Engine compression braking apparatus utilizing a variable geometry turbocharger

A braking control for an engine permits the timing and duration of exhaust valve opening events to be accurately determined independent of engine events so that braking power can be precisely controlled. According to one embodiment, further control over braking power can be accomplished by controlling turbocharger geometry.

DESCRIPTION 
1. Technical Field 
The present invention relates generally to engine retarding systems and 
methods and, more particularly, to an apparatus and method for engine 
compression braking using electronically controlled hydraulic actuation. 
2. Background Art 
Engine brakes or retarders are used to assist and supplement wheel brakes 
in slowing heavy vehicles, such as tractor-trailers. Engine brakes are 
desirable because they help alleviate wheel brake overheating. As vehicle 
design and technology have advanced, the hauling capacity of 
tractor-trailers has increased, while at the same time rolling resistance 
and wind resistance have decreased. Thus, there is a need for advanced 
engine braking systems in today's heavy vehicles. 
Problems with existing engine braking systems include high noise levels and 
a lack of smooth operation at some braking levels resulting from the use 
of less than all of the engine cylinders in a compression braking scheme. 
Also, existing systems are not readily adaptable to differing road and 
vehicle conditions. Still further, existing systems are complex and 
expensive. 
Known engine compression brakes convert an internal combustion engine from 
a power generating unit into a power consuming air compressor. 
U.S. Pat. No. 3,220,392 issued to Cummins on Nov. 30, 1965, discloses an 
engine braking system in which an exhaust valve located in a cylinder is 
opened when the piston in the cylinder nears the top dead center (TDC) 
position on the compression stroke. An actuator includes a master piston, 
driven by a cam and push rod, which in turn drives a slave piston to open 
the exhaust valve during engine braking. The braking that can be 
accomplished by the Cummins device is limited because the timing and 
duration of the opening of the exhaust valve is dictated by the geometry 
of the cam which drives the master piston and hence these parameters 
cannot be independently controlled. 
In conjunction with the increasingly widespread use of electronic controls 
in engine systems, braking systems have been developed which are 
electronically controlled by a central engine control unit which optimizes 
the performance of the braking system. 
U.S. Pat. No. 5,012,778 issued to Pitzi on May 7, 1991, discloses an engine 
braking system which includes a solenoid actuated servo valve 
hydraulically linked to an exhaust valve actuator. The exhaust valve 
actuator comprises a piston which, when subjected to sufficient hydraulic 
pressure, is driven into contact with a contact plate attached to an 
exhaust valve stem, thereby opening the exhaust valve. An electronic 
controller activates the solenoid of the servo valve. A group of switches 
are connected in series to the controller and the controller also receives 
inputs from a crankshaft position sensor and an engine speed sensor. 
U.S. Pat. No. 5,255,650 issued to Faletti et al. on Oct. 26, 1993, and 
assigned to the assignee of the present application, discloses an 
electronic control system which is programmed to operate the intake 
valves, exhaust valves, and fuel injectors of an engine according to two 
predetermined logic patterns. According to a first logic pattern, the 
exhaust valves remain closed during each compression stroke. According to 
a second logic pattern, the exhaust valves are opened as the piston nears 
the TDC position during each compression stroke. The opening position, 
closing position, and the valve lift are all controlled independently of 
the position of the engine crankshaft. 
U.S. Pat. No. 4,572,114 issued to Sickler on Feb. 25, 1986, discloses an 
electronically controlled engine braking system. A pushtube of the engine 
reciprocates a rocker arm and a master piston so that pressurized fluid is 
delivered and stored in a high pressure accumulator. For each engine 
cylinder, a three-way solenoid valve is operable by an electronic 
controller to selectively couple the accumulator to a slave bore having a 
slave piston disposed therein. The slave piston is responsive to the 
admittance of the pressurized fluid from the accumulator into the slave 
bore to move an exhaust valve crosshead and thereby open a pair of exhaust 
valves. The use of an electronic controller allows braking performance to 
be maximized independent of restraints resulting from mechanical 
limitations. Thus, the valve timing may be varied as a function of engine 
speed to optimize the retarding horsepower developed by the engine. 
A number of patents disclose the use of a turbocharger with an engine 
operable in a braking mode. For example, Pearman et al. U.S. Pat. No. 
4,688,384, Davies et al. U.S. Pat. No. 5,410,882 and Custer U.S. Pat. No. 
5,437,156 disclose compression release engine braking systems wherein the 
intake manifold pressure of the engine is controlled so that excessive 
stresses in the engine and engine brake are prevented. The Pearman et al. 
and Custer patents disclose the use of pressure release apparatus 
connected directly to the intake manifold whereas the system disclosed in 
the Davies et al. patent retards the turbocharger in any of a number of 
ways, such as by restricting the flow of exhaust gas to or from the 
turbocharger or by controlling the exhaust gas flow to bypass the 
turbocharger. 
Meneely U.S. Pat. No. 4,932,372 likewise discloses the use of a 
turbocharger with an engine operable in a braking mode. In addition to the 
mechanism for opening each exhaust valve of each cylinder of the engine 
near top dead center of each compression stroke, the Meneely apparatus 
includes means for increasing the pressure of gases in the exhaust 
manifold sufficiently to open exhaust valves of other cylinders on the 
intake stroke after each exhaust valve on the compression stroke is so 
opened. Such means comprises a device within the turbocharger for 
diverting the exhaust gases to a restricted portion of the turbine nozzle, 
thereby increasing the pressure of gases directed onto the turbine blades 
of the turbocharger and causing back pressure to be developed in the 
exhaust manifold. 
In each of the foregoing systems, controllability over engine braking 
levels is accomplished by varying boost magnitude alone inasmuch as the 
timing and duration of exhaust valve opening events are preset by 
establishing the lash between the exhaust valve actuator and the exhaust 
valve accomplished by varying boost magnitude alone inasmuch as the timing 
and duration of exhaust valve opening events are preset by establishing 
the lash between the exhaust valve actuator and the exhaust valve 
crosshead. Accordingly, only a limited degree of variability in braking 
magnitude can be accomplished. 
