EP2069640B1 - Hydrostatic drive unit - Google Patents

Abstract

A hydrostatic drive unit is disclosed for supplying pressure medium to a hydraulic consumer having two pressure spaces. According to the invention, the hydrostatic drive unit has an adjusting motor and two hydrostatic units which can be driven via the adjusting motor. Pressure medium is conveyed directly from one of the pressure spaces into the other pressure space via one of the hydrostatic units. The further hydrostatic unit conveys pressure medium from a tank into the lastmentioned pressure space or, depending on the drive direction, from the latter into the tank.

Description

The invention relates to a hydrostatic drive unit according to the preamble of claim 1.

Such hydrostatic drive units are used for example for actuating hydraulic cylinders and have a secondary controlled subsystem, which consists essentially of a hydraulic transformer which is connected to a system with impressed pressure. In principle, a hydraulic transformer is mechanically coupled hydrostatic units, one of which is connected to the system with the impressed operating pressure, and the other is connected to the consumer, for example a hydraulic cylinder. For extending the hydraulic cylinder against load, the unit connected to the cylinder operates as a pump which is driven by the motor fed by the system with impressed operating pressure. When the hydraulic cylinder is retracted under load, the functions of the hydrotransformer reverse and the unit, previously operating as a motor, now in turn travels the secondary system. The basic structure of such hydrotransformers is described, for example, in the book " The Hydraulic Trainer ", Volume 6," Hydrostatic Drives with Secondary Control ", Chapter 6; Vogel Buchverlag Würzburg described.

In the EP 0 851 121 a hydrotransformer with two axial piston machines is disclosed, which operate as a motor and pump or in reverse. The pistons of the two axial piston machines are supported on a common swash plate.

In the EP 1 100 670 B1 a hydrostatic drive unit is shown, in which a differential cylinder is actuated by means of a hydraulic transformer. The hydrotransformer is designed with a tank connection, a pressure connection and a working connection, with pressure applied to the pressure connection, for example via a hydraulic accumulator. This pressure also acts in the annulus of the differential cylinder. The bottom-side cylinder chamber is connected to the working connection of the hydrotransformer. Although such a drive system has a comparatively simple structure. However, it has been found that the cylinder must be sized larger compared to a drive unit with conventional valve control, because the pressure in the annulus B can not be reduced below the applied pressure.

In principle, it is also possible to design the hydrostatic drive system with an additional hydrotransformer whose working connection is connected to the annular space and at the pressure connection of which the pressure applied via a hydraulic accumulator is applied. In such an embodiment, although the cylinder may be made of the same size as in systems with a conventional valve control, it is disadvantageous, however, that due to the second hydraulic transformer, a considerable device complexity is required.

From the WO 2005/028879 A1 hydrostatic drive units with a differential cylinder and two hydrostatic units or a hydrostatic double unit are known, which are connected with their connections to the two pressure chambers of the differential cylinder and with a tank or a feed circuit. The way the units are powered remains open.

From the DE 10 2004 061 559 A1 are hydrostatic drive units with a differential cylinder and two hydrostatic units or a hydrostatic double unit known, which are connected with their connections to the two pressure chambers of the differential cylinder and with a hydraulic accumulator. How the units are powered remains open here.

In contrast, the invention has for its object to provide a hydrostatic drive unit which allows a control of a consumer, in particular a hydraulic cylinder with low device complexity.

This object is achieved by a hydrostatic drive unit with the features of claim 1.

According to the invention, a hydrotransformer used in such a hydrostatic drive unit is in principle made of three hydrostatic units, with two hydrostatic constant units being drivable by an adjustable hydraulic machine. The two ports of a hydrostatic unit with the two pressure chambers of the consumer, for example, the differential cylinder are connected, while a working port of the second hydrostatic unit with the larger of the pressure chambers and a tank port of this hydrostatic unit is connected to a tank. These two hydrostatic units are driven by the adjustable hydromachine, whose pressure connection is connected to a pressure line carrying the impressed pressure and whose tank connection is connected to a tank line leading to the tank. By the first-mentioned hydrostatic unit pressure medium from the shrinking annulus is promoted in the expanding bottom-side cylinder chamber, for example, when extending a differential cylinder. The further hydrostatic unit conveys pressure fluid from the tank into the increasing pressure chamber. To retract the differential cylinder, the direction of rotation of the adjustable hydraulic machine reversed and promoted from the first hydrostatic unit pressure fluid from the cylinder chamber into the annulus. The second unit conveys pressure medium back from the cylinder chamber to the tank. The hydrostatic drive unit is particularly compact, since the variable hydraulic machine together with the constant units is a double axial piston machine, wherein a double unit of the double axial piston machine forms both the constant units and the other unit of the double axial piston machine forms the adjustable hydraulic machine

The hydraulic consumer is preferably a differential cylinder, wherein the first pressure chamber has a larger effective area than the second pressure chamber.

