CN115618525A - Design method of miniaturized nonmetal hydraulic oil tank - Google Patents
Design method of miniaturized nonmetal hydraulic oil tank Download PDFInfo
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Abstract
The invention relates to a design method of a small-sized nonmetal hydraulic oil tank, which comprises the steps of calculating the minimum volume of the oil tank, calculating the volume of base oil, calculating the volume of functional oil, calculating the volume of changed oil, calculating the minimum theoretical volume of air, calculating the minimum theoretical volume of the oil tank, and combining the minimum theoretical volume of the oil tank and the criterion of triple pipe diameter of an auxiliary part of the oil tank to arrange the oil tank structure and arrange the shell structure of the oil tank, preliminarily setting the wall thickness of the oil tank to be 4mm, 6mm, 8mm, 10mm and 12mm respectively to obtain a three-dimensional model of the oil tank, performing finite element strength check on the three-dimensional model of the oil tank, finally obtaining the final structure and parameters of the shell of the oil tank after the strength check is passed, and the like.
Description
Technical Field
The invention relates to the technical field of hydraulic oil tanks, in particular to a design method of a small-sized nonmetal hydraulic oil tank.
Background
In actual engineering, a hydraulic oil tank is a container for storing oil required by a hydraulic system during operation. For a long time, the calculation method of the volume of the hydraulic oil tank is extended to an empirical formula recommended in a mechanical design manual, the accuracy of the mode of designing the volume of the oil tank according to an empirical coefficient is low, the situations of overlarge volume of the oil tank and excessive medium oil are easily caused, the layout space of mechanical equipment is occupied, meanwhile, the huge waste of energy is caused, particularly for engineering machinery, the mobility and the flexibility of the equipment are seriously influenced due to the increase of the volume and the weight of the oil tank, and the traditional design method of the hydraulic oil tank does not meet the requirements of most of the existing machinery any more. Therefore, the method has very important significance in calculating the minimum volume of the oil tank and designing the small-sized nonmetal hydraulic oil tank under the actual engineering background.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a method for designing a small-sized non-metal hydraulic oil tank, which divides the volume composition of the oil tank according to the function of the hydraulic oil tank, calculates the minimum theoretical volume of the oil tank, determines the shell structure of the oil tank to obtain the minimum volume of the oil tank under the required volume of hydraulic oil, and designs the shell structure of the oil tank, the wall thickness of the oil tank, and the forming technology of the oil tank under the condition of determining the minimum volume of the oil tank, thereby finally determining the overall structure of the non-metal hydraulic oil tank.
The technical scheme adopted by the invention is as follows:
the invention provides a design method of a miniaturized nonmetal hydraulic oil tank, which comprises the following steps:
s1, calculating the minimum volume of an oil tank, wherein the volume of the hydraulic oil tank is divided into an air volume and an oil volume according to a medium of the hydraulic oil tank, and the oil minimum volume and the air minimum volume are respectively obtained when the volume of the hydraulic oil tank is miniaturized;
s2, calculating the volume of the base oil liquid;
s3, calculating the volume of the functional oil;
s4, calculating the volume of the changed oil;
s5, calculating the minimum theoretical volume of air;
s6, calculating the minimum theoretical volume of the oil tank;
s7, arranging the oil tank structures by combining the minimum theoretical volume of the oil tank and the criterion of three pipe diameters of auxiliary parts of the oil tank;
s8, after arranging the shell structure of the oil tank, preliminarily setting the wall thicknesses of the oil tank to be 4mm, 6mm, 8mm, 10mm and 12mm respectively to obtain a three-dimensional model of the oil tank;
s9, carrying out finite element strength check on the three-dimensional model of the oil tank, and finally obtaining the final structure and parameters of the oil tank shell after the strength check is passed;
and S10, determining the material and the forming process of the oil tank according to the final volume of the nonmetal hydraulic oil tank.
Further, in the step S2, in order to prevent the hydraulic pump from generating suction and air entrainment at the oil return pipe during the operation of the equipment, a certain basic liquid level guarantee is required; the oil tank base liquid level is related to the installation conditions of an oil suction pipe and an oil return pipe, and through comprehensive analysis, the insertion modes of the oil suction pipe and the oil return pipe have three modes: top surface mounting, side surface mounting and bottom surface mounting; in either form, the base level height can be expressed as:
h＝h top roof +L+h Bottom
In the formula, h Top roof The height (mm) from the top of the pipe orifice to the liquid level; h is Bottom The height (mm) from the bottom end of the pipe orifice to the bottom of the oil tank; l is the distance (mm) from the top end of the pipe orifice to the bottom end of the pipe orifice;
when only the condition that the oil return of the oil return pipe does not generate air entrainment is considered, the installation requirement of the oil return pipe is as follows: the height from the top end of the pipe orifice to the liquid level is 2 times of the oil return pipe diameter; when only the oil suction pipe is considered without the air suction condition, the installation requirements of the oil suction pipe are as follows: the height of mouth of pipe top apart from the liquid level is 2 times oil absorption pipe diameter, promptly:
h oil return ＝L+2d Oil return
h Oil absorption ＝L+2d Oil absorption
In the formula (I), the compound is shown in the specification,h oil return The required liquid level height (mm) for the oil return element; h is Oil absorption The required liquid level height (mm) for the oil absorption element; d Oil return The drift diameter (mm) of the oil return element;
the volume of the base oil liquid needs to meet the requirement of the suction oil return pipe on the liquid level, so the height of the base oil liquid needs to be a large value, and the volume of the base oil liquid can be expressed as a formula.
h 0 ＝Max{h Oil return ,h Oil absorption }
V Foundation ＝S Bottom (C) ·h 0 ×10 -6
In the formula, S Bottom Is the area of the bottom of the oil tank (mm) 2 )；
At the beginning of the oil tank configuration, the shape of the oil tank is not determined, the bottom area of the oil tank can be estimated according to the design experience of the hydraulic oil tank, namely the pipe diameter with the distance between the outer edge of the shell of the oil suction pipe and the outer edge of the shell of the oil return pipe and the wall surface being 3 times is selected as the initial boundary of the bottom area of the oil tank, the calculation formula is shown as the formula, and the bottom area of the oil tank is corrected in the subsequent calculation;
V foundation ＝[(D Oil absorption +6d Oil absorption ) 2 +(D Oil return +6d Oil return ) 2 ]·h 0 ×10 -6
In the formula, D oil absorption is the diameter (mm) of the outer contour of the oil absorption element; d, the oil return is the diameter (mm) of the outer contour of the oil return element.
