[0001] This invention relates to engine control systems in general and more particularly
to electrohydraulic control systems for controlling the timing of the intake and exhaust
valves in internal combustion engines.
Background of the Invention
Prior Art
[0002] It has been long recognized by engine builders and more particularly by specialists
in high performance engines that control of valve timing will yield desired engine
operation results. The ideal timing of intake and exhaust valves at idle conditions,
at normal load range conditions and at high performance conditions is very different.
Since valves are controlled by cams it is necessary to compromise the timing to suit
a particular purpose. In production engines, valve timing is a compromise leaning
towards the normal load or speed ranges to the detriment of the idle range and the
high performance range. Likewise in high performance engines the timing is adjusted
toward the high performance demands of the engine and therefore at the idle and normal
load ranges valve timing is not optimal.
[0003] As early as 1903 Alexander Winton used a pneumatic device to vary valve lift. His
particular intent at that time was throttling the engine with intake valves as opposed
to throttling the engine with the conventional throttle plate. More recently there
have been centrifugal cam sprockets which are capable of varying valve timing as a
function of engine speed but not varying lift or duration of opening.
[0004] In addition there have been systems which - completely disable the operation of the
valves and therefore effectively close off one or more cylinders during different
engine operating ranges. A recent commercial engine using this concept is Cadillac's
8-6-4 engine. In most of the known control systems the forces involved in opening
and closing valves in the engine requires expensive and very high powered solenoids.
This places a high cost penalty on the engine for the consumer.
[0005] U.S. Patent 3,439,661 entitled "Control Displacement Hydraulic Lifter" by Weiler,
teaches a hydraulic valve lifter. U.S. Patent 4,112,884 entitled "Valve Lifter for
an Internal Combustion Engine" by Tominaga, teaches a valve lifter design. Both patents
operate to provide some timing control to the valves. U.S. Patent 4,111,165 entitled
"Valve Operating Mechanism of an Internal Combustion Engine" by Aoyama et al, teaches
control of the oil in a hydraulic valve lifter in response to engine speed and throttle
opening to spill the oil during deceleration thereby limiting the traveling of the
valve lifter. U.S. Patent 4,258,671 entitled "Variable Lift Mechanism used in Internal
Combustion Engine" by Takizawa et al, teaches electromagnetic valve control of hydraulic
valve lifters in an overhead cam (OHC) engine. In response to engine temperatures,
manifold pressure and speed, the oil pressure in the lifter is adjusted to form the
solid link necessary to operate the engine valve. This particular patent ('671) teaches
the control of all cylinders. Each of the last two patents ('165 and '671) does not
teach driving the oil back into the lifter for restoring the valve lifter to a normal
start position after each operation in order that each engine cycle is independently
controlled. Therefore, in the next engine cycle the electronic control unit controlling
the operation of the oil does not know the location of the lifter. If the next engine
cycle requires a later valve opening, the valve opening will not change from the previous
engine cycle inasmuch as the lifter has not been re-extended. Aoyama et al shows a
pump and a regulator to supply oil pressure to the lifter and Takizawa et al teaches
an oil supply gallery fed by an oil supply which is driven by the engine. Without
more, the normal engine oil pressures are inadequate to return a collapsed lifter
to its full height in the available time between engine cycles. In both systems, the
addition of a boost pressure pump of adequate pressure capacity is both expensive
and adds an unnecessary load on the engine, therefore defeating the purposes and the
advantages gained by controlling the valves of an engine.
[0006] To solve the above problems, there is disclosed herein an engine valve timing control
system using the engine oil supply to operate the hydraulic valve lifters or adjusters.
