JP2013047524A - Air-fuel ratio control method and device for lpg engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LPG engine that determine a composition of LPG whenever used to execute satisfactory air-fuel ratio control without increasing cost.SOLUTION: An air-fuel control device which adjusts a fuel injection amount by feedback control by continuously detecting an emission state via an emission characteristic detection means provided in an exhaust pipe of the LPG engine executes an air-fuel ratio control method. The air-fuel ratio control device generates a change in an output signal of the emission characteristic detection means by executing a specific operation, and determines a fuel composition of the LPG that is currently used by a specific determination method and reflects the composition on subsequent control.

Description

  The present invention relates to an air-fuel ratio control method and an air-fuel ratio control apparatus for an LPG engine using liquefied petroleum gas (hereinafter referred to as “LPG”) as fuel, and in particular, by determining the composition of LPG to be used, optimal fuel injection The present invention relates to an air-fuel ratio control method and an air-fuel ratio control apparatus for an LPG engine for adjusting a quantity to realize a theoretical air-fuel ratio.

  In conventional general LPG engines, air-fuel ratio control and ignition timing control are performed on the assumption that autogas (propane 20%, butane 80%) is used. In general, the fuel components (propane and butane composition ratios, etc.) differ depending on the production lot, etc., and the difference in the fuel components of LPG differs in the calorific value and octane number of propane and butane. This may lead to a reduction in power performance and fuel consumption.

  Therefore, in the LPG engine, it is indispensable to determine the composition of the LPG being used from the viewpoint of optimizing the fuel injection timing / ignition timing and air-fuel ratio control.

  Therefore, for example, in Japanese Patent Application Laid-Open No. 8-5596, a gas heat conduction sensor is used when using gas fuel whose mixing ratio is unknown, and hydrocarbons having 4 or less carbon atoms as a main component are known at a known ratio. By obtaining in advance a relationship index between the sensor output for a plurality of mixed reference gas mixtures and the theoretical air-fuel ratio of the reference gas mixture, the theoretical air-fuel ratio of the gas fuel used is determined according to this index. A technique has been proposed in which engine air-fuel ratio control is executed based on the theoretical air-fuel ratio.

However, the technique presented in this publication is to newly add components such as sensors to determine the composition of the gas fuel used, and to perform accurate air-fuel ratio feedback control according to the determination result, Since new parts are added, there is a problem that the cost is inevitably increased. Therefore, a technology that makes it possible to execute favorable air-fuel ratio control by determining the composition of the used LPG without causing a rise in cost by using parts and devices that are standardly mounted on a general LPG engine vehicle. Development of was desired.
JP-A-8-5596

  The present invention is intended to solve the above-described problems, and for the LPG engine, the composition of the LPG to be used can be determined each time without causing an increase in cost, and good air-fuel ratio control can be executed. The challenge is to do so.

  The present invention has been made in order to solve the above-described problem, and uses an air-fuel ratio control using a detection signal in a specific property of exhaust gas continuously detected by an exhaust property detecting means provided in an exhaust pipe of an LPG engine. In the air-fuel ratio control method in which the device adjusts the fuel injection amount by feedback control, the air-fuel ratio control device causes a change in the output signal from the exhaust property detection means, and based on this change, a predetermined determination method It is characterized in that the fuel composition of the LPG used is judged and reflected in the subsequent control.

For an LPG engine, an air-fuel ratio control method for an LPG engine based on an output signal from an exhaust property detection means such as an oxygen sensor disposed in an exhaust pipe. Normally, an air-fuel ratio control device that performs air-fuel ratio feedback control while adjusting the fuel injection amount is equipped. In this way, the air-fuel ratio control device intentionally operates to detect exhaust gas properties. By changing the output signal, it is possible to determine the composition of the LPG from the contents of the change, so that an accurate air-fuel ratio control can be performed according to the composition of the used LPG without adding new expensive parts. Can be executed.

  In this case, the exhaust property detection means is an oxygen sensor disposed in an exhaust pipe disposed between the LPG engine and the three-way catalyst, and the air-fuel ratio control device operates the air-fuel ratio during steady operation of the LPG engine. And then observing the output signal of the oxygen sensor, and if the output signal is in the vicinity of a preset reference voltage, it is determined that the stoichiometric air-fuel ratio is present, and the output signal is set to the preset output voltage. If it is lower than the reference voltage, the air-fuel ratio is judged to be lean, and the fuel injection amount is adjusted so that the output signal substantially matches the reference voltage while detecting the intake air amount, so that it substantially matches the reference voltage. The theoretical air-fuel ratio of the used LPG is obtained from the fuel injection amount and the intake air amount obtained by the predetermined calculation method, and the fuel composition of the used LPG is determined by the predetermined determination method based on the theoretical air-fuel ratio. It is, use of LPG fuel composition will be able to determine precisely a comparatively simple procedure. In this case, based on the determined fuel composition, if the H / C ratio of the used LPG is obtained using a map or a relational expression showing the relationship between the preset fuel composition and the H / C ratio (atomic ratio), In addition, accurate control is easy to execute.