DISCLOSURE OF THE INVENTION 
A brake control according to the present invention permits high braking 
levels to be achieved and affords a high degree of controllability over 
engine braking. 
More particularly, a brake control for an engine having a variable geometry 
turbocharger which is controllable to vary intake manifold pressure and 
wherein the engine is operable in a braking mode includes a turbocharger 
geometry actuator for varying turbocharger geometry and an exhaust valve 
actuator for opening an exhaust valve of the engine. Means are operable 
while the engine is in the braking mode and responsive to a command 
representing a desired load condition for operating the turbocharger 
geometry actuator and the exhaust valve actuator. 
Preferably, the operating means is implemented by an engine control module 
responsive to an engine condition. Also preferably, the operating means 
includes a look-up table responsive to engine speed and the command and 
developing a first signal representing commanded turbocharger geometry. 
The operating means may further include an additional look-up table 
responsive to the first signal for developing a second signal for 
operating the turbocharger geometry actuator. Still further, the operating 
means preferably includes means for providing means includes a third 
look-up table responsive to engine speed and the command. 
In accordance with further alternative embodiments, the command comprises a 
braking magnitude signal or a speed magnitude signal. In the latter event, 
the operating means is responsive to an actual speed signal representing 
actual load speed and further includes a summer for developing a 
difference signal representing a magnitude difference between the speed 
magnitude signal and the actual speed signal. 
In accordance with yet another alternative embodiment, the operating means 
includes a look-up table responsive to engine speed and the command and 
develops an operating signal for the exhaust valve actuator. In this 
embodiment, the operating means may further include a circuit which 
develops an additional operating signal at a constant magnitude for the 
turbocharger geometry actuator. 
According to another aspect of the present invention, a brake control for 
an engine including a variable geometry turbocharger having vanes that are 
movable to vary engine intake manifold pressure and wherein the engine is 
operable in a braking mode during which each of a plurality of engine 
exhaust valves is opened to allow compressed gases in an associated 
combustion chamber to escape during a compression stroke and thereby brake 
a vehicle propelled by the engine includes a vane actuator for varying 
turbocharger geometry and a plurality of exhaust valve actuators each for 
opening an associated exhaust valve. An engine control is operable while 
the engine is in the braking mode and is responsive to a sensed engine 
condition and an operator command representing a desired vehicle condition 
for variably operating both the vane actuator and the exhaust valve 
actuator. 
In accordance with yet another aspect of the present invention, a brake 
control for an engine having an intake manifold and operable in a braking 
mode during which an engine exhaust valve is opened to allow compressed 
gases in an associated combustion chamber to escape during a compression 
stroke and thereby brake a load driven by the engine includes means for 
controlling at least one of intake and exhaust manifold pressure of the 
engine and an exhaust valve actuator for opening the exhaust valve. Means 
are operable while the engine is in the braking mode and are responsive to 
a command representing a desired load condition for operating the 
controlling means and the exhaust valve actuator such that the exhaust 
valve is opened at a selectable timing and for a selectable duration. 
Other features and advantages are inherent in the apparatus claimed and 
disclosed or will become apparent to those skilled in the art from the 
following detailed description in conjunction with the accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to FIGS. 1-3, an internal combustion engine 30, which may be 
of the four-cycle, compression ignition type, undergoes a series of engine 
events during operation thereof. In the preferred embodiment, the engine 
sequentially and repetitively undergoes intake, compression, expansion and 
exhaust cycles during operation. As seen in FIGS. 2 and 3, the engine 30 
includes a block 32 within which is formed a plurality of combustion 
chambers or cylinders 34, each of which includes an associated piston 36 
therein. Intake valves 38 and exhaust valves 40 are carried in a head 41 
bolted to the block 32 and are operated to control the admittance and 
expulsion of fuel and gases into and out of each cylinder 34. A crankshaft 
42 is coupled to and rotated by the pistons 36 via connecting rods 44 and 
a camshaft 46 is coupled to and rotates with the crankshaft 42 in 
synchronism therewith. The camshaft 46 includes a plurality of cam lobes 
48 (one of which is visible in FIG. 3) which are contacted by cam 
followers 50 (FIG. 3) carried by rocker arms 54, 55 which in turn bear 
against intake and exhaust valves 38, 40, respectively. 
In the engine 30 shown in FIGS. 2 and 3, there are a pair of intake valves 
38 and a pair of exhaust valves 40 per cylinder 34 wherein the valves of 
each pair 38 or 40 are interconnected by a valve bridge 39 or 43, 
respectively. Each cylinder 34 may instead have a different number of 
associated intake and exhaust valves 38, 40, as necessary or desirable. 
The graphs of FIGS. 4 and 5A illustrate cylinder pressure and braking 
horsepower, respectively, as a function of crankshaft angle relative to 
top dead center (TDC). As seen in FIG. 4, during operation in a braking 
mode, the exhaust valves 40 of each cylinder 34 are opened at a time 
t.sub.1 prior to TDC so that the work expended in compressing the gases 
within the cylinder 34 is not recovered by the crankshaft 42. The 
resulting effective braking by the engine is proportional to the 
difference between the area under the curve 62 prior to TDC and the area 
under the curve 62 after TDC. This difference, and hence the effective 
braking, can be changed by changing the timing t.sub.1 at which the 
exhaust valves 40 are opened during the compression stroke. This 
relationship is illustrated by the graph of FIG. 5A. 
As seen in FIG. 5B, the duration of time the exhaust valves are maintained 
in an open state also has an effect upon the maximum braking horsepower 
which can be achieved. Still further, engine braking magnitude can also be 
controlled by varying engine intake and/or exhaust pressure. According to 
one embodiment of the present invention, this can be accomplished by 
controlling a turbocharger 63 (FIG. 1), as noted in greater detail 
hereinafter. 