Further, in the step S3, only the influence of accessory installation on the oil volume is considered when analyzing the minimum volume of the functional oil in the oil tank; according to different installation positions of oil tank accessories, the relationship between the element envelope volume and the element oil filling volume can be divided into three categories: in the first type, the element is completely immersed below the liquid level, and the envelope volume area is always filled with oil; in the second type, the element spans an air area and an oil area, and the volume of the oil in the envelope volume area changes along with the change of the liquid level; in the third category, the elements are completely arranged in an air area, and no oil liquid exists in an envelope volume area all the time; establishing a relation between the element oil filling volume and the element enveloping volume of the three types of elements according to the element mounting positions; to sum up, the minimum volume of functional oil is:
in the formula, V i envelope An envelope volume (L) for the ith functional element; v i element The self volume (L) of the ith functional element; lambda i The correction coefficient of the oil filling volume of the ith functional element; n is the number of functional elements;
further, in step S4, according to the mechanism causing the liquid level in the oil tank to change, the changing oil can be divided into 5 parts: the volume of the oil is reduced due to liquid level change caused by the volume of an asymmetric hydraulic element, compression change of the volume of the oil caused by system pressure change, expansion and contraction change of the oil caused by temperature change, space change caused by deformation of a hydraulic pipeline and external leakage;
s4.1, calculating the volume of the asymmetric hydraulic component, wherein the asymmetric volume in the hydraulic system is mainly generated by an asymmetric hydraulic cylinder; when there are multiple asymmetric cylinders in the system, the order of the motions will affect the asymmetric volume calculation, so the sequential and compound motions need to be calculated separately;
when a plurality of hydraulic cylinders act in sequence, the asymmetric volume of the hydraulic system can be obtained by summing the volume difference between the rodless cavity and the rod cavity of the hydraulic cylinder, namely the change of the volume of oil liquid in the oil tank is as follows:
in the formula, V Asymmetric Is the asymmetric volume (L) of the hydraulic cylinder; d 2i The piston rod diameter (m) of the ith asymmetric hydraulic cylinder is; l is a radical of an alcohol i The stroke (m) of the piston rod of the ith asymmetric hydraulic cylinder is taken;
when a plurality of hydraulic cylinders act compositely, the change of the oil volume is theoretically the difference value between the maximum and minimum sum of the oil storage volumes of all the hydraulic cylinders in one cycle period. So the asymmetric volume of all hydraulic cylinders is:
in the formula,. DELTA.A i Is the asymmetric area (m) of the ith asymmetric actuator 2 )；v i (t) is a function (m/s) of the motion speed of the piston rod of the ith asymmetric actuator with respect to time; n is the number of hydraulic cylinders; t1 is the lowest moment(s) of the liquid level of the oil tank; t2 is the highest moment(s) of the liquid level of the oil tank;
when the linkage relation of the hydraulic cylinders is unknown, the asymmetric volume of the hydraulic elements is calculated by adopting a formula;
s4.2, calculating the volume of the change of the oil pressure, and after the mechanical equipment is started, enabling the hydraulic pump to work to compress the volume of liquid in the hydraulic system and raise the oil pressure so as to drive the end load actuator of the hydraulic system to move; the pressure building process of the system needs to draw oil from an oil tank, so that the volume of the oil in the oil tank is reduced;
in the formula, beta l The bulk modulus (MPa) is the volume of the gassy oil liquid; delta P i The pressure change (MPa) of the ith pressure cavity is taken as the pressure change of the ith pressure cavity;
(ii) the ith pressure vessel volume (L); beta is a oil The volume modulus (MPa) of the pure oil liquid; r is a gas adiabatic index, 1 is taken for isothermal compression, and 1.4 is taken for adiabatic compression; p is hydraulic oil pressure (MPa); p 0 The initial pressure (MPa) of the hydraulic oil; t is gas temperature (. Degree. C.); t is 0 Initial temperature of gas (. Degree. C.); delta 0 Is the birth coefficient; v a The gas volume (L) when the oil liquid reaches the saturated solubility; alpha is the gas content of hydraulic oil; v air The initial volume (L) of free gas in oil liquid; v l The total volume (L) of the gas-containing oil liquid;
in addition, in the working process of the hydraulic system, the oil in the pressure chamber is always in a motion state, so the pressure in the pressure chamber also needs to consider the action of the inertia of the oil; at this time, the oil pressure on any section in the pressure containing cavity is as follows:
in the formula, Q i The flow rate (L/min) of the hydraulic oil on the cross section of the ith pressure cavity is shown; m is i The mass (kg) of the hydraulic oil on the cross section of the ith pressure chamber; a. The i The cross-sectional area (mm 2) of the ith pressure chamber; p i Working pressure (MPa) of the ith pressure cavity;
therefore, the oil compression volume calculation formula is as follows:
s4.3, calculating the volume of the oil liquid expansion caused by heat and contraction caused by cold, wherein in the working process of the equipment, one part of heat generated by the hydraulic system is emitted to the environment through the hydraulic element and the pipeline surface, and the other part of the heat generated by the hydraulic system is transmitted to the oil liquid to increase the temperature of the oil liquid; in the mechanical shutdown state, the temperature of the hydraulic oil in the system gradually approaches the ambient temperature; when the temperature of the hydraulic oil tank and the hydraulic system changes, the hydraulic oil expands with heat and contracts with cold; according to the lubricating oil volume correction coefficient table, the relative volume expansion coefficient of the oil at any two temperatures can be calculated:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 The volume correction coefficient of the oil liquid at 20 ℃ is obtained;
at a temperature of T 1 The volume correction coefficient of the oil liquid at the temperature of 20 ℃;
contain gas oil under the change of temperature, the phenomenon of expend with heat and contract with cold will take place for its volume to lead to the change of fluid volume, the volume change of fluid can be represented by volume correction coefficient under the different temperatures:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 Volume (L) of hydraulic oil;
at a temperature of T 1 Volume of hydraulic oil (L);
is temperature from T 1 Is changed into T 2 A temporal volume correction factor;
therefore, the volume change of the hydraulic oil in the oil tank during temperature change is as follows:
in the formula, V l The total volume (L) of oil liquid in the hydraulic system;
s4.4, calculating the volume of the change of the volume of the pipeline, wherein in the working process of a hydraulic system, along with the rise of the pressure of hydraulic oil, certain force can be generated on the inner wall of a container containing the oil, and the container can deform due to the force; in a hydraulic system, a container which is deformed mainly comprises a hydraulic steel pipe and a rubber pipe; when the volume of the hydraulic pipeline is increased, in order to fill the increased volume, a certain volume of hydraulic oil needs to be drawn from a hydraulic oil tank;
because the deformation quantity of the rubber tube is larger than that of the steel tube, the volume change of the rubber tube is mainly explained; when the hydraulic rubber pipe is subjected to high pressure, the inner diameter of the rubber pipe is increased under the action of force, in order to simplify analysis, the rubber pipe is regarded as a thick-wall cylinder, and the volume change of a certain section of rubber pipe is calculated by a formula through derivation;
in the formula, l is the length (mm) of the cut rubber pipe section; r is 1 Cutting the inner radius (mm) of the rubber pipe section; r is 2 Cutting the outer radius (mm) of the rubber pipe section; p is the hydraulic oil pressure (MPa) in the intercepted rubber pipe section; mu is the Poisson's ratio of the rubber tube material; e is the elastic modulus (MPa) of the rubber tube material;
is r = r 1 Inner radius variation (mm);
in the hydraulic pipeline, the rubber tube has a plurality of sections with different tube diameters, and in order to reduce the calculated amount, the equivalent inner radius and the equivalent length of the rubber tube are used for calculating the change volume of the pipeline; the outer diameter of the pipeline can be calculated by the inner diameter and the wall thickness of the pipeline, and the design of the wall thickness is related to the parameters of a hydraulic system; thus, the pipe outer radius can be expressed as:
in the formula, r 1 The equivalent inner radius (mm) of the rubber tube; r is a radical of hydrogen 2 The equivalent outer radius (mm) of the rubber tube; delta is the wall thickness (mm) of the rubber tube; sigma P Allowable stress (MPa) for the rubber tube; p is the working pressure (MPa) of the rubber tube;
