WO2011154075A1

WO2011154075A1 - Hydraulic system

Info

Publication number: WO2011154075A1
Application number: PCT/EP2011/002329
Authority: WO
Inventors: Frank Bauer; Daniel Feld
Original assignee: Hydac Technology Gmbh
Priority date: 2010-06-08
Filing date: 2011-05-11
Publication date: 2011-12-15
Also published as: DE102010023015A1; DE102010023015B4; EP2580079A1

Abstract

The invention relates to a hydraulic system, in particular for a commercial vehicle such as a construction machine, comprising a hydraulic fluid pump (2) which supplies hydraulic fluid (3) to a consumer. Said system is characterised in that the hydraulic fluid pump (2) removes a hydraulic fluid (3) from a low-pressure fluid chamber (4) of the hydraulic system (1) and delivers said fluid to a high-pressure fluid chamber (5) lying between a consumer and the hydraulic fluid pump (2), and in that a feed unit (8) can be actuated by the displacement of a piston (6, 7) in the high-pressure fluid chamber (5) or the low-pressure fluid chamber (4), allowing the low-pressure fluid chamber (4) to be replenished with hydraulic fluid (3) originating from a hydraulic fluid container (9).

Description

Hydac Technology GmbH, industrial area, 66280 Sulzbach / Saar

Hydraulic system

The invention relates to a hydraulic system, in particular for a commercial vehicle, such as a construction machine, with a pressure medium pump, which supplies a consumer with pressure medium. Hydraulic equipment for commercial vehicles, in particular for construction machinery, agricultural machinery and off-road work machines including forklifts, are generally composed of several hydrostatic drive systems. In addition to the steering hydraulics, these include the cooling, control and feeding hydraulics as well as the driving hydraulics. Depending on their basic structure, these systems can work partially independently of each other and fulfill their respective function.

In moving construction machines, the steering system is regularly operated with a steering valve with so-called "open center", a constant pump often formed as external gear pump promotes nichtbetätigtem steering system against the pressure fluid tank of the construction machine In passenger cars, the promotion of pressure medium within an open system thus formed usually takes a Vane pump with adjustable displacement volume By using a so-called open hydraulic circuit, for example, the components cooling, control and supply circuit can be supplied with only one pressure medium pump, which can be an external gear pump with a constant flow rate Displacement volume, which is attached to a power take-off of an internal combustion engine as a motor unit. After a cooling motor formed, for example, as an external gear constant motor, a parallel connection of the control and supply hydraulic circuit can be provided. The control pressure system is used for signal transmission of certain machine characteristics, such as the control of a disk parking brake or a swivel angle adjustment device of the drive pump by means of trigger valve. Through the use of the feed system, both the supply of fresh, purified hydraulic oil and an internal leakage compensation takes place.

The design of mobile work machines has been increasingly characterized in recent years by the requirements of European emissions legislation. For example, since 2008, the European emission standard INA has applied to all engine performance categories of mobile machinery. After the entry into force of the already closed exhaust gas level HIB, a further reduction in nitrogen oxides of up to 94% will apply from 2010, which, according to today's opinion, can only be achieved through the use of appropriate particle filters. A final emissions standard IV 2014 provides for a further reduction in nitrogen oxides of up to 88% compared to the HIB level. In particular, this last emission stage IV presents the construction machinery and diesel engine manufacturers with major challenges. For the installation of a selective catalyst system (SCR) together with the associated urea tank additional installation space on the respective machine is needed, which should lead to a high constructive and logistical effort, especially in large-scale machine series.

Taking into account the elaborate exhaust aftertreatment systems and the associated effects, especially the engine performance class up to 56kW represents an interesting alternative for machine manufacturers due to the omission of the EU emission standard IV. Optimization of the existing drive systems means that a diesel engine power reduction can be achieved below the aforementioned 56kW power limit, ie the so-called downsizing of the internal combustion engine is sought.

Furthermore, it is known in the post-published prior art to compensate for the power peaks of the motor unit, in particular in the form of an internal combustion engine, by the use of a pressure medium accumulator, wherein the accumulator is charged or discharged in response to a current power output of the motor unit. As a result, the total power of the motor unit in the sense of downsizing can be limited to a predefinable value, for example to the legally prescribed motor power class up to 56kW. The pressure medium supply to the consumers and to a pressure fluid reservoir of the hydraulic system is controlled by a priority valve. A connection and disconnection of the pressure medium supply to one or more consumers is controlled by a further valve.

