A rotational speed signal acquisition and calculation method based on a CVT gearbox

Abstract

The application belongs to the technical field of automobile electronic control, and specifically provides a rotating speed signal acquisition and calculation method based on a CVT gearbox, comprising the following steps: a Hall voltage type rotating speed sensor is used to sense the magnetic field change of the gearbox gear, and output a pulse signal; a controller captures the edge time stamp of the pulse signal and stores it to a ring array; based on the time stamp data in the ring array, the average pulse period and the pulse duty cycle of the effective pulse are calculated; the average frequency is calculated according to the average pulse period, and the real rotating speed is calculated in combination with the number of teeth of the corresponding gear; the rotating speed direction is determined by comparing the pulse duty cycle with a preset pulse width range. The method provided by the application can convert the pulse signal output by the rotating speed sensor when the rotating speed sensor can recognize the magnetic field change of the gear change into a rotating speed signal, without the need of processing or filtering by the rotating speed sensor itself.

Description

Technical Field

[0001] This invention belongs to the field of automotive control technology, specifically relating to a method for acquiring and calculating speed signals based on a CVT transmission. Background Technology

[0002] In the field of automotive automatic transmission control, real-time and accurate acquisition of turbine, input shaft, and output shaft speed signals is fundamental to realizing key functions such as shift logic, torque converter lock-up, and torque control. Currently, the industry commonly uses Hall effect-based speed sensors for signal acquisition. A common solution is to use a current-type Hall speed sensor. Its working principle is: the sensor senses the change in magnetic field caused by gear rotation and converts this change into a current signal, which is then output to the controller, which calculates the speed. However, this solution has significant drawbacks: firstly, current-type sensors are inherently expensive, and their continuous current output mode results in high overall system power consumption; secondly, in CVT (continuously variable transmission) applications with hydraulic torque converters, multiple speeds need to be acquired simultaneously and the direction of rotation needs to be identified, placing higher demands on sensor performance and system cost control.

[0003] Therefore, the industry is considering using voltage-type Hall effect speed sensors as an alternative. These sensors output signals in the form of pulse voltages, offering inherent advantages such as low cost and low power consumption. However, applying them to CVT transmissions faces three main technical challenges: First, voltage-type signals are generally less resistant to electromagnetic interference than current-type signals, and signal quality is easily affected in complex automotive electronic environments. Second, the gear teeth of CVT transmissions (especially turbine, input shaft, and output shaft gears) are often complex and irregular, resulting in non-standard pulse waveforms generated by the sensor, increasing the difficulty of accurate identification and counting. Third, to achieve direction determination, it is necessary to extract and stably identify characteristic information representing the direction (such as duty cycle) from the pulse signal, which is particularly difficult when the signal is noisy and distorted. Therefore, how to design a data acquisition and calculation method that can match the low-cost, low-power voltage-type Hall effect sensor, effectively overcome signal interference and the influence of complex tooth shapes, and reliably identify the rotational speed direction has become a pressing technical problem in this field. Summary of the Invention

[0004] This invention provides a method for acquiring and calculating speed signals based on a CVT transmission, in order to solve the technical problems mentioned in the background section.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A method for acquiring and calculating speed signals based on a CVT transmission includes the following steps: S1: The change in the magnetic field of the gearbox gears is sensed by a Hall voltage type speed sensor, and a pulse signal is output; S2: The controller captures the edge timestamps of the pulse signal and stores them in a circular array; S3: Based on the timestamp data in the circular array, calculate the average pulse period and pulse duty cycle of the effective pulses; S4: Calculate the average frequency based on the average pulse period, and calculate the actual rotational speed in combination with the number of teeth of the corresponding gear; S5: Determine the rotational speed direction by comparing the pulse duty cycle with the preset pulse width range.

[0006] A further improvement is that the number of members in the ring array is predetermined based on the number of teeth of the corresponding gear in the gearbox, the maximum speed, and the data acquisition cycle of the controller.