suppose the inner diameter r 'of a rubber pipe section' 1 ＝kr 1 And then:
r 'in the formula' 1 The inner diameter (mm) of a certain section of rubber tube; r' 2 Is r' 1 The outer diameter (mm) of the same section of rubber tube;
if the inner diameter of the pipeline is converted into the equivalent diameter, the equivalent length change of the pipeline is changed into the original k 2 Doubling, namely:
l＝k 2 l′
wherein l is the equivalent length (mm) of the rubber tube; l 'is and r' 1 、r′ 2 The length (mm) of the same section of rubber tube;
therefore, the total volume change of the hydraulic oil caused by pipeline deformation is as follows:
in the formula I i The length (mm) of the rubber tube at the section i; r is a radical of hydrogen i1 The inner radius (mm) of the rubber tube at the i-th section;
the i-th section of rubber pipe r = r 1 Inner radius variation (mm);
s4.5, calculating the volume of oil leakage, wherein the leakage of the hydraulic system can be divided into inner leakage and outer leakage, wherein the outer leakage can cause the volume change of hydraulic oil in the hydraulic system; because the reason for causing the external leakage of hydraulic system is complicated, the volume of leaked fluid can not be accurately calculated, and the supplement of the leaked fluid is considered to be carried out during mechanical maintenance, so the volume of leaked fluid can be regarded as a function related to the working time of the system:
ΔV leakage of ＝-γΔt
In the formula, gamma is the external leakage coefficient (L/h) of the hydraulic oil; delta t is hydraulic oil leakage time (h);
in conclusion, the variable oil volume consists of the volume of an asymmetric hydraulic element, the volume of the oil compressed and changed, the volume of the oil expanded with heat and contracted with cold, the volume of the pipeline and the volume of the oil leakage;
further, in step S5, the engineering mobile machine may shake and incline during operation, and at this time, the filter may be immersed by the liquid level to cause unsmooth air circulation and hidden danger that oil drops splash from the inside of the oil tank, so that the relationship between the liquid level and the arrangement position of the air filter under the inclined condition needs to be analyzed;
when the oil tank inclines left theta, prevent empty filter contact liquid level, establish the restraint:
obtaining by solution:
thus, the air zone height needs to meet:
in the formula, h Liquid for treating urinary tract infection The height (mm) of oil in a hydraulic oil tank; a is the width (mm) of the hydraulic oil tank; h is the height (mm) of the hydraulic oil tank; θ is the tilt angle (°); l 1 The height (mm) of the air filter extending into the oil tank; x is the distance (mm) between the left wall surface of the oil tank and the leftmost end of the air filter, wherein x is less than or equal to 0.5A;
when the oil tank inclines rightwards theta, the height constraint of the air area can be obtained by the same method as follows:
in the formula (d) 1 Air filter diameter (mm);
in summary, the constraints on the height of the air region are:
the minimum theoretical volume of the air zone is:
further, in step S6, the hydraulic oil in the oil tank is composed of three parts of changing oil, functional oil and base oil, and the sum of the volumes of the three parts of oil is the volume of the hydraulic oil required by the oil tank, namely:
when the functions of heat dissipation, degassing, impurity removal and the like of the hydraulic oil tank are all processed by external equipment, the internal functional elements do not need to be installed in the oil tank, so that the V-shaped structure Function(s) And not the necessary volume of oil. Therefore, theoretically, the minimum volume of the oil is the sum of the volume of the changed oil and the volume of the base oil, namely:
from the above analysis, it can be seen that when the tank is tilted, the minimum liquid level is also changed, so that the minimum theoretical volume of oil needs to be corrected. The corrected oil volume is as follows:
therefore, the minimum theoretical volume of the oil tank is the sum of the minimum theoretical volume of the oil and the minimum theoretical volume of the air, namely:
compared with the prior art, the invention has the following beneficial effects:
aiming at the development trend of the lightweight of the hydraulic oil tank, the systematic detailed analysis and research is carried out on the hydraulic oil tank miniaturization calculation method, a miniaturization hydraulic oil tank calculation model is established, and the following beneficial effects are achieved:
(1) The volume of the hydraulic oil tank is analyzed, including oil volume and gas volume, and the oil volume is defined as three parts, namely base oil volume, functional oil volume and variable oil volume. The volume of the base oil liquid is a base liquid level guarantee required for preventing the phenomena of air suction and air entrainment at an oil return pipe of the hydraulic pump; the volume of the functional oil is the element envelope volume and the element oil filling volume considering the installation of the auxiliary parts; the change of the oil liquid volume is the oil tank liquid level change caused by 5 aspects of liquid level change caused by asymmetric hydraulic element volume, oil volume compression caused by system pressure change, oil expansion and contraction caused by oil temperature change, circulation space change caused by pipeline container compression deformation, oil reduction caused by system leakage and the like. The oil volume and the top gas volume together constitute the internal volume of the oil tank.
(2) Main influence factors of the volume of the base oil are analyzed, and a calculation method of the volume of the base oil is provided; classifying and discussing the installation mode of the auxiliary parts, and providing a method for calculating the minimum volume of the functional oil; 5 relation change oil liquid volume calculation methods are deduced and listed in detail, and a change oil liquid theoretical minimum volume calculation model is established.
(3) A minimum theoretical oil volume calculation formula is given through analysis of the volume of the base oil, the volume of the functional oil and the volume of the changed oil; the constraint condition of the air volume is obtained by analyzing the liquid level change of the oil liquid under the inclined working condition, and a calculation formula of the minimum theoretical volume of the air is given. And determining a calculation formula of the minimum theoretical volume of the oil tank through comprehensive correction.
Drawings
FIG. 1 is a schematic illustration of the envelope volume of an element and the oil fill volume of an element;
FIG. 2 is a schematic view of a tank volume division;
FIG. 3 is a schematic diagram of the oil volume composition;
FIG. 4 is a schematic view of a line insertion pattern;
FIG. 5 is a schematic view of a base oil level analysis;
FIG. 6 is a schematic view of a component classification;
FIG. 7 is a schematic illustration of a lean condition;
FIG. 8 is a flow chart of the minimum theoretical volume design of the fuel tank of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
The invention provides a design method of a miniaturized nonmetal hydraulic oil tank, which comprises the following steps:
analyzing the function of a hydraulic oil tank, wherein the hydraulic oil tank is one of indispensable elements in a hydraulic system, and the main functions of the hydraulic oil tank comprise: the oil storage function, the heat dissipation function, the degassing function, the impurity removal function and the function of providing space for the installation of accessories. The heat dissipation function, the degassing function and the impurity removal function are generally realized in the hydraulic oil tank through accessories, such as a cooler, a filter and the like. The increase of the power-to-weight ratio by the tank auxiliary has been one of the trends of downsizing the tank, and therefore, it is necessary to consider the installation of the tank auxiliary in designing the capacity of the tank. As shown in fig. 1, in order to ensure that the accessory functions successfully when the accessory is installed, two factors need to be considered: firstly, the spatial arrangement of the auxiliary parts is ensured not to interfere, and the part of the volume expanded by the outline of the auxiliary parts is called as an element envelope volume; secondly, guarantee that the auxiliary part plays a function, need a certain amount of effective fluid to construct the flow field region, call this partial volume as the component oil filling volume, the component envelope volume all is relevant with oil tank auxiliary structure and lectotype with component oil filling volume, the component envelope volume can be regarded as the product of auxiliary length width height, and its computational formula is:
V envelope (envelope) ＝X·Y·Z×10 -6
Wherein X is the dimension (mm) of the auxiliary in the X-axis direction; y is the dimension (mm) of the accessory in the Y-axis direction; z is the dimension (mm) of the accessory in the Z-axis direction;
the volume composition of the hydraulic oil tank is analyzed, and different media are distributed in different space areas in the hydraulic oil tank to occupy different volume sizes. As shown in fig. 2, the internal space volume of the oil tank can be divided into two major parts, namely air volume and oil volume, according to different media. Therefore, when the oil tank is miniaturized, the volume calculation needs to respectively consider the air volume and the oil volume.
