The invention relates to a method and a system for controlling the driving engine and hydraulic pumps in a hydraulic machine, as well as a pile driving rig.
A hydraulic machine, such as an earth moving machine, a forest machine or an excavator, comprises several hydraulic actuators for controlling and moving the apparatuses of the machine (for example the crane and the bucket of an excavator) in a suitable way. For example in a hydraulic pile driving rig, hydraulic actuators are used for controlling the leader, for moving the hammer along the leader by hydraulic winches, and for generating the impacts of the ram. The pressurized medium (typically hydraulic oil) for these actuators is provided with a desired volume flow and pressure by means of one or more hydraulic pumps in the machine. In machines, hydraulic pumps are driven by the driving engine which is still—almost without exception—a combustion engine and typically a diesel engine.
At present, a driving engine that supplies power to hydraulic pumps for pumping pressurized medium to hydraulic actuators, is controlled to provide hydraulic power sufficient for producing the power/torque and velocity/rotation speed required by the hydraulic actuators in all situations required by the operation to be performed by said machine. This has to be done because in a situation in which the power demand of the hydraulic actuators becomes greater than the power generated by the driving engine at the time, the combustion engine used as the driving engine for the machine will stop. To prevent such a situation by using present control methods, the power of the driving engine is normally adjusted in such a way that one or more hydraulic pumps in the machine is capable of generating at least the hydraulic power corresponding to the highest mechanical power required of the actuator for performing said operation or said functions. If the power demand exceeds the maximum power of the driving engine and the hydraulic pumps in use are variable with respect to the displacement, and/or if the hydraulic actuators performing the function are hydraulic engines with variable displacement, it is possible to prevent the driving engine from stalling by controlling the displacement of the hydraulic pumps and/or engines. On the other hand, when the demand of mechanical power and the corresponding hydraulic power is lower than the above-mentioned maximum power demand, pressurized medium pumped in excess is guided by control valves past the actuators directly to the return lines of the hydraulic system and thereby back to the main tank.
A drawback of the present method is that the output capacity of the driving engine (that is, the desired rotation speed and torque) always have to be adjusted according to the maximum output required for performing the operation at hand or the functions of the machine, although carrying out the functions of the operation includes many steps in which this maximum hydraulic output (that is, volume flow and pressure of pressurized medium) is not needed all the time. As a result, much of the hydraulic energy produced by the system and thereby of the energy used by the driving engine is consumed in redundant circulating of pressurized medium from the main tank of the system to the valves and via the return lines back to the main tank of the system. In many situations, it also follows that the driving engine of the hydraulic machine has to be operated at power which is higher than that needed most of the time; as a result, the energy consumption and the emissions of the driving engine become unnecessarily high when the present control method is used. Furthermore, because variable displacement hydraulic pumps are often used in present machines, the same hydraulic power can be generated by applying a number of different rotation speeds of the driving engine. Consequently, the same specific minimum output can be generated by applying different rotation speeds of the driving engine, although only one normally gives the best possible performance of the driving engine and thereby the best energy performance and the lowest possible emissions. Therefore, methods of prior art for controlling the driving engine and the hydraulic pumps often result in inadequate uses of the machine with respect to fuel economy and emissions.
It is the aim of the invention to provide a method for reducing the energy consumption and improving the energy efficiency of the driving engine of a hydraulic machine, as well as for making the driving engine of the hydraulic machine always operate at an optimal rotation speed, for achieving a minimum energy consumption. It is also an aim of the invention to introduce a system according to the method of the invention, for controlling the driving engine and hydraulic pumps of a hydraulic machine.