By controlling the fluid pressures pulses developed within the oil supply as a result
of lifter operation, very high pulsed pressures are directed to the various lifters
to assist in returning or re-extending the lifters to their normal position between
engine cycles. The system is a microprocessor based control system wherein various
engine sensors sense the engine conditions and the microprocessor in response to the
sensed engine conditions addresses a memory unit containing a map of engine conditions
versus valve opening times. From the memory unit a signal is supplied to a particular
timer unit for a given cylinder. The timer, operating in conjunction with a known
position of the piston in the cylinder will operate electrohydraulic solenoid valves
for directing and maintaining a predetermined amount of oil in an associated hydraulic
lifter.
[0007] These and other advantages will be found in the following detailed description and
drawings.
Brief Description of the Drawings
[0008] In the drawings:
FIGURE 1 is a schematic view of the control system of the invention;
FIGURE 2 is a schematic of the hydraulic system of the invention;
FIGURE 3 is a sectional view of a valve lifter;
FIGURE 4 is an exploded view of the valve lifter of FIGURE 3;
FIGURE 5 is a sectional view of an overhead cam valve system;
FIGURE 6 is a sectional view of a push rod valve system; and
FIGURE 7 is a timing diagram.
Detailed Description
[0009] Referring to the FIGURES by the numerals and characters of reference there is disclosed
an engine valve timing control system. The system utilizes a microprocessor based
control system to control the opening time and duration of intake and exhaust valves
in one or more cylinders of an internal combustion engine.
[0010] FIGURE 1 is a schematic of the control system showing the various elements of the
system. The various engine operating conditions are sensed by one or more sensors
10 such as an exhaust gas sensor which is typically an oxygen gas sensor 12 indicating
the quality of combustion of the engine. Temperature sensors indicating the temperature
of the engine 14 and the temperature of the air 16 supply signals into the system.
Another sensor indicates the position 18 of the throttle and to determine the amount
of fuel required by the engine manifold absolute pressure 20 sensor may be employed.
However if such system is a speed-density fuel injection system, it must calculate
air flow by several sensed variables and an empirically determined volumetric efficiency
of the engine. For the present valve timing system it is advantageous to measure the
air intake into the system and therefore a mass airflow meter may be located in the
air intake of the engine. By measuring air flow directly, it is not necessary to store
an empirically determined volumetric efficiency map to determine air flow. By changing
valve timing, volumetric efficiency is intentionally changed complicating any air
flow calculations, therefore direct measurement of air flow is preferred.
[0011] Those sensors which develop an analog signal are processed through an analog-to-digital
converter 22 converting the sensor signals to digital equivalents used by the microprocessor
24. Additional inputs to the microprocessor indicate engine starting 26 and the extreme
positions 27, 28 of the throttle blade in the throttle body. The microprocessor 24
receives the several signals indicating the engine conditions and according to control
laws stored in its memory, various engine control signals are developed. The microprocessor
24 is a Motorola 68701.
[0012] The present system is concerned with the control of engine valves and has a memory
system such as a programmable read only memory (PROM) 30 containing a memory map of
the engine events for the particular engine with various valve opening positions.
In order to adapt this system to a family of engines, each member of the engine family
has its own particular PROM 30 which is plugged into the system. The microprocessor
addresses the PROM 30 as a result of the engine conditions to determine a particular
valve opening timing and duration for the various cylinders. The PROM 30 is a Motorola
2716.
[0013] The ECU 32 is synchronized with the engine by means of a timing means 34 coupled
to the engine camshaft. The timing means 34 generates a signal indicating the known
position of the piston in each cylinder such as top dead center (TDC) of the compression
stroke or bottom dead center (BDC) of the power stroke. The camshaft is coupled to
the engine crankshaft and rotates at half the speed of the crankshaft or once per
engine cycle. The engine crankshaft supplies power to drive the oil pressure pump
64 pumping engine oil through the engine. This oil is used in the valve lifters or
adjusters of the present system.
