FI104580B - Method and arrangement for regulating inlet feed pressure - Google Patents

Description

Method and apparatus for regulating feed pressure 104580

The present invention relates to a method for controlling the feed pressure in a hydraulic system comprising a feed pump for providing feed pressure, at least two hydraulic actuators, measuring means for measuring actuator pressure levels, and a pressure medium flow channel. The invention further relates to a hydraulic system according to the method.

10 Especially for forestry machines, systems have been developed in which the forward movement of the forestry machine is carried out with mechanical feet instead of wheels. This type of forestry machine causes less damage to the undergrowth of the forest. In addition, walking on difficult terrain is easier with feet than with a wheeled forestry machine.

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In order to ensure sufficient reliability and mobility, a walking machine using the prior art requires six feet and three degrees of freedom for each foot. In this case, the machine has a total of 18 so-called. servo axes. In order for these all servo shafts 20 to be operated at optimum efficiency, each servo shaft would need its own servo pump, i.e. a total of 18 servo pumps. In practical implementations, e.g. price, space requirements, reliability and serviceability limit the number of pumps used and the type of control used. In practice, the number of pumps is limited to one or two and the actuator is controlled by valve control.

In terms of efficiency, it is important to adjust the feed pressure of the hydraulics so that the feed pressure corresponds to the highest pressure of the load 30 seen with the actuators. This method is known per se. as load sensing (LS) hydraulic system. A typical load sensing hydraulic system is shown e.g. German Patent Publication DE-35 46 336. In practice, load-sensing hydraulic systems are mechanically hydraulically implemented in the so-called "patent application". utilizing load-sensing valves 35. When moving the actuator, these valves open a special load-sensing channel in a bypass valve chain integrated into a specific valve actuator. Using this chain, the pump regulator provides the highest load capacity pLmax required to move the actuators 104580 2. The pump regulator adjusts the pump supply pressure ps by a pre-set differential pressure Δρ above the corresponding maximum load pressure pLmax, ensuring that all movements can be performed.

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European patent application EP-104 613 discloses an electro-hydraulic system especially for machines having a plurality of working cylinders. One such example is a bucket loader having its own working cylinders for turning and lifting the bucket and a hydraulic motor for moving the bucket loader. The system disclosed in the publication seeks to achieve an optimum flow rate for the particular load situation. The system uses two pumps with different maximum output flows. In this case, either pump can be operated alone or at maximum loads, both pumps can be used simultaneously. The system is controlled on the basis of signals from the sensors (speed / position) connected to the cylinders and control commands from the operator so that the flow rates generated by the pumps correspond to the respective operating and loading situations. However, this publication does not disclose the specificity of the title application that only the pressure level of the actuators that perform the positive work is used to determine the pressure requirement.

German patent application DE-35 35 771 discloses a hydraulic system 25 having a hydraulic pump for applying pressure to the hydraulic system, valves for controlling actuators, a pressure relief valve and a pressure sensing line. The system measures · 1 · .. pressure in the pressure supply circuit. The pressure relief valve is connected to this »supply pressure line and to the pressure measuring line. ** 1. In these lines, the pressure relief valve is • »· closed, regardless of the absolute pressure level. In a situation where the position of a control valve in one of the actuators is changed, the pressure in the supply pressure line changes and the pressure in the pressure measuring line decreases momentarily. Thus, the differential pressure increases and the check valve opens, whereby the pressure of the feed pressure is limited by directing the flow of hydraulic fluid through the return channel to the hydraulic fluid reservoir. The system is a conventionally implemented load sensing system with control valves having pressure sensing lines. The adjustment is made hydraulically 3 104580 and no sensors have been used in the system to determine the direction of movement of the actuators.

