System for controlling ignition timing and fuel injection timing of a two-cycle engine

A temperature sensor is provided for detecting temperature of exhaust gas in an exhaust passage of a two-cycle engine. The temperature is compared with a reference temperature for activating a catalytic converter. When the temperature is lower than the reference temperature, the ignition timing and the fuel injection timing of the engine are retarded. The quantity of injected fuel is increased so as to compensate reduction of engine power caused by retarding the ignition timing.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for controlling ignition timing 
and fuel injection timing of a two-cycle engine at cold state, and more 
particularly to a control system for the two-cycle engine having an 
exhaust emission control system with a catalytic converter. 
In a four-cycle engine, temperature of exhaust gas is high comparing with 
that of the two-cycle engine, so that a catalyst in the catalytic 
converter provided in an exhaust pipe is sufficiently heated to be 
activated for ensuring exhaust emission control. 
In the two-cycle engine, however, a part of intake air escapes from a 
cylinder through an exhaust port at scavenging the cylinder. Thus, the 
temperature of the exhaust gas is lowered. In particular, in a low engine 
speed range and a light load range, the catalyst is not heated to an 
activated temperature. As a result, the exhaust gas containing poisonous 
elements is emitted to atmosphere. 
In order to maintain the activated temperature of the catalyst, it is 
proposed to provide the catalytic converter at an upper stream portion of 
the exhaust pipe so that the exhaust gas having a high temperature may 
pass through the catalytic converter. 
However, since the temperature of the exhaust gas is high in a full load 
range, durability and function of the catalyst are reduced. 
On the other hand, Japanese Utility Model Application Laid-Open 62-124211 
discloses a catalytic converter in which a heater is provided at an inlet 
thereof. The heater is adapted to change a heating value thereof in 
dependency on the temperature. It is effective to increase the temperature 
of the catalyst to the activated temperature. However, it consumes a large 
electric power, and it is difficult to heat the whole catalyst. Further, 
it is necessary to provide a control unit for heating the heater. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an exhaust emission 
control system for a two-cycle engine in which temperature for activating 
a catalyst is maintained, thereby ensuring to control exhaust gas 
emission. 
According to the present invention, there is provided a system for 
controlling a two-cycle engine having at least one cylinder, a fuel 
injector provided for injecting fuel directly in the cylinder, a spark 
plug for igniting the fuel, and a catalytic converter in an exhaust 
passage for exhaust gas emission. 
The system comprises a temperature sensor for detecting temperature of 
exhaust gas in the exhaust passage upstream of the catalytic converter, a 
comparator for comparing the temperature detected by the temperature 
sensor with a reference temperature for activating the catalytic converter 
and for producing a temperature signal when the detected temperature is 
lower than the reference temperature, retard quantity determining means 
responsive to the temperature signal for determining a retard quantity for 
the ignition timing and fuel injection timing, retarding means for 
retarding the ignition timing and the fuel injection timing based on the 
retard quantity, correcting means for increasing the quantity of injected 
fuel in accordance with the retard quantity so as to compensate reduction 
of engine power caused by retarding the ignition timing. 
Since the ignition timing is retarded, the temperature of the exhaust gas 
increases, thereby activating the catalytic converter. Thus, the control 
of the exhaust gas emission can be performed, even if the exhaust gas 
temperature is lower than the temperature for activating the catalyst 
In an aspect of the invention, the reference temperature is a lower limit 
temperature for activating the catalytic converter, and the retard 
quantity is set to increase with an increase of the difference between the 
detected temperature and the reference temperature. 
These and other objects and features of this invention will become 
understood from the following description with reference to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a two-cycle engine 1 comprises a cylinder 2, a piston 
3 provided in the cylinder 2, a connecting rod 6 connected with the piston 
3 and a crankshaft 5 disposed in a crankcase 4. A counterweight 7 is 
mounted on the crankshaft 5 so as to reduce inertia of the piston 3 
reciprocating in the cylinder 2. 
In a wall of the cylinder 2, an exhaust port 11 and a scavenge port 16 are 
formed in 90 degrees angular disposition or opposing one another. The 
ports 11 and 16 are adapted to open at a predetermined timing with respect 
to a position of the piston 3. 
A fuel injector 10 and a spark plug 9 are provided on a top of a combustion 
chamber 8 of the cylinder 2. The injector 10 is a type where a 
predetermined amount of fuel is directly injected in the cylinder and the 
quantity of the fuel is controlled with the injection pulse width. The 
fuel in a fuel tank 29 is supplied to the injector 10 through a fuel 
passage 26 having a filter 28, a pump 27 and a pressure regulator 30 for 
constantly maintaining the fuel at a predetermined fuel pressure. 
The engine 1 is supplied with air through an air cleaner 20, a displacement 
scavenge pump 19, and an intake pipe 17 having a scavenge chamber 18 for 
absorbing scavenge pressure waves when the scavenge port 16 is opened or 
closed. A bypass 21 is provided around the scavenge pump 19. The bypass 21 
is provided with a control valve 22. Exhaust gas of the engine 1 is 
discharged passing through the exhaust port 11, a rotary valve provided 
adjacent the exhaust port 11 in an exhaust pipe 13 having a catalytic 
converter 14 for controlling the exhaust gas emission, and a muffler 15. 
The scavenge pump 19 is operatively connected to the crankshaft 5 through a 
transmitting device 23 comprising an endless belt running over a crank 
pulley and a pump pulley. The scavenge pump 19 is driven by the crankshaft 
5 through the transmitting device 23 for producing a scavenge pressure. An 
accelerator pedal 24 is operatively connected with the control valve 22. 
