Zero-crossing control method for motor torque of new energy passenger car

Abstract

The invention provides a new energy passenger car motor torque zero-crossing control method. The method comprises the following steps that S1, the accelerated speed required by a driver and corrected by the motor rotating speed is calculated; s2, calculating the frequency of the motor; s3, judging acceleration rapid rise required by a driver; and S4, carrying out gradient processing on the acceleration. Through calculation of the motor frequency in the motor torque zero-crossing process, motor gear vibration in the vehicle driving process can be effectively weakened and eliminated on the basis of ensuring that the intention of a driver is achieved, and the driving stability of the vehicle is enhanced; meanwhile, the noise of the motor under the torque zero-crossing condition is avoided, and the NVH performance of the whole vehicle and the feeling comfort of a human body are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle. Background Art

[0002] When the motor of a new energy passenger car is running, when the speed is near zero, the motor rotor position or current direction changes, and the motor rotation direction changes from positive to negative or negative to positive. At this time, due to the change in torque, the gear teeth will be reversed, and the gap will be eliminated during the process, causing speed fluctuations, which will cause impacts and abnormal noises in the vehicle, and at the same time generate low-frequency noise that causes discomfort to the driver, affecting the NVH quality of the entire vehicle.

[0003] In order to alleviate or eliminate the torque zero-crossing impact caused by the motor gear clearance, the current control methods include: (1) filtering when the motor torque passes through zero to make the torque smooth; (2) increasing the rate of change of the torque.

[0004] The defects of the above two methods are: (1) the motor zero torque filtering will reduce the feedback of the driver's operation, making the driving experience worse, and reducing the effectiveness and real-time performance of torque transmission; (2) the torque change rate will increase, which will slow down the change of torque in a short period of time, which is not conducive to timely transmission of the driver's intention; it is to reduce the abnormal noise and impact when the motor torque passes through the zero range, but it cannot avoid the generation of low-frequency noise.

[0005] Currently, there is no control method that detects the frequency of the motor during the torque zero-crossing period without using a sensor and uses an algorithm to make the motor avoid this frequency range. Summary of the invention

[0006] To solve the above problems, the present invention discloses a method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle, which aims to use fewer sensor values ​​to calculate the motor frequency at the moment when the motor torque crosses zero, filter out the low-frequency noise that the human body is not adapted to, and adjust the motor torque through a control algorithm so that the motor avoids this low-frequency area, while reducing abnormal noise and impact during the torque zero crossing.

[0007] The specific plan is as follows:

[0008] A method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle comprises the following steps:

[0009] S1, calculating the acceleration required by the driver with motor speed correction;

[0010] S2, calculate the frequency of the motor;

[0011] S3, judgment of the rapid increase in acceleration required by the driver;

[0012] S4. Acceleration gradient processing.

[0013] Furthermore, the acceleration required by the driver after correction of the motor speed is calculated; wherein the acceleration required by the driver is the acceleration required by the driver calculated by the vehicle controller based on the accelerator pedal opening, gear position, brake pedal opening, maximum allowable torque of the motor, maximum allowable discharge / charging power of the battery, slope, vehicle speed, etc. This acceleration represents the acceleration the driver expects to obtain when driving the vehicle.

[0014] Furthermore, the motor speed is the speed value fed back by the motor controller, which needs to be low-pass filtered to remove the jitter and noise of the value. The purpose of MAP table correction based on the acceleration required by the driver and the motor speed is to appropriately reduce the acceleration value when the motor speed is near zero to prevent excessive acceleration from causing a large impact.

[0015] Furthermore, it also includes calculating the frequency of the motor; processing and determining the motor speed, including low-pass filtering of the motor speed signal to determine whether the motor speed is gradually increasing or decreasing over a period of time; calculating the motor frequency through the number of changes in the rising or falling state of the motor speed combined with a counter; if the motor frequency is within a certain range (a low frequency that is uncomfortable for the human body) and the number of occurrences of this frequency is greater than a limit value, then the motor torque zero crossing is determined to be activated, otherwise it is reset.

