METHOD AND DEVICE FOR A CONSTRUCTION MACHINE, PARTICULARLY AN EXCAVATOR

Abstract: A method and a device for changing the maximally obtainable hydraulic working pressure in the hydraulic working system (900) of a construction machine, especially an excavator. By setting means (701, 702), it is possible to control either both the pressure level of a pressure limiting unit (260) maximizing the maximum permissible working pressure and the pressure control level (p2) of the pump system (100), or only the pressure control level (p2) of the pump system (100). The setting means (701, 702) are supplied with the power signal D from a pressure level setting unit (700). The power signal D may alternatively also be used for simultaneously actuating a valve arrangement by means of which switching is effected to a certain type of digging or transport speed (e.g. low/high speed). Alternatively, the pressure level setting unit (700) is supplied with signals [Z] representing the position of the working equipment relative to the horizontal plane.

Description: METHOD AND DEVICE FOR AN CONSTRUCTION MACHINE, PARTICULARLY AN EXCAVATOR The present invention relates to a method and a device of the type stated in the preambles of the accompanying claims. A construction machine generally includes a number 5 of pressure medium-operated cylinders and motors (pneu¬ matic/hydraulic). Especially a hydraulic excavator ge¬ nerally has hydraulic cylinders, e.g. for the boom, dipper arm and bucket movements of the digging equip¬ ment, and for the dozer blade movement, as well as hy- 0 draulic motors for slewing and propulsion. The supply of pressure medium from the pressure source to the respective cylinder or motor is generally controlled by means of a control system the servo pressure of which actuates the main valves of the respective cylinder or motor. The hydraulic system used, like the rest of the construction machine, is usually adapted to the main task the construction machine is intended to perform. For instance, the maximum force and the maximum torque obtainable from the hydraulic cylinders and hydraulic motors, respectively, are then limited by the maximum hydraulic working pressure permissible or obtainable from the hydraulic system used. On certain occasions, it is desirable temporarily to increase the force of the hydraulic cylinder and/or the torque of the hydraulic motor for the construction machine, especially, for example, for affecting the lift¬ ing capacity of the excavator or the moment of propulsion thereof. This can be achieved by temporarily increasing the maximum permissible working pressure of the hydrau¬ lic working system and/or by temporarily increasing the working pressure obtainable from the working pump. The object of the present invention is to bring about the above-mentioned temporary increase of the working pressure, and this object is achieved by the method recited in the characterizing clauses of the accompanying claims. The invention also relates to a device of the type stated in the preambles of the accompanying claims. The device has the features stated in the characterizing clauses of the device claims. The invention will be described in more detail hereinbelow with reference to the accompanying drawings showing some embodiments of the invention. Fig. 1 shows a conventional device for driving and controlling a hydraulic cylinder, and Fig. 2 shows a conventional device for a corresponding hydraulic motor. Figs. 3 and 4 show pump characteristics for a commonly used power control pump, while Fig. 5 relates to the pump characteristics of a pressure control pump. Figs. 6, 7, 11, 12, 13 and 20 illustrate different basic embodi¬ ments of the invention. Figs. 14, 15, 16 and 17 show different ways of obtaining a signal from the control system as used in the invention, while Figs. 18 and 19 schematically show an embodiment referred to in the specification for illustrating a control system. Fig. 21 shows a more general embodiment of the inventive devices earlier shown. Fig. 22 shows a number of alterna- tive ways of connecting or disconnecting a pressure level setting unit 700 included in the device of the invention. Fig. 23 illustrates what is referred to in the specification as directly or indirectly obtained signals, and Figs. 24A, 24B and 25 show different variants of the invention. A commonly existing device for driving and con¬ trolling a hydraulic cylinder, especially intended for the digging equipment of an excavator, is shown in Fig. 1. This device consists of a hydraulic variable- displacement pump 101 included in a pump system 100 and driven by a motor M, a piston and cylinder assembly 210 (working cylinder) with connecting lines 231, 232 to a main valve 201, a control system 300 con¬ sisting of a manually operable control lever 320 ac¬ tuating pressure control valves 302, 303 for pressuriz¬ ing the control lines 310 and 311, and an associated servo pump 301 and a pressure relief valve 305, a working pump line 220 with an associated pressure relief valve 205 and associated branch lines 223, 224 to the main valve 201, recycling lines 226, 227, a return line 225 and a tank 202. In the illustrated hydraulic system, the hydraulic lines for the pump system 100 and for the hydraulic working system 200 are indicated by full lines while the control lines of the control system, by means of which the main valve 201 and thus the hydraulic working system are operated, are indicated by broken lines. The piston 211 of the working cylinder 210 is caused to move in one or the other direction by supply of pressure medium and drainage, respectively, by the lines 231 and 232 connected to the main valve 201. The spool of the main valve is in a neutral, central position and, by being displaced wholly or partly in one or the other direction, can connect the lines 231, 232 to the pump or the tank. The dis- placement of the spool of the main valve 201 is ef¬ fected by means of a servo system which is connected to the main valve 201 by the lines 310 and 311. The line 310 is connected to the pressure control valve 302 while the line 311 is connected to the pressure control valve 303. The pressure control valves are supplied with constant pressure from a servo pump 301. It appears from the Figure that by manually ope¬ rating the control lever 320, it is possible to obtain a servo pressure, the value of which depends on the control lever movement, in the lines 310, 311 to the main valve 201 to cause the valve spool to be displaced in one or the other direction. Since the magnitude of the displacement affects the amount of flow to the working cylinder 210, the piston speed can be varied. The arrangement now described is fully con¬ ventional. In order to cause the piston rod 212 of the work¬ ing cylinder 210 to move at the desired speed when subjected to a load, e.g. when lifting the boom of the digging equipment of an excavator, the spool of the main valve 201 is operated by means of the control lever 320 in order to obtain a corresponding oil flow to the working cylinder 210. As will of course be readily appreciated by any¬ one skilled in the art, that described above with reference to Fig. 1 regarding the working cylinder 2L0 also applies to a conventional hydraulic motor system 250, as exemplified in Fig. 2, which consists of a hydraulic motor 251 with non-return valves 252, 253, 254, 255, a pressure relief valve 256, a hydraulic line 259, and hydraulic lines 231, 232 connected to the main valve 201. That described hereinafter and exemplified by the working cylinder 210 also applies to a corresponding hydraulic motor system 250, and vice versa. The pump system 100 used in the invention and illustrated in Fig. 1 comprises a variable-displacement pump 101 and an associated control system for achieving suitable pump characteristics. The pump system here consists of the pump 101, adjusting means 102, a piston and cylinder assembly 110, 111, a throttle valve 136, a valve 130, a manually preloadable spring 131, a regulator unit 120 with setting means 125 and asso¬ ciated lines 103, 104, 105, 106, 107, 108, 109. Different pump characteristics are obtained de¬ pending on the type of the regulator unit 120. Generally, the unit 120 consists of a hydraulic- mechanical device actuating the adjusting means 102. The unit 120 may also comprise electromechanical or electrohydraulic-mechanical devices which, by acting on the adjusting means 102 or other means, set the displacement of the pump 101. In addition to manual presetting, it is also possible to use electric or hydraulic control signals applied to the regulator unit 120. This is exemplified in the pump system 100 by setting means 125 acting on the unit 120, as repre¬ sented by an arrow. For example, the setting means 125 normally consists of a manually operable screw device or of an electric input signal applied to a proportional magnet unit affecting the preload of a spring 121. The very build-up or disposition of the regulator unit 120 may here be disregarded since it is no part of the invention. For examples of pump characteristics in connection with power control (the product of work¬ ing pressure and displacement is maintained constant), see schematic relation between working pressure p and flow q for an assumed constant pump speed n in Fig. 3. The control is carried out in the following way. Over a preset pressure p, (beginning of the power control), the flow is controlled in relation to the working pressure p, such that the product of the flow q and the working pressure p in practice becomes almost constant. At a working pressure below the preset pressure p, , the pump operates with constant displace¬ ment. The pressure p- is generally preset by manually preloading a spring 121 by the means 125, with the aid of a set screw in the pump. This adjustment and, thus, adjustment of the beginning of the power control p. may also be carried out by electric or hydraulic action. If the pump system 100 has a valve 130 connected to the hydaulic circuit of the pump system 100, the valve 130 is caused, depending on the preloading of the valve spring 131 and at a corresponding working pressure, to connect both sides I and II of the adjust- ing piston 111 to the working pressure line 103. This results in a pressure control and thus cut-off (limita¬ tion) of the power control curve according to Fig. 3 at the pressure p^ according to Fig. 4. A pressure limi- tation is thus obtained when, according to the power control curve, the working pressure produced by the pump reaches a predetermined (preset) working pressure p~, the working pressure being maintained almost constant during the pressure control. The pressure-limiting level P y (pressure control level p„) is generally varied in known pump systems by preloading the above-mentioned spring 131 affecting the opening pressure of the valve 130. The valve 130 is generally integrated in the pump housing of existing known pump systems 100. If the pump system 100 has no regulator unit 120 with associated connections to the hydraulic lines 106 and 104, the known pressure control pump having the pump characteristics as schematically shown in Fig. 5 is provided by means of the valve 130. This valve is generally integrated with the pump housing of the pump system 100. In the illustrated pump system 100, the adjusting piston 111 may alternatively be actuated by pressure medium from a proportional valve (or valves) included in an electric or electrohydraulic control circuit the input signals of which consist e.g. of signals corresponding to the working pressure of the pump 101 and the desired pressure control level p„. Thus, the setting of the pressure control level p„ can be effected in a manner other than that shown in the pump system 100 now described. The manner in which the control of the desired or preset pressure control level p- and, thus, the change of the displacement of the pump 101 are obtained may here be disregarded since it is no part of the invention. The sole feature of interest here is the setting means by which the pressure control level of the pump system 100 can be changed. The setting means can then be supplied with manual, electric, pneumatic or hydraulic signals required for effecting the change. Alternatively, the pump system 100 may be equipped with a control circuit/control unit, whereby the above-mentioned setting signals (pressure level setting signals) are directly applied to this control circuit/control unit. The invented device has means for temporarily and automatically raising the pressure control level (pressure-limiting level) „ of the pump system 100. This increase of the pressure control level can be achieved only when certain conditions of use (e.g. low speed digging) are satisfied, e.g. to prevent overloading the construction machine. At the same time, an increase of the opening pressure (pressure level) of the associated pressure relief valve 205 in the hydraulic working system may of course also occur. An example of a pump system 100 used in the invention is a pressure control pump or a power control pump with pressure-limiting (pressure-cutting) function. The type of pump characteristics obtained from the pump system 100 by means of the regulator unit 120 is of no interest to the invention, but merely the pressure-limiting (pressure-cutting) function of the pump system 100. The pump system 100 may thus be alter¬ natively described as a (hydraulic) pump having both variable pump displacement and pressure-limiting (pressure-cutting) function. In the described embodi¬ ments of the invention, the pressure relief valve 205 may be dispensed with when using a quickly settable