GAS AND OIL POWER DISTRIBUTION RATIO OF A NEW HYDRAULIC BREAKER.doc

gas and oil power distribution ratio of a new hydraulic breakerabstract: the working principle of a new hydraulic breaker operated jointly by gas and hydraulic flow which has a reasonable structure, high efficiency and long piston life-span, is analyzed, and the optimal power distribution ratio of the sealed nitrogen gas to the high-pressure oil in the process of piston impacting is studied. through theoretical analysis, optimization simulation and detailed calculation, it is determined that the impact system has optimal mechanical performance and highest efficiency when the distribution ratio is between 0.3 and 0.5. the theoretical result is also verified by repeated tests. key words: hydraulic breaker power distribution ratio efficiencyabstract: the working principle of a new hydraulic breaker operated jointly by gas and hydraulic flow which has a reasonable structure, high efficiency and long piston life-span, is analyzed, and the optimal power distribution ratio of the sealed nitrogen gas to the high-pressure oil in the process of piston impacting is studied. through theoretical analysis, optimization simulation and detailed calculation, it is determined that the impact system has optimal mechanical performance and highest efficiency when the distribution ratio is between 0.3 and 0.5. the theoretical result is also verified by repeated tests. key words: hydraulic breaker power distribution ratio efficiencyfrom the operation principle described above, it can be found that the control pressure valve controls the impact system pressure. if all of other parameters are fixed, stepless adjustment of the control pressure px will cause the control pressure of the cone valve to change accordingly. therefore, the impact energy of the hydraulic breaker can also be changed. the impact energy becomes high when the pressure is high, and vice versa.the flow rate of the pump governs the impact frequency when the flow rate is low, it decreases. so both impact energy and which can also be adjusted steplessly. that is to say, when the frequency can be adjusted either simultaneously or separately, flow rate is high, the impact frequency increases. on the contrary, therefore the impact frequency can be adjusted to be very lowluevel and the impact energy to be very high. in this way, we can make full use of the engine load capacity to adapt it to various working conditions.on the other hand, if px is adjusted too high, the system pressure can not reach the value to open pressure control cone valve 16. the piston will continue its return stroke until end surface a crosses signal hole ii. on this occasion, the pressure oil will flow into pushing valve chamber 14 through front chamber 2 and ports i and a. then, the spool immediately moves right to change the direction of the return stroke. when the high-pressure oil enters the back chamber, the return stroke of the piston decelerates until the stroke movement begins. by this, the breaker would not be damaged because the maximum system pressure is limited, and the impact stroke and the impact energy are kept at sitable values by effective control.1.2 distribution valvea new oil distribution cone valve that characterizes cone surface seal and cylindrical surface seal is adopted in the breaker. when the spool moves to limited positions and keeps static, the valve port is sealed by the combination of the cone surface and the cylindrical surface. when the spool is in a moving state, the valve port is sealed only by the cylindrical surface. because the spool is usually in the limited position and keeps in a static state, the valve port leakage is nearly zero. because the flow coefficient of the spool port is very large, the pressure decrease is small when the oil passes through the valve port. accordingly, the energy loss is small. furthermore, the new oil distribution valve adopts the technique of the optimal and unequal open area of the valve port. when the hydraulic breaker requires more flow during the piston impacting period, the spool moves right where the valve port has a larger open area. when the hydraulic breaker requires less flow during the piston returning period, the spool moves left where the valve port has a smaller open area. therefore, the mo%g stroke of the spool is shortened compared with ttie ordinary distribution valve which leads to ths decline of efle?