With reference now to FIG. 6, a two-cylinder portion 70 of a brake control 
according to the present invention is illustrated. The portion 70 of the 
brake control illustrated in FIG. 6 is operated by an electronic control 
module (ECM) 72 to open the exhaust valves 40 of two cylinders 34 with a 
selectable timing and duration of exhaust valve opening. For a six 
cylinder engine, up to three of the portions 70 in FIG. 6 could be 
connected to the ECM 72 so that engine braking is accomplished on a 
cylinder-by-cylinder basis. Alternatively, fewer than three portions 70 
could be used and/or operated so that braking is accomplished by less than 
all of the cylinders and pistons. Also, it should be noted that the 
portion 70 can be modified to operate any other number of exhaust valves 
for any other number of cylinders, as desired. 
The ECM 72 operates a solenoid control valve 74 to couple a conduit 76 to a 
conduit 78. The conduit 76 receives engine oil at supply pressure, and 
hence operating the solenoid control valve 74 permits engine oil to be 
delivered to conduits 80, 82 which are in fluid communication with check 
valves 84, 86, respectively. The engine oil under pressure causes pistons 
of a pair of reciprocating pumps 88, 90 to extend and contact drive 
sockets of injector rocker arms (described and shown below). The rocker 
arms reciprocate the pistons and cause oil to be supplied under pressure 
through check valves, 92, 94 and conduits 96, 98 to an accumulator 100. As 
such pumping is occurring, oil continuously flows through the conduits 80 
and 82 to refill the pumps 88, 90. 
In the preferred embodiment, the accumulator 100 does not include a movable 
member, such as a piston or bladder, although such a movable member could 
be included therein, if desired. Further, the accumulator includes a 
pressure control valve 104 which vents engine oil to sump when a 
predetermined pressure is exceeded, for example 6,000 p.s.i. 
The conduit 96 and accumulator 100 are further coupled to a pair of 
solenoid control valves 106, 108 and a pair of servo-actuators 110, 112. 
The servo-actuators 110, 112 are coupled by conduits 114, 116 to the pumps 
88, 90 via the check valves 84, 86, respectively. The solenoid control 
valves 106, 108 are further coupled by conduits 118, 120 to sump. 
As noted in greater detail hereinafter, when operation in the braking mode 
is selected by an operator, the ECM 72 closes the solenoid control valve 
74 and operates the solenoid control valves 106, 108 to cause the 
servo-actuators 110, 112 to contact valve bridges 43 and open associated 
exhaust valves 40 in associated cylinders 34 near the end of a compression 
stroke. It should be noted that the control of FIG. 6 may be modified such 
that a different number of cylinders is serviced by each accumulator. In 
fact, by providing an accumulator with sufficient capacity, all of the 
engine cylinders may be served thereby. 
Also when operation in the braking mode is selected, the ECM 72 operates an 
intake and/or exhaust pressure controller 125 to controllably vary the 
pressure in the intake and/or exhaust manifolds of the engine. By 
controlling such pressure(s), and thus the air pressure in the engine 
cylinders, a high degree of controllability over engine braking magnitude 
can be achieved. 
FIGS. 7-11 illustrate mechanical hardware for implementing the control of 
FIG. 6. Referring first to FIGS. 7, 8 and 11, a main body 132 includes a 
bridging portion 134. Threaded studs 135 extend through the main body 132 
and spacers 136 into the head 41 and nuts 137 are threaded onto the studs 
135. In addition, four bolts 138 extend through the main body 132 into the 
head 41. The bolts 138 replace rocker arm shaft hold down bolts and not 
only serve to secure the main body 132 to the head 41, but also extend 
through and hold a rocker arm shaft 139 in position. 
Two actuator receiving bores 140 (only one of which is shown) are formed in 
the bridging portion 134. The servo-actuator 110 is received within the 
actuator receiving bore 140 while the servo-actuator 112 (not shown in 
FIGS. 7-11) is received within the other receiving bore. Inasmuch as the 
actuators 110 and 112 are identical, only the actuator 110 will be 
described in greater detail hereinafter. 
FIGS. 9-11 illustrate the servo-actuator 110 in greater detail. A passage 
148 (also seen in FIG. 8) receives high pressure engine oil from the 
accumulator 100 (FIG. 8). The passage 148 is in fluid communication with 
passages 170, 172 leading to the actuator receiving bore 140 and a valve 
bore 174, respectively. A ball valve 176 is disposed within the valve bore 
174. The solenoid control valve 106 is disposed adjacent the ball valve 
176 and includes a solenoid winding shown schematically at 180, an 
armature 182 adjacent the solenoid winding 180 and in magnetic circuit 
therewith and a load adapter 184 secured to the armature 182 by a screw 
186. The armature 182 is movable in a recess defined in part by the 
solenoid winding 180, an armature spacer 185 and a further spacer 187. The 
solenoid winding 180 is energizable by the ECM 72, as noted in greater 
detail hereinafter, to move the armature 182 and the load adapter 184 
against the force exerted by a return spring illustrated schematically at 
188 and disposed in a recess 189 located in a solenoid body 191. 
The ball valve includes a rear seat 190 having a passage 192 therein in 
fluid communication with the passage 172 and a sealing surface 194. A 
front seat 196 is spaced from the rear seat 190 and includes a passage 198 
leading to a sealing surface 200. A ball 202 resides in the passage 198 
between the sealing surfaces 194 and 200. The passage 198 comprises a 
counterbore having a portion 201 which has been cross-cut by a keyway 
cutter to provide an oil flow passage to and from the ball area. 
