JPH0718388B2 - Air-fuel ratio controller for LPG engine - Google Patents

Description

The present invention relates to an LPG engine, particularly an air-fuel ratio control valve for feeding back an air-fuel ratio, and a fuel cut valve for stopping fuel supply during deceleration operation. The present invention relates to an air-fuel ratio control device for an LPG engine.

(Prior Art) A PLG engine in which fuel is supplied from a fuel tank to a venturi portion of an intake passage via a vaporizer is disclosed in Japanese Patent Laid-Open No. 61-23857, for example. Feedback control may be performed.
That is, as shown in FIG. 5, in addition to the main fuel passage 5 that communicates from the fuel tank 1 to the venturi portion 4 of the intake passage 3 via the vaporizer 2, the vaporizer 2 and the intake passage 3 are provided in the vicinity of the throttle valve 6. An auxiliary fuel passage 7 communicating with the auxiliary fuel passage 7 is provided, and an air-fuel ratio control valve 8 for controlling the opening and closing of the passage 7 and an actuator 9 thereof are provided on the auxiliary fuel passage 7. Then, the control valve 8 is opened / closed via the actuator 9 by a signal from an air-fuel ratio sensor (for example, a residual oxygen concentration sensor installed on the exhaust passage) separately provided, so that the throttle valve can be opened from the auxiliary fuel passage 7. The amount of fuel supplied to the intake passage 3 is adjusted by the intake negative pressure downstream of the valve, and feedback control is performed so that the air-fuel ratio converges to the target value.

On the other hand, in this type of engine, a fuel cut valve for opening and closing the main fuel passage is provided, and the fuel cut valve is closed to stop the fuel supply during deceleration operation in which fuel supply is not required. This may improve fuel efficiency and exhaust performance during deceleration operation.

(Problems to be Solved by the Invention) By the way, when the auxiliary fuel passage and the air-fuel ratio control valve for feedback control of the air-fuel ratio as described above are provided and the fuel cut valve is provided in the main fuel passage, the Such a problem occurs. That is, even if the fuel cut valve is closed to stop the fuel supply during the deceleration operation, if the air-fuel ratio control valve on the auxiliary fuel passage is not completely closed, the fuel is sucked from the auxiliary fuel passage into the intake passage. As a result, fuel efficiency and exhaust performance will not be improved effectively. On the other hand, it is conceivable to close both the fuel cut valve on the main fuel passage and the air-fuel ratio control valve on the auxiliary fuel passage during deceleration operation. When the fuel pressure is lowered and fuel supply is restarted, fuel is simultaneously supplied from both the main fuel passage and the auxiliary fuel passage, and a shock is generated due to abrupt torque generation.

The present invention addresses the above-described problems in an LPG engine that performs air-fuel ratio control and fuel stop control, and effectively improves fuel economy performance and exhaust performance during deceleration operation while reducing fuel consumption. The purpose is to facilitate the transition to the idle area where supply is resumed.

(Means for Solving Problems) That is, the air-fuel ratio control device for an LPG engine according to the present invention,
In addition to the main fuel passage communicating from the vaporizer to the venturi portion of the intake passage, an auxiliary fuel passage also communicating from the vaporizer to the throttle valve downstream of the intake passage is provided, and the auxiliary fuel passage is provided on the auxiliary fuel passage in response to a signal from the air-fuel ratio sensor. In an LPG engine having an air-fuel ratio control valve for opening and closing the passage, a fuel cut valve for opening and closing the passage is provided in the main fuel passage, and the fuel cut valve and the air-fuel ratio control valve are closed during deceleration operation of the engine. The control means for operating is provided. Then, the control means is configured to hold the air-fuel ratio control valve in a closed state at a lower rotation speed than the fuel cut valve when the engine rotation speed decreases.

