Research On Closed Loop Control Method Of Vehicle Longitudinal Motion For Drivability

After a century of development,the automobile industry has gradually shifted from production/transportation to consumer goods,and people are paying more and more attention to the motion quality of the automobile driving process.In terms of longitudinal movement,the motion quality usually refers to the driveability of the car,which requires that the car’s speed is well controlled,the driving feeling is in line with people’s psychological expectations,the bad movement response is less,and the driving feeling is good.Good drivability has become an important factor driving consumers to buy cars.In order to ensure that the car has good drivability,on the one hand,due to the lack of a theoretical basis for driving adjustment,automobile manufacturers have extensively used experienced subjective appraisers to conduct a large number of field test calibrations to improve the car’s drivability.However,the problem of inconsistent driving feeling when the car speed is unstable,the driving feeling does not meet the psychological expectations,the dynamic response quality is not good,and the part characteristics/load/gradient changes are still inconsistent.On the other hand,in order to ensure that the batch products of the same vehicle model have a consistent driving feel,precise manufacturing and precise calibration of control parameters are required,which increases the manufacturing difficulty and production costs of automotive products.How to further improve the drivability of automobiles and ensure that mass-produced automobile products have a consistent driving feeling throughout the entire life cycle has become an important vision and industrial problem for automobile development.Aiming at the problem of drivability,this paper proposes a solution of longitudinal motion control for drivability.The driver’s pedal operation is analyzed as the longitudinal acceleration demand,and the longitudinal acceleration is taken as the intermediate quantity.The motion closedloop control method is adopted to accurately track the desired acceleration,so as to ensure that the pedal operation and longitudinal acceleration have a fixed mapping relationship when the road environment / load / component characteristics change,so as to achieve a consistent driving feeling.First,the longitudinal dynamics modeling research for drivability.Established a longitudinal dynamics model oriented to automobile drivability,and accurately described the key links that affect the dynamic process of automobile longitudinal motion.The dynamics model is integrated in the driving simulator to conduct a human-vehicle closed-loop test,and the accuracy of the model is verified by comparing with the actual vehicle field test.Provide a virtual test and verification platform for subsequent vehicle dynamic characteristics testing,control algorithm development,and driving feeling tuning.Second,the research on the driver’s longitudinal motion intention.In view of the lack of theoretical basis for driving intention design,the quality of driving feeling greatly depends on the subjective factors and level of the judges.The lack of expression of the intention of steady speed leads to the problem of unstable speed at low speeds.A setting method that uses acceleration to represent the person’s longitudinal movement intention is proposed:(1)By designing the lowsensitivity area of the accelerator pedal near the stable speed point,the speed of the car is easy to control,and the operating burden of the driver is reduced;(2)In the area far away from the stable speed point,according to the Weber-Fechner law,the nonlinear mapping relationship between the accelerator pedal operation amount and the expected acceleration is designed to ensure that the acceleration/deceleration movement of the car meets people’s psychological expectations and improves the driving feeling;(3)The longitudinal motion intention setting method of this article is applied to pedal map calibration,which provides a theoretical basis and calibration method for classic pedal map design,and reduces the difficulty of driving feeling adjustment.Third,the study on the closed-loop control of longitudinal motion.Aiming at the problem of poor consistency of driving feeling in the classic torque-based longitudinal control method,a closed-loop acceleration control method with direct feedforward and forward channel steady-state compensation correction is proposed: The steady-state compensation correction method is used to normalize the automobile drive/brake system,and the equivalent system transfer function identification of the normalized system is based on the Gauss Newton iteration method,On this basis,the H_∞ norm non-smooth optimization principle is further adopted to design the closed-loop control parameters to ensure that the response of the motion closed-loop control system conforms to the set ideal second-order system.Through closed-loop control,it is possible to appropriately relax the requirements for parts manufacturing accuracy and control parameter calibration accuracy.Even in the case of mass product manufacturing deviations or component performance degradation,the closed-loop automatic deviation correction can be carried out to ensure consistent driving feeling.At the same time,by designing a reasonable system frequency bandwidth,the dynamic response quality of longitudinal motion is improved,and the driving performance is improved.Fourth,in view of the problem of inconsistent driving feeling when the load/road gradient changes,this paper further proposes a closed-loop control method of longitudinal motion that considers the load/gradient.Based on the estimation of the gradient and the total mass of the vehicle,the steady-state compensation gain coefficient of the forward channel is dynamically corrected to ensure that the vehicle has a consistent driving feeling under the condition of the gradient/load change.Fifth,research on the process control of driving/braking/gear selection and switching.For the longitudinal control of the automobile,there are two independent actuating mechanisms,including multiple gears.The actuation source needs to be selected and switched during longitudinal motion control.Aiming at the problems of complicated gear shifting strategies and heavy calibration workload in the current automobile in a variety of driving styles,a gear selection strategy based on specific-force is proposed: In the case of meeting motion needs,energy efficiency is used as the evaluation index to design the shift schedule,and the specific force and vehicle speed are used as the selection parameters to select gears,so that a set of shift schedules can ensure the motion and economic requirements of the car,And solve the problem of the adaptability of the shift strategy,reduce the complexity of the shift schedule and the calibration workload.In order to avoid the shock of shifting,this paper adopts the control strategy of the shifting process to ensure the smooth movement of the shifting process.Finally,a test platform based on d SPACE and a driving simulator was built to test the effectiveness of the control method proposed in this paper.The test results show that the research in this paper improves the ease of control of the vehicle speed;improves the dynamic response quality of longitudinal motion;achieves a consistent driving feeling when the performance/load/gradient of the auto parts changes;The proposed gear selection strategy based on specific-force can solve the problem of gear shift adaptability with only a set of shifting rules,and at the same time,it can ensure that the driving economy of the whole vehicle is met while meeting motion needs,and the shifting rules are reduced.The complexity of the design and the calibration workload,at the same time,through the gear switching process control to ensure that the vehicle’s longitudinal motion impact meets the recommended standards.