German Patent Application DE-43 07 827 also discloses 5 electrohydraulic systems. In the system, the actuator is given setpoint values electronically, for example by potentiometers or the like, whereby the controller determines, based on the setpoint value of each actuator, the required supply pressure. This is determined mainly by the sum of the flow rates required for each actuator. The controller then adjusts the pump to achieve the desired flow rate. Conventional hydraulic load sensing valves are used for control. In addition, the system combines the load sensing lines of these valves with one-way pressure measurement valves through alternating-flow valves, whereby the highest pressure levels of the actuators can be measured. 15 The pressure measuring line has a pressure sensor for electrically measuring pressure. The system disclosed in this German publication also requires a load-sensing control valve, which e.g. complicates the structure, maintenance and adjustability of the hydraulic system.

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German patent application DE-35 32 816 discloses a control system for a hydraulic system. The hydraulic system comprises two or more actuators and at least one pump. The basic idea in this publication is that in the case of insufficient supply pressure provided by the pump, the supply pressure of each actuator is reduced; in substantially the same proportion. The purpose of this is to ensure that all the control valves are adjustable and that the volume flow M »· cannot escape from any control valve. This auxiliary pump is controlled by the actuator with the highest required pressure level.

30 This is a conventional pressure sensing hydraulics system that does not use electrical measuring and control instruments.

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German patent application DE-33 47 000 relates to an electro-hydraulic control system. The electro-hydraulic system disclosed in the publication: 35 controls a two-way cylinder / hydraulic motor comprising two .... actuator lines and valves therein. These two-way control systems are independent of each other except for the controller. The control system consists of two valves: 1 • · · 4 104580 and 4/4 proportional valves. The control system is formed in a so-called. fail-safe type, whereby, for example, when the controller fails, the control pressure is not transmitted to the hydraulic motor. The system also includes a measurement of the force generated by the hydraulic motor, whereby the thrust generated by the hydraulic motor can be limited. In addition, the pressure levels of the hydraulic motor feed pressures on both sides of the piston are measured and can be used to adjust the control valves. The system does not seek to control the pump feed pressure, but rather the pressure on the actuator lines. The hydraulic motor can be differentially controlled by placing a constant control on one side of the piston in the cylinder of the hyd-10 roller motor and on the other side a control signal corresponding to the need for adjustment to adjust the pressure and flow. The system disclosed in the publication does not use a control pump, but a volumetric flow is achieved by a constant volume pump. The system shown is relatively expensive especially for valves.

Walking the machine requires careful control of foot movements. This means that, due to their robustness, the use of normal load sensing valves for mobile machinery is not feasible. The highest load pressure can still be detected hydraulically using a separate check valve chain. However, in this case, the efficiency problem arises, which is due to the so-called. from a negative load. The hydraulic system cannot distinguish between load pressure due to load transfer 25 (positive work) or load braking (negative work). In some actuators, braking the load may result in • higher load pressure than other actuators. This gives the system the wrong idea of the required pressure level, which creates an unnecessarily high supply pressure to the hydraulic system, which degrades the efficiency of the system.

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1a and 1b illustrate one leg of a walking machine 2: 1. The leg 1 comprises the upper end of the machine 2a articulated to the body 2a by the hip joint L, the opposite end of the upper arm 3 by a knee joint. P pivoted to the lower arm 4 and lower arm pivoted to the opposite end of the tread portion 5. It is assumed that the machine is moved in the direction indicated by arrow S so that the body portion 2a of height relative to the ground remains constant.

• · «« 5 104580 The following definition agrees on the following definitions of joint movements in their range of motion. In the figure, the angle ΘΡ of the joint P increases when the lower arm 4 is rotated counterclockwise (indicated by a dashed line) in the image plane, and the angle L of the joint L increases when the upper arm 3 is rotated 5 anticlockwise (indicated by a dashed line). When the machine is moved in the direction of arrow S, the lower arm 4 actuators (not shown) to turn the lower arm 4 so that the lower arm 4 rotates clockwise, that is, the angle ΘΡ reduced. Then the knee joint P rises above the ground. The movement of the knee joint P is represented by the broken line SP in Fig. 1a. In order to maintain the machine body 2a at a constant height, the upper arm 3 must be rotated counterclockwise so that 0L increases. In this turnover, the external joint, mainly due to gravity, applied to the lower arm 4 tends to press downward from the knee joint, i.e., to rotate the lower arm 4 anticlockwise. The lower arm 4 actuators rotate the lower 15 arm 4 clockwise, which is the true direction of motion in this situation, i.e. the direction of external torque is opposite to the lower arm 4 direction. In this case, the actuators moving the lower arm 4 do a positive job. Instead, the external, mainly gravitational, external torque applied to the upper arm 3 tends to press downward from the hip joint 20 relative to the knee joint, i.e., rotate the upper arm 3 anticlockwise (0L increases). In this situation, the actuators that move the upper arm 3 also rotate the upper arm 3 anticlockwise, which is the true direction of motion in this situation. Because the external joint torque is in the same direction as the movement of the upper arm 3, the actuators work negatively.

