Components

The Pump transforms primary engine’s mechanical energy into hydraulic fluid’s flow energy. In mobile technique fluid power drives and hydrodynamic transmissions are used. Both get the energy from the diesel engine.

Hydrodynamic transmissions ,as a rule, are used in car transmissions, but sometimes for transmissions of an operating element (for example in heavy rope excavators). At the moving of such machines as graders, bulldozers, frontlifts, tractors etc., burden on the transmission constantly changes. As result of it, the operator always has to select modes of running. To free him from this laborious work and to defend the transmission from hard dynamic influence, they use automatic gearbox which is managed by a hydraulic transformer. It passes the energy on at the cost of movement speed of hydraulic fluid. Hydraulic transformer can automatically change the rotating frequency of an output shaft depending on the changes of torque moment, operating on this shaft. By the way, the crankshaft’s rotating frequency of diesel engine can remain continuous. Hydraulic transformer consists of an impeller, turbine and stator. Impeller, joint with engine crankshaft, accelerates the operating fluid up to high speed; getting onto the turbine blades, gives it its kinetic energy, making the output shaft rotate. The stator services for changing contact ratio and providing required technical characteristics of hydrodynamic transmission.

Impellers of hydraulic transformers in principle don’t practically differ from one another. They consist of definite number of blades installed under the corresponding ankle.

 

Hydrostatic power drive works by different principles. At the rotating of pump power shaft by one turn a definite amount of operating fluid displaces out of it. Influencing on operating fluid, enclosed in supply line and control apparatus, it makes the fluid move. Accordingly, such an amount of fluid (not counting leakage) occurs in the hydraulic engine and activates it moving by the definite quantity sucker of the hydraulic cylinder or rotating the hydraulic engine’s shaft. At the continuous rotation of the pump shaft the cycle of operating fluid’s displacement repeats, forming a stable flow. In machine building hydraulics exists a wide variety of displacement pump types and their fulfillment. In hydraulic shafts of cars established fixed construction of pumps. Displacement pumps are characterized by speed and power parameters.

 

Incoming. Minimal and Maximal rotation frequency of power shaft (nmin; nmax; rpm). In this range of values the pump works steadily. At the rotation frequency of power shaft over the published data occur off-design modes which at the end lead to pump’s untimely going out of order.

Outcoming. Volumetric capacity (v, cm3) – is the amount of operating fluid displaced by the pump for one turn of the power shaft. Product of rotation frequency of power shaft on the sixe of volumetric capacity gives the account of operating fluid’s cost per time unite (Q, dm3/min). Pumps with ability to regulate the volumetric capacity got wide spread occurrence. At the constant rotating frequency of power shaft they can change the amount of operating fluid cost from zero to maximal value.

 

Incoming. Maximal and nominal torque of power shaft

Outcoming. Hydraulic pressure

 

The pump itself doesn’t develop pressure. If connecting output port of a pump to hydraulic reservoir directly, then it’ll be sucking out the operating fluid at almost zero pressure. The pressure is made by loading which affects the hydraulic cylinder or hydraulic engine. External force affects the fluid through the sucker of the hydraulic cylinder (or swinging knot of hydraulic engine) transferring it to the stress position, that is producing pressure in the hydraulic system. The quantity of this pressure is proportional to the active external load and reciprocally proportional to the work area of the sucker (or swinging knot of hydraulic engine). The pump, overcoming this pressure, displaces operating fluid into hydraulic system thus activating the hydraulic engine.

The pressure also can be created within the working hydraulic system if the flow of operating fluid is prevented by a throttle, not fully opened window of a hydraulic valve (a valve) or other local resistance. To overcome the resistance the flowrate of operating fluid in bottleneck increases thanks to pressure growth under the local resistance. In this case yet the pump puts the operating fluid under the stress, overcoming the hydraulic resistance. The less area of section of local resistance, the higher pressure which is necessary for the flow to get over it.