A passage 204 (seen in phantom in FIGS. 9 and 11) extends from a bore 206 
(FIGS. 9 and 10) containing the front seat 196 to an upper portion 208 of 
the receiving bore 140. As seen in FIG. 11, the receiving bore 140 further 
includes an intermediate portion 210 which closely receives a master fluid 
control device in the form of a valve spool 212 having a seal 214 which 
seals against the walls of the intermediate portion 210. The seal 214 is 
commercially available and is of two-part construction including a carbon 
fiber loaded teflon ring backed up and pressure loaded by an O-ring. The 
valve spool 212 further includes an enlarged head 216 which resides within 
a recess 218 of a lash stop adjuster 220. The lash stop adjuster 220 
includes external threads which are engaged by a threaded nut 222 which, 
together with a washer 224, are used to adjust the axial position of the 
lash stop adjuster 220. The washer 224 is a commercially available 
composite rubber and metal washer which not only loads the adjuster 220 to 
lock the adjustment, but also seals the top of the actuator 110 and 
prevents oil leakage past the nut 222. 
A slave fluid control device in the form of a piston 226 includes a central 
bore 228, seen in FIGS. 11-13, which receives a lower end of the spool 
212. A spring 230 is placed in compression between a snap ring 232 carried 
in a groove in the spool 212 and an upper face of the piston 226. A return 
spring, shown schematically at 234, is placed in compression between a 
lower face of the piston 226 and a washer 236 placed in the bottom of a 
recess defined in part by an end cap 238. An actuator pin 240 is 
press-fitted within a lower portion of the central bore 228 so that the 
piston 226 and the actuator pin 240 move together. The actuator pin 240 
extends outwardly through a bore 242 in the end cap 238 and an O-ring 244 
prevents the escape of oil through the bore 242. In addition, a swivel 
foot 246 is pivotally secured to an end of the actuator pin 240. 
The end cap 238 is threaded within a threaded portion 247 of the receiving 
bore 140 and an O-ring 248 provides a seal against leakage of oil. 
As seen in FIG. 8, an oil return passage 250 extends between a lower recess 
portion 252, defined by the end cap 238, and the piston 226 and a pump 
inlet passage 160 which is in fluid communication with the inlet of the 
pump 88 (also see FIG. 6). 
In addition to the foregoing, as seen in FIGS. 9, 12 and 13, an oil passage 
254 is disposed between the lower recess portion 252 and a space 256 
between the valve spool 212 and the actuator pin 240 to prevent hydraulic 
lock between these two components. 
FIGS. 12 and 13 are composite sectional views which aid in understanding 
the operation of the actuator 110. When braking is commanded by an 
operator and the solenoid 74 is actuated by the ECM 72, oil is supplied to 
the inlet passage 160 (seen in FIGS. 6 and 8). As seen in FIG. 6, the oil 
flows at supply pressure past the check valve 84 into the pump 88. The 
pump 88 moves downwardly into contact with a fuel injector rocker arm. 
Reciprocation of the rocker arm causes the oil to be pressurized and 
delivered to the passage 148. The pressurized oil is thus delivered 
through the passage 172 and the passage 192 in the rear seat 190, as seen 
in FIG. 12. 
When the ECM 72 commands opening of the exhaust valves 40 of a cylinder 34, 
the ECM 72 energizes the solenoid winding 180, causing the armature 182 
and the load adapter 184 to move to the right as seen in FIG. 12 against 
the force of the return spring 188. Such movement permits the ball 202 to 
also move to the right into engagement with the sealing surface 200 (FIG. 
10) under the influence of the pressurized oil in the passage 192, thereby 
permitting the pressurized oil to pass in the space between the ball 202 
and the sealing surface 194. The pressurized oil flows through the passage 
198 and the bore 206 into the passage 204 and the upper portion 208 of the 
receiving bore 140. The high fluid pressure on the top of the valve spool 
212 causes it to move downwardly. The spring rate of the spring 230 is 
selected to be substantially higher than the spring rate of the return 
spring 234, and hence movement of the valve spool 212 downwardly tends to 
cause the piston 226 to also move downwardly. Such movement continues 
until the swivel foot takes up the lash and contacts the exhaust rocker 
arm 55. At this point, further travel of the piston 226 is temporarily 
prevented owing to the cylinder compression pressures on the exhaust 
valves 40. However, the high fluid pressure exerted on the top of the 
valve spool 212 is sufficient to continue moving the valve spool 212 
downwardly against the force of the spring 230. Eventually, the relative 
movement between the valve spool 212 and the piston 226 causes an outer 
high pressure annulus 258 and a high pressure passage 260 (FIGS. 9, 12 and 
13) in fluid communication with the passage 170 to be placed in fluid 
communication with a piston passage 262 via an inner high pressure annulus 
264. Further, a low pressure annulus 266 of the spool 212 is taken out of 
fluid communication with the piston passage 262. 
The high fluid pressure passing through the piston passage 262 acts on the 
large diameter of the piston 226 so that large forces are developed which 
cause the actuator pin 240 and the swivel foot 246 to overcome the 
resisting forces of the compression pressure and valve spring load exerted 
by valve springs 267 (FIG. 7). As a result, the exhaust valves 40 open and 
allow the cylinder to start blowing down pressure. During this time, the 
valve spool 212 travels with the piston 226 in a downward direction until 
the enlarged head 216 of the valve spool 212 contacts a lower portion 270 
of the lash stop adjuster 220. At this point, further travel of the valve 
spool 212 in the downward direction is prevented while the piston 226 
continues to move downwardly. As seen in FIG. 13, the inner high pressure 
annulus 264 is eventually covered by the piston 226 and the low pressure 
annulus 266 is uncovered. The low pressure annulus 266 is coupled by a 
passage 268 (FIGS. 9, 12 and 13) to the lower recess portion 252 which, as 
noted previously, is coupled by the oil return passage 250 to the pump 
inlet 160. Hence, at this time, the piston passage 262 and the upper face 
of the piston 226 are placed in fluid communication with low pressure oil. 