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The situation reverses as the lower arm moves: substantially to the other side of the vertical position depicted by the dashed line.

"... This situation is illustrated in Figure 1b. At this point, the body weight • tends to rotate lower arm 4 toward the ground (angle 0P further decreases 30). Actuators moving lower arm 4 also rotate lower arm toward the ground. the joint torque is parallel to the direction of movement of the lower arm 4. That is, the actuators do the positive work, respectively, the actuators moving the upper arm 3 do: positive work because the upward movement of the upper arm 3 is opposite to the external v: 35.

Figures 1c and 1d further show a reduced difference between positive and negative work in a double-acting hydraulic cylinder. Hydraulic Cylinder Piston • 104580 is connected to a lever arm V having a m at one end. In the negative working condition of Fig. 1c, the m is moved downwardly by applying pressure medium to the first block A of the double acting cylinder to form a torque M1 on lever V. in block B, there is a pressure p2 that inhibits the downward movement of the body m. The braking pressure p2 may be greater than the thrust p at the side of the first block A of the cylinder due to the ground force g on the body m.

The force g forms a torque M2 on the lever arm V having the same direction 10 as the movement of the cylinder piston. In this situation, the pressure required for actual work is ρυ

Similarly, Fig. 1d shows a situation similar to the previous one in which the piece m is lifted up. In order to provide a lifting force, i.e. a torque M1 15, a pressure medium is applied to the second block B of the double-acting cylinder to form a pressure p2. The force g forms a torque M2 on the lever arm V, the direction of which is opposite to that of the cylinder piston. The pressure required for the positive work, i.e. the lifting of the piece m, is then p2 and is greater than the pressure ensimmäτ in the first block A of the double-acting 20 cylinder.

In the state of the art prior art hydraulic systems, in the situation of Figure 1c, the hydraulic system would generate a supply pressure based on a braking pressure of 25 p 2 in the second block B, although in reality a lower pressure p ^ • I f • «· i would suffice. disadvantages to a great extent and provide a method and apparatus for adjusting the feed pressure in the hydraulic system so as to obtain the best possible efficiency. The process according to the invention is characterized in that the method comprises at least the following: • · · v 'steps: »Il: - electronically examine the direction of motion of the actuator and the direction of external torque applied to the actuator * <« 3 v 35 to determine whether the actuator is performing positive load-shifting work,104580 is selected from the highest pressure levels of the load-carrying actuators and adjusts the feed pressure based on the selected pressure level.

The hydraulic system according to the invention is characterized in that the hydraulic system further comprises: means for electronically detecting actuators performing a positive load transfer operation based on the direction of motion of the actuator and external torque applied to the actuator, means for selecting the maximum pressure level of the actuators; means for adjusting the supply pressure at the selected pressure level pe-15.

The invention is thus based on the idea of differentiating between actuators in each case for load transfer actuators (positive work) and load braking actuators (negative work). The pressure level of the 20 load-moving actuators is then examined and the highest is selected. The supply pressure is adjusted based on the selected pressure level.

The invention provides significant advantages over the solutions implemented by the prior art. By adjusting the feed pressure of the hydraulic system according to the method of the invention, the overall efficiency of the hydraulic system can be improved, since the feed pressure is always optimal. This reduces the power consumption of the hydraulic system. In addition, the reliability of the hydraulic system is improved and maintenance intervals can be extended as the average load on the hydraulic system is reduced. Better efficiency also increases the service life of the hydraulics system, for example. as a result of slower wear.

