Driving circuit of urea metering injection unit

Abstract

The utility model discloses a driving circuit of a urea metering injection unit, and the circuit comprises an MCU which is used for outputting an injection control signal of the urea metering unit according to a current signal in the driving circuit; a control pin of the pre-driving chip is connected with the MCU, and the pre-driving chip is used for receiving a control signal of the MCU; a grid electrode, a source electrode and a drain electrode of the external MOS are connected with the pre-driving chip, and the external MOS receives a control signal of the pre-driving chip and carries out voltage feedback; the freewheeling diode is matched with the external MOS and is used for providing a freewheeling path for the current in the circuit when the external MOS is switched off; the sampling resistor is used for collecting the current flowing through the urea metering injection valve; and the operational amplifier is used for amplifying the current signal acquired by the sampling resistor and feeding back the current signal to the MCU. The circuit realizes two-section accurate current control, so that the accuracy of the urea injection amount is ensured, and the emission of oxynitride in the tail gas of the diesel engine is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the technical field of internal combustion engine electronic control system - ECU hardware controller, and particularly relates to a drive circuit for a urea metering injection unit. Background Technology

[0002] With the implementation of the National VI emission standards for motor vehicles, restrictions on nitrogen oxide emissions from diesel engine exhaust have become increasingly stringent. Selective Catalytic Reduction (SCR) aftertreatment technology has emerged to address this need. It precisely injects automotive urea solution into the high-temperature exhaust gas of the engine, converting nitrogen oxides into harmless nitrogen and water vapor under the action of a catalyst, achieving a reduction removal efficiency of over 80%. Key components of an SCR system include a urea storage tank, a urea supply module, a urea metering injection unit, an SCR catalytic converter, an exhaust temperature sensor, and a control unit. However, existing urea metering injection unit hardware designs still have shortcomings in terms of precise control, making it difficult to meet emission standard requirements. Summary of the Invention

[0003] The purpose of this application is to provide a driving circuit for a urea metering injection unit, so as to solve the technical problem that the hardware design of the urea metering injection unit in the related art is insufficient in terms of precise control.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] A drive circuit for a urea metering injection unit includes:

[0006] The MCU is used to output control signals for the injection of urea metering unit based on the current signal in the drive circuit.

[0007] A pre-driver chip, wherein the control pin of the pre-driver chip is connected to the MCU and receives control signals from the MCU;

[0008] An external MOS is provided, wherein the gate, source, and drain of the external MOS are connected to the pre-driver chip, and the external MOS receives the control signal from the pre-driver chip and provides voltage feedback.

[0009] A freewheeling diode, which works in conjunction with the external MOS to provide a freewheeling path for the current in the circuit when the external MOS is turned off;

[0010] The sampling resistor is used to collect the current flowing through the urea metering injection valve;

[0011] An operational amplifier is used to amplify the current signal acquired by the sampling resistor and feed it back to the MCU.

[0012] Furthermore, the circuit is powered by a battery, with VBATT providing a 12V or 24V main power supply.

[0013] Furthermore, the MCU interacts with the pre-driver chip via SPI communication to exchange initialization and fault diagnosis information.

[0014] Furthermore, a logic level conversion transistor is used between the MCU and the pre-driver chip to convert the control signal into a level signal suitable for driving the pre-driver chip. The base of the logic level conversion transistor is connected to the control signal of the MCU, the emitter is grounded, and the collector is connected to the 5V power supply through a pull-up resistor and connected to the control pin of the pre-driver chip.

[0015] Furthermore, in the pre-driver chip, the pull-up and pull-down resistors of the enable pin are used to set the initial level state of the enable pin, and the charge pump capacitor in the circuit cooperates with the charge pump circuit inside the pre-driver chip.

[0016] Furthermore, the external MOS includes Q1A and Q1B. Q1A is a high-side switch control MOS for urea metering injection, and Q1B is a low-side switch control MOS. The gates of Q1A and Q1B are connected to the corresponding control signals through gate current limiting resistors R6 and R7, respectively. The source and drain are both connected to the pre-driver chip for voltage feedback.

[0017] Furthermore, the freewheeling diodes include D1 and D2. D1 is the high-side freewheeling diode for urea metering injection, and D2 is the low-side freewheeling diode. D1 and D2 cooperate with Q1A and Q1B respectively to provide a freewheeling path for the current in the circuit when the MOS is turned off.

