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Modern Mechanical Engineering, 2012, 2, 137-142 doi:10.4236/mme.2012.24018 Published Online November 2012 (http:/www.SciRP.org/journal/mme) Cop yrigh t 201 2 S ciR es . MME Structure Parameters Optimization Analysis of Hydraulic Hammer System * Guoping Yang, Jian Fang College of Automotive Engineering, Shanghai University of Engineering and Science, Shanghai, China Email: Received July 3, 2012; revised August 6, 2012; accepted August 21, 2012 ABSTRACT In order to improve the impact performance, the structure of hydraulic hammer should be optimized. In this paper, the ranges of eight vital structure parameters of piston and reversing valve system of hydraulic hammer were selected firstly; and then found the best value of different parameters under experiments with the method of computer optimization and the parametric analysis method provided by ADAMS software. These methods worked and the best design values of parameters of hydraulic hammer were obtained. At last, the optimal impact energy of virtual prototype of hydraulic breaking hammer was calculated and compared with the original impact performance. The results reveal that impact performance of hydraulic hammer has been improved significantly. Keywords: Hydraulic Hammer; Structure Parameters; Optimization Analysis; Impact Performance; ADAMS 1. Introduction Hydraulic breaker, mainly consisting of three essential partspiston, distribution valves and accumulator, is a breaking tool that converts hydraulic energy to mecha- nical impact energy and outputs impact energy via hy- draulic pressure driving the piston to do reciprocating motion 1. Owing to its remarkable features, such as high impact energy and productivity, superb use security, favorable working adaptability and reliability, it is widely applied in breaking mine rocks and engineering construction such as demolition of the concrete compo- nents and reconstruction of the old city 2,3. Despite its significant function, many problems are still existed in hydraulic hammer industry, such as the theoretical analy- sis; processing technology research and the test method. And the most important issue is how to improve the im- pact performance of hydraulic hammer 3. In order to improve the impact performance, the structure of hydrau- lic hammer should be optimized. In this paper, some vital structure parameters were chosen and optimized. After optimization, the results reveal that impact performance of hydraulic hammer has been improved significantly. 2. Selection of Hydraulic Hammer Optimization Goal and Design Variable As far as the current level of control theory development, the problem that how to match subsystem for nonlinear systems in order to achieve an optimal system was not be well resolved in theory. In the system of hydraulic breaking hammer, the relationship between valve and piston is close and interdependent, so its hard to find a separate valve for optimal performance or a separate pis- ton for optimal performance to compose an optimal per- formance broken hammer system. Hence, the ultimate goal of optimization design of hydraulic hammer is to obtain a set of optimal structure parameters of the whole hydraulic breaking system, but not necessarily to meet the need of optimal performance of each subsystem 4. 2.1. Selection of Optimization Target This paper selected the impact energy of hydraulic breaking hammer as the optimization goal, which has close relationship with the impact performance 5. Im- pact energy of hydraulic breaking hammer is defined as, under the stipulated conditions, the energy produced during the single impact of piston of hydraulic hammer. 2 1 EM V 2 ( 1) where, E is the impact energy of hydraulic hammer, M is the piston quality of hydraulic hammer, and V is the final impact velocity of hydraulic hammer piston. 2.2. Selection of Design Variables According to the final impact velocity of piston, the im- pact energy of the piston can be calculated. Theoretical * This project is supported by National Natural Science Foundation of China (Grant No. 50975169). G. P. YANG, J. FANG Cop yrigh t 201 2 S ciR es . MME 138 analysis and experimental results show that the piston velocity has relation with system parameters, such as input quantity of system and initial inflation pressure of nitrogen room 6,7. Whats more, it has relation with structural parameters of system, such as effective work area of former and rear cavity of piston and the location of feedback hole of return and impact stroke and so on. Energy consumption of reversing valve core consists of three main areas: the first one is the hydraulic energy losses, the second is the valve port throttling losses, and the third is leaking loss. They have direct relationship with effective work area of former and rear cavity of reversing valve core, and the location of reversing signal port of valve core 8. When these parameters were changed, reversing velocity of valve core and the quan- tity of hydraulic oil will be changed correspondingly 9. Through the analysis above, structural parameters of hydraulic hammer system that need to be optimized are listed in the Table 1 in detail. In order to enable optimum results more reliable, the actual working condition was referenced in experiment. Measured values of working parameters were imported into ADAMS 10, i.e. working pressure is 10 Mpa, ini- tial inflation pressure of nitrogen room is 0.8 Mpa, oil return back-pressure is 2.3 Mpa and travel of piston is limited in 90 mm. 3. Design and Study of Structural Parameters In order to observe the effects of structural parameters on impact performance of hydraulic hammer system, the following design and study of these parameters is to find Table 1. Design variables need to be optimized. Name of design variable Name in ADAMS Initial value (mm) Piston bottom radius R_piston_lower 34.1 Piston top radius R_piston_upper 32.25 Radius of former cavity of valve core R_valve_lower 19.75 Radius of rear cavity of valve core R_valve_upper 19.4 Location of reversing signal port of valve core of return stroke Signal_1 4.5 Location of reversing signal port of valve core of impact stroke Signal_2 12.5 Location of piston braking signal hole Signal_3 54.5 Location of piston braking signal hole Signal_4 66.5 Note: The location of signal port is the distance between the hole and the surface of former cavity of valve. which parameters have the maximum influence on the impact performance within the scope of the design re- spectively. 