[0007] A further improvement is that the number of members is determined by calculating the maximum number of pulse signals to be captured in a single capture cycle and setting the number of members according to storage requirements.

[0008] A further improvement is that the capture period is 5ms and the storage requirement is to retain pulse data from at least the most recent two capture periods.

[0009] A further improvement is that the number of members is not less than twice the number of the maximum pulse signals.

[0010] Further improvements are made in the following ways: the CVT transmission includes a turbine gear, an input shaft gear, and an output shaft gear; taking the output shaft gear as an example, it has 68 teeth, a maximum speed of 10000 RPM, and the maximum number of pulse signals within 5ms is calculated to be 57. The number of members in the ring array is set to 120.

[0011] A further improvement is made by sequentially selecting three consecutive edge timestamps to calculate the pulse period and level period, and determining whether the calculation results are within the preset effective range determined based on the gear working parameters, in order to filter valid pulses.

[0012] A further improvement is that the average frequency is obtained by mean filtering the instantaneous frequencies calculated from multiple consecutive capture cycles.

[0013] A further improvement is that the preset pulse width range is determined according to the chip design specifications of the Hall voltage type speed sensor used.

[0014] A further improvement is that the sensor is an Infineon TLE4959C sensor, with different characteristic pulse width ranges corresponding to forward and reverse rotation.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention is specifically adapted to Hall voltage-type speed sensors, eliminating the need for expensive current-type sensors and directly reducing hardware costs and system power consumption. Simultaneously, innovative software algorithms compensate for the potential shortcomings of voltage-type sensors in anti-interference capabilities, achieving "software-assisted hardware" and optimizing the overall system cost-effectiveness, thus achieving a balanced approach between cost and performance.

[0016] 2. The calculation method proposed in this invention does not rely on a specific regular tooth profile. Regardless of how complex or irregular the gear tooth profile is, as long as the sensor can detect changes in the magnetic field and generate a pulse signal, this method can accurately calculate the rotational speed through timestamp analysis and validity judgment logic. This gives the method good platform portability, making it applicable to different CVT transmission models and improving the robustness and versatility of the system.

[0017] 3. This invention manages the timestamp sequence using a circular array and designs a specific algorithm to stably calculate the average pulse period and pulse duty cycle from potentially noisy raw pulse signals. Based on this, it can not only accurately convert the rotational speed but also reliably determine the rotational direction based on whether the duty cycle falls within a preset forward / reverse characteristic range (e.g., based on chip design specifications similar to the Infineon TLE4959C sensor). Thus, it simultaneously acquires rotational speed and direction information in a single signal stream, achieving highly reliable integrated detection of rotational speed and direction.

[0018] 4. A circular array (FIFO) is used to cache timestamp data, retaining only the data needed for the most recent few calculation cycles, thus avoiding the infinite accumulation of historical data. This dynamic storage management method significantly reduces the static occupation of microcontroller (MCU) memory resources while ensuring calculation accuracy, improving resource utilization efficiency and optimizing controller resource usage.

[0019] 5. The actual rotation speed signal and clear rotation direction information ultimately provided by this invention constitute the key closed-loop feedback of the transmission control system. This provides reliable data input for advanced control functions such as shift timing decision-making, torque converter lock-up control, and precise gear ratio adjustment, thereby helping to improve the vehicle's driving smoothness, power, and fuel economy, and laying a solid foundation for precise transmission control.

[0020] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0021] Figure 1 This is a diagram illustrating the overall logical framework of the method provided by this invention. Figure 2 This is a schematic diagram of the output pulse signal waveform and timestamp acquisition of the Hall voltage type speed sensor of the present invention; Figure 3 This is a schematic diagram of the timestamp storage of the circular array (Timestamp_buff) provided by the present invention. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0023] Reference Figure 1 This invention relates to a method for acquiring and calculating the rotational speed of a CVT transmission. First, a Hall voltage-type speed sensor identifies gear rotation and converts it into a pulse signal. Then, a controller captures the rising and falling timestamps of the pulse signal. Finally, a software algorithm processes, calculates, and filters the captured timestamp data to obtain the gear's rotational speed and direction, providing a closed-loop condition for the transmission's control.

