JPH07158477A - Air-fuel ratio control method and device for gas engine heat pump - Google Patents

Abstract

PURPOSE:To provide a method and a device for controlling the air-fuel ratio of a gas engine heat pump capable of decreasing a nitrogen oxides concentration to the possible extent, and capable of suppressing various kinds of undersirable variations less than an allowable variable value. CONSTITUTION:Rotational speed of a compressor 22 is detected by a rotational pickup 11, and a rotational variable value is calculated from the rotational speed of a gas engine 1 by a CPU so as to whether the rotational variable value is within a target range or not, and an air-fuel ratio is controlled to the lean side when the rotational variable value is inside the target range and is controlled to the rich side when it is out of the target range by an actuator 9 and a bypass valve 8 by responding to the output of the CPU 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method and apparatus for a gas engine heat pump in which a lean burn gas engine and a heat pump are combined.

[0002]

2. Description of the Related Art In order to control the air-fuel ratio of a lean burn gas engine, open control in which the air-fuel ratio is set to a predetermined value in advance has been most often used. Further, although the absolute number is extremely small, control using a so-called “λ sensor” is also performed.

[0003]

However, when open control is adopted, individual variations of mass-produced engines, environmental conditions, etc. (especially in the case of the nitrogen oxide concentration of a lean burn gas engine, the influence of humidity is particularly significant). In order to be able to cope with the difference (large), the air-fuel ratio must be set to a considerably rich side from the operating limit. Therefore, it was not possible to sufficiently reduce the nitrogen oxide concentration.

On the other hand, when the λ sensor is used, there is a problem that the λ sensor itself is expensive and the cost is high. Also, because the combustion state of the engine changes even with the same air-fuel ratio due to variations in the air-fuel ratio control system that uses the λ sensor, environmental conditions, etc., control near the operating limit is difficult, and the control target λ is always set. There is no choice but to set it with plenty of room for rich eyes. As a result, the nitrogen oxide concentration could not be reduced sufficiently.

On the other hand, by combining a lean burn gas engine with a heat pump, a so-called gas engine heat pump (GH) is used.
In the case of configuring P), the set rotational speed of the compressor changes in response to the thermal load, but it is necessary for stable output maintenance that the rotational speed does not fluctuate at each set rotational speed.

In the gas engine heat pump, the rotation speed of the compressor is the same as that of the engine when the compressor is directly connected to the gas engine. However, when the compressor is driven by a belt, the rotation speed and rotation fluctuation amount of the gas engine are different from the rotation speed and rotation fluctuation amount of the compressor.

The present invention has been proposed in view of the problems of the prior art, and it is possible to reduce the nitrogen oxide concentration as much as possible, and moreover, the fluctuation of the operation of the compressor which occurs in combination with the gas engine. It is an object of the present invention to provide an air-fuel ratio control method and device for a gas engine heat pump so that is within a target value.

[0008]

As a result of various researches and developments, the inventor has shown, as shown in FIG. 1, fluctuations in frequency of electric power from a generator combined with, for example, a lean burn gas engine (in the upper half of FIG. 1). It was noted that the characteristics (shown in the figure) appear as they are in the fluctuations in the rotational speed of the gas engine (the characteristics shown in the lower half of FIG. 1). At the same time, the inventor also noticed that, as shown in FIG. 2, the fluctuation in the rotational speed of the gas engine increases as the air-fuel ratio (λ) increases. Here, the operating limit of the lean burn gas engine combined with the generator is the air-fuel ratio that satisfies the target value of the frequency fluctuation of the electric power.

The above is also applicable to a gas engine heat pump in which a lean burn gas engine and a heat pump are combined. That is, when controlling the gas engine heat pump, there is a method of detecting the number of revolutions of the gas engine and calculating and controlling the target value of the variation in the number of revolutions. Considering the case where it is different from the rotation speed fluctuation, it is best to detect the rotation speed fluctuation on the compressor side.

The air-fuel ratio control method for a gas engine heat pump according to the present invention based on the above-described findings includes a step of detecting the rotational speed of the heat pump compressor, and a rotational fluctuation value calculated from the detected rotational speed to obtain the rotational fluctuation. A step of determining whether or not the value is within the target range, and a step of controlling the air-fuel ratio to the lean side when the rotational fluctuation value is within the target range, and controlling it to the rich side if outside the target range Is included.

Further, the air-fuel ratio control apparatus for the lean burn gas engine heat pump according to the present invention has a detecting means for detecting the rotational speed of the heat pump compressor, and a rotational fluctuation value is calculated from the detected rotational speed to obtain the target rotational fluctuation value. Judgment means for determining whether or not it is within the range, and air-fuel ratio control means for controlling the air-fuel ratio to the lean side when the rotation fluctuation value is within the target range and to the rich side if it is outside the target range, Includes and.