pump system (or pump systems). A hydraulic device for use in the method for temporarily changing the pressure-limiting level (pres¬ sure-cutting level) of the pump system 100 (working pump) is shown in Fig. 6. The device shown in Fig. 6 is not dependent upon a certain condition of use (e.g. low speed digging) being satisfied, but can be directly or indirectly, manually operated. In the illustrated embodiment, a change of the obtainable working pres¬ sure for driving the associated working cylinder 210 is achieved in that pressure medium (hydraulic or pneumatic) at the same time affects the setting of the pressure, level of a pressure-limiting unit 260 and the preload of a spring 131 for setting the pres¬ sure-limiting level (pressure control level) p~ of said pump system 100. Generally, the pressure-limiting unit 260 consists of a pressure relief valve 205 with an associated spring 206 the preload of which deter¬ mines the opening pressure (pressure level) of the valve 205. In the embodiment of Fig. 6, the preload of the springs 131, 206 is acted on by two pressure medium-operated pistons 241, 244. In the embodiment of Fig. 6, the preload of the spring 131 is affected by a piston 244 in a cylinder 245 whose cylinder end III is pressurized by a control line 401, and the pre¬ load of the spring 206 is affected by a piston 241 in a cylinder 242 whose cylinder end IV is pressurized by a control line 402 connected to the control line 401. The control line 401 is pressurized by operating, as represented by arrow 420, a valve 403 for connecting the control line 401 to a pressure medium source 410, the pistons 244 and 241, by the action of the control pressure, pressing the springs 131, 206 inwards so as to achieve a spring preload suitable for adjustment to the desired maximum pressure level. The pistons 241 and 244 are movable between fixed, presettable maximum and minimum positions. The pressure source 410 may here consist of a hydraulic or pneumatic pres¬ sure source. Since the operation (control) of the hydraulic cylinder 210 is here effected by means of the control system 300, the pressure source in such cases generally consists of the servo pressure of the servo pump 301. The valve 403 may be operated in a conventional manner for pressurizing the lines 401 and 402 by operating the valve 403, either manually, electromagnetically, pneumatically or hydraulically, by a switching means illustrated by arrow 420. The corresponding suitable signal required for the switch- ing means 420 is designated G. If the pressure source consists of a hydraulic pressure medium, a return line 404 to the hydraulic tank is connected to the valve 403. When using a pneumatic pressure source, the return line 404 is not necessary since the compressed air used is generally directly discharged into the atmosphere. When only two fixed pressure levels are desired, the pressure source 410 may consist, instead of the servo pressure, of the working pressure since the pistons 241 and 244 are movable between two fixed, presettable maximum and minimum positions. One example of such a device is illustrated in Fig. 7. The working pressure in the line 411 and thus to the valve 403 is obtained in Fig. 7, either by the connection of the line 411 to the pump line 220 via the shuttle valve 413 and the line 412, or by the connection of the line 411 to the working cylinder lines 231 and 232 via the shuttle valve 413, a line 414, a shuttle valve 416 and one of the lines 415 and 417. Fig. 7 illustrates the simultaneous use of both of the above-mentioned alternatives, but an embodiment using only one of these alternatives is also possible. Thus, there may be pro¬ vided an alternative embodiment where the line 411 is directly connected to the pump line 220 while the lines 412, 414, 415, 417 and the shuttle valves 416 and 413 are excluded, or another alternative embodiment where the line 412, the shuttle valve 413 and the line 412 are excluded, and the line 411 is directly connected to the shuttle valve 416. Since these alternatives are self-evident, they are not shown in the drawings. The connection of the control line 402 to the control line 401, as illustrated in Figs. 6 and 7, is of course not necessary, but the control line 402, like the line 401, may instead be directly connected to another valve corresponding to the valve 403 as illustrated in Figs. 6 and 7, but this requires an additional corresponding valve 403. The additional valve is normally connected to the same pressure source as the other valve 403. It is of course also possible, but perhaps somewhat too complicated, to connect the valve 403 and the additional valve to different pres- sure sources. In such case, one pressure source may consist of the working pressure as in the embodiment according to Fig. 7, and the other pressure source may consist of the pressure source in the embodiment according to Fig. 6. In the above-mentioned devices, the pressure- limiting unit 260 consists of a conventional, modified pressure relief valve 205 which is adapted to the illustrated application and the pressure level of which can be set by means of a pressure medium-operated piston and cylinder assembly 241, 242. This arrangement is shown in Fig. 8A where it is assumed that the setting force (the force of the preload of the spring 206 of the pressure relief valve 205) is obtained by the action of a setting means consisting of the piston and cylinder assembly 241, 242, as represented by the arrow 701. Other principle embodiments of the pressure- limiting unit 260 are shown in Figs. 8C and 8D. In Fig. 8C, the pressure-limiting unit 260 consists of a two-position directional valve 261 of the ON/OFF type, to which two pressure relief valves 262, 263 are connected in parallel. The line 223 corresponds to the above-mentioned connection from the pressure- limiting unit 260 to the pump line 220. The pressure relief valve 263 is set for the higher pressure-limiting level, and the pressure relief valve 262 is set for the lower pressure-limiting level. For raising the pressure-limiting level of the working pressure to the higher pressure level, the directional valve 261 is switched directly or indirectly by manual, pneumatic, hydraulic or electromagnetic setting means 701. The embodiments hitherto described of the pressure-limiting unit 260 provide only two predetermined pressure-limit¬ ing levels. Use is sometimes made of an adjustable pump (variable-displacement pump) with a control func¬ tion as in the pump system 100, or a fixed-displace¬ ment pump for supplying a flow of pressure medium to more than one working cylinder (or cylinders), or a motor (or motors) which are used for bringing about separate partial movements of the construction machine (e.g. the boom cylinder of an excavator for lifting of the boom or propulsion of the excavator), and it is desirable to momentarily increase the maximal obtainable working pressure for the part or parts of the associated hydraulic working system which said pump, alone or conjointly with another/other pumps, supplies with oil flow. If different maximum pressure- limiting levels are desired for the hydraulic working system when only certain separate movements take place, both the pump and the pressure-limiting unit 260 must provide at least three different maximum pressure- limiting levels. For example, it is then possible to use the same pump and/or pressure-limiting unit 260 in an excavator, both for boom lifting with a certain predetermined maximally obtainable working pressure and for the propulsion of the excavator with a certain other predetermined maximally obtainable working pressure. Embodiments of the pressure-limiting unit 260 with three pressure-limiting levels are shown in Fig. 8D. The device exemplified in Fig. 8D corresponds to the device of Fig. 8C supplemented with a two-position di- rectional valve 268 and a pressure relief valve 269. The directional valve 268 is actuated for switching by a switching force produced by setting means, indicated by the arrow 704. The features of the setting means 701 correspond to those of the setting means 704. The embodiments of the pressure-limiting unit 260 described above with reference to Figs. 8C and 8D, for obtaining different pressure-limiting levels are all based on the principle that the hydraulic pressure in the line 223, by a suitable valve arrange¬ ment, is connected to the pressure relief valve set to the desired maximum working pressure. Further embodi- ments of the pressure-limiting unit 260 having more than three pressure-limiting levels obtained on the basis of the above-mentioned principle are of course conceivable. By using a proportional magnet instead of an electromagnet it is possible to continuously obtain all pressure-limiting levels from a minimum to a maximum working pressure. This continuously va¬ riable pressure limiting level can also be obtained for the pressure limiting unit 260 in Fig. 6 if the pressure source 410 consists of means by which different control pressures can be obtained in the control line 401. One example of such means is a proportional valve. If the pressure source 410 has means (e.g. a propor¬ tional valve) for producing different pressures in the control line 401 and, thus, in the control line 402, the pressure-limiting unit 260, including the piston and cylinder assembly 241, 242, may then be directly replaced by a commonly existing proportional pressure relief valve, the working pressure being li¬ mited to a maximum pressure which is proportional to the external control pressure in the control line 402, or a commonly existing pressure relief valve operated by external control pressure which consists of the pres¬ sure in the control line 402. Since the pressure-limiting unit 260 may be designed in several different ways, this unit is symbolized in the present patent specification by the pressure-limiting unit 260 with associated hydraulic lines 223, 225, as shown in Fig. 8B. The above-mentioned means which are exemplified by the pressure-limiting unit 260 (or the pressure relief valve 205 with the spring 206) and by means of which the pressure-limiting level of a pressure relief valve can be continuously or discontinuously set, espe¬ cially by directly or indirectly changing the preload of the regulating spring 206, are directly usable for setting the beginning of the power control (p, ) of the pump system 100 and the pressure control level (p-,) thereof by directly or indirectly acting on the springs 121 and 131, respectively, in a corresponding manner. The means described above for acting on the spring 121 thus correspond to the setting means 125 earlier mentioned. Thus, to facilitate the continued descrip- tion of the invention, the pump system 100 as sche¬ matically shown in Figs. 1, 2, 6 and 7 can be illustrat¬ ed in an even more simplified manner with reference to Fig. 9A. Arrow 702 symbolizes the setting means producing the force ensuring the preload of the spring 131. This setting means (pressure control-level setting means) 702 consists of means corresponding to those described above in connection with the setting means 701 of the pressure-limiting unit 260. Thus, the setting means 701 and 702 may consist of either a piston and cylinder assembly 244, 245 (242, 241), an electromagnet, a proportional magnet, adjusting means (e.g. a piston and cylinder assembly which by a lever rotates the set screw of the pump system 100 for setting the pres¬ sure control level ) , an electric motor which by a gear operates the set screw of the pump system 100 for pressure control-level setting, or a mechanical device for transmitting a mechanical or manual signal . The energy required for driving the setting means 701 and 702 is obtained via a connecting control line 703. The signal which by the control line 703 actuates the setting means 701 or 702 may consist of a pneu¬ matic, hydraulic, electric, mechanical or manual signal. (For example, the setting means 702 with the associated control line 703 in Fig. 6 corresponds to the piston and cylinder assembly 244, 245 with the associated hydraulic line 401). In the case of a mechanical or manual signal, the line 703 corresponds to the linkage and/or cable system. In order to power an electric device, two electric lines are generally required. Since one line, the so-called return line, is generally connected to ground, this line will be excluded from the continued description of the invention and only the input lines will be described in the form of signal lines. In the simple embodiments of the invention illustrat- ■ed in Figs. 6 and 7, the working pressure can be raised without stipulating any condition e.g. for the direc¬ tion of movement of the piston rod of the working cylinder 210. Assume, for example, that it is condi¬ tioned that an increase of the maximum level of the working pressure should only occur when the piston rod 212 of the working cylinder 210 moves inwardly towards the cylinder. In Figs. 6 and 7, this cylinder movement is obtained by moving the control lever 320 to the right in the Figures, the control line 310 being pressurized for setting the spool of the main valve 201. This control pressure may be used e.g. for governing the above-mentioned conditions, see Fig. 11. In the embodiment of Fig. 11, a directional valve 481 is connected between the pressure medium source 410 and the connecting line 418 to the valve 403. In the presence of control pressure in the line 310, the line 419 is pressurized, whereby the spool of the valve 481 is actuated and pressure medium is supplied from the pressure source 410 via the line 418 to the valve 403. The working pressure can