Injection control device

Abstract

Injection control device applied to an exhaust gas purification system comprising an injector (50) arranged in an exhaust passage (31a) of an internal combustion engine (30) and performing an injection to deliver a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies NOx in an exhaust gas, and a pump (44) which compresses the reducing agent and delivers it via a reducing agent passage (42) to the injector (50), wherein the injection control device comprises: a acquisition unit (S28) which is configured such that it acquires a current value of an excitation current flowing through the pump (44) when the pump (44) is excited as a rotation variation parameter (ΔN); a determination unit (S30) configured to determine, based on the rotation variation parameter (ΔN), whether air is present at the reducing agent passage (42); and a control unit (S42) which is configured to control an air release quantity (Dc) of an air release valve (60) based on a determination of whether air admixture is present in the reducing agent passage (42).

Description

Technical field

[0001] The present disclosure relates to an injection control device which determines whether air enters a reducing agent passage in an exhaust gas purification system comprising an injector, the reducing agent passage and a pump. background

[0002] Recently, a urea system for selective catalytic reduction (urea SCR system) was developed and produced as an exhaust gas purification system for a machine applied to a vehicle, such as a diesel engine, which cleans nitrogen oxides (NOx) in an exhaust gas with a high cleaning rate.

[0003] The urea SCR system comprises a pump which conveys urea water stored in a tank as a reducing agent to a reducing agent passage, and an injector which injects the urea water conveyed through the reducing agent passage into an exhaust pipe of the engine.

[0004] In the urea SCR system, the exhaust gas is cleaned by a NOx reduction reaction in the exhaust pipe using a NOx removal catalyst, which is equivalent to an SCR catalyst. During the NOx reduction reaction, the urea solution injected into the exhaust pipe by the injector is hydrolyzed by heat from the exhaust gas to produce ammonia (NH3), which is then adsorbed by the SCR catalyst. The NOx in the exhaust gas is further reduced by a reduction reaction carried out by the ammonia within the SCR catalyst, thus being cleaned.

[0005] In the urea SCR system, air can enter the reducing agent passage. In other words, air mixing or admixture can occur in the reducing agent passage. For example, the urea SCR system uses a suction and recirculation process to draw the urea solution into the reducing agent passage and return it to the tank to prevent it from freezing when the engine is off. Therefore, when the engine starts, the reducing agent passage in the urea SCR system fills with the urea solution. In this case, air can enter the reducing agent passage. If air enters the reducing agent passage, the injection quantity of the urea solution injected by the injector at the outlet line becomes unstable.

[0006] JP 5 338 696 B2 discloses a technology for detecting whether air is entering a fuel passage based on the fuel pressure in that passage. By applying this technology to the urea SCR system, it is possible to determine whether air is present in the reducing agent passage based on the pressure of the urea solution in that passage.

[0007] DE 199 47 197 A1 discloses the following: Device for metering a reducing agent used in the context of a catalytic exhaust aftertreatment, in particular a urea or a urea-water solution, comprising a tank for storing reducing agent, a pump for conveying reducing agent from the tank to an injection valve through which reducing agent can be introduced into a mixing chamber, wherein the tank, the pump and the injection valve are connected to each other via a line system having a first line between tank and pump and a second line between pump and injection valve, with a controllable venting circuit branching off from the second line and connected to the tank with feedback.

[0008] US 2013 / 0111882 A1 discloses the following: a method for an SCR system in which reducing agent in liquid form is supplied to a feed device and reducing agent is supplied from a container to at least one point of use via the feed device, comprising the steps of continuously sensing the feed pressure supplied by the feed device and controlling the operation of the feed device based on changes in the feed pressure, with the aim of reducing the effects of an unwanted air supply to the feed device. Furthermore, a computer program product comprising program code for a computer to carry out a method according to the invention. An SCR system and a motor vehicle equipped with the SCR system are also disclosed.

[0009] JP 2012-219655A discloses the following: An exhaust gas purification device for an internal combustion engine supplies a reducing agent by means of a pump from a reducing agent tank to a reducing agent supply device through a reducing agent supply channel during operation of the internal combustion engine and draws the reducing agent back from the reducing agent supply channel when the internal combustion engine is stopped. If the detected flow pressure is lower than a threshold value, an air ingress condition is determined in which air mixes into the reducing agent supply channel during the supply of the reducing agent from the pump, and the reducing agent boost control is executed in this case to increase the supply quantity of the reducing agent from the reducing agent supply device.

[0010] DE 10 2016 212 263 B3 discloses the following: The document relates to a method for determining the injected quantity of a fluid during an injection process carried out by means of an injection system of a motor vehicle, in which the fluid is conveyed to an injection element via a piping system, comprising the following steps: - Determining the time of occurrence of the maximum of the pressure gradient caused by the injection process using the output signals of a first pressure sensor, - Calculating a time difference between the time of occurrence of the maximum of the pressure gradient caused by the injection process and the time of commencement of the injection process, - Determining the propagation velocity of the fluid in the piping system using the calculated time difference.- Determination of the stiffness of the piping system using the propagation velocity and - Determination of the injected quantity of fluid using the determined stiffness of the piping system.

[0011] JP 2016-11621A discloses the following: A urea-water supply device for an internal combustion engine comprises: a tank that stores urea-water; a urea-dosing valve that meters the urea-water supplied from the tank into an exhaust duct; a pump that pumps the urea-water from the tank to the urea-dosing valve; and a pressure sensor that detects the pressure of the urea-water supplied to the urea-dosing valve. A control unit regulates the speed of the pump by means of feedback control based on a pressure deviation between the urea-water pressure detected by the pressure sensor and a setpoint urea-water pressure. This control unit suppresses an increase in the pump speed based on the pressure deviation if the water level of the urea-water stored in the tank is tilted by an angle equal to or greater than a predetermined value.

[0012] JP 2011-157925A discloses the following: In a fuel pump, a feed pump pumps fuel into a fuel tank via an upstream fuel channel and delivers the pumped fuel to a high-pressure pump via a downstream fuel channel. On the way to the downstream fuel channel, there is a main filter and a vent channel that leads to a fuel tank and is connected to the main filter. A first pressure sensor for detecting the fuel pressure in the fuel line is located in the upstream fuel line. A second pressure sensor for detecting the fuel pressure in the fuel line is provided in the downstream fuel line. A vent valve for opening and closing the vent line is provided in the vent line.An ECU controls the opening / closing of the air release valve based on detection signals input from the respective sensors. Summary

[0013] According to the technology described in JP 5 338 696 B2, the presence of air in the reducing agent passage is determined from the pressure of the urea solution in the reducing agent passage. Therefore, if the pressure of the urea solution in the reducing agent passage is kept constant by a pressure feedback control, it is not possible to determine with high accuracy whether air is present in the reducing agent passage based solely on the pressure of the urea solution. A suitable technology is required to determine whether air is present in the reducing agent passage. The above is not limited to urea solution and applies generally to cases where a liquid other than a reducing agent is used.

