Control device for valve system in automobile engine

A control device for a valve system in which low or high speed cams can be smoothly changed. The control device comprises: a valve system including low and high speed cam selecting means for activating and deactivating intake or exhaust valves; and a control unit for calculating, based on engine operation data, a target engine speed to provide a cam selecting signal to the low and high speed cam selecting means, a variation of the engine speed based on the engine speed data, a corrected target engine speed based on the engine speed variation, target engine speed, and delay time of the operation of the cam selecting means, and activating the cam selecting means at the corrected target engine speed.

FIELD OF THE INVENTION 
This invention relates to an improved control device which includes a 
mechanism for enabling a valve system to selectively operate low or high 
speed cams and activate or inactivate intake or exhaust valves by the 
selected low or high speed cams in an automobile engine, so that the 
intake or exhaust valves are operated in a desired target operation mode. 
BACKGROUND OF THE INVENTION 
There are known a number of automobile engines which include: a valve 
operating mechanism for selectively operating low or high speed cams and 
operating valves by the selected cams at proper timings so as to increase 
an engine output; or a valve operating mechanism for selectively operating 
low or high speed cams, operating valves by the selected cams, and 
allowing a partial cylinder operation mode by disconnecting a portion of 
the engine cylinders and suspending fuel supply to the disconnected 
cylinders, thereby increasing the engine output and reducing the fuel 
consumption. 
A control device for such a valve operating mechanism sets various 
operation modes according to information concerning the operation status 
of the engine. For instance, in a low speed operation mode, low speed cams 
are used to operate the intake and exhaust valves so as to increase volume 
efficiency. In a high speed operation mode, high speed cams are used to 
operate the intake and exhaust valves so as to increase the volume 
efficiency. 
The low or high speed cams are selectively operated in response to a cam 
selecting signal sent to the valve operating mechanism. Either the low or 
high speed cams are activated when the engine is operating at a target 
speed DN for selecting the low or high speed mode (called "target engine 
speed DN" hereinafter). The cam selecting signal is issued when the engine 
is operating at a given speed which is set with reference to an ordinary 
running condition. When the cam selecting signal is issued at the target 
engine speed DN while the engine is operating at a relatively low speed, 
either the low or high speed cams can be selectively operated without any 
trouble or delay. This is because the valve operating mechanism is very 
responsive to the cam selecting signal under such a condition. 
Conversely, when the engine is idling or when the engine speed is abruptly 
increased due to acceleration during the operation of a low speed gears, 
the valve operating mechanism is slow to respond to the cam selecting 
signal. In such a case, the engine speed would exceed the target engine 
speed DN for the desired operation mode, the valve operating mechanism 
would fail to follow the operation mode changing, or an engine torque 
would become too large. 
SUMMARY OF THE INVENTION 
According to the invention, there is provided a control device for a valve 
system to selectively operate low or high speed cams and activate valves 
by the selected cams in an automobile engine. The control device 
comprises: first rocker arms to be operated by low speed cams and for 
activating at least intake or exhaust valves; second rocker arms to be 
operated by high speed cams; pin members for coupling or decoupling the 
first and second rocker arms and being biased by spring members; an oil 
pump for moving the pin member against the spring member; solenoid valves 
for changing routes of pressured oil from the oil pump; and a control unit 
for controlling the solenoid valves based on a time-dependent variation of 
an engine speed. 
The control unit comprises: target engine speed calculating means for 
calculating a target engine speed at which a cam selecting signal is sent 
to cam selecting means; engine speed variation calculating means for 
calculating a variation of the engine speed; and corrective engine speed 
calculating means for calculating an engine speed for sending the cam 
selecting signal based on the variation of the engine speed. Thus, the cam 
selecting means will be activated at the corrected target engine speed 
which is responsive to the variation of the engine speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a control device 100 according to a first embodiment 
of the invention is applied to an in-line four-cylinder engine 1 including 
a DOCH type valve system. 
The engine 1 includes, on its cylinder head 2, an intake manifold IM 
communicating with respective cylinders, an intake pipe IR communicating 
with a surge tank 37, an exhaust manifold EM communicating with the 
cylinders, and an exhaust pipe ER connected to the exhaust manifold EM. 
A throttle valve 40 is located behind an air cleaner 38 in the intake pipe 
IR. A rotary shaft 41 of the throttle valve 40 is rotated by an actuator 
42 including a step motor. The actuator 42 is connected to and is 
controlled by an engine control unit ECU 32 to be described later. A 
negative pressure sensor 35 is attached to the surge tank 37 in the intake 
pipe IR. 
