JP4367297B2 - Bifuel engine stop control method - Google Patents

Description

  The present invention relates to a stop control method for a bi-fuel engine, and more particularly to a stop control method suitable for low temperatures.

  2. Description of the Related Art Recently, in automobiles and the like, gaseous fuel such as compressed natural gas (CNG) is attracting attention in place of liquid fuel such as gasoline and light oil from the viewpoint of air pollution control and resource saving. However, in the case of CNG, its energy density is lower than gasoline etc. (about 20-30% of gasoline), so vehicles equipped with engines that use CNG are compared to vehicles equipped with engines that use gasoline. The cruising range is short. In addition, due to delays in infrastructure development, the number of filling stations is not sufficient, and there are concerns about long-distance movement. In view of this, a dual fuel that can be supplied to the engine by switching at least one of the gaseous fuel and the liquid fuel, that is, a bi-fuel engine has been proposed.

  As such a bi-fuel engine, for example, the one described in Patent Document 1 is known. In this bi-fuel engine, in order to suppress discharge of unburned gas due to fuel adhesion at the time of cold start, gaseous fuel is injected from the gaseous fuel injection valve until the engine changes from a cold state to a predetermined warm-up state. After the predetermined warm-up state, the fuel is switched and controlled to inject liquid fuel from the liquid fuel injection valve.

  On the other hand, in order to improve the startability of the engine by eliminating sticking of the gaseous fuel injection valve at a low temperature due to the characteristics of the gaseous fuel in an engine using only the gaseous fuel, although it is not a bi-fuel engine. In Patent Document 2, when the engine temperature is equal to or lower than a predetermined value, the drive signal of the gaseous fuel injection valve is set to a larger current than in the normal time and the energization time is lengthened to eliminate sticking. Is disclosed.

  Furthermore, in Patent Document 3, in an engine using only gaseous fuel, in order to be able to release the sticking (adhesion) of the gaseous fuel injection valve at the start of cryogenic temperature, gaseous fuel injection is performed when the engine is stopped. A pressure relief control is performed to open and close the gaseous fuel injection valve and the communication path so as to reduce the fuel pressure applied to the valve, and at the time of start-up, a test valve that opens the gaseous fuel injection valve with the communication path closed ( A technique is disclosed in which control is performed.

JP 2000-213394 A JP-A-10-227248 Japanese Patent Laid-Open No. 2000-274312

  By the way, also in the low temperature start control in the bi-fuel engine, when using a gas such as CNG as the fuel, there is a problem of sticking the gaseous fuel injection valve as described above as in the case of the engine using only the gaseous fuel. Exist. Therefore, it is conceivable to start with a liquid fuel at the time of starting at a low temperature. However, in the case of liquid fuel, since it takes time to evaporate, that is, vaporize after being supplied by injection, it is necessary to increase the injection supply amount in anticipation of this, and it is necessary to inject such liquid fuel. In all starting operations, an increase in unburned components due to liquid fuel adhering to the port and the wall surface of the combustion chamber is observed, leading to deterioration in fuel consumption and emission of unburned HC. Therefore, it is preferable to start with a gaseous fuel that does not have such a problem of the adhesion of fuel. Although the problem of sticking of the injection valve can be prevented in advance, the pressure release control of the gaseous fuel is indispensable at the time of stop, and cannot be performed at the time of stop with liquid fuel.

  On the other hand, in a vehicle system using a bi-fuel engine, there is a case where selection of fuel at the time of starting is left to the user's intention. When starting is selected or when liquid fuel cannot be used due to the remaining amount of fuel, there is a possibility of causing a problem of starting failure at the time of gaseous fuel.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a stop control method for a bi-fuel engine that can reliably start a gas fuel at a low temperature.

A bifuel engine stop control method according to the present invention that solves the above-mentioned problems is a bifuel engine capable of independently injecting and supplying gaseous fuel and liquid fuel without switching to gaseous fuel after operation with liquid fuel. When stopping the engine, when the temperature of the gaseous fuel is at a low temperature stop lower than a predetermined value and the remaining amount of liquid fuel is greater than or equal to a predetermined value, the liquid fuel injection is stopped and stopped. When the remaining amount of the fuel is less than a predetermined value, the injection is switched from the liquid fuel to the gaseous fuel and the pressure release control is performed, and then stopped.