An opening degree of the control valve 22 is controlled so as to be 
inversely proportional to the depressing degree of the accelerator pedal 
24. Further, an accelerator pedal depressing degree sensor 31 and a crank 
angle sensor 32 are provided for determining engine operating conditions. 
An exhaust gas temperature sensor 33 is provided upstream of the catalytic 
converter 14 for detecting temperature of the exhaust gas. In addition, a 
pressure sensor 34 is provided in the fuel passage 26 downstream of the 
pressure regulator 30 for detecting a pressure of the fuel to be injected. 
Output signals from the sensors 31, 32, 33 and 34 are supplied to a control 
unit 40 which feeds an ignition signal and a fuel injection pulse signal 
to the spark plug 9 and the injector 10, respectively. 
Referring to FIG. 2, the control unit 40 comprises an engine speed 
calculator 46 to which a crank angle .theta. detected by the crank angle 
sensor 32 is applied for calculating engine speed N. The engine speed N 
and an accelerator pedal depressing degree .phi. detected by the 
accelerator pedal depressing degree sensor 31 are applied to a fuel 
injection quantity calculator 47. The crank angle .theta. is further 
applied to an ignition timing determining section 43 and a fuel injection 
timing determining section 44, respectively. 
The control unit 40 is further provided with a comparator 41 to which an 
output signal of exhaust temperature detected by the exhaust temperature 
sensor 33 is applied. In the comparator 41, a lower limit temperature for 
activating a catalyst in the catalytic converter 14 is previously 
provided. The exhaust temperature is compared with the lower limit 
temperature. If the exhaust temperature is lower than the lower limit 
temperature, the comparator 41 produces an output signal which is applied 
to an ignition/injection timing retard quantity determining section 42. In 
the section 42, quantity for retarding the ignition timing and for 
retarding the fuel injection timing are determined. The retard quantity is 
determined in accordance with the difference between the exhaust 
temperature and the lower limit temperature. If the difference is large, 
the retard quantity becomes large. However, the maximum retard value is 
determined. The retard quantity is applied to the ignition timing 
determining section 43 in which an ignition timing ts is determined. The 
ignition timing ts is applied to the spark plug 9 through a driver 51. The 
retard quantity is also applied to the fuel injection timing determining 
section 44 in which a fuel injection timing ti is determined. The fuel 
injection timing ti is applied to the injector 10 through a driver 52. 
Since the ignition timing is retarded, the power of the engine is reduced. 
In order to compensate the reduction of the engine power, the quantity of 
fuel injected from the injector 10 is increased. To this end, the control 
unit 40 is provided with a correcting injection quantity calculator 45 to 
which the retard quantity determined in the section 42 is applied for 
calculating a correcting injection quantity .DELTA.Q. The correcting 
injection quantity .DELTA.Q is applied to the fuel injection quantity 
calculator 47 where a corrected fuel injection quantity Qf is calculated. 
The fuel injection quantity Qf is applied to the fuel injector 10 through 
the driver 52 at the retarded injection timing ti. 
The operation of the system will be described herein after with reference 
to the flowchart of FIG. 3. 
When the engine starts, the temperature of the exhaust gas is detected at a 
step S101. At a step S102, the exhaust gas temperature is compared with 
the predetermined lower limit temperature of the temperature of the 
activated catalyst. If the exhaust gas temperature is lower than the lower 
limit, the program goes to a step S103. If not, the program returns to 
step S101. 
At the step S103, the retard quantity of the ignition timing and the fuel 
injection timing is determined. At a step S104, the fuel injection 
quantity is corrected based on the retard quantity. At a step S105, the 
fuel injection timing is determined. At a step S106, a predetermined 
increased quantity of fuel is injected from the injector 10. At a step 
S107, ignition is performed by the spark plug 9. 
In a normal engine operation, the fuel injection timing ti and ignition 
timing ts are determined at a proper interval before top dead center as 
shown in FIG. 4, so that charge stratification may be performed in the 
combustion. When the exhaust gas temperature is lower than the lower limit 
of the temperature of the activated catalyst, the timings ts and ti are 
retarded. The timings ts and ti are determined at a proper interval after 
top dead center. When the exhaust gas temperature rises and exceeds the 
lower limit temperature, the correcting operation to retard the timings is 
cancelled and the correcting operation to increase the fuel injection 
quantity is stopped. 
FIG. 5 shows variations of the fuel injection quantity, fuel injection 
timing and exhaust temperature corresponding to the ignition timing. 
Although the exhaust gas temperature is detected in the above described 
embodiment of the present invention, temperature of the catalyst may be 
detected in stead of the exhaust gas temperature. 
In accordance with the present invention, since the ignition timing is 
retarded, the temperature of the exhaust gas is increased, thereby 
activating the catalyst in the catalytic converter. Thus, the control of 
the exhaust emission can be performed, even if the exhaust gas temperature 
is lower than the temperature for activating the catalyst. 
The fuel injection quantity is increased when the ignition timing is 
retarded, so that the power of the engine is prevented from reducing. 
Since the quantity for retarding the ignition timing is determined in 
accordance with the lower limit of the temperature for activating the 
catalyst, the increase of the fuel consumption caused by an excess of 
retardation is avoided. 
While the presently preferred embodiment of the present invention has been 
shown and described, it is to be understood that this disclosure is for 
the purpose of illustration and that various changes and modifications may 
be made without departing from the scope of the invention as set forth in 
the appended claims.