In such a construction, it is preferable if a second delivery port of the second hydrostatic unit is also connected to the first pressure chamber.

The displacement volumes of the two constant units behave according to an advantageous development of each other as the ratio of the piston rod surface to the piston bottom surface.

In an advantageous embodiment of the invention, the impressing of the system pressure by means of a hydraulic accumulator, which is chargeable by a storage loading pump.

The dynamic behavior of the hydrostatic drive unit can be improved by a bias of the hydraulic cylinder.

• Figur 1 ein Prinzip-Schaltbild einer erfindungsgemäßen hydrostatischen Antriebseinheit;
• Figur 2 einen Längsschnitt durch einen bei einer erfindungsgemäßen hydrostatischen Antriebseinheit verwendbaren Hydrotransformator in Doppelaxialkolbenbauweise und
• Figur 3 ein Ausführungsbeispiel einer Vorspannung für den Hydrozylinder gemäß Figur 1.

Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. Show it:

• FIG. 1 a schematic diagram of a hydrostatic drive unit according to the invention;
• FIG. 2 a longitudinal section through a usable in a hydrostatic drive unit according to the invention hydrotransformer in Doppelaxialkolbenbauweise and
• FIG. 3 an embodiment of a bias voltage for the hydraulic cylinder according to FIG. 1 ,

FIG. 1 shows a circuit diagram of a hydrostatic drive unit 1 for a differential cylinder 2, which has a bottom-side cylinder chamber 4 and a piston rod side annular space 6. The hydrostatic drive unit 1 essentially has a dash-dotted line indicated hydrotransformer 8, consisting of a hydraulic adjusting motor 10, the two constant units, in the present case two constant displacement pumps 12, 14 drives. A pressure port P of the adjusting motor 10 is connected to a pressure line 16, which is impressed on a hydraulic accumulator 18, a system pressure. The hydraulic accumulator 18 is charged by means of a storage loading pump 20. A tank connection of the adjusting motor 10 is connected to a tank T via a tank line 22.

A delivery port P of the fixed displacement pump 12 opens into a working line 24 leading to the cylinder chamber 4 of the differential cylinder 2. The suction port T of this constant displacement pump 12 is connected to the tank line 22.

A delivery port P of the further constant pump 14 opens into the working line 24, while the other delivery port T - called here for simplicity suction port - is connected via a second working line 26 to the annular space 6.

Both constant pumps 12, 14 and the adjusting motor 10 are designed with reversible conveying direction, so that corresponding to the in FIG. 1 As a delivery port designated connections P of the constant pumps can also act as suction ports. The direction of rotation of the adjustment motor 10 is effected by appropriate adjustment of the pivot angle.

This is set to extend the differential cylinder 2 so that the constant displacement pump 12 draws pressure medium from the tank T via the tank line 22 and promotes via the delivery port P and the working line 24 in the bottom-side cylinder chamber 4. The displaced from the annular space 6 pressure fluid is summed over the second constant pump 14 to the funded by the constant pump 12 pressure medium flow in the working line 24, so that the differential cylinder 2 extends.

wobei die Flächendifferenz A - B der Kolbenstangenfläche C entspricht.The displacement volumes V1 and V2 of the two constant pumps 12 and 14 behave to the cylindrical surfaces A, B (see FIG. 1 ) as follows: $$\mathrm{V}\mathrm{1}\mathrm{/}\mathrm{V}\mathrm{2}\mathrm{=}\left(\mathrm{A}\mathrm{-}\mathrm{B}\right)\mathrm{/}\mathrm{B}$$

wherein the area difference A - B corresponds to the piston rod area C.

