Automobile steering adjustment method

Abstract

The invention discloses an automobile steering adjustment method. The method comprises the following steps: (1) performing parking and low-speed steering evaluation, and adjusting a power-assisted control module through evaluation; (2) evaluating steering along with the speed, and adjusting the interval of the power-assisted curve at each speed through evaluation; (3) steering along with angles is evaluated, and the increasing slope and the peak value of a power-assisted curve at each speed are adjusted through evaluation; 4) low-speed return evaluation: adjusting return parameters of a return control module at different angles and speeds through evaluation; 5) performing high-speed return evaluation, and adjusting a damping control module through evaluation; and 6) performing comprehensive steering evaluation, and adjusting the dynamic compensation module through evaluation. According to the method, the direction is adjusted according to the curve of assistance, return and damping control, and adjustment is carried out according to steps, so that the ideal curve of assistance, return and damping control is obtained, the objective of subjective evaluation and correction of comfort is met, and the purpose of taking a user as the center is achieved.

Description

Technical Field

[0001] The present invention relates to the field of automobile steering systems, and in particular to a steering adjustment method for new energy vehicles. Background Art

[0002] With the development of new energy vehicle technology, electric power steering is becoming more and more popular, and traditional hydraulic power steering systems are slowly withdrawing from the stage of history. Electric power steering is not exclusive to new energy vehicles. The electric power steering system on traditional gasoline vehicles can reduce fuel consumption by approximately 0.3L per 100 kilometers compared to the hydraulic transmission system. When we see more and more electric power steering on traditional gasoline vehicles and new energy vehicles, the adjustment method of this system becomes particularly important, because people's requirements for the steering system are not just the experience of hand strength, but they have increasingly higher requirements for steering comfort. In the car steering system, steering hand force, uniformity, middle position, and self-centering ability are important basic performance that consumers can directly perceive.

[0003] Common steering system problems are: poor steering hand force, large steering friction, fuzzy middle position, insufficient self-centering ability, etc. The adjustment range of the steering system is mainly carried out on the performance of steering force (level of each mode force, hand force uniformity, force establishment, etc.), steering accuracy (middle position) and self-centering performance. Good steering performance is manifested in clear and appropriate hand force in each mode, linear force gradient, low steering friction - that is, silky feeling, clear middle position, and good low, medium and high self-centering ability;

[0004] At present, most steering system adjustments are made by using hardware devices (such as sensors) to obtain parameter information and perform debugging based on the parameter information, which makes it difficult to achieve the best steering experience for the user. For example, the patent publication number is CN102530056A, the publication date is July 4, 2012, and the patent name is "A self-adjustment method for an electric assisted steering system". The self-adjustment method of the disclosed electric assisted steering system can self-normalize and adjust the distorted signal of the sensor to maintain a stable steering feel and improve the robustness and steering performance of the electric assisted steering system. The self-normalization method includes a signal offset compensation strategy and a signal zero point self-adjustment strategy. The self-normalization action is determined by a set judgment strategy. The judgment strategy includes the sensor power supply judgment, the sensor correctness judgment, and the self-adjustment start condition judgment. The accuracy of sensor sensing can be improved by the self-adjustment method.

[0005] In order to achieve comfortable steering performance, the steering system needs to be adjusted during the vehicle development process. However, there is currently a lack of an electric steering system adjustment method that can be applied to the development environment. Summary of the invention

[0006] The technical problem to be solved by the present invention is to realize a new energy vehicle electric power steering adjustment method, which can help manufacturers improve the steering adjustment effect.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for adjusting vehicle steering:

[0008] 1) Parking and low-speed steering evaluation, and adjustment of the power assist control module through evaluation;

[0009] 2) Speed-dependent steering evaluation, through which the interval size of the power assist curve at each speed is adjusted;

[0010] 3) Evaluate the steering angle and adjust the growth slope and peak value of the power assist curve at each speed through evaluation;

[0011] 4) Low-speed return evaluation: adjust the return control module through evaluation, and return parameters at different angles and speeds;

[0012] 5) High-speed return evaluation, through which the damping control module is adjusted;

[0013] 6) Comprehensive steering evaluation, and adjustment of dynamic compensation module through evaluation.