[0014] It is an objective of the present disclosure to provide an injection control device that can suitably detect whether air is present in a reducing agent passage.

[0015] This problem is solved by the features of claim 1. Further advantageous embodiments are the subject of the subsequent claims.

[0016] According to one aspect of the present disclosure, the injection control device is applied to an exhaust gas purification system comprising an injector arranged in an exhaust passage of an internal combustion engine and performing an injection to deliver a reducing agent in a liquid state to a NOx cleaning catalyst which cleans NOx in an exhaust gas, and a pump which compresses the reducing agent and delivers it via a reducing agent passage to the injector.The injection control device comprises a acquiring unit configured to acquire a current value of an excitation current flowing through the pump (44) when the pump (44) is excited, as a rotation variation parameter (ΔN); a determining unit configured to determine, based on the rotation variation parameter, whether air is present in the reducing agent passage; and a control unit configured to control an air release quantity of an air release valve based on a determination of whether air is present in the reducing agent passage.

[0017] When the injector delivers the reducing agent to the outlet line, the pressure in the reducing agent passage varies. When the pressure in the reducing agent passage varies, the pump speed also varies. If air enters the reducing agent passage, the rate of variation in the pump speed is greater due to the elastic deformation of the air in response to pressure variations in the reducing agent passage, compared to a case where air does not enter the reducing agent passage. In other words, since the rate of variation in the pump speed and the amount of air that has entered the reducing agent passage are correlated, the presence of air in the reducing agent passage can be appropriately determined based on the rate of variation in the pump speed. Brief description of the illustrations

[0018] The foregoing and further tasks, features, and advantages of the present disclosure will become more apparent from the following detailed description, which is provided with reference to the accompanying illustrations. The illustrations show: Fig. 1 a schematic diagram showing an outline of an exhaust gas purification system of a machine or engine; Fig. 2 a flowchart showing an injection control processing according to a first embodiment of the present disclosure; Fig. 3 a diagram showing a relationship between a measure or amount of variation of an injection speed and an air mixture quantity; Fig. 4 a diagram showing a relationship between the amount of air added and a duty cycle; Fig. 5A, Fig. 5B, Fig. 5C and Fig. 5D images showing a urea solution during injection control processing over time; Fig. 6 a diagram showing the rotational speed of a pump during injection control processing over time; Fig. 7 a diagram showing the speed of the pump in response to an injection from an injector over time; Fig. 8 a diagram showing a setting of the collective duty cycle; and Fig. 9 a flowchart showing the injection control processing according to a second embodiment of the present disclosure. Description of embodiments (First embodiment)

[0019] An exhaust gas purification system 10 is described below with reference to the figures. This system incorporates a pump control unit 70, which is connected to an injection control device according to a first embodiment of the present disclosure. The exhaust gas purification system 10 cleans NOx in the exhaust gas using a selective catalytic reduction (SCR) catalyst, and this system is designed as a urea SCR system. The exhaust gas purification system 10 can be applied to various vehicles equipped with a diesel engine 30, which corresponds to an internal combustion engine. According to the present embodiment, the diesel engine 30 is referred to as a machine or engine 30. The exhaust gas purification system 10 can also be applied to construction machinery, such as a crane truck, and agricultural machinery, such as a tractor.

[0020] As in Fig. As shown in Figure 1, the exhaust gas purification system 10 comprises an engine exhaust system. In the engine exhaust system, an exhaust pipe 31, which defines an exhaust passage 31a, is connected to the engine 30. A diesel particulate filter (DPF) 32 and the SCR catalyst 33 are arranged in the exhaust pipe 31 in this order, starting from an upstream end of the exhaust pipe 31.

[0021] A urea-water injector 50, which injects a solution of urea water towards the outlet passage 31a, is positioned in the outlet line 31 between the DPF 32 and the SCR catalyst 33. In this case, the urea water, which acts as a reducing agent, is in a liquid state and is a urea-water solution. According to the present embodiment, the urea-water injector 50 is referred to as an injector 50. The injector 50 is positioned so that only a pointed end portion of the injector 50 is located in the outlet line 31, thus preventing heat from the exhaust gas at a high temperature, such as 600 °C. According to the present embodiment, the SCR catalyst 33 is equivalent to a NOx purification catalyst.

[0022] The DPF 32 is a filter that collects particulate matter (PM) from the exhaust gas for removal. The DPF 32 incorporates a platinum group oxidation catalyst and removes soluble organic compounds (SOF), which are components of PM, hydrocarbons (HC), and carbon monoxide (CO). The PM collected by the DPF 32 can be removed by combustion, which occurs through post-injection after the main injection in the engine 30. Therefore, the DPF 32 can be used continuously.

[0023] The SCR catalyst 33 promotes a reduction reaction of NOx, which corresponds to an exhaust gas purification reaction. For example, the SCR catalyst 33 cleans NOx in the exhaust gas by promoting reactions described by equations (1), (2) and (3). 4NO+4NH3+O2→4N2+6H2O (1) 6NO2+8NH3→7N2+ 12 H2O (2) NO+NO2+2NH3→2N2+3H2O (3)

[0024] The injector 50, located at a position upstream of the SCR catalyst 33, performs an injection to supply the urea water to generate ammonia (NH3), which acts as a reducing agent for NOx in the above reactions.

[0025] An oxidation catalyst, acting as an ammonia removal device, can be positioned in the outlet line 31 downstream of the SCR catalyst 33. In this case, the oxidation catalyst removes excess ammonia corresponding to the ammonia emitted by the SCR catalyst 33.

[0026] The following describes the design of a reducing agent injection system 20 for the exhaust gas purification system 10. The reducing agent injection system 20 injects the urea solution by means of an injector 50. According to the present embodiment, if the urea solution is conveyed from a urea tank 40 of the exhaust gas purification system 10 to the injector 50, a region close to the urea tank 40 is referred to as an upstream region, and a region close to the injector 50 is referred to as a downstream region. Furthermore, the urea tank 40 is referred to as a tank 40.

[0027] As in Fig. As shown in Figure 1, tank 40 is constructed as a sealed container with a feed cap. Tank 40 stores the urea solution at a normal, predetermined concentration. According to the present embodiment, a urea solution concentration of 32.5% corresponds to a concentration at which the freezing point is lowest. At 32.5%, the urea solution freezes at -11 °C.

[0028] Tank 40 and injector 50 are connected to each other via a feed line 42. The feed line 42 comprises an upstream end section which is connected to a bottom surface of tank 40. The urea solution stored in tank 40 flows into the feed line 42. According to the present embodiment, the feed line 42 is equivalent to a reducing agent passage.