According to the stop control method for a bi-fuel engine according to the present invention, when the engine is stopped without switching to gaseous fuel after operation with liquid fuel, the liquid fuel is When the remaining amount of fuel is greater than or equal to a predetermined value, the injection of liquid fuel is stopped and the engine is stopped. On the other hand, when the remaining amount of liquid fuel is less than the predetermined value, the injection is switched from liquid fuel to gaseous fuel. Since the engine is stopped after the removal control is performed, the next starting failure can be avoided even when starting with gaseous fuel is selected. On the other hand, when the remaining amount of liquid fuel is greater than or equal to a predetermined value, the injection of the gaseous fuel is stopped without stopping the pressure release control, so that the fuel consumption is deteriorated without consuming the gaseous fuel wastefully. There is no.

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

  First, an outline of a bi-fuel engine 100 to which the present invention is applied will be described with reference to FIG. 101 is an engine body, 102 is a cylinder block, 103 is a cylinder head, 104 is a piston, 105 is a combustion chamber, 106 is an intake port, 107 is an exhaust port, and 109 is a spark plug disposed at the top of the combustion chamber 105. Show. The intake port 106 is connected to a surge tank 111 via an intake manifold 110, and the surge tank 111 is connected to an air cleaner 113 via an intake duct 112. An electrically controlled throttle valve 115 driven by a step motor 114 is disposed in the intake duct 112.

  The engine 100 in FIG. 1 includes a gaseous fuel supply system and a liquid fuel supply system. In the present embodiment, CNG is used as the gaseous fuel and gasoline is used as the liquid fuel. The gaseous fuel supply system includes a plurality of CNG injection valves 120 arranged to be able to inject fuel into the combustion chamber 105 in each cylinder, and the plurality of CNG injection valves 120 are connected to a delivery pipe 121 having a common fuel chamber. It is connected. The delivery pipe 121 is further connected to a CNG cylinder 124 as a gas fuel container mounted on a vehicle via a CNG supply line 123 provided with a delivery cutoff valve 122. A fuel cutoff valve and regulator 126 (not shown) are arranged near the outlet of the CNG cylinder 124 of the CNG supply line 123.

  The CNG filled in the CNG cylinder 124 with the filling pressure PF (for example, 20 MPa) is decompressed to a certain regulated pressure PH (for example, 5 MPa) by the regulator 126, and in the normal engine control state, this regulated pressure PH. Therefore, it is injected in the compression stroke from the CNG injection valve 120 as the gaseous fuel injection valve into the cylinder. This adjustment pressure PH is a pressure at which in-cylinder injection is always possible in the compression stroke regardless of the operating state, and from this point, it may be referred to as normal injection pressure.

  Similarly, the liquid fuel supply system includes a gasoline injection valve 130 serving as a liquid fuel injection valve disposed in an intake passage in the intake manifold 110 so as to be capable of injection. The gasoline injection valve 130 is connected via a gasoline supply line 132. It is connected to a gasoline tank 134 as a liquid fuel container mounted on the vehicle. Further, a fuel pump 133 is disposed in the gasoline supply line 132. These CNG injection valve 120 and gasoline injection valve 130 are controlled based on output signals from electronic control unit 300, respectively.

  The electronic control unit (hereinafter referred to as ECU) 300 is a digital computer, and as is well known, a ROM (Read Only Memory), a RAM (Random Access Memory), and a CPU (Microcontroller) connected to each other via a bidirectional bus. Processor), a B-RAM (backup RAM) that is always connected to a power source, an input port, an output port, and the like.