(Operation) According to the above configuration, the fuel from the vaporizer is sucked into the intake passage from the main fuel passage and the auxiliary fuel passage, but the air-fuel ratio control valve on the auxiliary fuel passage is opened / closed by a signal from the air-fuel ratio sensor. The air-fuel ratio is controlled and increased / decreased according to the air-fuel ratio of the air-fuel mixture actually supplied to the combustion chamber, so that the air-fuel ratio converges to and is maintained at the target value. . Further, during deceleration operation of the engine, not only the fuel cut valve on the main fuel passage is controlled by the control means,
Since the air-fuel ratio control valve is also closed, the fuel supply is completely stopped, and when the engine speed drops to the idle region and fuel supply is restarted, the fuel cut valve is first opened to open the main fuel. The fuel supply is started from the passage, and then the air-fuel ratio control valve is opened to start the fuel supply from the auxiliary fuel passage as well, so that the fuel supply from both passages is started simultaneously. The generation of various torques is avoided, and the idle operation is smoothly performed.

(Example) Hereinafter, an example of the present invention will be described.

FIG. 1 shows an air-fuel ratio control system for an LPG engine. The engine 10 has intake and exhaust valves 11 and 12 and a combustion chamber 13
The intake passage 14 has an intake passage 14 and an exhaust passage 15 respectively connected thereto, and the intake passage 14 has an air cleaner 16 at its upstream end and a venturi portion 17 at its downstream portion for reducing the passage cross-sectional area further downstream thereof. A dual throttle valve 18 is provided, and an exhaust gas purification device 19 is installed in the exhaust passage 15.

A fuel supply system 20 is connected to the intake passage 14. This fuel supply system 20 basically comprises a tank 21 storing LPG fuel, a vaporizer 23 connected to the tank 21 via an opening / closing valve 22, and a fuel vaporized by the vaporizer 23 in the intake passage. 14 and a main fuel passage 24 that leads to the venturi portion 17 of the intake air passage 14, and an auxiliary fuel passage 25 is branched from the main fuel passage 24.
In the downstream of the throttle valve 18.
The auxiliary fuel passage 25 is provided with an air-fuel ratio control valve 26, which is a duty solenoid, and an orifice 27 from the main fuel passage 24 side, and the intake passage 14 is provided between the control valve 26 and the orifice 27. The atmosphere introduction passage 28 led from the downstream side of the opening position of the main fuel passage 24 in the venturi portion 17 is joined.

On the other hand, a fuel cut valve 29 for opening and closing the main fuel passage 24 is provided on the downstream side of the branch position of the auxiliary fuel passage 25 in the main fuel passage 24, and a negative pressure responsive type that drives the valve 29 is provided. The actuator 30 and the first negative pressure control valve 31 for controlling the supply and discharge of negative pressure to and from the actuator 30. Further, in this embodiment, the fuel cut valve 29
Is provided with an orifice 32 and a bypass passage 33 that bypasses the orifice 32, a fuel increase valve 34 that opens and closes the bypass passage 33, and a negative pressure responsive actuator that drives the valve 34. 35 and the actuator
A second negative pressure control valve 36 for controlling the supply and discharge of negative pressure to and from 35 is provided.

In addition to the above configuration, the engine 10 is provided with a control unit 40 that controls the operations of the air-fuel ratio control valve 26 and the first and second negative pressure control valves 31, 36. The control unit 40 is provided in the exhaust passage 15 with a signal a from a throttle opening sensor 41 for detecting the opening of the throttle valve 18, a signal b from an engine rotation sensor 42 for detecting the engine speed. And a signal c from the air-fuel ratio sensor 43 that detects whether the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 13 is rich (the fuel ratio is large) or lean (the same is small) from the residual oxygen concentration in the exhaust gas. Enter. Then, the actual operating range is determined based on the throttle opening and the engine speed indicated by the signals a and b, and the air-fuel ratio control valve 26 is operated so as to perform predetermined control according to the range.
The control signals d, e, f are output to the first and second negative pressure control valves 31, 36, respectively.

