Adjusting of air-fuel ratio of a two-stroke internal combustion engine

Patent metadata

Field	Value
Publication number	US-10196972-B2
Application number	US-201715673656-A
Country	US
Kind code	B2
Filing date	Aug 10, 2017
Priority date	Aug 5, 2011
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

To meet stringent emission standards and improve performance of two-stroke crankcase-scavenged engines, the muffler ( 13 ) of the engine is provided with mixing means ( 130, 31 ) for mixing the exhaust gases ( 42 ) resulting from the mixture participating in combustion and gases resulting from scavenging, so that a substantially homogenous gaseous mixture is formed within the muffler ( 13 ), and means ( 81 ) for sensing oxygen concentration is located in the homogeneous gaseous mixture and are configured to provide an output value to a control unit ( 80 ) for controlling supply of fuel to the engine and thereby the air-fuel ratio in the combustion chamber ( 41 ). The muffler ( 13 ) suitably is provided with a catalytic element ( 140 ), preferably a three-way catalyst. The engine ( 1 ) preferably is a stratified charge engine.

First claim

What is claimed is:

1. A two-stroke crankcase-scavenged stratified internal combustion engine comprising:
a fuel supply section including a control unit configured to adjust an air-fuel ratio of the engine;
scavenging ducts including an air inlet; and
an oxygen content sensor,
wherein the engine produces exhaust gases including gases resulting from an air-fuel mixture participating in combustion and additional gases resulting from scavenging,
wherein a fresh air flow that is substantially free from fuel is provided through the air inlet into the scavenging ducts,
wherein the oxygen content sensor is disposed in a substantially homogeneous mixture of the exhaust gases, and
wherein the control unit is configured to:
a) detect an actual value of oxygen content via the oxygen content sensor;
b) compare the actual value to a target value; and
c) adjust the air-fuel ratio in response to the comparison to reduce a difference between the target value and the actual value;
d) detect at least one engine parameter;
e) for certain first conditions with respect to the at least one engine parameter, perform a) to c), where the first conditions occur at least during periods;
f) for certain second conditions with respect to the at least one engine parameter, replace a), b) and c), with g); and
g) use a fuel map for determining a desired air-fuel ratio, and adjusting the air-fuel ratio based on the fuel map, thereby providing for a smooth shifting between an open-loop fuel map mode using the fuel map and a closed-loop feedback control mode using the actual value of the oxygen content for regulating the desired air-fuel ratio.

2. The engine of claim 1 , wherein the control unit is configured to repeat a) to c).

3. The engine of claim 1 , wherein the control unit is configured to repeat a) to g).

4. The engine of claim 1 , wherein the at least one engine parameter includes at least one of an engine speed, or an engine load, or a temperature.

5. The engine of claim 1 , wherein the control unit is configured to execute g) in response to no actual value being detected in d).

6. The engine of claim 1 , further comprising a muffler directly mounted to an exhaust port of a cylinder of the engine.

7. The engine of claim 6 , wherein the engine configured to guide the exhaust gases through an exhaust gas duct to the muffler, and wherein a mixer is provided within the muffler, the mixer being configured to mix the exhaust gases to achieve the substantially homogenous mixture in at least a portion of the muffler.

8. The engine of claim 7 , wherein the muffler is provided with an inlet opening for receiving an exhaust gas flow of said exhaust gases, wherein the exhaust gas flow has a direction at the inlet opening, and wherein the mixer is a wall, an aperture, a net or a grid, and the exhaust gas flow is exposed to the mixer to make at least a portion of the exhaust gas flow divert from the direction.

9. The engine of claim 6 , wherein the oxygen content sensor is a lambda sensor, the lambda sensor being located in the substantially homogenous mixture in the muffler.

10. The engine of claim 6 , further comprising providing at least one catalytic element in the muffler.

11. The engine of claim 10 , wherein the catalytic element is a three-way catalyst.

12. The engine of claim 1 , wherein the control unit is configured to perform the adjustment of the air-fuel ratio in c) by reducing or increasing the air-fuel ratio by adjusting the fuel supply of the engine.

13. The engine of claim 12 , wherein the control unit is configured to adjust the fuel supply by controlling a fuel valve.

14. The engine of claim 1 , wherein the control unit is configured to adjust the air-fuel ratio in c) based on at least one other parameter.

15. The engine of claim 1 , wherein the target value is a lambda value near 1.

16. The engine of claim 1 , wherein the desired air-fuel ratio corresponds to a lambda value within a range 0.7 to 0.95 in a combustion chamber of the engine.

17. An air-fuel ratio control system of a two-stroke crankcase-scavenged stratified internal combustion engine, the system comprising:
a control unit configured to adjust an air-fuel ratio of the engine by controlling an amount of fuel supplied to the engine,
an exhaust gas duct configured to discharge exhaust gases from the engine; and
a muffler in communication with the exhaust gas duct to receive the exhaust gases,
wherein the control unit is configured to:
a) detect an actual value of oxygen content in the muffler via an oxygen content sensor;
b) compare the actual value to a target value; and
c) adjust the air-fuel ratio in response to the comparison to reduce a difference between the target value and the actual value;
d) detect at least one engine parameter;
e) for certain first conditions with respect to the at least one engine parameter, perform a) to c), where the first conditions occur at least during periods;
f) for certain second conditions with respect to the at least one engine parameter, replace a), b) and c), with g); and
g) use a fuel map for determining a desired air-fuel ratio, and adjusting the air-fuel ratio based on the fuel map, thereby providing for a smooth shifting between an open-loop fuel map mode using the fuel map and a closed-loop feedback control mode using the actual value of the oxygen content for regulating the desired air-fuel ratio.

18. The system of claim 17 , wherein the muffler is provided with a catalytic element.

19. The system of claim 17 , wherein the control unit is configured to repeat a) to c).

20. The system of claim 17 , wherein the control unit is configured to repeat a) to g).

Assignees

• Husqvarna Ab

Inventors

• Bergman Mikael

Classifications

• F02D35/0053

  by means of a carburettor · CPC title

• F02B33/04

  with simple crankcase pumps, i.e. with the rear face of a non-stepped working piston acting as sole pumping member in co-operation with the crankcase · CPC title

• F01N3/101

  Three-way catalysts · CPC title

• F02D2400/04

  Two-stroke combustion engines with electronic control · CPC title

• F02B2075/025

  two · CPC title