then be raised, as in the embodiment described above with reference to Fig. 6, by manually, pneumatically or electromagnetically actuating the valve 403 (represented by the arrow 420). To facilitate the further description of the invention, the device shown in Fig. 11 will first be commented on in more detail. In the device shown in Fig. 11 and in the devices earlier illustrated, there has been shown only a fully hydraulic control system 300, but the control system may also consist of an electrohydraulic control system 300, as shown in Fig. 12. In other respects, the device is identical with the device shown in Fig. 11. In Fig. 12, the electrohydraulic control system 300 is illustrated by a commonly existing control system 300 consisting of an electric control lever unit 330 with a control lever 320, an electrohydraulic servo unit 332 with a servo pump 301 (not shown) and the control lines 310, 311 illustrated in the above-men¬ tioned devices. The electric control lever unit 330 applies in a conventional manner, proportionally to the control lever movement, an electric control signal s to the electrohydraulic servo unit 332 by a control line 331. Generally, the electrohydraulic servo unit 332 consists of an electric unit which applies to a proportional magnet a current corresponding to the input signal for setting a proportional valve whose output signal is a hydraulic control signal in the control lines 310, 311. These hydraulic control signals consist of a hydraulic servo pressure. Thus, as above in connection with a fully hydraulic control system, there is obtained a servo pressure (hydraulic control signal) in the control lines 310, 311 which is propor¬ tional to the control lever movement, for which reason the operation of the working cylinder 210 by means of the main valve 201 takes place in the same way as in the devices described above. The value of the electric control signal Sa determines which of the control lines 310, 311 should be pressurized and at which control pressure. Thus, this involves the speed and the direction of movement of the piston rod 212 of the working cylinder 210. To easily distinguish which of the control lines 310, 311 should be pressur¬ ized, it is possible e.g. to let the control signal Sa have a zero value when the control lever is in neutral position (i.e. no movement of the piston rod of the working cylinder, negative lever signal S 3. when the control lever is moved in one direction, and positive lever signal S when the lever is moved in the oppo- site direction. Lever movement in one or the other direction gives a corresponding inward or outward movement of the piston rod of the working cylinder 210 by pressurizing one or the other side of the main valve 201. When the electric control signal consists of both negative and positive values, the signal S can be divided into two electric control signals, one consisting of the absolute value ( SaII ) of the control signal and the other signal of its sign (+/-). This requires two control lines between the electric control lever unit 330 and the electrohydraulic servo unit 332. Depending on the build-up of the electric circuit of the electrohydraulic servo unit, one or the other way of applying the signal S may be prefer- able, but the same hydraulic output signal (control pressure) is obtained from the proportional valve used. The only feature of interest in the invention are the electric control signal S or a corresponding signal possibly converted from this electric signal (S 3.), and the control signal (control pressure) in the lines 310, 311. That it is possible to divide an electric signal into two signals one signal of which consists of its absolute value ( S I) and the other signal of its sign (+/-) is self-evident. To facilitate the continued description of the invention, the designa- tion "electric control signal S 3." as used herein also comprises the corresponding divided signal (S 3. +/-) or any other equivalent signal obtained by conversion of the control signal S 3.. Thus, the Figures only show one electric control line for each divisible signal as above (e.g. S ) . a Fig. 13 shows a device corresponding to the device of Fig. 12, but the exemplified condition that an increase of the maximum level of the working pressure should only take place when the piston rod of the working cylinder 210 moves inwardly towards the cy¬ linder (negative movement), is obtained by using the electric control signal S . The above condition of course also corresponds to the case where an increase of the maximum level of the working pressure should only take place when the control lever 320 is moved from the neutral position in a direction correspond- ing to the condition for the piston rod movement, an electric control signal S being obtained for bring¬ ing about such movement. The signal S 3. is applied via a control line 436 to an electric unit 321 which supplies current to the solenoid valve 482 when the above-mentioned condition is satisfied. When the sole¬ noid valve is fed with current, the valve is switched such that the line (control line) 418 is connected to the pressure source 410 and is pressurized. This device then corresponds to the device of Fig. 12. (The line 419 in Fig. 12 is disregarded). When the power supply is interrupted, the valve 482 is reset and the pres¬ sure in the line is reduced to the pressure prevailing in the tank or to atmospheric pressure. The electric unit 321 of course contains an amplifier necessary for the power supply of the solenoid valve, and an elec¬ tric logical circuit (conditional circuit) determin¬ ing whether the control signal S satisfies the cor¬ responding set condition, e.g. the negative movement of the piston rod of the above-mentioned working cy- Under 210. If this condition is satisfied, current feed takes place from the electric unit 321 to the solenoid valve 482. If, as in this case, only one signal is applied to the electric unit 321 and the control signal in the line 436 only consists of a sign signal (+/-), the electric logical circuit can be excluded and the signal be directly amplified and feed current to the solenoid valve 482, so that the valve is switched if the line 485 from the electric unit 321 is connected to the electric circuit of the magnet, such that the coil, for the above-mentioned conditional case, is supplied with current in a direc- tion switching the valve 482. The signal S which is supplied from the control system 300 to the elec¬ tric unit 321 gives information on how the operation of the control lever 320 is effected and then also the direction of movement of the piston rod of the working cylinder 210. The signal S 3. is hereinafter referred to as "control information signal S ιr . It need not be a pure control signal, as exemplified in the control systems in Figs. 14, 15, 16, 17 and 18. In Fig. 14, the control information signal S is ob- tained by a pressure sensor or pressure switch 333 connected to the control line 310. In the invention, the control information signal S may also be represented by a signal produced by a sensor detecting the lever movement. In Fig. 15, the sensor consists of a potentio- meter 334 detecting the pivotal movement of the control lever about its suspension pin. This Figure only shows the control information signal S emitted. In Fig. 16A, the sensor consists of an electric switch 335 opening or closing an electric circuit. The control information signal S has a zero value or a non-zero value. The signal value S indicates the direction in which the lever is moved. Depending on the switch 335 used, the signal S may either record whether the lever is moved (angled) from the neutral position in one or the other direction. In Fig. 16B, use is made of two switches 340, 342. The switches are connected by input lines to a current source of different polarity (+/-) or of the same polarity with different current/voltage levels. The input lines are illustrated in Fig. 16B by signals 341, 343 applied to the switches 340, 342. The value of the signal S then indicates whether the lever is moved (angled) in one or the other direction. In Fig. 16C, use is made of two switches 346, 347 for recording the direction in which the lever 320 is moved (angled) from the neutral position. This circuit arrangement uses two control information signals S,, S for indicating the direction in which the lever is moved. For greater simplicity, these control in¬ formation signals may also be generally designated [s]. In the foregoing, the control information signal has only been described as obtained in connection with the electrohydraulic or fully hydraulic control system 300, but at least the same possibilities of applying sensors (e.g. switches, potentiometers) for obtaining at least one control information signal S can be attained when using a manual control system, if it is disre¬ garded that no electric control signal (e.g. S 3.) or signal derived from the hydraulic control pressure can be obtained when the control system is not provided, either with an electric control lever or a control line, e.g. 310, 311. A manual control system which is sometimes used in construction machines, especially excavators, is exemplified in Fig. 17A. The illustrated mechanical control system 500 is assumed to act on the spool of the above-mentioned main valve 201. Such a control system most often consists of a control lever 501 whose movements, via the linkage and/or wire cable system, cause the spool of the main valve 201 to move. For example, the control information signal S can be obtained by means of a potentiometer 334 in the fulcrum of the control lever 501. Since there is no limitation to the lever only, the control system provides greater possibilities of applying sensors for obtaining the control information signal S. Sensors actuated directly by the lever or indirectly by the linkage/wire cable system provide an equivalent information signal S. When using a manual control system, the control information signal can easily be obtained in the form of a pneumatic signal, see e.g. the control device in Fig. 17B. A sensor 510 is here used for obtaining a pneumatic signal when the control lever 501 is moved in one direction. A rod 512 is axially displaceable in a tube 522. The rod 512 is hingedly suspended in a point 521 and the tube 522 in a link arm 506 in the point 514. The valve 515 is fixed to the rod 512. A resilient valve pusher device 517 is fixed to the tube 522, and upon a lever movement causing the tube 522 and the rod 512 to move towards each other, the valve 517 is operated so that the line 518 is connected to a pressure source 410 and a pneumatic control information signal S is ob¬ tained. Alternatively, the sensor 510 may consist of a rotary valve/rotary valve device acted on directly or indirectly by the link arm 506, the point of sus¬ pension 505 of the link arm 506 or the point of sus- pension 504 of the control lever 501. This indicates that the signal S from a control system may also consist of a pneumatic signal. In the device of Fig. 17B, the pressure source 414 may alternatively consist of a hydraulic pressure source. In the above exemplification of the control infor¬ mation signal S, the control systems 300, 500 hitherto shown have consisted of control lever-operated control systems. The examples given are of course also applic¬ able to pedal-operated control systems. For a con- struction machine, especially a hydraulic excavator, two hydraulic working units (cylinder/motor) are most often simultaneously operated by one control lever. Lever movement in a predetermined plane actuates in a conventional manner the main valve spool of one of the two hydaulic working units, and lever movement in a plane at right angles to said plane actuates only the main valve spool of the other hydraulic working unit. Lever movements in other planes simultaneously act on both main valves. Information on the movement of the spool of each main valve or of the associated control lever is provided as earlier described where the control system only operated a single main valve. The only difference is that several control information signals [S] can be simultaneously obtained from the control system. In the devices described above for obtaining a control information signal (or signals) S, both fully hydraulic, electrohydraulic and manual control systems have been used. For the continued description of the invention, the term "control system" specifical- ly relates to the previously described fully hydraulic (often called servo system), electrohydraulic and manual control systems. Other alternative control systems may consist e.g. of pneumatic, electropneuma- tic or fully electrical systems. In the manual control system of an excavator, the manual control movements (e.g. lever movements) of the operator are generally transmitted to the spools of the main valves via the linkage system or the like. Thus, control systems concerning fully hydraulic or electrohydraulic control systems may be schematically represented according to Figs. 18A, B, C or D. Fig. 18A relates to a control system 300 operating a single main valve by control lines 310, 311 and a control information signal or signals designated [S] derived from the control system. Fig. 18B relates to a control system operating two main valves by control lines (hydraulic/pneumatic pressure control lines) 310, 311, 312, 313 and a con- trol information signal or signals designated [S] derived from the control system. Fig. 18C relates to a control system operating a main valve by control lines 310, 311 without the emission of a control infor- mation signal. Fig. 18D relates to