Adaptive control of camless valvetrain

A variable camless engine valve control system and method of control wherein each of the reciprocating intake and/or exhaust valves (10) is hydraulically controlled and includes a piston (26) subjected to fluid pressure acting on surfaces at both ends of the piston (26), is connected to a source of high pressure fluid (40) in one volume (27) while the volume (25) at the other end is connected to a source of high pressure fluid (40) and a source of low pressure fluid (42), and disconnected from each through action of controlling means such as a computer (74) controlling solenoid valves (64, 68). Optimum intake air and residual gas quantities in each engine cylinder having the aforementioned variable valve control system is assured by controlling electric pulses of variable duration and timing. The pulse timing and duration are calculated based upon values in permanent memory of the computer (74) corresponding to information obtained from sensors and correction values from a correction memory corresponding to feedback from other sensors.

FIELD OF THE INVENTION 
The present invention relates to a system for variably controlling internal 
combustion engine intake and exhaust valves. More specifically, it relates 
to an apparatus and control method for a camless engine valve system for 
variably controlling the lift schedule of engine valves. 
BACKGROUND OF THE INVENTION 
Conventional automotive internal combustion engines operate with one or 
more camshafts controlling the engine valves, i.e., intake and exhaust 
valves, according to a predetermined lift schedule. With this type of 
mechanical structure, the lift schedule is fixed. A fixed lift schedule, 
however, will not allow for optimum engine performance since in general 
different engine operating conditions require different optimum lift 
schedules. 
The enhancement of engine performance obtainable by varying the timing and 
lift as well as the acceleration, velocity and travel time of the intake 
and exhaust valves in an internal combustion engine is generally 
appreciated in the art. Nonetheless, the technology for providing a 
straight-forward, relatively inexpensive and highly reliable system has 
not been forthcoming. Increased use and reliance on microprocessor control 
systems for automotive vehicles and increased confidence in hydraulic as 
opposed to mechanical systems is now making substantial progress in engine 
valvetrain design possible. 
There are several reasons why a generally fixed lift schedule is not 
optimum. Control of gas exchange in a conventional engine with cam driven 
valves is limited and cannot be optimized for all engine operating 
conditions. Control of gas exchange, however, in a camless engine is 
fundamentally different. In an engine with a conventional mechanical 
valvetrain, with its fixed valve timing, the intake air flow is controlled 
by air throttling, which results in throttling losses. Further, the amount 
of residual exhaust gas retained in the cylinder cannot be controlled by a 
mechanical valvetrain, thereby requiring the addition of recirculated 
exhaust gas to the intake air by an external exhaust gas recirculation 
(EGR) system in order to reduce nitrogen oxide emissions. 
The latter limitation is also a concern with engines having lost motion 
engine valve systems connected between camshafts and engine valves, since 
they are still limited somewhat by the inflexibility of a camshaft. Lost 
motion control systems can control the amount of lift, but are very 
limited in controlling the timing of valve opening and closing, thus 
limiting their ability to control the residual gas content in a cylinder. 
Further, a camless electrohydraulic system has the advantage of completely 
eliminating the cost and weight of camshafts while providing increased 
flexibility in the timing and amount of opening of each engine valve. In 
general, variation of the timing of engine valve opening and closing is 
preferred, rather than controlling the lift only, to determine the amount 
of air that is inducted into a cylinder. 
In an engine with an electrohydraulic camless valvetrain, the engine valve 
events are flexible. The quantities of intake air and residual exhaust gas 
in each cylinder can be controlled by varying the timing of opening and/or 
closing for the intake and exhaust valves, which eliminates the need for 
intake air throttling and an external EGR system. On the other hand, while 
an electrohydraulic camless valvetrain provides more flexibility to 
enhance engine performance, there can be drawbacks not encountered with 
systems employing mechanical camshafts. 
For all of the inflexibility and inefficiency associated with a mechanical 
valvetrain, it has one major advantage: the accuracy with which a camshaft 
can be ground is such that a reasonably good cylinder-to-cylinder air 
distribution is inherently assured. In the case of an engine with a 
camless valvetrain, equal distribution of air and residual gas among 
cylinders is not inherent. While a lost motion type of system may not have 
as great of an inherent variation as a camless system, due to the fact 
that it is still driven by mechanical camshaft, it still has other 
disadvantages as noted above. 