[0014] In the above 1), the judging criteria are that the parking and low-speed conditions are required to be light, there is no periodic or non-periodic torque fluctuation, the left and right steering forces are symmetrical, and the left and right directions remain consistent.

[0015] In the above 2), the judging criteria are that the steering force should be clearly established as the speed increases, so that the vehicle has the ability to maintain straight driving, and the steering wheel should have sufficient steering stiffness when driving at high speed.

[0016] In the above 3), the judging criteria are that as the turning angle increases, the steering force should be clearly established, the steering force needs to increase when it deviates from the middle position, the dead zone of the steering force should be consistent on the left and right, the dead zone of the force should be small, and the middle position should be clear.

[0017] In the above 1), through the evaluation and adjustment method, the in-situ and low-speed power assistance curves are the highest, and as the vehicle speed increases, the steering assistance applied gradually decreases;

[0018] In the above 2), through the evaluation and adjustment method, at medium and high vehicle speeds, the assist torque in the curve remains unchanged when it increases to a certain value, and the maximum value gradually decreases with the increase of vehicle speed. The curve increases with the vehicle speed and the turning angle, the gap between each curve remains uniform, and the transition is smooth;

[0019] In the above 3), through the evaluation and adjustment method, within the small steering torque range, the power assist torque should be the smallest, and with the increase of the torque value, the power assist torque gradually increases and then remains at a certain value. With the increase of the vehicle speed, the area without power assist should increase, and the power assist will remain at a certain value after increasing.

[0020] In the above 4), the judging criteria are the speed and uniformity of the low-speed self-centering, the symmetry of the residual angle and the left and right self-centering performance;

[0021] Low speed return evaluation adjustment method:

[0022] The self-aligning torque is the largest under low-speed conditions. As the vehicle speed increases, the four-wheel active self-aligning torque increases, and the required torque gradually decreases. When the vehicle speed reaches a certain value, the assist torque is zero.

[0023] The return control gradually increases with the change of steering angle. After the steering reaches a certain angle, the torque is kept constant. In the case of 0-degree steering, the steering wheel is in the return state and the return torque is zero. The maximum torque return force is still maintained under small angle conditions.

[0024] In the above 5), the judging criteria are: judging the overshoot of the steering wheel angle, roll angle and yaw rate in the process of the vehicle returning to the middle position, as well as the convergence speed and the number of oscillations. The overshoot should be as small as possible, the convergence speed should be moderate, and the number of oscillations should be as small as possible;

[0025] The high-speed return evaluation adjustment method compensates for the overshoot during return through damping control. It is used for damping compensation at different vehicle speeds and different angular velocities. A certain reverse current is passed through the EPS motor for a certain period of time to offset the overshoot. When the speed is less than the set speed, no damping is added to prevent low-speed return jamming. When the speed is greater than the set speed, the faster the vehicle speed and steering rate, the greater the damping compensation.

[0026] In the above 6), the comprehensive steering evaluation is to set the standard, and is judged by excellent maneuverability, appropriate steering force, smooth turning performance, impact buffering caused by the road surface and reliable operation. The evaluation and adjustment method is to first adjust the basic power assist module, confirm the corresponding power assist current size, and then improve the dynamic effect of the car when steering based on dynamic compensation.

[0027] After each evaluation step is evaluated by multiple testers, an average score is obtained. If the average score is greater than the set value, the evaluation step is qualified. Otherwise, the improvement direction is obtained and corresponding adjustments are made. The evaluation of the evaluation step is then repeated until the average scores of all evaluation steps are greater than the set value.

[0028] The present invention adjusts the directions of the power assist, self-centering and damping control curves and performs adjustments in steps to obtain ideal power assist, self-centering and damping control curves to meet the subjective evaluation comfort target and achieve a user-centered purpose. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The following is a brief description of the contents expressed in each figure in the specification of the present invention:

[0030] Figure 1 This is the schematic diagram of the electric power steering;

[0031] Figure 2 is the dynamic compensation map;

[0032] Figure 3 This is a schematic diagram of the steering adjustment process. DETAILED DESCRIPTION

[0033] The following is a further detailed description of the specific implementation methods of the present invention, such as the shape, structure, relative position and connection relationship between the various components involved, the function and working principle of each part, the manufacturing process and operation method, etc., through the description of the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0034] Basic introduction of electric power steering:

[0035] 1.1 Working Principle of Electric Power Steering

[0036] When the driver steers, the torque and angle sensor installed in the steering column sends the detected torque angle to the steering controller. The steering controller then makes a judgment based on the vehicle speed signal in the vehicle CAN signal, and sends a command to the steering motor to output the corresponding steering assist torque based on the corresponding torque size in the assist curve, thereby producing an assist effect and reducing the driver's operating effort.

