Hydraulic system for driving a vibratory mechanism
A hydraulic system for driving a vibratory mechanism of a compaction roller includes at least one hydraulic motor connectable to a vibratory mechanism and a primary hydraulic pump fluidly connected to the at least one hydraulic motor and ordered for supplying pressurised hydraulic fluid into the at least one hydraulic motor. The hydraulic system further includes another hydraulic pump fluidly connected to the at least one hydraulic motor and ordered for supplying pressurised hydraulic fluid into the at least one hydraulic motor. A corresponding method for controlling a vibratory mechanism of a compaction roller is also provided.
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This disclosure relates to a hydraulic system for driving a vibratory mechanism of a compaction roller. The hydraulic system consisting of at least one hydraulic motor connectable to vibratory mechanics along with a hydraulic pump fluidly connected tothe at least one hydraulic motor and ordered for supplying pressurised hydraulic fluid to the at least one hydraulic motor. The disclosure also relates to a corresponding way of controlling a vibrator mechanism of a compaction roller. Thehydraulic system may be set up onto a compaction machine containing a single, double or more compaction rollers.
Compaction machines are used for compacting the ground on construction work sites to accomplish a smooth and flat ground surface, in particular in earthwork and street building. The ground surface may contain soil, gravel, asphalt and thelike. The compaction machine comprises at least one substantially cylindrical compaction roller which presses the dirt level. The compaction machine relies partly on its static mass and partly on a dynamic compacting force to generate a high compactingforce at the contact surface between the compaction roller and dirt surface. The dynamic compacting force is generated by operating a vibratory mechanism associated with the at least one compaction roller. The vibratory mechanism comprises at least oneweight that is eccentrically offset from a rolling axis of the compaction roller, and upon rotation of their weight by way of vibration push a centrifugal force is generated due to the eccentricity and a relatively high inertia, thereby producing thedynamic compacting force.
Compaction machines on the job site generally drive backward and forward at a sequence of for example 30 seconds. During every change of management the shaking drive is preferably switched off for preventing detrimental effects on the compactedsurface. The eccentric mass has large inertia that’s accelerated and decelerated each time the machine reverses the direction of travel. To prevent interference with natural frequencies of the construction of the machine and to improve the productivity,the vibration push need to be hastened and stopped quickly, rather than under 10 seconds and more preferably in less than 5 seconds. The shaking drive is typically of hydrostatic nature. The torque to accelerate the inertia isinverse proportional to the launching time. Thus the ability of the eccentrics’ hydraulic pumps and motors is designed for this start/stop activity. Throughout the steady run the needed torque (rotary power) is generally less than half of thestart-up torque.
In traditional hydraulic systems for vibration pushes comprising a fixed displacement pump a relatively large quantity of energy is lost in throttling; losses brought on by the difference in supplied flow by the pump and consumed flow by the motor.The flow difference, which gradually declines with increased motor rate, is directed back into the tank by means of a pressure relief valve. Document WO2011095200 describes a solution for decreasing the degree of energy losses without necessarily compromising onacceleration level. This solution includes a hydraulic accumulator and valve assembly for storing the kinetic energy of the eccentrics during the deceleration and for reusing the energy to quicken them again. There’s nevertheless still room forimprovements in regards to fuel efficiency and cost-efficiency of the compaction machine.
It is desirable to provide a hydraulic system which provides improved fuel performance of the eccentric drives and enables use of as power source with less maximal output power while keeping a quick acceleration phase of the eccentric drive.
The disclosure concerns, according to a first aspect, a hydraulic system for driving a vibratory mechanism of a compaction roller, whereas the hydraulic system containing at least one hydraulic motor connectable to vibratory mechanism and afirst hydraulic pump fluidly connected to the at least one liter engine and arranged for providing pressurised hydraulic fluid into the at least one liter engine.
The disclosure, according to the first aspect, is characterized in that the hydraulic system further comprises a second hydraulic pump fluidly connected to the at least one hydraulic motor and arranged for providing pressurised hydraulic fluidto the at least one hydraulic motor.