In a camless valvetrain system, instead of an air throttle and an external 
exhaust gas recirculation system, changes in the timing of control valves 
can be used to control the amount of air inducted into and the amount of 
residual gas retained in the combustion chamber. The engine valves can be 
electrically controlled by these control valves, such as solenoid valves, 
which respond to electric control signals from an on-board computer. To 
assure that the actions of the intake and exhaust valves in all cylinders 
are substantially equal, substantially identical performance of respective 
control valves in all cylinders must by achieved, which is a challenging 
task. 
A camless valvetrain can accomplish both proper intake air and exhaust gas 
distribution among cylinders combined with the elimination of exhaust gas 
recirculation in order to provide a complete engine optimization package. 
The need, then, arises to ensure that the system can accomplish the 
optimization continually while operating, as well as correct for any 
variations that tend to be inherent in this type of system. 
The timing and duration of the voltage signals that activate the control 
valves can be controlled with great accuracy and uniformity. 
Unfortunately, this does not translate into uniformity of control valve 
performance. Individual control valves tend to respond differently to 
identical voltage signals, due to inevitable minor differences in their 
physical systems. To achieve substantially identical performance by all 
control valves requires a set of control signals, each individually 
tailored to the needs of the specific control valve that it controls. 
This control is required to assure substantially even distribution of 
intake air and residual gas from cylinder-to-cylinder due to this inherent 
control valve-to-control valve variability. In addition, system 
sensitivity to changing ambient conditions, to gradual deterioration in 
performance of individual components and in quality of the working fluid 
can further contribute to deviation from the required performance. 
Tightening up manufacturing tolerances and applying post-manufacturing 
adjustments can reduce, but not totally eliminate, the 
control-valve-to-control-valve differences. Further, this does not resolve 
the problem of possible changes in control valve performance and quality 
of working fluid over time. This inherent variability creates the need for 
a camless valvetrain system that has an adaptive control system 
continuously monitoring the results of its performance under various 
engine operating conditions and which adjusts the system to account for 
the system tolerances to assure correct and equal distribution of intake 
air and residual gas among the cylinders at all times. 
Thus, a control system is needed that accounts for various engine operating 
conditions by changing the valve event of each engine valve based on 
values of required intake air and residual gas quantities placed in a 
computer memory and which has a feedback loop that monitors the actual air 
and residual gas quantity independently for each engine cylinder to create 
a correction memory that corrects for deviation from the required 
parameters in each cylinder for the various engine operating conditions. 
This will allow engine optimization for best fuel economy, emissions and 
torque as well as for best idle quality. 
SUMMARY OF THE INVENTION 
In its embodiments, the present invention contemplates a method of 
individually controlling engine valve opening and closing in a 
multi-cylinder internal combustion engine having a camless valvetrain with 
variable engine valve events. The method comprises sensing engine 
crankshaft rotational position and speed and engine torque demand and 
producing a corresponding position and speed signal and a corresponding 
torque demand signal; reading the position and speed signal and the torque 
demand signal into an on-board computer; determining a desired quantity of 
intake air and residual gas for each cylinder; for each cylinder, 
determining a corresponding nominal value of timing and duration of an 
activation signal to send to each of a plurality of high pressure and low 
pressure solenoid valves; reading correction values for the timing of the 
activation signal for each of the low pressure solenoid valves from a 
correction memory in the on-board computer; adding the correction values 
to the nominal values of timing for each of the low pressure solenoid 
valves to produce corrected values in corrected activation signals; 
activating each of the high pressure solenoid valves with the nominal 
activation signals and each of the low pressure solenoid valves with the 
corrected activation signals; monitoring the actual quantities of intake 
air and residual gas contained in each cylinder; comparing the actual 
quantities of intake air and residual gas for each cylinder to the 
corresponding desired amount of intake air and residual gas; determining a 
correction increment for each cylinder; and modifying the correction 
values in the correction memory of the on-board computer with a correction 
increment. 