Intake and exhaust ports (not shown) are opened and closed by intake valves 
(one example is shown in FIG. 2) and exhaust valves, respectively. The 
intake and exhaust valves are operated by the valve system 4 of the DOHC 
type. The valve system 4 comprises intake and exhaust cam shafts 5 and 6, 
and intake and exhaust rocker shafts 7 and 8, which are installed on the 
cylinder head 2. The cam shafts 5 and 6 have timing gears 9 and 10 as 
integral parts at their ends, respectively. The timing gears 9 and 10 are 
connected to a crankshaft (not shown) via a timing belt 11 so that the 
camshafts 5 and 6 are rotated at half engine speed. The intake and exhaust 
rocker shafts 7 and 8 are separately provided for the respective 
cylinders. 
The intake and exhaust valves of all the cylinders are opened and closed by 
the valve system 4. As shown in FIG. 2, a part of the valve system 4 
associated with the intake valves includes a low speed rocker arm 14 (as a 
first rocker arm) operated by a low speed cam 12, a high speed rocker arm 
15 (as a second rocker arm) operated by a high speed cam 13, and a rocker 
shaft 7 for pivotally supporting the rocker arms 14 and 15 thereon, and a 
T-shaped lever 16 which is integral with the rocker shaft 7. 
The T-shaped lever 16 is forked at one end thereof. A pair of intake valves 
3 are coupled to the forked ends of the T-shaped lever 16, and are opened 
and closed by the T-shaped lever 16. The low and high speed rocker arms 14 
and 15 have rollers 14a and 15a rotatably received in their rotary ends. 
The low and high speed cams 12 and 13 come into contact with the rollers 
14a and 15a, respectively. The low and high speed rocker arms 14 and 15 
have low and high speed cam selecting means ML and MH at opposite ends, 
respectively. The low and high speed cam selecting means ML and MH 
constitute a main part of the valve operating mechanism. 
The cam selecting means ML comprises a pin 17 housed in a cavity of the 
rocker shaft 7, an oil pressure chamber 21 for operating the pin 17 with 
oil pressure against a resilient force of the spring 19, an oil path 23 
communicating with an oil pressure chamber 21, and a solenoid valve 26 for 
the cylinders #1 and #4 and for intermittently connecting the oil path 23 
to an oil pump 25, and a solenoid valve 27 for the cylinders #1 and #4 for 
intemittently connecting the oil path 24 to the oil pump 25. Similarly, 
the cam selecting means MH comprises a pin 18 housed in another cavity of 
the rocker shaft 7, an oil pressure chamber 22 for operating the pin 18 
with oil pressure against a resilient force of the spring 20, an oil path 
24 communicating with the oil pressure chamber 22, a solenoid valve 30 for 
the cylinders #2 and #3 and for intermittently connecting the oil path 23 
to the oil pump 25, and a solenoid valve 31 for the cylinders #2 and #3 
and for intermittently connecting the oil path 24 to the oil pump 25. The 
oil pump 25 communicates with the fuel tank 50 shown in FIG. 1. 
The solenoid valves 26, 30, 27 and 31 are three-way valves functioning as 
oil control valves (OCV). When actuated, these solenoid valves supply 
pressured oil to the oil pressure chambers 21 and 22. Conversely, when 
remaining inactive, these solenoid valves connect the oil pressure 
chambers 21 and 22 to a drain. These valves are controlled by the engine 
control unit ECU 32. 
In the cam selecting means ML, when the solenoid valves 26 and 30 are 
inactive, the resilient forces of the spring 19 acts, and the low speed 
rocker arm 14 becomes integral with the T-shaped lever 16 via the pin 17 
at the locked position L1, and operates the intake valves 3 in the low 
speed mode. On the other hand, in the cam selecting means MH, when the 
solenoid valves 27 and 31 are inactive, the resilient force of the spring 
20 acts to move the pin 18 to the nonlocked position H1. 
When the solenoid valves 26 and 30 are active, the pin 17 is moved to the 
non-locked position L2 against the force of the spring 19 in the cam 
selecting means ML. On the other hand, when the solenoid valves 27 and 31 
are active, the pin 18 is moved to the locked position H2 against the 
force of the spring 20 in the cam selecting means MH. Thus, only the high 
speed rocker arm 15 becomes integral with the T-shaped lever 16, thereby 
operating the intake valves in the high speed mode. 
Referring to FIG. 1, fuel injectors 28 are disposed on the cylinder head 2 
so as to supply fuel to intake ports (not shown) of the respective 
cylinders. The fuel injectors 28 receive the fuel from the fuel tank 50 
via a regulator 29 for regulating the fuel to a preset pressure. Fuel 
injection is controlled by the engine control unit ECU 32. 
The engine control unit ECU 32 mainly comprises a microcomputer, and 
performs various control functions such as detecting, based on operation 
mode data, whether the engine is in the low speed operation mode using the 
low speed cam or in the high speed operation mode using the high speed 
cam, issuing a signal indicative of the detected operation mode, and 
controlling outputs for each operation mode, the operation of the fuel 
injectors, and ignition timings. 