The invention will now be further described with reference to the accompanying drawings, in which:

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.... Figures 1a-1d illustrate the principle of positive and negative work, 8 104580 Fig. 2 is a simplified hydraulic diagram for controlling the feed pressure of a hydraulic system according to the invention, Fig. 3 illustrates a reduced mechanical action of a mechanical foot, Fig. 4 Figure 5 illustrates a machine in which the invention can advantageously be applied.

Preferably, the walking machine 2 requires six mechanical feet 1, preferably with three degrees of freedom. Each leg 1 comprises at least the upper arm 3 hinged to the machine body 2a, the lower arm 4 hinged to the opposite end of the upper arm 3, and a step 5 attached to the opposite end of the lower arm preferably with two upper arms hinged to the body 2a. two independent pivot axes 20 by means of a pivotable pivot about the longitudinal pivot axis of the body, in which the upper arm is pivotable about a pivot axis. The third degree of freedom is obtained by the articulation between the upper arm 3 and the lower arm 4, whereby the lower arm 4 is pivotable in 25 vertical positions. The step member 5 may be either fixedly attached to the lower arm; 4 at one end, or the attachment may be flexible, whereby the step portion 5 i will slightly conform to the roughness of the terrain.

To move each leg 1, at least one actuator 8 is required for each 30 degrees of freedom. In this case, a first actuator 8a is provided with the hip joint to rotate the upper arm 3 and the entire mechanical leg 1 with respect to the articulated body. The second actuator 8b is arranged to pivot the lower arm 4 in the same plane where: the upper arm 3 pivots. In addition, the third actuator 8c pivots the spacer «I« - v 35 and the entire mechanical leg 1 about the longitudinal pivot axis ...., i.e. substantially perpendicular to the direction of motion provided by the first actuator 8a. The actuators 8a, 8b, 8c are preferably hydraulic cylinders or torque motors formed by a pair of hydraulic cylinders 9 104580. The implementation of mechanical leg movements is well known to those skilled in the art and is not described in greater detail. Among other things, the applicant's earlier Finnish patent 87171 and patent application FI-955297 disclose some 5 preferred embodiments of the leg mechanism.

The mechanical legs 1a-1f are provided with sensors which are capable of detecting, for each leg 1a-1f, the direction and, preferably, the position of the upper arm 3 and lower arm 4. In addition, the step portions 5 of the legs 10 may have sensors to determine whether the actuator portion 5 (and thus the corresponding leg 1) is on the ground or in the air. In addition, the actuators 8a-8c, which move the mechanical feet, are provided with sensors 12a-12f, which can in each case determine the pressure level of each actuator 8a-8c, either by pressure sensors or by 15 computational force vectors at least two, preferably three-dimensional . The force vector can be measured with force sensors, whereby joint moments can be determined and pressure levels can be calculated. Information on the pressure level and the direction of movement is used for example. determining which actuators 20 perform positive work and which actuators perform negative work.

Complex control logic is required to provide the machine 2 with a propulsive movement to provide the actuators 8a, 8b, 25 8c of the mechanical legs 1a to 1f with controls to control the actuators. Forward movement; During this period, some of the actuators 8 move the load in the • positive direction and some in the negative direction. Both situations cause an increase in the pressure level in the actuator pressure medium passage, in which case the feed pressure must be adjusted as required. In the presently known solutions, the braking actuator also has a · · · Y. '.' the change in pressure level is taken into account when determining the supply pressure, which in some cases may be unnecessarily high. Instead, in the present invention, the feed pressure is controlled only by: v on the basis of the load transfer actuators; 35 to achieve efficiency.

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The method of the invention will now be described with reference to

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racket for pictures 2 and 3.

