Patent Application
20190178226
This application claims priority under 35 U.S.C. § 119 to patent application number DE 10 2017 222 354.5, filed on Dec. 11, 2017 in Germany, the disclosure of which is incorporated herein by reference in its entirety.
The disclosure relates to a hydrostatic piston engine according to the following description.
A generic hydrostatic piston engine has a cylinder drum with cylinder bores and working pistons guided therein in a longitudinally displaceable manner. Said pistons are, on the one hand, supported in a sliding manner on a lifting surface running at a variable distance from the cylinder drum and, on the other hand, they delimit hydrostatic working chambers in the cylinder drum which they enter and leave alternately when the cylinder drum rotates on account of their support on the lifting surface. The hydrostatic working chambers each have an outlet to the cylinder drum which, when the cylinder drum rotates, is brought into alternating pressurizing medium connection with a high-pressure chamber and a low-pressure chamber. A reversing surface passed over by the outlet of the working chamber is arranged between the outlets of the low-pressure chamber and of the high-pressure chamber, via which reversing surface the outlet of the working chamber is separated in a fluid-tight manner from both the low-pressure chamber and also the high-pressure chamber during the passing over. In this way, a pressure change can take place in the working chamber without a hydraulic bypass between the high-pressure and low-pressure chambers. In pump mode, the cylinder drum is driven and a hydrostatic working chamber passing over the low-pressure chamber with its outlet is extended on account of the extending working piston. In this way, low-pressure pressurizing medium flows from the low-pressure chamber into the hydrostatic working chamber. Shortly before the working piston has reached its maximum stroke or dead point, the pressurizing medium connection of the hydrostatic working chamber to the low-pressure chamber is separated when passing over the reversing surface. Due to the lifting surface, the introduction of the working piston into the cylinder bore, and therefore the pressure increase in the hydrostatic working chamber, begins at the dead point. As the rotation continues, the outlet thereof then comes into pressurizing medium connection with the high-pressure chamber of the piston engine in which, for example, the load pressure of a load to be moved is applied. The introduction of the working piston causes the pressurizing medium to be ejected under load pressure into the high-pressure chamber and, for example, to a high-pressure connection of the piston engine and further to the consumer. Just before the next dead point is reached, at which the working piston is introduced to its maximum, the pressurizing medium connection of the hydrostatic working chamber to the high-pressure chamber is disconnected when the other reversing surface is passed over. Since the working piston is introduced a little further, there is usually a further pressure increase in the hydrostatic working chamber up to the dead point. If the cylinder drum is rotated further, then the hydrostatic working chamber comes into pressurizing medium connection with the low-pressure chamber via its outlet.
Since high pressure is still present at this point in the hydrostatic working chamber, the pressurizing medium decreases in pressure, insofar as no further precautions have been taken, into the low-pressure chamber. Large flow speeds which result in turbulence in the low-pressure chamber can occur during this. The greater the high pressure and/or the speed of the cylinder drum in this case, the more turbulent the effects in the low-pressure chamber. This can lead to vapor formation or cavitation in the low-pressure chamber which can have two effects. On the one hand, cavitation erosion can occur in this region; on the other hand, this means that the vapor formation reduces the incompressibility of the pressurizing medium, leading to a poorer filling of the aspirating hydrostatic chamber. The consequences may be: damage to engine components, poorer engine efficiency and uncoupling of the pressurizing medium volume flow from the speed.
In order to reduce these effects, solutions which propose reversing notches with a flow cross section that widens in the rotational direction are widespread in the prior art. These reversing notches originate with a cross section of zero in the reversing surface and extend with a substantially V-shaped or U-shaped cross section in the rotational direction up to the outlet of the low-pressure chamber into which they open.
Although an improvement is achieved by means of these reversing notches, the aforementioned problems can still occur as the high pressure is directly decreased in the low-pressure chamber and, depending on the speed and the high pressure, can guarantee the aforementioned turbulence there.
Other solutions show the connection of the high pressure-guiding hydrostatic working chamber in the region of the reversing surface to the inner chamber of the hydrostatic engine. This preliminary pressure drop or down-regulation of the working chamber means that during the subsequent connection to the working chamber, the pressurizing medium connection no longer swirls in such a manner, so that the negative effects described are reduced. Hence, for example, publication U.S. Pat. No. 3,457,873 discloses a connection of the hydrostatic working chamber via the reversing surface to the housing interior. This takes place via a pressurizing medium channel which extends from its outlet in the reversing surface through a connection plate which has outlets both of the high-pressure chamber and also of the low-pressure chamber into the housing interior.