a control system operating two main valves by control lines 310, 311, 312, 313 without the emission of a control informa¬ tion signal. A corresponding schematic illustration of a manual mechanical control system appears from Fig. 19. Reference numerals 511, 513 in Fig. 19 de¬ signate the linkage, line or the like associated with the control system for actuating the spool movement of the associated main valve. Thus, Figs. 19A and C relate ' to a control system for a single main valve, while Figs. 18B and D relate to a control system ope¬ rating two main valves. For the continued description of the invention, the control system or systems used will be schematical¬ ly described according to Fig. 18 or 19. It should be noted that the control information signal [S] may consist of several separate control information signals S, , S-. It should also be noted that the control infor¬ mation signals [S] may consist of electric signals, pneumatic or hydraulic (pressure medium) signals. Fig. 20 illustrates another embodiment of the device shown in Fig. 13. In the device of Fig. 20, the pres¬ sure level of the pressure—limiting unit 260 and the pressure control level of the pump system 100 are subjected to electromagnetic action. In addition to the control information signal [S] applied to the electric unit 350, the device comprises signal lines (electric lines) 709, 710, 711, an electric unit 360 consisting of an electric switch 322 with manual ac¬ tuation and automatic resetting, and setting means 701, 702. The setting means 701, 702 are electromagnetic units. The electromagnetic units (setting means) 701, 702 act on the pressure-limiting unit 260 and the pressure level p„ of the pump system 100 in a manner similar to that applied in connection with the device of Fig. 13 having pressure medium-operated pistons. It is assumed that the control information signal [s] consists of electric signals where lever movement in one direction corresponds to a positive electric signal value, and lever movement in the other direction corresponds to a negative electric signal value. In the device, the unit 350 consists only of an electric amplifier unit, e.g. a transistor amplifier, amplifying the negative and the positive signal S. Depending on how the lines 710, 711 are connected to the two connections, poles, of the magnet coil, the electro¬ magnetic units 701, 702 can be caused to act on the setting of the maximum pressure level of the pressure- limiting unit 260 and of the pump system 100 upon a lever movement corresponding to a positive or a negative electric control information signal. Alternatively, the electric unit 360 in Fig. 20 may consist of the electric unit 360 in Fig. 10. More¬ over, it is assumed that the electric unit 350 in this case consists of a conditional unit. The electric unit 360 in Fig. 10 consists of a relay 325, a current feed line 326, signal lines (electric lines) 327, 709, 710, an electric switch 322 with manual actuation and automatic resetting. When the signal [S] satisfies the condition according to the logical circuit (conditional circuit) of the electric unit 350, the electromagnetic unit 325 is supplied with current, and the line 327 is connected to a current source by the line 326. When the condition is satisfied, the electromagnetic units (setting means) 701, 702 can be supplied with current by manual actuation of the switch 322 for increasing the pressure control level of the pressure-limiting unit 260 and of the pump system 100. Any means necessary for amplifying the power signal D may alternatively be considered as part of the electromagnetic unit 701, 702 and/or the electric unit. One example of such means is an amplifier unit (e.g. transistor amplifier) with asso¬ ciated power source. Alternatively, the electromagnetic unit 701, 702 consists only of an electromagnet (electro¬ magnets) . The simplified examples of the invention as de¬ scribed above may be illustrated by Fig. 21. In the illustrated device, a change of the obtainable maximum working pressure level in the hydraulic working system for the movement of the working cylinder 210 is brought about by a setting means 701 affecting the setting of the pressure limiting level of the pressure-limiting unit 260, and by a setting means 702 indirectly or di- rectly acting on the preload of the spring 131 for setting the pressure control level of the pump system 100. The setting means 701, 702, represented by arrows 701, 702, may each, e.g. as in the devices shown in Figs. 6, 7, 11, 12 and 13, consist of a hydraulic/ pneumatic piston and cylinder assembly 241, 242 (244, 245), and according to Fig. 20 of an electromagnetic unit, a proportional magnet or like setting means 701, 702 providing a force for bringing about the above- mentioned setting of the maximum pressure level of the working pressure. If the pump system 100 is designed in such a way that the setting (change) of the pressure control level p„ of the pump system can or must be performed by means of an electric signal or pressure medium signal to an input specially provided therefor to the pump system, the setting means 702 may corre¬ spond to said input. The device also contains a pres¬ sure level setting unit 700 whose output line 710 (electric/hydraulic/pneumatic) is directly connected to the setting means 702 and via the branch line 711 to the setting means 701. It is of course self-evident that each setting means can also be directly connected by a line to seperate outputs on the pressure level setting unit. If the branching takes place in or after the pressure level setting unit 700 is of no conse¬ quence. If the setting means, for their function, require different signals or signal types (electric/ hydraulic/pneumatic), both lines 710 and 711 are direct¬ ly connected to the pressure level setting unit. The pressure level setting unit 700 consists of an activat¬ ing unit 721 for activating an increase or a decrease of the pressure limiting level of the hydraulic working system, and a power unit 722 for generating a suitable (power) signal to the setting means 701, 702. The pressure level setting unit 700 is supplied with a control information signal [S] which can be applied directly or indirectly to the activating unit 721. The activating unit has means for determining whether the control signal [S] satisfies the stipulated condi¬ tion for the movement of the control lever 320 or, alternatively, of the main valve 201 or the working cylinder. If this condition is satisfied, an activating signal A is emitted and applied to the power unit 722. The control information signal [S] may consist of an electric signal or a hydraulic/pneumatic pressure signal . The activating unit 721 has means for converting a control information input signal into a signal form (electric/hydraulic/pneumatic) suited for the condi¬ tional assessment, and, by conversion, for emitting an activating signal A of electric (I,. or ϋ, ) , pneumatic (p ) or hydraulic (p ) signal form. When an activating signal is applied to the power unit 722, this unit emits a signal form D of suitable strength (pneumatic (p_)/hydraulic (p )/electric(I D or U ) applied to the setting means 701, 702 for setting the pressure level of the pump system 100 and of the pressure-limit- ing unit 260. Especially, the change goes from a lower to a higher level, but an opposite change from a higher to a lower level is also possible to achieve. The pressure level setting unit may also be provided with means for connecting or disconnecting the pressure level setting unit 700 by means of a directly or indi¬ rectly applied signal B (manual, electric, pneumatic, hydraulic), as represented in Fig. 21 by an activating arrow 723. When the unit 700 is disconnected, no power signal D can be obtained for changing the maximum work¬ ing- pressure level. That the unit 700 need not necessari¬ ly be provided with a connecting/disconnecting option is illustrated by the broken arrow. This ON/OFF signal can actuate at least either the activating unit 700, the drive unit 722, the control information signal [S], the activating signal A or the power signal D. Such ac¬ tuation can be brought about by a signal connected (added) to one or more of the signal or signals of the pressure level setting unit and then entails a fixed (locked) un¬ altered output signal (e.g. a fixed constant power signal D or absence of a power signal D corresponding to a con¬ nection or disconnection, depending on the sign of the connected signal). This actuation can also be achieved by disconnecting (breaking) the signal. These actuation modes according to the invention are exemplified by the pressure level setting unit 700 in Fig. 22. Fig. 22 shows a number of alternative ways of con- necting or disconnecting the pressure level setting unit 700. At least one of these alternatives is used for achieving disconnection/connection. The applied ON/OFF signal B, 723, shown in Fig. 21 consists in Fig. 22 of corresponding alternative signals 723. The applied signal B, 723, may consist of a directly or indirectly received manual signal, mechanical signal F_, electric signal (ϋ β or I β ) hydraulic or pneumatic signal (p B )« (The signal F is of course the force, the movement or the force and movement provided by the manual actua- tion). The term "direct signal B, 723" as used herein relates to a signal obtained by manual actuation of the connecting/disconnecting means for opening or closing the connection to the signal source (electric, pneumatic, hydraulic), or a directly transmitted manual signal. Figs. 23A, B and C exemplify a number of di¬ rectly obtained signals B, 723. In Fig. 23A, there is obtained an electric signal B equal to I or U n upon manual actuation of the switch 761, in Fig. 23B there is obtained a pressure medium signal B = p n a when the valve 762 is manually activated, and in Fig. 23C there is obtained a mechanical signal B = F_ by means B of a wire cable (or linkage system) 765 connected to the manual movement of a lever 766. The term "in¬ direct signal 723" as used herein relates to a signal triggered by means operated by the above-mentioned direct signal, or a signal triggered by means in turn triggered by at least one further means, the means as last actuated in the chain being actuated by the above-mentioned direct signal. The term "indirect" as used herein also relates to an obtained converted signal. Figs. 23D, E, F exemplify a number of indirectly obtained signals B, 723. Fig. 22 exemplifies a few alternative ways of achieving connection/disconnection as represented by broken arrows (actuating signals) 723 with asso¬ ciated broken signal paths and switching units, e.g. 732, 744 and 745 or 738 and 756. When exemplifying the signal paths with associated connecting units, use is made, especially for the connecting units, of electric or hydraulic symbols representing electric connecting/disconnecting means or hydraulic directional valves for acting on the signals of the pressure level unit. Which type of signal (mechanical, electric, pneu¬ matic or hydraulic) with associated connecting unit is used of course depends on the actuating signals used and the type of signal to be actuated. All the connect- ing units illustrated in Fig. 22 may of course be re¬ presented by symbols used for the connecting units 732 or 734 for connecting or disconnecting electric, pneuma- tic or hydraulic signals, although these symbols are normally used in electrotechnics. To illustrate that the symbols used may also relate to the connection or disconnection of a hydraulic or pneumatic pressure medium, it has been especially assumed for the device in Fig. 22 that the power signal D in this case consists of a pressure medium signal p , especially hydraulic pressure, the connecting units used being exemplified by hydraulic valve units 735, 738. Since a pressure medium signal is contemplated, the alternative electric power signal I in Fig. 22 is within brackets. An oppo¬ site signal -D applied to the connecting unit 735 has not been illustrated by an arrow acting on the unit and corresponding to the opposite signal applied since in this case the opposite signal consists of a return line to the tank. If the power signal D consists of a pneuma¬ tic signal, the connecting units 738, 735 consist of pneumatic valves, and no return line is necessary to the tank. When exemplifying the connecting unit 735, two control signal paths 747 and 748 and, thus, two ON/OFF signals B (723) have been used for actuating the illu¬ strated hydraulic valve. By using e.g. a valve with spring resetting, the same function is achieved by a single control signal path. When using a connecting unit consisting e.g. of an electromagnetically con¬ trolled connecting/disconnecting means, e.g. the connect¬ ing unit 732, two ON/OFF signals B applied to the unit may also be necessary if the connecting means is not provided with spring resetting (e.g. relay) or an opposite signal -B is applied to the unit 732. Since the same connection function can be achieved with one or two ON/OFF signals B, it is indifferent whether one or two control signals actuate the connect¬ ing unit. To facilitate the understanding of the con- nection/disconnection of the pressure level unit 700, use is here preferably made of a single ON/OFF signal B as illustrated, but it should be noted that the signal B may relate to two signals having different signal paths or a single signal applied to the pressure level unit 700. The illustrated alternative signals applied to the activating unit 721 and the power unit 722 are used for actuating a suitable signal or signals in the activating unit 721 and the power unit 722 