In such and therefore also in other hydraulic systems, cavitation can not be ruled out in every case, so that it is desirable to bias the pressure medium, in particular in the suction line of a pressure medium pump. Any increase in pressure, however, leads to a reduction in performance in such hydraulic systems, which can be taken from a hybrid.

Based on the cited prior art, the invention is therefore based on the object to provide a hydraulic system for a commercial vehicle, which on the one hand allows a reduction in performance for the internal combustion engine and on the other hand, the problem of cavitation is solved. This object is achieved with a hydraulic system with the features of claim 1 in its entirety.

Characterized in that the suction side of the pressure medium pump pressure medium is removed from a low-pressure fluid chamber of the hydraulic system and conveyed into a high-pressure fluid chamber of the hydraulic system, a constructive measure is taken, always biased by the pressure medium pump pressure fluid or such that cavitation in the hydraulic system is avoided. In addition, a make-up device is part of the hydraulic system to automatically compensate for leakage oil losses and to supply the leakage losses to the low-pressure fluid chamber. The make-up device is thereby actuated during a displacement movement of a piston in the high-pressure fluid chamber, in particular when the pressure medium pump brings the piston into contact with the piston-cylinder arrangement of the make-up device.

Generally allows the hydraulic system with the two fluid chambers both during the charging cycle and during the Endladezyklus and thus in both possible directions of delivery of the pressure medium pump an adapted bias of the pressure medium, without being a hindrance for the operation of the consumer in the sense of too high Bias of the pressure medium or no bias of the same.

Preferred embodiments emerge from the content of the subclaims.

The low-pressure fluid chamber and the high-pressure fluid chamber are arranged in a particularly preferred embodiment of the hydraulic system part of a single double-piston accumulator and thus in a particularly compact form in the hydraulic system. In addition, the dessert makeup device may be housed in a housing containing the low pressure fluid space and the high pressure fluid space encloses be arranged. It is advantageous to design the make-up device as a piston-cylinder arrangement, wherein a single-acting piston in the sense of filling a working space of the piston-cylinder arrangement can be biased by a spring element with pressure medium. The spring element thus ensures automatic filling of the make-up device with pressure medium. This is possible in particular if the relevant piston in the high-pressure fluid space is not in an end position facing the make-up device, but the high-pressure fluid space is in a partially filled state. In particular, the make-up is done by the valve when it is switched by the piston.

The make-up device or the working space of the make-up device is connected to a fluid-carrying connection between the pressure medium container and the low-pressure fluid space such that in each case in the portion of the fluid-carrying connection between the pressure medium container and the make-up device or the make-up device and the low-pressure fluid space Check valve is arranged. The two check valves have an opening direction in the sense that pressure medium from the pressure medium container in the working space of the make-up device and from there into the low-pressure fluid space can flow, but not vice versa. The make-up device thus presents itself as a piston pump controlled by non-return valves as a function of the pressure in the high-pressure fluid chamber.

A push rod or a permanently connected to the piston of the make-up device component is thereby acted against the force of the piston acting on the spring with a pushing force. The thrust force applied to the push rod by the piston of the high-pressure fluid space displaces the pressure medium in the work space of the make-up device in the direction of the low-pressure fluid space. A backflow the pressure medium from the low pressure fluid space is prevented by the check valve.

The high pressure fluid space and the low pressure fluid space can be advantageously combined in a dual piston accumulator. The double piston accumulator has a housing which accommodates at least two longitudinally movable pistons. The pistons are connected to each other with a coupling element, wherein the coupling element is guided even in a central position longitudinally movable through a partition wall of the housing. The dividing wall defines with the two adjacently opposed pistons a high-pressure fluid space and a low-pressure fluid space, which is operatively connected to the coupling element and defines, at least with the housing, a biasing space. The pressure medium in the low-pressure fluid chamber can be used to supply a pilot control device for the flow rate and conveying direction of the pressure medium pump.

The coupling element is formed in a particularly preferred embodiment example as a coupling rod, the ends of which are each firmly connected to the associated piston. The entire pressure medium flow can be directed from the pressure medium pump to the consumer (s) via the double piston accumulator. In the coupling rod, the working space can be arranged for the dessert device. In the coupling rod can protrude a fixed housing piston, which changes the volume of the limited work space by a movement of the coupling rod. The piston is designed in the manner of a hollow piston and is able to guide the pressure medium out of the working space or to introduce it into the working space through a channel in the longitudinal direction in its interior. The piston of the high pressure fluid space may be biased by a gas pressure of a biasing space as mentioned. The biasing space may be acted upon by a gas pressure in a gas supply device. For this purpose, the preload space is limited by a fixed end wall of the housing of the high-pressure fluid chamber or the double-piston accumulator. The end wall preferably has a connection point for the gas supply device, for example in the manner of a nitrogen storage. In the following, the hydraulic system according to the invention will be explained in more detail with reference to various embodiments according to the drawing. This show in principle and not to scale representation of the

Figure 1 is a schematic diagram of a hydraulic system with a separate arrangement of a high-pressure fluid chamber of a low-pressure fluid chamber, with the inclusion of a pressure medium pump with Vörderrichtungsumkehr and variable displacement.