Next, the operation of the above embodiment will be described. The fuel supplied from the fuel tank 21 or the vaporizer 23 to the engine 10 passes through the main fuel passage 24 due to the negative pressure generated in the venturi portion 17 of the intake passage 14, The intake negative pressure in the passage 14 downstream of the throttle valve 18 passes through the auxiliary fuel passage 25 and is sucked and supplied into the intake passage 14, respectively. At this time, the control unit 40 causes the combustion chamber 13
Air-fuel ratio control is performed to converge and maintain the air-fuel ratio of the air-fuel mixture sucked into the target value. That is, the control unit 40 determines the operating region of the engine 10 based on the throttle opening and the engine speed indicated by the signals a and b,
When the region is in a predetermined air-fuel ratio control region II of the low-medium load low-medium rotation region including the idle region I shown in FIG. 2, the signal c from the air-fuel ratio sensor 43 is further input and supplied to the combustion chamber 13. It is determined whether the air-fuel ratio of the air-fuel mixture being operated is lean or rich. The control signal d is set to increase the duty ratio (valve opening time ratio) of the air-fuel ratio control valve 26 on the auxiliary fuel passage 25 when lean, and to decrease the duty ratio when rich. Is output. Thus, when the air-fuel ratio is lean, the amount of fuel sucked and supplied downstream from the throttle valve 18 in the intake passage 14 from the auxiliary fuel passage 25 is increased, and when the air-fuel ratio is rich, the fuel is increased. The amount is reduced and the air-fuel ratio is converged to a predetermined target value. An orifice 27 is provided on the downstream side of the air-fuel ratio control valve 26 in the auxiliary fuel passage 25, and an atmosphere introduction passage 28 is joined therewith. However, when the intake negative pressure is large (the throttle opening is small). In this case, a large negative pressure acts on the downstream side of the air-fuel ratio control valve 26 to prevent excessive intake and supply of fuel.

Further, when the operating region of the engine 10 is in the high load and high rotation region III shown in FIG. 2, the control unit 40 discharges the negative pressure in the actuator 35 of the fuel increase valve 34 (for introducing the atmosphere). 2) The control signal f is output to the second negative pressure control valve 36. This enables the actuator
The fuel increase valve 34 opens the bypass passage 33 via 35,
The fuel supplied from the main fuel passage 24 to the intake passage 14 is supplied through both the orifice 32 and the bypass passage 33, and the fuel supply amount is increased. The high load / high speed region III and the normal operation region I shown in FIG.
At V, the duty ratio of the air-fuel ratio control valve 26 is fixed to a predetermined value set in advance according to the region.

On the other hand, the operating range of the engine 10 is the deceleration range V shown in FIG. 2, that is, the throttle valve opening is a predetermined small opening θ.
_{When the value is 0} or less and the fuel is not required to be supplied, the control unit 40 sends the control signal e to the first negative pressure control valve 31 so that the negative pressure is introduced into the actuator 30 of the fuel cut valve 29. At the same time as the output, the air-fuel ratio control valve 26
The control signal d is output to the valve 26 so as to make the duty ratio of zero. Therefore, the fuel cut valve 29 is closed and the air-fuel ratio control valve 26 is also fully closed, so that both the main fuel passage 24 and the auxiliary fuel passage 25 are shut off, and the intake passage 14 or the combustion chamber 13 is closed. The fuel supply will be completely stopped. As a result, useless fuel supply during deceleration operation is reliably prevented, and fuel efficiency performance and exhaust performance are effectively improved.

When the engine speed decreases due to the deceleration operation in such a fuel supply stop state and the operating region shifts to the idle region I shown in FIG. 2, the control unit 40 causes the air-fuel ratio control valve 26 and the fuel cutoff. The control signals d and e are output to open the valve 29 to restart the fuel supply. The stop and restart of the fuel supply by the control unit 40 as described above is performed according to the flowchart shown in FIG. This is done as follows.

That is, the control unit 40 first determines in step S ₁ of the flowchart whether the throttle opening θ indicated by the signal a is less than or equal to a very small predetermined opening θ ₀ , that is, the throttle valve 18 is fully closed or substantially fully closed. If it is determined that the opening is not more than the predetermined opening θ ₀ , it is determined in step S ₂ that the engine rotation speed Ne indicated by the signal b is close to the idle rotation speed.
It is determined whether or not the rotation speed is equal to or higher than the predetermined rotation speed N ₁ . If the rotation speed is N ₁ or more, the control signal d is output so that the duty ratio of the air-fuel ratio control valve 26 is made zero in step S ₃ , that is, the valve 26 is completely closed (fourth step). Symbol a).
Further, in step S ₄ , the control unit 40 controls the second engine speed Ne to be higher than the first predetermined speed N ₁ to be the second speed side.
It is determined whether or not the rotational speed is equal to or higher than a predetermined rotation speed N ₂ , and if it is higher than or equal to the predetermined rotation speed, a control signal e is output to the first negative pressure control valve 31 so as to close the fuel cut valve 29 in step S ₅ (first 4 code slot). As a result, the air-fuel ratio control valve shown in FIG. 2 is operated in the deceleration region V where the engine speed Ne is equal to or higher than the second predetermined speed N _2.
Both 26 and the fuel cut valve 29 will be closed.

