Foreword
In the development and testing of a unit pump common rail diesel engine ECU, it is essential to excite the camshaft (or crankshaft) speed signal. Instead of using an actual engine, a speed sensor can be replaced to generate and output the required frequency signal. However, this signal is not standardized—its phase, number of cylinders, and amplitude vary, making it difficult to find a ready-made solution. Although dSPACE simulation can be used for camshaft speed signal simulation, it requires a large instrument, a computer for display, and is both expensive and inconvenient to operate. Therefore, developing a compact, portable, and cost-effective diesel engine speed generator is highly beneficial. The Hall sensor from the camshaft speed sensor outputs a square wave, while magnetic sensors produce a sine wave. Regardless of the input type, the CPU front-end processing circuit can convert the signal into a square wave that the CPU can recognize. Hence, designing the system to output a versatile square wave signal makes it adaptable for various applications. The ECU typically operates on 12V or 24V power, so the power supply circuit is designed to accept 12–24V input. The C8051F310 microcontroller is selected due to its timer, ADC, and I/O resources, which meet the system requirements. The speed output is continuously adjustable, allowing the simulation of starting, idle, and controlled speeds. Displaying engine simulation data helps developers configure settings effectively. Since the information displayed is limited, a cost-effective character LCD module like LCM1602 is used. Additionally, different toothed disc structures are stored in memory, encoded for easy selection, enabling the device to support various ECU software development tasks.Hardware Design
The hardware architecture of the camshaft speed simulation device is illustrated in Figure 1. It consists of a microcontroller system, an LCD display circuit, a speed reference circuit, a parameter storage circuit, and a power supply circuit. The C8051F310 serves as the central processing unit. It features an internal watchdog for power-on reset and program monitoring. The device is powered by a 12–24V DC source and uses two-stage voltage regulation to provide 5V and 3.3V supplies. An IO port expansion button allows users to select the gear plate serial number, which is stored in E2PROM. The speed reference potentiometer’s output is converted by the CPU’s on-chip ADC into a digital signal proportional to the speed. Two CPU IO ports control the adjustable frequency of the camshaft square wave signal. The LCM1602 character LCD displays the rotational speed and the toothed disc structure, using an 8-bit bus mode. The housing is made from a standard plastic shell with minor modifications.
Figure 1: System Hardware Structure Diagram
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