2 shows a schematic circuit diagram of a hydraulic system with an arrangement of the high-pressure fluid chamber and the low-pressure fluid chamber in a common housing of a double piston accumulator with actuation of the piston of the make-up device by a piston in the low-pressure fluid chamber.

3 shows a schematic circuit diagram of a hydraulic system according to the illustration according to FIG. 1, wherein the piston of the make-up device can be actuated from another piston side of the piston in the low-pressure fluid chamber;

4 is a schematic circuit diagram of a hydraulic system with an arrangement of the high-pressure fluid space and the low-pressure fluid space in a common housing of a Double piston accumulator, wherein a working space of the make-up device is arranged in a coupling element of the two pistons of the double piston accumulator; and FIG. 5 shows a concluding further schematic circuit diagram of a hydraulic system according to the illustration according to FIG. 4, wherein a housing-fixed piston of the make-up device is guided through a housing wall of the low-pressure fluid chamber and fixed thereon.

In Fig. 1, a hydraulic circuit 1 for a work machine, for example in the form of a conventional construction machine, partially in a schematic circuit diagram. The hydraulic system 1 has a pressure medium pump 2, which can be driven by an internal combustion engine, for example in the form of a diesel engine. The

Pressure medium pump 2 is designed as a reversible pump in its conveying direction, the delivery rate is also adjusted by a hydraulic pilot control device 21 accordingly. Upstream on the high pressure side of the pressure medium pump 2, a trained in the manner of a piston accumulator high-pressure fluid chamber 5 is arranged. The high-pressure fluid chamber 5 is in turn arranged in a cylindrical housing 26, in which a piston 6 is guided longitudinally movable. The piston 6 can be biased towards the high-pressure fluid chamber 5 by various constructive measures. On its rear side, for example, a working gas in the form of nitrogen gas or the like act.

The pressure medium pump 2 takes biased pressure medium 3 from a low-pressure fluid chamber 4, which may be arranged in a likewise cylindrical housing 27. Another piston 7 is in the housing 27th also arranged axially movable and biased by a spring element or working gas in the direction of the low-pressure fluid chamber 4 out. The pressure medium pump 2 thus extracts prestressed pressure medium 3 and, independently of the pressure medium requirement of the consumption or of the plurality of consumers, always conveys prestressed pressure medium into the high-pressure fluid space 5, so that cavitation in the hydraulic system is avoided. In addition, the fluid pressure medium 3 prestressed in a fluid-conducting connection 28 between the low-pressure fluid chamber 4 and the pressure medium pump 2 is suitable for providing energy for the pilot-control device 21 of the pressure medium pump 2. For example, the flow rate can be changed by the actuation of a hydraulic cylinder unit and a cam ring, on the inside of which conveying elements of the pressure medium pump 2 roll off or slide off. The designated 27 device needs to be no piston accumulator and could also consist of a different type of hydraulic accumulator.

In order to enable at least one iterative dessication of pressure medium 2 in the low-pressure fluid chamber 4 and to achieve a continuous operation of the hydraulic system 1 with biased pressure means 3, a make-up device 8 is provided.

In the embodiment shown in FIG. 1, the make-up device 8 can be actuated by the piston 6 in the high-pressure fluid chamber 5. The make-up device 8 is formed as a piston-cylinder arrangement 1 1, including arranged in a thickened housing cover 29, a single-acting piston 12 in a cylindrical working space 13 movable. The piston 12 is acted upon on the back by a spring element 14 in the manner of a helical compression spring with a compressive force. On its other, opposite side, the piston 12 has a piston rod 30, which opens in the direction of the piston 6 in the direction of an actuating part in the high-pressure fluid chamber 5 and the rest in the housing cover 29 is slidably guided. In the position of the piston 12 shown in FIG. 1, the rear working space 13 is filled with pressure medium 3. In an acceleration phase of the pressure medium pump 2, in which increased pressure medium 3 is conveyed into the high-pressure fluid chamber 5, the piston 6 moves upward in the viewing direction of FIG. 1, pushing the piston rod 30 and the piston 12 of the make-up device 8 also against the pressure of the spring element 14 further up. The spring bias of the compression spring 14 may also be selected such that upon an upward movement of the piston 6, the displaced volume is sufficient to move the piston 12 without the two pistons having to abut one another.