The disadvantage of this solution is that when the rotational direction is reversed an air/oil mixture can be drawn in via the pressurizing medium channel, which in turn leads to the aforementioned problems.
In order to solve this problem, publication DE 10 2010 055 398 A1 proposes that a non-return valve opening towards the housing interior should be inserted in the aforementioned pressurizing medium channel. In this way, only the originally intended reset takes place via the pressurizing medium channel without any further aspiration.
A further disadvantage of both solutions, however, is that the aforementioned pressurizing medium channels have a further tendency towards cavitation at sufficiently high pressures or speeds.
In view of this, the problem addressed by the disclosure is that of creating a hydrostatic piston engine with a reset which, with otherwise identical operating state variables such as speed and working pressure, has a lesser tendency towards cavitation of the reset.
This problem is solved by a hydrostatic piston engine having the features of the following description.
Advantageous developments of the hydrostatic piston engine are described below.
A hydrostatic piston engine has a housing with a cylinder drum with cylinder bores mounted rotatably therein, each of which cylinder bores receives a working piston in a longitudinally displaceable manner. The piston engine may, for example, be a radial piston engine or a hydrostatic axial piston engine with a swash plate design. It may take the form of a hydraulic motor and/or a hydraulic pump. In the case of the radial piston engine, the working pistons extend in relation to a rotational axis of the cylinder drum radially therefrom; in the second case, they emerge at the face side of the cylinder drum substantially parallel or parallel to the rotational axis. Each cylinder bore delimits a hydrostatic working chamber of variable volume with its working piston guided therein, said working chamber having an opening on an outer surface of the cylinder drum—in the case of the radial piston engine on a radial curved surface and in the case of the axial piston engine on a curved surface on the face side. During a rotation of the cylinder drum, outlets in a high-pressure chamber and a low-pressure chamber of the piston engine and a reversing surface arranged in the rotational direction between the two outlets are capable of being passed over, in particular are passed over, alternately by the openings in the working chambers. In this case, at least one pressurizing medium channel is provided, in particular to reset the high pressure of the working chambers in a pressurizing medium trough separate from the low-pressure chamber, which pressurizing medium channel opens out, on the one hand, in the reversing surface and, on the other hand, in the pressurizing medium trough, in particular in a housing interior of the piston engine. According to the disclosure, this pressurizing medium channel has a first portion along which a flow cross section increases towards the pressurizing medium trough.
Due to the increasing flow cross section, the flow speed in the pressurizing medium channel can drop along the first portion, something that is associated with a pressure rise along the first portion. In this way, vapor formation or cavitation is more effectively prevented. Consequently, the piston engine is better protected from cavitation-related wear in this region. Since the low-pressure chamber is no longer as highly swirled following the reset, the efficiency and aspiration are improved.
In a development, the pressurizing medium channel has a second portion in the direction of the pressurizing medium trough arranged downstream of the first portion. The flow cross section along this is constant up to the pressurizing medium trough, or it diminishes. In other words, the pressurizing medium channel narrows once again. Alternatively or in addition, the second portion in the flow direction has a curvature via which the pressurizing medium volume flow is deflected in the pressurizing medium channel in the direction of the pressurizing medium trough. Tests show that through the further narrowing of the pressurizing medium channel and/or the curvature, even better protection against cavitation can be achieved.
In one development the pressurizing medium channel opens with its first portion into the pressurizing medium trough or, if there is a second portion, it opens with its second portion into the pressurizing medium trough.
Particularly good protection from cavitation is exhibited by the pressurizing medium channel in a development in which the flow cross section of at least the first portion increases in a continuous or stepless manner. In this way, separations of the flow from an inner curved surface of the pressurizing medium channel that promote cavitation are prevented.
A development in which an inner curved surface of the pressurizing medium channel or at least of the first portion has a smooth and/or stepless design, at least sectionally, has proved advantageous in principle.
A smooth or stepless inner curved surface is produced, for example, when it has a tangentially constant design. In other words, there are no edges on the inner curved surface. The inner curved surface exhibits an even greater surface quality if it is configured with a constant curvature, for example. In other words, the change in tangent on the inner curved surface is also continuous.
In a further development, the pressurizing medium channel extends up to the pressurizing medium trough at least sectionally with the rotational direction.
Alternatively or in addition, the pressurizing medium channel may extend up to the pressurizing medium trough at least sectionally against the rotational direction.
