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英文原文
Hydraulic actuation system design and computation
1. clearing about the design request to carry on the operating mode analysis.
When design hydraulic system below, first should be clear about the question, and takes it as the design basis.
Main engine use, technological process, overall layout as well as to hydraulic gear position and spatial size request; The main engine to the hydraulic system performance requirement, like the automaticity, the velocity modulation scope, the movement stability, the commutation pointing accuracy as well as the request which to the system efficiency, warm promotes; Hydraulic system working conditions, like temperature, humidity, vibration impact as well as whether has situation and so on corrosiveness and heat-sensitive material existence.
In in the above work foundation, should carry on the operating mode analysis to the main engine, the operating mode analysis including the movement analysis and the mechanical analysis, also must establish the load and the operating cycle chart to the complex system, from this understood the hydraulic cylinder or the oil motor load and the speed change as necessary the rule, below makes the concrete introduction to the operating mode analysis content
1.1 movements analyses
The main engine functional element according to the technological requirement movement situation, may use the displacement circulation chart (L—t), the speed circulation chart (v—t), or the speed and the displacement circulation chart indicated, from this carries on the analysis to the movement rule.
1.1.1 displacements circulation attempts L—t
The chart 1.1 is the hydraulic press hydraulic cylinder moves the circulation chart, the y-coordinate L expression piston moves, the x-coordinate t expression starts from the piston to the reposition time, the rate of curve expression movement of plunger speed.
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Chart 1.1 displacements circulation chart
1.1.2 speeds circulation chart v—t (or v—L)
In the project the hydraulic cylinder movement characteristic may induce is three kind of types. The chart 1.2 is three kind of types hydraulic cylinders v —t chart, the first kind of like chart 1.2 center solid lines show, the hydraulic cylinder starts to make the uniform accelerated motion, then uniform motion,
Chart 1.2 speeds circulation chart
Finally uniform retarded motion to end point; The second kind, the hydraulic cylinder preceding partly makes the uniform accelerated motion in the overall travelling schedule, in another one partly makes the uniform retarded motion, also the acceleration value is equal; The third kind, the hydraulic cylinder one most above makes the uniform accelerated motion in the overall travelling schedule by a smaller acceleration, then uniform decelerates to the travelling schedule end point. V—t chart three velocity curve, not only clearly has indicated three kind of types hydraulic cylinders movement rule, also indirectly has indicated three kind of operating modes dynamic performance.
1.2 mechanical analyses
1.2.1 hydraulic cylinders loads and duty cycle chart
1.2.1.1 hydraulic cylinders load strength computations
When the operating mechanism makes the straight reciprocating motion, the hydraulic cylinder must overcome the load is composed by six parts
(1.1)
In the formula: Fc In order to resistance to cutting; Ff In order to friction drag; Fi For inertia resistance; Fg For gravity; Fm In order to seal the resistance; Fb In order to drain the oil the resistance.
1.2.1.2 hydraulic cylinders cycle of motion various stages overall load strength
The hydraulic cylinder cycle of motion various stages overall load strength computation, generally includes the start acceleration, quickly enters, the labor enters, quickly draws back, decelerates applies the brake and so on several stages, each stage overall load strength has the difference.
(1) starts the acceleration period: By now the hydraulic cylinder or the piston were in from static enough to starts and accelerates to the certain speed, its overall load strength including guide rail friction force, packing assembly friction force (according to cylinder mechanical efficiency ηm=0.9 computation), gravity and so on item, namely:
(1.2)
(2) fast stage:
(1.3)
(3) the labor enters the stage:
（1.4）(4)decelerates:
(1.5)
To the simple hydraulic system, the above computation process may simplify. For example uses the single proportioning pump to supply the oil, only must calculate the labor to enter the stage the overall load strength, if the simple system uses the limiting pressure type variable displacement pump or a pair of association pumps for the oil, then only must calculate the fast stage and the labor enters the stage the overall load strength.
1.2.2 oil motors load
When the operating mechanism makes the rotary motion, the oil motor must overcome the outside load is:
(1.6)
1.2.2.1 operating duties moment of force Me. The operating duty moment of force is possibly a definite value, also possibly as necessary changes, should carry on the concrete analysis according to the machine working condition.