[0016] Furthermore, it also includes the judgment of the rapid increase of acceleration required by the driver, which is to keep the acceleration demand of the driver first. This is achieved by calculating the average value of the change of acceleration in unit time. This method avoids the influence of the acceleration step on the overall judgment. Since the rapid increase of acceleration means that the driver has a strong acceleration demand, the jitter demand of torque zero crossing will be placed in a secondary position.

[0017] Furthermore, it also includes acceleration gradient processing, which is to calculate the ascent / descent gradient by multiplying the set ascent / descent rate and sample time. This method ensures the continuity of the gradient, and at the same time, due to the increase in the association with the sample time, the real-time nature of the acceleration gradient is guaranteed.

[0018] The beneficial effects of the present invention are:

[0019] By calculating the motor frequency during the motor torque zero-crossing process, the motor gear vibration during vehicle driving can be effectively weakened and eliminated while ensuring the driver's intention is achieved, thereby enhancing the vehicle's driving stability. At the same time, the noise of the motor when the torque passes through zero is avoided, thereby improving the NVH performance of the entire vehicle and the comfort of the human body. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1It is a schematic flow diagram of the method of the present invention;

[0021] Figure 2 is a schematic diagram of a flow chart for calculating the motor frequency in the present invention;

[0022] Figure 3 It is a schematic diagram of the changes after acceleration filtering in the invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] New energy vehicles are driven by drive motors. There is an energy recovery condition during the driving process, which is generally set to a positive driving torque in the vehicle's forward direction and a negative energy recovery torque. The driver's drive motor will produce positive and negative changes in torque during driving. This positive and negative change in the torque of the drive motor is called the torque zero crossing phenomenon. The torque zero crossing phenomenon is a basic common problem that all new energy vehicles must consider. For new energy vehicles, if there is no torque zero crossing control, the vehicle will shake when switching between deceleration and acceleration, accompanied by noise from the motor hitting the gear gap.

[0025] In order to alleviate or eliminate the torque zero-crossing impact caused by the motor gear clearance, the current control methods include (1) filtering when the motor torque passes through zero to make the torque smooth, and (2) increasing the rate of change of the torque. The defects of the above two methods are: (1) the motor zero-crossing torque filtering will reduce the feedback of the driver's operation, making the driving experience worse, and reducing the effectiveness and real-time performance of the torque transmission; (2) the increase in the rate of change of the torque will cause the change of the torque to slow down in a short period of time, which is not conducive to timely transmission of the driver's intention; it is to reduce the abnormal noise and impact when the motor torque passes through the zero interval, but it cannot avoid the generation of low-frequency noise.

[0026] It should be noted that the technical solution of the present application is applicable to the torque zero-crossing jitter control of new energy two-wheel drive vehicles and four-wheel drive vehicles, wherein new energy two-wheel drive vehicles are not limited to front-wheel drive or rear-wheel drive. The following embodiments of the present application are described in detail using the front-wheel drive situation as an example. At this time, the motor torque request of the vehicle can be considered as the front motor torque request. It should be understood that the above-mentioned application scenarios and changes in technical terms do not constitute a limitation on the technical solution of the present application.

[0027] The technical solution of the present application is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 is a flow chart of the motor torque zero-crossing control method provided in the embodiment of the present application. Figure 1 As shown, the motor torque zero-crossing control method may specifically include:

[0029] Step S1: Calculate the driver's acceleration (after motor speed correction);

[0030] Step S2: motor frequency calculation;

[0031] Step S3: acceleration gradient determination;

[0032] Step S4: Acceleration gradient processing.

[0033] In this embodiment, the vehicle includes new energy vehicles, such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid vehicles, etc. The vehicle data includes but is not limited to the following types of data: driver-required acceleration, vehicle speed, motor speed, etc., wherein the driver-required acceleration is the acceleration calculated by the vehicle controller based on the accelerator pedal opening, gear position, brake recovery intensity, brake pedal opening, maximum allowable motor torque, maximum allowable battery discharge / charging power, slope, vehicle speed, etc. This acceleration represents the acceleration that the driver expects to obtain when driving the vehicle. The vehicle speed data is the real-time vehicle speed information generated during the vehicle's driving process, which is generally calculated by the wheel speed sensor in the ABS; the motor speed data is the real-time motor speed information generated during the motor's movement, which is generally calculated by the motor controller.