The present invention further contemplates a hydraulically operated camless 
valve control system for at least one intake and at least one exhaust 
valve in a cylinder within an internal combustion engine. The system 
comprises a high pressure source of fluid, a low pressure source of fluid 
and a cylinder head member adapted to be affixed to the engine and 
including at least one enclosed intake valve bore and chamber and at least 
one exhaust valve bore and chamber, the intake and exhaust valves each 
being shiftable between a first and a second position within the 
respective cylinder head bores and chambers. The intake and exhaust valves 
each have a valve piston coupled thereto and slidable within its 
respective enclosed chamber which thereby forms a first and a second 
cavity that vary in displacement as the respective intake or exhaust valve 
moves. The cylinder head member has high pressure ports extending between 
the first and second cavities and the high pressure source of fluid, and 
low pressure ports extending between the first cavities and the low 
pressure source of fluid. The intake and the exhaust valve each have an 
associated high pressure valve and an associated low pressure valve, 
respectively, to regulate the flow of fluid in their respective first 
cavities. A control means cooperates with the high and low pressure valves 
for selectively coupling the first cavities to the high pressure and the 
low pressure source to oscillate the intake and exhaust valves in timed 
relation to engine operation. A first correction means cooperates with the 
control means for correcting the timing of the coupling of the first 
cavity, associated with the intake valve, to the low pressure source, and 
a second correction means cooperates with the control means for correcting 
the timing of the coupling of the first cavity, associated with the 
exhaust valve, to the low pressure source. 
Accordingly, an object of the present invention is to provide a camless 
engine with an electrohydraulically controlled valvetrain that optimizes 
engine performance under various engine operating conditions while 
eliminating the need for air throttling and external exhaust gas 
recirculation and which maintains substantially identical performance of 
the intake valves and the exhaust valves in order to maintain equal 
amounts of intake air and residual gas between the cylinders. 
An advantage of the present invention is the ability to operate a camless 
valvetrain that has the cost and weight advantage arising from the 
complete elimination of a camshaft as well as air throttling and external 
EGR, while improving engine performance for various engine operating 
conditions by providing an adaptive control system that accounts for 
variations between valves in the system. 
A further advantage to this adaptive control is that it can properly 
activate the intake and exhaust valves using nominal activation values for 
the timing and duration of the high pressure solenoids and for the 
duration of the low pressure solenoid valves, while only needing to use 
corrected activation values for the timing of the low pressure solenoid 
valve activation associated with the intake valve in order to assure the 
proper distribution of intake air among the cylinders and while only 
needing to use corrected activation values for the timing of the low 
pressure solenoid valve associated with the exhaust valve to assure proper 
distribution of residual gas among the cylinders.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Camless engine valvetrains increase the flexibility in both valve timing 
and lift, even over those systems employing lost motion types of 
electrohydraulic systems, which allow somewhat more flexibility than a 
conventional camshaft driven valvetrain. An electrohydraulic camless 
valvetrain is shown in detail in U.S. Pat. No. 5,255,641 to Schechter 
(assigned to the assignee of this invention), which is incorporated herein 
by reference. 
FIG. 1 shows a single engine valve assembly 8 of an electrohydraulically 
controlled valvetrain. An engine valve 10, for inlet air or exhaust as the 
case may be, is located within a cylinder head 12. A valve piston 26, 
fixed to the top of the engine valve 10, is slidable within the limits of 
a piston chamber 30. 
Fluid is selectively supplied to volume 25 above piston 26 from a high 
pressure oil source 40 and a low pressure oil source 42 hydraulically 
connected through a high pressure line 44 and a low pressure line 46, 
respectively, to a high pressure port 48 and a low pressure port 50, 
respectively. 