1.2.2.2 friction moments. In order to revolve the part journal place friction moment, its formula is:
(1.7)
In the formula: G is revolves the part weight (N); F is the rubbing factor, when the start for the factor, after the start for moves the rubbing factor; R is the journal radius (m).
1.2.2.3 moment of inertiaMi. The moment of inertia which in order to revolve the part acceleration or decelerates when produces, its formula is:
(1.8)
In the formula: ε Is the angle acceleration (r/s2);is the acceleration or decelerates the time (s); J is revolves the part rotation inertia (),
In the formula: In order to rotate the part the flywheel effect ().
Each kind may look up
According to the type (1.6), separately figures out the oil motor in a operating cycle various stages load size, then may draw up the oil motor the duty cycle chart
2 determinations hydraulic system main parameter
2.1 hydraulic cylinders design calculations
2.1.1 initially decides the hydraulic cylinder working pressure
In the hydraulic cylinder working pressure main basis cycle of motion various stages biggest overall load strength determined, in addition below, but also needs to consider the factor:
2.1.1.1 each kind of equipment different characteristic and use situation.
2.1.1.2 considerations economies and the weight factor, the pressure elects lowly, then part size big, the weight is heavy; The pressure chooses high somewhat, then part size small, the weight is light, but to the part manufacture precision, the sealing property requests high.
Therefore, the hydraulic cylinder working pressure choice has two ways: One, elects according to the mechanical type; Two, according to cuts the load to elect.
If the table 2.1, the table 2.2 shows.
The table 2.1 presses the load to choose the execution file the working pressure
Load
/N
＜5000
500～10000
10000～20000
20000～30000
30000～50000
＞50000
Working pressure
/MPa
≤0.8～1
1.5～2
2.5～3
3～4
4～5
＞5
The table 2.2 presses the mechanical type to choose the execution file the working pressure
Mechanical type
Engine bed
Farm machinery
Project machinery
Grinder
Aggregate machine-tool
Dragon Gate digs the bed
Broaching machine
Working pressure
/MPa
a≤2
3～5
≤8
8～10
10～16
20～32
2.2 oil motors design calculation
2.2.1 computations oil motor displacement
Under oil motor displacement according to the type decided that,
(2.1)
In the formula: T is the oil motor load moment of force (N·m); For oil motor import and export pressure difference (n/m3);is the oil motor mechanical efficiency, the common gear and the plunger motor takes 0.9 ~ 0.95, the leaf blade motor takes 0.8 ~ 0.9.
2.2.2 computations oil motor needs the current capacity oil motor the maximum current capacity
(2.2)
In the formula: is the oil motor displacement (m3/r); is the oil motor highest rotational speed (r/s).
3 hydraulic pressure parts choice
3.1 hydraulic pumps determinations with need the power the computation
3.1.1.1 determines the hydraulic pump the biggest working pressure. The hydraulic pressure pumping station must the working pressure determination, mainly acts according to the hydraulic cylinder in the operating cycle various stages to have most tremendous pressure p1, in addition the oil pump loses Sigma Delta p the oil mouth to the cylinder place always pressureΣΔp, namely
(3.1)
loses, the pipeline including the oil after the flow valve and other parts local pressures along the regulation loss and so on, before system pipeline design, may act according to the similar system experience to estimate, common pipeline simple throttle valve velocity modulation system ΣΔp is (2 ~ 5) ×105Pa, with the velocity modulation valve and pipeline complex system is (5 ~ 15) ×105Pa, also may only consider flows after various control valves pressure loss, but ignores the circuitry along the regulation loss, various valves rated pressure loses may searches from the hydraulic pressure part handbook or the product sample, Also may refer to the table 1.3 selections
The table 3.1 is commonly used, the low pressure each kind of valve pressure loses (Δpn)
Valve
Δpn (×105Pa)
Valve
Δpn (×105Pa)
Valve
Δpn (×105Pa)
Valve
Δpn (×105Pa)
Cone-way valve
0.3～0.5
Cone-way valve
3～8
Cone-way valve
1.5～2
Cone-way valve
1.5～2
Cross valve
1.5～3
Cross valve
2～3
Cross valve
1.5～3
Cross valve
3～5
3.1.2 determines the hydraulic pump current capacityqB
Pumps the current capacity basis functional element operating cycle must the maximum current capacity and the system divulges the determination
3.1.2.1 At the same time when more than hydraulic cylinders movement, the hydraulic pump current capacity must be bigger than the maximum current capacity which at the same time the movement several hydraulic cylinders (or motor) needs, and should consider the system divulging wears the volumetric efficiency drop after the hydraulic pump, namely
(3.2)
In the formula: K is the system leakage coefficient, generally takes 1.1 ~ 1.3, the great current capacity takes the small value, the small current capacity takes the great value; For at the same time movement hydraulic cylinder (or motor) is biggest (m3/s).