[0029] A urea water pump 44, referred to as pump 44, is arranged in the supply line 42. Pump 44 is an electric pump that is driven by a current supplied by the pump control unit 70. Pump 44 compresses and delivers the urea water via the supply line 42 to the injector 50.

[0030] Pump 44 includes a gear 45. Pump 44 supplies the urea solution in response to the rotation of the gear 45. The gear 45 in pump 44 can rotate in a normal direction and in reverse. When the gear 45 rotates in the normal direction, pump 44 subsequently rotates in the normal direction. When the gear 45 rotates in the reverse direction, pump 44 rotates in reverse. The normal rotation of pump 44 draws the urea solution from tank 40, and the reverse rotation of pump 44 returns the urea solution to tank 40.

[0031] A rotation detection unit 46 is attached to the pump 44. The rotation detection unit 46 detects a rotational speed N, which corresponds to the number of rotations of the pump 44 per unit of time. For example, the rotation detection unit 46 detects a discharge rate, which corresponds to the delivery rate of the urea solution generated by the pump 44.

[0032] A pressure sensing unit 48 is arranged in the supply line 42 downstream of the pump 44. The pressure sensing unit 48 detects a line pressure P, which corresponds to a pressure in the supply line 42. The pressure sensing unit 48 detects, for example, the discharge pressure of the urea solution generated by the pump 44. According to the present embodiment, the pressure sensing unit 48 is equivalent to the pressure sensing unit.

[0033] The injector 50 is connected to a downstream end of the supply line 42. The injector 50 is essentially identical in design to a known injector. The injector 50, which corresponds to an electromagnetic on / off valve, comprises a drive unit with an electromagnetic solenoid and a valve body unit with a needle 52, which opens and closes an injection port located at the tip end of the injector 50. The injector 50 opens and closes based on a drive signal Sm transmitted by the pump control unit 70. In other words, when the electromagnetic solenoid is energized based on the drive signal Sm, the needle 52 moves in response to the energization of the electromagnetic solenoid in a valve opening direction, and the injection port is opened by the movement of the needle 52, injecting the urea solution.

[0034] An air release line 54 is connected to the supply line 42. The air release line 54 is connected to a branch section B in the supply line 42 downstream of the pump 44 and to the tank 44. The pressure sensing unit 48 is arranged in the supply line 42 between the pump 44 and the branch section B. According to the present embodiment, the air release line 54 is equivalent to an air release passage.

[0035] The air release line 54 has one end that connects to the surface of the tank 40. An air release valve 60 is located at the end of the air release line 54. The air release valve 60 opens and closes the air release line 54 based on a control signal Sc transmitted by the pump control unit 70. The duration for which the control signal Sc is applied to the air release valve 60 is referred to as the control duration Tc, as shown in Fig. Figure 8 shows that when the air release valve 60 is opened during the control time Tc based on the control signal Sc, the urea solution flowing from the feed line 42 to the air release line 54 is returned (drawn back) to the tank 40.

[0036] The air release valve 60 also serves as a shut-off valve during a control stop time Tn, in which the control signal Sc is not input from the pump control unit 70, as in Fig. Figure 8 shows that during the control stop time Tn, the air release valve 60 is opened in response to a pressure in the air release line 54 that is greater or higher than a predetermined pressure, and the air release valve 60 is closed in response to the pressure in the air release line 54 that is lower than the predetermined pressure.

[0037] A first heating element is arranged in tank 40. The first heating element 62 corresponds, for example, to an electric heater. The first heating element 62 thaws the urea solution frozen in tank 40 by energizing it based on a command signal transmitted by the pump control unit 70. It is preferable that the first heating element 62 be arranged in a position where it can thaw the frozen urea solution. The first heating element 62 can, in particular, be arranged in the vicinity of an inlet of the supply line 42.

[0038] A second heating element 64 is arranged in the vicinity of an outer periphery of the supply line 42. The second heating element 64 corresponds, for example, to an electric heater. The second heating element 64 thaws the urea water frozen in the supply line 42 by energizing it based on an instruction signal transmitted by the pump control unit 70.

[0039] A temperature sensor 66 is located in tank 40. The temperature sensor 66 is, for example, a temperature-sensitive diode or a thermistor. The temperature sensor 66 detects the temperature of the urea solution in tank 40. An ambient temperature sensor 68 is located outside tank 40. The ambient temperature sensor 68 is, for example, a temperature-sensitive diode or a thermistor. The ambient temperature sensor 68 is located in a position separate from tank 40 and detects the ambient temperature around a vehicle on which the engine 30 is mounted.

[0040] The pump control unit 70 is an electronic control unit (ECU) that performs control functions related to outlet cleaning. The pump control unit 70 is comprised of a microcomputer with a CPU, ROM, RAM, and an input / output interface.

[0041] The pump control unit 70 obtains the rotational speed N from the rotation detection unit 46, the line pressure P from the pressure detection unit 48, the temperature of the urea solution in the tank 40 from the temperature sensor 66, and the ambient temperature from the ambient temperature sensor 68. The pump control unit 70 controls various components of the reducing agent injection system 20 based on the obtained values.

[0042] In particular, when the urea solution is pumped towards injector 50, the pump 44 is driven to rotate in its normal direction by the energizing current. Therefore, the urea solution is drawn into tank 40 and flows downstream. Pump 44 pumps the urea solution to deliver it to injector 50. Excess urea solution is returned to tank 40 via air release valve 60.

[0043] When the urea solution is returned to tank 40, pump 44 is driven in a reverse rotation direction. This draws the urea solution in the supply line 42 towards tank 40. This prevents the urea solution from remaining in the supply line 42 when the vehicle is parked after engine 30 is stopped, and it suppresses damage to the supply line 42 caused by freezing or expansion of the urea solution.

[0044] In a case where the vehicle is parked while the urea solution is being returned to tank 40 in the supply line 42 after the engine 30 has stopped, the supply line 42 will be filled with the urea solution when the engine 30 starts. In this case, air Ar, which corresponds to a bubble shape, enters the supply line 42, as in the Fig. 5A, Fig. 5B, Fig. 5C and Fig. 5D is shown. If air Ar enters the supply line 42, it is possible that the injection quantity of the urea water injected by the injector 50, which is to be led to the outlet line 31a, becomes unstable.

[0045] In particular, when injector 50 injects the urea solution, the line pressure P varies. To correct for this pressure variation in line pressure P, the rotational speed N increases, and the urea solution is directed to the supply line 42. When air Ar enters the supply line 42, it repeatedly alternates between elastic expansion and contraction in response to the pressure variation in line pressure P. Consequently, the magnitude of the variation ΔN of the rotational speed N is greater than when air Ar does not enter the supply line 42. Since the quantity of urea solution directed to the supply line 42 becomes unstable when the magnitude of the variation ΔN of the rotational speed N increases, the quantity of urea solution injected by injector 50, which is intended to be directed to the outlet line 31a, also becomes unstable.