3.1. Design and Study of Piston Parameters Impact energy is associated with the final impact velocity, which is related to stroke time and acceleration, while the stroke time is directly related to the travel of the piston. Besides, stroke time and acceleration are interconnected. As can be seen in Figure 1, when the piston bottom radius is changed from 33.6 mm to 34.6 mm, the impact energy of hydraulic hammer remains unchanged, and then goes down. As the piston bottom radius increased to 34.35 mm, the piston impact energy and travel are sharply reduced. When the area of former cavity further reduced, as shown in the Trail5 of Figure 2, the piston is not work normally. So the piston bottom radius can not be too large, which should be contained within 34.35 mm. Although when the area of former cavity of piston in- creases, the system can achieve high impact energy, we cannot blindly increase the operation area. Because from Trail1 of Figure 2, we can see that when the bottom ra- dius is 33.6 mm, whose travel is close to 90 mm, approach- ing the alert value of piston stroke travel, and impact energy is not rising than that bottom radius is 33.85 mm. Through design and research comprehensively, piston bottom radius should be controlled from 33.85 mm to 34.35 mm. In the same way, the piston top radius should be con- trolled from 31.125 mm to 33.25 mm, the location of braking signal port of valve core of return stroke should be controlled from 63.25 mm to 69.75 mm, and the loca- tion of braking signal port of valve core of impact stroke should be controlled from 54 mm to 60 mm. Through the design and study of structural parameters of piston, the scope of each design variable was deter- mined. Then, the sensitivity of these design variables within the scope was calculated and analyzed. The results were shown in the Figures 3 and 4. Judging from the analysis results, the top and bottom radius of piston have higher sensitivity, and the location of braking signal port of valve core of impact stroke and return stroke have a much lower sensitivity, but their mutual impact on the impact energy can not be over- looked. So, the relation of the location of braking signal port of valve core of impact stroke and return stroke, and the relationship between the top and bottom radius of piston will be analyzed in experimental study of struc- tural parameters. 3.2. Design and Study of Structural Parameters of Reversing Valve Core The ranges of valve core structure parameters can also be G. P. YANG, J. FANG Cop yrigh t 201 2 S ciR es . MME 139 Figure 1. Impact energy curve. Figure 2. Piston displacement curves. Figure 3. Sensitivty of bottom radius of piston. Figure 4. Sensitivty of location of piston stroke signal port. G. P. YANG, J. FANG Cop yrigh t 201 2 S ciR es . MME 140 determined through experiment initially. The working area of former cavity of reversing valve should be con- trolled from 19.55 mm to 19.75 mm. And the working area of rear cavity of reversing valve should be con- trolled from 19.05 mm to 19.55 mm. When the location of signal port of valve core of return stroke moves up, both the piston travel and the impact velocity increase, but the overall change is relatively small, and the influ- ence on the impact energy is not very significant. On the contrary, the location of signal port of valve core of im- pact stroke has little influence. The impact energy can vary within a very small area, and the piston motion characteristics recorded virtually have no change. Through experimental analysis, R_valve_lower and R_valve_upper are more sensitive than signal_1 and sig- nal_2. Considering from design variables singly, radii of former and rear cavity of valve core show much more influence on impact energy than the location of braking signal port of valve core of impact and return stroke, but the influence from the interaction of them cannot be ig- nored. In the follow-up study, depending on the influence of interaction of these variables, accurate range of R_valve_lower and R_valve_upper and optimal design value of signal_1 and signal_2 can be determined, which can improve the efficiency of optimization analysis. 4. Experimental Study on Structural Parameters It is difficult to find a mutual influence on impact energy of virtual prototype of hydraulic hammer between dif- ferent design parameters. In order to find the optimal combination of design parameters, which has the best effects on impact energy, experiments are designed to research on different design parameters combinations. 