And (3) analyzing the volume of air in the hydraulic oil tank to provide enough space for liquid level change and ensure that return oil can smoothly return to the hydraulic oil tank. On the mobile machinery, working conditions such as mechanical impact shaking and inclination need to be considered, the change of the liquid level of oil liquid in the oil tank is developed and analyzed, and a theoretical volume calculation model of the minimum air volume of the oil tank is established.
The oil volume analysis, as shown in fig. 3, further divides the functions that the oil needs to undertake, and can be divided into three parts: and changing the oil volume, the functional oil volume and the base oil volume. The oil liquid used for ensuring the oil tank to realize the most basic oil absorption performance is defined as the volume of the base oil liquid; the hydraulic oil tank also has the functions of providing places for heat dissipation, degassing, impurity removal and accessory installation, and the volume of the part of oil is defined as the volume of functional oil; the volume of oil causing the level of the oil tank to change up and down as the state of the hydraulic system changes is defined as the changing oil volume. Therefore, when the oil volume is calculated, the influence factors of the three oil volumes need to be analyzed, and a calculation model of the oil volumes of all parts needs to be established.
The specific design method comprises the following steps:
s1, calculating the minimum volume of an oil tank, wherein the volume of the hydraulic oil tank is divided into an air volume and an oil volume according to a medium of the hydraulic oil tank, and the oil minimum volume and the air minimum volume are respectively obtained when the volume of the hydraulic oil tank is miniaturized; the minimum theoretical volume of the oil in the hydraulic oil tank and the minimum theoretical volume of the oil tank are composed of which parts, and factors influencing the minimum theoretical volume of the oil in the hydraulic oil tank and the minimum theoretical volume of the oil tank are certain, so that the method for calculating the minimum volume of the hydraulic oil tank is a precondition for realizing the method for calculating the minimum volume of the hydraulic oil tank;
s2, calculating the volume of the base oil, wherein a certain base liquid level guarantee is needed to prevent the phenomena of air suction and air entrainment at an oil return pipe of the hydraulic pump in the operation process of the equipment; the oil tank base liquid level is related to the installation conditions of an oil suction pipe and an oil return pipe, and the insertion modes of the oil suction pipe and the oil return pipe have three modes through analysis and synthesis: top mount, side mount and bottom mount, as shown in fig. 4; in either form, the base level height can be expressed as:
h＝h top roof +L+h Bottom
In the formula, h Top roof The height (mm) from the top of the pipe orifice to the liquid level; h is Bottom The height (mm) from the bottom end of the pipe orifice to the bottom of the oil tank; l is the distance (mm) from the top end of the pipe orifice to the bottom end of the pipe orifice;
as shown in fig. 5, when only the condition that the oil return of the oil return pipe does not generate air entrainment is considered, the installation requirements of the oil return pipe are as follows: the height from the top end of the pipe orifice to the liquid level is 2 times of the oil return pipe diameter; when only the oil suction pipe is considered and no air suction condition occurs, the installation requirement of the oil suction pipe is as follows: the height of mouth of pipe top apart from the liquid level is 2 times oil absorption pipe diameter, promptly:
h oil return ＝L+2d Oil return
h Oil absorption ＝L+2d Oil absorption
In the formula, h Oil return The required liquid level height (mm) for the oil return element; h is Oil absorption To suckThe required level height (mm) of the oil element; d Oil return The drift diameter (mm) of the oil return element;
the volume of the base oil liquid needs to meet the requirement of the suction oil return pipe on the liquid level, so the height of the base oil liquid needs to be a large value, and the volume of the base oil liquid can be expressed as a formula
h 0 ＝Max{h Oil return ,h Oil absorption }
V Foundation ＝S Bottom ·h 0 ×10 -6
In the formula, S Bottom Is the area of the bottom of the oil tank (mm) 2 )；
At the beginning of the oil tank configuration, the shape of the oil tank is not determined, the bottom area of the oil tank can be estimated according to the design experience of the hydraulic oil tank, namely the pipe diameter with the distance between the outer edge of the shell of the oil suction pipe and the outer edge of the shell of the oil return pipe and the wall surface being 3 times is selected as the initial boundary of the bottom area of the oil tank, the calculation formula is shown as the formula, and the bottom area of the oil tank is corrected in the subsequent calculation;
V foundation ＝[(D Oil absorption +6d Oil absorption ) 2 +(D Oil return +6d Oil return ) 2 ]·h 0 ×10 -6
In the formula, D oil absorption is the diameter (mm) of the outer contour of the oil absorption element; d, the oil return is the diameter (mm) of the outer contour of the oil return element;
s3, calculating the volume of the functional oil, and only considering the influence of accessory installation on the volume of the oil when analyzing the minimum volume of the functional oil in the oil tank; according to different installation positions of oil tank accessories, the relationship between the element envelope volume and the element oil filling volume can be divided into three categories: in the first type, the element is completely immersed below the liquid level, and the envelope volume area is always filled with oil; in the second type, the element spans an air area and an oil area, and the volume of the oil in the envelope volume area changes along with the change of the liquid level; in the third category, the elements are completely arranged in an air region, and no oil exists in an envelope volume region all the time, as shown in fig. 6;
establishing a relation between the element oil filling volume and the element enveloping volume of the three types of elements according to the element mounting positions;
as shown in Table 1-1, wherein the second type of element λ 2 Can be calculated according to a formula;
in the formula, h 1 The height (mm) of the element which needs to be immersed in the oil for realizing the self function;
TABLE 1-1 relationship between oil fill volume of element and envelope volume of element
To sum up, the minimum volume of function fluid is:
in the formula, V i envelope An envelope volume (L) for the ith functional element; v i element The self volume (L) of the ith functional element; lambda [ alpha ] i The correction coefficient of the oil filling volume of the ith functional element; n is the number of functional elements;
s4, calculating the volume of the changed oil, wherein the changed oil can be divided into 5 parts according to different mechanisms causing the liquid level change in the oil tank: the volume of the oil is reduced due to liquid level change caused by the volume of an asymmetric hydraulic element, compression change of the volume of the oil caused by system pressure change, expansion and contraction change of the oil caused by temperature change, space change caused by deformation of a hydraulic pipeline and external leakage;
s4.1, calculating the volume of the asymmetric hydraulic component, wherein the asymmetric volume in the hydraulic system is mainly generated by an asymmetric hydraulic cylinder; when there are multiple asymmetric cylinders in the system, the order of the motions will affect the asymmetric volume calculation, so the sequential and compound motions need to be calculated separately;
when a plurality of hydraulic cylinders act in sequence, the asymmetric volume of the hydraulic system can be obtained by summing the volume difference between the rodless cavity and the rod cavity of the hydraulic cylinder, namely the change of the volume of oil liquid in the oil tank is as follows:
in the formula, V Asymmetric Is the asymmetric volume (L) of the hydraulic cylinder; d 2i The piston rod diameter (m) of the ith asymmetric hydraulic cylinder is; l is i The stroke (m) of the piston rod of the ith asymmetric hydraulic cylinder is taken;
when a plurality of hydraulic cylinders act compositely, the change of the oil volume is theoretically the difference value between the maximum and minimum sum of the oil storage volumes of all the hydraulic cylinders in one cycle period. So the asymmetric volume of all cylinders at this time is:
in the formula,. DELTA.A i Is the asymmetric area (m) of the ith asymmetric actuator 2 )；v i (t) is a function (m/s) of the motion speed of the piston rod of the ith asymmetric actuator with respect to time; n is the number of hydraulic cylinders; t1 is the lowest moment(s) of the liquid level of the oil tank; t2 is the highest moment(s) of the liquid level of the oil tank;
and when the linkage relation of the hydraulic cylinder is unknown, calculating the asymmetric volume of the hydraulic element by adopting a formula.