[0046] In this case, the presence of air Ar in the supply line 42 can be determined from the pressure variation of the line pressure P. However, in the case of the exhaust gas purification system 10, which controls the line pressure P by means of a pressure feedback control to maintain a constant pressure, it cannot determine from the line pressure P whether air Ar is present in the supply line 42, since the variation of the line pressure P is controlled to remain within a predetermined range.

[0047] According to the present embodiment, the pump control unit 70 performs injection control processing to solve the aforementioned problems. During injection control processing, the pump control unit 70 obtains the variation ΔN of the rotational speed N in response to the injection from the injector 50 and determines, based on this variation ΔN, whether air Ar is present in the supply line 42. In other words, the pump control unit 70 determines, based on the variation ΔN, whether there is an admixture of air Ar in the supply line 42. Therefore, the presence of an admixture of air in the supply line 42 can be suitably determined based on the variation ΔN of the rotational speed N. The admixture of air in the supply line 42 corresponds to the admixture of air Ar in the supply line 42.

[0048] Fig. Figure 2 is a flowchart of the injection control processing according to the present embodiment. The pump control unit 70 performs the injection control processing when the engine 30 is in operation.

[0049] When the engine 30 starts, that is, when the ignition switch of the vehicle on which the engine 30 is mounted is turned on, the pump control unit 70 starts the injection control processing. When the pump control unit 70 starts the injection control processing, it fully opens the injector 50 at signal S10 and energizes the pump 44 to start a rotary drive of the pump 44 in its normal direction of rotation. This starts the supply of urea solution to the supply line 42. When the injection control processing starts, the air release valve 60 acts as a shut-off valve without receiving the control signal Sc.

[0050] At S12, the pump control unit 70 performs speed feedback control to control a drive of the pump 44 in order to control the speed N detected by the rotation sensing unit 46 to a predetermined target speed Ntg, as shown in Fig. Figure 6 is shown. The target speed Ntg corresponds to a maximum speed of the pump 44.

[0051] In S14, the pump control unit 70 determines whether the line pressure P reaches a reference pressure Po, as in Fig. Figure 6 shows that the reference pressure Po is set to a pressure at which the urea solution supplied to the feed line 42 reaches a position in the vicinity of the injector 50. If the pump control unit 70 detects a negative result at S14, it returns to S12. If the pump control unit 70 detects a positive result at S14, it closes the injector 50 and proceeds to S16. This prevents some of the urea solution filled into the feed line 42 from escaping to the outlet line 31 and thus prevents the urea solution from reaching the outlet line 31.

[0052] In S16, the pump control unit 70 performs the pressure feedback control to control the drive of the pump 44 in order to control the line pressure P detected by the pressure sensing unit 48 to a predetermined setpoint pressure Ptg, as shown in Fig. Figure 6 shows that the target pressure Ptg corresponds to the line pressure P when injector 50 is in an injection state. The target pressure Ptg is greater than the reference pressure Po. According to the present embodiment, the processing at S16 is equivalent to a feedback control unit.

[0053] At S18, the pump control unit 70 determines whether the line pressure P reaches the setpoint pressure Ptg. If the line pressure P remains within a predetermined range for a specified time period, which is predefined using the setpoint pressure Ptg as an average value, the pump control unit 70 determines that the line pressure P has reached the setpoint pressure Ptg. If the pump control unit 70 determines a negative result at S18, it returns to S16. If the pump control unit 70 determines a positive result at S18, it performs a recovery process to obtain the variation measure ΔN of the rotational speed N at S20, S22, S24, S26, and S28.

[0054] During acquisition processing, the pump control unit 70 sets the drive signal Sm at S20.

[0055] The drive signal Sm corresponds to a signal comprising two values, representing an on voltage and an off voltage. When the drive signal Sm becomes the off voltage, the injector 50 is closed, and the injection of urea solution by the injector 50 is stopped. According to the present embodiment, the duration during which the drive signal Sm becomes the off voltage is referred to as an injection stop duration Ts, as shown in Fig. Figure 7 shows that when the drive signal Sm becomes the on voltage, injector 50 opens and injects the urea solution. According to the present embodiment, the duration during which the drive signal Sm becomes the on voltage is referred to as the injection duration Tp.

[0056] The drive signal Sm is switched between on and off voltage during a normal cycle Tk, which is predetermined. The pump control unit 70 can variably control a duty cycle Dm, which corresponds to an injection duty cycle Dm. The injection duty cycle Dm corresponds to a value obtained by dividing the injection duration Tp by the normal cycle Tk. The injection duty cycle Dm is proportional to the injection quantity Q injected by the injector 50 per unit of time. According to the present embodiment, the injection duty cycle Dm is equivalent to the injection quantity per unit of time. According to the present embodiment, the normal cycle Tk is set to 2 Hz.

[0057] The pump control unit 70 calculates the injection quantity Q at injector 50 according to the operating condition of the engine 30 at a given time, such as a load and speed. The pump control unit 70 sets the drive signal Sm by adjusting the injection duty cycle Dm, which achieves the injection quantity Q while taking into account the temperature of the SCR catalyst 33, as determined by a temperature sensor (not shown). At S22, the pump control unit 70 transmits the drive signal Sm, set at S20, to injector 50 to actuate it.

[0058] At S24, the pump control unit 70 sets an increase threshold Ru and a decrease threshold Rd, which are used to determine the air mixture. The increase threshold Ru corresponds to a minimum value of the variation measure of the rotational speed N, which increases in response to the air Ar entering at the supply line 42. In this case, the variation measure corresponds to an increase variation measure. The decrease threshold Rd corresponds to a minimum value of the variation measure of the rotational speed N, which decreases in response to the air entering at the supply line 42. In this case, the variation measure corresponds to a decrease variation measure. In other words, the increase threshold Ru and the decrease threshold Rd correlate with the injection of the injector 50. Therefore, the pump control unit 70 sets the increase threshold Ru and the decrease threshold Rd according to the injection duty cycle Dm set at S20 and proceeds to S26.According to the present embodiment, the processing at S24 is equivalent to a setting unit.

[0059] At S26, the pump control unit 70 achieves an injection speed Np using the rotation detection unit 46, which corresponds to the speed N in the injection duration Tp, as in Fig. Figure 7 shows this. In particular, the pump control unit 70 obtains the injection speed Np as a current value of an excitation current flowing through the pump 44 when the pump 44 is energized. At S28, the pump control unit 70 performs a computation to calculate a rotation variation parameter that indicates a variation in the injection speed Np. According to the present embodiment, the current value of the excitation current flowing through the pump 44 when the pump 44 is energized is equivalent to a correlation value.

