever
12
begins to pivot in a counterclockwise direction around support shaft
30
. As previously noted, the crosshead lash L for normal valve actuation is set so large that rocker lever
12
and crosshead
18
do not contact during the brake lift portion
34
. However, since braking fluid has filled high pressure circuit
46
and thus actuator piston bore
52
, a hydraulic link is created in high pressure circuit
46
preventing actuator piston
42
from moving inwardly as piston
42
pushes against exhaust valve
16
. Reset valve
56
functions as a check valve to prevent the flow of braking fluid from high pressure circuit
46
thereby creating the hydraulic link. As a result, brake lift portion
34
of cam
24
and the initial braking movement of rocker lever
12
causes actuator piston
42
to move exhaust valve
16
to an open position as shown in
FIG. 1B
without moving crosshead
18
. Consequently, compressed gas within an engine cylinder is released to the exhaust system to achieve the engine braking effect desired.
During the braking mode exhaust valve opening event, the reset pin lash will be reduced to zero causing reset pin
74
to contact reset contact element
76
forcing reset pin
74
upwardly as shown in
FIG. 1C
causing valve head
70
to move into an open position. Pressurized braking fluid in high pressure circuit
46
will then flow through high pressure circuit
48
into accumulator
64
as shown in FIG.
1
C. As actuator piston
42
moves inwardly into actuator piston bore
52
, exhaust valve
16
will close due to the force of valve return spring. During the dwell portion
36
and the main lift portion
38
of cam
24
, reset valve
56
is maintained in an open position allowing the free flow of braking fluid between high pressure circuit
46
and braking fluid supply line
62
, including accumulator
64
as shown in
FIGS. 1D and 1E
. Specifically, referring to
FIG. 1E
, during the main lift portion
38
of cam
24
, rocker lever
12
continues to pivot in the counterclockwise direction around support shaft
30
causing element
20
to contact crosshead
18
and force crosshead
18
and thus valves
14
downwardly as shown in FIG.
1
E. As cam
24
continues to rotate and cam roller
26
moves from main lift portion
38
back to inner base portion
32
, rocker lever
12
will pivot in the counterclockwise direction. As shown in
FIG. 1F
, a valve return spring force will cause exhaust valves
14
to move into the closed position and crosshead
18
to move upwardly. Although rocker lever
12
and specifically element
20
separates from crosshead
18
, actuator piston
42
will be maintained in contact with the outer end of exhaust valve
16
by low pressure braking fluid flowing into actuator piston bore
52
via reset valve
56
. Although reset pin
74
has separated from reset contact element
76
during the retraction pivot movement of rocker lever
12
, the flow of low pressure braking fluid into actuator piston bore
52
due to the movement of actuator piston
42
outwardly causes the low pressure braking fluid to force valve head
70
into an open position against the bias force of spring
72
. Valve head
70
separates from reset pin
74
to allow much less restriction during the low pressure fill by moving above the high pressure passage connecting reset valve
56
to actuator piston bore
52
. When actuator piston bore
52
fills with braking fluid and the inner base portion
32
is reached, bias spring
72
will force valve head
70
into the closed position in preparation for another cycle as shown in FIG.
1
B.
Referring to
FIGS. 3A and 3B
, it is important to control the exhaust valve seating velocity during the opening of reset valve
56
immediately upon contact with reset contact element
76
. As shown in
FIG. 1C
, when reset valve
56
moves into an open position, high pressure fluid quickly escapes from high pressure circuit
46
causing the hydraulic link in high pressure circuit
46
and actuator piston bore
52
to collapse. In response, actuator piston
42
quickly moves inwardly toward actuator piston bore
52
. The present invention effectively controls the flow of high pressure fluid escaping high pressure circuit
46
thereby preventing exhaust valve
16
from slamming shut and causing excessive wear and stress on exhaust valve
16
and its associated valve seat. The exhaust valve seating velocity is controlled by designing reset valve
56
with a check ball geometry sufficient to initially restrict the flow around check ball
70
upon initial opening while becoming relatively insensitive to the lift of check ball
70
after the initial lift of the check ball as shown in FIG.