And S4.2, calculating the volume of the change of the oil pressure, and after the mechanical equipment is started, enabling the hydraulic pump to work to compress the volume of the liquid in the hydraulic system and raise the oil pressure so as to drive the tail end load actuator of the hydraulic system to move. The pressure building process of the system needs to draw oil from an oil tank, so that the volume of the oil in the oil tank is reduced;
in the formula, beta l The bulk modulus (MPa) is the volume of the gassy oil liquid; delta P i The pressure change (MPa) of the ith pressure cavity;
the volume (L) of the ith pressure chamber; beta is a oil The volume modulus (MPa) of the pure oil liquid; r is a gas adiabatic index, 1 is taken for isothermal compression, and 1.4 is taken for adiabatic compression; p is hydraulic oil pressure (MPa); p 0 The initial pressure (MPa) of the hydraulic oil; t is gas temperature (. Degree. C.); t is 0 Initial temperature of gas (. Degree. C.); delta 0 Is the birth coefficient; v a The gas volume (L) when the oil liquid reaches the saturated solubility; alpha is the gas content of hydraulic oil; v air The initial volume (L) of free gas in oil liquid; v l The total volume (L) of the gas-containing oil liquid;
in addition, in the working process of the hydraulic system, the oil in the pressure chamber is often in a moving state, so the pressure in the pressure chamber also needs to consider the action of the inertia of the oil. At this time, the oil pressure on any section in the pressure containing cavity is as follows:
in the formula, Q i The flow rate (L/min) of the hydraulic oil on the cross section of the ith pressure cavity is shown; m is i The mass (kg) of the hydraulic oil on the cross section of the ith pressure chamber; a. The i The cross-sectional area (mm 2) of the ith pressure chamber; p i Is the ith pressureThe working pressure (MPa) of the force cavity;
therefore, the oil compression volume calculation formula is as follows:
s4.3, calculating the volume of the oil liquid which expands with heat and contracts with cold, wherein in the working process of the equipment, one part of heat generated by a hydraulic system is emitted to the environment through a hydraulic element and the surface of a pipeline, and the other part of the heat generated by the hydraulic system is transmitted to the oil liquid to increase the temperature of the oil liquid; in the mechanical stop state, the temperature of the hydraulic oil in the system gradually approaches the ambient temperature. When the temperature of the hydraulic oil tank and the hydraulic system changes, the hydraulic oil expands with heat and contracts with cold; the volume correction factor of oil converted to standard temperature at non-standard temperature is given in GB/T1885-1998 oil meter, as shown in Table 1-2. According to the lubricating oil volume correction coefficient table, the relative volume expansion coefficient of the oil at any two temperatures can be calculated:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 The volume correction coefficient of the oil liquid at the temperature of 20 ℃;
at a temperature of T 1 The volume correction coefficient of the oil liquid at 20 ℃ is obtained;
TABLE 1-2 VOLUME CORRECTION COEFFICIENT TABLE
Contain gas oil under the change of temperature, the phenomenon of expend with heat and contract with cold will take place for its volume to lead to the change of fluid volume, the volume change of fluid can be represented by volume correction coefficient under the different temperatures:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 Volume (L) of hydraulic oil;
at a temperature of T 1 Volume (L) of hydraulic oil;
is temperature from T 1 Is changed into T 2 A temporal volume correction factor;
therefore, the volume change of the hydraulic oil in the oil tank during temperature change is as follows:
in the formula, V l The total volume (L) of oil liquid in the hydraulic system;
s4.4, calculating the volume of the change of the volume of the pipeline, wherein in the working process of a hydraulic system, along with the rise of the pressure of hydraulic oil, certain force can be generated on the inner wall of a container containing the oil, and the container can deform due to the force; in a hydraulic system, a container which is deformed mainly comprises a hydraulic steel pipe and a rubber pipe; when the volume of the hydraulic pipeline is increased, in order to fill the increased volume, a certain volume of hydraulic oil needs to be drawn from a hydraulic oil tank;
because the deformation quantity of the rubber tube is larger than that of the steel tube, the volume change of the rubber tube is mainly explained; when the hydraulic rubber pipe is subjected to high pressure, the inner diameter of the rubber pipe is increased under the action of force, in order to simplify analysis, the rubber pipe is regarded as a thick-wall cylinder, and the volume change of a certain section of rubber pipe is calculated by a formula through derivation;
in the formula, l is the length (mm) of the cut rubber pipe section; r is 1 Cutting the inner radius (mm) of the rubber pipe section; r is 2 Cutting the outer radius (mm) of the rubber pipe section; p is the hydraulic oil pressure (MPa) in the intercepted rubber pipe section; mu is the Poisson's ratio of the rubber tube material; e is the elastic modulus (MPa) of the rubber tube material;
is r = r 1 Inner radius variation (mm);
in the hydraulic pipeline, the rubber tube has multiple sections with different tube diameters, and in order to reduce the calculated amount, the equivalent inner radius and the equivalent length of the rubber tube are used for calculating the change volume of the pipeline; the outer diameter of the pipeline can be obtained by calculating the inner diameter and the wall thickness of the pipeline, and the design of the wall thickness is related to the parameters of a hydraulic system; thus, the pipe outer radius can be expressed as:
in the formula, r 1 The equivalent inner radius (mm) of the rubber tube; r is 2 The equivalent outer radius (mm) of the rubber tube; delta is the wall thickness (mm) of the rubber tube; sigma P Allowable stress (MPa) for the rubber tube; p is the working pressure (MPa) of the rubber tube;
suppose the inner diameter r 'of a rubber pipe section' 1 ＝kr 1 And then:
in the formula (II), r' 1 The inner diameter (mm) of a certain section of rubber tube; r' 2 Is r' 1 The outer diameter (mm) of the same section of rubber tube;
therefore, if the inner diameter of the pipeline is converted intoThe equivalent length change of the pipeline is changed into the original k by measuring the diameter 2 Doubling, namely:
l＝k 2 l′
wherein l is the equivalent length (mm) of the rubber tube; l 'is and r' 1 、r′ 2 The length (mm) of the same section of rubber tube;
therefore, the total volume change of the hydraulic oil caused by pipeline deformation is as follows:
in the formula I i The length (mm) of the rubber tube at the section i; r is i1 The inner radius (mm) of the rubber tube at the i-th section;
the i-th section of rubber pipe r = r 1 Inner radius variation (mm);
s4.5, calculating the oil leakage volume, wherein the hydraulic oil flows back to a hydraulic oil tank from the oil tank in the circulation process of the hydraulic oil through elements such as a hydraulic pump, a hydraulic pipeline, a hydraulic valve group and a hydraulic oil cylinder, and the leakage possibility exists in many links in the process; the leakage of the hydraulic system can be divided into an inner leakage and an outer leakage, wherein the outer leakage can cause the volume change of hydraulic oil in the hydraulic system; due to the complex reasons for causing the external leakage of the hydraulic system, the oil leakage volume cannot be accurately calculated; the replenishment of the leaked oil is taken into account during mechanical maintenance, so that the volume of oil leakage can be regarded as a function of the operating time of the system:
ΔV leakage of ＝-γΔt
In the formula, gamma is the external leakage coefficient (L/h) of the hydraulic oil; delta t is hydraulic oil leakage time (h);
the external leakage coefficient of the hydraulic oil is difficult to calibrate, and when the minimum theoretical volume of the hydraulic oil is preliminarily calculated, the recommended external leakage coefficient of the hydraulic oil is gamma = 0.005-0.007L/h by referring to the hydraulic oil part in a general check standard for leakage of oil (REF. AMM REV.62);
in conclusion, the variable oil volume consists of the volume of an asymmetric hydraulic element, the volume of the oil compressed and changed, the volume of the oil expanded with heat and contracted with cold, the volume of the pipeline and the volume of the oil leakage; under the actual working condition, the factors do not necessarily act independently, and can also influence simultaneously, so that in order to accurately describe the change of the oil volume in the oil tank, the working states of the hydraulic system at different working stages need to be integrated, and a calculation method for the change of the oil volume of the oil tank along with the change of the hydraulic system is given in tables 1-3;
tables 1-3 changes in volume of oil in a tank during typical operating phases
Due to DeltaV Compression 、ΔV Deformation of And Δ V Asymmetric There may be a negative number, therefore Δ V Compression of +ΔV Deformation of +ΔV Expansion of +ΔV Asymmetric The time when the liquid level in the oil tank is the highest is not necessarily the moment, and the highest position and the lowest position of the liquid level in the oil tank are obtained by calculating and comparing the accumulated change values of the volume of the oil liquid in each working stage.