[0034] In this embodiment, the torque zero-crossing interval can be considered as a time period or a torque change interval. This application regards the process of converting the positive and negative values ​​of acceleration combined with the positive and negative values ​​of motor speed as a complete torque zero-crossing process.

[0035] In this embodiment, the positive and negative values ​​of the motor speed are obtained after the motor controller processes the motor speed. A positive value of the motor speed represents that the motor speed is consistent with the vehicle's travel direction, and a negative value of the motor speed represents that the motor speed is opposite to the vehicle's travel direction.

[0036] In this embodiment, step S1: calculating the driver's acceleration (after the motor speed is corrected)

[0037] This step uses the acceleration required by the driver and the motor speed to calculate the MAP table, and obtains the acceleration required by the driver after the motor speed is corrected; the corrected acceleration is to optimize the acceleration value when the motor speed is in the range near zero, and appropriately reduce the acceleration value to achieve the effect of reducing the gear impact and vibration of the motor; but the acceleration value cannot be reduced too much, so that the vehicle cannot reflect the driver's real driving intention, resulting in poor vehicle drivability. The MAP table uses the X and Y axes as input quantities, and obtains the calculation method of the Z axis output quantity by looking up the table.

[0038] The process of calculating the motor speed corrected driver acceleration MAP table will be described in detail below in conjunction with a specific embodiment. In actual applications, the input X-axis is the motor speed, the input Y-axis is the acceleration required by the driver, and the output Z-axis is the driver required acceleration after the motor speed is corrected; the expression of the MAP table is described below in conjunction with a specific example. It should be noted that the following motor speed corrected acceleration MAP table is only a table that may be involved in the actual application scenario of this application, but the specific content of the table does not constitute a limitation on the technical solution of this application.

[0039] In a specific example, as shown in Table 1 below, Table 1 is a motor speed table of the input X-axis generated in an actual application scenario according to an embodiment of the present application.

[0040] Table 1: Motor speed table

[0041] 0 1 2 3 4 -200 -150 0 150 200

[0042] The first row in Table 1 represents the input serial number, and the value starts from 0; the second row represents the motor speed, and negative values ​​represent negative speeds.

[0043] In another specific example, as shown in Table 2 below, Table 2 is a driver demand acceleration table of the input Y-axis generated in an actual application scenario according to an embodiment of the present application.

[0044] Table 2: Driver demand acceleration table

[0045] 0 1 2 3 4 0 1.5 2.5 3.5 4.5

[0046] The first row in Table 2 represents the input serial number, which starts from 0; the second row represents the acceleration required by the driver.

[0047] In another specific example, as shown in Table 3 below, Table 3 is a motor speed correction driver demand acceleration table in an actual application scenario of an embodiment of the present application.

[0048] Table 3: Motor speed correction driver demand acceleration table

[0049] -200 -150 0 150 200 0 -0.2 -0.15 -0.15 -0.1 -0.2 1 -0.3 -0.2 -0.2 -0.15 -0.3 2 -0.4 -0.25 -0.25 -0.2 -0.4 3 -0.5 -0.3 -0.3 -0.25 -0.5 4 -0.6 -0.35 -0.35 -0.3 -0.6

[0050] The abscissa in Table 3 represents the motor speed, the ordinate represents the driver's required acceleration, and the value obtained by looking up the table is the decrease value of the acceleration.

[0051] It can be seen that the acceleration MAP table provided by the embodiment of the present application can characterize the preset value of the acceleration correction change with the motor speed request acceleration under different driver's required acceleration changes. Specifically, this corrected acceleration preset value will be used as the source input for the acceleration gradient processing in step S4.

[0052] In this embodiment, step S2: Motor frequency calculation, torque zero-crossing judgment

[0053] Step S2 is to calculate the motor frequency and judge the activation state of the motor torque zero-crossing according to the activation state of the motor at a specific frequency.