Further, the ECU 32 functions as the following means: target engine speed 
calculating means which calculates, based on the engine speed Ne and 
negative intake pressure in an intake pipe, a target engine speed DN at 
which the cam selecting signal should be sent to the cam selecting means; 
engine speed variation calculating means for calculating a variation 
.DELTA.Ne of the engine speed Ne based on the engine speed Ne; corrected 
engine speed calculating means for calculating an engine speed Ne2 for 
sending the cam selecting signal (called "corrected target engine speed 
Ne2") based on the variation .DELTA.Ne of the engine speed, the target 
engine speed DN, and delay time TD indicative of delayed operation of the 
cam selecting means. The low or high speed cams are selectively operated 
in response to the cam selecting signal which is issued at the corrected 
target engine speed Ne2. 
As shown in FIG. 1, the ECU 32 receives various operation data such that 
the engine speed Ne from an engine speed sensor 33 (i.e. a crank angle 
sensor), a cooling water temperature Twt from a temperature sensor 34, a 
negative intake pressure Pb from a negative pressure sensor 35, and a 
throttle opening 8s from a throttle opening sensor 36. 
The operation of the control device of the present invention will be 
described with reference to control programs shown in FIGS. 5 to 7. 
Referring to FIG. 5, the actuation of the main switch allows the ECU 32 to 
perform its control operations according to the main routine. 
In step al, the ECU 32 checks various functions, performs initialization, 
and goes to step a2. In step a2, the ECU 32 reads various engine operation 
data, and stores data such as the engine speed Ne and negative intake 
pressure Pb. Then, the ECU 32 advances to steps a3, a4 and a5, where it 
controls the ignition timing, fuel injection timings, and so on. Under 
this condition, the solenoid valves 26, 30, 27 and 31 remain inactive, so 
that the engine E is in the low speed operation mode by means of the low 
speed cams. 
During the control operation in the main routine, the ECU 32 performs the 
.DELTA.Ne calculating routine and the Ne2 calculating routine at every 50 
milliseconds and at every 5 milliseconds, respectively, as shown in FIGS. 
6 and 7. At every 50 milliseconds in the main routine, the .DELTA.Ne 
calculating routine is started. In this routine, the ECU 32 subtracts the 
previous engine speed Ne1 from the current engine speed Ne to obtain the 
variation .DELTA.Ne of the engine speed, and stores the variation 
.DELTA.Ne. 
At every 5 milliseconds in the main routine, the Ne2 calculating routine is 
carried out. In step c1, the target engine speed DN is calculated by using 
a map which is plotted based on the engine speed Ne and the negative 
intake pressure Pb, and is stored in the ECU 32. Then, the ECU 32 goes to 
step c2. 
In step c2, the ECU 32 subtracts the product of the engine speed variation 
.DELTA.Ne and delay time TD from the target engine speed DN, thereby 
obtaining the corrected target engine speed Ne2. In other words, the cam 
selecting signal is issued at the corrected target engine speed Ne2 which 
precedes the target engine speed DN by the period corresponding to the 
estimated delay time TD, so that the low or high speed selecting means can 
be activated exactly at the target engine speed DN. 
In step c3, the ECU 32 compares the corrected target engine speed Ne2 with 
the current engine speed Ne. When Ne2.gtoreq.Ne, the ECU 32 goes to step 
c4, where it checks whether engine E completes its start-up and is stable 
and suitable for the high speed operation mode. When the engine E is 
judged to be stable, the ECU 32 activates the solenoid valves 26, 30, 27 
and 31, and changes the low speed cam over to the high speed cam. 
Conversely, when Ne2.ltoreq.Ne in step c3, the ECU 32 judges that the 
engine is just after its startup and is too unstable to perform the high 
speed operation, and advances to step c6. Under this condition, the 
solenoid valves 26, 30, 27 and 31 are kept inactive. 
In the present invention, the cam selecting means are used to selectively 
operate the high or low speed cams. Alternatively, it is also possible to 
carry out the partial cylinder operation mode as follows: only the 
solenoid valve 26 for disconnectable #1 and #4 cylinders is activated to 
move the pin 17 to the non-locked position by the force of the oil 
pressure chamber 21 and the resilient force of the spring 20, and keep the 
T-shaped lever 16 inactive. 