in order to connect/disconnect the pressure level setting unit 700 in a manner similar to that earlier described for the control information ([S]), the acti- vating (A) and the power signal (D). The signals CSr Δ __], [S ] applied to the connecting units 733 and 734 may consist of a suitable electric, pneumatic or hydraulic signal or signals. In a part hydraulic working system/hydraulic working system having more than one working cylinder or hydraulic motor with associated main valves using a common pump flow, problems often arise in regard of the simultaneous supply of pressure medium to several cylinders or hydraulic motors so as to achieve, by the lever movement of the control system, the desired speed and accuracy for the simultaneous movement of the cylinders since the pressure demand of the cylin¬ ders often differs from one cylinder to another and the pressure medium tends to first flow to the cylinder having the lowest pressure. In this case, it is possible when simultaneously using several cylinders/hydraulic motors for providing a working movement, e.g. the working movement of an excavator, to distribute the cylinders/hydraulic motors on different part hydraulic working systems so that the working movement is provided by only one cylinder in one of the part hydraulic working systems or so divided as to cause minimum problems. This also minimizes the power of the pump drive motor M. Another alternative is, by different means, to provide throttling of the oil to the cylinders having lower pressure demand, which of course means power losses. This technique is also usable in the case of a single working pump for several cylinders where simultaneous movement of the piston rod of at least one cylinder takes place. Generally, hydraulic ex¬ cavators use at least two working pumps of which e.g. one pump is used in the part hydraulic working system for providing slewing of the excavator and the other for the part hydraulic working system producing the boom, dipper arm and bucket movements. One or some of the pumps are also used for propelling the excava- tor and/or driving other additional equipment connect- ible to the excavator. In order to increase the piston rod movement of the cylinder or the speed of rotation of the hydraulic motor and, thus, increase e.g. the speed of the digging movement (or transport speed of the excavator) from a lower speed for the digging movement (or transport speed) (low speed) to a higher speed (high speed), use is made e.g. of the pressure flow of the pumps employed for the digging movement, conjointly for all cylinders and/or hydraulic motors. When using several pumps conjointly for providing a pressure flow, one way of alleviating the above- mentioned problems in connection with simultaneous piston rod movement of the cylinders and different hydraulic pressures in the cylinders is, e.g. when employing two working pumps, to use a double set of main valves for each cylinder, one set of main valves being connected parallel to the pressure line (pump line) of one pump and the other set of main valves veing correspondingly connected to the other working pump, one main valve of each set being at the same time operated by the control system for controlling the piston rod movement of the associated cylinder and is connected in parallel with said cylinder. By a special arrangement of the main valves in the two sets, as disclosed in U.S. Patent 4,207,740, the above- mentioned problems can be considerably reduced. By this technique, high speed is thus obtained when simul- taneously using associated main valves in the two sets, and low speed is obtained when only one of each doubled main valve of one of the sets is operated by the control system. At low speed, the control system in one main valve set with associated pump only operates one or more main valves for the associated cylinder and in the other main valve set with associated pump another or several other main valves for the associated other cylinders. Thus, at least two main valves can be used in a hydraulic working system for controlling a single common cylinder. The invention as used in a commonly existing hydraulic excavator provided with tracks, is illustrat¬ ed in Fig. 24A and 24B. The invention is of course also applicable to other construction machines. An excavator generally consists of a superstructure, an undercarriage, and a digging equipment articulated to the superstructure. The superstructure is slewable through 360° in a conventional manner in relation to the undercarriage, e.g. by means of a hydraulic motor 951. The propulsion of an excavator is also provided in a conventional manner by means of an under¬ carriage having tracks or wheels. It is here assumed that tracking is achieved in a conventional manner by means of two hydraulic motors 955, 956 (track motors). The digging equipment (digging tool) traditionally consists of boom, dipper arm and bucket the movements of which generally in one plane are operated by the associated boom cylinder 952, dipper cylinder 953 and bucket cylinder 954. These boom, dipper arm and bucket movements often include the movement of the digging equip¬ ment when performing a digging movement (working movement) In certain excavators and most often tractors equipped with digging equipment (of tractor shovel type), the entire digging equipment can be rotated (pivoted) at the point where the boom is mounted on the construe- tion machine in a plane at right angles to the plane in which, as earlier described, the digging equipment normally moves. This pivotal movement may be regarded as part of the movement of the digging equipment. Further, there are digging equipments in which one or more of the link arms or the bucket of the digging equipment can be angled to achieve a digging movement in planes other than the conventional one. This is also regarded as part of the movement of the digging equipment. The term "digging equipment" also comprises digging equipments having one or more than two digging arms (digging links). In some cases, the bucket of the digging equipment is replaced by some type of additional equipment and often by a device (e.g. hook) for lifting purposes. Thus, the designation "working equipment of excavator" covers both this use and "digging equipment". In the case of excavators, the digging movement (working movement) generally implies digging equipment movement and slewing movement of the super- structure of the excavator. The control systems 300 with their control levers 320 constitute the control system 370 for operating the (working) movement of the working equipment, especially the digging equipment. Generally, one control lever is used for operating the slewing and dipper arm movements and the other control lever for operating the boom and bucket move¬ ments. The control systems 300 or the control system 370 bring about operation of the associated cylinders and the hydraulic motor by actuating the associated main valve (or valves) in a working hydraulics valve system 950. As will have appeared from the foregoing, the number of main valves used for controlling the piston rod movement of a single working cylinder or the rota- tion of the output shaft of a hydraulic motor may vary. In addition, these and other valves necessary for the hydraulic working system can be interconnected or connected, by lines or similar flow paths, to sepa¬ rate or common pump lines 220 and the return line 225 in different ways. Since this is of minor interest in the invention, it is only schematically illustrated in Figs. 24A and 24B by a working hydraulics valve system 950. The valve system 950 of course also includes any necessary hydraulic lines, non-return valves, filters, oil coolers, optional throttle devices and the like. In Figs. 24A and 24B, hydraulic lines ex- tend in a conventional manner from the right-hand side of the system boundary of the working hydraulics valve system 950 to hydraulic cylinders or hydraulic motors illustrated in the Figure. In practice, these hydraulic lines are partly concluded in the working hydraulics valve system 950, but this is of no imme¬ diate importance to the invention. The only feature of the valve system 950 which is of interest in the invention is the movement of the spool of the main valve or spools of the main valves and optional inter- connection of the oil flow of the pumps. Of special interest in the invention is however the use of a pump (or pumps) or pump system together with the associated pressure limiting unit (units) in the hydraulic working system 900 of the construction machine while the working hydraulics valve system 950 can at the same time be de¬ signed in several different ways. In the embodiment of the invention illustrated in Figs. 24A and 24B, the working hydraulics valve system 950 is supplied with pump flow from three pump systems 100 with associated pressure limiting units 260. One, some or all of the pump systems 100 may alternatively consist of a constant- displacement pump (or pumps). Figs. 24A and 24B show three pump systems 100 but, alternatively, the number of pump systems 100 ranges from one to several pump systems 100 driven by a common motor M or separate motors M. (For greater clarity, Figs. 24A and 24B do not show the motor M/motors M). If the pump system 100 consists only of a constant-displacement pump, the associated pressure limiting unit 260 is of course normally replaced by a conventional pressure relief valve. The propulsion (displacement forwards or back- wards) of the construction machine, especially the excavator, is controlled by means of a control system 390 whose output control lines, as in the control system 370, act on the main valves in the working hydraulics valve system 950 for controlling the rota- tional movement of the respective hydraulic motor 955, 956. In the case of excavators, it is also possible to perform the digging operation (digging movement) at low or high speed. This has been described above. In the device shown in Fig. 24A, shifting between low speed and high speed digging movement is carried out by means of a switching unit 780 whose output signal R is applied to the two control systems 300 (indicated by signal paths 781, 782 in full lines). A large pump flow for achieving high speed may alterna- tively be obtained by interconnecting pump lines 220 by a valve arrangement (not shown) in the working hy¬ draulics valve system 950, since the invention is not dependent upon the valve arrangement used. When shifting to low/high speed, the above-mentioned switching signal R is applied (acts on) the working hydraulics valve system 950 via a signal path/line 783 shown in Fig. 24A, for providing a disconnection or connection of pump flow from pumps by means of the valve arrangement used. At the same time, the pressure level setting unit 700 is supplied, via the signal path/line 794, with a direct or indirect switching signal R. Alternative¬ ly, the signal (switching signal) R can be applied to one or both of the control systems 300 and the control system 370 for controlling the movement of the working equipment. Moreover, the signal R may alternatively be simultaneously applied to one of the control systems 300 and the working hydraulics valve system 950 or, concurrently, both the control system 370 and the working hydraulics valve system 950. In all the alternatives, the pressure level setting unit 700 is supplied with a switching signal R via the signal path/line 794. In Figs. 24A and 24B, the switching unit 780 is illustrated by an electric switch which is manually operable by the machine operator and connected to an electric power source ϋ . An elec¬ tric signal R can then be obtained for shifting between low and high speed (low-high speed). In Figs. 24A and 24B, the switching signal R is applied e.g. to the two control systems 300 for achieving high speed, the signal R acting e.g. on solenoid valves for connect¬ ing the control signals to the above-mentioned double set of main valves. Thus, interconnection is effected at least of several pumps/pump systems for using a common pump flow to the working cylinders and/or hy¬ draulic motor employed for the digging movement. When shifting back to low speed by means of the switching unit 780, the solenoid valves of course disconnect the control signals to the double set of main valves. Alternatively, the solenoid valves may of course be arranged in such a manner in the control systems 300 that shifting between low and high speed can be achieved with a reversed switching signal. The switching unit 780 shown in Fig. 24A emits a switching signal R having signal values +U or 0 (zero). (The zero signal of course corresponds to absence of a signal ) . To the electric switch 780 shown in Figs. 24A and 24B it is possible to connect either two signals sources of different polarity (+U and -ϋ ) or both a signal source and a signal of reverse polarity from this signal source, for obtaining two different switching signals R of different polarity. In this case, the signal value -U of the switching signal R corresponds e.g. to the zero signal obtained upon connection to a single signal source. Alternatively, the signal source +ϋ may of course consist of a pressure medium source and the switching unit 780 of some-type of ON/OFF valve. The signal R may then consist of a manual¬ ly triggered electric (U/I), pneumatic (p) or hydraulic (p) signal. The signal paths illustrated in Figs. 24A and 24B then consist of electric lines or pressure medium lines. In this case, the switching unit 780 may also consist of a manually operable mechanical lever unit whose output signal R is a mechanical ove- ment. In such