  Alternatively, the exhaust gas property detection means is an oxygen sensor disposed on the upstream side and the downstream side of the three-way catalyst in the exhaust pipe, and the air-fuel ratio control device stops air-fuel ratio feedback control during steady operation of the LPG engine, Thereafter, a predetermined waveform signal is superimposed on the basic fuel injection signal to cause an air-fuel ratio fluctuation to activate the three-way catalyst, and an operation of adding or subtracting the predetermined injection amount to the basic injection amount is repeated. As a result, in the output signal of the oxygen sensor on the downstream side of the three-way catalyst, a phenomenon of stopping at the voltage value at the time of complete combustion of the fuel is caused to measure the stopping time, and a predetermined determination is made based on the stopping time. The means for determining the fuel composition of the LPG used by the method can accurately determine the fuel composition in the same manner as the above means.

  Alternatively, the exhaust property detection means is an air-fuel ratio sensor disposed downstream of the three-way catalyst in the exhaust pipe, and the air-fuel ratio control device stops air-fuel ratio feedback control during steady operation of the LPG engine, and then By superimposing a predetermined waveform signal on the basic fuel injection signal, causing the air-fuel ratio fluctuation to activate the three-way catalyst, and further repeating the operation of adding or subtracting the predetermined injection amount to the basic injection amount, The theory of LPG used by a predetermined determination method based on a retention time measured by causing a phenomenon that the output signal of the air-fuel ratio sensor on the downstream side of the three-way catalyst is retained in the output signal indicated when the fuel is completely burned. Calculate the air-fuel ratio and use the map or relational expression showing the relationship between the stoichiometric air-fuel ratio and the fuel composition set in advance based on the stoichiometric air-fuel ratio. Composition as means for determining, becomes capable of determining precisely the fuel composition similar to the above means. In this case, if the H / C of the used LPG is obtained using a map or relational expression showing the relationship between the fuel composition and the H / C ratio set in advance based on the determined fuel composition, more accurate control is executed. It will be easy to do.

  Further, an LPG is provided in an engine system having a three-way catalyst and an exhaust property detection means in the exhaust pipe, and adjusts the fuel injection amount by feedback control by continuously detecting the exhaust state via the exhaust property detection means. An air / fuel ratio control apparatus for an LPG engine comprising an intake air amount detecting means and a fuel injection amount adjusting means, and performing the above-described air / fuel ratio control method for an LPG engine. This makes it possible to accurately determine the composition of the used LPG without adding new expensive sensors simply by installing it in a general LPG engine system, and can easily execute good air-fuel ratio control. It will be a thing.

  According to the present invention in which the fuel composition is determined by intentionally operating with the air-fuel ratio control device and changing the output signal of the exhaust property detection means, a standard LPG engine is provided as standard. It is possible to determine the fuel composition of the used LPG without causing an increase in cost by using an apparatus or a component, and to execute good air-fuel ratio control.

  The best mode for carrying out the present invention will be described below with reference to the drawings. The air-fuel ratio control apparatus for carrying out the air-fuel ratio control method of the present invention is based on feedback control by continuously detecting the state of exhaust through an exhaust property detecting means provided in an exhaust pipe provided with a three-way catalyst. An air-fuel ratio control device for an LPG engine that adjusts the fuel injection amount, and also serves as a fuel composition determination device.

  The present invention is characterized in that the output signal by the exhaust property detecting means such as an oxygen sensor changes in the mixing ratio (theoretical air-fuel ratio) of the intake air amount and the fuel injection amount when the fuel completely burns, and flows into the three-way catalyst. Pay attention to the characteristic that the exhaust gas that has passed through the three-way catalyst stays at the theoretical air-fuel ratio for a certain period of time when the exhaust gas fluctuates between the fuel lean region and the fuel rich region, and add expensive sensors and other parts Without any problem, it is possible to detect the fuel composition of the LPG when traveling on the road of a vehicle equipped with an LPG engine, etc., and to provide means for performing optimal air-fuel ratio control according to the composition of the LPG used at low cost It is.

  FIG. 1A shows a first embodiment of the present invention, and an exhaust property detection that is an oxygen sensor on the LPG engine 1 side of a pre-three-way catalyst 3 provided in an exhaust pipe 2 of an LPG engine 1 is shown. A rear three-way catalyst 5 is disposed downstream of the means 4 and the pre-three-way catalyst 3, and the fuel injection amount of the LPG engine 1 is adjusted by feedback control of the exhaust state continuously detected by the exhaust property detecting means 4. To do. First, when the LPG engine 1 is, for example, a vehicle-mounted engine, the air-fuel ratio control device performs an operation of stopping the air-fuel ratio feedback control during relatively stable steady running.

