Ignition control system and method based on online detection of pressure relay

Abstract

The invention discloses an ignition control system based on online detection of a pressure relay. The ignition control system comprises an ignition unit, a gas storage device, an ignition controller and the pressure relay. The ignition unit is connected to the gas inlet end of the gas storage device in parallel, and the pressure relay is arranged on a gas path of the gas storage device. The ignition controller is electrically connected with the ignition unit and the pressure relay at the same time, and the ignition controller is used for collecting the output state of the pressure relay and controlling the ignition unit to ignite according to set ignition conditions so as to inflate the gas storage device; the invention further discloses a corresponding control method. The mechanical pressure relay is adopted as a pressure detection element, ignition conditions based on online detection of the pressure relay are designed, regular verification is not needed on the premise that accurate and reliable ignition control is guaranteed, and maintenance-free operation can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pyrotechnic energy and power technology, and in particular relates to an ignition control system and method based on online detection of a pressure relay. Background Art

[0002] In pyrotechnic energy power devices, power output is usually achieved by igniting and burning the ignition unit to produce high-temperature and high-pressure gas. A series of ignition units are connected to the gas storage device, and the gas generated by the combustion of the ignition unit is first stored in the gas storage device, and then the gas storage device exhausts the gas to the outside to generate power, relying on the buffering effect of the pressure change of the gas storage device to achieve energy storage and matching. In order to ensure that the gas volume in the gas storage device is always sufficient, a suitable control algorithm is required to control the ignition of the ignition unit to ensure that the gas volume can be replenished in time when it is insufficient.

[0003] The conventional ignition control system tests the pressure of the gas storage device through a pressure sensor and compares it with the set pressure threshold. When the feedback pressure is lower than the set pressure, the ignition unit is controlled to ignite and replenish gas to the gas storage device. However, the above control system has the following problems:

[0004] (1) Pressure sensor calibration issues

[0005] Pressure sensors usually need to be calibrated regularly (usually once a year). Usually, pyrotechnic energy power devices are installed inside closed compartments of weapons and equipment, and the compartments need to be disassembled and unshelled during calibration. In addition, the disassembly of pressure sensors also involves high-temperature and high-pressure sealing issues at the installation interface, and the air tightness test must be performed again after disassembly, so the operation is extremely inconvenient.

[0006] (2) Accuracy of pressure sensor

[0007] When the pressure sensor fails or a local disturbance is caused by interference, it may cause mis-ignition or mis-ignition, resulting in excessive pressure or insufficient gas in the gas storage device, causing the pyrotechnic energy power device to fail; therefore, the use of pressure sensors reduces the overall reliability of the system. Summary of the invention

[0008] In response to one or more of the above defects or improvement needs in the prior art, the present invention provides an ignition control system based on online detection of a pressure relay, which uses a mechanical pressure relay as a pressure detection element. It can ensure accurate and reliable ignition control without the need for regular calibration and can be maintenance-free.

[0009] To achieve the above object, according to one aspect of the present invention, there is provided an ignition control system based on online detection of a pressure relay, comprising an ignition unit, a gas storage device, an ignition controller and a pressure relay;

[0010] The ignition unit is connected in parallel to the air inlet end of the gas storage device, and the pressure relay is arranged on the gas path of the gas storage device; the ignition controller is electrically connected to the ignition unit and the pressure relay at the same time, and the ignition controller is used to collect the output state of the pressure relay and control the ignition unit to ignite according to the set ignition conditions, so as to inflate the gas storage device;

[0011] The ignition units include the first ignition unit to the nth ignition unit, n≥2;

[0012] The ignition condition of the first ignition unit is: the pressure relay is in the disconnected state, and the current time t is greater than or equal to the preset time threshold t0;

[0013] The ignition conditions of the second ignition unit to the nth ignition unit are: the pressure relay is in the disconnected state, and the time difference △t between the current time and the previous ignition unit is greater than or equal to the preset time interval threshold t m .

[0014] As a further improvement of the present invention, the ignition controller includes a self-checking module, a pressure interval detection module and an ignition decision module;

[0015] The self-test module is used to collect the initial state of the pressure relay. When the initial state is an open circuit state, the self-test passes; otherwise, the self-test fails.

[0016] The pressure interval detection module is used to collect the output state of the pressure relay within a sampling period and transmit it to the ignition decision module;

[0017] The ignition decision module is used to make an ignition decision according to the output state of the pressure relay and the set ignition conditions.

[0018] As a further improvement of the present invention, the preset time threshold t0 is based on the control system ready time t c , Ignition unit gas production time t r and the starting time t when the gas storage device needs gas q Determine, satisfy t c <t0<t q -t r .