Volume 25 can be connected to high pressure oil source 40 through a 
solenoid valve 64 or a check valve 66, or to low pressure oil source 42 
through a solenoid valve 68 or a check valve 70. A volume 27 below piston 
26 is always connected to high pressure oil source 40. A fluid return 
outlet 72 provides a means for returning to a sump (not shown) any fluid 
that leaks out of piston chamber 30. High pressure solenoid valve 64 and 
low pressure solenoid valve 68 are activated and deactivated by signals 
from an on-board computer 74. On-board computer 74 is electrically 
connected to a torque demand sensor 54 and an engine speed and position 
sensor 56. It is also electrically connected to feedback sensors 58 for 
determining the actual quantities of intake air and residual gas in each 
engine cylinder. 
During engine valve opening, high pressure solenoid valve 64 opens and the 
net pressure force acting on piston 26 accelerates engine valve 10 
downward. When high pressure solenoid valve 64 closes, pressure above 
piston 26 drops, and piston 26 decelerates pushing the fluid from volume 
27 below it back into high pressure oil source 40. Low pressure fluid 
flowing through low pressure check valve 70 prevents void formation in 
volume 25 during deceleration. When the downward motion of engine valve 10 
stops, low pressure check valve 70 closes and engine valve 10 remains 
locked in its open position. 
The process of valve closing is similar, in principle, to that of valve 
opening. Low pressure solenoid valve 68 opens, the pressure above piston 
26 drops and the net pressure force acting on piston 26 accelerates engine 
valve 10 upward. When low pressure solenoid valve 68 closes, pressure 
above piston 26 rises, and piston 26 decelerates pushing the fluid from 
volume 25 through high-pressure check valve 66 back into high-pressure oil 
source 40. 
FIGS. 3A and 3B further illustrate the relationship between solenoid valve 
activation an engine valve lift. FIG. 3A shows a diagram of engine valve 
lift 80 versus engine crank angle and FIG. 3B shows a corresponding 
diagram of high and low pressure solenoid valve lifts, 82 and 84 
respectively, versus engine crank angle. Engine valve opening 86 is 
controlled by high-pressure solenoid valve 64 (FIG. 1). When high pressure 
solenoid valve opening 92 occurs, this causes engine valve opening 86 to 
begin. When high pressure solenoid valve closing 94 occurs, this causes 
engine valve deceleration. Engine valve 10 then remains in an open 
position 88. Opening 96 and closing 98 of low pressure solenoid valve 68 
controls engine valve closing 90, similar to engine valve opening. 
As can be seen from FIGS. 3A and 3B, the timing of engine valve closure 90 
is determined by the timing of low-pressure solenoid valve lift 84, which 
corresponds to a solenoid voltage pulse from an on-board computer 74 (FIG. 
1) that activates low pressure solenoid valve 68. Varying the timing of 
activation of high-pressure solenoid valve 64 and low-pressure solenoid 
valve 68, then, varies the timing of the engine valve opening and closing, 
respectively. The amount of engine valve lift is controlled by varying the 
duration of the solenoid voltage pulse to high pressure solenoid valve 64 
and low pressure solenoid valve 68. 
With the ability to control the amount and timing of engine valve opening 
and closing, engine operation can be optimized for various engine 
operating conditions. FIGS. 2A-2D show four circular diagrams which 
illustrate optimum duration and timing of intake and exhaust events for 
different engine operating conditions. The flexibility of a camless 
valvetrain system allows for the control of the timing and amount of valve 
lift to accomplish the various optimum lift schedules. A mechanical 
camshaft driven valvetrain, with or without a lost motion system, could 
not accommodate all of these different lift schedules. 
As shown in FIG. 2A, during an engine idle condition, it is desired to have 
overlap, between the intake and exhaust valve open conditions within a 
given cylinder, small in order to minimize the residual gas fraction. 
Intake valve opening 100 begins just prior to piston top dead center (TDC) 
102 and closing 104 is shortly after TDC 102. This air intake event 106 is 
short, in order to trap only a small volume of air in the cylinder, thus 
avoiding the need for air throttling. The exhaust event 108 begins at 
exhaust opening 110 just prior to bottom dead center (BDC) 112 and closes 
114 just after TDC 102. 