The aim of the invention is achieved by a method in which the rotation speed of the driving engine as well as the displacement of one or more hydraulic pumps driven by the driving engine are automatically controlled according to a predetermined value for the volume flow of the pressurized medium, set by the driver of the machine, so that the torque of the driving engine, corresponding to said volume flow, corresponds to the torque required by the hydraulic pump, whereby the driving engine will produce the desired volume flow of pressurized medium with the lowest possible energy consumption. As the power demand and thereby the pressure effective in the system increase, the volume flow produced by the hydraulic pump is automatically turned down by reducing the displacement of the hydraulic pump and, on the other hand, by increasing the rotation speed of the driving engine (when this is possible), whereby the adjusted output of the driving engine of the machine is always sufficient for performing the desired functions. To put it more precisely, the method according to the invention is characterized in what will be presented in the independent claim 1, the system according to the invention in what will be presented in the independent claim 11, and the pile driving rig according to the invention in what will be presented in the independent claim 14. The dependent claims 2 to 10 will present some advantageous embodiments of the method according to the invention, and the dependent claims 12 and 13 will present some advantageous embodiments of the system according to the invention, and the dependent claim 15 will present an advantageous embodiment of the pile driving rig according to the invention.
The method, the system according to the invention have the advantage that it can be applied to make the machine and the hydraulic system of the machine operate in such a way that the energy consumption of the driving engine is reduced and the emissions (particularly carbon dioxide emissions) resulting from the use of the machine are reduced. For example a pile driving rig used for driving rammed piles or bored piles into the ground has a high power demand. Therefore, by reducing the fuel consumption it is possible to significantly reduce the carbon dioxide emissions formed, as well as naturally also influence the costs of the pile driving by reducing the fuel costs.
In the following, the invention will be described in more detail with reference to the appended drawings, in which
The machine 10 of
The pile driving apparatus 12 comprises a leader 17 and an apparatus 26 which may be, for example, a pile driving auger, the hammer of a pile driving rig, or a vibrator. In
In the machine 10 of
For estimating if the torque Td output by the driving engine M will be exceeded, a special reference parameter to be defined for this purpose, i.e. so-called deficiency divisor h, is used in the method according to this invention. In general, in such a hydraulic system that comprises a driving engine for powering one or more hydraulic pumps, the relation between the torque output by the driving engine and the torques required by the hydraulic pumps can be assessed by defining a deficiency divisor h(i) dependent on the rotation speed of the driving engine as follows:
wherein:
Td(i) is the torque output by the driving engine at the rotation speed i,
Tpkok(i) is the total torque of all the hydraulic pumps powered by the driving engine,
n is an index representing the running number of the hydraulic pump,
m is the total number of hydraulic pumps powered by the driving engine (e.g. m=2 in the machine of
Thus, by means of the deficiency divisor h, e.g. the operation of the driving engine M and the hydraulic pumps PUMP1 and PUMP2 of the machine of
In all cases where the total torque Tptot of the torques T1p and T2p required by the hydraulic pumps PUMP1 and PUMP2 does not exceed the torque Td of the driving engine M, that is, when the deficiency divisor h>1, the requested volume flows Q1P ja Q2p of the hydraulic pumps PUMP1 and PUMP2 will be output as set by the driver of the machine applying controls in the cabin of the machine. However, when h>1, the rotation speed i of the driving engine M and the requested displacements V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 will be adjusted so that said requested volume flows Q1P and Q2p can be output with optimal fuel economy, that is, in a way that the torque Td output by the driving engine M is as close to the sum Tptot of the torques T1p and T2p required by the hydraulic pumps PUMP1 and PUMP2 (and thereby the deficiency divisor h≈1, typically 0.9 . . . 1.2 and advantageously 1.0 . . . 1.1). It should be noted that both the rotation speed i of the driving engine M and the (requested) displacements V1p ja V2p of the hydraulic pumps PUMP1 and/or PUMP2 have to be adjusted, because the real volume flows Q1t and Q2t are dependent on both of these. Therefore, the adjustment is made by searching for such a combination of the rotation speed i of the driving engine M and the displacements V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 that the volume flows Q1t and Q2t are realized but the driving engine M runs at a rotation speed at which its energy consumption is the lowest possible. In this way, the driving engine M can always be run in such a way that its energy consumption (consumption of diesel fuel) is as low as possible but it still never stalls because of the sum Tpkok of the torques T1p and T2p required by the pumps PUMP1 and PUMP2 exceeding the torque Td output by the driving engine M.
