Electronic throttle detection system based on PC and single chip microcomputer

As an indispensable and important part of the car, the throttle directly affects the safety performance of the car. Since the 21st century, most cars have replaced the conventional cable throttle with an electronic throttle. Compared with the old cable throttle, the electronic throttle controls the electronic signal to issue instructions through the depth of the accelerator pedal, so that the engine can provide matching power. Its biggest feature is that it can control the throttle valve opening through the ECU. When the accelerator pedal position changes, the signal output by the electronic throttle can be used as a basis for measuring the accuracy of the electronic throttle automatic control. The electronic throttle detection system is based on these real-time signals and uses various solutions to evaluate the quality and reliability of the electronic throttle to achieve its performance detection.

1 System inspection items and types

The main function of the electronic throttle is to convert the angle of the driver's accelerator pedal into a voltage signal proportional to it, and at the same time, make various special positions of the accelerator pedal into contact switches, and convert engine operating conditions such as idling, high load, acceleration and deceleration into electrical pulse signals and transmit them to the controller ECU of the electronic engine to achieve optimized automatic control of fuel supply, injection and speed change. This detection system mainly adopts 5 detection schemes according to the type of electronic throttle: including dual signal detection, dual signal plus switch detection, single signal detection, single signal plus switch detection, and electronic throttle detection with KD device.

1.1 System inspection items

Most electronic throttles need to be tested for synchronization, linearity, pedal force and other information. The specific definitions of these test items are as follows:

(1) Synchronicity: The degree of equality of the two throttle output signal values ​​at a certain travel angle.

(2) Linearity: The difference between the theoretical voltage value and the actual voltage value of the throttle signal at a certain travel angle.

(3) Idle travel angle: refers to the pedal travel angle at which the signal remains unchanged when the pedal begins to change angle.

(4) Pedal force: includes pressure and elastic force, which is the force curve of the pedal from idle to full stroke and then from full stroke to idle.

(5) Throttle signal curve: includes idle signal and full stroke signal, the voltage output signal curve of the accelerator pedal from idle to full stroke.

(6) Hysteresis: At a given angle, the output pressure is measured in two different rotation directions. The hysteresis effect is the difference between the two output pressures. The maximum acceptable difference is ±1% of Ua.

(7) Repeatability: Under the same conditions, after 10 complete back and forth strokes, for a sensor with a given temperature of (23±5)°C and at any point in the same direction, the recorded voltage difference shall not exceed 0.5%.

(8) Tilt error: The calculation formula is as follows:

Where: VGR is a variable about the slope; △X represents the distance between the bending points in mm; △Us1 is the difference between full load Vs1 and slow speed Vs1; Us1n and Us1n-1 represent the voltage at position n and n-1; Xn and Xn-1 represent the stroke at position n and n-1.

1.2 System detection type

The electronic throttle with KD device is the most complex throttle in the test project. In the throttle test graph with angle as the horizontal axis, the throttle of KD device needs to be converted into stroke display, and the stroke can be calculated according to the formula L="2"*R*sin(Θ/2). Where: L is the stroke; R is the rotation radius; Θ is the rotation angle. Among them, R is the set value, and Θ is the angle sensor detection value. In addition, the specific judgment conditions for the idle position, force, stroke and voltage value range can be referred to Figures 1 and 2. Figure 1 is the ideal force curve of the throttle with KD device. It can be seen from the figure that the starting point (2 mm on the horizontal axis) of the KD throttle is point F1, the sensing point (50 mm on the horizontal axis) is point F2, and the maximum force point is point F3.

For example, if there is a maximum KD force point within the set stroke of 50-56 mm, determine whether the force value at this point meets the set requirements, determine whether the distance from this point to the set 50 mm is less than the set value (2 mm in Figure 2); whether the output electrical signal corresponding to the stroke position after adding 0.7 mm from the stroke corresponding to the maximum KD force point is 4.1 V (set value); whether the stroke from the output electrical signal 4.1 V position to the mechanical limit position (i.e. the maximum stroke position 56 mm point) is greater than 3.3 mm, etc. Figure 2 is a judgment condition diagram of the throttle signal with a KD device.

The single signal detection function mainly detects whether the synchronization and linearity of the main signal voltage SIG1 are within the set range. Single signal plus switch quantity detection adds switch quantity detection on the basis of single signal detection, as shown in Figure 3.

