Optimum design of working device of wheel loader*
Yang Yu, Lianguan Shen, Mujun Li
Department of Precision Machinery and Precision Instrumentation
USTC (University of Science and Technology of China)
Hefei, Anhui Province, China
lgshen@ustc.edu.cn
Abstract?ome performances of ZL50 wheel loader do not meet the requirements, like delivering ratio, translation feature in lifting and automatic reset of the bucket. An optimal strategy for working device is adopted based on a virtual prototype in ADAMS. There are total 22 design variables which are 9 points? (x,
y) coordinates of the reverse six-bar linkage and two hydraulic
cylinders' extend and retract length in their axial direction. The
simulation is focused on the affect of design variables on the
performances of working device. Four different combinations of
design variables are selected in optimization based on their
sensitivity on the optimum objectives. They are ?ll Parameters? ?Base on Sensitivity? ?Bucket Unchanged? and ?ucket and Lift Arm Unchanged? Some robust optimal solutions with multi constraints are obtained. All the constraints are given some margin. The optimum results show that three end
points of the rocker arm and the joint point of tilt cylinder on the
frame play an important role in optimizing the performance of the structure. After comparison, the scheme ?Base on Sensitivity? can get the optimal solution with relatively fewer variables. It optimizes the delivering ratio from 0.314 to 0.450, the translation feature in lifting from 24.6? to 12.3?, the automatic reset of the bucket from 23.7? to 2.5?. The improvement of the performances after optimum design is obvious.
Keywords-optimum design; wheel loader; working device; ADAMS; sensitivity analysis
I. INTRODUCTION
Wheel loader is a kind of engineering machinery, which has been widely used in many construction projects such as roads, buildings, ports, mines and others, mainly for transporting and loading bulk materials. Its work process is divided into four working phases: shovel, transport, unloading and flat down. The structure size of six-linkage working mechanism directly affects on the performances, such as translation feature in lifting,
automatic reset, the ratio of delivering power, unloading angle, unloading height, unloading distance and bucket angle at carrying position, etc. It is extremely significant to obtain productive and dependable performances and a strong and robust main structure.
Reno Filla presented simulation of complete machines for analysis and optimization of overall performance to develop products of equally high performance, efficiency and operational in a shorter time and at a lower total development cost, but with more robustness [1]. Rongyi Zhang used Genetic Algorithm, Ant Colony Algorithm and Particle Swarm Optimization to optimize the work mechanism to make
*The work is_supported by National Natural Science Foundation of China under contract 10775128.
978-1-4244-7739-5/10/$26.00 ?010 IEEE
the ratio of delivering power maximum [2]. Hongzhong Huang optimized the working device of loader based on satisfactory degree theory [3]. Yangmin Li used Huston method and software MBDA to establish dynamics equations of working mechanism and solve the acceleration of the bucket to predict
security of the mechanism [4]. Xiaobin Ning analyzed the strength of the arm, lever and link by coupling Hydraulic and mechanism [5]. Xuyang Cao built up a rigid- flexible coupling model of working mechanism of wheel loader to match the real situation [6]. Wenyue Dai carried out an orthogonal experiment to improve performances of the working device. They obtained a satisfactory result for automatic reset and translation feature in lifting [7]. Xiuhua Gao optimized the performances of parallel moving and automatic reset [8]. Yingli Zu optimized the bucket
angle and the force of the tilt cylinder [9].
The types of loaders in china are mainly 3t, 4t and 5t models. 5t loader is the most popular. Even so, the performance of it is not so perfect. There is a ZL50 Wheel Loader has following
problems: 1, Delivering ratio of working mechanism is too small. The hydraulic cylinder should provide much more force to shovel and dig the same materials.
2. The bucket swing is too much in the lifting process, the material is easy to be spilled out. 3, The bottom of the bucket can not be flat down automatically when it goes back to its original location after unloading. In the case, the operator has
to do an additional operation to flat it down. The action would increase the complexity of the operation and waste energy.
The research establishes a virtual model of the working mechanism in ADAMS and optimizes the three mentioned performances to meet the requirements.