[0014] Signals 35 from the timing means 34 are supplied to a timing phase lock loop timing
circuit 36 wherein the frequency of each input signal 35 is multiplied by a factor
of ten for fine timing. The output signals 38 of the phase lock loop timing circuit
36, namely the fine timing signal 38, is supplied to several programmable timing units
40, one timing unit for each cylinder. The fine timing signal 38 operates to bring
the timing units 40 to a predetermined timing position for initiating valve operation
of each cylinder. There is an additional timing unit 42 which responds to the known
position of the piston in a given cylinder, more particular to the position of the
piston in the number one cylinder. From this timing unit 42 the relative positions
of the pistons in the remaining cylinders are determined. The programming timing units
40 are Motorola 6840 units.
[0015] The predetermined signals from each of the-timing units 40 are supplied to the microprocessor
24 for generating control signals to solenoid control valves 44-50. The valves 44-50,
in response to the signals control the flow of oil out of a hydraulic valve lifter
51-58 for controlling the time of the engine valve in a manner as will hereinafter
be explained.
[0016] Referring to FIGURE 2 there is illustrated a schematic of the hydraulic circuit for
the engine valve timing control system. For the purpose of illustration this system
will be described in a four cylinder internal combustion spark ignited engine. The
particular firing order of the ignition system for the engine is one-two- four-three.
[0017] FIGURE 2 illustrates the grouping of the engine valves which are 180 camshaft degrees
apart. In particular, the intake valve for cylinder one and the intake valve for cylinder
four are grouped together and controlled by a first solenoid valve 44. Likewise exhaust
valve one and exhaust valve four controlled by a second solenoid valve 46; intake
valve two and intake valve three controlled by a third solenoid valve 48; and exhaust
valve two and exhaust three controlled by a fourth solenoid valve 50; are grouped.
Thus in FIGURE 2 the four solenoid valves 44-50 control the four cylinders. The oil
supply galleries 60, which are found in the engine block, provide supply 60 and return
lines 62 for the engine oil between the various valve lifters 51-58. The engine oil
pump 64 supplies engine oil under pressure to the system, which is a closed loop system,
through a check valve 66 preventing the oil in the system from returning back to the
engine oil pump 64. The check valve 66 allows only oil to be supplied to the system
to replace any oil lost due to leakage such as around the valve lifter sliding seals.
Additional check valves 67. 69 are located in both the supply 60 and the return 62
lines for each valve lifter 51-58. The ECU 32, which is more fully illustrated in
FIGURE 1, is shown in schematic form, controls each solenoid valve 44-50. In the particular
system to be described, the solenoid valves 44-50 are actuated to close the return
lines 62 maintaining the oil in the various lifters causing the engine valves to be
opened.
[0018] Referring to FIGURE 5 there is illustrated the control for one engine valve in an
overhead cam system showing the bleed solenoid control valve 44, the engine valve
lifter 51, the cam follower 68, the overhead cam 70, the engine valve spring 72 and
the engine valve 74. Additionally the various oil supply galleries 60 and the lifter
oil bleed passages 62 for supplying oil to and from the lifter are shown.
[0019] The overhead cam 70 has a base diameter 76 and extending therefrom at a particular
annular position is a lobe 78. As the cam follower 68 rides along the cam surface
the rise and fall surfaces of the lobe cause the engine 72 valve to open and close.
This is conventional valve operation and will not be explained here.
[0020] The present invention in the overhead cam system utilizes the length of height of
the valve lifter piston 80 for controlling the pivot point for the cam follower 68.
As the piston 80 of the valve lifter 51 is extended further out of its housing 82,
the cam follower 68 will respectively operate to open or close the valve earlier or
later on the cam 70 profile. Earlier valve opening and therefore a larger valve opening
for a longer duration may be used in a high speed engine operation or heavy load where
more fuel is desired to be injected into the cylinder. If the lifter piston 80 is
retracted into the housing 82 of the valve lifter 51 the profile of the cam will cause
the cam follower 68 to be driven down onto the lifter. When the overall length of
the lifter 51 is fixed at its length then the profile of the cam 70 will cause the
follower 68 to be driven down on the engine valve 74 and against the valve spring
72 opening the valve 74.