case, the illustrated signal paths consist of some type of wire cable and/or linkage system. The low speed/high speed signal (switching signal) R ap¬ plied to the control systems 300, 370 or the working hydraulics valve system 950 may consist of a directly (shown in Fig. 24A) or an indirectly obtained signal R. The meaning of a direct or indirect signal has been discussed above in connection with Fig. 23. Fig. 24A shows the switching unit 780 with a single (signal) output 784 for connecting illustrated (signal) lines, but the (signal) lines may of course alter¬ natively be directly connected to separate signal outputs with the same or different types of signal (mechanical, electric, hydraulic or pneumatic signals). In the manner described above, the pressure level setting unit 700 in Fig. 24A is supplied either with one of the control information signals [S], [S, ], [S 2 ] or simultaneously with [S, ] and [S 2 ]. In Fig. 24A, the signal paths of the control information signals are designated 785, 786 and 787. Alternatively, the pressure level setting unit 700 is supplied with one of the above-mentioned control information signal options depending on the condition or conditions placed on the digging movement for providing an increase of the maximally obtainable hydraulic working pressure for one or more of the hydraulic working cylinders 952, 953, 954 and/or the hydraulic motor 951. If the condition for the digging movement is satisfied and the optional ON/OFF signal B is present, the power signal D is applied to the setting means 702 of each pump system 100 shown in Figs. 24A and 24B and, optional¬ ly, the setting means 701 of the associated pressure limiting unit 260 from the pressure level setting unit 700 via signal lines 788, 789, 790, 791, 792 and 793. It is of course self-evident that the pres¬ sure level setting means 702 of each pump system 100 or the setting means 701 of the pressure limiting unit 260 may, alternatively, by means of separate or various common signal lines be directly or indirect¬ ly connected to separate or common outputs on the pressure level setting unit 700. Using separate and/or common signal outputs from the level setting unit 700 is necessary if the setting means 701, 702 for their function or different signal types (electric, hydraulic or pneumatic signals) so require. It is necessary to use separate outputs from the pressure level setting unit especially when different conditions require that the setting means 701, 702 for different pumps systems with associated pressure limiting unit should be actuated. Whether optional signal line branch¬ ing takes place for the same type of signal in or after the pressure level setting unit is unessential. By type of signal is here meant e.g. an electric, pneumatic or hydraulic signal. If the requirement or requirements placed on the digging movement for providing an increase of the obtainable working pressure also involve the con- dition that such an increase should only be effected at low or high speed for the digging movement (low speed or high speed), the pressure level setting unit is supplied directly or indirectly with the low/high speed signal R by means of the signal line 794 connect- ed to one of the lines 781, 782, 783, 795 or the (signal) output 784 or (signal) outputs of the switching unit 780. If, as in the device illustrated in Fig. 24A, the switching signal R for low/high speed directly actuates the control system 370 or both or one of the control systems 300, the switching signal R applied to the pressure level setting unit 700 may optionally be replaced by a corresponding low/high speed detecting signal H. This alternative signal H, represented by a broken arrow in Fig. 24A, may alternatively be applied to the pressure level setting unit 700, either from the control system 370, one or both of the control system ' s 300 or the working hydraulics valve system 950. For the sake of clarity, the associated signal paths/lines have been excluded from Fig. 24A. The line 794 shown in Fig. 24A is of course excluded when using the above-mentioned alternative signal H. When relying, for instance, on connection or disconnection of one or more doubled main valves for obtaining high/ low speed, the control signal (servo pressure signal) of at least one of the doubled main valves or the sole doubled main valve may, directly or after con- version of the pressure control signal into an elec¬ tric signal, constitute the low/high speed detecting signal H. Alternatively, the low/high speed detect¬ ing signal H may be a signal derived by indirect or direct detection of the movement (or movements) of the spool (or spools) of the doubled main valve (or main valves). Examples of such recordings have pre¬ viously been described in connection with the descrip¬ tion of the control information signal [S]. In order to raise the obtainable working pressure for one or more of the working cylinders of the digging equipment when controlling the digging movement, the pressure level setting unit 700 may, instead of one or conjointly with control information signals [S], [S, ] t s 2 ^ applied as earlier shown, alternatively be supplied with a signal (or signals) [z] representing the position, movement and speed of movement of the digging equipment (especially at least the boom) in relation to ground level, horizontal plane or super¬ structure of the machine. If the conditional unit of the pressure level setting unit 700 requires wholly or partly a signal (signals) directly corresponding to the position, movement or speed of movement of the digging equipment, the pressure level setting unit 700 or the conditional unit has electric means, especially a microcomputer unit, in order to make computations on the basis of the signal or signals applied to the unit 700. Alternatively, these computa¬ tions may of course be carried out wholly or partly in one or more electrocomputing units and thereafter be applied to the pressure level setting unit 700. Sensors or angular measuring means are used for de- tecting the rotation of at least the boom about its mounting in the superstructure of the machine and, optionally, the rotation of the dipper arm about its joint common to the boom and, optionally, also the rotation of the bucket about its joint common to the dipper arm. The sensors or the angular measuring means are disposed at the respective joint. The sensors are provided for detecting a fixed preset rotational position and consist e.g. of electric switches. Two sensors are required for recording two fixed angular positions. The angular measuring means are arranged to detect the angle of rotation, e.g. by means of rotary potentiometers. Besides, one or more angular measuring means are optionally disposed in or on the superstructure of the machine for recording the in- clination of the superstructure in relation to the horizontal plane. The angular measuring means used in this case are arranged to measure this inclination by gravity. One example of such angular measuring means is a pendulum potentiometer. Alternatively, the inclination of at least the boom and/or dipper arm in relation to the horizontal plane is detected by angular measuring means disposed on the boom and the dipper arm, respectively, and optionally simul¬ taneously also the inclination of the superstructure of the excavator in relation to the horizontal plane in the manner described above. All the angular mea- suring means used in this alternative are arranged, by gravity, to measure the inclination relative to the horizontal plane. One example of such angular measuring means is a pendulum potentiometer. Alter¬ natively, both of the above-mentioned options for detecting the movement of the digging equipment can be combined, or detection can be performed wholly or partly indirectly by sensors or angular measuring means recording the rotation of one or more working cylinders about their mounting point or the inclination of a cylinder relative to the horizontal plane. The embodiment of the invention shown in Fig. 24A is of course also applicable to a construction machine lacking the possibility of shifting between low and high speed during digging or where the condition for increasing the maximally obtainable working pressure is not related to whether digging is carried out at high or at low speed. In such case, the switching unit 780 shown in Fig. 24A and the associated signal paths/lines 781, 782, 783, 784, 794, 795 and the signal H in Fig. 24A are excluded. If, in such case, for increasing the maximally obtainable working pressure, conditions for the digging speed are also stipulated, the value of the control information signal [S] or a signal [Y] representing the speed of movement of the boom, the dipper arm or the boom and the dipper arm of the digging equipment can be applied to the pressure level setting unit 700. In the diagram schematically shown in Fig. 24A for a hydraulic excavator, the propulsion (transport) of the excavator is provided by the hydraulic motors (track motors) 955 and 956. The propulsion is con- trolled by the control system 390 which, like the control system 300, actuates by control lines (hydrau¬ lic pressure control lines) the main valves of the working hydraulics valve system 950 for controlling the flow of hydraulic oil to the hydraulic motors 955, 956. One or more pump systems 100 and/or constant- displacement pumps may alternatively be used for pro¬ viding hydraulic oil flow to the hydraulic motors 955, 956. In the case of a hydraulic excavator pro- vided with tracks, the forward and rearward propulsion (transport) of the excavator is generally operated by a control means, e.g. the pedal (acting on valves), which is included in the control system 390 and by means of which the direction of rotation of the drive shafts of the hydraulic motors 955, 956 is operated, and the control of the movement is operated by another control means, e.g. a transport control lever, which is included in a control system and by means of which the speed of rotation of the hydraulic motors 955, 956 is operated. The control means 390 for controlling the construction machine during transport may consist e.g. of a control lever simultaneously actuating a double set of pressure control valves of which e.g. one set of the pressure control valves is supplied with control pressure from the servo pump during trans¬ port in the forward direction and the other set of pres¬ sure control valves is supplied with control pressure from the servo pump during transport in the rearward direction. Shifting of servo pressure from the servo pump to the respective set of pressure control valves is brought about by the above-mentioned pedal control means. Each set of pressure control valves operated by the above-mentioned (transport) control lever corresponds, except that the pressure control valves here supply maxi- mum control pressure (servo pressure) to the control lines (pressure control lines) when the (transport) con¬ trol lever is in neutral position, to the control system 300 illustrated in Figs. 1 and 2. The main valves of the working hydraulics valve system 950 are ope¬ rated in a conventional manner by the control lines for supplying the hydraulic oil flow to the hydraulic motors 955, 956 so as to provide control of the speed of rotation of the output shafts of the hydraulic motors. The exemplification of the control system 390 has involved a fully hydraulic system, but the control system may, like the control system for the digging movement, consist of an electrohydraulic or a manual control system. In a manner corresponding to that described above for the control information signals in connection with the control of the digging movement, a corresponding control information signal (or signals) [TS] or a low/high speed detecting signal TEC is here obtained from the control system 390 or from the working hydraulics valve system. The two signals TG and [TS] are similar to and are obtained in the same way as earlier described for the corresponding signals H and [S], but are here preceded by the additional letter T (T = "Transport") to be distinguished from signals obtained from the digging movement. For shifting from load to high transport speed (low/high speed), one or more additional pumps or pump systems can be inter- connected in a corresponding manner as described above for achieving high digging speed. Moreover, for achiev¬ ing high transport speed the track motors (hydraulic motors) 955, 956 can be connected in series by a valve arrangement in the working hydraulics valve system 950 so that the common oil flow of the pump or pumps used will first drive one hydraulic motor and immediately afterwards also the other hydraulic motor. If the torque and the speed of rotation required for propulsion (transport) are provided in that the torque and the speed of rotation of the output shaft or shafts of one or more hydraulic motor (or motors) are transmitted by one or more gears (e.g. gear unit or gear boxes (which is common in wheeled excavators), shifting between low and high transport speed (or alternatively, intermediate levels' of the transport speed) can be achieved e.g. by changing the gear ratio of the gear unit or the gear ratio derived from the gear box. Al¬ ternatively, shifting between low and high transport speed may of course also be achieved by both changing the above-mentioned gear ratio and changing the hydrau- lie oil flow to the hydraulic motor (or motors) in the manner described above. Shifting between low and high transport speed is effected by means of a switching unit 720 whose output signal TR (low/high speed signal during transport) is