  A pressure sensor 140 that generates an output voltage proportional to the absolute pressure in the surge tank 111 is attached to the surge tank 111 connected to the intake manifold 110. In the CNG supply line 123 at the outlet of the CNG cylinder 124, a CNG residual pressure sensor 141 that generates an output voltage proportional to the residual CNG amount in the CNG cylinder 124, that is, the residual pressure, is disposed. A gasoline remaining amount sensor 142 that generates an output voltage proportional to the amount of remaining gasoline in the gasoline tank 134 is disposed. The output voltages of these sensors 140, 141, and 142 are respectively input to the input ports of ECU 300 via corresponding AD converters. Further, the input port includes a rotation speed sensor 143 that generates an output pulse representing the engine rotation speed N, a throttle opening sensor 144 that detects the rotation angle of the throttle valve 115, and an accelerator opening that detects the amount of depression of the accelerator pedal. A sensor 145, a coolant temperature sensor 146 for detecting the engine coolant temperature, a fuel temperature sensor 147 for detecting the fuel temperature of the CNG cylinder 124, and the like are connected. On the other hand, the output ports of the ECU 300 are connected to the spark plug 109, the step motor 114, the CNG injection valve 120, the delivery cutoff valve 122, the fuel pump 133, the gasoline injection valve 130, and the like via corresponding drive circuits. .

  Here, the stop control of the present invention for the bi-fuel engine having the above configuration will be described. First, in the first embodiment in which the fuel at the time of starting the engine is automatically selected on the system side of the vehicle on which the bi-fuel engine 100 is mounted, for example, according to the stop control routine shown in FIG. The stop control is executed. This control routine is executed by interruption every predetermined crank angle after the ignition switch is turned off.

  That is, if it is determined in step S201 that the ignition switch has been turned off from the standby state, the process proceeds to step S202, and it is determined whether or not the operation is stopped at a low temperature. The determination as to whether or not to stop at a low temperature is made based on the detection value from the fuel temperature sensor 147 that detects the fuel temperature of the CNG cylinder 124, whether or not this is below a predetermined value (for example, 0 ° C.). If the determination in step S202 is not a low-temperature stop, that is, "NO", the process proceeds to step S206, and normal stop control is performed by stopping the fuel being supplied.

  On the other hand, if it is determined in step S202 that the stop is at a low temperature, that is, "YES", the process proceeds to step S203, and it is determined whether the gasoline operation mode or the CNG fuel operation mode is selected. Here, when it is not the CNG fuel operation mode, that is, when the gasoline operation mode is “NO”, the process proceeds to step S207, and it is determined whether or not the gasoline amount is equal to or greater than a predetermined value. When the gasoline amount is equal to or greater than the predetermined value, that is, when “YES”, the process proceeds to step S210, and normal engine stop control is performed in which the gasoline injection supply from the gasoline injection valve 130 to the intake port 106 is stopped. On the other hand, when the gasoline amount is not equal to or greater than the predetermined value, that is, when it is less than the predetermined value and “NO”, the next start must be performed with the CNG fuel, and this start must be performed with certainty. Proceed to, and switch to CNG fuel. And it progresses to step S209, and after CNG pressure release control mentioned later is performed, stop control by stopping fuel supply from CNG injection valve 120 is performed.

  By the way, when the CNG fuel operation mode is selected in the determination of whether or not the gasoline operation mode or the CNG fuel operation mode is selected in step S203 described above, whether or not the gasoline amount is greater than or equal to a predetermined value in step S204. It is determined whether or not. When the amount of gasoline is equal to or greater than the predetermined value, that is, “YES”, it is possible to start with gasoline fuel. Therefore, the process proceeds to step S205, and the fuel supply from the CNG injection valve 120 is simply performed without performing the CNG depressurization control. Normal stop control is performed by stopping.

  On the other hand, if the determination in step S204 is “NO”, that is, if the gasoline amount is less than the predetermined value, the next start must be performed with CNG fuel, and this start must be performed reliably. Therefore, it progresses to step S209, and after CNG pressure relief control mentioned later is performed, stop control by stopping fuel supply from CNG injection valve 120 is performed.