[0021] At an idle condition a late engine valve opening is desired and the amount of opening
of the valve is small, the closing of the valve is quicker than before. This causes
less fuel to be injected into the engine therefore the emissions of the engine at
idle speed are improved. Also at idle condition the short duration of the engine valve
opening eliminates valve overlap thereby reducing the contamination of the fresh incoming
fuel charge by the exhaust residue. Valve overlap is less of a problem to combustion
quality at high speeds and loads where the time is shorter and the manifold pressure
differential across the engine is reduced because of reduced contamination. However
at high speeds and loads, overlap improves power and economy.
[0022] In order to have the lifter piston 80 move in and out of its housing the supply of
the oil to the hydraulic lifter 51 is controlled. When the correct operate time is
reached the solenoid control valve 44 is closed sealing off the return line 62 and
keeping the oil in the hydraulic lifter 51. This forms a solid oil link causing the
lifter piston 80 to remain stationary and the cam follower 68 then pivots on the lifter
piston under the operating force of the cam 70 to actuate the valve 74.
[0023] An exploded view of a valve lifter 51 as shown in FIGURE 4 is used in the present
application. The valve lifter illustrated has a lifter body 82 in which is a return
spring 84, check valve retainer 86, check ball valve 88 and spring 90, check valve
piston 92, lifter piston 80 and a piston retainer 94. It is a function of the return
spring 84 to return the lifter piston 80 to its extended positon and as will herein
be shown the force of the return spring 84 plus the pressure pulse as shown in Figure
7, from the oil lines 60 cooperate to return the piston 80. The check ball 88, ball
spring 90 and valve retainer 86 operate to maintain oil in the interior of the check
valve piston 92 and permit the oil to flow out of the lifter to the return lines 62.
As illustrated in FIGURE 3, the oil supply line 62 comes into the valve lifter at
the upper portion of the valve body 82 and flows out of an orifice 96 in the bottom
of the valve body 82. Thus the flow of oil is through the check valve 88 into the
cavity where the return spring 84 is located and out of the bottom of the lifter through
the orifice 96.
[0024] FIGURE 6 illustrates the adaptation of the present invention to a push rod construction.
The cam 98 is below the piston and a push rod 100 is connected between the cam 98
and a rocker arm 102 to open or close the engine valve 104. Again the operation uf
the cam, push rod, rocker arm and valve assemblies are well known and will not be
explained here. However between the cam 98 and the rocker arm 102 and in line with
the push rod 100 is the solenoid controlled hydraulic valve lifter 106. The operation
of this system is similar to that previously explained in that the hydraulic link
is formed under the control of the solenoid 110 between both ends of the piston 108,
109 in the lifter 106. Thus when the control solenoid 110 is not energized the oil
will flow from the oil supply gallery 60 through the check valve 67 and through the
hydraulic lifter. If the lower push rod piston 109 is being moved up the cam 98 surface
the oil is pushed out of the lifter into the bleed passageways 62. However once the
solenoid is energized the bleed passageways are closed and the oil between the two
pistons 108, 109 forms a solid link coupling the-motion of the lower piston 109 to
the push rod piston 108 causing the push rod 100 to operate on the rocker arm 102
in a conventional manner for opening the valve. Thus in this particular system as
in the system of FIGURE 5 the formation of the solid link controls the timing of the
engine valve 104.
[0025] FIGURE 7 is a graphic representation of the timing of the system. More particularly
the upper trace 112 illustrates the closing of the solenoid control valve 110, the
center trace 114 illustrates the pressure pulses in the galley lines 60, 62 and the
lower trace 116 is a trace depicting the travel of the engine valve. Referring to
the center trace, which shows the pressure pulses on the system, the first pulse 118
is the cam follower 68 contacting the cam 70 in such a manner as to push the lifter
piston 80 down causing oil to be removed from the lifter 51. The second pulse 120
is the pulse generated by the closing of the solenoid and the forming of the solid
oil link and the suddenly applied pressure of the cam through the cam follower onto
the link. It is believed that the third pulse 122 is an echo in the oil lines as a
result of reflections from the interior of the hydraulic passages.