[0019] As a further improvement of the present invention, the preset time interval threshold t m Greater than the gas production time t of the ignition unit r , that is, satisfying t r <t m .

[0020] As a further improvement of the present invention, the pressure relay includes a magnetic piston, a reed switch and a reset spring; one end of the reset spring is fixed, and the other end is connected to the magnetic piston; the reed switch is arranged on the side of the reset spring to sense the magnetic field of the magnetic piston; the magnetic piston is facing the air path pressure detection point, and can compress or stretch the reset spring under pressure changes, so that the magnetic piston is close to or away from the reed switch.

[0021] As a further improvement of the present invention, the pressure relay includes two reed switches, and the reset spring is arranged between the two reed switches, and can output two on-off signals at the same time.

[0022] As a further improvement of the present invention, the pressure relay is of normally-off type. When the pressure P at the detection point is less than or equal to the set pressure threshold P m When the pressure at the detection point is greater than the set pressure threshold P, the pressure relay output is disconnected; m When , the pressure relay output is closed.

[0023] As a further improvement of the present invention, the pressure threshold value P set by the pressure relay m According to the maximum working pressure P of the gas storage device max , the pressure increment △P of the gas storage device caused by the gas production of the ignition unit, and the minimum working pressure P of the gas storage device min Take a value that satisfies P min <P m <P max -△P.

[0024] As a further improvement of the present invention, the gas outlet end of the gas storage device is connected to the exhaust device, and the exhaust device is electrically connected to the exhaust controller.

[0025] According to another aspect of the present invention, there is provided an ignition control method based on online detection of a pressure relay, using the ignition control system, comprising the following steps:

[0026] S101, self-checking the pressure relay through the self-checking module of the ignition controller. If the pressure relay is in the disconnected state, the self-checking passes; otherwise, the self-checking fails;

[0027] S102, after the self-check is passed, if the current time is greater than the control system ready time t c , it is determined whether the first ignition unit has been ignited;

[0028] S103, if the first ignition unit is not ignited, the output state of the pressure relay is collected through the ignition controller, and when the pressure relay is in the disconnected state and the current time t is greater than or equal to the preset time threshold t0, the first ignition unit is controlled to ignite;

[0029] If the first ignition unit has been ignited, the output state of the pressure relay is collected through the ignition controller. When the pressure relay is in the disconnected state, and the time difference △t between the current time and the last ignition unit is greater than or equal to the preset time interval threshold t m When , the 2nd to nth ignition units are controlled to ignite.

[0030] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0031] (1) Compared with the traditional pressure closed-loop control method, the ignition control system based on online detection of pressure relay of the present invention adopts a mechanical pressure relay with strong anti-interference ability, reliable operation, high stability and no need for periodic calibration as a pressure detection element, and designs ignition conditions based on online detection of pressure relay. Under the premise of ensuring accurate and reliable ignition control, it does not require periodic calibration and can be maintenance-free, which is particularly suitable for pyrotechnic energy power devices.

[0032] (2) The ignition control system based on online detection of the pressure relay of the present invention optimizes the design of various preset threshold values ​​in the ignition controller, and can accurately and reliably determine the ignition timing, thereby ensuring that the pressure of the gas storage device is always within a suitable range suitable for the operation of the system.

[0033] (3) In the ignition control system based on online detection of pressure relays of the present invention, the pressure relays adopt a dual-channel redundant output structure. The ignition condition can be triggered only when both pressure relays output a disconnected state, thereby improving the reliability of pressure detection and the safety of ignition.

[0034] (4) The ignition control method based on online detection of the pressure relay of the present invention first performs self-check on the pressure relay through the self-check module, and then determines whether the first ignition unit has been ignited. If not, first determine whether the pressure relay is in the output state. If it is in the output state and meets the set time preset, the first ignition unit is controlled to ignite. Further determine whether the pressure relay is in the output state. If it is in the output state and meets the set time preset, the subsequent ignition units are controlled to ignite. The control method is accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a connection diagram of an ignition control system according to an embodiment of the present invention;

[0036] Figure 2 It is a schematic diagram of an ignition controller module involved in an ignition control system according to an embodiment of the present invention;

[0037] Figure 3It is a structural principle diagram of a pressure relay involved in an ignition control system of an embodiment of the present invention (disconnected state);

[0038] Figure 4 It is a structural principle diagram of a pressure relay involved in an ignition control system of an embodiment of the present invention (conduction state);

[0039] Figure 5 This is a flow chart of an ignition control method according to an embodiment of the present invention;

[0040] Figure 6 This is a semi-physical simulation result diagram of an embodiment of the present invention.