  Further, in the vehicle system in which the bi-fuel engine 100 is mounted, in the second embodiment in which the fuel at the start of the engine 100 can be selected only by the user's selection, for example, according to the stop control routine shown in FIG. 100 stop control is executed. Note that this control routine is also the same as that in the previous embodiment that is executed by interruption every predetermined crank angle after the ignition switch is turned OFF.

  Therefore, if it is determined in step S301 that the ignition switch has been turned OFF from the standby state, the process proceeds to step S302, where it is determined whether or not the operation is stopped at a low temperature. The determination as to whether or not to stop at a low temperature is made based on the detection value from the fuel temperature sensor 147 that detects the fuel temperature of the CNG cylinder 124, as in the previous embodiment, based on whether or not it is a predetermined value or less. If it is determined in step S302 that the stop is not at a low temperature, that is, "NO", the process proceeds to step S304, and normal stop control is performed by stopping the fuel being supplied.

  On the other hand, if it is determined in step S302 that the stop is at a low temperature, that is, "YES", the process proceeds to step S303, and it is determined whether the gasoline operation mode or the CNG fuel operation mode is selected. Here, when it is not the CNG fuel operation mode, that is, when “NO” in which the gasoline operation mode is selected, there is a possibility that the start by the CNG fuel may be selected at the next start, so the process proceeds to step S305 and the CNG fuel Is switched to. And it progresses to step S306, and after the CNG pressure relief control mentioned later is performed, stop control by stopping the fuel supply from the CNG injection valve 120 is performed. Further, in the determination in step S303, when the CNG fuel operation mode is selected, the process proceeds directly to step S306, and after the CNG depressurization control is executed, the fuel supply from the CNG injection valve 120 is stopped. Stop control is performed.

  The CNG pressure release control will be described with reference to the time chart of FIG. This CNG depressurization control is usually performed in a paired relationship with idle driving control at the next start.

  In this CNG depressurization control, the delivery cutoff valve 122 is closed (see FIG. 4b) almost simultaneously with the operation of turning off the ignition switch (see FIG. 4c). Then, while sending a drive signal to the CNG injection valve 120 and an ignition signal to the spark plug 109 for a predetermined time (for example, about 1 second) (see f and g in FIG. 4), the ISC correction value and the ignition delay amount are set. Increase (see d and e in FIG. 4) to accelerate fuel consumption. As a result, the fuel pressure in the delivery pipe 121 is set to 0 or below a predetermined value (see FIG. 4a). This prevents the CNG injection valve 120 from sticking or sticking while the vehicle is stopped and the engine is stopped due to the CNG fuel pressure. Then, the CNG fuel pressure at the time of starting with the next CNG fuel is set to 0 or a predetermined value or less.

  An example of the next start time fuel injection control routine after the above stop control is performed is shown in the flowchart of FIG. This control routine is executed by interruption every predetermined crank angle when the ignition switch is turned on and the starter is operated.

  First, in step S501, when the starter is turned on from the standby state, the process proceeds to step S502, and it is determined whether or not the start is a low temperature. This low temperature start determination can be made based on engine coolant temperature, engine oil temperature, or intake air temperature, which is representative of the engine temperature. In this example, the detection value from the coolant temperature sensor 146 is used. Whether or not this is below a predetermined value (for example, 0 ° C.) is performed.

  If it is determined in step S502 that the engine is not cold start, that is, “NO”, the process proceeds to step S510, in which gasoline is supplied from the gasoline injection valve 130 to the intake port 106, or the CNG injection valve 120 to CNG in the cylinder. Normal engine start and operation control is performed by injecting and supplying the fuel in the compression stroke. It should be noted that normal engine start and operation control other than the low temperature start are not included in the gist of the present invention, and thus detailed description thereof is omitted.