High pressure oil is vented from the cavity above the piston 226 and the 
exhaust valves 40 stop in the open position. 
Thereafter, the piston 226 slowly oscillates between a first position, at 
which the inner high pressure annulus 264 is uncovered, and a second 
position, at which the low pressure annulus 266 is uncovered, to maintain 
the exhaust valves 40 in the open position as the cylinder 34 blows down. 
During the time that the exhaust valves 40 are in the open position, the 
ECM 72 provides drive current according to a predetermined schedule to 
provide good coil life and low power consumption. 
When the exhaust valves 40 are to be closed, the ECM 72 terminates current 
flow in the solenoid winding 180. The return spring 188 then moves the 
load adapter 184 to the left as seen in FIGS. 12 and 13 so that the ball 
202 is forced against the sealing surface 194 of the rear seat 190. The 
high pressure fluid above the valve spool 212 flows back through the 
passage 204, the bore 206, a gap 274 between the load adapter 184 and the 
front seat 196 and a passage 276 to the oil sump. In response to the 
venting of high pressure oil, the valve spool 212 is moved upwardly under 
the influence of the spring 230. As the valve spool 212 moves upwardly, 
the low pressure annulus 266 is uncovered and the high pressure annulus 
258 is covered by the piston 226, thereby causing the high pressure oil 
above the piston 226 to escape through the passage 268. The return spring 
234 and the exhaust valve springs 267 force the piston 226 upwardly and 
the exhaust valves 40 close. The closing velocity is controlled by the 
flow rate past the ball 202 into the passage 276. The valve spool 212 
eventually seats against an upper surface 280 of the lash stop adjuster 
220 and the piston 226 returns to the original position as a result of 
venting of oil through the inner high pressure annulus 264 and the low 
pressure annulus 266 such that the passage 268 is in fluid communication 
with the latter. As should be evident to one of ordinary skill in the art, 
the stopping position of the piston 226 is dependent upon the spring rates 
of the springs 230, 234. Oil remaining in the lower recess portion 252 is 
returned to the pump inlet 160 via the oil return passage 250. 
The foregoing sequence of events is repeated each time the exhaust valves 
40 are opened. 
When the braking action of the engine is to be terminated, the ECM 72 
closes the solenoid valve 74 and rapidly cycles the solenoid control valve 
106 (and the other solenoid control valves) a predetermined number of 
cycles to vent off the stored high pressure oil to sump. 
FIGS. 14 and 15 illustrate the ECM 72 in greater detail as well as the 
wiring interconnections between the ECM 72 and a plurality of 
electronically controlled unit fuel injectors 300a-300f, which are 
individually operated to control the flow of fuel into the engine 
cylinders 34, and the solenoid control valves of the present invention, 
here illustrated as including the solenoid control valves 106, 108 and 
additional solenoid valves 301a-301d. Of course, the number of solenoid 
control valves would vary from that shown in FIG. 14 in dependence upon 
the number of cylinders to be used in engine braking. The ECM 72 includes 
six solenoid drivers 302a-302f, each of which is coupled to a first 
terminal of and associated with one of the injectors 300a-300f and one of 
the solenoid control valves 106, 108 and 301a-301d, respectively. Four 
current control circuits 304, 306, 308 and 310 are also included in the 
ECM 72. The current control circuit 304 is coupled by diodes D1-D3 to 
second terminals of the unit injectors 300a-300c, respectively, while the 
current control circuit 306 is coupled by diodes D4-D6 to second terminals 
of the unit injectors 300d-300f, respectively. In addition, the current 
control circuit 308 is coupled by diodes D7-D9 to second terminals of the 
brake control solenoids 106, 108 and 301a, respectively, whereas the 
current control circuit 310 is coupled by diodes D10-D12 to second 
terminals of the brake control solenoids 301b-301d, respectively. Further, 
a solenoid driver 312 is coupled to the solenoid 74. 
In order to actuate any particular device 300a-300f, 106, 108 or 301a-301d, 
the ECM 72 need only actuate the appropriate driver 302a-302f and the 
appropriate current control circuit 304-310. Thus, for example, if the 
unit injector 300a is to be actuated, the driver 302a is operated as is 
the current control circuit 304 so that a current path is established 
therethrough. Similarly, if the solenoid control valve 301d is to be 
actuated, the driver 302f and the current control circuit 310 are operated 
to establish a current path through the control valve 301d. In addition, 
when one or more of the control valves 106, 108 or 301a-301d are to be 
actuated, the solenoid driver 312 is operated to deliver current to the 
solenoid 74, except when the solenoid control valve 106 is rapidly cycled 
as noted above. 
It should be noted that when the ECM 72 is used to operate the fuel 
injectors 300a-300f alone and the brake control solenoids 106, 108 and 
301a-301d are not included therewith, a pair of wires are connected 
between the ECM 72 and each injector 300a-300f. When the brake control 
solenoids 106, 108 and 301a-301d are added to provide engine braking 
capability, the only further wires that must be added are a jumper wire at 
each cylinder interconnecting the associated brake control solenoid and 
fuel injector and a return wire between the second terminal of each brake 
control solenoid and the ECM 72. The diodes D1-D12 permit multiplexing of 
the current control circuits 304-310; i.e., the current control circuits 
304-310 determine whether an associated injector or brake control is 
operating. Also, the current versus time wave shapes for the injectors 
and/or solenoid control valves are controlled by these circuits. 