3
B. As shown in
FIG. 3A
, high pressure passage
47
is positioned relative to valve seat
49
and check ball
70
sized so that the smallest effective flow area between check ball
70
and the opposing wall of rocker lever
12
is positioned a predetermined axial distance R from passage
47
. As a result, as shown in
FIG. 3B
, during the initial opening lift of check ball
70
, the total cross sectional flow area through reset valve
56
is restricted to a predetermined maximum area A until check ball
70
has lifted an axial distance greater than R into a new position, for example as shown by the dashed lines in
FIG. 3A
, at which point the cross sectional flow area increases as passage
47
is uncovered. This design makes the reset velocity relatively insensitive to reset lash while the exhaust valve seating velocity remains the same.
FIG. 4
illustrates a second embodiment of the braking system of the present invention indicated generally at
100
which is similar to the previous embodiment in that a rocker lever
102
is pivotally mounted on a support shaft
104
for pivoting motion by the cam and cam roller arrangement of
FIG. 1A
so as to open and close exhaust valve
16
of
FIG. 1A
during a braking mode and open both valves
14
during a normal engine power mode of operation. Thus, the braking system
100
of the present embodiment may be utilized with the cam roller
26
, cam
24
, crosshead
18
and exhaust valves
14
of the embodiment of
FIG. 1A
even though these components are not shown in
FIG. 4
for simplicity purposes. The present embodiment fundamentally differs from the previous embodiment in that low pressure braking fluid is continuously supplied to high pressure circuit
106
when the engine is operating in the normal power mode and when the engine is operating in the braking mode except during the braking mode exhaust valve opening event. Thus, in the present embodiment, a reset valve
108
is designed to be maintained in an open position at all times except to create the hydraulic link within high pressure circuit
106
and actuator piston bore
110
to cause the exhaust valve to open during the braking mode event.
Specifically, reset valve
108
includes a reset plunger
114
positioned in a bore formed in rocker lever
102
to create a bias chamber
116
. Reset valve
108
, like the previous embodiment, includes a ball check valve
118
and a reset pin
120
. However, reset pin
120
extends through rocker lever
102
for abutment against reset plunger
114
. Low pressure braking fluid circuit
122
includes an actuator supply circuit
124
and a bias chamber supply circuit
126
positioned in parallel. Actuator supply circuit
124
delivers low pressure braking fluid from the supply
128
through passages
130
formed in, for example, shaft supports (not shown) for supporting support shaft
104
, transfer passages
132
formed in support shaft
104
and a passage
134
connecting passages
132
to a supply cavity
136
immediately adjacent check ball
118
. An accumulator
138
is positioned along actuator supply circuit
124
. Therefore, supply cavity
136
is continuously connected to braking fluid supply
128
. Bias chamber supply circuit
126
connects at one end to bias chamber
116
and at an opposite end to actuator supply circuit
124
via passages formed in rocker lever
102
, support shaft
104
and other engine components such as a shaft support. Importantly, reset pin
120
extends from supply cavity
136
through a sealing bore
140
into bias chamber
116
for abutment against reset plunger
114
. Reset pin
120
may be formed integrally with or separate from reset plunger
114
. Thus, as can be appreciated, supply cavity
136
is fluidically separate from bias chamber
116
. A control valve
142
, similar to that of the previous embodiment, connects bias chamber supply circuit
126
to a drain
144
during operation of the engine in normal power mode. When braking is desired, control valve
142
is energized to connect bias chamber supply circuit
126
to braking fluid supply
128
. A reset contact element
146
is mounted on an engine component, such as pedestal
148
, for abutment by reset plunger
114
. Preferably, reset contact element
146
is mounted to adjustably set the reset lash or distance between reset contact element
146
and reset plunger
114
. For example, reset contact element
146
may include a threaded bolt
150
and a threaded locknut
152
for adjustably securing bolt
150
in an axial position so that a predetermined portion of bolt
150
extends from pedestal
148
.