[0012]

According to the air-fuel ratio control method for a gas engine heat pump of the present invention having the above-described structure, the set engine speed of the gas engine changes in response to a cooling load or a heating load (thermal load). Determine a target range of speed variation in response to the changed set speed. Then, it is determined whether or not the rotation fluctuation value is within the target range, and when the rotation fluctuation value is within the target range, the air-fuel ratio is controlled so as to shift to the lean side. Control to shift to the side. In other words, since the control shifts to the lean side or steps as long as the rotation fluctuation value is within the target range, it is not necessary to perform the control on the rich side more than necessary unlike the conventional control. Since the lean side is controlled as much as possible, the nitrogen oxide concentration is reduced to an extremely low level.

Here, as the control shifts or steps to the lean side, the fluctuation of the rotation speed increases, but according to the present invention, when the control goes too far to the lean side and the fluctuation value of the rotation speed exceeds a predetermined range. Is stepped to the rich side.
As shown in FIG. 2, if the control is stepped to the rich side, fluctuations in the rotational speed of the gas engine are reduced.

As described above, according to the present invention, the control stepped to the lean side as much as possible is performed while the heat load of the heat pump is within a certain range. Therefore, it is possible to reduce the nitrogen oxide concentration as much as possible under the control stepped to the lean side while maintaining the performance of the compressor side.

[0015]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 3 shows a gas engine heat pump 20 in which a lean burn gas engine 1 to which the present invention is applied and a heat pump 21 are combined. The gas engine 1 includes an air supply passage 3, a fuel supply passage 4, a fixed fuel adjustment screw (adjustment screw) 25, a mixer 5,
The mixture of fuel gas and air generated via the mixture supply passage 6 is supplied via the throttle 13. A bypass passage 7 branches from the fuel supply passage 4, and the bypass passage 7 merges with the mixer 5 via a bypass valve 8. In other words, the bypass passage 7 and the bypass valve 8 are another controllable adjusting screw bypassing the fixed adjusting screw 25. As is well known, the heat pump 21 is provided with a compressor 22, a condenser 23 and an evaporator 24.

The bypass valve 8 is opened and closed by an actuator 9 composed of, for example, a stepping motor, and its opening is determined by a CPU 10 which is a control means. The CPU 10 is supplied with a detection signal from the rotary pickup 11 that detects the rotation speed of the compressor 22 and a detection signal from the load sensor 12 that detects the load of the heat pump 20. The throttle valve 13 of the engine is controlled by a throttle controller 14, and the controller 14 operates based on a signal from the rotary pickup 11A that detects the rotation speed on the engine side, or a rotation speed signal that replaces the signal.

The air-fuel ratio of the gas engine 1 depends on the bypass valve 8
It is performed by adjusting the opening degree of. That is, the control of the opening degree of the bypass valve 8 is performed according to the flow chart as shown in FIG.
U10 and the actuator 9 are used. Before explaining the control shown in the flowchart of FIG.
The main routine of the air-fuel ratio control shown by is explained.

In FIG. 5, when the operation of the gas engine 1 and the heat pump 20 is started (steps S1 and S).
2) The load of the heat pump 20 is detected by the load sensor 12, and the detection result is determined by the CPU 10 (step S3). Then, first, it is determined whether or not the steady operation is being performed (step S4).

During unsteady operation (step S4 is N
O) Load fluctuation, start / stop control is performed (step S
5) If it is a steady operation (YES in step S4), the present setting speed or actual rotation speed of the compressor is determined (step S40), and the rotation fluctuation target value is determined based on the rotation speed of the compressor determined in step S40. Is determined (step S42). However, the process or algorithm for determining the rotation fluctuation target value in step S42 differs depending on the individual case, and thus detailed description thereof will be omitted. Then, the rotation variation value is calculated or determined from the detection result of the rotary pickup 11 (step S7), and the opening degree of the bypass valve 8 is controlled using the calculation (determination) result of the rotation variation value (step S8). In addition,
Step S7 will be described later with reference to FIG. 6, and
Details of step S8 will be described later with reference to FIG.

After controlling the opening degree of the bypass valve 8, the system waits for a period required for changing the combustion state of the gas engine 1 and the operating state of the heat pump 22 (step S).
9). Then, the load of the heat pump 21 is determined again (step S3).

The above-described process of calculating or determining the rotational fluctuation value (step S7 in FIG. 5) will be described with reference to FIG. First, the output from the rotary pickup 11 is read a predetermined number of times (for example, n) (NO in steps S10 and S11). If the reading of a predetermined number of times is completed (YES in step S11), the n variation data is used to calculate or determine the rotation fluctuation value. Here, "calculation or determination" of the rotation fluctuation value
The phrase "is used" means that the method of obtaining the rotation fluctuation value from the output of the rotary pickup 11 is not limited to arithmetic processing (there are many types), but there are various methods. This is to clarify that there is no limitation.

When the rotation fluctuation value is calculated or determined, the numerical value is stored (step S13) and the process returns to the initial stage (step S14).