FIG. 15 illustrates the balance of the ECM 72 in greater detail, and, in 
particular, circuits for commanding proper operation of the drivers 
302a-302f and the current control circuits 304, 306, 308 and 310. The ECM 
72 is responsive to the output of a select switch 330, a cam wheel 332 and 
a sensor 334 and a drive shaft gear 336 and a sensor 338. The ECM 72 
develops drive signals on lines 340a-340j which are provided to the 
drivers 302a-302f and to the current control circuits 304, 306, 308 and 
310, respectively, to properly energize the windings of the solenoid 
control valves 106, 108 and 301a-301d. In addition, a signal is developed 
on a line 341 which is supplied to the solenoid driver 312 to operate 
same. The select switch 330 may be manipulated by an operator to select a 
desired magnitude of braking, for example, in a range between zero and 
100% braking. The output of the select switch 330 is passed to a high wins 
circuit 342 in the ECM 72, which in turn provides an output to a braking 
control module 344 that is selectively enabled by a block 345 when engine 
braking is to occur, as described in greater detail hereinafter. The 
braking control module 344 further receives an engine position signal 
developed on a line 346 by the cam wheel 332 and the sensor 334. The cam 
wheel is driven by the engine camshaft 46 (which is in turn driven by the 
crankshaft 42 as noted above) and includes a plurality of teeth 348 of 
magnetic material, three of which are shown in FIG. 15, and which pass in 
proximity to the sensor 334 as the cam wheel 332 rotates. The sensor 334, 
which may be a Hall effect device, develops a pulse type signal on the 
line 346 in response to passage of the teeth 348 past the sensor 334. The 
signal on the line 346 is also provided to a cylinder select circuit 350 
and a differentiator 352. The differentiator 352 converts the position 
signal on the line 346 into an engine speed signal which, together with 
the cylinder select circuit 350 and the signal developed on the line 346, 
instruct the braking control module 344, when enabled, to provide control 
signals on the lines 340a-340f with the proper timing. Further, when the 
braking control module 344 is enabled, a signal is developed on the line 
341 to activate the solenoid driver 312 and the solenoid 74. 
The sensor 338 detects the passage of teeth on the gear 336 and develops a 
vehicle speed signal on a line 354 which is provided to a noninverting 
input of a summer 356. An inverting input of the summer 356 receives a 
commanded speed signal on a line 358 representing a desired or commanded 
speed for the vehicle. The signal on the line 358 may be developed by a 
cruise control or any other speed setting device. The resulting error 
signal developed by the summer 356 is provided to the high wins circuit 
342 over a line 360. The high wins circuit 342 provides the signal 
developed by the select switch 330 or the error signal on the line 360 to 
the braking control module 344 as a signal % BRAKING on a line 361 in 
dependence upon which signal has the higher magnitude. If the error signal 
developed by the summer 356 is negative in sign and the signal developed 
by the select switch 330 is at a magnitude commanding no (or 0%) braking, 
the high wins circuit 342 instructs the braking control module 344 to 
terminate engine braking. 
If desired, the high wins circuit 342 may be omitted, and the signal on the 
line 361 may be supplied by the select switch 330, the summer 356 or the 
cruise control on the line 358. 
A boost control module 362 is responsive to the signal % BRAKING on the 
line 361 and is further responsive to a signal, called BOOST, developed by 
a sensor 364 on a line 365 which detects the magnitude of engine intake 
manifold air pressure. In the preferred embodiment, the turbocharger 63 
has a variable nozzle geometry which can be controlled by a vane actuator 
366 to allow boost level to be controlled by the boost control module 362. 
The module 362 may receive a limiter signal on a line 368 developed by the 
braking control module 344 which allows for as much boost as the 
turbocharger 366 can develop under the current engine conditions but 
prevents the boost control module from increasing boost to a level which 
would cause damage to engine components. 
The braking control module includes a look-up table or map 370 which is 
addressed by the signal developed at the output of the differentiator 352 
and the signal on the line 361 and provides output signals DEG. ON and 
DEG. OFF to the control of FIG. 17. FIG. 16 illustrates in three 
dimensional form the contents of the map 370 including the output signals 
DEG. ON and DEG. OFF as a function of the addressing signals ENGINE SPEED 
and % BRAKING. The signals DEG. ON and DEG. OFF indicate the timing of 
solenoid control valve actuation and deactuation, respectively, in degrees 
after a cam marker signal is produced by the cam wheel 332 and the sensor 
334. Specifically, the cam wheel 332 includes twenty-four teeth, 
twenty-one of which are identical to one another and each of which 
occupies 80% of a tooth pitch with a 20% gap. Two of the remaining three 
teeth are adjacent to one another (i.e., consecutive) while the third is 
spaced therefrom and each occupies 50% of a tooth pitch with a 50% gap. 
The ECM 72 detects these non-uniformities to determine when cylinder 
number 1 of the engine 30 reaches TDC between compression and power 
strokes as well as engine rotation direction. 
The signal DEG ON is provided to a computational block 372 which is 
responsive to the engine speed signal developed by the block 352 of FIG. 
15 and which develops a signal representing the time after a reference 
point or marker on the cam wheel 332 passes the sensor 334 at which a 
signal on one of the lines 340a-340f is to be switched to a high state. In 
like fashion, a computational block 374 is responsive to the engine speed 
signal developed by the block 352 and develops a signal representing the 
time after the reference point passes the sensor 334 at which the signal 
on the same line 340a-340f is to be switched to an off state. The signals 
from the blocks 372, 374 are supplied to delay blocks 376, 378, 
respectively, which develop on and off signals for a solenoid driver block 
380 in dependence upon the marker developed by the cam wheel 332 and the 
sensor 334 and in dependence upon the particular cylinder which is to be 
employed next in braking. The signal developed by the delay block 376 
comprises a narrow pulse having a leading edge which causes the solenoid 
driver block 380 to develop an output signal having a transition from a 
low state to a high state whereas the timer block 378 develops a narrow 
pulse having a leading edge which causes the output signal developed by 
the solenoid driver circuit 380 to switch from a high state to a low 
state. The signal developed by solenoid driver circuit 380 is routed to 
the appropriate output line 340a-340f by a cylinder select switch 382 
which is responsive to the cylinder select signal developed by the block 
350 of FIG. 15. 