[0024] Specifically, this patent relates to a method for calculating the rotational speed of a CVT transmission, as detailed below.

[0025] 1. The speed sensor identifies gear rotation: The speed sensor used is a Hall voltage type speed sensor. The sensor itself may not have noise suppression capabilities; however, through the following software algorithm, when the gear rotates, the Hall speed sensor senses the change in the magnetic field and outputs a pulse signal (similar to a square wave signal), as follows: Figure 2 .

[0026] 2. The controller acquires and processes pulse signals: The controller continuously acquires the pulse signal from the first step through its internal hardware circuitry. The pulse signal is divided into rising edge timestamps and falling edge timestamps, as follows: Figure 2 It is then stored and retrieved for calculation in the next 5ms cycle.

[0027] 3. Software algorithm calculates rotational speed frequency and rotational direction: The timestamps captured by the controller are stored in the software using a 120-member array Buffer, specifically Buff 0 to Buff 119. The software captures data every 5ms, and each time the timestamp data is added, the system continues filling the array. When Buff 119 becomes insufficient, the system restarts filling from Buff 0, as follows: Figure 3 .

[0028] After capturing a buff every 5ms, timestamp data is retrieved according to the buff order. Multiple sets of timestamp intervals are calculated iteratively. The average frequency of all pulses captured in the past 5ms is obtained by averaging these timestamp intervals. The pulse width (duty cycle) can also be calculated to determine the rotational direction. The detailed process is as follows: ① Define a 120-member buff array `Timestamp_buff`, where each member is 4 bytes in size. The number of members and the size of the bytes can be increased or decreased according to the speed range and MCU memory resources. For example, if the CVT transmission currently has 30 turbine teeth, 50 input shaft teeth, and 68 output shaft teeth, and the maximum output shaft speed is 10000 RPM, then a maximum of 10000 / 60 * 68 = 11333 teeth need to be identified per second. Therefore, a maximum of 11333 / 200 = 57 pulse signals need to be captured every 5ms. Based on retaining the two most recent pulse data, the number of members in the array is set to 120. If the number of teeth and the maximum speed are small, the buff array can be adjusted accordingly to save MCU memory resources. For example, if a maximum of 8 pulse signals need to be captured every 5ms, then the number of members in the buff array can be set to 20. Similarly, the turbine speed and input shaft speed can be configured with the relevant array member number parameters based on the number of teeth and the maximum speed.

[0029] ② In the 5ms task, periodically capture the timestamp Buff 5ms before the update and fill it into Timestamp_buff in order. When the number of data exceeds 120, start filling from 0 again in order to achieve circular array storage. At the same time, record the array index Buff_index after the current update, and use Buff_index_old to record the last array index stored last time.

[0030] ③ Calculate the number of timestamps retrieved this time using the following algorithm. Because it is a circular array, the calculation needs to be performed using the following formula: Ts_cnt (number of timestamps) = (( 120 + Buff_index - Buff_index_old) % 120); ④ Starting from the initial array of this record, i.e., Buff_index_old+1, denoted as Index, take the following three sets of timestamp data: Timestamp_buff[Index], Timestamp_buff[Index+1], and Timestamp_buff[Index+2]. These three consecutive array members store three consecutive edge timestamps (rising-falling-rising or falling-rising-falling).