When the oil tank changes from the initial liquid level to the lowest liquid level, the accumulated volume change quantity of oil liquid in the oil tank is as follows:
when the oil tank changes from the initial liquid level to the highest liquid level, the accumulated volume change quantity of oil liquid in the oil tank is as follows:
therefore, the total volume change of the oil is as follows:
to simplify the calculation, Δ V may be used Compression 、ΔV Deformation of 、ΔV Asymmetric 、ΔV Expansion of And Δ V Leakage of The sum of absolute values of the two values is taken as the oil change volume, namely:
V variations in ＝∑|ΔV j |
In the formula, | Δ V j The absolute value (L) of the oil volume change caused by the jth factor is |;
s5, calculating the minimum theoretical volume of air, wherein the engineering mobile machinery can generate shaking and inclining working conditions in the working process, and the filter can be immersed by the liquid level to cause unsmooth air circulation and hidden danger that oil drops splash from the inside of an oil tank, so that the relation between the liquid level and the arrangement position of the air filter under the inclining working condition needs to be analyzed;
fig. 7 b) shows a schematic view of the tank when it is tilted left θ, preventing the air filter from contacting the liquid level, establishing the constraint:
obtaining by solution:
thus, the air zone height needs to meet:
in the formula, h Liquid for medical purpose The height (mm) of oil in a hydraulic oil tank; a is the width (mm) of the hydraulic oil tank; h is the height (mm) of the hydraulic oil tank; θ is the tilt angle (°); l 1 The height (mm) of the air filter extending into the oil tank; x is the distance (mm) between the left wall surface of the oil tank and the leftmost end of the air filter, wherein x is less than or equal to 0.5A;
fig. 7 c) shows a schematic view of the tank at right tilt θ, which in the same way yields an air zone height constraint:
in the formula, d 1 Air filter diameter (mm);
in summary, the constraints on the height of the air region are:
the minimum theoretical volume of the air zone is:
s6, calculating the minimum theoretical volume of the oil tank, wherein the hydraulic oil in the oil tank consists of three parts of changed oil, functional oil and base oil, and the sum of the volumes of the three parts of oil is the volume of the hydraulic oil required by the oil tank, namely:
when the functions of heat dissipation, degassing, impurity removal and the like of the hydraulic oil tank are all processed by external equipment, the internal functional elements do not need to be installed in the oil tank, so that the V-shaped structure Function(s) And is not a necessary volume of oil. Therefore, theoretically, the minimum volume of the oil is the sum of the volume of the changed oil and the volume of the base oil, namely:
from the above analysis, it can be seen that when the tank is tilted, the minimum liquid level is also changed, so that the minimum theoretical volume of oil needs to be corrected. The corrected oil volume is as follows:
therefore, the minimum theoretical volume of the oil tank is the sum of the minimum theoretical volume of the oil and the minimum theoretical volume of the air, namely:
and S7, arranging the oil tank structures by combining the minimum theoretical volume of the oil tank and the criterion of three pipe diameters of auxiliary parts of the oil tank.
And S8, after the oil tank shell structure is arranged, preliminarily setting the wall thickness of the oil tank to be 4mm, 6mm, 8mm, 10mm and 12mm respectively, and obtaining a three-dimensional model of the oil tank.
And S9, carrying out finite element strength check on the three-dimensional model of the oil tank, and finally obtaining the final structure and parameters of the oil tank shell after the strength check is passed.
And S10, determining the material and the forming process of the oil tank according to the final volume of the nonmetal hydraulic oil tank.
The invention is not to be regarded as an admission of common general knowledge.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.
Claims (6)
1. A method for designing a miniaturized nonmetal hydraulic oil tank is characterized by comprising the following steps:
s1, calculating the minimum volume of an oil tank, wherein the volume of the hydraulic oil tank is divided into an air volume and an oil volume according to a medium of the hydraulic oil tank, and the oil minimum volume and the air minimum volume are respectively obtained when the volume of the hydraulic oil tank is miniaturized;
s2, calculating the volume of the base oil liquid;
s3, calculating the volume of the functional oil;
s4, calculating the volume of the changed oil liquid;
s5, calculating the minimum theoretical volume of air;
s6, calculating the minimum theoretical volume of the oil tank;
s7, arranging the oil tank structures by combining the minimum theoretical volume of the oil tank and the criterion of three pipe diameters of auxiliary parts of the oil tank;
s8, after arranging the shell structure of the oil tank, preliminarily setting the wall thicknesses of the oil tank to be 4mm, 6mm, 8mm, 10mm and 12mm respectively to obtain a three-dimensional model of the oil tank;
s9, carrying out finite element strength check on the three-dimensional model of the oil tank, and finally obtaining the final structure and parameters of the oil tank shell after the strength check is passed;
and S10, determining the material and the forming process of the oil tank according to the final volume of the nonmetal hydraulic oil tank.