The dual signal detection mainly detects whether the synchronization and linearity of the two voltage signals SIG1 and SIG2 are within the set range, ensuring that the measured signal curve is between the ideal signal curve. In addition, there are specific detection regulations for the idle voltage of the empty trip, etc. Here, the standards are set separately according to the different throttle types. The dual signal plus switch detection mainly adds a switch detection on the basis of the above dual signal detection, detects the high and low changes of the switch voltage within the set voltage range, and then judges its correctness, as shown in Figure 4.

2 System Communication Protocol

This system uses serial communication protocol, and the baud rate is set to 9600 b/s by default, which is adjustable. The character format is set to 1 start bit, 8 data bits and 2 stop bits, and the middle 8 bits are valid data.

The command format sent by the host computer is: 0xAA+command+check code (the sum is 0 check). The command content is single test command: 0x91; cycle test command: 0x92; test end: 0x94.

The data format sent by the lower computer for each single test is: 6 0xBB bytes as the start mark of the data, the middle is the collected real-time data (data is sent in groups, one group of data in one cycle, and each group of data has an angle increment of 0.5 degrees as a value), and finally 6 0xCC bytes as the end mark of the data. The data content is the original value collected by the 10-bit A/D, and the reference voltage is 5 V. The specific real-time data format collected in the middle is data type (6 binary bits) + data content (10 binary bits). The specific definition of some data types is shown in Table 1.

3 System Software Implementation

3.1 Software Implementation of Main Functional Modules

The electronic throttle detection system consists of two parts: the upper computer software and the lower computer software and hardware. The lower computer software is written in C language, and the specific hardware design circuit and software programming parts are not described in detail here. The upper computer software consists of three main functional modules, which are the throttle communication module, the parameter setting module, and the information management module. The overall design process is shown in Figure 5. First, the system is initialized, including serial port communication initialization, product parameter setting initialization (reading the first record in the background database as the default setting data), waiting for the upper computer to send a detection command, and the lower computer transmits real-time signal detection data after verification according to the protocol, and displays the real-time signal curve at the same time, and then judges whether the product is qualified according to the setting conditions, and stores the results for post-processing.

In the communication module, Microsoft communication control MSComm is directly used. Considering the speed of serial port data transmission and reception, the program here adopts the method of receiving first and then processing when processing real-time data to prevent the loss of real-time data in serial port communication. The specific program implementation process is shown in Figure 6.

3.2 Main interface of the detection system host computer

This detection system uses VC++ as the host computer development tool and a graphical interface to complete and intuitively reflect its detection process and detection results. At the same time, the background uses ACCESS to manage and store a large amount of test data, which is convenient for operators to view the test status and demonstrate the online test process, and can update the database at any time, so that various types of throttles can be tested.

In the command selection area of ​​the menu, when you click on the product information parameter, the product setting interface will appear, and the throttle standard parameters will be set. The current information after configuration will appear in the display setting information interface; when you click on the history record, the product part number that has been set and tested in the past will appear. Click on any of them, and the display setting information interface will show the various parameters of the product; when you click on print and save, the current product setting information, test results and current interface will be saved to Excel. The main interface of the throttle detection with KD device is shown in Figure 7. The left side of the middle display area is the signal display area, and the right side is the throttle pressure and elasticity display area; the bottom of the interface is the test result display area. Click the "Show Setting Information" button to view the current product setting information, and click the "Synchronization Curve" to view the throttle synchronization curve.

4 Conclusion

Based on the real-time communication and data processing method between PC and single-chip microcomputer under VC++ environment , an electronic throttle detection system is designed. The powerful data analysis ability of VC++ is fully utilized to greatly improve the development efficiency. According to the different styles and types of electronic throttles, 5 detection schemes are mainly used to detect the synchronization, linearity, hysteresis, idle travel angle of the throttle voltage signal, etc. Finally, through the acquisition of real-time data, the electronic throttle real-time signal change curve is obtained, which intuitively reflects the electrical signal characteristics inside the throttle, ensures the safe and reliable detection purpose, and has certain practicality. At present, the electronic throttle detection system has been put into use. Practice shows that the test system is reliably designed and the test effect is good.