EP0601047B1 - Hydraulic vibration dampening system for machines provided with tools - Google Patents

Abstract

PCT No. PCT/EP92/02019 Sec. 371 Date Mar. 2, 1994 Sec. 102(e) Date Mar. 2, 1994 PCT Filed Sep. 2, 1992 PCT Pub. No. WO93/05244 PCT Pub. Date Mar. 18, 1993.A hydraulic system for machines provided with tools, particularly for wheel loaders, fork lifts or the like, including comprising at least one hydraulic accumulator, distributing valves, manometric switches and at least one nozzle for variably adapting the load pressure of the hydraulic accumulator to the load pressure of the lifting cylinder, wherein the load-damping system formed by the hydraulic accumulator is connected to the hydraulic lines responsible for lifting and lowering and extending between the hydraulic cylinder(s) and a control valve.

Description

The invention relates to a hydraulic system for mobile working machines provided with implements, in particular for wheel loaders, forklifts or the like Control valve is connected, wherein the load suspension system can be switched on or off depending on predetermined operating states.

Pneumatic-tipped construction machines often cover longer distances when used on the construction site. You carry out the change of construction site as well as the journey to its locations on your own axis, as they meet the admission requirements for participation in public transport, albeit with requirements on a case-by-case basis.

The driving speeds that can be achieved during operation make a significant contribution to the handling performance and thus the economy of the machine. But even with devices that are often moved from construction site to construction site or that have to travel longer distances to reach them, the time they need for this is a significant factor in the cost calculation of the entrepreneur.

Now the driving speed in this type of work machine is not limited by the engine power - apart from negotiating steep inclines - but by the vibrations into which the vehicle gets as a result of the uneven ground. The driver is therefore required to choose a speed that is in many cases far below the performance that is possible. The main reason for the "rocking" of the machine is the lack of suspension. Suspensions on construction machines have so far only been used on machines for special purposes, e.g. in military use with the requirement for speeds up to over 60 km / h. The reasons why these types of construction machines are built unsprung are, on the one hand, that for the loading processes a suspension would even be disadvantageous because of its yielding under the lifting and tearing forces. On the other hand, the installation of a suspension represents a relatively high construction effort, which of course would have to result in considerable additional costs.

From DE-C 39 09 205, a hydraulic system for construction machines, in particular wheel loaders, tractors and the like, is known which contains a work tool which can be actuated by hydraulic cylinders, in particular a loading shovel, one for actuating the hydraulic cylinders from a pressure source via a control valve to the Hydraulic cylinders leading main line is provided, one of which leads to at least one hydraulic accumulator after the control valve Branch line branches in which a switchable shut-off valve is arranged. A filling line bridging the shut-off valve is provided, which connects the main line to the hydraulic accumulator, a pressure reducing valve being arranged in the filling line. The pressure reducing valve is set to the carrying pressure of the hydraulic cylinders and is preferably designed as a pressure relief valve or pressure cutter. The switchable shut-off valve is designed as a solenoid valve which is controlled as a function of the driving speed or as a function of the tilting angle of the working tool, the switching point being set when the solenoid valve is controlled as a function of the driving speed so that it can only be exceeded in second gear.

Since only a predetermined carrying pressure (e.g. 120 bar) can be set when using pressure reducing valves, which is not to be regarded as a realistic value in every working state, the load suspension system used here is to be regarded as inadequate for all operating states of the working machine. The gear or driving speed-dependent switching of the pressure reducing valve also cannot optimally do justice to the pitching vibrations that occur in the operating state.

The international patent application WO 90/05814 discloses a shock absorption system for a mobile machine, such as a wheel loader, forklift or the like. The damping system is provided here between the hydraulic cylinder (s) and a directional valve and contains a memory which is connected to the pressure side of the respective cylinder via lines and an intermediate valve. The suction side of the respective cylinder is connected to the tank via further lines and the same valve. When the piston is acted on as a result of an impact acting from the outside, the latter is deflected and the pressure on the pressure side of the cylinder is increased, hydraulic oil being released into the accumulator via the associated lines. At the same time, oil is drawn in from the tank via the corresponding other lines and delivered to the side of the cylinder facing away from the pressure chamber. When this condition is reached, the accumulator releases oil under pressure via a throttle valve arranged in a bypass in front of the valve and leads it to the pressure side of the cylinder. This St.dT can be used to dampen shocks introduced into the system, but this does not make it possible to adapt the work equipment to variable loads and vibrations, so that pitching vibrations of the work equipment cannot be compensated for during transport trips. The system is switched on manually and the valve switched to passage, whereby the load, for example a bucket, suddenly drops depending on the storage size by a predetermined amount, since the working pressure did not adapt to the storage pressure before the system was switched on.