Coming in a fluid-carrying connection 15 from a pressure medium container 9 in the form of a conventional tank, via the make-up device 8 to the low-pressure fluid chamber 4, two check valves 16, 1 7 are arranged. The check valve 16 is arranged between the pressure medium container 9 and the working space 1 3 of the make-up device 8, seen with a blocking position in the direction of the pressure medium container 9 and with an opposite opening direction, ie in the direction of the make-up device 8. The further check valve 1 7 is arranged between the make-up device 8 and the low-pressure fluid chamber 4, wherein the locking direction takes place in the direction of the make-up device 8 and the opposite opening direction in the direction of the low-pressure fluid chamber 4 is provided. With regard to the extent provided opening and locking directions of the two check valves 16, 1 7 it is ensured that during the working stroke of the piston 12 pressure medium 3 is conveyed by the Nachspeiseeinrichtung 8 in the low-pressure fluid chamber 4. This happens at each load change or, at each acceleration phase of the pressure medium pump 2. The check valves 16, 1 7 also prevent so far unintentional backflow of the pressure medium 3 of the Nie derdruck-fluid space 4 in the high-pressure fluid chamber 13 and further in the direction of the pressure medium container. 9

FIGS. 2 to 5 show further exemplary embodiments of the arrangement of the high-pressure fluid chamber 5 and the low-pressure fluid chamber 4. The fluid spaces mentioned here are summarized in the design of a double-piston accumulator 10. In this case, a cylindrical housing 18 of the double-piston accumulator 10 has a partition wall 20 arranged approximately in its axial center. The fluid spaces 4, 5 are located on both sides of the partition wall 20. In the FIGS. 2 to 5 shown on the left in the respective viewing direction, a high pressure fluid space 5 and on the right side a low pressure fluid space 4 are arranged. In each fluid space, a piston 6, 7 arranged axially movable. Between the pistons 6, 7 and the dividing wall 20 are each the high-pressure fluid chamber 5 (left side) and the low-pressure fluid chamber 4 (right side). The pistons 6, 7 are firmly connected to one another with the aid of a coupling element 19 designed as a cylindrical piston rod, so that its axial travel path, in contrast to the pistons in FIG. 1, always together in the sense of a forced connection in the same, but changing direction over the same distance he follows. Furthermore, the coupling rod 22 is sealingly guided with sealing elements 31 in the partition wall 20.

In the embodiments according to FIGS. 2 to 5, the piston 6 in the high-pressure fluid chamber 5 is biased on its side facing away from the piston rod 22, originating from a pressure accumulator 25 with a working gas. The end wall 32 of the prestressing space 24 formed so far has a connection point 33 for this purpose. The pressure in the preload space 24 can be predetermined. The low-pressure fluid chamber 4 is in all the embodiments shown starting from Fig. 2, designed in principle the same way as the high-pressure fluid chamber 5, both of which have comparable storage volumes in the other. The desserts tion 8, the pressure means 3 via check valves 16, 1 7 removes the pressure medium tank 9 is arranged in an end wall 34 of the housing 18 of the double piston accumulator 10. The end wall 34 is arranged diametrically opposite the end wall 32. Furthermore, the filled with the pressure medium 3 low-pressure fluid space 4 between the piston 7 and the partition wall 20 of the double piston accumulator 10 is arranged. From the low-pressure fluid chamber 4 takes the pressure medium pump 2, the pressure medium 3 and conveys it into the high-pressure fluid chamber 5, wherein the pertinent conveying direction is so far also reversible, so that a flow idströmung in the opposite direction can also be short-term.

In FIGS. 1 to 5, the total volumes of the fluid spaces consisting of biasing space, high-pressure and low-pressure fluid space, as well as the respective rear space to the piston are substantially the same size.