2. The design method of a miniaturized non-metallic hydraulic oil tank according to claim 1, characterized in that: in the step S2, in the operation process of the equipment, in order to prevent the phenomena of air suction of the hydraulic pump and air entrainment at the oil return pipe, certain basic liquid level guarantee is needed; the oil tank base liquid level is related to the installation conditions of an oil suction pipe and an oil return pipe, and through comprehensive analysis, the insertion modes of the oil suction pipe and the oil return pipe have three modes: top surface mounting, side surface mounting and bottom surface mounting; in either form, the base level height can be expressed as:
h＝h top roof +L+h Bottom
In the formula, h Top roof The height (mm) from the top end of the pipe orifice to the liquid level; h is Bottom (C) The height (mm) from the bottom end of the pipe orifice to the bottom of the oil tank; l is the distance (mm) from the top end of the pipe orifice to the bottom end of the pipe orifice;
when only the condition that the oil return of the oil return pipe does not generate air entrainment is considered, the installation requirement of the oil return pipe is as follows: the height from the top end of the pipe orifice to the liquid level is 2 times of the oil return pipe diameter; when only the oil suction pipe is considered without the air suction condition, the installation requirements of the oil suction pipe are as follows: the height of mouth of pipe top apart from the liquid level is 2 times oil absorption pipe diameter, promptly:
h oil return ＝L+2d Oil return
h Oil absorption ＝L+2d Oil absorption
In the formula, h Oil return The required liquid level height (mm) for the oil return element; h is Oil absorption The required liquid level height (mm) for the oil absorbing element; d Oil return The drift diameter (mm) of the oil return element;
the volume of the base oil liquid needs to meet the requirement of the suction oil return pipe on the liquid level, so the height of the base oil liquid needs to be a large value, and the volume of the base oil liquid can be expressed as a formula.
h 0 ＝Max{h Oil return ,h Oil absorption }
V Foundation ＝S Bottom ·h 0 ×10 -6
In the formula, S Bottom Is the area of the bottom of the oil tank (mm) 2 )；
At the beginning of the oil tank configuration, the shape of the oil tank is not determined, the bottom area of the oil tank can be estimated according to the design experience of the hydraulic oil tank, namely the pipe diameter with the distance between the outer edge of the shell of the oil suction pipe and the outer edge of the shell of the oil return pipe and the wall surface being 3 times is selected as the initial boundary of the bottom area of the oil tank, the calculation formula is shown as the formula, and the bottom area of the oil tank is corrected in the subsequent calculation;
V foundation ＝[(D Oil absorption +6d Oil absorption ) 2 +(D Oil return +6d Oil return ) 2 ]·h 0 ×10 -6
In the formula, D oil absorption is the diameter (mm) of the outer contour of the oil absorption element; d, the oil return is the diameter (mm) of the outer contour of the oil return element.
3. The design method of the miniaturized non-metallic hydraulic oil tank according to claim 2, characterized in that: in the step S3, only considering the influence of accessory installation on the oil volume when analyzing the minimum volume of the functional oil in the oil tank; according to different installation positions of oil tank accessories, the relationship between the element envelope volume and the element oil filling volume can be divided into three categories: in the first type, the element is completely immersed below the liquid level, and the envelope volume area is always filled with oil; in the second type, the element spans an air area and an oil area, and the volume of the oil in the envelope volume area changes along with the change of the liquid level; in the third category, the elements are completely arranged in an air area, and no oil liquid exists in an envelope volume area all the time; establishing a relation between the element oil filling volume and the element enveloping volume of the three types of elements according to the element mounting positions; to sum up, the minimum volume of functional oil is:
in the formula, V i envelope An envelope volume (L) for the ith functional element; v i element The self volume (L) of the ith functional element; lambda [ alpha ] i The correction coefficient of the oil filling volume of the ith functional element; n is the number of functional elements.
4. The design method of the miniaturized non-metallic hydraulic oil tank according to claim 3, characterized in that: in step S4, according to different mechanisms causing liquid level change in the oil tank, the changed oil can be divided into 5 parts: the volume of the oil is reduced due to liquid level change caused by the volume of an asymmetric hydraulic element, compression change of the volume of the oil caused by system pressure change, expansion and contraction change of the oil caused by temperature change, space change caused by deformation of a hydraulic pipeline and external leakage;
s4.1, calculating the volume of the asymmetric hydraulic component, wherein the asymmetric volume in the hydraulic system is mainly generated by an asymmetric hydraulic cylinder; when there are multiple asymmetric cylinders in the system, the sequence of motion will affect the asymmetric volume calculation, so the sequential and compound motions need to be calculated separately;
when a plurality of hydraulic cylinders act in sequence, the asymmetric volume of the hydraulic system can be obtained by summing the volume difference between the rodless cavity and the rod cavity of the hydraulic cylinder, namely the change of the volume of oil liquid in the oil tank is as follows:
in the formula, V Asymmetric Is the asymmetric volume (L) of the hydraulic cylinder; d 2i The piston rod diameter (m) of the ith asymmetric hydraulic cylinder is; l is i Is the ith asymmetric hydraulic cylinder piston rodA stroke (m);
when a plurality of hydraulic cylinders act compositely, the change of the oil volume is theoretically the difference value between the maximum and minimum sum of the oil storage volumes of all the hydraulic cylinders in one cycle period. So the asymmetric volume of all cylinders at this time is:
in the formula,. DELTA.A i Is the asymmetric area (m) of the ith asymmetric actuator 2 )；v i (t) is a function (m/s) of the motion speed of the piston rod of the ith asymmetric actuator with respect to time; n is the number of hydraulic cylinders; t1 is the lowest moment(s) of the liquid level of the oil tank; t2 is the highest moment(s) of the liquid level of the oil tank;
when the linkage relation of the hydraulic cylinders is unknown, the asymmetric volume of the hydraulic elements is calculated by adopting a formula;
s4.2, calculating the volume of the change of the oil pressure, and after the mechanical equipment is started, enabling the hydraulic pump to work to compress the volume of liquid in the hydraulic system and raise the oil pressure so as to drive the end load actuator of the hydraulic system to move; the pressure building process of the system needs to draw oil from an oil tank, so that the volume of the oil in the oil tank is reduced;
in the formula, beta l The bulk modulus (MPa) is the volume of the gassy oil liquid; delta P i The pressure change (MPa) of the ith pressure cavity is taken as the pressure change of the ith pressure cavity;
the volume (L) of the ith pressure chamber; beta is a beta oil The volume modulus (MPa) of the pure oil liquid; r is a gas adiabatic index, 1 is taken when isothermal compression is performed, and 1.4 is taken when adiabatic compression is performed; p is hydraulic oil pressure (MPa); p 0 The initial pressure (MPa) of the hydraulic oil; t is gas temperature (. Degree. C.); t is a unit of 0 Initial temperature of gas (. Degree. C.); delta 0 Is the birth coefficient; v a The gas volume (L) when the oil liquid reaches the saturation solubility; alpha is the gas content of hydraulic oil; v air The initial volume (L) of free gas in oil liquid; v l Is the total volume (L) of the gas-containing oil liquid;
in addition, in the working process of the hydraulic system, the oil in the pressure chamber is always in a motion state, so the pressure in the pressure chamber also needs to consider the action of the inertia of the oil; at this time, the oil pressure on any section in the pressure containing cavity is as follows:
in the formula, Q i The flow rate (L/min) of the hydraulic oil on the cross section of the ith pressure cavity is shown; m is i The mass (kg) of the hydraulic oil on the cross section of the ith pressure chamber; a. The i The cross-sectional area (mm 2) of the ith pressure chamber; p i Working pressure (MPa) of the ith pressure cavity;