Figure 1. Reverse six-bar linkage model in ADAMS
ESTABLISH THE PARAMETERIZED MODEL OF SIX-BAR
LINKAGE OF LOADER
The working device of wheel loader is a reverse six-bar linkage which mainly consists of six parts which are: a lift arm, a rocker arm, a connecting rod, a bucket, a tilt cylinder and a lift cylinder. Fig. 1 shows the model in ADAMS. In it, the tooth's cusp of bucket is as the origin point and the shoveling condition is as the initial state. The parametric model based on structure point is added the restrict pairs and driven functions of hydraulic cylinders. The sliding pairs on hydraulic cylinders are parameterized to follow the changes of
structure points in the optimum design process. ? II.
angle variation range of bottom of the bucket in lifting process. The delivering ratio represents the capability of the power provided by the hydraulic cylinder. With the same force provided by the hydraulic cylinder, the larger the delivering ratio is, the greater the Max. digging force is. Max. digging force is one of the most important performances of the loader. We use the requirements of the translation feature in lifting and the automatic reset as constraints. But only use the ratio of delivering power as the target of optimization. The function of delivering ratio expression is as follows.
? F?? LFG? LBE?? sin(
UE)??????
UF)?? sin(
LCB?? LOGX?? sin(UC)
Herein, LFG represents the distance between hinge point F
and hinge point G on bucket (mm). LBE is the length of the lower rocker arm BE (mm). LCB is the length of the upper rocker arm CB (mm). LOGX is the length of the bottom of bucket(x-component of OG minus 100)(mm). UC is the angle between upper the rocker arm BC and the tilt cylinder CD: с BCD (?). UF is the angle between short tie rod FE and GF on bucket: сGFE (?). UE is the angle between short tie rod FE and lower rocker arm EB: сFEB (?).
Figure 2. Delivering ratio of the mechanism work cycle. The delivering ratio reaches its peak point during Fig. 2 sh
the lifting process. But in fact, the biggest resistance produces
III. OPTIMIZATION OBJECT SELECTION on the bucket is at the shoveling position of initial state. It
Desired improving performances of the mechanism consist means that the delivering ratio at the initial location should be
the bigger the better. Therefore, the delivering ratio at the
of delivering ratio, translation feature in lifting and automatic reset of the bucket. The translation feature is the continuous initial loc
TABLE I.
Coordinate Delivering
Variables of points ratio
ANALYSIS OF VARIABLES ON PERFORMANCES OF LOADER
Bucket angle
Translation
Unloading Unloading Unloading at carrying feature in angle Automatic
distance height position lifting reset
DV_1 G_X -0.0003811 -3.188 -4.4868 0.22358 -0.08456 0.00061 -2.48E-02 DV_2 G_Y -0.00080485 -21.865 -13.846 1.14330 0.13424 0.01209 -6.53E-02 DV_3 F_X 0.0001245 8.1727 5.7828 -0.47231 0.089826 -0.00102 2.57E-02 DV_4 F_Y 0.0010468 8.9019 6.3019 -0.51464 -0.22226 -0.01721 7.18E-02 DV_5 E_X 2.50E-05 -11.886 -8.2374 0.68306 0.00068 -0.00033 9.48E-04 DV_6 E_Y 0.00020986 11.538 8.1168 -0.66624 0.00647 -0.00261 2.93E-02 DV_7 B_X 3.48E-05 8.424 5.996 -0.48783 -0.00464 0.00144 0.011585 DV_8 B_Y -0.00095452 -5.0802 -3.705 0.29642 0.17496 0.01486 -0.079622 DV_9 C_X -9.21E-05 -1.0879 -0.78391 0.06319 -0.00003 0.00143 -0.014148 DV_10 C_Y 0.00052259 2.2758 1.6428 -0.13227 -0.10076 -0.0479 0.047653 DV_11 H_X - 1.289 -0.61031 -0.02198 0.00012 5.12E-06 1.18E-05 DV_12 H_Y - -2.617 1.2421 0.04450 -0.00033 -1.3E-05 -3.38E-05 DV_13 ZD_SD - -4.6982 -3.4236 0.27404 -0.29177 -0.16624 -0.21813 DV_14 ZD_XZ - -4.6982 -3.4236 0.27404 - - -0.21813 DV_15 DB_JS - 11.936 -5.7745 -0.19812 - 9.55E-05 -0.0005706 DV_16 DB_SD - 11.936 -5.7745 -0.19812 -0.12009 0.00014 -0.0005706 DV_17 D_X 3.54E-06 4.5393 3.3059 -0.26471 -0.00434 0.10177 0.00050514 DV_18 D_Y -2.01E-05 5.503 4.0283 -0.32153 0.04512 0.18314 -0.0027619 DV_19 A_X - -2.584 -3.767 0.21823 0.00752 -0.10378 0.00043155 DV_20 A_Y - 12.723 -10.273 -0.00167 -0.05423 -0.14237 -0.0017216 DV_21 K_X - -4.2763 2.0374 0.07239 -0.00435 -1.4E-05 -0.0002383 DV_22 K_Y - -13.51 6.6531 0.21921 0.01588 -0.00015 0.0006876
IV. CONSTRAINTS
The measurement functions and running functions in