[0060] During the calculation processing, the pump control unit 70 first obtains a reference speed No at the start of the injection duration Tp, as in Fig. Figure 7 is shown. According to the present embodiment, the reference speed No is lower than the target speed Ntg. Subsequently, the pump control unit 70 achieves a maximum speed Nu and a minimum speed Nd of the injection speed Np.

[0061] The pump control unit 70 calculates an absolute value of the difference between the maximum speed Nu and the reference speed No, and this is subsequently obtained as an increase variation measure ΔNu. The pump control unit 70 also calculates an absolute value of the difference between the minimum speed Nd and the reference speed No, and this is subsequently obtained as an decrease variation measure ΔNd. According to the present embodiment, the increase variation measure ΔNu and the decrease variation measure ΔNd are equivalent to the rotation variation parameter, and the processing at S28 is equivalent to a acquisition unit.

[0062] At S30, the pump control unit 70 compares the increase variation measure ΔNu obtained at S28 with the increase threshold Ru set at S24, and compares the decrease variation measure ΔNd obtained at S28 with the decrease threshold Rd set at S24.

[0063] If the increase variation measure ΔNu is less than the increase threshold Ru and the decrease variation measure ΔNd is less than the decrease threshold Rd, the pump control unit 70 determines a positive result. If the pump control unit 70 determines a positive result at S30, it proceeds to S34. At S34, the pump control unit 70 determines that air is not entering the supply line 42. In other words, the pump control unit 70 determines that there is no air contamination in the supply line 42.

[0064] If the increase variation measure ΔNu is greater than the increase threshold Ru and the decrease variation measure ΔNd is greater than the decrease threshold Rd, the pump control unit 70 determines a negative result. If the pump control unit 70 determines a negative result at S30, it proceeds to S36. At S36, the pump control unit 70 determines that air is entering the supply line 42. In other words, the pump control unit 70 determines that air is present in the supply line 42. The pump control unit 70 determines whether air is present in the supply line 42 based on the rotation variation parameter, more precisely, based on a comparison of the rotation variation parameter and the thresholds Ru and Rd. According to the present embodiment, the processing at S30 is equivalent to a determination unit.

[0065] When the pump control unit determines at S34 that air is not entering the supply line 42, the pump control unit 70 advances to S38. At S38, the pump control unit 70 causes the air release valve 60 to stop. In other words, the pump control unit 70 maintains a state in which the control signal Sc is not transmitted to the air release valve 60.

[0066] If the pump control unit 70 determines at S36 that air is entering the supply line 42, the pump control unit 70 performs removal processing at S40, S42 and S44 to remove the air that has entered the supply line 42.

[0067] During distance processing, the pump control unit 70 first estimates an air admixture quantity Ax in the supply line 42 at S40. As in Fig. As shown in Figure 3, the pump control unit 70 stores a first conversion table that specifies a relationship between the variation measures ΔNu, ΔNd of the injection speed Np and the air mixture quantity Ax. The first conversion table has a relationship such that the air mixture quantity Ax increases according to an increase in the variation measures ΔNu, ΔNd of the injection speed Np. The pump control unit 70 converts the larger of the increasing variation measure ΔNu and the decreasing variation measure ΔNd, as obtained at S28, to the air mixture quantity Ax using the first conversion table in order to estimate the air mixture quantity Ax. In other words, the pump control unit 70 estimates the air mixture quantity Ax based on the rotational variation parameter. According to the present embodiment, the processing at S40 is equivalent to an estimation unit.

[0068] Subsequently, the pump control unit 70 sets the control signal Sc at S42.

[0069] The control signal Sc corresponds to a signal including two values, representing an on voltage and an off voltage. When the control signal Sc becomes off voltage, the air release valve 60 closes, and the return of the urea solution to tank 40, initiated by the air release valve 60, is stopped. When the control signal Sc becomes on voltage, the air release valve 60 opens, and the urea solution and air Ar are returned to tank 40 via the air release valve 60.

[0070] The control signal Sc is switched between on and off voltage during the normal cycle Tk, similar to the drive signal Sm. The pump control unit 70 can variably control a duty cycle Dc, which corresponds to a cumulative duty cycle Dc. The cumulative duty cycle Dc corresponds to a value obtained by dividing the time during which the control signal Sc becomes the on voltage by the normal cycle Tk. The cumulative duty cycle Dc is proportional to an air release quantity, which corresponds to a quantity of air Ar that is returned to the tank 40 via the air release valve 60 per unit time. According to the present embodiment, the cumulative duty cycle Dc is equivalent to the air release quantity per unit time.

[0071] As in Fig. As shown in Figure 4, the pump control unit 70 stores a second conversion table that specifies a relationship between the air mixture quantity Ax and the collecting duty cycle Dc. This second conversion table has a relationship such that the collecting duty cycle Dc increases with an increase in the air mixture quantity Ax. Using the second conversion table, the pump control unit 70 converts the air mixture quantity Ax, estimated at S40, to the collecting duty cycle Dc in order to set the control signal Sc. In other words, the pump control unit 70 sets the collecting duty cycle Dc based on the air mixture quantity Ax. Subsequently, at S44, the pump control unit 70 outputs the control signal Sc, set at S20, to the air release valve 60 to actuate the air release valve 60. According to the present embodiment, the processing at S42 is equivalent to a control unit.

[0072] In the second conversion table, the collecting duty cycle Dc is set to increase in accordance with an increase in the air admixture quantity Ax, and a minimum value of the collecting duty cycle Dc is set greater than a maximum value of a blocking duty cycle Dr, which corresponds to a duty cycle Dr of the air release valve 60, which acts as the blocking valve. Since the collecting duty cycle Dc is set using the second conversion table, the collecting duty cycle Dc is thus set greater than the blocking duty cycle Dr. In other words, the duty cycle of the air release valve 60, when the pump control unit 70 determines that air enters the supply line 42, is controlled such that it is greater than the duty cycle of the air release valve 60 when the pump control unit 70 determines that air does not enter the supply line 42.

[0073] At S38, the pump control unit 70 stops the air release valve 60 for a predetermined duration and then proceeds to S46. At S44, the pump control unit 70 actuates the air release valve 60 for a predetermined duration and then proceeds to S46. At S46, the pump control unit 70 determines whether the machine or engine 30 is stopped. If the ignition switch of the vehicle on which the engine 30 is mounted is still switched on, the pump control unit 70 determines a negative result at S46 and returns to S16.