A step of controlling the opening degree of the bypass valve 8 by using the rotation fluctuation value calculated or determined in this way (see FIG. 5).
Step S8) will be described with reference to FIG.
When controlling the opening degree of the bypass valve 8, first, the rotation fluctuation target value obtained in step S42 of FIG. 5 is read (step S20). Next, the rotation fluctuation value obtained in the step described above with reference to FIG. 6 and step S7 in FIG. 5 is read (step S21). Then, it is determined whether or not the rotation fluctuation value is within the range of the rotation fluctuation target value (step S22).

In the embodiment shown in FIG. 3, the actuator 9 for controlling the opening degree of the bypass valve 8 is composed of a stepping motor. Then, based on the determination result in step 22, when the opening degree of the bypass valve 8 is decreased to increase the air-fuel ratio, the lean side is stepped, and when the air-fuel ratio is decreased, the rich side is stepped. Has been done. That is, when the rotation fluctuation value is within the range of the rotation fluctuation target value (YES in step S22), the CPU 10 controls the stepping motor so that the control is made leaner and the nitrogen oxide concentration is further reduced. Send a signal to step to the lean side. Therefore, the step position is calculated (step S23), the step speed is calculated (step S24), and then the lean side is stepped (steps S25 and S26).

On the other hand, when the rotation fluctuation value exceeds the range of the rotation fluctuation target value (NO in step S22), it is determined that the air-fuel ratio is set too high and the rotation speed fluctuation is slightly increased. Then, necessary processing is performed to reduce the air-fuel ratio and make the control rich. That is, the step position is calculated (step S27), the step speed is calculated (step S28), and then the rich side is stepped (steps S29 and S30).

After the necessary processing is performed based on the determination result of step S22, the control is returned to the initial stage (step S31).

It should be noted that the illustrated embodiment is merely an example and is not intended to limit the technical scope of the present invention.

[0029]

The effects of the present invention are listed below.

(1) Since information is obtained from the compressor by the rotary pickup, it is not affected by engine performance, sensors, or variations in them.

(2) Since the control is performed on the basis of fluctuations in the rotational speed, which is a parameter related to the rotational speed of the gas engine, it is not affected by changes in environmental conditions such as humidity.

(3) It is not necessary to perform control on the rich side more than necessary as in conventional control.

(4) Since the lean side is controlled as much as possible while maintaining the performance of the compressor, it is possible to control near the operating limit, and it is possible to suppress the nitrogen oxide concentration to the limit. .

(5) Since the control system can be simplified, the reliability and durability can be improved and the cost can be reduced.

(6) Since the control is performed on the basis of the fluctuation of the rotation speed, the operability of the gas engine heat pump is directly evaluated.

(7) The operation fluctuation of the gas engine heat pump combined with the lean burn gas engine can be kept within a certain range.

(8) The nitrogen oxide concentration can be reduced as much as possible under the control stepped to the lean side, while the gas engine heat pump can be operated appropriately.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a frequency fluctuation characteristic of electric power from a generator and a rotation fluctuation of a lean burn gas engine.

FIG. 2 is a characteristic diagram showing the relationship between the rotation fluctuation of the lean burn gas engine and the air-fuel ratio.

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4 is a view showing a flowchart of a bypass valve opening control routine.

FIG. 5 is a diagram showing a main flowchart.

FIG. 6 is a diagram showing a flowchart of a control routine for calculating or determining a rotation fluctuation value.

[Explanation of symbols]

 1 ... Lean combustion gas engine 3 ... Air supply passage 4 ... Fuel supply passage 5 ... Mixer 6 ... Mixture supply passage 7 ... Bypass passage 8 ... Bypass valve 9 ...・ Actuator 10 ・ ・ ・ CPU 11 ・ ・ ・ Rotary pickup 12 ・ ・ ・ Load sensor 13 ・ ・ ・ Throttle valve 14 ・ ・ ・ Throttle valve control means 20 ・ ・ ・ Gas engine heat pump 21 ・ ・ ・ Heat pump 22 ・ ・ ・ Compressor 23 ... Condenser 24 ... Evaporator 25 ... Adjust screw

Claims (2)

[Claims] 1. A step of detecting the rotational speed of a heat pump compressor, a step of calculating a rotational fluctuation value from the detected rotational speed to determine whether the rotational fluctuation value is within a target range, and a rotational fluctuation. And a step of controlling the air-fuel ratio to the lean side when the value is within the target range and to the rich side when the value is outside the target range. 2. A detection means for detecting the rotation speed of the heat pump compressor, and a judgment means for calculating a rotation fluctuation value from the detected rotation speed to judge whether or not the rotation fluctuation value is within a target range. An air-fuel ratio of the gas engine heat pump, characterized in that it includes an air-fuel ratio control means for controlling the air-fuel ratio to the lean side when the rotational fluctuation value is within the target range and to the rich side if the rotational fluctuation value is outside the target range. Control device.