A torque value Td(i) corresponding to a given rotation speed i of the driving engine is obtained by entering the corresponding torque values, measured or provided by the engine manufacturer and corresponding to different rotation speeds i, in the memory of the control unit of the machine (e.g. in table format), or by forming a function whose graph corresponds to the torque graph, measured or provided by the engine manufacturer, as well as possible in the coordinate system of rotation speed and torque. A suitable function for calculating the torque Td(i) corresponding to a given rotation speed i of the driving engine M is, for example, the graph of the secondary equation that follows the torque graph obtained by measuring or provided by the engine manufacture as well as possible
Td(i)=Ai2+Bi+C, [2]
wherein A, B, and C are constants.
This kind of an adaptation is presented for the machine of
It is also possible to adapt the graph by applying different values for the constants A, B and C at different ranges of the rotation speed, whereby the adaptation can further be made to follow more closely the torque graph provided by the engine manufacturer. It is also possible to apply other functions, for example polynomial functions of different degrees, for driving engines of different types, depending on the way of operation of the driving engine. In combustion engines, however, the torque often follows quite closely the shape of the graph of the secondary polynomial function; therefore, the secondary polynomial function in many cases represents well the relationship of the torque and the rotation speed of the driving engine.
Because the driving engine M has to power not only the hydraulic pumps PUMP1 and PUMP2 but also the auxiliary devices of the machine, such as the coolant pump, the battery charger and the blower unit of the air conditioner, the effective torque of the driving engine is used as the torque for the driving engine M in the control:
T
deff(i)=kd*Td(i), [3]
wherein
kd is a so-called auxiliary device coefficient (for the machine of
In the present case, the value kd=0.80 is used, whereby 20% of the available torque of the driving engine M is always at the disposal of devices other than the hydraulic pumps PUMP1 and PUMP2. Normally, the value of the auxiliary device coefficient may vary from Kd=0.5 to Kd=0.95, depending on e.g. the rotation speed. In some cases, a value variable as the function of the rotation speed may also be used as the auxiliary device coefficient. Thus, the auxiliary device coefficient may be determined as a value of a suitable function depending on the rotation speed. Thus, in practical applications, the equation [1] may also be written in a format in which the effect of the auxiliary devices of the driving engine on the produced torque is taken into account:
In the working machine of
The working pressures p1 and p2 of the hydraulic pumps PUMP1 and PUMP2 are measured by pressure transmitters B1 and B2. In practice, the control unit is supplied with the ranges I1min . . . I1max and I2min . . . I2max of the current values I1 and I2 as input parameters produced by the pressure transmitters B1 and B2 (for the pressure transmitters of the machine of
The relationship between the current values of the pressure transmitters B1 and B2 obtained from the system, and the working pressures p1 and p2 is obtained by the equation:
wherein
pn(i) is the measured pressure of a hydraulic pump PUMPn, that is, p1 or p2 in the machine of
In(p) is the current value corresponding to the measured pressure (that is, between 4 and 20 mA);
Inmin is the lowest current value of a pressure transmitter Bn;
Inmax is the highest current value of the pressure transmitter Bn;
pnmax is the highest pressure that can be measured by the pressure transmitter of the pump PUMPn (that is, the maximum pressure of said pressure transmitter).
Further, in the equation [5], the lower index n thus indicates the hydraulic pump which the measurement of the pressure transmitter Bn relates to.