3.1.2.2 chooses the hydraulic pump the specification
Table 3.2 hydraulic pumps overall effectiveness indices
Hydraulic pump type
Gear pump
The screw rod pumps
Vane pump
Ram pump
Overall effectiveness index
0.6～0.7
0.65～0.80
0.60～0.75
0.80～0.85
Rotational speed and pumps which according to the above power, may select the standard electric motor from the product sample, again carries on, causes when the electric motor sends out the maximum work rate, in permission scope.
3.2 valves class parts choice
3.2.1 choices bases
The choice basis is: Rated pressure, maximum current capacity, movement way, installment fixed way, pressure loss value, operating performance parameter and working life and so on.
3.2.2 selector valves class parts should pay attention question
3.2.2.1 should select the standard stereotypia product as far as possible, only if does not have already time only then independently designs special-purp
3.2.2.2 valves class parts specification main basis class after this valve fat liquor most tremendous pressure and maximum current capacity selection. When chooses the overflow valve, should according to the hydraulic pump maximum current capacity selection; When chooses the throttle valve and the velocity modulation valve, should consider its minimum stable current capacity satisfies the machine low-speed performance the request
3.3 accumulators choices
3.3.1 accumulators use in to supplement when the hydraulic pump supplies the oil insufficiency, its dischargeable capacity is
(3.3)
In the formula: A is the hydraulic cylinder active surface (m2); L is the hydraulic cylinder travelling schedule (m); K is the hydraulic cylinder loss coefficient, when the estimate may take K = 1.2; Supplies the oil current capacity for the hydraulic pump (m3/s); T is the operating time (s).
3.3.2 accumulators make the emergency energy, its dischargeable capacity is:
(3.4)
When the accumulator uses in absorbs the pulsation to relax the hydraulic pressure impact, should take it as in the system a link if to be connected partially together synthesizes considers its dischargeable capaci
According to the dischargeable capacity which extracts and considered other requests, then chooses the accumulator the form
3.4 pipelines choices
3.4.1 drill tubings types choice
In the hydraulic system uses the drill tubing divides the hard tube and the hose, the choice drill tubing should have enough passes flows the section and the bearing pressure ability, simultaneously, should reduce the pipeline as far as possible, avoids the extreme turn and the section sudden change.
3.4.1.1 steel pipes: Center the high tension system selects the seamless steel pipe, the low pressure system selects the welded steel pipe, the steel pipe price lowly, performance good, the use is widespread
3.4.1.2 copper pipes: The copper tube working pressure below 6.5 ~ 10MPa, the instable tune, is advantageous for the assembly; Yellow copper pipe withstanding pressure higher, reaches 25MPa, was inferior to the copper tube is easy to be curving. Copper pipe price high, earthquake resistance ability weak, is easy to cause the fat liquor oxidation, should as far as possible little use, only uses in the hydraulic unit to match meets not the convenient spot.
3.4.2 drill tubings sizes determination
3.4.2.1 drill tubings inside diameters d presses down the type computation
In the formula: Q is passes the drill tubing the maximum current capacity (m3/s); V speed of flow which permits for the pipeline in (m/s). The common oil suction pipe takes 0.5 ~ 5 (m/s); The pressure oil pipe takes 2.5 ~ 5 (m/s); The oil return pipe takes 1.5 ~ 2 (m/s).