performance and rearranging them, a new list is obtained Comprehaccording to the degree of the sensitivity in descending order. This is the basis for selecting optimization variables. The new
ADAMS are utilized to establish constraints of each operating conditions separately. The main constraints are set up to be the queue arupper limit of translation feature in lifting, lower and upper limit DV_2, DV_4, DV_3, DV_6, DV_8, DV_20, DV_5, DV_7, of bucket angle at carrying position, drive angle, unloading DV_10, DV_13, DV_16, DV_18, DV_22, DV_1, DV_17, distance, unloading height, unloading angle and automatic reset. DV_15, DV_14, DV_19, DV_9, DV_21, DV_11, DV_12. The optimal solution obtained by the numerical optimization It is obviously that the variables DV_11, DV_12 and DV_21 algorithm often falls on the border of the constraints without a have slightly affect and can be ignored. good robustness. It is necessary to consider the errors arose in
manufacturing and assembly process. That is, there should be In order to obtain a comparable result, four optimization
necessary redundancy on the constraints. The performance schemes are considered. First, all residual 19 variables are taken requirements in TABLE II and TABLE III are constraint?s detail. into account to optimize the working device. We call this
The mechanism must satisfy all these constraints.
TABLE II. COMPARISON OF THE INITIAL MODEL AND THE OPTIMIZED MODEL ON THE MAIN PERFORMANCES
Main performance Translation Automatic Delivering
parameters feature in
reset ratio lifting
Performance
<14? <6? - requirements
Before optimum 24.598? 23.684? 0.314 All Parameters 11.415? 5.967? 0.450 Based on Sensitivity 12.251? 2.453? 0.450 Bucket Unchanged 5.877? 5.980? 0.411 Bucket and Lift Arm 5.214? 5.968? 0.352 Unchanged
V. SENSITIVITY ANALYSIS AND SELECTION OF
OPTIMIZATION SCHEME
There are total 22 design variables which are 9 hinge points? (x, y) coordinates of the reverse six-bar linkage and the extend and retract length of the two hydraulic cylinders separately. In
TABLE I, ZD_SD is the variable corresponding to the extending of the tilt cylinder, while ZD_XZ means the retraction of the tilt cylinder. The variable DB_JS represents the first phase of extending of the lift cylinder. While DB_SD is the variable which corresponds to the second phase of extending of the lift cylinder.
It is necessary to analyze the sensitivity of the influence of variables on each performance firstly and then to discuss the possibility and feasibility of reducing the problem's complexity. The result of the sensitivity analysis is listed in TABLE I. From it, we can determine the finally screening of optimum design variables. It can be seen that DV_1, DV_2, DV_3, DV_4, DV_6, DV_8 and DV_10 have a great effect on delivering ratio. While the factors from DV_2 to DV_7, DV_15, DV_16, DV_20 and DV_22 have a great effect on unloading distance and unloading height. The factors from DV_2 to DV_8, DV_13, DV_14, DV_17 and DV_18 have a great effect on unloading angle. DV_1, DV_2, DV_3, DV_4, DV_8, DV_10, DV_13, DV_16, DV_18, DV_20 and DV_22 have a great effect on bucket angle at carrying position. DV_2, DV_4, DV_8, DV_10, DV_13, DV_17, DV_18, DV_19 and DV_20 have a great effect on translation feature in lifting. The factors from DV_1 to DV_4, DV_6 to DV_10, DV_13 and DV_14 have a great effect on automatic reset.
scheme ?ll Parameters? Then, the previous 12 of 22 factors are selected to optimize the design. We call the second scheme ?Base on Sensitivity? Actually, from the result of sensitivity analysis, we can see
that the position of point C, E and D seriously impact on the loader's performance, while the points F, G and A do not act decisive role. So, the third optimization scheme is done with the bucket unchanged. We call it ?Bucket Unchanged? Finally, in order to make the optimal results without changing the device too much, the last optimization scheme is carried out with the bucket and lift arm unchanged. We call it ?Bucket and Lift Arm Unchanged? The strategy is done under such consideration that the structure of the products should not be frequently changed to reduce the costs in the industrial sector.
Figure 3. The angle of bucket bottom relative to the horizontal position in
lifting process
Figure 4. The delivering ratio curve
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