therefore, the calculation formula of the oil compression volume is as follows:
s4.3, calculating the volume of the oil liquid which expands with heat and contracts with cold, wherein in the working process of the equipment, one part of heat generated by a hydraulic system is emitted to the environment through a hydraulic element and the surface of a pipeline, and the other part of the heat generated by the hydraulic system is transmitted to the oil liquid to increase the temperature of the oil liquid; in the mechanical shutdown state, the temperature of the hydraulic oil in the system gradually approaches the ambient temperature; when the temperature of the hydraulic oil tank and the hydraulic system changes, the hydraulic oil expands with heat and contracts with cold; according to the lubricating oil volume correction coefficient table, the relative volume expansion coefficient of the oil at any two temperatures can be calculated:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 The volume correction coefficient of the oil liquid at the temperature of 20 ℃;
at a temperature of T 1 The volume correction coefficient of the oil liquid at the temperature of 20 ℃;
contain gas oil under the change of temperature, its volume will take place expend with heat and contract with cold's phenomenon to lead to the change of fluid volume, the volume change of fluid can be represented by volume correction coefficient under the different temperatures:
in the formula (I), the compound is shown in the specification,
at a temperature of T 2 Volume (L) of hydraulic oil;
at a temperature of T 1 Volume (L) of hydraulic oil;
is temperature from T 1 Is changed into T 2 A temporal volume correction factor;
therefore, the volume change of the hydraulic oil in the oil tank during temperature change is as follows:
in the formula, V l The total volume (L) of oil liquid in the hydraulic system;
s4.4, calculating the volume of the change of the volume of the pipeline, wherein in the working process of a hydraulic system, along with the rise of the pressure of hydraulic oil, certain force can be generated on the inner wall of a container containing the oil, and the container can deform due to the force; in a hydraulic system, a container which is deformed mainly comprises a hydraulic steel pipe and a rubber pipe; when the volume of the hydraulic pipeline is increased, in order to fill the increased volume, a certain volume of hydraulic oil needs to be drawn from a hydraulic oil tank;
because the deformation quantity of the rubber tube is larger than that of the steel tube, the volume change of the rubber tube is mainly explained; when the hydraulic rubber pipe is subjected to high pressure, the inner diameter of the rubber pipe is increased under the action of force, in order to simplify analysis, the rubber pipe is regarded as a thick-wall cylinder, and the volume change of a certain section of rubber pipe is calculated by a formula through derivation;
in the formula, l is the length (mm) of the cut rubber pipe section; r is 1 Cutting the inner radius (mm) of the rubber pipe section; r is 2 Cutting the outer radius (mm) of the rubber pipe section; p is hydraulic oil pressure (MP) in the intercepted rubber pipe sectiona) (ii) a Mu is the Poisson's ratio of the rubber tube material; e is the elastic modulus (MPa) of the rubber tube material;
is r = r 1 Inner radius variation (mm);
in the hydraulic pipeline, the rubber tube has a plurality of sections with different tube diameters, and in order to reduce the calculated amount, the equivalent inner radius and the equivalent length of the rubber tube are used for calculating the change volume of the pipeline; the outer diameter of the pipeline can be calculated by the inner diameter and the wall thickness of the pipeline, and the design of the wall thickness is related to the parameters of a hydraulic system; thus, the pipe outer radius can be expressed as:
in the formula, r 1 The equivalent inner radius (mm) of the rubber tube; r is 2 The equivalent outer radius (mm) of the rubber tube; delta is the wall thickness (mm) of the rubber tube; sigma P Allowable stress (MPa) for the rubber tube; p is the working pressure (MPa) of the rubber tube;
suppose the inner diameter r 'of a rubber pipe section' 1 ＝kr 1 And then:
r 'in the formula' 1 The inner diameter (mm) of a certain section of rubber tube; r' 2 Is r' 1 The outer diameter (mm) of the same section of rubber tube;
if the inner diameter of the pipeline is converted into the equivalent diameter, the equivalent length change of the pipeline is changed into the original k 2 Doubling, namely:
l＝k 2 l′
wherein l is the equivalent length (mm) of the rubber tube; l 'is and r' 1 、r′ 2 The length (mm) of the same section of rubber tube;
therefore, the total volume change of the hydraulic oil caused by pipeline deformation is as follows:
in the formula I i The length (mm) of the rubber tube of the i-th section; r is i1 The inner radius (mm) of the rubber tube at the i-th section;
the i-th section of rubber pipe r = r 1 Inner radius variation (mm);
s4.5, calculating the volume of oil leakage, wherein the leakage of the hydraulic system can be divided into inner leakage and outer leakage, wherein the outer leakage can cause the volume change of hydraulic oil in the hydraulic system; because the reason for causing the external leakage of hydraulic system is complicated, the volume of leaking fluid can not be accurately calculated, and the supplement of considering leaking oil is carried out when mechanical maintenance, therefore the volume of leaking fluid can be regarded as the function related to the working time of the system:
ΔV leakage of ＝-γΔt
In the formula, gamma is the external leakage coefficient (L/h) of the hydraulic oil; delta t is hydraulic oil leakage time (h);
in conclusion, the variable oil volume is composed of the volume of the asymmetric hydraulic element, the volume of the oil compressed and changed, the volume of the oil expanded with heat and contracted with cold, the volume of the pipeline and the volume of the oil leakage.
5. The design method of the miniaturized non-metallic hydraulic oil tank according to claim 4, characterized in that: in the step S5, the engineering mobile machinery can generate working conditions of shaking and inclination in the working process, and at the moment, the filter can be immersed by the liquid level to cause the hidden troubles that the air circulation is not smooth and oil drops splash from the inside of the oil tank, so that the relation between the liquid level and the arrangement position of the air filter under the inclined working condition needs to be developed and analyzed;
when the oil tank inclines left theta, prevent empty filter contact liquid level, establish the restraint:
obtaining by solution:
thus, the air zone height needs to meet:
in the formula, h Liquid for medical purpose The height (mm) of oil in a hydraulic oil tank; a is the width (mm) of the hydraulic oil tank; h is the height (mm) of the hydraulic oil tank; θ is the tilt angle (°); l 1 The height (mm) of the air filter extending into the oil tank; x is the distance (mm) between the left wall surface of the oil tank and the leftmost end of the air filter, wherein x is less than or equal to 0.5A;
when the oil tank inclines rightwards theta, the height constraint of the air area can be obtained by the same method as follows:
in the formula (d) 1 Air filter diameter (mm);
in summary, the constraints on the height of the air region are:
the minimum theoretical volume of the air zone is:
6. the design method of a miniaturized non-metallic hydraulic oil tank according to claim 5, characterized in that: in the step S6, the hydraulic oil in the oil tank consists of three parts of change oil, functional oil and base oil, and the sum of the volumes of the three parts of oil is the volume of the hydraulic oil required by the oil tank, namely:
when the functions of heat dissipation, degassing, impurity removal and the like of the hydraulic oil tank are all processed by external equipment, the internal functional elements do not need to be installed in the oil tank, so that the V-shaped structure Function(s) And not the necessary volume of oil. Therefore, theoretically, the minimum volume of the oil is the sum of the volume of the changed oil and the volume of the base oil, namely:
from the above analysis, it can be seen that when the tank is tilted, the minimum liquid level is also changed, so that the minimum theoretical volume of oil needs to be corrected. The corrected oil volume is as follows:
therefore, the minimum theoretical volume of the oil tank is the sum of the minimum theoretical volume of the oil and the minimum theoretical volume of the air, namely:
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