4.1. Experimental Study on Piston Structural Parameters In order to obtain the impact performance of hydraulic hammer under the influence of interplay of different structural parameters of piston, two groups of experiment were carried out. Before experiment, , the ratio of working area of former and rear cavity of piston, was defined, through which the impact performance of hydraulic hammer un- der the influence of the value of R_piston_lower and R_piston_upper can be analyzed. Then determine the accurate value of signal_3 and signal_4, by analyzing the impact performance of hydraulic hammer under the in- fluence of them. 4.1.1. Experimental Study on Top and Bottom Radii of Piston After analysis of test data of piston structural parameters, the figure can be obtained, which shows the relation of impact energy and in Figure 5. From this figure, the value of should be controlled from 0.5 to 0.6, whose impact energy is higher than 500 J. From experimental analysis, the range of is from 0.5 to 0.6, which pro- vides reference for optimization analysis. 4.1.2. Experimental Study on the Location of Braking Signal Port of Piston From the previous design study and sensitivity analysis of parameters, the ranges of the distance of the two signal ports are determined. The next step is to find the ratio of these two arguments, which can improve the impact en- ergy of hydraulic hammer system. From experimental research results, the maximum and minimum impact energy and corresponding value of two arguments are shown in Table 2. The Table 2 shows that the impact energy changes in a small region when signal_3 and signal_4 are changed. Moving the location of the two signal ports down appro- priately, the piston travel and impact energy can be im- proved to some extent. In short, the location of braking signal port of piston has little influence on impact per- formance. For the sake of reducing computing time for subsequent optimization, the value of signal_3 and sig- nal_4 is determined as 57 mm and 68.75 mm respec- tively. 4.2. Experimental Study on Structural Parameters of Reversing Valve Core On the same way, before experiment, , the ratio of Figure 5. Impact energy distribution of different . Table 2. Design of Experiments of position of brake signal. Trial Energy (J) Signal_3 (mm) Signal_4 (mm) S (mm) Min 400.84 58.50 64. 625 69.38 Max 464.69 57 68.75 72.14 Original463.48 54 66.5 71.07G. P. YANG, J. FANG Cop yrigh t 201 2 S ciR es . MME 141 working area of former and rear cavity of reversing valve core ,was defined, through which the impact performance of hydraulic hammer under the influence of the value of R_valve_lower and R_valve_upper can be analyzed. Then determine the accurate values of signal_1 and sig- nal_2, by anglicizing the impact performance of hydrau- lic hammer under the influence of them, which were listed in Table 3. From experimental analysis, the range of is from 1.066 to 1.2, which provides reference for optimization analysis. From the research of experimental results, the maxi- mum and minimum impact energy and corresponding value of two arguments are shown in Table 4. Moving the location of the two signal holes up appro- priately, the piston travel can be increased, so that the impact energy improved. 5. Optimization Design Analysis of Structural Parameters Through the design and experiment study of structural parameters of piston and reversing valve core, final range or accurate value of each parameter was determined. In order to get maximum impact energy of hydraulic ham- mer and the value of the individual design variables, op- timum design and analysis is needed. After final structural parameters optimization design analysis, the parameters corresponded to optimal impact energy of hydraulic hammer was shown in table 5 and the performance comparison before and after optimiza- tion were shown in Table 6. Through parametric analysis of design parameters, impact energy of hydraulic hammer was improved. Com- parisons of impact performance before and after optimi- zation were shown in Figure 6. 6. Conclusions This article provides the structural parameters optimiza- tion of piston system and reversing valve core system of virtual prototype of hydraulic hammer, so that its impact energy can be improved compared with the original per- formance to some extent. On the basis of the initial design parameters of original model, all of the ranges of parameters were determined by design study. Then, through the parameters sensitivity analyses, the regularity and extent of impact energy in- fluence caused by design parameters are obtained. After parameter design research and follow-up experimental study, the efficiency of optimization analysis was greatly improved. On the basis of four experiments on piston top and bottom radius, radius of former and rear cavity of re- versing valve, location of reversing signal port of valve core and location of braking signal port of piston, two Table 3. Impact energy range with different valve area ra- tio. Energy (J) The average of Energy 500 1.075 470 Energy 500 1.212 460 Energy 470 1.368 450 Energy 460 1.685 440 Energy 450 1.957 Table 4. Design of experiments of signal port location of valve. Trial Energy (J) signal_2 (mm) signal_1 (mm) S (mm) Max 500.69 16.50 8.50 76.50 Min 411.89 4.50 0.50 67.30 Original463.48 54 66.5 71.07 Table 5. Comparison of structural parameters before and after optimization. Name of design variable Initial value (mm) Optimal value (mm) R_piston_lower 34.1 33.85 R_piston_upper 32.25 31.25 R_valve_lower 19.75 19.6 R_valve_upper 19.4 19.45 Signal_1 4.5 8.5 Signal_2 12.5 16.5 Signal_3 54.5 57 Signal_4 66.5 68.75 Table 6. Prototype performance comparison before and after optimization. Energy (J) V (mm/s) S (mm) Impact frequency (bpm) Before optimization 463.48 8.37 71.07 923 1.40170.6047 After optimization 636.91 9.81 82.85 909 1.16250.5515 designed variables, and , were constructed suc- cessfully. 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