  FIG. 2 is a graph showing the oxygen (O2) sensor output (voltage V) in the vicinity of the theoretical air-fuel ratio (λ = 1). The air-fuel ratio control device detects and observes the output signal of the oxygen sensor at that time, and outputs it. If the signal is higher than a preset reference voltage (for example, 0.45 V), it is determined that the air-fuel ratio of the exhaust gas is on the rich side. Similarly, when the output signal is lower than the reference voltage, it is determined that the air-fuel ratio is on the lean side. On the other hand, if the output signal is near the reference voltage, it is determined that the stoichiometric air-fuel ratio is reached.

  Next, after measuring or calculating the intake air amount, the air-fuel ratio control device decreases the fuel injection amount if the air-fuel ratio due to the exhaust gas is excessively rich, and increases it if it is lean. The fuel injection amount is repeatedly adjusted so that the output signal from the oxygen sensor is in the vicinity of a preset reference voltage.

  Then, the air-fuel ratio control device calculates the theoretical air-fuel ratio of the used LPG from the fuel injection amount determined by this adjustment and the intake air amount at that time. By applying the calculated theoretical air-fuel ratio to, for example, a preset graph (map or the like) in FIG. 3 or a relational expression described in the upper right of the graph, the air-fuel ratio control apparatus determines the fuel composition of the used LPG.

  Further, the air-fuel ratio control device applies, for example, a predetermined relationship graph (such as a map) between the fuel composition and the H / C ratio shown in FIG. 3 or a relational expression described in the upper right of the graph based on the determined fuel composition. The H / C ratio of the used LPG can be obtained. When the air-fuel ratio control apparatus executes such a procedure, it becomes possible to execute good air-fuel ratio control according to the fuel composition of the LPG to be used, and other control can be easily performed accurately.

  FIG. 1B shows a second embodiment of the present invention. The upstream side of the pre-three-way catalyst 3 in the exhaust pipe 2, the downstream side of the pre-three-way catalyst 3, and the rear three-way catalyst 5 are shown. Exhaust property detecting means 4A and 4B each comprising an oxygen sensor are disposed between the upstream sides of the two. First, when the LPG engine 1 is, for example, a vehicle-mounted engine, the air-fuel ratio control device performs an operation of stopping the air-fuel ratio feedback control during a relatively stable steady running as in the first embodiment.

  Next, the air-fuel ratio control device generates a relatively large air-fuel ratio fluctuation from the rich side to the lean side or from the lean side to the rich side by superimposing a predetermined waveform signal on the basic fuel injection signal. The pre-three-way catalyst 3 is then activated, and then the air-fuel ratio is stepped from the rich side to the lean side or from the lean side to the rich side by performing an operation of adding or subtracting the predetermined injection amount to the basic injection amount. To generate fluctuations. At this time, the voltage value (theoretical value) when the fuel is completely burned in the output signal of the exhaust property detection means 4B, which is an oxygen sensor attached between the downstream side of the pre-three-way catalyst 3 and the upstream side of the rear three-way catalyst 5. Since the phenomenon of stopping in the output voltage of the oxygen sensor at the air-fuel ratio occurs, this stopping time is detected and measured.

  Since this stop time has a property that depends on the H / C ratio of the LPG to be used, the air-fuel ratio control device determines the fuel composition of the used LPG based on the relationship between the stop time of the oxygen sensor voltage at the stoichiometric air-fuel ratio and the fuel composition. Determine. By executing such a procedure, the air-fuel ratio control apparatus can execute good air-fuel ratio control according to the fuel composition of the used LPG as described above.

  FIG. 1 (c) shows a third embodiment of the present invention. The downstream side of the pre-three-way catalyst 3 and the rear three-way catalyst 5 in the second embodiment shown in FIG. 1 (b). The exhaust property detection means 4C comprising an oxygen sensor between the upstream sides of the two is an air-fuel ratio sensor. First, when the LPG engine 1 is, for example, a vehicle-mounted engine, the air-fuel ratio control device performs an operation of stopping the air-fuel ratio feedback control during the relatively stable steady running as described above.

  Next, the air-fuel ratio control device generates a relatively large air-fuel ratio fluctuation from the rich side to the lean side or from the lean side to the rich side by superimposing a predetermined waveform signal on the basic fuel injection signal. Then, the pre-three-way catalyst 3 is activated, and then the operation of adding or subtracting the predetermined fuel injection amount to or from the basic injection amount is performed, so that the air-fuel ratio is changed from the rich side to the lean side or from the lean side to the rich side. Generate step-like fluctuations. At this time, the fuel as shown in FIG. 5 is completely burned in the output signal of the exhaust property detection means 4C which is an air-fuel ratio sensor attached between the downstream side of the pre-three-way catalyst 3 and the upstream side of the rear three-way catalyst 5. Since the phenomenon of stopping in the output signal shown in this case occurs, this stopping time is detected and measured.