[0041] In all the drawings, the same figure marks represent the same technical features, specifically: 1. pressure relay; 2. gas storage device; 3. ignition controller; 4. ignition unit; 5. exhaust controller; 6. exhaust device; 11. magnetic piston; 12. reed switch; 13. reset spring. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0044] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0045] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0047] As a preferred embodiment of the present invention, Figure 1 As shown, the ignition control system based on online detection of the pressure relay of the embodiment of the present invention comprises a pressure relay 1, a gas storage device 2, an ignition controller 3 and an ignition unit 4, wherein a plurality of ignition units 4 are connected in parallel to the air inlet end of the gas storage device 2, for receiving the ignition command issued by the ignition controller 3, and completing the inflation action; the pressure relay 1 is arranged on the gas path of the gas storage device 2, for detecting the gas path pressure; the ignition controller 3 is electrically connected to the ignition unit 4 and the pressure relay 1 at the same time, and the ignition controller 3 is used to collect the output state of the pressure relay 1, and control the ignition of the ignition unit 4 according to the set ignition conditions, and after the ignition unit 4 is ignited, gas is generated to inflate the gas storage device 2.

[0048] Specifically, the ignition unit 4 includes the first ignition unit to the nth ignition unit, n≥2;

[0049] The ignition condition of the first ignition unit is: the pressure relay 1 is in the disconnected state, and the current time t of the ignition controller 3 is greater than or equal to the preset time threshold t0;

[0050] The ignition conditions for the second ignition unit to the nth (n≥2) ignition unit are: the pressure relay 1 is in the disconnected state, and the time difference △t between the current time of the ignition controller 3 and the previous ignition unit is greater than or equal to the preset time interval threshold t m .

[0051] Preferably, in the ignition controller 3, the preset time threshold t0 is based on the control system ready time tc , Ignition unit gas production time t r and the starting time t when the gas storage device needs gas q Determine, satisfy t c <t0<t q -t r , which can ensure that the first ignition unit ignites effectively and can complete the charging of the gas storage device in time.

[0052] Preferably, in the ignition controller 3, the preset time interval threshold t m Greater than the gas production time t of the ignition unit r , that is, satisfying t r <t m When the ignition is turned on, the possibility of multiple ignition units producing gas at the same time can be eliminated, ensuring the safety of the inflation process.

[0053] In a preferred embodiment, Figure 2 As shown, the ignition controller 3 includes a self-check module, a pressure interval detection module and an ignition decision module, and the self-check module, the pressure interval detection module and the ignition decision module all work after the ignition controller 3 is powered on. The self-check module is used to collect the initial state of the pressure relay 1. When the initial state is an open circuit state, the self-check passes, otherwise the self-check fails. Before ignition, the pressure relay 1 is self-checked to ensure that the pressure relay 1 is in a normal working state; the pressure interval detection module is used to collect the output state of the pressure relay 1 within the sampling period and transmit it to the ignition decision module; the ignition decision module is used to make an ignition decision according to the output state of the pressure relay 1 and the set ignition conditions.

[0054] In a preferred embodiment, the gas outlet of the gas storage device 2 is connected to the exhaust device 6, and the exhaust device 6 is electrically connected to the exhaust controller 5. The exhaust device 6 receives the exhaust control instruction issued by the exhaust controller 5 to complete the exhaust action.

[0055] In a preferred embodiment, Figure 3 and 4 As shown, the pressure relay 1 includes a magnetic piston 11, a reed switch 12 and a reset spring 13. One end of the reset spring 13 is fixed and the other end is connected to the magnetic piston 11. The reed switch 12 is arranged on the side of the reset spring 13 to sense the magnetic field of the magnetic piston 11. The magnetic piston 11 is directly opposite to the gas circuit pressure detection point. The magnetic piston 11 can compress or stretch the reset spring 13 under pressure changes, so that the magnetic piston 11 is close to or away from the reed switch 12, thereby controlling the reed switch 12 to be turned on or off, thereby realizing the pressure relay 1 to be turned on or off.

[0056] like Figure 3As shown, when the pressure at the pressure measuring point of the gas storage device 2 is less than the preset elastic force of the reset spring 13, the magnetic piston 11 is at a position away from the reed switch 12, the reed switch 12 is not affected by the magnetic field of the magnetic piston 11, the reed switch 12 is not turned on, and the pressure relay 1 outputs the disconnected state.