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104580 10

Figure 2 shows a control circuit for a single mechanical leg 1a. In the preferred embodiment of the invention, the other control circuits are substantially identical to the circuit shown in Figure 2, so that they are not shown in more detail. The actuators 8a-8c are preferably dual-acting, whereby the pressure medium for the actuators can be guided either along the first actuator line 9a, 9c, 9e or along the second actuator line 9b, 9d, 9f based on the desired actuator direction. In this preferred embodiment, the actuator lines 9a-9f are connected to a three-position, two-to-ten-acting valve 10a-10c (4/3-way valve). In Figure 2 the valves are shown in the middle position, so that no pressure medium is supplied to the actuators 8a-8c. The valves 10 are preferably electrically controllable, whereby the position of the valve 10 can be changed by an electrical control signal. This is well known to one of ordinary skill in the art, so it is unnecessary to disclose it here. The supply pressure is applied to the actuators 8a, 8b, 8c via a supply pressure line 11 and valves 10a-10c. In the supply pressure line 11, the supply pressure of the pressure medium is generated by a supply pump and valve control in a manner known per se.

For measuring the pressure levels of the actuator lines 9a, 9b, the pressure message is preferably converted to a voltage or current signal. Prior art pressure to voltage converters (p / U converter) 12a to 12g may be used. The pressure-to-voltage converters generate a voltage proportional to the pressure applied to the control unit 13. In the control-25 unit 13, the analog voltage signal generated by the p / U converter is preferably converted into a digital message by an analog-to-digital converter (A / D converter). Instead of a pressure-to-voltage converter 12a-12f, converters can also be used to convert the pressure message directly into a digital message. The digital message may be either parallel, i.e. having its own line for 30 bits, or serial, whereby the digital message is conducted in successive bits along the same line. When using a parallel converter, more wiring is needed than with a serial converter: for example, 8-bit v: conversion resolution requires 8 separate wires for each converter v 35.

The control unit 13 is provided with information on the movement directions of the arms 3, 4 of each leg from the motion sensors 24a, 24b, 24c. The motion sensors 24a-24c are per se «·

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11 104580 known, for example, quadrature pulse sensors or pulse counters. The quadrature pulse sensors form two pulse-shaped signals of the same frequency, with a phase difference between them, e.g. + 90 °, whereby the direction of motion can be inferred from the phase difference direction (+/-) of the signals. With pulse counters, the direction of motion can advantageously be deduced from the direction of change in the reading of the pulse counter: whether the count increases or decreases. The motion direction data transmitted to the control unit 13 may also be a voltage message, whereby the direction of voltage change (increasing / decreasing) indicates the direction of movement. The voltage signal is preferably converted to digital format by the A / D converter 10. The control unit 13 uses the signal of the motion sensor 24a-24c e.g. to determine whether the actuator controlling said arm 3, 4 is performing positive or negative work.

Voltage messages in digital form in the control unit 13 are preferably passed to a microprocessor MPU for processing. The control unit 13 further comprises a Read Only Memory (ROM) for the microprocessor application software, which may also be an Electrically Erasable Programmable Read Only Memory (EEPROM). Further, the control unit 13 comprises random access memory (RAM) and other control electronics. The control unit 13 can also be formed in a so-called. using a Micro Controller Unit MCU, whereby most of the functions of the control unit 13 can be implemented by a single integrated circuit. Preferably, a microcontroller with A / D converters, program memory ROM, read / write memory RAM, digital-to-analog converter (D / A converter), and a microprocessor: MPU can be used. The control unit 13 may also be implemented by another control element known per se. This is a technique known to those skilled in the art, so that more detailed handling of the control unit 13 in this context is not necessary.

