斜盘式轴向柱塞泵马达的负载和压力分析

1.外文原文（复印件）

Load and Stress Analysis for the Swash

Plate of an Axial Piston Pump/Motor

M. Z. Norhirni M. Hamdi S. Nurmaya Musa N. Hilman

Abstract

In an axial piston pump design, the swash plate plays an important role in controlling the displacement of the pump, especially in a closed loop system. In this paper, the axial piston pump is incorporated into the design of a hydraulic regenerative braking system for hybrid vehicles. The pump in this configuration should function in dual mode, as a pump and as a motor. For this to occur, the swash plate should swing in two opposite directions. The swash plate presented

in this paper is designed for stability and ease of control. Analytical analysis of torque and forces were conducted using MATLAB software to verify the motion of the swash plate. Furthermore, finite element analysis was also carried out to evaluate the rigidity and stress in the system. The analytical evaluation has shown that as the swash plate angle increases, the required control force and

torque increase almost linearly. However, the change of the plate angle was found to have no effect on the force exerted on the X-axis and the torque exerted on the Z-axis.

Keywords: swash plate, axial piston pump, finite element analysis,

hydraulic regenerative braking, hybrid vehicle

Introduction

The hydraulic regenerative braking system (HRBS) is a mechanism that reduces vehicle speed by converting some of the kinetic energy into potential energy by storing it inside a hydro-pneumatic accumulator for future use [1]. The system is made up of four main components: working fluid, reservoir,

pump/motor (variable-displacement, axial-piston type pump), and accumulator, to power a vehicle at low speeds and to augment the gasoline engine [2]. Normally, when the driver presses the brake pedal, friction force is applied on the disc brakes. In this situation, the vehicle’s kinetic energy is transferred as heat energy and wasted into the air. During braking, the hydraulic axial piston pump installed in the system operates as a pump, extracting kinetic energy and storing it in the accumulator. Supposing that the accumulator reaches maximum capacity before the vehicle has stopped, conventional brakes are used to bring the vehicle to a stop. Whenever the vehicle accelerates from stationary mode, pressurized working fluid discharges from the accumulator, which in turn converts potential energy into kinetic energy directly to the driveshaft to move the

vehicle .

In order to make the system work and capture the kinetic energy, the hydraulic axial piston pump has to store more energy and work in dual mode. However, most hydraulic axial piston pumps available on the shelf are made with fixed displacementstatic control with small flow rate, which are not suitable for installation in heavy vehicles. Furthermore, conventionally, axial piston pumps work only in single mode—either as a pump or as a motor. Previous research conducted on bent-axis piston pump showed that it is capable of operating in dual function. The bentaxis piston pump=motor has been designed for hydraulic hybrid vehicles by the US Environmental Protection Agency (EPA), Abuhaiba et al. [5]. Analysis and results have provided a useful guide for design improvement. In an axial piston, the major part is the swash plate angle because it determines the mode of the pump [6]. Variable displacements of the axial piston pump were controlled by its swash plate angle; therefore, by varying swash plate angle, the flow and pressure of an axial piston can be controlled.

In addition to the structural design of the swash plate, another important consideration is the dynamic control of the system. The ability to dynamically control the swash plate angle would increase the efficiency in supplying variable flow rate and pressure required for the hydraulic circuit. Zeiger and Akers

explain that it is necessary to have a mathematical model representing the equation of motion of the swash plate in order to study the behavior of the swash plate actuation and control system. The most important factor in the model is the torque on the swash plate about its pivot. Several studies have been conducted to determine the control torque of the swash plate, mainly by empirical test data or

numerical methods .

The numerical method of analysis is in the form of mathematical description of the torque components, which enables the effects of different designs, tolerance variations, and varying operating conditions on the torque characteristics . Based on the mathematical description, the equation of swash plate motion can be written in a linearized form, thus the system for controlling the pump output variables can be designed. The geometrical features of the pump and the operating conditions both have significant effects on the torque load .

In addition, Manring reported that bearing and actuator forces for the swash plate control depend on the swash plate design. The forces and torque, which act upon the swash plate in three dimensions, were considered for adequate control and containment of the swash plate during machine operation. Likewise, the cradle-mounted design and the related applied forces on the swash plate by the control devices have been the topic of study by past researchers .

This study presents a new design for a dual-mode axial piston pump which can be