FIG. 2 shows a concrete embodiment of such a hydraulic transformer 8, in which the three hydrostatic units are summarized as an axial piston machine in a compact housing. The basic structure of such a "floating-cup axial piston machine" is for example from the post-published application 10 2005 056 631.1 known, so that only the components required for understanding the invention will be described here. Such a hydraulic transformer 8 in Axial piston construction has a housing with a central part 28 which is closed at the end by two connection covers 30, 32. In the housing, a shaft 34 is mounted, which has approximately centrally a radially projecting drive flange 36, in the axis parallel zur.Wellenachse 38 a plurality of double piston 40 are inserted, the remote from the drive flange 36, spherical end sections each dip into a cylinder sleeve 42 and limit each with a working space 60 with this. In the FIG. 2 To the right of the drive flange 36 arranged cylindrical sleeves 42 are biased by a spring displaceable against a cylinder drum 44, which in turn is supported on the front side of a swash plate 46 which is pivotally mounted with its convex rear side in a corresponding bearing recess 47. In this kidneys 48, 50 are formed, which are hydraulically connected to a pressure channel 54 and a tank channel 52, which lead to the pressure port P and the tank port T of the adjustment motor 10. The cylinder drum 44 is rotatably connected via a driver 64 with a bearing portion of the shaft 34. This driver 64 is designed so that the cylinder drum 44 can perform a wobbling motion.

In order to enable the hydraulic connection between the kidneys 48, 50 and the associated channels 52 and 54 at different pivoting angles, control pockets 56, 58 are formed on the convexly executed rear side of the swashplate 46. The limited by a respective cylinder sleeve 42 and an end portion of the double piston 40 working spaces 60 of the axial piston unit are connected by one connecting channel 62 - depending on the angle of rotation of the cylinder drum 44 with one of the control kidneys 48 and 50, so that pressure medium via the pressure channel 52 in Working spaces 60 flow or can be displaced from these via the tank channel 54 to the tank port T.

In the FIG. 2 To the left of the drive flange 36 arranged end portions of the double piston 40 dive accordingly in cylinder sleeves 42, which are sealingly guided on a further cylinder drum 66. Also, this cylinder drum 66 is connected via a further driver 68 with another bearing portion of the shaft 34 such that it can perform a tumbling motion. In the FIG. 2 The left end face of the cylinder drum 66 is biased against a swashplate 70 on which two radially inner control kidneys 72, 74 and two radially outer control kidneys 76, 78 are formed. The control kidneys 72, 74 are assigned to the constant displacement pump 12 and the outer control kidneys 76, 78 of the constant displacement pump 14. The trained in the swash plate 70 control kidneys 74 and 76 are connected via working channels 80 and 82 with the first working line 24, which in turn opens into the cylinder chamber 4 of the differential cylinder 2. The radially inner control kidney 72 is over another. Working channel 86 with the other working line 26 and the control kidneys 78 connected via a tank channel 84 to the tank line 22, so that the in FIG. 1 Formed pressure fluid flow paths form.

As continues in FIG. 2 shown, each second of the left end portions of the double piston 40 and the respective associated cylinder sleeve 42 limited work spaces 88 via a slanted channel 90 in the cylinder drum 66 with the control kidneys 76 or via a further inclined channel 92 with the control kidney 78 connectable. The intervening work spaces 68 can be connected via the dashed lines indicated channels 94, 96 with the control kidneys 74 and 72, respectively. That is, each second end portion of the double piston 40 to the left of the drive flange 36 is thus a piston of the fixed displacement pump 12, while the intermediate end portions piston of the further constant pump 14 are. Such a design principle is known as a so-called "split flow double pump".

The above-described double axial piston machine is characterized by an extremely simple and compact design. For further details, in particular the sealing guidance of the cylinder sleeves 42 on the associated cylinder drum 44 and 66, reference is made to the aforementioned subsequently published application, which shows a so-called "floating cup pump".

The dynamic behavior of the hydrostatic drive unit can be improved by biasing the differential cylinder 2. In FIG. 3 is shown a possibility for such a bias. Accordingly, branch from the two working lines 24, 26 bias lines 98 and 100 from. The biasing line 100 leads to a storage line 102, in which a first orifice 104 with a comparatively large diameter is formed. The biasing line 102 is connected on the one hand with a hydraulic accumulator 106 and on the other hand via a second orifice 108 with a comparatively small diameter to the tank T. In the region between the first diaphragm 104 and the hydraulic accumulator 106, a branch line 110 branches off from the preload line, in which a third diaphragm 112 and a fourth diaphragm 114 are arranged and which opens into the tank T beyond the fourth diaphragm 114. The biasing line 98 is connected to the region between the two apertures 112, 114. In other words, via the two bias lines 98, 100, a biasing pressure for the differential cylinder 2 is tapped between each associated aperture 104, 108 and 112, 114, wherein the low pressure medium losses through the small apertures 108, 114 to the tank T out in Purchase can be taken.