[0074] When the ignition switch of the vehicle on which the engine 30 is mounted is switched off, the pump control unit 70 detects a positive result at S46 and proceeds to S48. At S48, the pump control unit 70 reverses the rotation of the pump 44, performs a pull-in process to draw the urea solution in the supply line 42 to the tank 40, and terminates the injection control process.

[0075] The Fig. 5A, Fig. 5B, Fig. 5C, Fig. 5D and Fig. Figure 6 shows an example of injection control processing. In particular, the Fig. 5A, Fig. 5B, Fig. 5C and Fig. 5D the urea water during injection control processing over time. Fig. 5A shows the reducing agent injection system 20 during the start of the injection control processing, 5B shows the reducing agent injection system 20 after the urea water has been filled, Fig. 5C shows the reducing agent injection system 20 during removal processing and Fig. 5D shows the reducing agent injection system 20 after removal processing.

[0076] Fig. Figure 6 shows the rotational speed N during injection control processing over time. Fig. Figure 6 shows the line pressure P, the rotational speed N, and the injection duty cycle Dm over time. As in Fig. As shown in Figure 6, a pulsation or fluctuation in the rotational speed N and the line pressure P in the supply line 42 caused by a disturbance other than the injection of the injector 50 and an elastic deformation of the air Ar is removed. Fig. 7 and Fig. 8 show something similar.

[0077] As in Fig. As shown in Figure 5A, at the start of the injection control processing, a section in the supply line 42 downstream of the pump 44 and the air release line 54 are filled with excess air. When the engine 30 starts, while the vehicle's ignition switch is turned on at time t1, the injection control processing starts at time t2, the pump 44 is caused to enter normal rotation, and the supply line 42 and the air release line 54 are filled with the urea solution (S10), as shown in Figure 5A. Fig. 6 is shown.

[0078] Specifically, at time t2, the pump control unit 70 fills the urea solution via speed feedback control in a state where the injector 50 is open (S12). Then, when the line pressure P reaches the reference pressure Po (S14: positive determination), the pump control unit 70 fills the urea solution at time t3 via pressure feedback control in a state where the injector 50 is closed. Then, when the line pressure P reaches the setpoint pressure Ptg (S16: positive determination), the pump control unit 70 stops filling the urea solution at the supply line 42 and the air release line 54 at time t4.

[0079] As in Fig. As shown in Figure 5B, air Ar enters the supply line 42 after the urea solution has been filled. Therefore, when the injection of the urea solution caused by the injector 50 starts, while an output of the drive signal Sm starts, the variation measure ΔN of the rotational speed Np at time t5 becomes large.

[0080] Fig. Figure 7 shows the rotational speed N in response to the injection of injector 50 over time. Fig. Figure 7 shows the drive signal Sm, the rotational speed N when the air Ar does not enter the supply line 42, the line pressure P when the air Ar does not enter the supply line 42, and the rotational speed N when the air Ar enters the supply line 42, over time.

[0081] As in Fig. As shown in Figure 7, during the injection stop time Ts, the rotational speed N is controlled to the reference speed No by the pressure feedback control of pump 44. During the injection time Tp, the line pressure P decreases from the target pressure Ptg in response to injection. To correct this pressure decrease, the amount of urea solution delivered by pump 44 via the pressure feedback control is increased, and the injection speed Np increases in response to this increase in the urea solution quantity. The variation measure ΔN of the rotational speed N corresponds to a variation in the injection speed Np from the reference speed No in response to injection.

[0082] As in Fig. As shown in Figure 7, the injection speed Np increases monotonically in response to the injection from injector 50 if air Ar does not enter the supply line 42. When the injection speed Np reaches the maximum speed Nu, the injection speed Np decreases monotonically to return to the reference speed No. Therefore, the minimum speed Nd is essentially equal to the reference speed No.

[0083] As in Fig. As shown in Figure 7, the air Ar is elastically deformed by a variation in the line pressure P in response to the injection from the injector 50, and the injection speed Np fluctuates when the air Ar enters the supply line 42. Consequently, when comparing a case in which the air Ar enters the supply line 42 with a case in which the air Ar does not enter the supply line 42, the maximum speed Nu increases and the minimum speed Nd decreases. If the variation measures ΔNu and ΔNd of the injection speed Np, which are calculated from the maximum speed Nu and the minimum speed Nd, are greater than the thresholds Ru and Rd, respectively, the pump control unit 70 performs the distance processing (S40, S42, and S44).

[0084] As in Fig. As shown in Figure 5C, during distance processing the control signal Sc is output and the air release valve 60 is driven in a state in which the pump 44 is caused to be in normal rotation. The collecting duty cycle Dc of the control signal Sc is set based on the amount of air admixture Ax in the supply line 42 (S42).

[0085] Fig. Figure 8 shows a setting sequence for the collective duty cycle Dc. Fig. Figure 8 shows the drive signal Sm, the rotational speed N, and the duty cycle Dc of the control signal Sc over time. Furthermore, as shown in Fig. Figure 8 shows that dashed lines F1 indicate a case in which the amount of air added Ax is relatively small, and solid lines F2 indicate a case in which the amount of air added Ax is relatively large.

[0086] As with the in Fig. The dashed lines F1 shown in Figure 8 indicate that the variation measures ΔNu, ΔNd of the injection speed Np become relatively small when the air mixture quantity Ax is relatively small. When the variation measures ΔNu, ΔNd of the injection speed Np are relatively small, the pump control unit 70 determines that the air mixture quantity Ax is relatively small and sets the summing duty cycle Dc of the control signal Sc to a first summing duty cycle Dc1. In this case, the first summing duty cycle Dc1 is greater than zero and less than one.

[0087] Like the in Fig. In the continuous lines F2 shown in Figure 8, the variation measures ΔNu, ΔNd of the injection speed Np become relatively large when the air mixture quantity Ax is relatively large. When the variation measures ΔNu, ΔNd of the injection speed Np are relatively large, the pump control unit 70 determines that the air mixture quantity Ax is relatively large and sets the collecting duty cycle Dc of the control signal Sc to a second collecting duty cycle Dc2. In this case, the second collecting duty cycle Dc2 is greater than the first collecting duty cycle Dc1 and less than one.

[0088] The control signal Sc with the collective duty cycle Dc set as above is output to the air release valve 60, and the air release valve 60 is actuated. Consequently, as in Fig. As shown in 5D, the air Ar that had entered the supply line 42 was appropriately removed.

[0089] When the engine 30 is stopped while the vehicle's ignition switch is off, the pump control unit 70 also stops the injection of urea solution by the injector 50 by stopping the output of the drive signal Sm, and executes the pull-in process (S48) at time t6. During the pull-in process, the pump control unit 70 reverses the rotation of the pump 44.