[0018] Furthermore, the operational amplifier feeds the amplified current signal back to the fast comparator module of the MCU. The fast comparator module compares the received current signal with a predetermined current threshold and drives the switch of the external MOS.

[0019] This application also provides a urea metering injection unit, including the aforementioned drive circuit.

[0020] This application also provides an SCR system, including the urea metering injection unit described above.

[0021] The technical solutions provided by the embodiments of this application may include the following beneficial effects:

[0022] As can be seen from the above embodiments, this application achieves two-stage precise current control by using an MCU in conjunction with an external MOS of the pre-drive chip and current sampling feedback. Based on the feedback signals from the engine and sensors, the MCU calculates the injection duration and uses control signals to precisely drive the urea metering injection unit, thereby ensuring the accuracy of urea injection quantity, effectively reducing nitrogen oxide emissions in diesel engine exhaust, and meeting the requirements of the China VI emission standard.

[0023] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0025] Figure 1 This is a schematic diagram of the drive circuit topology of a urea metering injection unit according to an exemplary embodiment.

[0026] Figure 2 This is a schematic diagram of the design of a drive circuit for a urea metering injection unit according to an exemplary embodiment.

[0027] Figure 3 This is a schematic diagram of the drive current of a urea metering injection unit according to an exemplary embodiment. Detailed Implementation

[0028] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0029] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0030] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0031] This application provides a driving circuit for a urea metering injection unit. The circuit may include: an MCU (Microcontroller Unit) for outputting control signals for urea metering injection based on current signals in the driving circuit; a pre-drive chip, whose control pins are connected to the MCU to receive control signals from the MCU; an external MOS, whose gate, source, and drain are connected to the pre-drive chip to receive control signals from the pre-drive chip; a freewheeling diode, which works with the external MOS to provide a freewheeling path for current in the circuit when the external MOS is turned off; a sampling resistor for acquiring the current flowing through the urea metering injection valve; and an operational amplifier for amplifying the current signal acquired by the sampling resistor and feeding it back to the MCU.

[0032] The circuit also includes a battery-powered VBATT and a 5V-powered VDD5. VBATT provides a 12V or 24V main power supply for the entire circuit, while VDD5 provides a stable 5V power supply for some circuit components.

[0033] In one embodiment, the MCU can be a Renesas microcontroller U3 (RH850_U2B6) as the control core of the entire circuit, which exchanges initialization and fault diagnosis information with the L9945 pre-driver chip U1 via SPI communication. The L9945 pre-driver chip receives control signals from the Renesas microcontroller, thereby controlling the switching action of the external MOS (Q1A and Q1B), and also has fault diagnosis function.

[0034] Logic level conversion can be achieved between the MCU and the L9945 pre-driver chip using logic level conversion transistors (Q2 and Q3), converting the control signal into a level suitable for driving the L9945 pre-driver chip. The bases of Q2 and Q3 are connected to the MCU's control signal, the emitters are grounded, and the collectors are connected to VDD5 via pull-up resistors (R10 and R11), and then connected to the control pin of the L9945.

[0035] In the L9945 pre-driver chip, the pull-up and pull-down resistors (R8 and R9) of the enable pin are used to set the initial voltage level of the L9945 enable pin. The charge pump capacitors (C4, C6, C7) work in conjunction with the internal charge pump circuit of the L9945 pre-driver chip to provide the chip with the required high voltage to drive the gate of the external MOS.

[0036] The external MOS includes Q1A and Q1B. Q1A is the high-side switch control MOS for urea metering injection, and Q1B is the low-side switch control MOS. The gates of Q1A and Q1B are connected to the corresponding control signals through gate current limiting resistors R6 and R7, respectively, to realize the drive control of the urea metering injection unit. The source and drain of Q1A and Q1B are both connected to the pre-driver chip for voltage feedback, thereby realizing diagnosis.