During operation of the embodiment shown in
FIG. 4
, with the engine operating in the normal power mode, control valve
142
is de-energized to connect bias chamber supply circuit
126
to drain
144
. Meanwhile, actuator supply circuit
124
is continuously connected to low pressure braking fluid supply
128
. As a result, bias chamber
116
is connected to the vent/drain
144
. Thus, reset check ball
118
is moved into an open position by the low pressure braking fluid in supply cavity
136
acting on reset check ball
118
in combination with the biasing force of a bias spring
154
, i.e. a leaf or coil spring, positioned between reset plunger
114
and the upper end of reset contact element
146
. Alternatively, bias spring
154
may be positioned between reset plunger
114
and rocker lever
102
. As a result, during normal power mode operation, a hydraulic link is not created in high pressure circuit
106
and thus the exhaust valves are not opened during the brake lift portion of the cam (FIG.
1
A). Moreover, reset plunger
114
does not contact reset contact element
146
during the main lift portion of the cam. When braking is desired, control valve
142
is energized to connect bias chamber supply circuit
126
to low pressure braking fluid supply
128
while blocking flow to the vent/drain
144
. Consequently, low pressure braking fluid flows through bias chamber supply circuit
126
into bias chamber
116
causing reset plunger
114
to move downwardly compressing the bias spring
154
and contacting reset contact element
146
. As a result, reset check ball
118
and reset pin
120
(if not formed integrally with reset plunger
114
) move downwardly allowing reset check ball
118
to seat in its closed position. When the cam begins the brake lift portion, the braking fluid trapped in high pressure circuit
106
and piston bore
110
creates a hydraulic link maintaining the actuator piston in an outward position and causing the exhaust valve or valves to open to allow compression relief from the combustion chamber (not shown).
The primary advantage of the system disclosed in
FIG. 4
is the ability to maintain braking fluid in the portion of the system which controls operation of the actuator piston and reset valve
108
throughout engine operation in both the power and braking modes thereby reducing the adverse affects of transients when going between the power and braking modes. Specifically, if actuator supply circuit
124
were not continuously connected to low pressure braking fluid supply
128
, e.g. communication blocked during engine operation in the power mode, air pockets may develop in the low and high pressure circuits. When switching back to the braking mode, these air pockets may then cause unpredictable braking operation until filled with fluid. The present embodiment ensures that high pressure circuit
106
, actuator piston bore
110
and actuator supply circuit
124
are continuously connected to low pressure braking fluid supply
128
thereby minimizing the likelihood of air pockets and partial fill conditions which may result in large transient loads in the system during the brake on and off events thus avoiding the delay in waiting for the passages to purge air and fill thereby ensuring more reliable operation.
FIGS. 5A and 5B
illustrate another embodiment of the present invention which is the same as the previous embodiment of
FIG. 4
except that a reset disk
170
is utilized instead of reset check ball
118
. Of course, reset disk
170
could also be used in the embodiment of
FIGS. 1A-1F
. Reset disk
170
is designed to reduce stresses at the reset disk/reset pin interface and at the reset disk/valve seat interface. The flow restriction discussed hereinabove relative to reset check ball
118
is achieved with the reset disk
170
of the present design by the use of flutes
172
formed along the outer surface of disk
170
as shown in FIG.
5
B.
FIG. 6
illustrates yet another embodiment of the reset valve, indicated generally at
180
, which is similar to the embodiment of
FIG. 4
except that a modified reset plunger and reset pin is provided. Specifically, this embodiment includes a reset plunger
182
modified to allow a reset pin
184
to slide through plunger
182
in one direction, i.e. upwardly as shown in FIG.
6
. Also, the leaf spring of the previous embodiment has been replaced by a helical coil spring
186
retained by a circular clip
188
positioned in a groove formed in the rocker lever. It should be noted that the function of spring
186
is the same as the function of the leaf spring in the embodiment of
FIG. 4
in biasing reset plunger
182
upwardly and, therefore, a leaf spring could be used in place of coil spring
186
. The operation of the assembly is essentially the same as the embodiment of
FIG. 4
, however, since reset pin
184
can slide through reset plunger
182
, there is very little fluid flow through bias chamber supply circuit
126
when in the braking mode. Specifically, during the braking lift portion of the cam, when the rocker lever is pivoted and reset pin
184
contacts reset contact element
146
, reset pin
184
moves upwardly forcing check ball
118
into an open position without requiring movement of reset plunger
182
. Therefore, braking fluid need not be pushed out of bias chamber
116
into bias chamber supply circuit
126
while reset valve
180
is being moved into the open position. In addition, this design is more compact since the pin overtravel can be accommodated. When the control valve
142
(
FIG. 4
) is de-energized for the normal power mode, reset plunger
182
moves up and positions the check ball as shown by the phantom outline in FIG.