Produced pumps have a pressure limit, which they can get over. According to accepted maximal pressure limit resistance parameters and areas of operating pump elements are calculated.

Each type of a pump has in principle different swinging knot. Let’s consider most spread types of pumps.

 

Gear pumps are divided into two types – external and internal gearing. Gear pumps of external gearing present gear pair with two same gears, rotating in carcass. Drive gear is tightly connected with power shaft, and driven gear is installed on an axle freely. Gears are covered by internal cylindrical surfaces of the carcass. Interstice between gears and shears and also between teeth and internal cylindrical surfaces of the carcass are minimal. They should provide unobstructed rotating of gears at the drop of temperature of operating fluid from -30÷-40 °Ñ to +80÷+90 °Ñ and also minimize the size of leakage.

At rotating of gears operating fluid from soaking cavity falls into throats of teeth, i.e. spaces limited by two teeth, side walls and internal cylindrical surfaces of the carcass. These amounts the pump transfers into ingoing side of the pump.

At approach action tooth of the drive gear plunges into the hollow of the driven one. At this moment the operating fluid is displaced from the hollow and moves to the hydraulic system. Then, in turn, teeth of the driven gear falls into the hollow of the drive one and new portion of operating fluid rushes toward the hydraulic system. During one rotation of the power shaft all teeth of both gears come to approach action and displace definite amounts of operating fluid, sum of which makes up the work space of a pump.

Gear pumps of internal gearing possessed inside-installed gearwheel with internal teeth, which come to approach action with a smaller inside gearwheel which external teeth. The gearwheels are installed against one another with eccentricity (offset). Between them a crescent-shaped element is installed which with its work surfaces covers from one side internal, from the other – external teeth of both gearwheels. The crescent-shaped element divides soaking and forcing cavities. The smaller gearwheel with external teeth appears to be drive one and freely installed in bearing. Forcing of operating fluid works the same way, at the expense of displacing amounts from the gearwheel hollows.

Gear pumps of internal gearing are less noisy, possess better characteristics, but more laborious in producing and expensive.

Wide spread of power shaft mobile hardware got the gear pumps of external gearing. They are simple in producing, cheap and unpretentious at working. Such pumps steadily work with foul operating fluids with solid particles up to 40 micrometers.

Wide usage gear pumps found in construction and road, communal, agricultural equipment. They are used in power shafts with intermediate pressure – up to 16,0÷18,0 mPa. They’re often installed on the knot of additional diesel engine power selection for shaft of auxiliary hydraulic systems. Gear pumps supply limited slewing excavators, bulldozers, pavement rollers, fork lifts and others. In Russia gear pumps are produced at OAO “GIRDOSILA” (Kirovograd) and Group of Companies “Vinnizky Aggregative Factory”.

Mostly mentioned producers make single-sectional pumps. For each dimension type of a pump they pour off its own aluminum carcass and cover. Molding rough stocks need a lot of machining. A lot of valuable material goes to waste. In developed machine building world, especially in Italy, the other approach is used. On specialized light alloy factories produce several dimension types of aluminum long-length profiles with special configuration in section. They are only used for gear pumps production. Special profiles differ by its high preciseness and small dimensional allowance for mechanical treatment which reduces to the minimum.

Different dimension types of profiles define group of a future pump: superlight, light, intermediate and etc.

A rough stock is clipped from the profile by the definite value, which defines the dimension type of a definite group. Gears are made of the according size too. Flange covers and power shafts are produced with port size on standards of DIN or SAE. Dimension type row of pumps in this groups differ only in length. Remaining overall dimensions are the same. This approach made it possible to produce pumps with a long line of pump work sizes. Pump sections of each group as well as previous and following can be connected into a single knot. Thus, it’s possible to gather up in one carcass two, three and even four pumps of different work space. Limits in such construction are only in solidity of power shaft and common overhanging length.

Multisection of gear pumps placed on one power shaft and getting energy from the same engine, enabled to create machines with independent outline of hydraulic drive. Such technical decisions visibly make operating the machine easier, lower power consumption, increase the reliability.