The aim of the subject matter of the invention is to further develop the system specified in WO 90/05814 in such a way that the pitching vibrations of the load that occur during transport journeys, in particular on unfavorable road surfaces, are largely avoided, with an undesired lowering of the load being reliably avoided when the system is switched on.

This aim is achieved according to the invention in that at least one nozzle is provided in connection with a plurality of directional valves between the load suspension system and the lifting cylinder (s) in order to variably adapt the load pressure of the hydraulic accumulator to the respective load pressure of the lifting cylinder (s), the valves via pressure switches provided in pilot lines between a pilot transmitter and the control valve are actuated.

Advantageous further developments of the subject matter of the invention can be found in the subclaims.

The hydraulic system according to the invention is particularly suitable for transfer and transport journeys with an empty or loaded implement.

If the driver actuates the pilot control transmitter, the directional control valves are switched to neutral position by the pressure switches interacting with them and the load suspension system is switched off. The hydraulic pressure in the hydraulic accumulators is adjusted via the nozzle according to the load pressure in the lifting cylinder or cylinders. If the driver returns the pilot control to the neutral position, the load suspension system switches on automatically. After the load pressure via the nozzle in the hydraulic accumulator has almost adjusted, there is no significant sagging of the implement when the load suspension system is automatically switched on. For safety reasons, inadmissible deflections of the lifting cylinder (s) via the hydraulic accumulator (s), the load suspension system is automatically switched off from a certain lifting height via an inductive switch.

• Figur 1 - Darstellung eines Radladers
• Figur 2 - Hydraulikschaltplan für den Radlader gemäß Figur 1

The subject matter of the invention is explained in more detail using an exemplary embodiment. Show it:

• Figure 1 - Representation of a wheel loader
• Figure 2 - Hydraulic circuit diagram for the wheel loader according to Figure 1

FIG. 1 shows a schematic diagram of a wheel loader 1 that can be moved on pneumatic tires 2. The wheel loader 1 includes, among other things, a chassis 3 with a driver's cab 4 and a bucket 5 which is articulated on an equipment 6, the equipment 6 being connected to a plurality of hydraulic cylinders 7, 8 which are provided for the purpose of lifting and tipping the bucket 4 .

Figure 2 shows the hydraulic circuit diagram 9 (load suspension system) for the wheel loader 1 shown in Figure 1, whereby it is pointed out as a precaution that this also in the same way on another machine, such as. a forklift can be transferred. According to hydraulic circuit diagram 9, the load suspension system is connected to the hydraulic lines 10, 11 responsible for lifting and lowering between the lifting cylinders 12, 13 and the control valve 14. The hydraulic line 10 responsible for lifting is connected to one or more hydraulic accumulators 16, 17, 18, 19 via a 2-2-way valve 15 - neutral position, switching position - free passage. The hydraulic accumulators 16-19 have a vehicle-specific gas preload. In the bypass 20 between the hydraulic accumulators 16-19 and the lifting cylinders 12, 13 there is a nozzle 21 on the lifting side 10. The lower side 11 is blocked via a further 2-2-way valve 22 - neutral position, switching position - free passage with the Return 23 connected. In the pilot lines 24, 25, 26, 27 (lifting, lowering, tipping, dumping) there are pressure switches 29, 30, 31, 32 between the pilot transmitter 28 and the control valve 14. An inductive switch, also not shown, is provided at a predetermined height on the front frame of the wheel loader 1, which is not further numbered.

A main switch (not shown) is arranged in the driver's cab 4 of the wheel loader 1 for switching the load suspension system on and off. If the load suspension system is activated via the main switch and the pilot control 28 is in the neutral position, the 2-2-way valves 15, 22 in the lifting 10 and lowering line 11 switch to free passage. The lifting side 10 and the lifting cylinders 12, 13 are thus connected to the hydraulic accumulators 16-19. The lower side 11 and the lifting cylinders 12, 13 are accordingly connected to the return 23. Pitching movements of the wheel loader 1, initiated by uneven road surfaces, are thus variable via the hydraulic accumulators 16-19, i.e. depending on the respective operating state, damped and reduced, whereby high driving speeds are made possible.