Operation
[0026] Referring to FIGURES 1, 2 and 5 the various fill and return check valves 67, 69 and
69a prevent the flow of the oil except in those directions in which the designer wants
the oil to flow. The present system is mainly concerned with controlling the opening
time of the engine valve which thereby, because of the cam design, controls not only
the length of time the valve is open but the amount of lift of the valve itself. As
previously explained the ECU 32 determines, under actual engine operating conditions,
the ideal time for the engine valve to open.
[0027] This is done by means of timing units 40, 42 wherein the first timing unit 42 is
an absolute timing unit indicating the time from a predetermined engine event such
as top dead center of the engine piston on the compression stroke in cylinder one.
As illustrated in FIGURE 1 the sensor 124 coupling the timing means 34 into the logic
of the phase lock loop 36, will generate a particular signal indicating the engine
piston position at top dead center of cylinder one and any other known position on
the system. By suitable design of the timing means 34 it may well indicate the position
of top dead center of each and every engine piston and by further design of the timing
means the signal will be generated such that the position of top dead center of cylinder
one is particularly identified.
[0028] Located in the map of the engine events located in the PROM 30 for a given engine
condition the time of an intake engine valve opening for a particular cylinder is
stored as the time from the top dead center of a known cylinder or event. This time
value is located in the time units 40 and the phase lock loop fine timing signal 38
operates to count down the timing unit 40 of a particular cylinder to a predetermined
number. An output signal 126 is generated indicating the time the valve should be
actuated which in the present system is the time that the solenoid control valve 44-50
should be closed. The signals are processed through the microprocessor 32 to the particular
solenoid control valve for actuation.
[0029] The above system describes how to control the opening time of either an intake valve
or an exhaust valve for a given cylinder. In order to control the actual closing of
the engine valve 74 which is on the fall side of the cam lobe 78, a heavy duty solenoid
is required. The forces bearing against the lifters and the forces transmitted through
the oil to bear against the plunger of the solenoid control valve 44 are very high
making the plunger very difficult to move. However the closing time of the engine
valve 74 is a direct function of the opening time and the closer that the opening
time gets to the top of the lobe 78 of the cam 70 the closer the closing time is to
the top of the lobe 78 of the cam on the reverse side of the cam.
[0030] As stated with reference to FIGURE 7 the various pressure pulses 118, 120, 122 which
are generated are supplied through the fluid system. These pulses operate to force
additional oil into the various lifters 51-58 to return the lifter pistons 80 to their
normal position. However for the lifter that is under control by the lobe 78 of the
cam 70 the pressure pulse to the lifter piston 80 will not move the piston as the
cam 70 begins to move the valve stem 74.
[0031] As the cam opening ramp begins to move the cam follower 68, the open solenoid valve
44 allows the lifter piston 80 to collapse. The flow of oil out of the lifter 51 closes
the lifter fill check valve 88. This forces the oil flowing out of the lifter to open
the return check valve 69 and flow through the open solenoid valve 44. The return
check valve 69a on the lifter 57 paired on the same solenoid valve 44 is closed by
this flow to prevent uncontrolled flow from going back into the other lifter 57 of
the pair. Thus, the solenoid valve 44 has absolute control of the flow of oil out
of the lifter 51. The flow of oil out of the solenoid valve 4*4 is then channeled
into idle lifters to pump them back to the full extended position. The lifter 51 collapse
continues until the ECU 32 determines that it is the correct time to start to open
the engine valve 74. The ECU 32 then generates an electrical signal to close the solenoid
valve 44, stopping the flow of oil out of the lifter 51, and creating a solid hydraulic
link inside the lifter body. At this point the force to compress the hydraulic fluid
in the lifter 51 is much greater than the force required to compress the valve spring
72. The motion of the cam then opens the engine valve 74 rather than collapsing the
lifter.