In conventional hydraulic systems for driving a vibratory system a power supply, typically a petrol engine pushes a single fixed displacement hydraulic pump for providing hydraulic fluid to a hydraulic motor via a control valve assembly.Relief pressure valves offer a secure and appropriate operation of the hydraulic system by eliminating excessive and potentially harmful pressure build-up from the hydraulic system. The only fixed displacement pump has to have enough flow capability toaccelerate the hydraulic motor and the affiliated vibratory mechanism to a nominal speed. During the speed period of this vibratory mechanism the only fixed displacement hydraulic pump consistently provides high flow volumes. On account of this constantflow of this pump approximately half of the energy will be dissipated at the strain relief valves, since the hydraulic motor at the eccentrics speed up continuously and the flow through the hydraulic pump increases from zero to complete pump flow. Thepressure relief valve, which influences the speed level of the hydraulic motor, is chosen to prevent any harms of this hydraulic system due to excessive pressure. The only fixed displacement pump program may consequently expect a relativelyhigh power output in the engine throughout the comprehensive acceleration time.
The hydraulic system according to a first feature includes a first and a second hydraulic pump fluidly connected to the at least one hydraulic motor and are both organized for supplying pressurised hydraulic fluid to the hydraulic motor. Thisarrangement empowers, by appropriate dimensioning and operation of their first and second hydraulic pumps, improved fuel efficiency of the eccentric drives while keeping a quick acceleration phase of the eccentric drive. These advantageous aspects may forexample be realised by supplying pressurised hydraulic fluid into the at least one hydraulic motor from just one of the first and second hydraulic pumps during a first part of a hydraulic motor acceleration phase, and to supply pressurised hydraulic fluidto the at least one hydraulic motor from both of the first and second hydraulic pumps during a second part of the hydraulic motor acceleration phase. This structure has the benefit that each hydraulic pump may exhibit a smaller displacement comparedwith that the displacement of the single fixed displacement pump in line with the conventional solution. Operation of a smaller displacement pump requires less engine power compared to operation of a bigger displacement pump in precisely the exact same engine speed during theacceleration phase because less leak, i.e. energy will be dissipated in the pressure relief valve. After a specific time period of operation of one hydraulic pump also the second hydraulic pump is operated. The combined displacement of the firstand second hydraulic pumps may be chosen to correspond to the displacement of their conventional single pump design, like the hydraulic motor might be accelerated to the desired rate.
According to farther aspect of this revelation, the hydraulic, system further may comprise a hydraulic accumulator fluidly connected to the at least one hydraulic motor. Thereby at least part of this kinetic energy of this eccentric can duringdeceleration thereof be converted into hydraulic energy and temporarily stored at the hydraulic accumulator, and upon after acceleration of the eccentric the stored hydraulic energy can be used to quicken the eccentric. The use of this accumulator enablessignificant reduction or even a complete elimination of dissipation of energy at the relief valve, therefore reducing total gas consumption.
According to yet a further feature of the disclosure, among the first and second hydraulic pumps has a bigger maximal displacement volume than the other of their first and second hydraulic pump. Both pumps in sum guaranty the nominalspeed of the hydraulic engine is accomplished. The recovered amount of rotary power of the eccentrics is obviously less than the power required to hasten the eccentrics to exactly the identical speed again due to ordinary inevitable energy losses associated with theenergy conversion and friction in bearings etc.. However, the required additional energy in form of further fluid flow is relatively small because the energy reduction is comparatively small. In the event the additional energy is supplied after completed discharge of theaccumulator that the entire fluid flow that must be supplied from the first and second pumps is relatively large since it corresponds with the flow in minimal motor speed. The supply pressure must also be somewhat high to supply the mandatory accelerationlevel. The present engine torque input signals present pump supply pressure times present total pump supply stream. Therefore, the engine must have the ability to supply a relatively large peak output power in this short period to accelerate the hydraulic motorup into the nominal speed. Also the parts of the power train, especially the engine and the pump have to be designed with this peak power.