3.4.2 drill tubings δ sizes determination
(3.5)
In the formula: P is in the tube the biggest working pressure; When n is the safety coefficient, steel pipe p < 7MPa, takes n=8; When p < 17.5MPa, takes n=6; When p > 17.5MPa, takes n=4.
According to drill tubing inside diameter and wall thickness which calculates, looks up the handbook selection standard specification drill tubing
3.5 fuel tank design
The fuel tank function is the oil storage, disperses the oil discharge the quantity of heat, in the precipitation oil the impurity, is leisurely in the oil the gas
3.5.1 fuel tanks designs main point
3.5.1.1 fuel tanks should have the enough volume to satisfy the radiation, simultaneously its volume should guarantee in the system the fat liquor completely flows when the fuel tank does not seep out, the fat liquor liquid level should not surpass the fuel tank highly 80%.
3.5.1.2 suction boxes tubes and the oil return pipe spacing should be as far as possible big
3.5.1.3 fuel tanks bases should have the suitable ascent, releases the oil mouth to set to the most low spot, in order to drains the oil
3.6 oil filters choices
Chooses the oil filter the basis to have following several
3.6.1 bearing capacities
According to system pipeline working pressure determination.
3.6.2 filters the precision:
According to is protected the part the precision request determination
3.6.3 flow the ability:
According to through maximum current capacity determination.
3.6.4 resistance pressure drops:
Should the satisfied filter material intensity and the coefficient request.
4 hydraulic systems performance
In order to judge the hydraulic system the design quality, needs to lose to the system pressure, to give off heat , the efficiency and system dynamic characteristic and so on
4.1 circuitries pressure loses
After hydraulic pressure part specification model and pipeline size determination, may the more accurate computing system pressure loss, the pressure loss include: The oil loses , the local pressure after the pipeline along the regulation pressure damages flows after the valve class part pressure loss, namely:
(4.1)
System adjustment pressure:
(4.2)
In the formula: P0For hydraulic pump working pressure or leg adjustment pressure; P1In order to execution working pressure.
If calculates in the primary election system working pressure time the is sketchier than designation pressure to lose is much bigger than, should remove entire related part, auxiliary specification, again definite pipeline size.
4.2 systems give off heat
The system gives off heat originates from the system interior energy loss, like the hydraulic pump and the functional element power loss, the overflow valve overflow loses, the hydraulic valve and the pipeline pressure loss and so on.
The system gives off heat the power P computation
(4.3)
In the formula: PB is the hydraulic pump power input (W); η Is the hydraulic pump overall effectiveness index
If in a operating cycle has several working procedures, then may act according to each working procedure the calorific capacity, extracts the system unit time the average calorific capacity:
(4.4)
In the formula: T is the operating cycle cycle (s); ti For i working procedure operating time (s); pi is in the circulation the i working procedure power input (W).
4.3 systems efficiency
The hydraulic system efficiency is by the hydraulic pump, the functional element and the hydraulic pressure return route efficiency determined
The hydraulic pressure return route efficiency generally may use the type to calculate:
(4.5)
In the formula: p1，q1；p2，q2；…… For each functional element working pressure and current capacity; pB1，qB1；pB2，qB2 is each hydraulic pump supplies the oil pressure and the current capacity.
Hydraulic system overall effectiveness index:
(4.6)
In the formula: For hydraulic pump overall effectiveness index; In order to functional element overall effectiveness index; For return route efficiency
5 draws up the regular worker mapping and the compilation technology document
Passes through after the hydraulic system performance and the essential revision, then may draw up the regular worker mapping, it including plan hydraulic system schematic diagram, system pipeline assembly drawing and each kind of non- standard part design drawing.
In the official hydraulic system schematic diagram must mark various hydraulic pressure part the model specification. Regarding automaticity higher engine bed, but also should include the movement part the cycle of motion chart and the electro-magnet, the pressure switch active status.
5.1 determinations hydraulic system parameter
May know by the operating mode analysis in, the labor enters the stage the load strength to be biggest, therefore, the hydraulic cylinder working pressure according to this load strength computation, according to the hydraulic cylinder and the load relations, p1=40×1