In one development the pressurizing medium channel extends up to the pressurizing medium trough radially outwards at least sectionally, in particular in and/or against the rotational direction. A spiral arm-shaped embodiment of the pressurizing medium channel relative to a rotational plane of the cylinder drum results, for example, from a radially outward extension in the rotational direction.
In a preferred development, a control plate that is detachable from the housing portion is arranged between the cylinder drum and a housing portion which supports a low-pressure connection and a high-pressure connection connected to the low-pressure chamber and the high-pressure chamber, respectively. The outer surface of the cylinder drum is in abutment with the control plate. In this design, the reversing surface or reversing surfaces, the outlets of the at least one pressurizing medium channel and of the high-pressure and low-pressure chamber are configured on the control plate.
With this design, the low-pressure chamber and the high-pressure chamber each have a main portion in the housing portion and one or more end portions in the control plate. The end portions in this case are, in particular, in the shape of one or more through-bores or control kidneys.
In the case of the design with the housing portion and detachable control plate, a development in which the pressurizing medium channel is configured at least sectionally by a groove formed on the housing portion and the control plate covering this groove sectionally proves easy to produce. The groove-like embodiment in this case allows simple production by milling, for example. Unlike in the case of solutions of the prior art, as discussed, the pressurizing medium channels are not therefore inserted through bores into the housing portion. By milling, a substantially more versatile and variable cross-sectional profile can be produced at very little expense. The covering control plate then completes the inner curved surface of the pressurizing medium channel.
In one development the groove in the flow direction has a trough-shaped base. This is the case, for example, if a base of the groove drops off along the first portion and rises again along the second portion relative to a bearing surface of the housing portion on which the control plate rests. Tests have shown that the rising portion reduces the cavitation tendency in the pressurizing medium channel due to its decreasing flow cross section and/or due to its curvature formed in the flow direction.
In one development the second portion is not covered by the control plate. In other words, the second portion is only delimited or created by the groove and not by the control plate. This is the case, for example, if the pressurizing medium channel, in particular the groove, extends beyond an outer circumference of the control plate.
The pressurizing medium channel is comparatively easy to produce when the first portion extends starting from the bearing surface of the housing portion on which the control plate rests. In other words, the first portion with the widening flow cross section does not begin right at the reversing surface of the control plate, but only at the housing portion. A portion of the pressurizing medium channel can then be configured as a simple through-bore hole from the outlet thereof in the reversing surface up to the bearing surface.
Alternatively, the first portion may extend at a distance from the bearing surface of the housing portion. For example, starting from the bearing surface a bore can initially be placed in the housing portion, from which the first portion with the widening flow cross section then extends.
As an alternative to the aforementioned solutions, the first portion may also extend, however, starting from the reversing surface of the control plate.
Tests have shown that the reset is less threatened by cavitation if more than one pressurizing medium channel of this kind is provided per reversing surface. There may be two or three pressurizing medium channels or more, for example. These may extend, for example, in or against the rotational direction or individually, one in and one against the rotational direction. A combination of a pressurizing medium channel that extends in the rotational direction and another pressurizing medium channel that extends against the rotational direction has proved advantageous.
Outlets in both or multiple pressurizing medium channels are arranged in the reversing surface that can be passed over. A substantially synchronous pressurizing medium connection between the opening in the working chamber that is passing over and the pressurizing medium channels takes place when these have outlets offset radially to one another relative to the rotational axis of the cylinder drum, for example. This is a preferred solution in axial piston engines. Alternatively or in addition, an offset of the outlets of the pressurizing medium channels in the reversing surface can of course also be provided in the rotational direction.
In one development the piston engine is configured for a rotational direction and/or torque reversal. In this case, a development in which one or more pressurizing medium channels open out, as described, in another reversing surface arranged diametrically to the aforementioned reversing surface, has proved advantageous. In this way, the aforementioned reset is possible for each rotational direction.
In order to avoid the aspiration of an air/oil mixture via the pressurizing medium channel when the rotational direction is reversed, the pressurizing medium channels preferably each have a non-return valve opening towards the pressurizing medium trough.
As an alternative to the design with the aforementioned control plate, the outside surface of the cylinder drum may be directly in abutment with the housing portion. The outlets of the high-pressure and low-pressure chamber and the reversing surface or reversing surfaces are then formed on the housing portion, in particular on the connection plate or the housing cover. Although this design comprises one fewer component—the control plate is missing—an ever-present possibility of wear on the face side of the housing portion which exhibits the aforementioned outlets of the high-pressure and low-pressure chamber compared with the design with the control plate leads to a high repair cost, since the housing portion which is expensive to produce has to be reworked or replaced instead of the simple control plate.