applied to the control system 390 or the working hydraulics valve system 950, or is re¬ placed by a signal corresponding to the low/high speed signal TH. The signal TH is obtained in a manner corre¬ sponding to that of the low/high speed detecting signal H for the digging movement. The switching unit 720 is identical with the above-mentioned switch 780. The alter¬ native embodiments of the switch 780 described above thus also apply to the switch 720. Alternatively, the signal TR is applied to the working hydraulics valve system 950 by a signal path/line 716 or to the control system 390 by a signal path/line 717. Moreover, the pressure level setting unit 700 is alternatively supplied with the control information signal [TS] or the high/low speed recording signal TH. In those cases where shift¬ ing between low and high transport speed is carried out by changing the gear ratio in the mechanical gear/ gear box as described above, the switching unit 720 supplies the gear or gear box whose gear ratio should be changed, with a signal TG (manual, mechanical, elec¬ tric, pneumatic or hydraulic signal) acting on means for changing the gear ratio of the gear or the gear box. The signal TG may then simultaneously be applied directly or indirectly (alternatively after conversion into another corresponding signal type) to the pressure level setting unit 700. Alternatively, a correspond¬ ing signal TN (manual, mechanical, electric, pneumatic or hydraulic signal) from the gear or the gear box representing the gear ratio (e.g. low or high speed) can be applied to the pressure level setting unit 700. The signal TN can of course be divided into se¬ veral similar and/or different signal types applied to the pressure level setting unit 700. In other respects, the signals TG and TN correspond to the switching signal TR, i.e. the switching signal R. With the above-mentioned arrangement, the obtain¬ able hydraulic working pressure used for the propulsion (transport) of the excavator can be increased, as described above, by means of the hydraulic motors 955, 956 for increasing the torque of the output drive shafts of the hydraulic motors, with or without any condition being set for the speed' (low/high speed) and/or control of the propulsion (transport). If, for instance, it is conditioned that an increase of the torque of the output drive shafts of the hydraulic motors 955, 956 used for the propulsion should only be automatically increased or permit being increased at high speed, the pressure level setting unit 700 is supplied with the low/high speed signal TR, or the signals TG, TN or TH, and when the condition is satisfied, the pressure level setting unit applies the power signal D as described above at least to the setting means 702 of the pump system 100 for the hydraulic motors and to the setting means 701 for the pressure limiting unit optionally associated with the pump systems/pumps. By using the ON/OFF signal B, the torque can be automatically increased or allowed to increase when the condition is satisfied. In the illustrated device, use is made of two hydraulic motors, 955, 956, but the torque of the output drive shafts of one or more than two hydraulic motors may also be increased in this way. If both the torque of the output drive shaft of the hydraulic motor and the gear ratio of the gear/gear box used for propulsion are changed, the signal TN may alternatively be applied to the pressure level setting unit instead of the low/high speed signal TR or TG. The embodiment of the invention shown in Fig. 24A is of course also applicable to a construction machine lacking the function of shift¬ ing between low/high transport speeds or where the condition for increasing the maximally obtainable working pressure is not low or high transport speed. In such a case, the switching unit 720 shown in Fig. 24A and the associated signal paths/lines 716, 717, 718 are excluded, as are also the signals TH, TN and TG applied to the pressure level setting unit 700. The same applies to the digging movement if, additionally, shifting between low and high digging speed cannot be effected. If, in such case, the maximally obtainable working pressure should be increased for increasing the torque obtainable by the hydraulic motor/hydraulic motors and if a condition for increasing the maximally obtainable working pressure is set for the transport speed, the control information signal [TS] or a signal W can be used directly or indirectly by means of sen- sors detecting the transport speed, for applying to the pressure level setting unit 700. What applies in other respects for obtaining a higher hydraulic motor torque corresponds to that previously described for in¬ creasing the maximally obtainable working pressure for a digging movement since an increase of the hydraulic motor torque is achieved by an increase of the maxi¬ mally obtainable working pressure. For the digging movement, it is necessary, if signals derived from sensors detecting the movement of the working equipment are disregarded, only to replace the control systems 300 or the control system 370 with the control system 390 and replace the signals R and H with TR and TH and relate any conditions optionally used for the digging movement (working movement) to the movement of propulsion. In the devices for temporarily achieving an in- crease of the maximally obtainable working pressure where the condition from the digging and/or propulsion movement is of the high/low speed type, it is possible, alternatively, to use conditions of another or other divisions of the speed of movement. In the above-mentioned embodiments of the invention, it is possible to dispense with the pressure limiting unit 260 when using the pump system 100 with rapidly adjustable control pressure level (p^)- In the illu¬ strated devices, one, more or all of the pressure limit- ing units 260 used for the pump systems 100 may thus be excluded. In the devices described above, the setting of the pressure limiting level of the pressure limiting unit 260 and of the pressure control level of the pump system 100 is carried out by the setting means 701, 702. If the pressure limiting unit 260 or the regulator circuit/regulator unit of the pump system 100 for controlling the pressure limiting level does not require any special setting means 701, 702, a suit¬ able power signal D directly corresponding to the re- spective unit or system is applied to the respective regulator circuit/regulator unit used. In the above- mentioned embodiments of the invention, the illustrated control signals [S], [S^ [S-ϋr TS] are directly de¬ rived (obtained) from the respective control system, but these signals may also be wholly or partly indirectly derived from sensors detecting the spool movement of a main valve. Although the main valve is not included in the control systems per se but in the hydraulic working system, such a derived signal is considered equiva- lent to the corresponding control information signal in the associated control system. In this description, the control lines from each control system 300, 370, 390 as indicated by broken lines, to the respective main valves are drawn, for greater clarity, outside the system boundary of the respective control system, but these control lines are included in (belong to) the respective control system. The same applies to the corresponding, alternatively used mechanical control system or systems 500. In the above-exemplified embodi¬ ments of the invention, the control systems 300, 370, 390 have been used, but these embodiments also apply to an alternatively corresponding mechanical control system or systems 500. The control lines 310, 311 or 310, 311, 312, 313 indicated by broken lines in the Figures consist of wire cable and/or linkage systems 500 or 511, 513. The junctions (branching points) of the control lines illustrated here consist of corre¬ sponding mechanical branching devices. Alternative embodiments of the invention as exem¬ plified in Figs. 6, 7, 11, 12 and 13 are obtained if the pressure limiting unit 260 illustrated consists of a conventional, manually settable pressure relief valve 205 according to Fig. 1 and the illustrated piston and cylinder assembly 241, 242 and the control line 402 are excluded. (See e.g. Fig. 25 where the arrange¬ ment consists of the above-mentioned alternative embo- diment of the device according to Fig. 6). Corresponding alternative embodiments of the invention shown in Figs. 20 and 21 are obtained if the illustrated pressure limiting unit 260 only consists of a conventional, manually settable pressure relief valve 205 according to Fig. 1 and if the setting means 701 with the asso¬ ciated control line 711 shown in Figs. 20 and 21 is excluded. Further, the alternative embodiments of the invention exemplified in Figs. 24A and 24B are obtained if one or more of the illustrated pressure limiting units 260 each consist only of a conventional, manually settable pressure relief valve 205 according to Fig. 1. For the pressure limiting unit (or units) which only consist of the above-mentioned pressure relief valve 205, the setting means 701 in Fig. 24 with the associated control lines 789, 790, 791, 792 and 799, respectively, is of course excluded. In the alternative embodiments of the devices as described above and exem¬ plified in Figs. 6, 7, 11, 12, 13, 20, 21, 24A, 24B and 25 where the pressure limiting unit 205 or the pressure limiting units wholly or partly have been re¬ placed by a conventional pressure relief valve (or valves 205), the pressure relief valve 205 used is set to a pressure level (e.g. , n in Fig. 4 or 5) which is higher than the settable low (e.g. p, 5 in Fig. 4 or 5) pressure control level (pressure limiting level) of the pump system 100. When temporarily increasing the maximally obtainable working pressure, the pressure control level of the pump system 100 is raised to a pressure level (e.g. p ? in Fig. 4 or 5) which is at least ^max equal to the preset pressure level (e.g. p, Q in Fig. 4 or 5) of the pressure relief valve 205. The device shown in Fig. 6 for temporarily increas¬ ing the maximally obtainable hydraulic working pressure can also be provided so as to be dependent on one or more conditions (conditions of use) being satisfied in order to provide the (switching) signal G for switch- ing the valve 403. One example of such a condition is that the maximally obtainable hydraulic working pressure should be obtainable only at low speed (alter¬ natively high speed) of the digging movement (low speed) and/or at low (alternatively high) propulsion speed. That described earlier regarding the setting means 701 and the associated (power) signal D, except that the means 701 can also be a proportional magnet, also applies to the switching means 420 and the associat¬ ed signal G. The switching signal G may then consist of the same switching signal R or TR as used for shifting between low/high speed. Alternatively, the signal G may consist of a switching signal R or TR converted into another signal form. Alternatively, the switching signal G may consist of a signal TH, H, TN or TG cor ¬ responding to the switching signal R or TR. Alterna- tively, the condition can also be satisfied by causing the pressure medium in the control line 401 shown in Fig. 6 to also actuate the valve arrangement which is used in the control system 300, 370, 390 and/or the hydraulic working system/working hydraulics valve system 950 and by means of which switching to a certain type of digging/equipment movement and/or speed of the movement or transport movement and/or speed of the transport movement. This can be exemplified, e.g. for the digging speed (high/low speed), in Fig. 25. It should be noted that the device in Fig. 25 consists of the previously described alternative embodiment of the invention according to Fig. 6 with only a ma¬ nually presettable pressure relief valve 205, but addi¬ tionally provided with a branch control line 405 con- nected to the control line 401. The control line 405 is used for operating the control system 300, 370 for effecting the movement and/or the valves used for the hydraulic working system, by means of which switching to high/low speed is achieved. In other words, the valve 403 in the unit 400 is used for switch¬ ing to a certain type of digging/machine movement (or alternatively, digging/equipment movement speed) or transport movement and/or transport speed, this pressure being also used in the control line 401. (The same applies to the embodiments exemplified in Figs. 11, 12, 13 and also to the embodiments exemplified in Figs. 20 and 21 if the above-mentioned control line 405 is connected to the illustrated control line 710, and the control line 405 may also consist of an electric (control) line.) The unit 400 in Fig. 6 corresponds to the pressure level setting unit 700 in the device according to Fig. 24A only consisting of the power unit 722. (See also the pressure level setting unit 700 according to Fig. 21. ) The unit 400 in Fig. 25 corre¬ sponds to the pressure level setting unit in the device according to Fig. 24B consisting of both the activating unit 720 and the power unit 722 and to the power signal D of the pressure level setting unit 700 being also used for actuating the valve arrangement which is used in the control system 300/370 (via line 777) and/or the working hydraulics valve system 950 (via line 779) and by means of which switching is effected to a certain type of digging/machine movement and/or speed of movement. (The same applies to a certain type of transport movement and/or transport speed, in which case the line 778 and/or 779 shown in Fig. 24B is used) .