6
. At this point, the braking fluid pressure in high pressure circuit
106
cannot increase since reset ball check
118
is held in the open position.
FIG. 7
illustrates yet another embodiment of the reset valve for use in the engine braking system illustrated in FIG.
4
. In this embodiment, the reset valve
200
still relies on the motion of the rocker lever
202
to contact a reset contacting element
204
on a pedestal
206
. However, reset valve
200
includes a reset valve element
208
of the spool valve plunger type mounted in a bore formed in the rocker lever to form a bias chamber
210
positioned at the top of the bore. Reset valve
200
also includes a spring biased reset check ball
212
positioned within spool valve plunger
208
. The bias chamber
210
is connected to a bias chamber supply circuit
214
which is the same as bias chamber supply circuit
126
of the previous embodiment. An actuator supply circuit
216
connects to the upstream side of reset check ball
212
via a lower port
218
formed in spool valve plunger
208
. An upper port
220
connects high pressure circuit
106
to a downstream side of reset check ball
212
. Thus, when operating in the braking mode, with control valve
142
(
FIG. 4
) actuated, braking fluid is supplied through bias chamber supply circuit
214
to bias chamber
210
causing spool valve plunger
208
to move downwardly as shown in
FIG. 7
thereby depressing leaf spring
154
to allow spool valve plunger
208
to contact reset contact element
204
on pedestal
206
. In this position, high pressure circuit
106
is sealed from actuator supply circuit
216
. However, if makeup braking fluid is required to fully charge high pressure circuit
106
and actuator piston bore
110
, braking fluid will flow one way through check ball valve
212
. As the cam
24
begins the brake lift portion
34
(FIG.
1
A), braking fluid pressure will increase in actuator piston bore
110
and the exhaust valve or valves will open to allow compression relief. As the spool type plunger
208
continues to move upwardly, lower port
218
will register with high pressure circuit
106
thereby relieving high pressure from actuator piston bore
110
and allowing the exhaust valve to reset, i.e. seat in the closed position as with the previous embodiments. When the control valve
142
is de-energized and the engine placed in the normal power mode, the pressure in bias chamber supply circuit
214
is reduced to substantially zero pressure to allow leaf spring
154
to lift spool type plunger
208
to the point where lower port
218
is maintained in communication with high pressure circuit
106
. Accordingly, the hydraulic link cannot be achieved in high pressure circuit
106
and actuator piston bore
110
thus preventing the actuator piston from actuating the exhaust valve during the brake lift rocker lever motion.
FIGS. 8A and 8B
illustrate yet another embodiment of the reset valve for use in the engine braking system illustrated in FIG.
4
. In this embodiment, the reset valve
300
still relies on the motion of the rocker lever (not shown) to contact a reset contacting element (not shown) mounted on the engine as shown in FIG.
4
. However, instead of utilizing low pressure braking fluid from low pressure braking fluid supply
302
to hold check ball
304
off its seat during the power mode, a detent assembly
306
engages a reset pin
308
to hold the pin
308
and check ball
304
in the position shown in FIG.
8
B. Specifically, reset pin
308
includes an elongated element having an annular recess
310
sized for engagement by detent assembly
306
. Detent assembly
306
includes a detent pin
312
positioned in a detent bore
314
and a bias spring
316
for biasing detent pin
312
toward reset pin
308
. Referring to
FIG. 8A
, when in the braking mode, control pressure from control pressure circuit
318
acts against detent pin
312
so as to move detent pin
312
to the left as shown in
FIG. 8A
against the bias force of spring
316
and out of engagement with reset pin
308
. Thus, reset pin
308
may move downwardly into contact with the reset contact element while check ball
304
moves downwardly into a seated position as discussed in the previous embodiments. Referring to
FIG. 8B
, during the power mode, control pressure in circuit
318
is vented, as discussed in the previous embodiments, causing detent pin
312
to engage annular recess
310
of reset pin
308
as reset pin
308
moves upwardly. As a result, check ball
304
is moved off its seat into the open position. Low pressure braking fluid may then flow easily between actuator supply circuit
302
and high pressure circuit
320
preventing significant pressure build-up thereby preventing the exhaust valve from opening during the brake lift portion of the cam. The primary advantages of the present embodiment utilizing detent assembly
306
includes a more compact package and a relatively small braking fluid flow required through circuit
318
during operation, i.e. basically zero during braking operation and only a small amount moved during the on/off events.