However, if the additional fluid flow in the pump is supplied concurrently with the flow in the accumulator the deliver flow amount should only correspond to said energy reduction occasioned by said energy conversion connected with thehydraulic accumulator through deceleration/acceleration. Consequently, by having a bigger displacement pump and a larger displacement pump, and by working only the bigger displacement pump through the acceleration period, i.e. as a immersion pump,and by working the larger displacement pump just upon having reached the nominal motor speed, i.e. a steady-state manner, the motor peak power can be significantly reduced. The pump may also be be made as a high pressure pump capable ofdeliver flow at the high pressure required for adequate acceleration amount of the eccentrics. The larger pump nevertheless may be made to deliver only the steady state strain amount of the conducting eccentrics, which stress amount is significantly lowerthan the speed pressure. The larger pump may thus be fabricated in less lasting material and with lesser demands with respect to tolerances, like the price of the larger pump may be reduced. Additional since the compacted volume of thesmaller pump is comparatively modest, even at high pressure the necessary torque output in the motor shaft is comparatively small. Because of the reduced requirement of peak power the installed engine dimensions can be lessened with the effect of better fuel efficiencyand easier setup in the system. Furthermore, this solution also empowers variability at the frequency of the vibration by operating the smaller and larger pumps together or by working only the larger pump of the hydraulic system. Operation ofonly the larger pump provides a lesser frequency manner and by working both pumps simultaneously a higher frequency mode is supplied, all without the need for any additional elements for providing both different vibration frequencies.
After the eccentrics achieved their nominal speed the bigger pump could be connected too. The bigger displacement pump of the first and second hydraulic pump has a displacement quantity in the assortment of 10%-90% of the bigger displacement pump,preferably in the assortment of 20%-70%, and more preferably in the assortment of 25%-50%. The true relative dimensions of the initial and second pumps will be determined depending on the true system design including specifically the amount of energy conversion losses.
The disclosure also concerns a method for controlling a vibratory mechanism of a compaction roller according to the first facet. The vibratory mechanism is mechanically connected to at least one hydraulic motor arranged to be provided withpressurised hydraulic fluid in the primary and a second hydraulic pump. The method comprising steps of
Quickening the hydraulic motor by providing pressurised hydraulic fluid to the one or more hydraulic motor from only one of the first and second hydraulic pumps during a first portion of a hydraulic, motor speed phase, and
Quickening the hydraulic engine by providing pressurised hydraulic fluid to the at least one hydraulic motor from the first and second hydraulic pumps during a second part of the hydraulic engine acceleration phase. This method willexhibit advantages corresponding to the hydraulic system of this first aspect described previously. A smaller and a bigger hydraulic pump enable usage of a more cost-efficient and simple elements to decrease the energy intake of this vibratory drive of acompaction system and permit substantial decrease in engine peak torque necessity. Additionally, the smaller displacement pump might be made to withstand a higher working, pressure compared to the larger hydraulic pump since the bigger displacement pump possibly arranged to be operated first upon having reached the nominal motor speed. In a point where the acceleration phase associated with the smaller displacement pump has terminated and the steady-state has been reached, a less complex and less costly pumpis considered adequate.
Further benefits are accomplished by implementing one or even a number of the characteristics of the dependent claims.
According to a further feature of the disclosure, one of the first and second hydraulic pumps is a variable displacement pump and the other of the first and second hydraulic pumps is a fixed displacement pump. This layout enables an infinitevariability of this frequency in a certain range if necessary for optimizing the compaction result connected to the environmental substance. It’s helpful to replace just the smaller displacement pump by a variable displacement pump and also to maintain thelarger displacement pump for the basic steady state flow. The potential combination of high flow at low pressure and small variable flow at high pressure with both of these pumps permit a low-cost variable frequency drive.
The disclosure further relates to a compaction machine containing this type of hydraulic system, a computer program comprising program code means for executing the steps of the described system, a computer readable medium carrying out a computer programcomprising program code means for executing the steps of the described method when said program product is run on a computer, and a control unit for controlling the described hydraulic system.
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