[0037] Correspondingly, the freewheeling diodes include D1 and D2. D1 is the high-side freewheeling diode for urea metering injection, and D2 is the low-side freewheeling diode. In conjunction with the corresponding MOS, when the high-side MOS Q1A is turned off, the current flows from the urea injection unit through the low-side MOS Q1B and back to the high end of the urea injection unit through D1. When both the low-side MOS Q1B and the high-side MOS Q1A are turned off, the current flows from the urea injection unit to D2 and then to the battery. This provides a freewheeling path for the current in the circuit when the MOS is turned off, protecting the MOS and the circuit from damage.

[0038] Current flows from VBAAT through the high-side switch to the ECU connector, which connects to the urea injection metering unit valve. The current then flows through the valve body, through the ECU connector, to the low-side switch, and finally to ground, forming the urea metering injection circuit. A sampling resistor R1 is connected in series in the urea metering injection circuit to collect the current flowing through the urea metering injection valve.

[0039] Operational amplifier 2 (MC34072) amplifies the current signal acquired by sampling resistor R1 and then feeds it back to the Renesas microcontroller's FCMP (Fast Comparator) module for current closed-loop control. The Renesas microcontroller's FCMP receives the current signal from the operational amplifier and compares it with a predetermined current threshold to control the output of the pre-driver chip, thereby driving the switching action of the external MOS transistor and achieving precise two-stage current closed-loop control of the urea metering injection unit. The configuration resistors (R2, R3, R4, R5) of the operational amplifier determine its amplification factor.

[0040] Bypass capacitors (C1, C2, C3, C5, etc.) are placed between each power supply pin and ground to filter and stabilize the power supply voltage, reducing the impact of power supply ripple and interference on the circuit.

[0041] like Figure 2 As shown, the specific working process of this circuit is as follows:

[0042] 1. Based on feedback from engine and sensor signals, the MCU calculates the injection quantity and sends MCU_FCMPU2_T2 and MCU_FCMPU2_T3 signals to the L9945 pre-driver chip. A high level of MCU_FCMPU2_T2 controls Q1A to turn on, and a low level controls Q1A to turn off. A high level of MCU_FCMPU2_T3 controls Q1B to turn on, and a low level controls Q1B to turn off.

[0043] 2. When the urea metering unit injects urea, the MCU controls the MCU_FCMPU2_T2 and MCU_FCMPU2_T3 signals to simultaneously output high levels, which are connected to the bases of Q2 and Q3 respectively. The emitters of Q2 and Q3 are grounded, and the collectors are pulled up to 5V through R10 and R11 respectively. The collectors of Q2 and Q3 are connected to the control pins NO2 and NO3 of L9945 respectively. When the outputs of MCU_FCMPU2_T2 and MCU_FCMPU2_T3 are high, the logic level of Q2 / Q3 is reversed to input a low level to the control pins NO2 and NO3 of L9945. L9945 controls the output to turn on Q1A and Q1B.

[0044] 3. O_T_RAMVH and O_T_RAMVL are output to the external connector port. The urea metering injection unit is connected to both ends of the connector. When Q1A and Q1B are turned on, the current flows from the battery power supply VBATT through Q1A to the urea metering injection unit, to Q1B, through the sampling resistor R1 to ground. The current flows through R1, and the two ends of R1 are connected to the operational amplifier U2A through R2 / R3 respectively. After being amplified by the operational amplifier through R4 / R5, the output is fed back to the MCU_FCMPAN20 signal of the MCU.

[0045] 4. The FCMP module of the MCU receives the current feedback signal from MCU_FCMPAN20. The received signal is compared with the set current. The current setting is divided into two stages, A and B. If the actual current reaches the set current, it switches to stage B, and otherwise it switches to stage A. First, the current thresholds for stages A and B are configured through the MCU registers: Upper-limit Threshold A (upper current limit for stage A), Lower-limit Threshold A (lower current limit for stage A), Upper-limit Threshold B (upper current limit for stage B), and Lower-limit Threshold B (lower current limit for stage B). The MCU_FCMPAN20 feedback current is compared with Upper-limit Threshold A. When the MCU_FCMPAN20 feedback current reaches the Upper-limit Threshold A threshold, MCU_FCMPU2_T2 controls Q1A to turn off, and MCU_FCMPU2_T3 controls Q1B to remain on. The urea metering injection unit current begins to decrease. When a stage change interrupt command is received, the control stage switches from A to B. At this point, the urea metering injection unit current continues to decrease, and the MCU_FCMPAN20 feedback current reaches the Lower-limit Threshold. B. MCU_FCMPU2_T2 controls Q1A to turn on, and MCU_FCMPU2_T3 controls Q1B to remain on. The current of the urea metering injection unit begins to rise. When the feedback current of MCU_FCMPAN20 reaches the Upper-limit Threshold B, MCU_FCMPU2_T2 controls Q1A to turn off, and MCU_FCMPU2_T3 controls Q1B to remain on. This process repeats until a fast comparator end command is received. At this point, MCU_FCMPU2_T2 controls Q1A to turn off, and MCU_FCMPU2_T3 controls Q1B to turn off, ending the current injection cycle of the urea metering unit.