Thus, for the machine of
The torque graph for the driving engine M is obtained, in the case of the machine according to
For the hydraulic pumps PUMP1 and PUMP2, the volume flows Q1p and Q2p requested by the driver, guideline values o1po and o2po (proportioned to the rotation speed i of the driving engine M), as well as the displacements (V1p and V2p) and the respective torques (T1p and T2p) are calculated as follows:
wherein
Qnp is the volume flow requested of the hydraulic pump PUMPn;
Qnmax is the maximum volume flow of the hydraulic pump PUMPn;
on is a relative share of the maximum volume flow of the hydraulic pump PUMPn (in percent).
In some cases, adjusted volume flow values Qnp (that is, the volume flow values Q1p and Q2p requested by the driver in the case of the machine of
Guideline control values o1po and o2po for the hydraulic pumps PUMP1 and PUMP2 are obtained by the equation:
wherein
onpo is a guideline control value for the hydraulic pump PUMPn (that is, the guideline position in percentage of the position of the control from the maximum value of the adjustment range of the control), for achieving the volume flow Qnp controlled by the driver of the machine,
Vngmax is the maximum displacement of the hydraulic pump PUMPn; and
ηnv is the volumetric efficiency of the hydraulic pump PUMPn.
A set value for the displacements V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 is obtained on the basis of the guideline rotation speed.
wherein
Vnp is thus the set value for the displacement of the hydraulic pump PUMPn, for achieving the volume flow Qnp.
On the basis of this, it is possible to determine the torque T1p and T2p required by the hydraulic pumps PUMP1 and PUMP2.
wherein
ηnmh is the mechanical hydraulic efficiency of the hydraulic pump PUMPn,
Tnp is the torque required by the hydraulic pump PUMPn;
pn is the working pressure of the hydraulic pump PUMPn.
In this way, a value for the deficiency divisor h(i) can be derived from the torques T1p and T2p required for the hydraulic pumps PUMP1 and PUMP2, defined for the machine of
If the deficiency divisor h>1, the rotation speed i of the driving engine M is adjusted in the above mentioned way, that is, in such a way that the value of the deficiency divisor will approach the value h≈1. In general, such optimization of the running of the driving engine entails, applying the equation [4], that the rotation speed i is solved from the equation:
wherein
m is the number of pumps (that is, m=2 for the machine of
Tdeff(i)=kd·Td(i) that is, the effective torque of the driving engine.
When the deficiency divisor h>1, the rotation speed i of the driving engine corresponding to the value h≈1 can be found by solving a function of optimization corresponding to the value h=1 by deriving the following equation from the equation [10]:
wherein
ηnkok is (n the total efficiency of the hydraulic pumps (ηnkok=ηnhm×ηnv). In the case of a combined pile driving rig shown in
From this equation, the zero position (iopt#) is solved in the range from imin to imax by the split half method. For the driving engine M of the machine 10 of
However, this solution does not take into account that the hydraulic pumps have a maximum displacement Vngmax which, for example for the hydraulic pumps PUMP1 and PUMP2 in the machine 10 of
wherein
n indicates the hydraulic pump in question (that is, n=1 or n=2 for the machine of
ηnvol is the volumetric efficiency of the hydraulic pump PUMPn. For the hydraulic pumps PUMP1 and PUMP2, ηnvol=ηvol=0.95.
imin_n is the lowest rotation speed of the driving engine, at which the volume flow Qnp is supplied by the PUMPn (that is, for example PUMP1 or PUMP2).