Then, as shown in FIG. 4, when the engine speed Ne decreases and first becomes smaller than the second predetermined speed N ₂ , the control unit 40 does not execute step S ₅ of the flowchart and the fuel cut valve 29 is turned off. The opening operation is performed (reference numeral C in FIG. 4), whereby the fuel supply from the main fuel passage 24 shown in FIG. 1 is restarted. Also, the engine speed Ne is the first
When it becomes smaller than the specified speed N ₁ , the control unit
40 does not execute step S ₃ further and the air-fuel ratio control valve 26
Is opened (symbol D in FIG. 4), and the amount of fuel required to converge the air-fuel ratio to the target value is supplied from the auxiliary fuel passage 25.

In this way, the operating region of the engine 10 shifts to the idle region I where the air-fuel ratio control is performed, but in this case, there is a time difference in the fuel supply from the main fuel passage 24 and the auxiliary fuel passage 25. Since the fuel is restarted and the fuel in the fuel chamber 13 is gradually restarted accordingly, the air-fuel ratio control valve and the fuel cut valve are simultaneously opened, and the fuel supply is started simultaneously from both the main fuel passage and the auxiliary fuel passage. In this case, abrupt torque generation or shock is avoided, and the operating range smoothly shifts from the deceleration range V to the idle range I.

It is also conceivable to first open the air-fuel ratio control valve 26 and then open the fuel cut valve 29 at the time of transition from the deceleration area V to the idle area I. However, the main fuel provided with the fuel cut valve 29 may be considered. Since the venturi portion 17 communicating with the passage 24 is far from the fuel chamber 13, the fuel supply from the main fuel passage 24 to the fuel chamber 13 may be delayed and an engine stall may occur after the opening operation of the fuel cut valve 29.

As described above, according to the present invention, in the LPG engine configured to perform the air-fuel ratio control and the fuel stop control in the deceleration region, both the fuel cut valve and the air-fuel ratio control valve in the deceleration region are provided. The fuel cut performance is improved because fuel consumption performance and exhaust performance are improved by reliably preventing unnecessary fuel supply during deceleration operation, and the fuel cut is performed when shifting from the deceleration area to the idle area where fuel supply is restarted. Since the valve and the air-fuel ratio control valve are opened with a time lag, the operating range can be smoothly changed without causing a shock.

[Brief description of drawings]

FIG. 1 is an air-fuel ratio control system diagram of an LPG engine showing an embodiment of the present invention, FIG. 2 is a graph showing its control region, FIG. 3 is a flow chart diagram showing operations at the time of stopping and resuming fuel supply, FIG. 4 is also a time chart diagram. FIG. 5 is a schematic diagram showing a conventional air-fuel ratio control system. 10 …… Engine, 14 …… Intake passage, 17 …… Venturi part, 18 …… Throttle valve, 23 …… Vaporizer, 24
...... Main fuel passage, 25 …… Auxiliary fuel passage, 26 …… Air-fuel ratio control valve, 29 …… Fuel cut valve.

Claims (1)

[Claims] 1. A main fuel passage communicating from a vaporizer to a venturi portion of an intake passage, an auxiliary fuel passage communicating from the vaporizer to a throttle valve downstream of the intake passage, and a signal from an air-fuel ratio sensor installed on the auxiliary fuel passage. LPG having an air-fuel ratio control valve for opening and closing the passage according to
In the engine, a fuel cut valve for opening and closing the main fuel passage is provided, and the fuel cut valve and the air-fuel ratio control valve are closed during the deceleration operation of the engine, and the air-fuel ratio control valve is operated from the fuel cut valve. Also, an air-fuel ratio control device for an LPG engine, which is provided with a control means for maintaining a closed state even at a low engine speed.