[0090] Subsequently, the pump control unit 70 stops the reversal of the pump 44's rotation at time t7 and opens the injector 50 at time t8. Therefore, the line pressure P, reduced by the reverse rotation of pump 44, is returned to atmospheric pressure. The pump control unit 70 then closes the injector 50 and terminates the injection control processing at time t9. As in Fig. As shown in Figure 5A, the urea water is returned to tank 40 via the feed line 42.

[0091] According to the present embodiment, the following effects can be achieved.

[0092] The variation measures ΔNu, ΔNd of the injection speed Np of pump 44, which are generated in response to the injection of injector 50, and the air mixture quantity Ax in the supply line 42 are related. Therefore, according to the present embodiment, it can be suitably determined, based on the variation measures ΔNu, ΔNd of the injection speed Np, whether air mixture is present in the supply line 42.

[0093] The line pressure P also varies in response to the injection from injector 50. Since the variation of the line pressure P is controlled such that it lies within the predetermined range, including the target pressure Ptg, as a midpoint when the pump 44 is controlled by the pressure feedback control, it is not possible to determine whether air is present in the supply line 42 based solely on the line pressure P. However, since, according to the present embodiment, it is determined whether air is present in the supply line 42 based on the variation of the injection speed Np ΔNu, ΔNd when the pump 44 is controlled by the pressure feedback control, it is possible to determine whether air is present in the supply line 42.

[0094] Since, according to the present embodiment, the variation measures ΔNu, ΔNd of the injection speed Np and the injection duty cycle Dm of the injector 50 are related, the thresholds Ru, Rd are set according to the injection duty cycle Dm. Therefore, based on a comparison of the variation measures ΔNu, ΔNd of the injection speed Np and the thresholds Ru, Rd, it can be determined with high precision whether air is mixed in at the supply line 42.

[0095] According to the present embodiment, the collecting duty cycle Dc of the air release valve 60, when it is determined that air Ar enters the supply line 42, is greater than the blocking duty cycle Dr, when it is determined that air Ar does not enter the supply line 42. Therefore, when comparing a case in which the collecting duty cycle Dc is greater than the blocking duty cycle Dr with a case in which the collecting duty cycle Dc is less than the blocking duty cycle Dr, the air Ar that has entered the supply line 42 can be returned to the tank 40 via the air release valve 60 at an early stage.

[0096] According to the present embodiment, the air mixture quantity Ax in the supply line 42 is estimated using the variation measures ΔNu, ΔNd of the injection speed Np, and the collecting duty cycle Dc is set based on the estimated air mixture quantity Ax. This prevents the air release valve 60 from opening insufficiently, even if the estimated air mixture quantity Ax is relatively large. Therefore, the air Ar that has entered the supply line 42 can be returned to the tank 40 via the air release valve 60 at an earlier stage. Furthermore, it prevents the air release valve 60 from opening excessively, even though the estimated air mixture quantity Ax is relatively small.Therefore, the power required for distance processing, which corresponds to a drive power of the air release valve 60 or a drive power of the pump 44 in response to an increase in the injection speed Np caused by an opening of the air release valve 60, can be suppressed.

[0097] According to the present embodiment, the air Ar that has entered the supply line 42 is returned to the tank 40 by controlling the opening and closing of the air release valve 60, which serves as the shut-off valve. Therefore, compared to a design in which an on / off valve, which returns the air Ar that has entered the supply line 42 to the tank 40, and a line to which only the on / off valve is attached, are individually provided for the air release valve 60, which serves as the shut-off valve, and the air release line 54, to which the air release valve 60 is attached, the design of the reducing agent injection system 20 can be simplified. (Second embodiment)

[0098] The pump control unit 70 according to a second embodiment of the present disclosure is described with reference to Fig. 9 described. The pump control unit 70 according to the second embodiment differs from the pump control unit 70 according to the first embodiment in its injection control processing. The injection control processing according to the second embodiment is described below.

[0099] As in Fig. As shown in Figure 9, the injection control processing according to the second embodiment differs from the injection control processing according to the first embodiment with respect to a setting of the drive signal Sm. In addition, the essentially identical processing operations as in the first embodiment are indicated with the same reference numerals, and the corresponding description is omitted.

[0100] If the pump control unit 70 detects a positive result at S18, it proceeds to S62. At S62, the pump control unit 70 sets the injection duty cycle Dm according to the operating state of the engine 30. At S64, the pump control unit 70 determines whether the set injection duty cycle Dm is greater than a predetermined reference duty cycle Do. The reference duty cycle Do corresponds to a minimum injection duty cycle Dm, which is used to determine, using the variation measures ΔNu, ΔNd of the injection speed Np, whether air is present at the supply line 42. According to the present embodiment, the reference duty cycle Do is set to 50%. Furthermore, according to the present embodiment, the reference duty cycle Do is equivalent to a reference injection quantity.

[0101] If the pump control unit 70 detects a positive result at S64, it proceeds to S20. At S20, the pump control unit 70 sets the drive signal Sm using the injection duty cycle Dm set at S62. Subsequently, at S24, the pump control unit 70 sets the thresholds Ru and Rd according to the injection duty cycle Dm set at S62.

[0102] If the pump control unit 70 detects a negative result at S64, it advances to S66. At S66, the pump control unit 70 resets the injection duty cycle Dm to a target duty cycle Dtg, which is predetermined and greater than the reference duty cycle Do. The target duty cycle Dtg corresponds to the injection duty cycle Dm at which the variation measures ΔNu, ΔNd of the injection speed Np are sufficiently generated to suitably determine whether air is present at the supply line 42. According to the present embodiment, the target duty cycle Dtg is set to 80%. In other words, if the injection duty cycle Dm is less than the reference duty cycle Do, the pump control unit 70 adjusts the injection duty cycle Dm to be greater than the reference duty cycle Do.

[0103] When the pump control unit 70 sets the injection duty cycle Dm at S66, it advances to S20. At S20, the pump control unit 70 sets the drive signal Sm using the injection duty cycle Dm set at S66. Subsequently, at S24, the pump control unit 70 sets the thresholds Ru and Rd according to the injection duty cycle Dm set at S66.

[0104] As in the preceding description, according to the present embodiment, the injection duty cycle Dm is compared with the reference duty cycle Do according to the operating state of the engine 30. If the injection duty cycle Dm is smaller than the reference duty cycle Do, the injection duty cycle Dm is adjusted to the target duty cycle Dtg, which is larger than the reference duty cycle Do.

[0105] The injection duty cycle Dm and the variation measure ΔN of the injection speed Np are related such that the variation measure ΔN of the injection speed Np increases with an increase in the injection duty cycle Dm. Therefore, using the variation measures ΔNu, ΔNd of the injection speed Np, it cannot be determined with high precision whether air is present at the feed line 42 when the injection duty cycle Dm is smaller than the reference duty cycle Do.