The braking control module 344 is enabled by the block 345 in dependence 
upon certain sensed conditions as detected by sensors/switches 383. The 
sensors/switches include a clutch switch 383a which detects when a clutch 
of the vehicle is engaged by an operator (i.e., when the vehicle wheels 
are disengaged from the vehicle engine), a throttle position switch 383b 
which detects when a throttle pedal is depressed, an engine speed sensor 
383c which detects the speed of the engine, a service brake switch 383d 
which develops a signal representing whether the service brake pedal of 
the vehicle is depressed, a cruise control on/off switch 383e and a brake 
on/off switch 383f. If desired, the output of the circuit 352 may be 
supplied in lieu of the signal developed by the sensor 383c, in which case 
the sensor 383c may be omitted. According to a preferred embodiment of the 
present invention, the braking control module 344 is enabled when the 
on/off switch 383f is on, the engine speed is above a particular level, 
for example 950 rpm, the driver's foot is off the throttle and clutch and 
the cruise control is off. The braking control module 344 is also enabled 
when the on/off switch 383f is on, engine speed is above the certain 
level, the driver's foot is off the throttle and clutch, the cruise 
control is on and the driver depresses the service brake. Under the second 
set of conditions, and also in accordance with the preferred embodiment, a 
"coast" mode may be employed wherein engine braking is engaged only while 
the driver presses the service brake, in which case the braking control 
module 344 is disabled when the driver's foot is removed from the service 
brake. According to an optional "latched" mode of operation operable under 
the second set of conditions as noted above, the braking control module 
344 is enabled by the block 345 once the driver presses the service brake 
and remains enabled until another input, such as depressing the throttle 
or selecting 0% braking by means of the switch 330, is supplied. 
The block 345 enables an injector control module 384 when the braking 
control module 344 is disabled, and vice versa. The injector control 
module 384 supplies signals over the lines 340a-340f as well as over lines 
340g and 340h to the current control circuits 304 and 306 of FIG. 14 so 
that fuel injection is accomplished. 
Referring again to FIG. 17, the signal developed by the solenoid driver 
circuit 380 is also provided to a current control logic block 386 which in 
turn supplies signals on lines 340i, 340j of appropriate waveshape and 
synchronization with the signals on the lines 340a-340f to the blocks 308 
and 310 of FIG. 14. Programming for effecting this operation is completely 
within the abilities of one of ordinary skill in the art and will not be 
described in detail herein. 
FIG. 18 illustrates the boost control module 362 in greater detail. The 
module 362 includes a braking boost control 390 and a fueling boost 
control 392 which are coupled to a select switch 394. The select switch 
394 is responsive to one or both of the signals developed by the block 345 
of FIG. 15 to pass either a signal developed by the braking boost control 
390 on a line 396 or a signal developed on a line 398 by the fueling boost 
control 392 to the vane actuator 366 at FIG. 15 in dependence upon whether 
braking or fueling (i.e., normal) operation is commanded. 
The braking boost control 390 includes a look-up table or map 400 which 
develops a vane position signal in response to addressing thereof by the % 
BRAKING signal on the line 361 and the signal representing engine speed as 
developed by the differentiator 354 of FIG. 15. The vane position signal 
is passed to a further look-up table 402 which develops an actuator 
voltage signal as a function of the vane position signal developed by the 
look-up table 400. The actuator voltage signal may be limited at vane 
position signal magnitudes in excess of a given level, as shown by the 
dotted lines 404. The limit may be set at a constant magnitude or may be 
variably and/or adaptively established by the signal on the line 368. The 
look-up table 402 supplies the signal over the line 396 to the select 
switch 394. 
If desired, the open loop control strategy implemented by the braking boost 
control 390 shown in FIG. 18 may be replaced by a closed loop strategy 
wherein the vane position signal developed by the look-up table 400 is 
summed with a signal representing actual vane position to develop an error 
signal which is used as the input to the look-up table 402. 
The fueling boost control circuit 392 is responsive to a number of 
parameters, including engine speed, as developed by the differentiator 352 
of FIG. 15, the signal on the line 365 and a signal on a line 406 
representing commanded fuel delivery (i.e., rack) limits. The fueling 
boost control 392 may alternatively be responsive to fewer than all of 
such parameters, or may be responsive to additional parameters, such as 
exhaust gas recovery (EGR) valve position, or the like. Further or 
alternatively, engine boost magnitude may be sensed and a signal 
representative thereof may be used in a closed-loop boost control, if 
desired. Inasmuch as the design of the fueling boost control 392 is 
conventional and well within the capabilities of one of ordinary skill in 
the art, it will not be described further in detail herein. 
It should be noted that the values stored in the map 370 and the look-up 
table 400 are selected in dependence upon a desired braking control 
strategy to be implemented. For example, the stored values may be 
implemented to establish: (a) fixed timing points for engine exhaust valve 
opening events for either fixed or controllably variable exhaust valve 
open durations in combination with controllably variable vane positioning 
of the turbocharger; (b) controllably variable timing of engine exhaust 
valve opening events with fixed or controllably variable exhaust valve 
open durations in combination with a fixed vane positioning; or (c) 
controllably variable timing of engine exhaust valve opening events for 
fixed or controllably variable exhaust valve opening durations in 
combination with a controllably variable turbocharger vane position. 
During operation under control strategy (c), valve timing and vane 
position may be continuously and infinitely variable, or either or both 
parameters can be varied in discrete steps as a function of desired 
braking or commanded vehicle speed. In the latter case, the signal 
provided to the look-up table 402 would be developed by the control of 
FIG. 20. With specific reference to such FIG., a signal representing 
commanded vehicle speed, as developed by an on the line 358 of FIG. 15, is 
supplied to a look-up table or map 391 which stores signals representing 
commanded vane position as a function of commanded vehicle speed. The 
signal developed by the map 391 is delivered to a first, noninverting 
input of a summer 393. The commanded vehicle speed signal on the line 358 
is also supplied to a noninverting input of a further summer 395 having an 
inverting input that receives a signal representing actual vehicle speed 
as developed by any suitable means, such as the vehicle speedometer. The 
summer 395 develops a vehicle speed error signal which is processed by a 
proportional-integral (P-I) controller 397 and delivered to a further 
noninverting input of the summer 393 where such a signal is summed with 
the signal developed by the map 391 to obtain an input for the look-up 
table 402. In this case, the table 402 is stored with appropriate values 
to develop the signal on the line 396 of FIG. 18. 
