1. New instruments and functions for full electric cars
①Power battery indicator: It is connected to the power battery and provides the driver with relevant information on the power status of the power battery.
②Charge status indicator: Indicates the remaining working capacity of the power battery. Using an analog or digital display, it can be permanently displayed, or an indication can be given at any time when the driver needs it. If the power battery is used to replace the system, it is best to reset it automatically. If it cannot be automatically restored to a fully charged state, it should be reset manually.
③Voltmeter: used to display the voltage of the power battery. The proper working voltage range should be marked on the dial of the meter. In order to increase the accuracy of the indicated value, the extended scale should be used within the working range.
④ Ammeter: used to display the current flowing through the power battery. The accurate zero position should be specified on the dial of the instrument. For cars with regenerative braking, the range of normal operating current should be marked in both directions of the zero position of the dial.
⑤Drive motor indication table: Provide the driver with relevant information on the working state of the drive motor.
⑥Tachometer: Indicates the instant speed of the motor. Using an analog or digital display, when the speed exceeds a certain specified value, it should be clearly marked.
⑦ Warning and indication signal device: used to inform the driver about the correct operating conditions of the electric drive system and power battery, optical and/or acoustic signals are preferred. The device is powered by a low-voltage auxiliary system, and protection should be provided if it is powered by the live part of the power battery. Warning and indicating signal devices can be replaced by indicating instruments.
⑧ Overheating warning: When the temperature of a certain device is too high, it may have a serious impact on the safety or performance of the car, a warning should be issued to the driver.
⑨Overspeed warning: When the motor is overspeeding, it is better to use the sound signal together with the light signal to warn the driver.
⑩ Low capacity warning: When the remaining capacity of the power battery is lower than a certain percentage (for example, 25%), the driver should be reminded through a signal device.
⑪Insulation resistance/creepage distance indication: When the insulation resistance and/or creepage distance is lower than the specified value, the driver should be reminded by the signal device. Insulation resistance includes insulation resistance of power battery, insulation resistance between power system and car electrical chassis, insulation resistance between power system and auxiliary circuit, creepage distance includes creepage distance between battery connection terminals, creepage distance between live parts and electrical chassis electrical distance.
⑫ “car controller on” indication: It shows to the driver that the controller is on, and the power supply can be supplied to the drive system by pressing the accelerator pedal. It can be combined with a power off button if indicated by a visual signal. The device can be switched off when the car is in motion.
⑬ Auxiliary battery charging monitoring device: When charging the auxiliary battery during the normal driving of the car, if the charging component fails, the driver should be reminded through the signal device.
⑭Stopping instruction: When the driver leaves the car, if the drive system is still in the “drivable” state, the driver should be reminded by the signal device.
⑮ Power battery charging indication: When the charger is charging the power battery, the driver should be reminded through a signal device.
⑯ Interlock monitoring device: If any interlock device in the car interlock mechanism works to prevent the car from running, a warning should be issued to the driver.
2. Information display mode
There are three types of information display methods for full electric cars: combination instrument type, digital type and LCD type. The combination instrument has high display accuracy, fast information refresh, and time-sharing display using numbers, which can simplify the instrument panel and display a large amount of information. The advantage of using a digital display and a large LCD screen is that as long as the instrument has enough memory and a high-resolution LCD display, the degree of freedom of LCD graphic modeling will be very high. The driver can manually select what is normally displayed on the instrumentation, and most systems can also automatically display and issue an alert to alert the driver when the car is in a potentially dangerous situation.
The motor tachometer of full electric car is generally not designed separately, and is replaced by a power meter, as shown in Figure 1.
The motor power controller and the temperature of the motor can be displayed by the instrument or liquid crystal display. The instrument displays the measured data in the form of pointer, number or bar graph. Some high-end cars adopt the display method of virtual instrument , so that the inner space of such instrument can be fully utilized and the tension of instrument space is avoided. As shown in Figure 2, when “READY” is green, it means that the idle start/stop function is available at this time; when “READY” is yellow, it means that the idle start/stop function is disabled at this time, and the energy flow or battery can also be displayed in the middle of the meter SOC level, etc.