[0106] If the injection duty cycle Dm, according to the operating state of the engine 30, is smaller than the reference duty cycle Do, the injection duty cycle Dm, according to the present embodiment, is set to the target duty cycle Dtg, which is larger than the reference duty cycle Do. Therefore, it can be determined with high precision whether air is being mixed at the supply line 42, even though the injection duty cycle Dm, according to the operating state of the engine 30, is smaller than the reference duty cycle Do.

[0107] The present disclosure is not limited to the foregoing embodiments and may, for example, be applied to the following.

[0108] The reducing agent, which is in a liquid state, is not limited to urea water. For example, a compound other than urea water, obtained from ammonia, can be injected as the reducing agent.

[0109] The increase variation measure ΔNu and the decrease variation measure ΔNd are calculated as the rotational variation parameter, and this is not restricted. For example, a quantity can be calculated from the increase variation measure ΔNu and the decrease variation measure ΔNd as the rotational variation parameter. Alternatively, the increase variation measure ΔNu, the decrease variation measure ΔNd, and an absolute value of the difference between the maximum speed Nu and the minimum speed Nd of the injection speed Np can be calculated as the rotational variation parameter. Alternatively, instead of the increase variation measure ΔNu and the decrease variation measure ΔNd, the absolute value of the difference between the maximum speed Nu and the minimum speed Nd of the injection speed Np can be calculated as the rotational variation parameter. In the above cases, the reference speed No cannot be obtained.

[0110] Alternatively, the increase variation measure ΔNu, the decrease variation measure ΔNd, and a fluctuation time during which the injection speed Np fluctuates can be obtained as the rotational variation parameter. Alternatively, the fluctuation time during which the injection speed Np fluctuates can be obtained as the rotational variation parameter instead of the increase variation measure ΔNu and the decrease variation measure ΔNd. If the air mixture quantity Ax in the supply line 42 is relatively large, the time during which the air Ar entering the supply line 42 is released becomes longer, and the fluctuation time also becomes longer. In other words, the fluctuation time and the air mixture quantity Ax are related such that the air mixture quantity Ax increases with an increase in the fluctuation time.Therefore, based on the fluctuation time during which the injection speed Np fluctuates, it can be determined whether air is mixed in at the supply line 42.

[0111] The injection quantity per unit of time is adjusted by the injection duty cycle Dm, and this is not limited. For example, the opening degree of injector 50, which specifies a release level of injector 50, can be adjusted. The air release quantity per unit of time is adjusted by the collective duty cycle Dc, and this is not limited. For example, the opening degree of air release valve 60, which specifies a release level of air release valve 60, can be adjusted.

[0112] The pump control unit 70 can continuously achieve the variation parameters ΔNu, ΔNd of the injection speed Np during the time period in which the air release valve 60 is actuated. If the variation parameters ΔNu, ΔNd of the injection speed Np are correspondingly smaller than the thresholds Ru, Rd, the air release valve 60 can be stopped in response to the fact that the air Ar that entered at the supply line 42 has been returned to the tank 40 by actuating the air release valve 60.

[0113] The present disclosure has been described with reference to the examples; however, the present disclosure is not limited to the examples or the structures. The present disclosure includes various modification examples and modifications in the same area. In addition to the preferred combinations and configurations, further combinations and configurations with more, fewer, or only a single element are also within the scope of protection of the appended claims.

Claims

[1] Injection control device applied to an exhaust gas purification system comprising an injector (50) arranged in an exhaust passage (31a) of an internal combustion engine (30) and performing an injection to deliver a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies NOx in an exhaust gas, and a pump (44) which compresses the reducing agent and delivers it via a reducing agent passage (42) to the injector (50), wherein the injection control device comprises: a acquisition unit (S28) which is configured such that it acquires a current value of an excitation current flowing through the pump (44) when the pump (44) is excited as a rotation variation parameter (ΔN); a determination unit (S30) configured to determine, based on the rotation variation parameter (ΔN), whether air is present at the reducing agent passage (42); and a control unit (S42) which is configured to control an air release quantity (Dc) of an air release valve (60) based on a determination of whether air admixture is present in the reducing agent passage (42). [2] Injection control device according to claim 1, further comprising: a setting unit (S24) which is configured to set a threshold (Ru, Rd) for determining the air mixture according to an injection quantity (Dm) of the injector (50) per unit of time, wherein The determination unit (S30) determines, based on a comparison result between the rotation variation parameter (ΔN) obtained by the acquisition unit (S28) and the threshold (Ru, Rd) set by the adjustment unit (S24), whether air admixture is present at the reducing agent passage (42). [3] Injection control device according to claim 2, wherein the exhaust gas purification system further comprises a tank (40) which stores the reducing agent, an air release passage (54) which is connected to the reducing agent passage (42) and communicates with the tank (40), and the air release valve (60) which is attached to the air release passage (54) and opens and closes the air release passage (54), the injection control device further comprises: the control unit (S42), which is configured to variably control the amount of air released (Dc) per unit of time, wherein The control unit (S42) controls the air release quantity (Dc) such that, when the determination unit (S30) determines that air is present at the reducing agent passage (42), it is greater than the air release quantity (Dc) when the determination unit (S30) determines that air is not present at the reducing agent passage (42). [4] Injection control device according to claim 3, further comprising: an estimation unit (S40) configured to estimate an air admixture quantity (Ax) in the reducing agent passage (42) based on the rotation variation parameter (ΔN) obtained by the acquisition unit (S28) when the determination unit (S30) determines that the air admixture is present at the reducing agent passage (42), wherein The control unit (S42) sets the air release quantity (Dc) based on the air admixture quantity (Ax) estimated by the estimating unit (S40) when the determining unit (S30) determines that the air admixture is present at the reducing agent passage (42). [5] Injection control device according to one of claims 2 to 4, wherein The setting unit (S24) adjusts the injection quantity (Dm) per unit of time in response to an operating state of the internal combustion engine (30) to be greater than a predetermined reference injection quantity (Do) if the injection quantity (Dm) per unit of time is less than the reference injection quantity (Do), and the setting unit (S24) sets the threshold (Ru, Rd) in response to the injection quantity (Dm) per unit of time set by the setting unit (S24). [6] Injection control device according to any one of claims 1 to 5, wherein the exhaust gas purification system further comprises a pressure sensing unit (48) which detects a pressure in the reducing agent passage (42), the injection control device further comprises: a feedback control unit (S16) configured to perform feedback control of a pump drive (44) to control the pressure of the reducing agent detected by the pressure sensing unit (48) during injection by the injector (50) to a predetermined setpoint pressure (Ptg), wherein The acquisition unit (S28) obtains the rotation variation parameter (ΔN) when the pressure in the reducing agent passage (42) is controlled to the target pressure (Ptg) by the feedback control unit (S16).

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