A method of measuring the instantaneous speed of an engine

Abstract

This application discloses a method for measuring instantaneous engine speed. The engine is equipped with a flywheel and a speed sensor. The flywheel has signal holes evenly distributed around its circumference, and also has missing hole positions. The speed sensor collects the sensing signals triggered by the signal holes during rotation. The method includes the following steps: Step 1: Obtain the interval angle between adjacent signal holes around the circumference of the flywheel; Step 2: During flywheel rotation, acquire and store the sensing signals using an oscilloscope to obtain the correspondence between the sensing signals and time; Step 3: Eliminate the offset of the sensing signals; Step 4: Obtain the positive and negative critical voltage values ​​and corresponding sampling times of the voltages adjacent to the falling edge of the sensing signals; Step 5: Obtain the time corresponding to 0 potential using interpolation; Step 6: Calculate the instantaneous speed based on the time difference between adjacent 0 potentials and the angle between the corresponding signal holes of the flywheel, and arrange the instantaneous speeds in chronological order to obtain a more accurate correspondence between instantaneous speed and time.

Description

Technical Field

[0001] This application relates to a method for measuring instantaneous engine speed, and particularly to applications such as internal combustion engine performance testing, fault diagnosis, and CAE simulation verification (calculation of speed fluctuations), belonging to the field of engine technology. Background Technology

[0002] When an engine is operating under stable conditions, although the average speed is relatively stable, the instantaneous speed varies, and these fluctuations correspond one-to-one with the firing and power stroke of each cylinder. In a multi-cylinder internal combustion engine, each cylinder works in a cyclical manner, following the processes of intake, compression, combustion, and exhaust. The torque acting on the crankshaft changes periodically, and the instantaneous speed also fluctuates regularly. This periodically fluctuating instantaneous speed signal contains a wealth of information about the engine's operating state. When other factors influence the engine, the output torque changes, and this torque change is directly reflected in the fluctuations of the instantaneous speed. Therefore, the operating state of each cylinder in an internal combustion engine can be monitored using instantaneous speed data.

[0003] When the engine's output torque exceeds the effective resistance torque, the flywheel accelerates; conversely, it decelerates, causing fluctuations in flywheel speed. This phenomenon of fluctuating flywheel speed is called flywheel rotational unevenness. Fluctuations in engine speed can lead to a series of adverse consequences. For example, impacts can occur between the engine's driving components and the driven components, affecting operational reliability, reducing service life, and generating noise. It can also cause instability in testing instruments. Furthermore, flywheel rotational unevenness can cause flywheel vibration. Therefore, flywheel rotational unevenness should be controlled within acceptable limits.

[0004] The non-uniformity of flywheel rotation is represented by the steady-state speed fluctuation rate β. n Measured by steady-state speed fluctuation rate β n The steady-state speed fluctuation rate of an internal combustion engine refers to the envelope width Δ of the speed fluctuation around the average value under constant power. n Expressed as a percentage of the rated speed, it is calculated using the following formula:

[0005]

[0006] Where, n r This is the steady-state speed.

[0007] Current methods for measuring the instantaneous speed of an engine flywheel involve recording data for 20 seconds after the engine has stabilized. This data is obtained by counting the pulses of the gear ring. The engine speed is set to 550 rpm as idle speed, with all other speeds considered full load. 100 speed data points are calculated per second, meaning the calculation time for one data point is 1 / 100 = 0.01 seconds. For example... Figure 1For a newly developed four-stroke six-cylinder engine with a 1 / 2 working cycle and a crank angle of 360°, taking a speed of 1000 r / min as an example, the calculated data is 1000 / 60 / 100 = 1 / 6, meaning the data calculated in 0.01 seconds falls within 1 / 6 of the working cycle, or within 60°. At this point, the average speed error is large, making it impossible to accurately measure the instantaneous speed, resulting in inaccurate calculations using the formula. If 1000 speed data points are calculated per second, still using 1000 r / min as an example, the calculated data is 1000 / 60 / 1000 = 1 / 60. However, current technology collects the number of gears. Taking a current geared ring (with 143 teeth) as an example, 143 / 60 = 2.38, or 2 / 3 of a tooth. Current technology cannot achieve this, leading to a large deviation in the calculation results and low accuracy in instantaneous speed calculation. Summary of the Invention

[0008] The technical problem this application aims to solve is how to improve the accuracy of instantaneous engine speed measurement.