In the embodiment shown in FIG. 3, as a significant difference from the embodiment shown in FIG. 2, the make-up device 8 is arranged directly in the dividing wall 20 so that the piston rod side of the piston 7 seals the piston rod 30 of the piston 12 of the piston-cylinder Can press arrangement. The check valves 16, 1 7 are integrated in an advantageous manner in the housing wall of the housing 18 or in the partition wall 20 at a suitable location. The same applies to the fluid-carrying connection 15. FIGS. 4 and 5 each show schematic longitudinal sections through the

Double piston accumulator 10 in modified embodiments, the make-up device 8 for leakage oil compensation and the Nachspeisung of pressure medium 3 in the low-pressure fluid chamber 4 in other ways than those make-up devices 8, as shown in Figs. 1 to 3, is formed. The working space 13 of the make-up device 8 is in this case arranged in the coupling element 19. The working space 13 is designed as an elongate, narrow cylinder or working space 13 running essentially over the entire length of the coupling rod 22. The rod-shaped piston 12 protrudes into the working space 13 either from the end wall 34 of the housing part for the low-pressure fluid space 4 or from the end wall 32 of the high-pressure fluid space 5. The piston 12 is fixedly arranged in the respective end wall 32, 34, so that the volume of the working space 13 is changed by the displacement movement of the coupling rod 22. The piston 12 is designed as a hollow piston 23, wherein a continuous channel leads in the longitudinal direction of the piston 12 from the pressure medium container 9 to the working space 13 and via a coupling rod 22 arranged in the check valve 1 7 in the low-pressure fluid chamber 4. Another check valve 16 is provided between the pressure medium tank 9 and the dessert device 8. The check valves 16, 1 7 open depending on the fluid pressure in the same manner as already described above.

Claims

Patent claims

1. Hydraulic system, in particular for commercial vehicle, such as a construction machine, with a pressure medium pump (2) which supplies a consumer with pressure medium (3), characterized in that the pressure medium pump (2) a pressure medium (3) of a low-pressure fluid space ( 4) of the hydraulic system (1) takes and promotes in a high-pressure fluid chamber (5), which is arranged between a consumer and the pressure medium pump (2) and that by a movement of a piston (6, 7) in the High-pressure fluid space (5) or the low-pressure fluid chamber (4) a make-up device (8) is actuated, whereby pressure medium (3) from a pressure medium container (9) originating in the low-pressure fluid space (4) is fed.

2. Hydraulic system according to claim 1, characterized in that the low-pressure fluid chamber (4) and the high-pressure fluid chamber (5) are combined in a double-piston accumulator (10).

Hydraulic system according to claim 1 or 2, characterized in that the make-up device (8) is a piston-cylinder arrangement (1 1) and that a single-acting piston (12) in the sense of filling a working space (13) of the piston-cylinder -Anordnung (1 1) with pressure medium (3) by an energy store (spring element 14) is biased.

Hydraulic system according to claim 2 or 3, characterized in that in a fluid-carrying connection (15) between the pressure medium container (9) and the dessert device (8) and between the make-up device (8) and the low-pressure fluid chamber (4) each have a check valve ( 16, 1 7) is arranged, which a Druckmit- telstrom from the pressure medium container (9) to the low-pressure fluid chamber (4) allows.

Hydraulic system according to one of Claims 2 to 4, characterized in that the make-up device (8) can be actuated by the pistons (6, 7) in the high-pressure fluid chamber (5) or the low-pressure fluid chamber (4) of the double-piston accumulator (10) ,

Hydraulic system according to one of the preceding claims, characterized in that the double piston accumulator (10) has a housing (18) in which at least two longitudinally movable pistons (6, 7) are arranged, each with an adjacently opposed piston (7, 6). are connected to one another via a coupling element (19), which is guided longitudinally in a dividing wall (20) of the housing (18) such that the dividing wall (20) of the housing (18) engages with the two adjacently opposed pistons (6, 7) High-pressure fluid chamber (5) and the low-pressure fluid chamber (4) limit, and that the make-up device (8) in the housing (18) or in the coupling element (19) is arranged.

Hydraulic system according to one of the preceding claims, characterized in that the pressure medium (3) in the low-pressure fluid chamber (4) for supplying a pilot control device (21) for the flow rate and conveying direction of the pressure medium pump (2) and / or for a leakage oil compensation.

Hydraulic system according to one of the preceding claims, characterized in that the coupling element (19) is formed from a coupling rod (22) whose ends are fixedly connected respectively to the associated piston (6, 7) and that in the coupling rod (22) Working space (13) of the piston-cylinder assembly (1 1) is arranged in a housing-fixed hollow piston (23) protrudes, which is penetrated by the fluid-carrying connection (15) from the pressure medium container (9), starting in the direction of the make-up device (8).

Hydraulic system according to one of the preceding claims, characterized in that at least one piston (6) of the double piston accumulator (10) delimits a preload space (24) with a predefinable internal gas pressure and that the preload space (24) is connected to a pressure accumulator (25).