[0054] Specifically, for the activation state judgment of the motor torque zero-crossing in step S2 to be effective, the following conditions need to be met: ① The motor speed is within a certain range. Specifically, the motor speed MotorSpeed_Lowpass processed in step S21 is greater than the minimum motor speed setting value Motspdlowlimit, and the motor speed MotorSpeed_Lowpass is less than the maximum motor speed setting value Motspduplimit, that is, (Motspdlowlimit < MotorSpeed_Lowpass < Motspduplimit); and ② The activation determination of the specific frequency in step S24 is activation, that is, the freq_avoidance value is 1.

[0055] As Figure 2 shown, it is a schematic flow diagram of the embodiment of the motor frequency calculation of the present invention, which includes: step S20: Judge whether the motor speed signal is effective. When it is invalid, execute step S25: Use the previous valid motor speed value. When it is valid, then in step S21: Motor speed processing; then in step S22: Calculate the rising state of the motor speed according to the processed motor speed signal; step S23: Calculate the frequency output of the motor according to the rising state of the motor speed; then in step S24, combine the rising state of the motor speed and the motor frequency to judge the activation of the specific frequency of the motor.

[0056] In this embodiment, step S21: The motor speed processing adopts a sampling low-pass filtering processing method to prevent mutations in the motor speed; where Δt in the low-pass filter uses sample time, T c is the time constant of the filter.

[0057] In this embodiment, step S22: the motor speed MotorSpeed_Lowpass after being processed in step S21, calculates the difference between the motor speed at this moment and the motor speed at the previous moment, and compares this difference with zero; the comparison result result_motspd will be processed by the accumulator counter, and the processing method of the accumulator counter is: the accumulator counter has the functions of activating value accumulation and resetting to the initial value. When result_motspd is greater than zero, the counter accumulation is activated, and the output value counter is increased by 1; the accumulator counter has an upper limit max_counter. When the upper limit of the accumulator counter is reached, even if result_motspd is still greater than zero, the accumulator counter value output is the upper limit value max_counter of the accumulator counter; the reset condition of the accumulator counter is: the counter output value counter at the previous moment is greater than the value at the current moment.

[0058] In this embodiment, step S22: compare the output value counter of the counter with the upper limit value max_counter of the cumulative counter. If counter≤max_counter at the previous moment and counter>max_counter at the current moment, it is determined to be the motor speed rising state flag_motrev_upedge, and flag_motrev_upedge=1; otherwise, it is determined to be a non-rising state, and flag_motrev_upedge=0.

[0059] In this embodiment, step S23: calculate the frequency of the motor, specifically use a timing module for timing, the accuracy of the timer is 10ms; the timing module has two trigger conditions: activation and reset, activation means that the timer starts timing from time zero, and reset means that the timer returns to time zero; the timer activation is always valid, and the reset requires a conditional trigger.

[0060] The specific reset condition of the counter is that when the motor speed rising state flag_motrev_upedge is at this moment flag_motrev_upedge=0, and at the previous moment flag_motrev_upedge=1, the timing module is reset, and the timing time motspd_time is restored to zero.

[0061] The specific motor frequency freq_mot is calculated as

[0062] Specifically, when flag_motrev_upedge=1, the motor frequency freq_mot is output, and when flag_motrev_upedge=0, the motor frequency value at the previous moment is used.

[0063] In this embodiment, step S24: Activation judgment of a specific frequency. Specifically, an accumulative counter is used. When the value of the accumulative counter is equal to the upper limit of the accumulative counter output, it is determined that the specific frequency freq_avoidance is activated, that is, the value of freq_avoidance is 1; otherwise, it is determined that it is not activated, that is, the value of freq_avoidance is 0.