Claims: CLAIMS 1. A method for changing the obtainable hydraulic working pressure in the hydraulic system of a construc¬ tion machine, especially an excavator, comprising a control system (300, 370, 390, 500), a hydraulic working system (900) and, included in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump (or pumps) (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limiting unit (260), c h a r a c ¬ t e r i z e d by automatically changing the pressure control level (p~) of one or more pumps systems (100), and/or one or more of the pressure control level of both the pump system (100) and the associated pressure limiting unit (260) in connection with switching, especially manual, to a certain type of digging/machine movement (e.g. movement when the piston rods of the working cylinders of the boom, the dipper arm and the bucket of the working equipment are moving out from the cylinder), and/or the speed of the movement (e.g. low/high speed) or transport movement and/or the speed of the transport movement. 2. Method for controlling the obtainable hydraulic working pressure in the hydraulic system of a construc- tion machine, especially an excavator, comprising, in¬ cluded in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump or pumps (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limit¬ ing unit (260) c h a r a c t e r i z e d by changing both the pressure control level (p.-,) of the pump system (100) and the pressure level (opening pressure) of the pressure limiting unit (260), or only the pressure control level (p~) of the pump system (100) in depen¬ dence upon both the position relative to the ground level (horizontal plane) of at least one of the boom, the boom and dipper arm or the boom, dipper arm and bucket of the (digging/Iifting) equipment, and the permissible tipping load with regard to the stability of the construction machine, established (predetermined) for the machine in this position of the working equip- ment (digging/lifting equipment). 3. A device for changing the obtainable hydraulic working pressure in the hydraulic system of a construc¬ tion machine, especially an excavator, comprising a control system (300, 370, 390, 500), a hydraulic working system (900) and, included in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump (or pumps) (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limiting unit 260, c h a r a c ¬ t e r i z e d in that the pressure level setting unit (700) is supplied with one or more control infor¬ mation signals ([S], [TS]), that the pressure level setting unit (700) has means which are arranged, in dependence upon the control information signal ([S], [TS] ) applied, to apply to one or more setting means (702) a power signal D for setting the pressure control level (p 2 ) °f the respective pump system (100), and/or to simultaneously apply the power signal D to both the setting means (702) of one or more pump systems (100) and the setting means (701) for the pressure limiting unit (260) used by the pump system. 4. Device for changing the obtainable hydraulic working pressure in the hydraulic system of a con- struction machine, especially an excavator, comprising a control system (300, 370, 390, 500), a hydraulic working system (900) and, included in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump (or pumps) (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limiting unit (260), c h a ¬ r a c t e r i z e d in that a pressure level setting unit (700) is supplied with one or more switching signals (G, H, R, TR, TH, TN, TG) and/or one or more control information signals ([S], [TS]), that the pressure level setting unit (700), when a signal is applied, has means for applying to one or more setting means (702) a power signal D for setting the pressure control level of the respective pump system (100), and/or for simultaneously applying the power signal D to both the setting means (702) of one or more pump systems (100) and the setting means (701) for the pres¬ sure limiting unit (260) used by the pump system (100). 5. Device for changing the obtainable hydraulic working pressure in the hydraulic system of a construc- tion machine, especially an excavator, comprising a control system (300, 370, 390, 500), a hydraulic working system (900) and, included in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump (or pumps) (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limiting unit (260), c h a ¬ r a c t e r i z e d in that a pressure level setting unit (700) is supplied with one or more switching sig- nals (G, H, R, TR, TH, TN, TG) and/or one or more con¬ trol information signals ([S], [TS]), that the pressure level setting unit (700), when a signal is applied, has means for applying to one or more setting means (702) a power signal D for setting the pressure control level (p~) of the respective pump system (100), and/or for simultaneously applying the power signal D to both the setting means (702) of one or more pump systems (100) and the setting means (701) for the pressure limiting unit (260) used by the pump system (100), that the power signal D also actuates a valve arrange¬ ment which is used in the control system (300, 370, 390, 500) and/or the hydraulic working system/working hydraulics valve system (950) and by means of which switching is effected to a certain type of digging/ equipment movement and/or speed of the movement (e.g. high/low speed) or transport movement and/cr speed of the transport movement). 6. Device for controlling the obtainable hydraulic working pressure in the hydraulic system of a construc¬ tion machine, especially an excavator, comprising, in¬ cluded in the hydraulic working system (900), one or more pump systems (100), e.g. a variable-displacement pump (or pumps) (adjustable pump or pumps) with power and/or pressure control of a pressure medium flow supplied by a pump, with or without a pressure limiting unit (260), c h a r a c t e r i z e d in that a pres- sure level setting unit (700) is supplied with a signal (or signals) [Z] representing the position relative to the ground level (horizontal plane) of at least one of the boom, the boom and dipper arm or the boom, dipper arm and bucket of the (digging/lifting) equipment, that the pressure level setting unit (700) has means for providing a suitable power signal (or signals) D with respect to the permissible tipping load for maintaining the stability of the construction machine, that the pressure level setting unit (700) applies to one or more setting means (702) a power signal D for setting the pressure control level (p ? ) of the respective pump system (100), and/or simultaneously applies the power signal D to both the setting means (702) of one or more pump systems (100) and the setting means (701) of the pressure limiting unit (260) used by the associated pump system (100). 7. Device as claimed in claim 5, c h a r a c ¬ t e r i z e d in that the pressure level setting unit (700) consists of an electric activating unit (721), e.g. a conditional unit (350), and a drive unit (722), that the activating unit is supplied with a control information signal (or signals) ([S], [TS]) and/or one or more switching signals (G, H, R, TR, TH, TN, TG, W), that the activating unit (721) has means for applying an activating signal (A) to the drive unit (722), that the drive unit, when the acti¬ vating signal A and/or the switching signal G is applied, has means for providing an output power signal D from the drive unit. 8. Device as claimed in claim 6, c h a r a c - t e r i z e d in that the pressure level setting unit (700) consists of an electric activating unit (721), especially a microcomputer unit and a drive unit (722), that the activating unit (721) is supplied with the signal/signals [Z], that a signal (or signals) corresponding to this/these signals [Z] and applied to the unit (721) and relating to the predetermined permissible tipping load for the construction machine are compared, and that a control signal (activating signal ) A derived from the comparison and applied to the drive unit (722) is produced. 9. Device as claimed in claim 7 or 8 , c h a ¬ r a c t e r i z e d in that the drive unit (721) consists of at least one electrohydraulic control system (332) emitting a hydraulic power signal D, or one or more electric drive units (voltage unit)/DA- (digital-to-analog)converter, with or without signal amplification, emitting an electric power signal D suitable for the setting means (701, 702) used. 10. Device as claimed in claim 7, c h a r a c - t e r i z e d in that the drive unit (721) consists of a hydraulic, pneumatic, electromagnetic or manually operable pressure medium valve (403) connected to a pressure source (410), especially a servo pump (301). 11. Device as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that the setting means (701, 702) consist of either a piston and cylinder assembly (244, 245, 242, 241), an electromagnet with or without electric amplifier unit, a propotional magnet with or without electric amplifier unit, adjust¬ ing means (e.g. a piston and cylinder assembly rotating by a lever the set screw of the pump system (100) for pressure control level setting), an electric motor actuating by gear means a set screw for pressure level setting or a mechanical device for transmitting a mechanical or manual signal. 12. Device as claimed in any one of the preced- ing claims, c h a r a c t e r i z e d in that the activating signal A/power signal D consists of an electric signal (I), a pneumatic or hydraulic pres¬ sure medium signal. 13. Device as claimed in claim 5, c h a r a c - t e r i z e d in that the pressure level setting unit (700) consists of an electric, hydraulic or pneu¬ matic power unit (722, 400) supplied with a switching signal G. 14. Device as claimed in claim 13, c h a r a c - t e r i z e d in that the power unit (722, 400) con¬ sists of a hydraulic drive unit having an ON/OFF valve (403) which upon switching connects the output (or out¬ puts) (401, 405) of the power unit (400, 722) to a pres¬ sure source (410), especially the servo pump (301), or alternatively to the working pressure line (220)/ working cylinder (210 )/pressure medium line (or lines) (231, 232) of the working cylinders in the pump system or systems used, via one or more connecting lines (412, 417, 415) and shuttle valves (413, 416). 15. Device as claimed in claim 13, c h a r a c ¬ t e r i z e d in that the signal G applied is a pneuma¬ tic, hydraulic, electric, mechanical or manual signal. 16. Device as claimed in claim 14, c h a r a c ¬ t e r i z e d in that the valve (403) consists of a hydraulically, pneumatically, eleetromagnetically, mechanically or manually operated valve.

Inventors: CARLQVIST OLA, OLOFSSON BERTIL, CARLQVIST, OLA, OLOFSSON, BERTIL
Applicants: AKERMANS VERKSTAD AB, AAKERMANS VERKSTAD AB
Application year: 1987
Main classification: F15B13
IPC codes: E02F9