 

Lamellar pumps consist of a carcass with rounded cylindrical camera in which eccentrically installed rotor, hardly connected to the power shaft. In rotor radial slots are made. In them plates are movably installed. Ends of the plates are in constant contact with internal cylindrical surface of the carcass. Between rotor with plates and side walls of the carcass, as in gear pumps, a small spacing is foreseen.

At rotating of the rotor in soaking cavities plates move out. It occurs because of centrifugal forces and back-pressure of the operating fluid. After going through the extreme point (maximal distance from the rotor’s axle to internal cylindrical surface of the carcass) plates start going in rotor’s slots at the expense of reaction from cylindrical surface of the carcass. At this moment the fluid from work camera is forced to hydraulic drive system. Construction of such a pump is a single-stage. It can be regulated, i.e. can change work space by changing the eccentricity. For the purpose of increasing productivity, saving a minimal overall size, lamellar pumps are produced multistage. In such construction at one turn of power shaft two or more trips of plates take place by internal profile of carcass making a special configuration. But multistage lamellar pumps can not be regulated.

Advantages of lamellar pumps – their simplicity and reliability. Disadvantage – unstable work in cold temperature of environment. That’s why on Russia mobile cars they didn’t find a wide application. In western countries lamellar pumps are widely used in communal facilities and some road-building machines.

 

This kind of pumps has found its application mostly in heavy road-building equipment, farming combines and other complex machines.

Axial-piston pump consists of a block of cylinders and pistons, which move in these cylinders. At the stage of soaking up the piston move out of cylinders, filling the work hollows with fluid.

In open hydraulic schemes work hollows of pump are filled in from a reservoir at the cost of pressure of operating fluid column. Hydraulic reservoir is installed over the lever of the pump.  Inflated hydraulic reservoirs are also used in which a surplus air pressure is created. In closed hydraulic schemes soaking is produced by the steam of discharge and re-charge.

After the piston is moved to maximal distance, the soaking process finishes and forcing begins, at which piston goes to the depth of cylinder, displacing all the operating fluid into the hydraulic system. At one turn of power shaft each piston succeeds a full cycle of movements: from its initial position to its most extended (or drawn-in) position in an corresponding cylinder, thence from maximal drawn-in position (or extended) to initial.

Dividing of soaking and forcing steams is produced by a dispenser with crescent-shaped with work windows. Its working surface is performed in flare or spherical. The dispenser installs at the end of cylinders’ block. In axial-piston pumps summed-up square of end section of piston that are in forcing cycle, is a work area of swinging knot. Moving of the piston in soaking as well as in forcing cycles provides two principal types of pump construction: with a sloping end of cylinders and with swash plate. In first case the block of cylinders will be sloped against the power shaft under the ankle of 26°. The carcass of such pumps has a G-shaped form. The pumps with constant displacement from some leading companies (for example, BOSH, REXROTH) have the slope ankle of cylinder block of 40°. On the power shaft perpendicularly to its axle a disc is installed, on which with the help of spherical hinges, the connecting rods of pistons are set. Second end, with also help of spherical hinges, the connecting rods are joint to pistons. Pumps with the slope ankle of cylinder block 40° connecting rods are missed and pistons are created to be conic. Pumps with sloping cylinder block usually have 7 pistons.

The work area of the disc accordingly is sloped under the same ankle against the end surface of cylinder block (so it looks like V-shaped figure). Thus the interstice between spherical embedding of connecting rod on the disc and the position of cylinder holes at the end of block are different (by analogy in V-shaped figure the distance between compiled pieces below is less and above is more). That’s why pistons from the external side of surface of G-shaped carcass are always extended from the cylinders’ block and from its internal side are drawn-in. From side faces pistons take interpositions. 