3. Meters Driven and Drawn
The instrument mostly adopts 8-bit or 16-bit single-chip microcomputer, including multi-channel high-current output stepping motor drive control and cross coil drive control, which can directly drive LCD liquid crystal display, with online programmable Flash ROM, SRAM storage with low voltage CPU reset detection function, CAN channel, multi-channel 8/10-bit AD converter, multi-channel 8/16-bit input capture channel, etc.
The pointer type instruments are mostly driven by stepper motor and cross coil, mostly by stepper motor, and the stepper motor has a capture channel and so on. Four-coil and two-coil type, mostly two-coil type.
The micro stepping motor shown in Figure 3 is a two-phase permanent magnet stepping motor, which consists of coils, coil cores, pins, stators and rotors. The rotor step angle is 60°. There is a 180:1 reduction gear mechanism inside the motor, which reduces the speed through gear reduction and obtains (1/3)° resolution on the output pointer shaft. In order to reduce the cost, the PWM port of the single-chip microcomputer is used to directly simulate the micro -step drive, and the micro-step motor has become the mainstream solution. Usually two PWM ports and two I/O ports are used to drive a stepper motor. Although the PWM mode simulates the micro-step drive, the effect of the drive is still a little worse than that of the dedicated drive chip. The two coils are energized to form different pole breaking on the two stator iron cores, which drives the rotor to rotate. This rotation is transmitted to the pointer shaft through the multi-stage deceleration mechanism, which drives the point er to rotate. The rotor deceleration mode can also use the screw gear deceleration mechanism to drive the pointer to rotate.
The precise stepper motor drive circuit is shown in Figure 4. Each phase in the two-phase coil is controlled by two inverters. The microcontroller can realize the forward and reverse currents of the L1 coil and the L2 coil as long as the microcontroller controls the input terminals of the four inverters, thereby producing different changes in the iron core. The magnetic pole, the rotor rotates, and is output to the pointer shaft through the multi-stage deceleration mechanism.
The graphic and text contents of the LCD are stored data frame by frame (displayed frame by frame on the display screen), which frame data is externally triggered. Instrument lighting, warning lights, and indicator lights are LEDs. The lighting LEDs can also be triggered externally for PWM dimming. Almost all instruments have built-in buzzers for audible warnings. The buzzer will only work when there may be danger.
The contents displayed by the combination instrument of the electric car include the indicator (pointer) indicator and the alarm (indicator) display.
Figure 5 shows a schematic diagram of the signal input and output of the main instrument circuit of an electric car, in which the indicator light and warning light circuit are divided into two types: control negative and control positive, as shown in Figure 6 and Figure 7.
The speedometer is consistent with the traditional car, used to display the speed of the car, and the signal is taken from the motor controller or the car controller.
The state of charge table is used to display the remaining working capacity of the power battery, which is represented by the symbol “SOC” and shows the percentage of the remaining power of the power battery to the total capacity. The SOC is related to the discharge rate of the power battery, the working environment temperature and the aging degree of the battery. When the SOC is lower than a certain value, an alarm should be issued, and the signal is mostly taken from the battery management system.
The voltmeter is used to measure (display) the voltage of the power battery. The voltage range should be marked on the dial of the combination meter, usually the voltage is above 30V, and the signal is taken from the battery management system.
The ammeter is used to measure (display) the current of the power battery. The exact zero position should be specified on the dial of the combination meter. For cars with regenerative braking function, the range of normal operating current should be marked in both directions of the zero position of the dial. Negative current indicates energy recovery. , the signal is taken from the battery management system.
The content displayed by the ammeter, voltmeter and state of charge meter is related to the power battery, and its signals are all derived from the battery management system, that is, the signal input by the battery management system to the meter. For example, the electric car uses a lithium iron phosphate power battery, the single cell is 52A h, 3.2V, a total of 112 batteries are used, and the car voltage is 360V, so the voltage range of the voltmeter is set to 0~400V. The current range of the ammeter is designed to be -100~200A, in which the negative current direction indicates the energy recovery of the electric car during braking.