[0037] Torque relationship during car steering: steering resistance torque = motor assist torque + driver steering wheel torque

[0038] The steering resistance torque is mainly affected by the vehicle load, four-wheel parameters and steering system stiffness, which are determined by the vehicle parameters. The driver can only intuitively feel the steering wheel torque, and the steering wheel torque can only be adjusted by optimizing the electric power steering curve. The steering curve mainly includes two parts: basic power and dynamic compensation. The specific working principle is shown in Figure 1 .

[0039] Basic power assistance includes three major controls: power assistance, return and damping. According to the established curve relationship, the corresponding power assistance torque is output based on the real-time collected steering wheel torque, angle and vehicle speed signals, without considering the dynamic factors of the driver when steering, and the corresponding power assistance current is obtained from the pre-established basic power assistance curve. Dynamic compensation includes three major compensations: friction, damping and inertia, which mainly make up for the shortcomings of motor power assistance, improve the overall effect of steering, and improve the dynamic effect of vehicle steering.

[0040] 1.2 Main functions of electric power steering

[0041] 1.2.1 Power assist control

[0042] Function introduction: Provides power-assist torque according to vehicle speed and steering wheel torque, so that the steering feel is uniform at various vehicle speeds and steering wheel torques, achieving speed-dependent power assistance.

[0043] Basic principle: The higher the vehicle speed, the smaller the assist torque provided by the motor, and the greater the steering wheel force, the greater the assist torque provided by the motor.

[0044] 1.2.2 Return control

[0045] Function introduction: After the steering wheel is turned to a certain angle, the power-assisted motor generates an auxiliary self-centering torque, which makes the steering wheel return to the middle position within a certain period of time, thus improving the vehicle's self-centering performance.

[0046] Basic principle: At low speed, the lower the speed, the greater the self-aligning torque. After the speed exceeds a certain limit, the higher the speed, the smaller the self-aligning torque. When the steering wheel torque exceeds a certain value, the self-aligning torque compensation is exited and the power assist is mainly used.

[0047] 1.2.3 Damping control

[0048] Function introduction: Damping control is mainly aimed at medium and high speed conditions. It is used for damping compensation at different speeds and angular velocities to avoid the vehicle's own self-aligning torque being too large and difficult to converge. The EPS motor is passed a certain reverse current and maintained for a certain period of time to offset it.

[0049] Basic principle: When the vehicle speed is less than a certain speed, no damping is added to prevent the occurrence of low-speed return jamming; when the vehicle speed is greater than a certain speed, the faster the vehicle speed and steering rate, the greater the damping compensation, to limit the back and forth and left and right swinging of the steering wheel after it returns to the normal position.

[0050] 1.2.4 Dynamic compensation

[0051] Since the electric power steering system adds a power motor and a deceleration structure to the mechanical steering system, the mass of the entire steering system increases, which in turn increases the system inertia. Therefore, dynamic compensation must be added. According to the estimated power motor speed, a certain reverse compensation torque is generated to avoid the steering motor having a steering sticky feeling at the beginning and end stages, resulting in poor steering power followability. See the dynamic compensation diagram Figure 2 .

[0052] Friction compensation: Due to the existence of friction in the steering system, the positive and negative rotation torques of the steering wheel are different. Friction compensation can effectively make up for this torque difference, avoid the driver's "floating" feeling, and enhance the road feel.

[0053] Damping compensation: It is used to overcome the influence of motor damping on the dynamic performance of EPS, to ensure the suppression of overshoot and oscillation when returning to the correct position at high speed, and to generate torque in the opposite direction of the power-assist motor.