[0057] like Figure 4 As shown, when the pressure at the pressure measuring point of the gas storage device 2 is greater than the preset elastic force of the reset spring 13, the magnetic piston 11 is close to the reed switch 12, the reed switch 12 is turned on by the magnetic field of the magnetic piston 11, and the pressure relay 1 outputs the on state.

[0058] In the ignition control system of the present invention, the pressure relay 1 is an on-off type mechanical structure, which is provided with a pressure-sensitive magnetic piston 11 and a reed switch 12 capable of inducing a magnetic field. The relative positions of the magnetic piston 11 and the reed switch 12 are different in different pressure ranges, so that the reed switch 12 outputs two states of magnetization / non-magnetization, and exhibits two states of conduction / disconnection in terms of electrical characteristics. It has the advantages of strong anti-interference ability, reliable operation, high stability, and no need for regular calibration.

[0059] Further preferably, the pressure relay 1 is of normally-off type. When the pressure P at the detection point of the pressure relay 1 is less than or equal to the set pressure threshold P m When the pressure relay 1 detection point pressure P is greater than the set pressure threshold P m The pressure relay output is in a closed state. Specifically, the pressure threshold P set by the pressure relay can be determined by the preset elastic force design of the reset spring 13, the relative position design of the magnetic piston 11 and the reed switch 12, the area matching of the magnetic piston 11, the magnetic sensing distance matching of the reed switch 12, and other designs. m size.

[0060] Further preferably, the pressure threshold value P set by the pressure relay 1 is m According to the maximum working pressure P of the gas storage device max , the pressure increment △P of the gas storage device caused by the gas production of the ignition unit, and the minimum working pressure P of the gas storage device min Take a value that satisfies P min <P m <P max -ΔP, so that the maximum pressure of the ignition unit 4 after ignition will not exceed the maximum working pressure of the gas storage device 2.

[0061] Further preferably, the pressure relay 1 includes two reed switches 12, and the reset spring 13 is arranged between the two reed switches 12, which can output two on-off signals at the same time. Through the above-mentioned dual redundant output structure design, the ignition decision module of the ignition controller 3 can judge the two output signals of the pressure relay 1 at the same time, and the ignition condition can be triggered when and only when the two signals of the pressure relay 1 are both output in the disconnected state, thereby improving the reliability of pressure detection and ignition safety.

[0062] Furthermore, if Figure 5 As shown, the ignition control method based on online detection of a pressure relay according to an embodiment of the present invention comprises the following steps:

[0063] S101, self-checking the pressure relay 1 through the self-checking module of the ignition controller 3, if the pressure relay 1 is in the disconnected state, the self-checking passes, otherwise the self-checking fails;

[0064] S102, after the self-check is passed, if the current time is greater than the control system ready time t c , it is determined whether the first ignition unit has been ignited;

[0065] S103, if the first ignition unit is not ignited, the output state of the pressure relay 1 is collected through the ignition controller 3, and when the pressure relay 1 is in the disconnected state and the current time t is greater than or equal to the preset time threshold t0, the first ignition unit is controlled to ignite; otherwise, the output state of the pressure relay 1 continues to be collected;

[0066] If the first ignition unit has been ignited, the output state of the pressure relay 1 is collected through the ignition controller 3. When the pressure relay 1 is in the disconnected state and the time difference △t between the current time and the last ignition unit is greater than or equal to the preset time interval threshold t m When the ignition status of the second to nth ignition units is controlled, the ignition status of the pressure relay 1 is continued to be collected.

[0067] For example, in a specific embodiment of the present invention, the ignition unit 4 includes the first ignition unit to the sixth ignition unit, and the control system is ready for use. c =5s, ignition unit gas production time t r = 30s, the starting time t when the gas storage device needs to use gas q =55s, the preset time threshold t0 = 10s, satisfying t c <t0<t q -t r The preset time interval threshold t mr = 35s, satisfying t r <t m . Maximum working pressure of gas storage device Pmax =35MPa, minimum working pressure of gas storage device P min =4MPa, the pressure increment of the gas storage device caused by the ignition unit gas production △P = 25MPa, the set pressure threshold P m =7MPa, satisfying P min <P m <P max -△P.

[0068] Figure 6 The experimental results of the semi-physical simulation of the above specific embodiment include the real pressure curve, the pressure relay output state curve, the ignition command curve and the preset pressure threshold curve. As can be seen from the figure, the pressure relay can accurately sense the pressure change and output the correct pressure state; the ignition control algorithm can accurately determine the ignition time, both within the set pressure threshold P m =7MPa, and the pressure of the gas storage device is kept at P during the whole working process. min =4MPa to P max =35MPa, indicating that the pressure is sufficient and does not exceed the upper limit.