In the basic position of the adjusting motor 10 is pivoted back to 0, ie the swash plate 46 according to FIG. 2 is set transversely to the shaft axis 38 with its face facing the cylinder drum 44. To extend the differential cylinder 2, the control disk 46 ( FIG. 2 ) pivoted so that the constant displacement pump 12 promotes pressure fluid from the tank T in the working line 24 and from there into the bottom-side cylinder chamber 4. To retract the cylinder, the conveying direction of the constant displacement pumps 12, 14 is reversed by opposing pivoting of the control disk 46, so that corresponding pressure medium from the cylinder chamber 4 via the working line 24 and the constant displacement pump 12 is conveyed into the tank line 22 and from there into the tank T. At the same time promotes the constant-displacement pump 14 pressure medium directly from the pressure line 24 via the second working line 26 in the increasing annular space. 6

In contrast to conventional drive systems, the tilt angle of the adjustment motor is no longer associated with a precisely defined drive speed, but with impressed system pressure a specific torque.

Constant pumps 12, 14 were used in the embodiments described above. In principle, however, variable displacement pumps could also be used.

Disclosed is a hydrostatic drive unit for supplying pressure medium to a hydraulic consumer with two pressure chambers. The hydrostatic drive unit according to the invention has an adjusting motor and two hydrostatic units which can be driven via the adjusting motor. Via one of the hydrostatic units, pressure medium is conveyed directly from one of the pressure chambers into the other pressure chamber. The further hydrostatic unit conveys pressure fluid from a tank in the latter pressure chamber or depending on the drive direction of this in the tank.

Claims (8)

1. Hydrostatic drive unit for the supply of pressure medium to a hydraulic consumer (2) having a first pressure space (4) and a second pressure space (6), for example a differential cylinder, with a first hydrostatic constant unit (12) which has a conveying connection (P) connectable to the first pressure space (4), and with a second hydrostatic constant unit (14) which has a conveying connection (T) connectable to the second pressure space (6), and with a machine by which the two hydrostatic units (4, 6) can be jointly driven mechanically, characterized in that the machine is an adjustable hydraulic machine with a suction connection (T), which is connected to a tank (T), and with a pressure connection (P), which is connected to a pressure line (16), and together with the constant units forms a double axle piston machine, one double unit of the double axle piston machine forming both constant units (12, 14), and the other unit of the double axle piston machine forming the adjustable hydraulic machine (10).
2. Hydrostatic drive unit according to Patent Claim 1, the hydraulic consumer being a differential cylinder (2), and the first pressure space (4) having a larger active area than the second pressure space (6).
3. Hydrostatic drive unit according to Patent Claim 2, a further conveying connection (P) of the second hydrostatic unit (14) likewise being connected to the first pressure space (4).
4. Hydrostatic drive unit according to Patent Claim 2 or 3, the displacement volumes of the two hydrostatic units (12, 14) having the following ratio to the active areas of the pressure spaces (4, 6): $$\mathrm{V}\mathrm{1}\mathrm{/}\mathrm{V}\mathrm{2}\mathrm{=}\left(\mathrm{A}\mathrm{-}\mathrm{B}\right)\mathrm{/}\mathrm{B}$$

   

   
   with V1 the displacement volume of the first hydrostatic unit,
   with V2 the displacement volume of the second hydrostatic unit,
   with A the body-side cylinder area,
   with B the annular-space-side cylinder area.
5. Hydrostatic drive unit according to one of the preceding patent claims, a pressure being imparted to the pressure line (16).
6. Hydrostatic drive unit according to one of the preceding patent claims, the pressure being imparted by means of a hydraulic accumulator (18) which can be charged by an accumulator charging pump (20).
7. Hydrostatic drive unit according to one of the preceding patent claims, the pressure spaces (4, 6) of the consumer being pressurized.
8. Hydrostatic drive unit according to Patent Claim 7, each pressure space (4, 6) being connected to a hydraulic accumulator (106) via a first diaphragm (104, 112) and the tank via a second, smaller diaphragm (108, 114).

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