At the rotation of power shaft and accordingly the above mentioned disc the pistons by its side face move the cylinders’ block and simultaneously make the reciprocal motions, by turns extending out of its cylinders and soaking in again. There are constructions of pumps when the power shaft moves the block of cylinders by teeth gearing, transferring the rotation under an ankle. This technical decision enables to unload the pistons from the affection of radial (side face) forces. At changing of slope ankle of the block of cylinders against the power shaft, amount of work space of the pumps changes too. In pumps with slop block of cylinders, its slope ankle changes only to one side. That’s why the slope ankle is regulated from values close to zero, up to maximum. Corresponding, the amount of the steam can change, but not its direction. Pumps with nonconstant work space are equipped with various regulators: constant power, pressure, cost and etc. Regulators enable to provide required technical characteristics of pump control.

Axial-piston pumps with slope ankle of block of cylinders are wide spread in open hydraulic schemes. Such systems of hydraulic drive possess single-stocked and piston executive hydraulic cylinders. Acceptable degree of operating fluid’s pollution for pumps with sloping ankle of block of cylinders makes 25 micrometers.

In Russia a wide variety of pumps with sloping ankle of cylinders’ block offers OAO “PnevmoStroyMashina” and OAO “Shakhtinsky factory “GIDROPRIVOD””. In dimension type line of these factories there’re hydraulic machines from 12 to 250 cm3. Shakhtinsky factory serially produces pumps with sloping ankle of cylinders’ block of 40°. This hydraulic machine with constant work space of 56 ñì3 is compact, light and is meant to work with a bigger pressure than its analogs. In pumps with sloping washer the block of cylinders is accordingly installed with power shaft and hardly tightened to it. Power shaft enter through the hole of the washer which is installed in carcass. Its work space lies under the ankle against axle of power shaft. Pistons with the help of spherical hinges that are joint to the shoes which with the flat surface lean on the work space of the washer. Pumps with sloping washer have usually 9 pistons.

At the rotation of power shaft the block of cylinders passes the movement onto pistons which are sliding on shoes onto the flat surface of the sloping washer, simultaneously make reciprocal motions, soaking up the operating fluid while moving from the block of cylinders and forcing it to hydraulic system while pulling.

At the change of slope ankle of the washer against the axle of cylinders’ block and, correspondingly, the power shaft, the work space will change as well. At the position when the surface of sloping washer is perpendicular to the block of cylinders (i.e. its slope ankle makes 90o) the work space equals zero and the operating fluid doesn’t go in hydraulic system. In this case pistons rotate altogether with the block of cylinders but don’t make the reciprocal motions. If continue sloping the ankle of the washer then the work space increases, but the direction of regulative operating flow changes as well. Forcing supply line becomes exhausting, and exhausting – becomes forcing. This feature of steam reversibility finds a wide application in close hydraulic schemes: hydrostatic transmission (GST) of machine running or operating parts’ drive of rotary action.

GST are used in frontlifts, industrial tractors, farming combines, tree crop harvesters. Operating parts with rotary action have drilling rigs, snow and mechanical grain loaders, and also other equipment. Pumps with sloping washer for hydrostatic transmission are equipped with additional systems which are installed in one single carcass. These are the replenishment pumps, safety and anti-cavitational valve, ventilation valves of operating fluid, soaking filters, regulators (of pressure, discharge, constant power and etc.. in addiction, the regulated pumps can be equipped with different systems of proportional managing: mechanical, hydraulic, electric.

Pumps with sloping washer are absolutely more progressive and efficient but demand more preciseness at making, and at operating – culture of service. Degree of filtering should no more than 10 micrometers.

Axial-piston pumps can work under the pressure of 35,0 MPa.

Leading foreign companies produces pumps with sloping washer for the work under nominal pressure of 42,0 MPa.

Pumps with sloping washer in Russia are produced by OAO “Kovrovsky electro-mechanical factory” (Vladimirskaya region). OAO “GIDROMASH” (Bashkorstan, c. Salavat), OAO “Pnevmostroymashina” (Yekaterinburg).