[0009] To solve the above-mentioned technical problems, the technical solution of this application is to provide a method for measuring the instantaneous speed of an engine. The engine is equipped with a flywheel and a speed sensor. The flywheel has signal holes evenly distributed around its circumference and has missing hole positions. The speed sensor collects the sensing signals triggered by the signal holes during rotation, directly facing the signal holes. The method includes the following steps:

[0010] Step 1: Obtain the interval angle between adjacent signal holes around the circumference of the flywheel;

[0011] Step 2: During the rotation of the engine flywheel, the sensor signal is acquired and stored using an oscilloscope to obtain the correspondence between the sensor signal U and time t.

[0012] Step 3: Obtain the offset value through the sensor signal data at the notch position, and eliminate the offset of the sensor signal;

[0013] Step 4: Obtain the positive critical voltage A1 and the negative critical voltage A2 adjacent to the falling edge of the sensing signal, as well as the corresponding sampling time ta1 and sampling time ta2.

[0014] Step 5: Use interpolation to obtain the time corresponding to the 0 potential voltage;

[0015] Step 6: Calculate the instantaneous rotational speed based on the time difference between adjacent 0 potentials and the angle between the corresponding signal holes of the flywheel. Arrange the instantaneous rotational speeds in chronological order to obtain the correspondence between the instantaneous rotational speed and time t.

[0016] Preferably, the spacing angle between adjacent signal holes in step one is the actual measured precise angle.

[0017] Preferably, the method further includes step seven: plotting an instantaneous speed-time curve based on the correspondence between instantaneous speed and time t.

[0018] Preferably, the method further includes step eight: calculating the maximum speed, minimum speed, average speed, and speed fluctuation based on the correspondence between instantaneous speed and time t.

[0019] This application has the following advantages:

[0020] 1. By utilizing the signal hole at the notch of the engine flywheel (which is conventionally built into electronically controlled engines), a circumferential positioning function is achieved compared to the conventional flywheel gear ring signal measurement method, eliminating manufacturing errors between signal teeth, in order to measure the speed signal;

[0021] 2. This method provides higher accuracy in calculating instantaneous rotational speed;

[0022] 3. After the engine leaves the factory, the speed can be directly obtained by using the signal hole, without relying on the previous method of measuring based on the number of teeth on the gear ring (the gear ring method requires additional drilling);

[0023] 4. This method enables remote monitoring of the engine's operating status and timely feedback on faults. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the instantaneous speed change of an engine flywheel as it rotates 360°.

[0025] Figure 2 This is a schematic diagram showing the distribution of signal holes around the circumference of the flywheel;

[0026] Figure 3 This is a schematic diagram showing the correspondence between the sensing signal U and time t.

[0027] Figure 4 A schematic diagram illustrating the elimination of offset values ​​from sensor signals;

[0028] Figure 5 This is a schematic diagram of the instantaneous rotational speed-time curve. Detailed Implementation

[0029] To make this application more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0030] Example

[0031] This embodiment provides a method for measuring instantaneous engine speed, which specifically includes the following steps:

[0032] Step 1: Obtain the actual angles between adjacent signal holes distributed around the circumference of the flywheel. This can be obtained by consulting manufacturing data based on the flywheel model or through actual measurement. Figure 2As shown, the interval angle of the signal holes on the flywheel is 6°, and two holes are missing in one circle, so there are a total of 58 signal holes. Due to manufacturing errors, the actual angle between each signal hole may be inaccurate. Therefore, it is preferable to eliminate the manufacturing error of the flywheel by actually measuring the angle value.