  On the other hand, if it is determined in step S502 that the engine is cold starting, that is, "YES", the process proceeds to step S503, and it is determined whether or not the CNG fuel operation mode is selected. Here, the CNG fuel operation mode is a switching / switching in which the fuel to be used is switched automatically or in response to the intention of the driver in order to effectively exhibit the characteristics of the bi-fuel engine. In a bi-fuel engine equipped with a selection system, the mode of operation selected to use CNG fuel. Normally, since driving with CNG fuel is advantageous from the viewpoint of suppressing fuel consumption deterioration and unburned HC emission, it is in the CNG fuel operating mode, and the process proceeds to step S504 after step S503. However, when the driver is not in the CNG fuel operation mode, that is, when the gasoline operation mode is selected, the process proceeds to step S511, and normal engine start and operation control with gasoline, which will be described later, is performed.

  Therefore, in step S504, it is determined whether or not the gasoline amount is greater than or equal to a predetermined value. The predetermined value of the gasoline amount is determined from the viewpoint of whether or not traveling to the nearest gas station or filling station is sufficiently possible. The gasoline amount being less than the predetermined value means that the gasoline amount was less than the predetermined value even when the engine was stopped last time. Therefore, in order to surely start with CNG fuel regardless of gasoline fuel, the aforementioned pressure release control at the time of stop is performed at the previous stop, so when the gasoline amount is less than a predetermined value, Proceeding to step S512, CNG idle start control described later is executed. On the other hand, when the gasoline amount is equal to or greater than the predetermined value, the process proceeds to step S505, and normal start control in CNG fuel injection is performed. In this normal start control by CNG fuel injection, in this example, a predetermined drive signal is sent from the ECU 300 to the CNG injection valve 120, and CNG is injected and supplied from the CNG injection valve 120 into the cylinder in the compression stroke. Control is performed. The data regarding the injection timing and injection period of the starting fuel injected from the CNG injection valve 120 are respectively the absolute pressure PM in the surge tank 111 and the engine speed N representing the temperature state of the engine 100 and the engine load. Is stored in the ROM in advance in the form of a map. Here, the CNG injection period is a period required to inject CNG into the cylinder by the required amount under the normal injection pressure set by the regulator 126 under a reduced pressure.

  After the normal start control in the CNG fuel injection in step S505 is performed, the process proceeds to step S506, and it is determined whether or not the CNG fuel injection is failed. That is, in normal start control in CNG fuel injection, a fail signal IJf that is generated when the CNG injection valve 120 is not driven for some reason (such as sticking) even though the drive signal is sent from the ECU 300. Is detected by the ECU 300 and determined. The determination of whether or not the CNG fuel injection is failed is performed, for example, when a drive signal is sent to the CNG injection valve 120 once or twice and a fail signal IJf is generated. When the fail signal IJf is issued, the process proceeds to step S507, where the control is performed by switching to gasoline.

  In this starting control by gasoline, the engine is started by injecting gasoline in the intake stroke, and thereafter, uniform combustion by the stoichiometric air-fuel ratio or lean region is performed. Data relating to the injection timing and injection period of the fuel injected from the gasoline injection valve 130 at the time of starting is also stored in advance in the form of a map in the ROM. The gasoline injection period is a period required to inject gasoline into the intake passage in the intake stroke under a constant pressure boosted by the fuel pump 133.

  After the engine is started by injecting gasoline in step S507, the process proceeds to step S508, and it is determined whether or not the engine 100 has been warmed up. The determination as to whether or not the warm-up has been completed is made based on a detection value from the cooling water temperature sensor 146 based on whether or not this is a predetermined value (for example, 50 ° C.) or more. Such a predetermined value is obtained by experiments as a temperature at which the cause of sticking of the CNG injection valve 120 is eliminated. When the warm-up is completed, the process proceeds to step S509, and the operation is switched to the operation using CNG injection.

  Next, normal engine start-up and operation control with gasoline performed in step S511 when the determination in step S503 described above is not the CNG fuel operation mode, that is, the gasoline operation mode is selected will be described. In the normal engine start-up and operation control with gasoline, only gasoline fuel is injected and supplied into the intake passage or intake port 106 in the intake stroke by the gasoline injection valve 130. As described above, the data relating to the injection timing and the injection period of the fuel injected from the gasoline injection valve 130 are stored in the ROM in advance in the form of a map corresponding to the gasoline start state of the engine 100. On the basis of this, a predetermined amount of gasoline is injected and supplied.