[0054] Inertia compensation: The main purpose is to overcome the influence of the inertia of the steering motor on the output, suppress the output torque disturbance, avoid torque fluctuation in the output, and affect the steering feel. It can be understood as a purely advanced correction link, which mainly compensates for the rotational inertia of the motor.

[0055] 1.2.5 Other functions

[0056] Soft stop: When the steering wheel approaches the limit position, the current is actively reduced to reduce the impact on the steering gear and reduce system noise. It is related to the steering wheel angle and angular velocity. The closer the angle is to the limit position, the smaller the motor torque output is, and the greater the angular velocity is, the smaller the motor torque output is.

[0057] Overheat protection: Detect or evaluate the controller temperature and motor temperature, and provide different protection measures for different temperatures to prevent the controller and motor from overheating and damage.

[0058] Overload protection: Hardware overload protection is achieved through hand force, steering wheel speed, etc.

[0059] Overvoltage protection: voltage overload protection function.

[0060] Extended functions: automatic parking, lane keeping, torque steering compensation, EPS processes advanced function signals, and implements steering and provides torque according to control signals.

[0061] Multiple power-assist modes: EPS can provide two or more power-assist modes according to vehicle requirements, and they can be switched by a switch.

[0062] 2. Steering performance evaluation method

[0063] 2.1 Subjective evaluation method

[0064] In the subjective evaluation method of automobile steering, the evaluation is carried out on a 10-point scale, see Table 1:

[0065] Evaluation points: steering force performance in each steering mode, steering response, steering accuracy, steering return and steering system NVH, etc.

[0066] Table 1 Subjective evaluation table

[0067]

[0068] 3. Adjustment method

[0069] The current automobile performance development still strictly follows the rule of "coming from human feelings and going back to human feelings", that is, the system performance development starts from human feelings, and then sets the performance engineering goals of the steering system. Finally, the performance development goals of the steering system are verified by subjective evaluation, with objective testing as an aid.

[0070] 3.1 Power assist control

[0071] 3.1.1 Evaluation method:

[0072] Parking, low-speed steering evaluation, speed-dependent steering evaluation, and angle-dependent steering evaluation.

[0073] 3.1.2 Evaluation points:

[0074] ① Parking and low-speed conditions require lightness, avoid periodic or non-periodic torque fluctuations, and ensure symmetry of left and right steering forces, with left and right directions remaining consistent.

[0075] ② As the speed increases, the steering force should be clearly established so that the vehicle can maintain the ability to drive in a straight line and achieve the purpose of high-speed stability. In particular, the steering wheel should have sufficient steering stiffness when driving at high speed. The so-called "steering stiffness" refers to the slope of the curve of the relationship between steering torque and steering wheel angle at 0 angle.

[0076] ③ As the turning angle increases, the steering force must be established clearly. When the steering deviates from the middle position, the steering force needs to increase. The size of the dead zone of the steering force needs to be consistent on the left and right. The dead zone of the force should be as small as possible to make the middle position clear.

[0077] 3.1.3 Curve adjustment direction:

[0078] Basic power control is the core item in the steering curve, and its directions mainly include the following:

[0079] ① In the small torque range of steering, the power-assist torque should be the smallest. As the torque value increases, the power-assist torque gradually increases and then remains constant. The purpose of the motor's small power-assist or no power-assist within the small torque range is to transmit the feeling of the road surface during driving, prevent the loss of road feeling and save electricity. In order to maintain a better feeling of the middle position, the area without power-assist should be increased as the vehicle speed increases. On the other hand, the power-assist remains constant after it increases, which is also subject to the peak power limit of the motor, so as to protect the motor and avoid overload.

[0080] ②According to the characteristics of automobile steering, the steering resistance of the automobile is the largest when it is stationary and at low speed, and the power assist value required is the largest. In order to achieve the purpose of parking at low speed and ease, the power assist curves at fixed position and low speed are the highest. As the speed increases, the steering assist should be gradually reduced, so that the driver's hand force gradually increases, so as to obtain a better sense of the road, achieve the purpose of high-speed stability, and improve driving safety.