FIG. 19 illustrates alternative embodiments of the present invention 
wherein one or more optional devices are added to assist in controlling 
engine braking. On the turbine (i.e., exhaust) side of the turbocharger 
63, a wastegate 410 may be employed between the engine exhaust manifold 
and the turbocharger exhaust gas inlet to divert a variable quantity of 
exhaust gases around the turbocharger turbine in response to commands 
issues by the ECM 72. Also or alternatively, a flapper valve 412 may be 
employed between the turbocharger exhaust gas outlet and the vehicle 
exhaust system to provide a variable restriction under control of the ECM 
72 to exhaust gases. 
On the air intake or compressor side of the turbocharger 63, a flow control 
valve 414 may be included and operated by the ECM 72 to provide a 
controlled restriction to air entering the turbocharger 63. Still further, 
a pressure control valve 416 may be provided between the air outlet of the 
turbocharger and the intake manifold of the engine and which is effective 
to maintain the pressure of air in the intake manifold at a selected 
controllable level in response to commands from the ECM 72. 
As noted above, any combination of elements 410, 412, 414 or 416 may be 
employed. Further, any or all of those elements 410-416 that are employed 
may alternatively be controlled by a different device and/or may be 
maintained at a fixed setting during braking. Also, the turbocharger 63 
may be maintained at a fixed vane position during braking or may be 
replaced by a turbocharger not having a variable geometry. In the last 
case, control over intake manifold air pressure would be effected by 
having at least one of the elements 410-416 responsive to commands issued 
by a controller, such as the ECM 72. 
It should be noted that if one or more of the elements 410-416 is used and 
is (are) to be responsive to controller commands, one or more braking 
control modules similar to the braking control module 390 of FIG. 24 would 
be utilized to control such element(s). In this case, a look-up table like 
the look-up table 400 would develop a commanded control element position 
or operation signal as a function of engine speed and the signal 0% 
BRAKING on the line 361. The module would further include a look-up table 
like the look-up table 402 which develops an actuator command signal for 
controlling the element 410-416 as a function of the commanded control 
element position or operation signal. Alternatively, the signal for the 
look-up table corresponding to the table 402 would be derived from the 
control of FIG. 20. Again, the values stored in such look-up tables are 
selected in coordination with the selection of values stored in the map 
370 of FIG. 15 as described above. 
It should be noted that any or all of the elements represented in FIGS. 15, 
17, 18 and 20 may be implemented by software, hardware or by a combination 
of the two. 
The foregoing system permits a wide degree of flexibility in setting the 
timing and duration of exhaust valve opening and the intake manifold 
and/or exhaust manifold pressure. This flexibility results in an 
improvement in the maximum braking achievable within the structural limits 
of the engine. Also, braking smoothness is improved inasmuch as all of the 
cylinders of the engine can be utilized to provide braking. Still further, 
smooth modulation of braking power from zero to maximum can be achieved 
owing to the ability to precisely control timing and duration of exhaust 
valve opening at all engine speeds and intake and/or exhaust manifold 
pressure. Still further, in conjunction with a cruise control as noted 
above, smooth speed control during downhill conditions can be achieved. 
Moreover, the use of a pressure-limited bulk modulus accumulator permits 
setting of a maximum accumulator pressure which prevents damage to engine 
components. Specifically, with the accumulator maximum pressure properly 
set, the maximum force applied to the exhaust valves can never exceed a 
preset limit regardless of the time of the valve opening signal. If the 
valve opening signal is developed at a time when cylinder pressures are 
extremely high, the exhaust valves simply will not open rather than 
causing a structural failure of the system. 
Also, by recycling oil back to the pump inlet passage 160 from the actuator 
110 during braking, demands placed on an oil pump of the engine are 
minimized once braking operation is implemented. 
It should be noted that the integration of a cruise control and/or a 
turbocharger control in the circuitry of FIG. 15 is optional. In fact, the 
circuitry of FIG. 15 may be modified in a manner evident to one of 
ordinary skill in the art to implement use of a traction control therewith 
whereby braking horsepower is modulated to prevent wheel slip, if desired. 
The integration of the injector and braking wiring and connections to the 
ECM permits multiple use of drivers, control logic and wiring and thus 
involves little additional cost to achieve a robust and precise brake 
control system. 
As the foregoing discussion demonstrates, engine braking can be 
accomplished by opening the exhaust valves in some or all of the engine 
cylinders at a point just prior to TDC. As an alternative, the exhaust 
valve(s) associated with each cylinder may also be opened at a point near 
bottom dead center (BDC). This event, which is added by suitable 
programming of the ECM 72 in a manner evident to one of ordinary skill in 
the art, permits a pressure spike arising in the exhaust manifold of the 
engine to boost the pressure in the cylinder just prior to compression. 
This increased cylinder pressure causes a larger braking force to be 
developed owing to the increased retarding effect on the engine 
crankshaft. 
Numerous modifications and alternative embodiments of the invention will be 
apparent to those skilled in the art in view of the foregoing description. 
Accordingly, this description is to be construed as illustrative only and 
is for the purpose of teaching those skilled in the art the best mode of 
carrying out the invention. The details of the structure may be varied 
substantially without departing from the spirit of the invention, and the 
exclusive use of all modifications which come within the scope of the 
appended claims is reserved.