  This stop time depends on the amount of the oxidizing substance or reducing substance adsorbed on the catalyst layer and has a property that the starting air-fuel ratio of the air-fuel ratio step-like fluctuation becomes shorter as it approaches the stoichiometric air-fuel ratio. Performs an operation of gradually changing the start point air-fuel ratio, searches for the start point air-fuel ratio at which the stop time becomes 0 second, and determines the start point air-fuel ratio at that time as the theoretical air-fuel ratio of the used LPG. Then, by applying this theoretical air-fuel ratio to, for example, a preset relationship graph (such as a map) of the theoretical air-fuel ratio and fuel composition in FIG. To do.

  Further, the air-fuel ratio control device applies the fuel composition to the H / C of the LPG to be used by applying the fuel composition to a relational graph (such as a map) of the fuel composition and the H / C ratio in FIG. The ratio can be determined. By executing such a procedure, the air-fuel ratio control device can execute good air-fuel ratio control according to the fuel composition of the LPG used in the same manner as described above.

  The above-described three embodiments can be substantially implemented by using devices and components that are standardly installed in a general LPG engine system (the second embodiment requires two oxygen sensors). ) Since only the software side of the electronic control unit, which is an air-fuel ratio control device, can be changed, there is no need to add new expensive parts, so the fuel composition of the LPG used can be accurately handled at a relatively low cost. Thus, excellent air-fuel ratio control can be executed.

  Furthermore, as shown in the LPG fuel composition detection flow of FIG. 6, the fuel can be further increased by combining the first embodiment and the second embodiment, or the first embodiment and the third embodiment. The accuracy of composition detection can be increased.

  As described above, regarding the LPG engine, according to the present invention, it is possible to accurately determine the composition of the LPG to be used without causing an increase in cost and to execute good air-fuel ratio control.

It is explanatory drawing which shows embodiment of this invention, (a) is 1st Embodiment, (b) is 2nd Embodiment, (c) is description explaining 3rd Embodiment. Figure. The graph of the O2 sensor output signal in the theoretical air fuel ratio ((lambda) = 1) vicinity. The graph which shows the relationship between a theoretical air fuel ratio and a fuel composition. The graph which shows the relationship between a fuel composition and H / C ratio. Explanatory drawing which shows the stationary phenomenon of the post-catalyst air-fuel ratio sensor voltage at the time of the air-fuel-ratio step change in 3rd Embodiment of FIG.1 (c). Explanatory drawing which shows an example of the LPG fuel composition detection procedure.

1 LPG engine, 2 exhaust pipe, 3 pre three-way catalyst, 5 rear three-way catalyst, 4
, 4A, 4B, 4C Exhaust property detection means

Claims (2)

  In an air-fuel ratio control method in which an air-fuel ratio control device adjusts a fuel injection amount by feedback control using a detection signal in a specific property of exhaust gas continuously detected by an exhaust property detection means provided in an exhaust pipe of an LPG engine. The air-fuel ratio control device causes a change in the output signal from the exhaust property detection means, and based on this change, determines the fuel composition of the currently used LPG by a predetermined determination method, and performs subsequent control. In the air-fuel ratio control method for the LPG engine to be reflected, the exhaust property detection means is an oxygen sensor disposed on the upstream side and the downstream side of the three-way catalyst in the exhaust pipe, respectively, and the air-fuel ratio control device is a steady state of the LPG engine. Air-fuel ratio feedback control is stopped during operation, and then a predetermined waveform signal is superimposed on the basic fuel injection signal to change the air-fuel ratio The fuel is generated in the output signal of the oxygen sensor downstream of the three-way catalyst by repeating the operation of generating and activating the three-way catalyst and adding or subtracting a predetermined injection amount to the basic injection amount. An air-fuel ratio of an LPG engine that causes a phenomenon of stopping at a voltage value at the time of complete combustion, measures a stopping time, and determines a fuel composition of an LPG to be used by a predetermined determination method based on the stopping time Control method.   An LPG engine that is disposed in an engine system that includes the three-way catalyst and the oxygen sensor in the exhaust pipe and that adjusts the fuel injection amount by feedback control by continuously detecting the state of exhaust through the oxygen sensor. 2. An air-fuel ratio control apparatus for an LPG engine, comprising: an intake air amount detection means and a fuel injection amount adjustment means, wherein the air-fuel ratio control method for an LPG engine according to claim 1 is implemented. apparatus.