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Each actuator 8a, 8b, 8c thus receives two voltage or current signals proportional to the pressure. The difference between the messages from the same actuator indicates which direction the actuator is moving when the actuator is actively moving a load. Figure 3; the motion directions of the mechanical leg in one plane, for example, in the vertical plane, are shown in a simplified manner. The first actuator 8a, which displaces the upper arm 3 in a vertical plane, preferably to provide a rotational movement with respect to the hip joint L 104580, preferably comprises two hydraulic cylinders 14a, 14b. Similarly, the second actuator 8b, which displaces the lower arm 4 in a vertical plane, preferably to provide rotation with respect to the knee joint P, preferably comprises two hydraulic cylinders 15a, 15b. The corners 0L and ΘΡ in Figure 3 5 correspond to those in Figures 1a and 1b, so that reference will be made to the descriptions in Figures 1a and 1b previously provided in this specification. Figure 3 further shows the pressure levels of the actuator lines 9a, 9b of the first actuator 8a as follows: pa represents the pressure level of the first actuator line 9a, and pa + 1 represents the pressure level of the second actuator line 9b. Similarly, the pressure levels of the actuator lines of the second actuator 8b are denoted by pb and pb + 1. Thus, the effect of external joint torques can be deduced from Figure 3. Suppose the foot is on the ground. Thus, when raising the body load, the first actuator 8a guiding the upper arm 3 tends to rotate the upper arm 3 clockwise (0L decreases), and for this purpose the pressure level pa of the first actuator line 9a is greater than the pressure level pa + 1. upper arm in the opposite direction (0L increases). Similarly, when lowering the load, the first actuator 8a 20 tends to rotate the upper arm 3 anticlockwise (0L increases). Again, due to the load-induced braking force, the pressure level pa of the first actuator line 9a is higher than the pressure level pa + 1 of the second actuator line 9b. It can be noted that a comparison of pressures across the two-way actuator symmetrical. Examining the situation in which the foot is in the air and the upper arm is moved also gives the same result. In this case, the weight of the foot ··· · forms a load which causes an external torque acting in the direction "0L decreases". The 30 columns to the left of Table 1 summarize the above options. In the middle • · · '.V. the column shows the direction of motion of the upper arm 3 according to the information provided by the motion sensor, i.e. the actual direction of motion. The right-hand column shows the work done in the first v: actuator 8a based on the aforementioned columns: V represents a positive job and v 35 represents a negative job.

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13 104580

Pressure Level External Joint - Direction of Work _ torque_____

Pa +1> Pa 0L decreases 0L increases +

Pa> Pa +1 ol increases 0L increases

Pa +1> Pa 0L decreases 0L decreases pa> pa + 1_0, increases 0, decreases _ + _

table 1

In the case of lower arm 4, the situation is analogous to the above, except that in the mechanical foot 1a-1f of the walking machine 2 of the present invention, the pistons of the hydraulic cylinders of the second actuator 8b are connected to the upper arm 3. Referring to the entries, Table 2 is obtained in which the columns have the same meaning as the columns in Table 1.

Pressure Level External Joint - Direction of Work _ torque_________

Pb +1> Pb θρ increases 0P increases pb> pb +1 0P decreases 0P increases +

Pb +1> Pb 0P increases ΘΡ decreases +

Ph> Ph + i_0p decreases 0P decreases _: _

Table 2

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i.i i 15 In the position of Figure 3, assuming the foot is on the ground, the external joint • ·: 1 ·· tends to influence the “0P decreases” direction. With the lower arm in the upright position on the other side, the joint torque acts in the "0P increase" direction. References are also made in this connection to the entries in Figures 1a and 1b and their review. Tables 1 and 2 above-20 may also be generalized to other legs 1b to 1f.

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The application software of the control unit 13 measures the pressure level of each actuator line and examines the position and direction of motion of the actuator or the direction of motion of the joint 25 with its own motion sensor, which also •

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• t 14 104580 direction. The above tables are then applied to determine whether the actuator is performing positive or negative work. Negative pressure actuator pressure levels are ignored and the highest positive pressure actuator pressure levels are selected. Thus, the above operations are performed in the control unit 13, preferably in digital numbers, whereby the selected pressure level is converted to analog in the digital-to-analog converter 16. An analog voltage signal proportional to the selected pressure level is output from the digital-to-analog converter 16 to the first sum-10 a voltage message proportional to the supply pressure of the pressure line formed by the pressure-voltage converter 12g of the supply pressure line. Here, the output of the first adder 17 provides the difference between the selected pressure level and the current pressure level of the supply pressure line. The difference is led to the P1-15 controller 18, which is thus an integrating controller. The control variable formed by the P1 controller 18 is applied to an amplifier 19 where the analog voltage signal is preferably converted into a current signal proportional to the voltage signal. By means of the current message, the control of the supply pressure is carried out in a manner known per se.