[0031] ⑤ Calculate the time. Based on the three data points obtained in the previous step, perform the following calculations: Time_all (one pulse cycle) = Timestamp_buff[Index+1] - Timestamp_buff[Index] Time_first (first level cycle) = Timestamp_buff[Index+1] - Timestamp_buff[Index] Time_second (second level cycle) = Timestamp_buff[Index+2] - Timestamp_buff[Index+1] The calculated Time_all, Time_first, and Time_second are judged. If they are within a set range (the set range is set based on the theoretical calculation value of the highest and lowest speed of the gear, for example, the effective range of Time_all can be set to [X,Y] microseconds), the frp_cal_cnt (effective pulse) count is increased, and Time_all is accumulated. Otherwise, it remains unchanged. The next time, the three data points Timestamp_buff[Index+2], Timestamp_buff[Index+3], and Timestamp_buff[Index+4] are taken and calculated, and the calculation continues until the last data is obtained.

[0032] ⑥. Divide the accumulated Time_all from the previous step by frp_cal_cnt to obtain the average pulse period T of this 5ms.

[0033] ⑦ Divide 5ms by T to get the frequency calculated in the current 5ms. Here, you can take the frequency calculated in the previous 5ms or even the frequency of the previous several 5ms periods and first calculate the average, that is, mean filtering, to get the average frequency F (Hz) of the most recent period.

[0034] 4. Gearbox speed conversion: The frequency calculated in step 3, combined with the number of teeth, gives the actual speed of the gearbox. For example, if the number of teeth is 68, the calculated speed is S = F*60 / 68. The level period Time_first or Time_second calculated in step 5 is the pulse width. Taking Infineon TLE4959C as an example, one configuration of its chip design specification is a forward low-level pulse width of 38-52us and a reverse low-level pulse width of 76.5-103.5us. The current speed direction can be determined based on the pulse width time.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for collecting and calculating the speed signal of a CVT gearbox, characterized in that, Includes the following steps: S1: The change in the magnetic field of the gearbox gears is sensed by a Hall voltage type speed sensor, and a pulse signal is output; S2: The controller captures the edge timestamps of the pulse signal and stores them in a circular array; S3: Based on the timestamp data in the circular array, calculate the average pulse period and pulse duty cycle of the effective pulses; S4: Calculate the average frequency based on the average pulse period, and calculate the actual rotational speed in combination with the number of teeth of the corresponding gear; S5: Determine the rotational speed direction by comparing the pulse duty cycle with the preset pulse width range.

2. The method of claim 1, wherein, The number of members in the circular array is predetermined based on the number of teeth of the corresponding gear in the gearbox, the maximum speed, and the data capture cycle of the controller.

3. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 2, characterized in that, The number of members is determined by calculating the maximum number of pulse signals to be captured in a single capture cycle and setting the number of members according to storage requirements.

4. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 3, characterized in that, The capture period is 5ms, and the storage requirement is to retain pulse data from at least the most recent two capture periods.

5. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 4, characterized in that, The number of members is not less than twice the number of the maximum pulse signals.

6. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 5, characterized in that, The CVT transmission includes a turbine gear, an input shaft gear, and an output shaft gear; taking the output shaft gear as an example, it has 68 teeth, a maximum speed of 10000 RPM, and the maximum number of pulse signals within 5ms is calculated to be 57. The number of members in the ring array is set to 120.

7. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 1, characterized in that, In step S3, three consecutive edge timestamps are selected sequentially to calculate the pulse period and level period, and it is determined whether the calculation results are within the preset valid range determined based on the gear working parameters, so as to filter valid pulses.

8. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 7, characterized in that, In step S4, the average frequency is obtained by mean filtering the instantaneous frequencies calculated from multiple consecutive capture cycles.

9. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 1, characterized in that, In step S5, the preset pulse width range is determined according to the chip design specifications of the Hall voltage type speed sensor used.

10. The method for acquiring and calculating speed signals based on a CVT transmission according to claim 9, characterized in that, The sensor is an Infineon TLE4959C sensor, with different characteristic pulse width ranges corresponding to forward and reverse rotation.

Images