NISSAN_TECHNICAL_REVIEW_89 (2023)

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Technical Awards : 2021 JSAE Award The Outstanding Technical Paper Award - An Approach to Exploring Vehicle Motion to Enhance Ride Quality of Passenger2. Ride quality analysis using inverse vehicle dynamicsTable.1 Variables and functions for optimal controlFig.1　 Schematic fl ow of the inverse vehicle dynamics methodology by optimal control: Ride quality is refl ected to stage cost to describe motion design.expanded to include passengers.If optimal control is employed, it is possible to “derive the desired vehicle motion and the control inputs for its realization by converting the matter into deriving the minimum value of the evaluation function.” In other words, “the characteristics of vehicle motion that can enhance ride quality can be extracted using the evaluation function by using various values that are considered to have impact on ride quality.”The following section of this paper describes the case where inverse vehicle dynamics analysis is performed using optimal control and indicates that the analysis method is limited when applied for analyzing the behavior of passengers. Subsequently, technical solutions for overcoming these limitations are described. Lastly, the method for exploring the ride quality of a passenger is presented using transient motion as a case example and by describing the calculations, actual vehicle testing, and evaluations.If the forward vehicle dynamics analysis is considered as “set the control inputs and derive the corresponding vehicle motion,” inverse vehicle dynamics analysis(7) can cause-and-effect be relationship, specify the desired vehicle motion, and derive the control inputs and vehicle motion that satisfy the specifi ed motion.” For the inverse direction, the calculation method will differ depending on what is specifi ed for the desired vehicle motion. In this study, the travel scene was specifi ed as the precondition, the motion comfort of the passengers was explored, and inverse vehicle dynamics analysis was performed using optimal control (the schematic fl ow of the inverse vehicle dynamics methodology is shown in Fig. 1, and the variable names are provided in Table 1). considered as Optimal control uses the stage cost function The travel scene is specifi ed by setting the initial and terminal values of the state variables and control inputs in the vehicle motion task. In other words, the state of the vehicle motion is fi xed at both ends (the analysis becomes a boundary value problem). Therefore, it is possible to that minimize the stage derive the control inputs cost function value.the “reverse To evaluate the ride quality of passengers, in the vehicle model, reproducing three-dimensional movements of the vehicle body in which the passengers ride is necessary. In addition, when formulating the optimal control using the ordinary variational principle, the vehicle model (in the form of a state equation) is added to the stage cost function using the adjoint variables. However, there are limitations in the model description for the evaluation function, which are related to the time integration of the added values. Specifi cally, in the description of the state equation, the differential needs to be quantities described using the state variable, as shown in equation (2), and not in the form of equation (1):, which is described using variables such as the input and state variables that represent the variables . The objective is to state of the subject of motion derive the vehicle motion that yields the minimum value of the function. From a different perspective, the vehicle motion is designed using the stage cost function. The forms of functions that can actually be used for description are limited, such as the quadratic forms of the variables. However, vehicle motion can be designed at least using this function. In a previous study,(7) the authors developed a vehicle model to express the vehicle dynamics accurately, including the load transfer among the wheels, while observing the restrictions for describing the equation. Table 2 and Fig. 2 present the vehicle model, including the of the state variable 71110No.88 (2022) NISSAN TECHNICAL REVIEW