If the driver actuates the pilot control transmitter 28, the 2-2-way valves 15, 22 are switched to the neutral position by the pressure switches 29-32 and that Load suspension system is switched off. The hydraulic pressure in the hydraulic accumulators 16-19 is adjusted via the nozzle 21 in accordance with the load pressure in the lifting cylinders 12, 13. If the driver returns the pilot control transmitter 28 to the neutral position, the load suspension system switches on automatically. After the load pressure via the nozzle 21 in the hydraulic accumulators 16-19 has variably adapted to the respective operating state, there is no significant sagging of the bucket 5 or the equipment 6 when the load suspension system is automatically switched on.

For safety against impermissible deflections of the lifting cylinders 12, 13 via the hydraulic accumulators 16-19, the load suspension system is automatically switched off from a predetermined lifting height via the inductive switch on the frame of the wheel loader 1. For certain applications in the operating state of the wheel loader 1, it may be necessary to switch off the nozzle 21, for example by means of a solenoid valve 33.

The function of the hydraulic system according to the invention will be clarified using a practical example.

When driving empty, the cylinders 12, 13 (empty buckets) are under a pressure of, for example, 30 bar, the hydraulic accumulators 16-19 being under their own preload of 18 bar. As a result of these pressures, maximum driving speeds can be achieved when driving empty, whereby vibrations, in particular pitching vibrations, can be largely suppressed.

During the loading process of the bucket 5, the valves 15 and 22 are switched neutral and the valve 33 is switched to passage via the pressure switches 29-32. Via the pressure generated by the pump, not shown, and the nozzle 21, the hydraulic accumulators 16-19 are brought to the respective operating pressure. At a pressure in the hydraulic cylinders 12, 13 of 200 bar, this can result in a pressure of approximately 200 bar in the hydraulic accumulators 16-19.

On the wall, for example, a cylinder support pressure of 180 bar would occur in the area of the hydraulic cylinders 12, 13 via the valve 33, whereas the storage pressure would approach this value via the valve 33 and the nozzle 21 in order in this way to achieve equilibrium bring about. As soon as the driver actuates the pilot control transmitter 28, the valves 15 and 22 are switched on via the pressure switches 29-32, so that the hydraulic accumulators 16-19 are connected to the cylinders 12, 13. As already mentioned, the inductive switch is actuated at a predetermined lifting frame height and the load suspension system is switched off.

Claims (6)

1. Hydraulic system for work machines that are provided with work equipment, especially for wheel loaders (1), fork lift trucks or the like, having a load suspension system (9) consisting of at least one hydraulic accumulator (16-19), which load suspension system is connected to the hydraulic lines (10, 11) that are responsible for lifting and lowering the work equipment and that are arranged between the lifting cylinder(s) (12, 13) and a control valve (14), the load suspension system (9) being arranged to be switched on and off in dependence on given operating states, characterized in that, for the variable equalizing of the load pressure of the hydraulic accumulator (16-19) with the respective load pressure of the lifting cylinder(s) (12, 13), at least one nozzle (21) that is connected to a plurality of directional control valves (15, 22, 33) is provided between the load suspension system (9) and the lifting cylinder(s) (12, 13), the valves (15, 22, 33) being actuated by way of pressure switches (29-32) that are provided in pilot control lines (24-27) between a pilot control transducer (28) and the control valve (14).
2. Hydraulic system according to claim 1, characterized in that the directional control valves (15, 22, 33) are in the form of 2-port/2-way valves.
3. Hydraulic system according to claims 1 or 2, characterized by a bypass (20) between the load suspension system (9) and the hydraulic cylinder (12, 13) on the lifting side (10), which bypass is provided with the nozzle (21).
4. Hydraulic system according to any one of claims 1 to 3, characterized by a directional control valve (33), especially a magnetic valve, that closes off the nozzle (21).
5. Hydraulic system according to any one of claims 1 to 4, characterized by at least one switch, especially an inductive switch, that is provided at a given height on the frame, especially on the front frame of the work machine (1), for switching the load suspension system (9) off.
6. Hydraulic system according to any one of claims 1 to 5, characterized by a main switch that activates the load suspension system (9), which main switch is arranged especially in the driver's cabin (4) of the work machine (1).

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