The embodiments of the present invention described hereinabove advantageously permit the use of a single rocker lever for controlling actuation of exhaust valves during both normal power mode and braking mode operation while effectively achieving optimal braking operation with a compact design in a cost effective manner. The braking system of the present invention advantageously permits braking operation utilizing a single exhaust valve in an engine having dual exhaust valves mounted on a common crosshead, while avoiding asymmetric loading of the crosshead. In addition, the present invention effectively permits resetting or closing of the exhaust valve after an initial braking mode exhaust valve opening event independent of the movement of an actuator piston thereby more predictably controlling the resetting process. Moreover, the present engine braking system effectively reduces the likelihood of partial fill conditions and air pockets in the braking fluid circuit thereby enhancing the reliability and performance of the braking system.
INDUSTRIAL APPLICABILITY
The integral rocker lever and reset valve of the present invention can be utilized in an internal combustion engine for controlling the movement of any engine member to achieve an initial movement period followed by a resetting of the member. The integral rocker lever and reset valve is particularly suited for engine compression braking systems for use in heavy duty internal combustion engines used in vehicles.
Claims
- 1. A braking system for an internal combustion engine having at least one engine piston reciprocally mounted within a cylinder for cyclical successive compression and expansion strokes and at least one exhaust valve operable to open near the end of an expansion stroke of the engine piston when the engine is operated in a power mode and operable to open in a timed relationship to the engine piston compression stroke when the engine is operated in a braking mode, said braking system comprising:a rocker lever pivotally mounted adjacent said at least one exhaust valve for opening said exhaust valve; a braking fluid circuit formed in said rocker lever and including a low pressure circuit and a high pressure circuit; a control valve positioned along said braking fluid circuit and operable in a first position to cause engine operation in said power mode and a second position to cause engine operation in said braking mode; an actuator piston bore formed in said rocker lever in communication with said high pressure circuit; an actuator piston slidably mounted in said actuator piston bore; and a reset valve mounted on said rocker lever a spaced distance from said actuator piston so as to be free from contact with said actuator piston, said reset valve operable to relieve fluid pressure from said high pressure circuit during operation in said braking mode.
- 2. The braking system of claim 1, further including a reset contact element mounted on the engine adjacent said rocker lever and positioned for contact by said reset valve during movement of said rocker lever to move said reset valve into an open position.
- 3. The braking system of claim 2, wherein said reset contact element is mounted for adjustment to vary a distance between said reset contact element and said reset valve.
- 4. The braking system of claim 2, wherein said reset valve includes a valve head positioned for abutment against a valve seat, and a reset pin positioned in abutment against said valve head.
- 5. The braking system of claim of 4, wherein said valve head is a ball and said reset pin is positioned for contact with said reset contact element.
- 6. The braking system of claim 4, wherein said reset valve includes a reset plunger positioned to contact said reset contact element, said reset pin extending between said valve head and said reset plunger.
- 7. The braking system of claim 6, further including a bias chamber receiving said reset plunger, wherein fluid pressure in said bias chamber generates pressure forces on said reset plunger to move said reset plunger toward said reset contact element to cause movement of said reset valve into a closed position.
- 8. The braking system of claim 1, wherein said reset valve is movable into a closed position to create a hydraulic link in said high pressure circuit causing opening of the exhaust valve upon movement of said rocker lever to define a braking mode exhaust valve opening event, said low pressure circuit being connected to a low pressure braking fluid supply continuously throughout the braking mode and the power mode.
