Fuel vapor treatment system for internal combustion engine

Abstract

A butterfly valve restricts flow passage areas of a purge passage and a blow-by gas passage by the same degree. A first pressure sensor detects variation in pressure of the purge gas, which is generated by the butterfly valve. A second pressure sensor detects variation in pressure of the blow-by gas, which is generated by the butterfly valve. Since a fuel vapor concentration of the blow-by gas is lower than that of the purge gas, the blow-by gas can be treated as air of 100%. Hence, the fuel vapor concentration is calculated based on the variations in pressure detected by the first pressure sensor and the second pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, feature and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic view showing a fuel vapor treatment system according to a first embodiment of the invention;

FIG. 2 is cross sectional view showing a fuel vapor concentration detector shown in FIG. 1;

FIG. 3 is a main flow chart according to the first embodiment;

FIG. 4 is a flow chart showing a purge-executing routine shown in FIG. 3;

FIGS. 5A and 5B are graphs showing a relationship between a throttle valve opening degree and a butterfly valve opening degree;

FIG. 6 is a graph showing a relationship between a quantity of blow-by gas and a quantity of purge gas of which fuel vapor concentration is 0%;

FIG. 7 is a graph showing a relationship between a fuel vapor concentration and a ratio between a purge gas quantity and a purge gas quantity of which fuel vapor concentration is 0%;

FIG. 8 is a cross sectional view showing a fuel vapor concentration detector according to a second embodiment;

FIG. 9 is a cross sectional view showing a fuel vapor concentration detector according to a third embodiment;

FIG. 10 is a cross sectional view showing a fuel vapor concentration detector according to a fourth embodiment;

FIG. 11 is a cross sectional view showing a fuel vapor concentration detector according to a fifth embodiment;

FIG. 12 is a cross sectional view showing a fuel vapor concentration detector according to a sixth embodiment;

FIG. 13 is a schematic view showing a fuel vapor treatment system in which a pair of absolute pressure sensor is used;

FIG. 14 is a schematic view showing a fuel vapor treatment system in which an intake air pressure sensor is used as an absolute pressure sensor;

FIG. 15 is a schematic view showing a fuel vapor treatment system in which two butterfly valves are used;

FIGS. 16A and 16B are graphs showing a relationship between an intake air pressure and a butterfly valve opening degree; and

FIGS. 17A and 17B are graphs showing a relationship between an intake air quantity and a butterfly valve opening degree.

Claims

1. A fuel vapor treatment system for an internal combustion engine, comprising: a canister that is connected to a fuel tank through a vapor introduction passage and has an adsorbent for temporarily adsorbing fuel vapor, the fuel vapor being produced in the fuel tank and being introduced into the canister through the fuel vapor introduction passage;a purge passage introducing a desorbed fuel vapor from the adsorbent into an intake pipe of the engine;a purge valve provided in the purge passage, the purge valve controlling a flow rate of fuel vapor flowing through the purge passage;a first throttle provided in the purge passage;a first pressure detecting means for detecting a variation in pressure of a purge gas passing through the first throttle;a second throttle provided in a gas passage of a positive crankcase ventilation apparatus that recirculates a blow-by gas into the intake pipe;a second pressure detecting means for detecting a variation in pressure of a gas passing through the second throttle; anda concentration calculation means for calculating a concentration of fuel vapor in an air-fuel mixture introduced into the intake pipe from the canister based on the variation in pressure detected by the first pressure detecting means and the variation in pressure detected by the second pressure detecting means.

2. A fuel vapor treatment system for an internal combustion engine, comprising: a canister that is connected to a fuel tank through a vapor introduction passage and has an adsorbent for temporarily adsorbing fuel vapor, the fuel vapor being produced in the fuel tank and being introduced into the canister through the fuel vapor introduction passage;a purge passage introducing a desorbed fuel vapor from the adsorbent into an intake pipe of the engine;a purge valve provided in the purge passage, the purge valve controlling a flow rate of fuel vapor flowing through the purge passage;a first throttle provided in the purge passage;a first pressure detecting means for detecting a variation in pressure of a purge gas passing through the first throttle;a second throttle provided in a gas passage of a positive crankcase ventilation apparatus that recirculates a blow-by gas into the intake pipe;a second pressure detecting means for detecting a variation in pressure of a gas passing through the second throttle;a first quantity calculation means for calculating a quantity of fuel vapor in an air-fuel mixture introduced into the intake pipe from the canister based on the variation in pressure detected by the first pressure detecting means and the variation in pressure detected by the second pressure detecting means; anda second quantity calculation means for calculating a quantity of air in an air-fuel mixture introduced into the intake pipe from the canister based on the variation in pressure detected by the first pressure detecting means and the variation in pressure detected by the second pressure detecting means.

3. A fuel vapor treatment system according to claim 1, wherein the first pressure detecting means detects a differential pressure between two points across the first throttle in the purge passage.

4. A fuel vapor treatment system according to claim 1, wherein the second pressure detecting means detects a differential pressure between two points across the second throttle in the gas passage.

5. A fuel vapor treatment system according to claim 1, wherein the first throttle and the second throttle are arranged in such a manner as to be close to each other.

6. A fuel vapor treatment system according to claim 1, wherein the first throttle and the second throttle are adjacently arranged to each other.

7. A fuel vapor treatment system according to claim 1, wherein at least one of the first throttle and the second throttle is a valve.

8. A fuel vapor treatment system according to claim 6, wherein the first throttle and the second throttle is structured by a butterfly valve which turns in the purge passage and the gas passage so that a flow passage areas of the purge passage and the gas passage are identical to each other.

9. A fuel vapor treatment system according to claim 1, wherein the first throttle is a first butterfly valve provided in the purge passage,the second throttle is a second butterfly valve provided in the gas passage, andthe first and the second butterfly valve are driven in such a manner that flow passage areas of the purge passage and the gas passage are identical to each other.

10. A fuel vapor treatment system according to claim 6, wherein the first throttle and the second throttle is structured by a needle valve which reciprocates in the purge passage and the gas passage so that a flow passage areas of the purge passage and the gas passage are identical to each other.

11. A fuel vapor treatment system according to claim 1, wherein the first throttle is a first needle valve provided in the purge passage,the second throttle is a second needle valve provided in the gas passage, andthe first and the second needle valve are operated in such a manner that flow passage areas of the purge passage and the gas passage are identical to each other.

12. A fuel vapor treatment system according to claim 7, wherein an opening degree of the valve is controlled according to a throttle valve position, an intake air pressure, or an intake air quantity.

13. A fuel vapor treatment system according to claim 1, wherein the first throttle and the second throttle are structure by orifices of which opening degrees are identical to each other.

14. A fuel vapor treatment system according to claim 1, wherein the first throttle and the second throttle are structure by nozzles of which opening degrees are identical to each other.

15. A fuel vapor treatment system according to claim 1, wherein the purge valve functions as the first throttle.

16. A fuel vapor treatment system according to claim 1, wherein the second throttle is a blow-by gas control valve which is provided in the gas passage to control a flow rate of the blow-by gas.

17. A fuel vapor treatment system according to claim 1, wherein the first pressure detecting means includes a pressure sensor detecting a pressure upstream of the first throttle and an intake pressure sensor detecting an intake air pressure in the intake pipe.

18. A fuel vapor treatment system according to claim 1, wherein the second pressure detecting means includes a pressure sensor detecting a pressure upstream of the second throttle and an intake pressure sensor detecting an intake air pressure in the intake pipe.