[0064] In this embodiment, the accumulative counter in step S24 has the functions of activating the numerical accumulation and resetting to the initial value. The activation condition of the accumulative counter is: the motor speed rising state flag_motrev_upedge = 1 and the motor frequency freq_mot is greater than the minimum value freqlowlimit of the frequency setting and less than the maximum value frequplimit of the frequency setting, (freqlowlimit < freq_mot < frequplimit). At this time, the activation counter accumulates, and the output frequency counter value freq_counter is incremented by 1; the accumulative counter has an upper limit freqmax_counter. When the upper limit freqmax_counter of the accumulative counter is reached, even if the activation condition of the accumulative counter still holds, the output value of the accumulative counter is the upper limit value freqmax_counter of the accumulative counter; the reset condition of the accumulative counter is: the motor speed rising state flag_motrev_upedge = 1 and the motor frequency freq_mot is less than the minimum value freqlowlimit of the frequency setting or greater than the maximum value frequplimit of the frequency setting.

[0065] In this embodiment, step S24: Activation judgment of a specific frequency. When step S25 uses the previous valid motor speed, the activation determination of the specific frequency is determined to be not activated, that is, the value of freq_avoidance is 0.

[0066] Specifically, for the activation state judgment of the motor torque passing through zero in step S2 to be valid, the following conditions need to be met: ① The motor speed is within a certain range. Specifically, the motor speed MotorSpeed_Lowpass after the processing of step S21 is greater than the minimum value Motspdlowlimit of the motor speed setting and less than the maximum value Motspduplimit of the motor speed setting, that is, (Motspdlowlimit < MotorSpeed_Lowpass < Motspduplimit); and ② The activation determination of the specific frequency in step S24 is determined to be activated, that is, the value of freq_avoidance is 1. When one of the above conditions is not met, the activation state judgment of the motor torque passing through zero is determined to be invalid.

[0067] In this embodiment, step S3: acceleration gradient judgment, the activation or inactivation of the acceleration gradient increase or decrease is determined by the motor torque zero-crossing judgment in step S2 and the acceleration rapid increase judgment required by the driver.

[0068] In this embodiment, step S3, the specific judgment of the rapid rise of the acceleration required by the driver is that the difference between the acceleration required by the driver at this moment and the acceleration at the previous moment is subtracted, and the acceleration difference at this moment, the acceleration difference at the previous moment and the acceleration difference at the previous moment are averaged (dfaclreq_diff_ave), and this average dfaclreq_diff_ave is used as the change value of the acceleration required by the driver.

[0069] In this embodiment, in step S3, if the specific change value of the driver's required acceleration dfaclreq_diff_ave is greater than the acceleration setting value set_aclvalue, it is determined that the driver's required acceleration is rising rapidly, otherwise it is determined that the driver's required acceleration is not rising rapidly.

[0070] In this embodiment, step S3: acceleration gradient determination is specifically performed using a basic RS trigger, where R and S are Reset and Set, respectively. In a specific embodiment, the truth table of the basic RS trigger is shown in Table 4.

[0071] Table 4: Basic RS flip-flop truth table

[0072] R S Q 1 0 0 0 1 1 0 0 Keep 1 1 indefinite

[0073] The first row in Table 4 represents the input and output of the basic RS flip-flop, where R represents the input reset, S represents the input set, and Q represents the output; "0" in Table 4 represents false, "1" represents true, and the driver requires acceleration. The "hold" in Q represents the retention of the output value at the previous moment, and the "indeterminate" in Q represents that it is not allowed to be used.

[0074] In a specific embodiment of step S3, the input set value of the basic RS trigger is "1" when the motor torque zero crossing judgment in step S2 is activated, and the driver's required acceleration is not rising rapidly. The input reset value of the basic RS trigger is "1" when the motor frequency freq_mot in step S24 is less than the minimum frequency setting value freqlowlimit, or greater than the maximum frequency setting value frequplimit; or the driver's required acceleration rises rapidly in step S3.

[0075] In this embodiment, Q in the basic RS trigger represents acceleration gradient judgment. When the Q value is "1", it means that the acceleration gradient judgment is valid / activated; when the Q value is "0", it means that the acceleration gradient judgment is invalid / not activated.