The selected optimum rotation speed iopt is the highest rotation speed determined according to the volume flows Qnp requested by the single hydraulic pumps PUMPn, or the optimum rotation speed determined by the equation (11), if it is applicable, that is, if the maximum displacement Vngmax of any of the hydraulic pumps is not exceeded. Consequently, the optimum rotation speed is selected by comparison:
i
opt=MAX(imin_1,imin_2 . . . imin_m,iopt#) [13]
where m indicates the number of hydraulic pumps; that is, m=2 in the embodiment of
Next, the realized displacements (V1t and V2t) are selected for the hydraulic pumps PUMP1 and PUMP2. In general, this is done by comparing three values for each hydraulic pump driven by the driving engine M: the requested displacement multiplied by the deficiency divisor h (h*Vnp), the requested displacement (Vnp), and the maximum displacement of the hydraulic pump (Vngmax), and by selecting the lowest value:
V
nt=min(h·Vnp,Vnp,Vngmax) [14]
In other words, if the deficiency divisor h<1, then the displacement multiplied (scaled down) by the deficiency divisor h determined on the basis of the volume flow Qnp requested by the driver applying the control) is selected. If the deficiency divisor h>1, then the requested displacement Vnp is selected. If both of the above displacements exceed the maximum displacement Vngmax of the hydraulic pump (the equations for calculation make this possible before this step), then the maximum displacement Vngmax is selected. Thus, in a case where h<1, the displacement Vnp of each hydraulic pump is reduced to the value Vnt<Vnp accordingly.
Consequently, in loading situations in which one of the hydraulic pumps produces a low pressure but has a maximum displacement, and another hydraulic pump produces a high pressure but has a small displacement correspondingly, and the deficiency divisor h is slightly below 1 (typically from 0.9 to 1), then the displacement of the hydraulic pump producing the higher working pressure is restricted first when this control method is applied. This will be continued until the displacement Vnp multiplied by the deficiency divisor h becomes lower than the maximum displacement Vngmax.
In the machine of
wherein
Inop is the control current for the hydraulic pump PUMPn, corresponding to the displacement Vnt
Inopmin is the minimum control current for the hydraulic pump PUMPn,
Inopmax is the maximum control current for the hydraulic pump PUMPn (thereby corresponding to the displacement Vngmax).
When a combined pile driving rig of
The control of the pumps PUMP1 and PUMP2 of the machine 10 of
The second step prevents the hydraulic pumps PUMP1 and PUMP2 from providing the actuators with too much output. This step has second priority in the control. The hydraulic pumps PUMP1 and PUMP2 are controlled according to the loading (electronic control). This is implemented in a way known as such, that is, by comparing the pressure difference between the working pressures p1, p2 and the load pressures of the hydraulic pumps. Thus, the control routine can be, for example, of the following type:
Pressure difference>20 bar→the displacement Vp1 of the hydraulic pump PUMP1 and/or the displacement Vp2 of the hydraulic pump PUMP2 is turned down
Pressure difference=15 to 20 bar→the displacements V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 are not changed
Pressure difference>15 bar→the displacement V1p of the hydraulic pump PUMP1 and/or the displacement V2p of the hydraulic pump PUMP2 is turned up.
The third step adjusts the displacement V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 according to the sum of the openings of the control valve stems. A program in the control unit adds up the volume flows Q1p and Q2p (e.g. valve current values) requested by the driver applying the controls, and adjusts the displacements V1p and V2p of the hydraulic pumps PUMP1 and PUMP2 to correspond to these volume flow values Q1p and Q2p. Instructions for controlling the currents of the control valve stems are taken from the same valve block. The control unit adjusts the rotation speed i of the driving engine M according to predetermined rotation speeds, depending on the movement performed by the driver of the machine 10.
The method and the system according to the invention for controlling the driving engine and the hydraulic pumps of a machine can be implemented, in many respects, in a way different from the example embodiment presented above. As can be understood from the above presented theory, the method can also be applied for the control of systems which, deviating from the machine 10 of
In principle, the method according to this invention can be applied in any machines with a driving engine for powering hydraulic pumps that supply pressurized medium to the apparatuses of the machine. Further, the application of the method is not limited to the pressurized medium used in the hydraulic system. In principle, the same method could also be applied in systems applying a gaseous pressurized medium (compressed air). Thus, the method according to the invention is not limited to the above presented example embodiments but it can be implemented in various ways within the scope of the appended claims.
Filing Document | Filing Date | Country | Kind |
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PCT/FI2016/050225 | 4/8/2016 | WO | 00 |