FIG. 2B shows the desired engine valve timing for optimum engine 
performance at a condition of light engine load. The timing of intake 
opening 100 and exhaust opening 110 are the same as the engine idle 
condition. However, the exhaust valve closure 114' is retarded to increase 
the valve overlap and thus increase the residual gas quantity, which helps 
to control nitrogen oxide emissions, thus avoiding the need for an 
external EGR system. The timing of the intake engine valve closure 104' is 
also adjusted in order to trap a somewhat greater quantity of intake air 
in the cylinder than at engine idle. Since this condition also does not 
need maximum intake air, the camless valvetrain control avoids the need 
for air throttling under this condition also. Here, the prime symbol used 
on the numbers represents a different timing, of the particular event 
being discussed, from the engine idle operating condition. 
As shown in FIG. 2C, during an engine heavy load and low speed condition, 
it is desired to have the valve opening overlap reduced further by exhaust 
valve closure 114" taking place immediately after piston TDC 102. It is 
further desired to have the intake valve closure 104" after piston BDC 112 
to maximize the quantity of intake air trapped in the cylinder. At an 
engine condition of heavy load and high speed, as shown in the curves of 
FIG. 2D, the timing of the intake valve closure 104"' is significantly 
past BDC 112 and the exhaust valve opening 110"' is significantly ahead of 
BDC 112 to take advantage of an intake air ram charging effect. 
It is clear from the diagrams in FIGS. 2A-2D that the quantities of intake 
air and residual gas in the cylinder can be controlled by varying the 
respective timings of the intake and exhaust valve closures, 104 and 114 
respectively, to optimize engine performance for various conditions. This 
timing can be accomplished by varying the timing of the respective 
solenoid voltage signals to the low pressure solenoid valves as shown in 
FIGS. 3A and 3B. Thus, only the timing of the intake and exhaust valve 
closures are critical to determining the quantity of intake air and 
residual gas in a particular cylinder. 
The process of adaptive control of the camless valve system, to control 
engine valve operation and to assure uniformity and correctness of intake 
air and residual gas distribution among the cylinders can be explained 
with greater detail with an example of the air flow and residual gas 
control for one of the engine cylinders and is illustrated in FIG. 4, with 
reference to FIG. 1. A first basic control signal is an engine torque 
demand signal, which is supplied by torque demand sensor 54, typically 
monitoring accelerator pedal position. A second control signal is one that 
includes the engine speed and crankshaft position, supplied by engine 
speed and position sensor 56 that typically measures the rate of change of 
the crank angle. On-board computer 74 reads torque demand signal 130 and 
reads engine speed and crankshaft position signal 132. 
Memory in on-board computer 74 contains information for optimum engine 
performance based upon the control signals. On the basis of these signals, 
and using the information contained in the memory of on-board computer 74, 
on-board computer 74 determines the quantities of intake air and residual 
gas 134 desired in each cylinder for optimum engine performance. On-board 
computer 74 also contains a memory table in which, for each value of 
torque and engine speed, the required timing, lift and duration of intake 
and exhaust valve opening is specified. These quantities are converted 
into the nominal timing and duration of the electric pulse signals 136 
that are sent to high pressure and low pressure solenoid valves, 64 and 68 
respectively, to activate them. The information needed for this conversion 
is contained in algorithms stored in another memory table in on-board 
computer 74. 
The memory containing the information on the low pressure solenoid pulse 
timing consists of two parts. The first, as described above, is a basic 
permanent memory containing nominal pulse timing data, each representing 
an empirically established statistical average of the required pulse 
timing for the particular engine. A second part is a correction memory, 
which contains pulse timing increments to be added to or subtracted from 
the values in the basic permanent memory. On-board computer 74 reads the 
correction values for low pressure solenoid valve pulse timing 138. The 
initial values in the correction memory in a new engine are equal to zero. 
This allows the engine to have a starting point and to calibrate and tune 
itself as it operates. The values in the correction memory are added to 
the nominal values 140. 
The numbers in the correction memory can be changed during engine operation 
as needed to assure equal intake air flow and residual gas content among 
the cylinders. There is a separate correction memory in on-board computer 
74 for each engine cylinder to correct individually for tolerances between 
valves causing unequal distribution of intake air and residual gas between 
cylinders. 