[0046] In one embodiment, according to the technical requirements of the urea metering injection unit, the Upper-limit Threshold A is 1.33A, the Upper-limit Threshold B is 0.39A, and the Lower-limit Threshold is 0.29A. The injection duration is calculated by the MCU based on feedback from the engine and sensor signals, and controlled by MCU_FCMPU2_T2 and MCU_FCMPU2_T3. The final urea metering injection unit drive current waveform is as follows: Figure 3As shown, the circuit provided in this application is based on the Renesas microcontroller's fast comparator module, combined with the pre-drive chip's external MOS and current sampling feedback to achieve two-stage current closed-loop precise control of the drive current. This enables two-stage precise current control to achieve precise control of the urea injection quantity, meeting the stringent limits on nitrogen oxide emissions under the China VI emission standards.

[0047] Based on the above-described driving circuit, this application also provides a urea metering injection unit including the above-described driving circuit, and an SCR system including the urea metering injection unit.

[0048] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0049] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A driving circuit for a urea metering injection unit, characterized in that, include: The MCU is used to output control signals for the injection of urea metering unit based on the current signal in the drive circuit. A pre-driver chip, wherein the control pin of the pre-driver chip is connected to the MCU and receives control signals from the MCU; An external MOS is provided, wherein the gate, source, and drain of the external MOS are connected to the pre-driver chip, and the external MOS receives the control signal from the pre-driver chip and provides voltage feedback. A freewheeling diode, which works in conjunction with the external MOS to provide a freewheeling path for the current in the circuit when the external MOS is turned off; The sampling resistor is used to collect the current flowing through the urea metering injection valve; An operational amplifier is used to amplify the current signal acquired by the sampling resistor and feed it back to the MCU.

2. The circuit according to claim 1, characterized in that, The circuit is powered by a battery, with VBATT providing a 12V or 24V main power supply.

3. The circuit according to claim 1, characterized in that, The MCU communicates with the pre-driver chip via SPI to exchange initialization and fault diagnosis information.

4. The circuit according to claim 3, characterized in that, A logic level conversion transistor is used between the MCU and the pre-driver chip to convert the control signal into a level signal suitable for driving the pre-driver chip. The base of the logic level conversion transistor is connected to the control signal of the MCU, the emitter is grounded, and the collector is connected to the 5V power supply through a pull-up resistor and connected to the control pin of the pre-driver chip.

5. The circuit according to claim 3, characterized in that, In the pre-driver chip, the pull-up and pull-down resistors of the enable pin are used to set the initial level of the enable pin, and the charge pump capacitor in the circuit works in conjunction with the charge pump circuit inside the pre-driver chip.

6. The circuit according to claim 1, characterized in that, The external MOS includes Q1A and Q1B. Q1A is a high-side switch control MOS for urea metering injection, and Q1B is a low-side switch control MOS. The gates of Q1A and Q1B are connected to the corresponding control signals through gate current limiting resistors R6 and R7, respectively. The source and drain are both connected to the pre-driver chip for voltage feedback.

7. The circuit according to claim 6, characterized in that, The freewheeling diodes include D1 and D2. D1 is the high-side freewheeling diode for urea metering injection, and D2 is the low-side freewheeling diode. D1 and D2 work with Q1A and Q1B respectively to provide a freewheeling path for the current in the circuit when the MOS is turned off.

8. The circuit according to claim 1, characterized in that, The operational amplifier feeds the amplified current signal back to the fast comparator module of the MCU. The fast comparator module compares the received current signal with a predetermined current threshold and drives the switch of the external MOS.

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