  Note that after the CNG idling start control in step S512 and in the determination in step S506, if there is no failure in the injection from the CNG injection valve 120, the process proceeds to step S513, and the operation control in CNG is performed. Is called.

  Here, the CNG idle start control executed in step S512 when it is determined in step S504 that the gasoline amount is less than the predetermined value will be described with reference to the time chart of FIG. The CNG idle driving start control is performed in a paired relationship with the above-described pressure release control when the engine is stopped.

  Therefore, in the CNG idle driving start control, the delivery shutoff valve 122 is closed by the above-described pressure release control (see i in FIG. 6B), and the fuel pressure (delivery fuel pressure) in the delivery pipe 121 is 0 or less than a predetermined value. In the state (see FIG. 6 (B) j), the CNG injector 120 is normal from the start of cranking (see FIG. 6 (B) b) to the cylinder discrimination (see FIG. 6 (B) c). The driving is performed with a driving signal having a large driving current and a long driving period (see FIGS. 6B to 6H), which is indicated as an injector in the figure. Thereby, this sticking of the CNG injection valve 120 sticking or sticking due to the low temperature is peeled off. Then, after cylinder discrimination, the delivery cutoff valve 122 is opened (refer to FIG. 6 (B) i), and the fuel amount at start is injected and started. In addition, as shown in FIG. 6A, the drive signal of the CNG injection valve 120 is a DCDC drive having a larger driving force in order to securely remove the sticking or sticking of the CNG injection valve 120. Control is performed so as to have a period Td, a battery voltage driving period Tb with a large driving force, and a holding current driving period Th for maintaining the valve open state.

  In the above-described embodiment, the CNG fuel is injected and supplied directly into the cylinder in the compression stroke to perform stratified combustion, and the gasoline fuel is injected and supplied into the port in the intake stroke to perform homogeneous combustion. Both the gasoline fuel and the gasoline fuel may be injected into the cylinder or the port.

  Furthermore, in the embodiments described so far, an example in which CNG is used as the gaseous fuel and gasoline is used as the liquid fuel has been described. However, as the gaseous fuel, for example, natural gas and petroleum gas which are primary fuels, or coal conversion gas and petroleum conversion gas which are secondary fuels can be used. Needless to say, hydrocarbons such as isooctane, hexane, heptane, light oil, and kerosene, butanes that can be stored in a liquid state, hydrocarbons such as propane, and methanol can be used as the liquid fuel.

It is a whole line figure showing an outline of a bi-fuel engine to which the present invention is applied. It is a flowchart which shows an example of the stop control routine in this invention. It is a flowchart which shows the other example of the stop control routine in this invention. It is a time chart for demonstrating stop pressure release control, and shows the operation timing of each part. It is a flowchart which shows an example of the starting control routine performed after the stop control in this invention is performed. It is a time chart for demonstrating start time blanking control, (A) shows the drive pattern of the drive signal of a CNG injection valve, (B) shows the operation timing of each part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Bi-fuel engine 120 CNG injection valve 122 Delivery shut-off valve 123 CNG supply line 124 CNG cylinder 126 Regulator 130 Gasoline injection valve 134 Gasoline tank 141 CNG residual pressure sensor 142 Gasoline remaining amount sensor 146 Cooling water temperature sensor 147 Fuel temperature sensor 300 Electronic control unit

Claims (1)

In a bi-fuel engine that can inject and supply gas fuel and liquid fuel independently,
When stopping the engine without switching to gaseous fuel after operation with liquid fuel, when the temperature of the gaseous fuel is at a low temperature stop lower than a predetermined value and the remaining amount of liquid fuel is equal to or higher than the predetermined value, this A bi-fuel engine characterized in that the injection of liquid fuel is stopped and stopped, and when the remaining amount of liquid fuel is less than a predetermined value, the injection is switched from the liquid fuel to the gaseous fuel and then the pressure release control is performed and then stopped. Stop control method.

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