/ry consumption of the spool direction changingt?.2 gas and oil work distribution ratioas we know, the maximum volume of the nitrogen chamber is where knmu and knmin are the maximum and minimum action volumes of the nitrogen chamber cylinder (m3); s is the piston stroke (m); and aj is the effective action area of the nitrogen chamber (m2).the ratio of the working volume of the nitrogen chamber is defined asconsidering from the point of gas sealing, the ratio of the operation volume of the nitrogen chamber can not be too large when the gas volume is frequently changed. generally, the allowable range of this ratio is x = 1.31.5.supposing the piston displacement is y, the volume of the nitrogen chamber at the time is the variation of volume is dk = a,dy. the power applied by nitrogen on the piston iswhere p is the pressure in the nitrogen chamber.as the hydraulic breaker works in a high frequency, the heat transmission between the nitrogen chamber and the surroundings can be neglected in a given time. therefore, the compression ofnitrogen can be considered as an insulation process. according to the equation of the gas state, we obtainsupposing the resistance coefficient of piston movement is k and the movement energy of the piston is e, w can be expressed asaccording to eqs. (1) and (2), the volume of the nitrogen chamber at impact time is. from the equation of the gas state, the maximum pressure in the nitrogen chamber isin addition, in order to make the piston undergo the return stroke successfully, the system pressure must satisfywhere 4 is the effective action area of the front high-pressure oil chamber.if the system pressure is lower than /?, the impact systemcan not work. during the working process, the system pressure must fulfill the following condition in order for the hydraulic breaker to gain the required impact energyit means that if the system pressure is lower than p2, the impact energy will be insufficient.3 determination of gas and oil power distribution ratioif the gas and oil work distribution ratio is low, the charging pressure in the nitrogen chamber p will be low and thepower wf, applied by nitrogen will be small. although reducing the system pressure can accelerate the return stroke, the peak oil flow which needed at the stroke will be increased with the increase of action area of back chamber a, which leads to pressure loss and system inefficiency. so the gas and oil power distribution ratio can not be too low.on the other hand, if the gas and oil power distribution ratio is too high, the charging pressure pnmin in the nitrogen chamberwill be high and the power ffn applied by nitrogen will be large.hence the action area of the piston back chamber a2 becomessmall. with less oil flow being needed, the stored energy increases during the return stroke. however, the reduction in return stroke speed will cause the oil pressure of the system to exceed the threshold pressure of system components. therefore, the gas and oil work distribution ratio can not be too high either18101.to determine the optimal distribution ratio a a lot of simulation calculations and experiment tests are carried out.giving the pump flow rate q =120 l/min, the control pressure px=14.0 mpa, and changing the original charging pressure p of the nitrogen chamber continually, the result of simulationcalculation is shown in figs. 2,3 and 4.giving the pump flow rate q =120 l/min, the control pressure px=4.0 mpa, and changing the original charging pressure p . of the nitrogen chamber continually, the experiment result is shown in figs. 5 and 6 3.0through the analysis of the results of simulation calculation and experiment tests, we can obtain the following conclusions.(1)on the condition that the pump flow rate q and the feedback control pressure of direction alteration px are fixed, the pressure in the nitrogen chamber p . is low when the value of f issmall. in this case, the piston stroke s will be quite long. as the stroke feedback controls the direction alteration of the return stroke, the impact system pressure can not rise to the required value. in short words, the smaller the value of , the lower the pressure of the impact system. consequently, the lower the impact energy e.(2) with the increase of the value of fi, the charging pressure in the nitrogen chamber increases. the system pressure also increases until the pressure feedback is established. as the piston stroke s decreases, the impact frequency f becomes higher and higher. hence the impact system efficiency rj also improves.(3) the charging pressure in the nitrogen chamber becomes higher as increases. however, the feedback control pressure is fixed. so when the hydraulic pressure reaches the feedback control pressure, it can rise no longer. without sufficient hydraulic pressure, the piston can not be driven to return. for this reason, the breaker can not be started.(2) in order to achieve good breaker performance, must be maintained within a certain range. the pressure p in the nitrogenchamber also has an optimal range. if is too small, it is easy to establish stroke feedback because the system pressure is low, but the impact pressure can not be high either. as a result, the impact energy will be low. on the contrary, when is too large, the pressure in me nitrogen chamber is too high. in this case, the impact system pressure must be very high in order to start the hydraulic breaker. if so,