[0069] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An ignition control system based on online detection of a pressure relay, characterized in that: It includes an ignition unit, a gas storage device, an ignition controller and a pressure relay; The ignition unit is connected in parallel to the air inlet end of the gas storage device, and the pressure relay is arranged on the gas path of the gas storage device; the ignition controller is electrically connected to the ignition unit and the pressure relay at the same time, and the ignition controller is used to collect the output state of the pressure relay and control the ignition unit to ignite according to the set ignition conditions, so as to inflate the gas storage device; The ignition units include the first ignition unit to the nth ignition unit, n≥2; The ignition condition of the first ignition unit is: the pressure relay is in the disconnected state, and the current time t is greater than or equal to the preset time threshold t0; The ignition conditions of the second ignition unit to the nth ignition unit are: the pressure relay is in the disconnected state, and the time difference △t between the current time and the previous ignition unit is greater than or equal to the preset time interval threshold t m .

2. The ignition control system based on online detection of pressure relay according to claim 1 is characterized in that: The ignition controller includes a self-check module, a pressure range detection module and an ignition decision module; The self-test module is used to collect the initial state of the pressure relay. When the initial state is an open circuit state, the self-test passes; otherwise, the self-test fails. The pressure interval detection module is used to collect the output state of the pressure relay within a sampling period and transmit it to the ignition decision module; The ignition decision module is used to make an ignition decision according to the output state of the pressure relay and the set ignition conditions.

3. The ignition control system based on online detection of pressure relay according to claim 1 is characterized in that: The preset time threshold t0 is based on the control system ready time t c , Ignition unit gas production time t r and the starting time t when the gas storage device needs gas q Determine, satisfy t c <t0<t q -t r .

4. The ignition control system based on online detection of a pressure relay according to any one of claims 1 to 3, characterized in that: The preset time interval threshold t m Greater than the gas production time t of the ignition unit r , that is, satisfying t r <t m .

5. The ignition control system based on online detection of pressure relay according to claim 1 is characterized in that: The pressure relay includes a magnetic piston, a reed switch and a reset spring; one end of the reset spring is fixed, and the other end is connected to the magnetic piston; the reed switch is arranged on the side of the reset spring to sense the magnetic field of the magnetic piston; the magnetic piston is facing the air path pressure detection point, and can compress or stretch the reset spring under pressure changes, so that the magnetic piston approaches or moves away from the reed switch.

6. The ignition control system based on online detection of pressure relay according to claim 5 is characterized in that: The pressure relay comprises two reed switches, and the reset spring is arranged between the two reed switches, and can output two on-off signals simultaneously.

7. The ignition control system based on online detection of a pressure relay according to any one of claims 1-3 or 5-6, characterized in that: The pressure relay is of normally-off type. When the pressure P at the detection point is less than or equal to the set pressure threshold P m When the pressure at the detection point is greater than the set pressure threshold P, the pressure relay output is disconnected; m When , the pressure relay output is closed.

8. The ignition control system based on online detection of pressure relay according to claim 7 is characterized in that: The pressure relay sets the pressure threshold P m According to the maximum working pressure P of the gas storage device max , the pressure increment △P of the gas storage device caused by the gas production of the ignition unit, and the minimum working pressure P of the gas storage device min Take a value that satisfies P min <P m <P max -△P.

9. The ignition control system based on online detection of a pressure relay according to any one of claims 1-3 or 5-6, characterized in that: The gas outlet end of the gas storage device is connected to the exhaust device, and the exhaust device is electrically connected to the exhaust controller.

10. An ignition control method based on online detection of a pressure relay, using the ignition control system according to any one of claims 1 to 9, characterized in that: The steps include: S101, self-checking the pressure relay through the self-checking module of the ignition controller. If the pressure relay is in the disconnected state, the self-checking passes; otherwise, the self-checking fails; S102, after the self-check is passed, if the current time is greater than the control system ready time t c , it is determined whether the first ignition unit has been ignited; S103, if the first ignition unit is not ignited, the output state of the pressure relay is collected through the ignition controller, and when the pressure relay is in the disconnected state and the current time t is greater than or equal to the preset time threshold t0, the first ignition unit is controlled to ignite; If the first ignition unit has been ignited, the output state of the pressure relay is collected through the ignition controller. When the pressure relay is in the disconnected state, and the time difference △t between the current time and the last ignition unit is greater than or equal to the preset time interval threshold t m When , the 2nd to nth ignition units are controlled to ignite.

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