[0033] Step 2: Under a certain speed and load, the flywheel rotates. Position the speed sensor directly opposite the flywheel signal port. During the flywheel's rotation, the signal port periodically passes through the speed sensor, allowing the sensor to collect a periodic signal. Use an oscilloscope to acquire and store the sensor signal (sampling frequency can be 20kHz) to obtain the correspondence between the sensor signal U and time t. See [link to relevant documentation]. Figure 3 ;

[0034] Step 3: Obtain the offset value of the sensor signal and eliminate the offset. The median value of the sensor signal actually acquired by the oscilloscope is generally not zero. This is because the sensor and the entire acquisition system have not been calibrated to zero. The flywheel has two missing holes; the missing hole positions are reference positions. When the reference position passes the speed sensor, the voltage value of the sensor signal is the actual offset value. Subtracting the offset value from the total sensor signal will eliminate the offset. See [link to relevant documentation]. Figure 4 ;

[0035] Step 4: For the sensor signal after offset elimination, obtain the falling edge voltage using voltage truncation. The falling edge voltage represents the critical voltage A1 at which the voltage changes from positive to negative in the sensor signal and the critical voltage A2 at the next sampling point. Taking the partial sensor signal voltage sequence table below as an example, the critical voltage A1 is 1.2 (a reference value after amplification of the actual measured signal from the speed sensor using an oscilloscope, dimensionless), and the critical voltage A2 is -3.6. Simultaneously obtain the sampling time ta1 of the critical voltage A1 and the sampling time ta2 of the critical voltage A2, as shown in the table below.

[0036]

[0037] Step 5: Obtain the time corresponding to the 0 potential voltage using interpolation. The sensing signal passes through the 0 potential from sampling time ta1 to sampling time ta2. Since there are no sampling points in between, interpolation can only be used to estimate the time corresponding to the 0 potential voltage. The time corresponding to the 0 potential voltage is obtained through linear interpolation, as shown in the table below.

[0038]

[0039] Step Six: Calculate the rotational speed based on the time difference between each adjacent 0-potential and the angle between the corresponding signal holes on the flywheel. The entire calculation process uses the position of the missing two holes as the reference point. One rotation of the flywheel is defined as the time it takes for the speed sensor to pass the position of the missing two holes and then pass it again. The position of the 0-potential in one rotation of the flywheel indicates the corresponding hole position. Even if there are manufacturing errors in the flywheel, a more accurate angle between adjacent holes can be obtained through actual measurement. The instantaneous rotational speed at the position of the missing two holes is filled in by linear interpolation using the rotational speeds at the adjacent hole positions, resulting in a more accurate correspondence between the instantaneous rotational speed and time t, as shown in the table below.

[0040]

[0041] The above steps yield a more accurate correspondence between instantaneous rotational speed and time t. After storing the data in a data table, an instantaneous rotational speed-time curve can be plotted. (See [link to data]). Figure 5 It can also perform other calculations such as maximum speed, minimum speed, average speed, and speed fluctuation, as shown in the table below.

[0042]

Claims

1. A method for measuring instantaneous engine speed, characterized in that, The engine is equipped with a flywheel and a speed sensor. The flywheel has signal holes evenly distributed around its circumference, and also has missing hole positions. The speed sensor is positioned directly opposite the signal holes to collect the sensing signals triggered by the signal holes during rotation, including the following steps: Step 1: Obtain the interval angle between adjacent signal holes around the circumference of the flywheel; Step 2: During the rotation of the engine flywheel, the sensor signal is acquired and stored using an oscilloscope to obtain the correspondence between the sensor signal U and time t. Step 3: Obtain the offset value through the sensor signal data at the notch position, and eliminate the offset of the sensor signal; Step 4: Obtain the positive critical voltage A1 and the negative critical voltage A2 adjacent to the falling edge of the sensing signal, as well as the corresponding sampling time ta1 and sampling time ta2. Step 5: Use interpolation to obtain the time corresponding to the 0 potential voltage; Step 6: Calculate the instantaneous rotational speed based on the time difference between adjacent 0 potentials and the angle between the corresponding signal holes of the flywheel. Arrange the instantaneous rotational speeds in chronological order to obtain the correspondence between the instantaneous rotational speed and time t.

2. The method for measuring instantaneous engine speed as described in claim 1, characterized in that, In step one, the angle between adjacent signal holes is the actual measured precise angle.

3. The method for measuring instantaneous engine speed as described in claim 1, characterized in that, It also includes step seven: plotting the instantaneous speed-time curve based on the correspondence between instantaneous speed and time t.

4. The method for measuring instantaneous engine speed as described in claim 3, characterized in that, It also includes step eight: calculating the maximum speed, minimum speed, average speed, and speed fluctuation based on the correspondence between instantaneous speed and time t.

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