[0081] ③ At medium and high speeds, the assist torque in the curve should remain unchanged when it increases to a certain value, and the maximum value should gradually decrease with the increase of speed, so that the driver can have a clear feeling of increased hand force and improve driving pleasure. As the curve increases with speed and turning angle, the gap between each curve should be kept uniform and the transition should be smooth, so that there is no sudden change or fluctuation in the force increase process, and the linearity of the force is good.

[0082] 3.2 Return control

[0083] 3.2.1 Evaluation method:

[0084] Low speed return evaluation

[0085] 3.2.1 Evaluation points:

[0086] Low-speed return mainly evaluates the return speed, uniformity, residual angle and symmetry of left and right return performance of the vehicle steering system. High-speed return hopes that the return speed is as fast as possible, the return process is as smooth as possible, the residual angle is as small as possible, and the left and right performances are as consistent as possible.

[0087] 3.2.3 Curve adjustment direction:

[0088] Return to center control is a common working condition for drivers, usually used in normal warehouse transfer and turning conditions. Its directions mainly include the following:

[0089] ① The return control is mainly aimed at medium and low speed conditions, and the return parameters at different angles and different vehicle speeds. There is no return performance in the stationary condition. The return torque required under low speed conditions is the largest. As the vehicle speed increases, the four-wheel active return torque increases, and the required torque gradually decreases. When the vehicle speed reaches a certain value, the power-assisting torque is zero to prevent the power-assisting torque from being greater than the steering drive torque under the same working condition without power assistance, resulting in a "beating" phenomenon.

[0090] ② The return control gradually increases with the change of steering angle. After the steering reaches a certain angle, the torque is kept constant. In the case of 0-degree steering, the steering wheel is already in the return state and the return torque is zero. In the case of 5-10 small angle working conditions, the return torque is the largest to avoid non-returning.

[0091] 3.3 Damping control

[0092] 3.3.1 Evaluation method:

[0093] High-speed return evaluation

[0094] 3.3.2 Evaluation points:

[0095] High-speed return mainly evaluates the overshoot of the steering wheel angle, roll angle and yaw angular velocity, as well as the convergence speed and the number of oscillations when the vehicle returns to the middle position. It is hoped that the overshoot is as small as possible, the convergence speed should be moderate, and the number of oscillations should be as small as possible.

[0096] 3.3.3 Curve adjustment direction:

[0097] Damping control mainly compensates for the overshoot during return to center, mainly for medium and high speed conditions, and its directions mainly include the following:

[0098] ① Damping control is mainly aimed at medium and high speed conditions, and is used for damping compensation at different vehicle speeds and different angular velocities. Mainly to prevent the vehicle's self-aligning torque from being too large and difficult to converge, the EPS motor is passed a certain reverse current for a certain period of time to offset it. Below a certain speed, no damping is added to prevent low-speed return jams. When the speed is greater than a certain speed, the faster the vehicle speed and steering rate, the greater the damping compensation, to limit the back and forth and left and right swings of the steering wheel after it returns to the center.

[0099] ② Another purpose of damping control is to reduce the impact of road impact on the steering wheel. When the car is driving at high speed, due to the greater excitation of the road, the vibration transmitted to the steering wheel is much greater than that at low speed. In order to suppress this vibration and optimize the feel, damping control must be used.

[0100] The requirements for steering performance mainly include: superior maneuverability, appropriate steering force, smooth turning performance, buffering the impact of the road surface and reliable operation. Excellent steering performance is usually: easy parking at low speed and stable at high speed. To achieve this goal, it is necessary to continuously optimize the corresponding parameters in the steering power curve. First, find the problems and deficiencies in the steering performance from the perspective of subjective evaluation, first adjust the basic power module (power control, return control, damping control) to confirm the corresponding power current, and then improve the dynamic effect of the car when steering according to dynamic compensation (friction, damping, inertia).

[0101] After the power assist curve was adjusted, the prototype vehicle was subjectively evaluated and verified from three aspects: steering force, steering response, and steering linearity.

[0102] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for adjusting vehicle steering, characterized in that: 1) Parking and low-speed steering evaluation, and adjustment of the power assist control module through evaluation; 2) Speed-dependent steering evaluation, through which the interval size of the power assist curve at each speed is adjusted; 3) Evaluate the steering angle and adjust the growth slope and peak value of the power assist curve at each speed through evaluation; 4) Low-speed return evaluation: adjust the return control module through evaluation, and return parameters at different angles and speeds; 5) High-speed return evaluation, through which the damping control module is adjusted; 6) Comprehensive steering evaluation, and adjustment of dynamic compensation module through evaluation.