The warning and signalling device used to inform the driver about the correct operating conditions of the electric drive system and the power battery is customarily called “XX warning light”. Commonly used alarm indicators in the combination instrument of electric cars include running ready, overheating, overspeed, low limit of remaining capacity, insulation resistance, drive controller ready, energy feedback fault, parking indication, charging lock indication, system fault, power battery fault, etc. .
The indicator meter is mainly used to display the relevant information of the power battery, the motor and the whole car. There are generally five indicator heads in the electric car combination instrument, which are respectively used to indicate the motor speed, the driving speed, the ammeter, the voltmeter and the state of charge. The table is driven by a stepping motor.
The motor tachometer is used to display the real-time speed of the motor, generally above 1000r/min.
In order to reduce the number of wires leading to the instrument, the modern automobile instrument adopts CAN bus to share the signals of each electronic control unit of the whole car. For example, the electronic control unit puts the motor speed signal on the CAN bus , and the instrument can receive it. Recently, the whole car adopts a fully digital management method. The electronic control unit is used to convert all the signals into digital quantities, and the data is sent to the CAN bus for sharing. Such an instrument has only four wires, namely power supply and grounding two, CAN. High and low two lines (some CAN use three or more as a wake-up line).
The hardware circuit of the combination meter is mainly composed of a power supply circuit, an analog input signal circuit, a digital input signal circuit, a diagnostic function circuit, and a power failure protection circuit.
(1) Power circuit
The fluctuation of the power supply voltage of the instrument panel will cause the change of the current in the circuit, which will cause the indication error of the instrument. In order to avoid this error, a voltage regulator is installed in the instrument panel to keep the working voltage of the instrument constant. For example, the instrument panel linear voltage regulator IC7812 can output 12V instrument panel power supply after voltage stabilization, to ensure that the instrument panel voltage does not fluctuate with the change of the motor (generator) output voltage . There are three types of voltage regulators in the instrument panel: Zener diode regulator, linear regulator circuit regulator, and switching regulator. In order to prevent the reverse connection of the battery from damaging the instrument, add diode protection when the power is input. As long as the external power supply of the instrument, the ignition switch is reset, and the grounding wire is correct, the instrum ent can be stabilized normally.
Since the auxiliary battery of the car provides a 12V voltage, voltage conversion and filtering are required. Among them, +5V is the analog power supply, and Vcc is the digital power supply and the working power of the microcontroller.
(2) Analog input signal circuit
Analog input signals include motor and motor controller temperature signals, coolant temperature signals, air pressure sensor signals, voltmeter voltage signals, etc.
(3) Digital input signal circuit
Digital input signals include car speed signal, ABS fault signal, airbag fault signal, energy feedback signal, etc. The off signals include parking light switch signal, left turn switch signal, right turn switch signal, high beam switch signal, gear position signal, seat belt switch signal, motor (generator) power generation signal, door switch signal, brake pad fault signal , Parking brake switch signal, front fog light switch signal, coolant level switch signal, insufficient air pressure signal, etc.
The above signals differ depending on whether it is a full electric car or a hybrid car.
(4) Diagnostic function circuit
CAN bus communication interface.
(5) Power failure protection circuit
The power failure protection circuit is to record the data such as the mileage of the car in time when the power is turned off. Using the power-off protection circuit, the voltage can be maintained for a period of time when the power is off, ensuring that the single-chip microcomputer completes the storage of the mileage data, and adjusts the pointer position to make it return to zero. In order to save the mileage data in time when the power is turned off, add a 1000μF or 2200μF electrolytic capacitor to the power ground input. When the external power supply is disconnected, the capacitor can maintain the power supply of the microcontroller for a long enough time, so that the microcontroller can complete the external interrupt. service program.