An exemplary embodiment of a hydrostatic piston engine according to the disclosure is depicted in the drawings. The disclosure is explained in greater detail below with the help of the figures in these drawings.
In the drawing:
According to
On the opposite face side 36 of the cylinder drum 16 the hydrostatic working chambers 24 have openings 34. The face side 36 is in abutment with a control plate 38 via which an alternating pressurizing medium connection to a high-pressure chamber 40 arranged in the connection plate 6 and a low-pressure chamber 42 arranged there is made. The high-pressure chamber 40 has a high-pressure opening 41 on the connection plate 6 and the low-pressure chamber 42 has a low-pressure outlet 43 on the connection plate 6. The outlets 41, 43 are suitable for being connected to a pressurizing medium connection. The control plate 38 has through-recesses in a known manner for the alternating pressurizing medium connection of the hydrostatic working chambers 24 to the pressure chambers 40, 42. See
A low-pressure kidney 44′ corresponding to the low-pressure kidney 44 and a high-pressure kidney 46′ corresponding to the through-bores 46 of the control plate 38 are formed in the bearing surface 62a. The bearing surface 62a has a comparatively small extension in the radial direction, which means that in the region of the low-pressure and high-pressure kidneys 44′, 46′ a bearing of the control plate 38 with a comparatively high surface pressure takes place, in this way both the low-pressure kidney 44′ and the high-pressure kidney 46′ are already sealed comparatively well in respect of one another by the pressing force of the control plate 38 onto the bearing surface 62a. Consequently, a high-pressure field expands during operation, starting from the high-pressure kidney 46′, between the inner bearing surface 62a and the supported plate 38. In order to delimit this high-pressure field, in particular to delimit the unloading force resulting from the high-pressure field and acting in a lifting manner on the control plate 38, two grooves 66 and 68 running in a radial direction are provided in the connection plate 6. Radially inwards of the inner bearing surface 62a is attached a ring-shaped low-pressure area 70 lowered axially in respect of the aforementioned bearing surface. Via the surface and groove system made up of the ring surface 70, radial grooves 68, 66 and the ring groove 64, there results on the face side of the connection plate 6 shown according to
On observing
On observing
If the openings 34 pass over the low-pressure kidney 44 according to the aforementioned rotational direction, the working pistons 22 according to
After the last through-recess 46 has been passed over, the opening 34 of a respective working chamber 24 passes over the reversing surface 78. Consequently, the hydrostatic working chamber 24 is fluidically separated from the high-pressure chamber 40. Up to the dead point of the reversing surface 78, which is diametrically opposite the dead point of the reversing surface 76, there is a further introduction of the working piston 22 and therefore a reduction in the volume of the hydrostatic working chamber 24.
As already described, connecting the high-pressure-guiding working chamber 24 directly to the low-pressure chamber 42 during further rotation has proved problematic. As depicted above, there would be an abrupt decrease in the pressure of the pressurizing medium in the hydrostatic working chamber 24 into the low-pressure chamber 42 and therefore high flow speeds. In traditional piston engines, this affects the induction performance in the working cycle until cavitation occurs due to high flow speeds and low pressure. Pressurizing medium channels formed by the reset grooves 72 and 74 have a bearing on these problems.
According to
Returning to the description of the cycle of the hydrostatic working chamber 24 and its opening 34, when passing over the reversing surface 78 the aforementioned opening initially comes into pressurizing medium connection with the two through-recesses 80, 82 before it brings the working chamber 24 into pressurizing medium connection with the low-pressure kidney 44. In this way, the so-called “resetting” of the high pressure prevailing in the hydrostatic working chamber 24 is possible via the pressurizing medium channels 80, 72 and 82, 74 (as already mentioned, created by covering by the control plate 38). The decrease in pressure of the pressurizing medium from the hydrostatic working chamber 24 does not therefore take place in the low-pressure kidney 44, but in a controlled manner via the reset grooves 72, 74 in the housing interior 58.
According to
The dimensions of the first portion 84 according to
According to
A hydrostatic piston engine with hydrostatic working chambers is disclosed, the openings of which come into alternating pressurizing medium connection with outlets in a high-pressure chamber and a low-pressure chamber of the piston engine and a reverse surface arranged therebetween, wherein at least one pressurizing medium channel is provided which, on the one hand, opens out in the reversing surface and, on the other, into a pressurizing medium trough in the piston engine, wherein a flow cross section increases at least along a first portion of the pressurizing medium channel to the pressurizing medium trough.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 222 354.5 | Dec 2017 | DE | national |