[0032] The cam follower 68 and valve 74 track the remainder of the cam profile giving the
valve the motion dictated by the cam 70 profile, but reduced by the amount of initial
lifter collapse. As the cam 70 closes the engine valve 74, the follower 68 loses contact
with the cam 70 as the engine 74 valve seats and the cam profile continues to ramp
toward the base circle 76. At this point with the solenoid valve 44 still closed,
pulses from other lifters 52-58 enter through the fill check valve 67 and with help
from the lifter return spring 84, pump the lifter piston 80 up so that the cam follower
68 remains in contact with the cam base circle 76. At some point with the lifter fully
extended again and the cam follower 68 again in contact with the cam base circle 76
the solenoid valve 44 can be opened again to complete the cycle and prepare for the
next cycle. To open the solenoid valve before this time would allow the pressure pulses
from other cylinders to flow in the fill check valve 67, through the lifter, and out
through the open solenoid valve without doing any work to return the piston.
[0033] It is to be appreciated that the various valve springs 72 and the resulting cam forces
applied to the valve 74, 104 by the cam follower 68, 102 are very high and therefore
the cam follower will take the path of least resistance as it is being positioned
for opening or closing of the valve. Such path of least resistance is the piston on
the lifter operating against the oil pressure of the oil system and the cam follower
will drive the oil out of the lifter until the solenoid valve is closed.
[0034] The performance benefits of the system are that the engine will develop more power
for a given engine size and in the very large engines there will be better fuel efficiency
and less dilution charge at idle from reduced valve overlap. In addition by controlling
the intake and exhaust valves, hydrocarbons and emission qualities are better controlled.
During deceleration operations the amount of fuel entering the cylinder is less and
therefore deceleration emission and fuel economy performances are improved.
[0035] In the present system, it is a distinct advantage to use the pressure pulses 118-122
from collapsing lifters to return the piston of the inactive lifters to the cam base
circle. By doing this the start position of each valve opening time is identified
and is repeatable. Further, by returning the lifter piston such as to place the cam
follower against the cam base circle, the wear of the cam striking the follower has
been diminished as is the associated noise.
[0036] To improve lifter response in the system it is imperative that the oil supply to
the lifter be free.of restrictions so that oil can be pulsed and pushed into the lifter
quickly and undiminished. It has been further noted that the use of such high pressures
on the system due to the pressure pulses generated, suitable oil rings 128 must be
positioned about the lifters as illustrated in FIGURE 5.
[0037] The interior of the lifter 51 must be such that the lifter piston 80 is able to be
compressed without binding the return spring 84. Such feature is a matter of design
such that the lifter piston does not return so close to the bottom as to bind the
coils of the return spring.
[0038] While the system has been described as a single function microprocessor based system
mainly for controlling of engine valves such a control system may be combined with
ignition and fuel injection systems into an overall system. This is easily done inasmuch
as both ignition and fuel injection systems require much of the same input signals
and have much of the same processing capabilities as the present system.
[0039] There has thus been shown and described an engine valve timing control system utilizing
a microprocessor based control system and operating such that in a closed loop hydraulic
oil system the pressure pulses generated by means of cam actuations operate to generate
high pressure pulses on the fluid lines for returning the off lifters to the base
line position on the cams. The system illustrates the method of controlling each cylinder
individually such that its timing is unique and not dependent upon or a function of
the previous or next cylinder's timing nor is it a function of the previous cycle
of the same cylinder. Various parameters are functions of design such as the parameter
supplying the signal to the absolute timer indicating that a known position of a known
cylinder which may be just one cylinder of the whole engine or each particular cylinder
in the engine.