2. The vehicle steering calibration method according to claim 1, characterized in that: In the above 1), the judging criteria are that the parking and low-speed conditions are required to be light, there is no periodic or non-periodic torque fluctuation, the left and right steering forces are symmetrical, and the left and right directions remain consistent.

3. The vehicle steering calibration method according to claim 2, characterized in that: In the above 2), the judging criteria are that the steering force should be clearly established as the speed increases, so that the vehicle has the ability to maintain straight driving, and the steering wheel should have sufficient steering stiffness when driving at high speed.

4. The vehicle steering calibration method according to claim 3, characterized in that: In the above 3), the judging criteria are that as the turning angle increases, the steering force should be clearly established, the steering force needs to increase when it deviates from the middle position, the dead zone of the steering force should be consistent on the left and right, the dead zone of the force should be small, and the middle position should be clear.

5. The vehicle steering calibration method according to claim 4, characterized in that: In the above 1), through the evaluation and adjustment method, the in-situ and low-speed power assistance curves are the highest, and as the vehicle speed increases, the steering assistance applied gradually decreases; In the above 2), through the evaluation and adjustment method, at medium and high vehicle speeds, the assist torque in the curve remains unchanged when it increases to a certain value, and the maximum value gradually decreases with the increase of vehicle speed. The curve increases with the vehicle speed and the turning angle, the gap between each curve remains uniform, and the transition is smooth; In the above 3), through the evaluation and adjustment method, within the small steering torque range, the power assist torque should be the smallest, and with the increase of the torque value, the power assist torque gradually increases and then remains at a certain value. With the increase of the vehicle speed, the area without power assist should increase, and the power assist will remain at a certain value after increasing.

6. The vehicle steering calibration method according to any one of claims 1 to 5, characterized in that: In the above 4), the judging criteria are the speed and uniformity of the low-speed self-centering, the symmetry of the residual angle and the left and right self-centering performance; Low speed return evaluation adjustment method: The self-aligning torque is the largest under low-speed conditions. As the vehicle speed increases, the four-wheel active self-aligning torque increases, and the required torque gradually decreases. When the vehicle speed reaches a certain value, the assist torque is zero. The return control gradually increases with the change of steering angle. After the steering reaches a certain angle, the torque is kept constant. In the case of 0-degree steering, the steering wheel is in the return state and the return torque is zero. The maximum torque return force is still maintained under small angle conditions.

7. The vehicle steering calibration method according to claim 6, characterized in that: In the above 5), the judging criteria are: judging the overshoot of the steering wheel angle, roll angle and yaw rate in the process of the vehicle returning to the middle position, as well as the convergence speed and the number of oscillations. The overshoot should be as small as possible, the convergence speed should be moderate, and the number of oscillations should be as small as possible; The high-speed return evaluation adjustment method compensates for the overshoot during return through damping control. It is used for damping compensation at different vehicle speeds and different angular velocities. A certain reverse current is passed through the EPS motor for a certain period of time to offset the overshoot. When the speed is less than the set speed, no damping is added to prevent low-speed return jamming. When the speed is greater than the set speed, the faster the vehicle speed and steering rate, the greater the damping compensation.

8. The vehicle steering calibration method according to claim 1, characterized in that: In the above 6), the comprehensive steering evaluation is to set the standard, and is judged by excellent maneuverability, appropriate steering force, smooth turning performance, impact buffering caused by the road surface and reliable operation. The evaluation and adjustment method is to first adjust the basic power assist module, confirm the corresponding power assist current size, and then improve the dynamic effect of the car when steering based on dynamic compensation.

9. The vehicle steering calibration method according to claim 1 or 8, characterized in that: After each evaluation step is evaluated by multiple testers, an average score is obtained. If the average score is greater than the set value, the evaluation step is qualified. Otherwise, the improvement direction is obtained and corresponding adjustments are made. The evaluation of the evaluation step is then repeated until the average scores of all evaluation steps are greater than the set value.

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