- 9. The braking system of claim 2, further including a bias chamber receiving said reset valve, wherein fluid pressure in said bias chamber generates pressure forces on said reset valve to move said reset valve toward said reset contact element to cause movement of said reset valve into a closed position, said low pressure circuit including an actuator supply circuit and a bias chamber supply circuit for delivering braking fluid to said bias chamber, said reset valve controlling flow through said actuator supply circuit.
- 10. The braking system of claim 9, wherein said control valve is movable into a first position to connect said bias chamber supply circuit to a low pressure drain and a second position to connect said bias chamber supply circuit to a low pressure braking fluid supply.
- 11. The braking system of claim 1, wherein said reset valve is movable into an open position permitting communication between said high pressure circuit and said low pressure circuit, further including a detent pin positioned to hold said reset valve in said open position when the engine is operated in the power mode.
- 12. The braking system of claim 11, wherein said reset pin includes an annular recess, said detent pin sized to engage said annular recess.
- 13. A braking system for an internal combustion engine having at least one engine piston reciprocally mounted within a cylinder for cyclical successive compression and expansion strokes and at least one exhaust valve operable to open near the end of an expansion stroke of the engine piston when the engine is operated in a power mode and operable to open in a timed relationship to the engine piston compression stroke when the engine is operated in a braking mode, said braking system comprising:a rocker lever pivotally mounted adjacent said at least one exhaust valve for opening said exhaust valve; a braking fluid circuit formed in said rocker lever and including a low pressure circuit and a high pressure circuit; a control valve positioned along said braking fluid circuit and operable in a first position to cause engine operation in said power mode and a second position to cause engine operation in said braking mode; an actuator piston bore formed in said rocker lever in communication with said high pressure circuit; an actuator piston slidably mounted in said actuator piston bore; and a reset valve mounted on said rocker lever and movable between an open position permitting communication between said high pressure circuit and said low pressure circuit and a closed position blocking communication between said high pressure circuit and said low pressure circuit, wherein movement of said rocker lever causes movement of said reset valve into said open position.
- 14. The braking system of claim 13, further including a reset contact element mounted on the engine adjacent said rocker lever and positioned for contact by said reset valve during movement of said rocker lever to move said reset valve into an open position.
- 15. The braking system of claim 14, wherein said contact element is mounted for adjustment to vary a distance between said reset contact element and said reset valve.
- 16. The braking system of claim 14, wherein said reset valve includes a valve head positioned for abutment against a valve seat, and a reset pin positioned in abutment against said valve head.
- 17. The braking system of claim of 16, wherein said valve head is a ball and said reset pin is positioned for contact with said reset contact element.
- 18. The braking system of claim 16, wherein said reset valve includes a reset plunger positioned to contact said reset contact element, said reset pin extending between said valve head and said reset plunger.
- 19. The braking system of claim 18, further including a bias chamber receiving said reset plunger, wherein fluid pressure in said bias chamber generates pressure forces on said reset plunger to move said reset plunger toward said reset contact element to cause movement of said reset valve into a closed position.
- 20. The braking system of claim 13, wherein said reset valve is movable into a closed position to create a hydraulic link in said high pressure circuit causing opening of the exhaust valve upon movement of said rocker lever to define a braking mode exhaust valve opening event, said low pressure circuit being connected to a low pressure braking fluid supply continuously throughout the braking mode and the power mode.
- 21. The braking system of claim 14, further including a bias chamber receiving said reset valve, wherein fluid pressure in said bias chamber generates pressure forces on said reset valve to move said reset valve toward said reset contact element to cause movement of said reset valve into a closed position, said low pressure circuit including an actuator supply circuit and a bias chamber supply circuit for delivering braking fluid to said bias chamber, said reset valve controlling flow through said actuator supply circuit.
- 22. The braking system of claim 21, wherein said control valve is movable into a first position to connect said bias chamber supply circuit to a low pressure drain and a second position to connect said bias chamber supply circuit to a low pressure braking fluid supply.
- 23. The braking system of claim 13, further including a detent pin positioned to hold said reset valve in said open position when the engine is operated in the power mode.
- 24. The braking system of claim 23, wherein said reset pin includes an annular recess, said detent pin sized to engage said annular recess.
US Referenced Citations (14)
Foreign Referenced Citations (1)
Number |
Date |
Country |
9325803 |
Dec 1993 |
WO |