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Figure 4 shows one solution for controlling the supply pressure of the hydraulic system. In this embodiment, a safety factor Δρ is applied to the input side of the digital controller as a digital number. In the first adder 17, a digital voltage signal proportional to the selected pressure level generated by the control unit 25 is added to the safety factor Δρ. Subtract the voltage signal proportional to the supply pressure of the supply • line to ps. The difference voltage is applied to a digital controller ··· · 20, which preferably comprises a digital P1 controller 18, an amplifier 19 * and a digital-to-analog converter. From the digital regulator 20, the analog control signal 30 is supplied to the feed pump regulator 21. Feedback to the feed pump regulator 21 is provided based on the angle of the feed pump 23, which corresponds to the rotational volume of the feed pump. In this case, the feed pump regulator 21 generates a feed pump for the actuator 22: a control signal for adjusting the feed pump angle to the selected pressure level.

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15 104580

The invention is not limited only to the above embodiments, but can be modified within the scope of the appended claims.

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Claims (9)

A method of controlling input pressure (ps) in a hydraulic system comprising at least one input pump (23) to produce the input pressure (ps), at least two hydraulic actuators (8a, 8b, 8c), measuring means for measuring the actuators (8a, 8b, 8c) pressure levels, and a flow channel system for pressure medium, characterized in that the method comprises at least the following steps: 10. the direction of movement of the electric actuator (8a, 8b, 8c) and the direction of action of an actuator (8a) is investigated; 8b, 8c) directed external torque to determine if in the actuator (8a, 8b, 8c) positive load transfer work is performed, 15. one chooses the largest pressure level of the load transfer work performed by the actuators (8a, 8b, 8c), and - one controls the input pressure (ps) at the base of the selected pressure level. 20 2. A method according to claim 1, characterized in that the working stroke is tested by measuring the pressure levels of the operating directions corresponding to the operating means (8a, 8b, 8c) and the directions of movement provided with the operating means, whereby in the base of each operating direction in the direction of movement, (8a, 8b, j in 8c) is calculated if, in some actuators, positive work is performed. 3. A method according to claim 1 or 2, characterized in that the hydraulic fluid. . ·. the body system is in communication with a load-bearing foot structure. • · · 30 4. A method according to claim 3, characterized in that the hydraulic system is a hydraulic system for an upright machine (2), such as a: ** forestry machine. • · Hydraulic system comprising an inlet pump (23) for producing an inlet pressure (ps), at least two hydraulic actuators (8a, 8b, 8c), measuring means for measuring actuators (8a, «I« 104580 8b, 8c) pressure levels, and a flow channel system for pressure medium, characterized in that the hydraulic system further comprises: - means for investigating the positive load transfer work performed by the actuators (8a, 8b, 8c) electrically on the base of the actuators (8a, 8b, 8c) of the actuator the direction of action of an external torque directed towards the actuator (8a, 8b, 8c), - means for selecting the greatest pressure level of the actuating actuators (8a, 8b, 8c), and - means for controlling the input pressure (ps) on the base of the selected pressure level. Hydraulic system according to claim 5, characterized in that it comprises sensors (12a, 12b; 12c, 12d; 12e, 12f) for measuring pressure of the opposite directions of movement of the actuators corresponding to working positions and sensors (24a, 24b, 24c) for measure the direction of movement provided by the actuators, and calculating means for separating load transfer actuators and load braking actuators. Hydraulic system according to claim 5 or 6, characterized in that in the means for separating load-transferring actuators and load-braking actuators and the means for selecting the greatest pressure level of the pressure-levels of the load-transferring actuators comprises a control unit (13), and that means for regulating the input • · · ·. . ·. the pressure at the base of the selected pressure level comprises a P1 controller (18). • · · • t · tl · I · « Hydraulic system according to claim 5, 6 or 7, characterized in that it is a hydraulic system for an upright machine (2), such as a forestry machine. • · · • · · • 1 · * 9 9 • I I <