[0076] Wherein step S4: acceleration gradient processing, such as Figure 3 Specifically, when the acceleration gradient of S3 is determined to be valid / activated, the driver's required acceleration after the motor speed correction in S1 is increased or decreased according to the gradient processing.

[0077] In this embodiment, the acceleration gradient processing is calculated using the gradient processing descent factor, the gradient processing rise factor, and the gradient descent change time; the specific acceleration descent gradient processing uses the following formula to calculate the final motor torque zero-crossing acceleration:

[0078] T , acl_output =T acl_input -Δt×Factor down

[0079] T acl_output =T , acl_output -Δt×Factor down

[0080] Among them, T acl_output represents the acceleration after gradient processing, T , acl_output represents the acceleration after a gradient process, T acl_input represents the driver's acceleration (after motor speed correction), Δt represents the gradient descent change time, Factor down Represents the gradient processing descent factor.

[0081] In this embodiment, the specific acceleration gradient reduction process uses the following formula to calculate the final motor torque zero-crossing acceleration:

[0082] T , acl_output =T acl_input +Δt×Factor up

[0083] T acl_output =T , acl_output +Δt×Factor up

[0084] Among them, T acl_output represents the acceleration after gradient processing, T , acl_output represents the acceleration after a gradient process, Tacl_input represents the driver's acceleration (after motor speed correction), Δt represents the gradient descent change time, Factor up Represents the gradient processing rise factor.

[0085] In this embodiment, when the acceleration gradient is judged to be valid / activated in step S3, the acceleration T of the gradient processing is acl_output Increase the driver acceleration (after motor speed correction) by Δt×Factor in each operating cycle up to calculate; when the acceleration gradient is judged to be invalid / inactive, no gradient processing is performed on the driver acceleration (after motor speed correction).

[0086] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle, characterized in that: The following steps are involved: S1, calculating the acceleration required by the driver with motor speed correction; S2, calculate the frequency of the motor; S3, judgment of the rapid increase in acceleration required by the driver; S4. Acceleration gradient processing.

2. A method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle according to claim 1, characterized in that: In step S1, the acceleration required by the driver is the acceleration required by the driver calculated by the vehicle controller based on the accelerator pedal opening, gear position, brake pedal opening, maximum allowable torque of the motor, maximum allowable discharge / charging power of the battery, slope, and vehicle speed. This acceleration represents the acceleration the driver expects to obtain when driving the vehicle.

3. A method for controlling zero-crossing torque of a motor of a new energy passenger vehicle according to claim 2, characterized in that: In step S1, the motor speed is the speed value fed back by the motor controller, which is low-pass filtered to remove the jitter and noise of the value; the MAP table is corrected by the acceleration required by the driver and the motor speed. When the motor speed is near zero, the acceleration value is appropriately reduced to prevent excessive acceleration from causing a large impact.

4. A method for controlling zero-crossing torque of a motor of a new energy passenger vehicle according to claim 1, characterized in that: The step S2 includes processing and determining the motor speed, low-pass filtering the motor speed signal to determine whether the motor speed is gradually increasing or decreasing over a period of time; calculating the motor frequency by the number of changes in the increasing or decreasing state of the motor speed in combination with a counter; if the motor frequency is within a certain range and the number of occurrences of this frequency is greater than a limit value, the motor torque zero crossing is determined to be activated, otherwise it is reset.

5. The method for controlling the zero-crossing torque of a motor of a new energy passenger vehicle according to claim 1, characterized in that: In step S3, in order to give priority to the driver's acceleration demand, this is achieved by calculating the average value of the acceleration change in unit time, thereby avoiding the influence of the acceleration step on the overall judgment; since the rapid increase in acceleration represents that the driver has a strong acceleration demand, the torque zero-crossing jitter demand will be placed in a secondary position at this time.

6. A method for controlling zero-crossing torque of a motor of a new energy passenger vehicle according to claim 1, characterized in that: In step S4, the ascent / descent gradient is calculated by multiplying the set ascent / descent rate and the sample time, thereby ensuring the continuity of the gradient. At the same time, due to the added association with the sample time, the real-time nature of the acceleration gradient is ensured.

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