The four solenoid valves 26, 30, 27 and 31 are used in the foregoing 
embodiment. Alternatively, the solenoid valves 26 and 30 are combined into 
one, and the valves 27 and 31 are also combined into one. Then, the oil 
paths 23 and 24 may be merged. In addition, the low and high speed cam 
selecting means for #2 and #3 cylinders, or for all the four cylinders may 
be replaced with cam selecting means shown in FIG. 9 as a second 
embodiment. Specifically, a valve system 4 of FIG. 9 comprises a T-shaped 
lever 30L (serving as the first rocker arm) and a high speed rocker arm 65 
(serving as the second rocker arm). The T-shaped lever 30L includes a 
rocker shaft 7a, a low speed arm member 64 and forked ends as integral 
parts. The low speed arm member is integral with the rocker shaft 7a and 
has a roller bearing 66 at its one end. The low speed cam 12 comes into 
contact with the roller bearing 66. The T-shaped lever 30L has adjust 
screws and adjust nuts 68 attached at the forked ends. The adjust screws 
67 are coupled, at their ends, to intake or exhaust valves at their upper 
ends. 
The high speed rocker arm 65 is rotatably supported on the rocker shaft 7a, 
and has a roller bearing 69 at one end thereof. The high speed cam 13 
comes into contact with the roller bearing 69. The high speed rocker arm 
65 also includes an arm member 70 as an integral part at the other end 
opposite to the roller bearing 69. An arm spring 71 acts on the arm member 
70 in such a manner that the high speed rocker arm 65 is urged toward the 
high speed cam 13. Further, cam selecting means 72 allows the high speed 
rocker arm 65 to rotate integrally with the rocker shaft 7a. Specifically, 
the rocker shaft 7a has a cavity 73 at a position thereof associated with 
the high speed rocker arm 65. A pin 74 is movable in the cavity 73, and is 
supported and biased by a spring member 75. The high speed rocker arm 65 
has a cavity 76. The pin 74 is disengaged from the cavity 76 by the spring 
member 75. A pressured oil path 77 is axially formed in the rocker shaft 
7a to communicate with the cavity 73. An oil path 78 is formed near the 
bottom of the cavity 76, and communicates with the cavity 76. 
Normally, in the high speed rocker arm 65, the pin 74 remains free from the 
cavity 76 by the spring member 75, so that the high speed rocker arm 65 is 
disengaged from the rocker shaft 7a and is not rotatable with the rocker 
shaft 7a. Thus, the low and high speed cams 12 and 13 rock the low speed 
arm 64 and the high speed rocker arm 65, respectively. The force of the 
low speed cam 12 is transmitted to the intake valves 3, thereby rocking 
the intake valves 3. Then, the pressured oil is supplied from the oil pump 
25 to the oil path 77 in the rocker shaft 7a via the solenoid valve 26 or 
30. In the high speed rocker arm 65, the pressured oil flows via the oil 
path 78 to the bottom of the cavity 73, thereby engaging the pin 74 with 
the cavity 76. Thereafter, the high speed rocker arm 65 engages with the 
rocker shaft 7a, and rotates integrally with the rocker shaft 7a. Thus, 
the high speed cam 13 rocks the high speed rocker arm 65, of which force 
is transmitted to the intake valves 3 via the rocker shaft 7a and the low 
speed arm portion 64, and activates the intake valves 3. 
In the first embodiment of the invention, the corrected target engine speed 
Ne2 is calculated by using the variation .DELTA.Ne of the engine speed 
derived by subtracting the previous engine speed Ne1 from the current 
engine speed Ne. Alternatively, an engine speed increasing ratio 
.DELTA.Ne1 derived in the routine shown in FIG. 8 may be used in place of 
.DELTA.Ne in the second embodiment. 
In the routine shown in FIG. 8, the ECU 32 reads the current engine speed 
Ne from the engine speed sensor 34 in step d1. In step d2, a filtering 
speed Nf is calculated by adding the previous filtering speed Nf(n-1) 
multiplied by a filtering constant Xt, and the present engine speed Ne(S) 
multiplied by (1-Xt) [i.e. Nf=Xt.times.Nf(n-1)+(1-Xt).times.Ne(S)]. In 
step d3, the engine speed increasing ratio .DELTA.Ne1 is derived by 
subtracting the filtering speed Nf from the current engine speed Ne. The 
engine speed increasing ratio .DELTA.Ne1 is relatively gentle compared 
with the corrected target engine speed .DELTA.Ne. In other words, since 
the filtering speed Nf is adjusted by the filtering constant Xt, the 
engine speed increasing ratio .DELTA.Ne1 is averaged. The corrected target 
engine speed Ne2 is calculated by using .DELTA.Ne1 so that Ne2 is set 
relatively in a wide range by the amount in which the .DELTA.Ne is 
averaged. Thus, the low or high speed cams can be smoothly changed to the 
high or low speed cam while the engine speed is maintained below the 
target engine speed DN at which the cam selecting means is activated, 
thereby suppressing noise produced during the cam selection. 
The control device of the invention can correct the timing to provide the 
cam selecting signal to the cam selecting means in response to a varying 
engine speed increasing ratio. Therefore, a desired cam selecting means 
can be always activated at the target engine speed, so that the cam 
selecting means can operate without trouble for a long period of time and 
variation of an engine torque can be suppressed. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modification as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.