The system reads the basic timing signal from permanent memory 136, adds to 
it the correction signal 138 from the correction memory 140 for the 
specific cylinder and thus establishes the value of the timing of low 
pressure solenoid valve 68 activation for this valve, intake or exhaust as 
the case may be, under these operating conditions in order to optimize 
engine operation. The values of the pulse duration for the low pressure 
solenoid valve and the pulse duration and timing for the high pressure 
solenoid valve remain at a nominal value since they are not needed to 
determine quantities of intake air and residual gas. The nominal and 
corrected signals are sent from on-board computer 74 to the high and low 
pressure solenoid valves 64 and 68 to activate them 142, which in turn, 
activates the intake or exhaust valve 10, as the case may be. The system 
also includes a set of sensors which supply information permitting the 
engine controller to read and determine the actual quantities of intake 
air and residual gas in each cylinder during each cycle 144. 
Evaluating the actual quantities of intake air and residual gas in each 
cylinder can be done in a variety of ways. For example, the intake air 
quantities can be measured by mass air flow sensors installed in 
individual intake runners. Another method could involve computing the air 
quantities from the values of the air-to-fuel ratios measured by using 
oxygen sensors installed within individual exhaust runners. Alternatively, 
a single mass air flow sensor in the intake air stream and/or a single 
oxygen sensor in the exhaust stream can be used on a time-resolved basis 
to calculate individual intake air values within each cylinder. With air 
quantity known, the residual gas fraction can be determined by measuring 
the pressure and temperature in the cylinder at a specific reference 
piston position, such as for example at piston bottom dead center. 
On-board computer 74 compares the actual quantities of intake air and 
residual gas inducted into each cylinder to the desired ones 146 to 
determine the amount of system error and generate separate correction 
increments for low pressure solenoid valve pulse timing 148 in each 
cylinder. An error in the amount of intake air in the particular cylinder 
will require a correction in the timing of the low pressure solenoid 
associated with the intake valve in that cylinder while an error in the 
residual gas in that cylinder will require a correction in the timing of 
the low pressure solenoid associated with the exhaust valve in that 
cylinder. Whenever a discrepancy exists, the correction memory in on-board 
computer 74 is modified 150 for that cylinder at the given engine torque 
and speed combination until, after several cycles, the actual quantities 
at this torque and speed substantially equal the required ones. The 
magnitude of the correction increment is directly proportional to the 
system error and inversely proportional to the engine speed. As a result 
of this, the timing of the solenoid is retarded and the quantity is 
increased if the system error is positive. Conversely, the timing of the 
solenoid is advanced and the quantity is reduced if the error is negative. 
Regardless of any initial discrepancies between the actual and required 
quantities of intake air and residual gas, on-board computer 74 of a 
running engine will quickly fill its correction memory with data that will 
assure proper composition of the charge in each engine cylinder at all 
engine speeds and loads. Moreover, the system will continue to monitor the 
engine operation and make corrections at regular intervals in order to 
compensate for changes in working fluid properties as well as for any 
sudden or gradual deterioration in solenoid valve performance, thus 
assuring optimum and substantially equal intake air and residual gas 
quantities between all cylinders under all operating conditions. 
In an alternative embodiment, sequential fuel injection is also controlled 
by on-board computer 74 similar to the control of the engine valves, 
except that the controlled variable is the fuel injector pulse duration 
instead of the solenoid pulse duration. The nominal fuel quantities needed 
are determined from correlating sensor information with values stored in a 
memory in on-board computer 74. The actual fuel quantities are computed 
from the values of the air-to-fuel ratios measured by oxygen sensors 
installed in individual exhaust runners, or by measuring the acceleration 
pulses of an engine flywheel generated by individual cylinders. Correction 
values are then determined and are used to adjust a separate correction 
memory, which is added to the nominal values to determine the individual 
fuel injector pulse width needed for each cylinder. 
While certain embodiments for carrying out the present invention have been 
described in detail, those familiar with the art to which this invention 
relates will recognize various alternative designs and embodiments for 
practicing the invention as defined by the following claims.