Axial piston pump with oblique disk

Details Axial piston pump with oblique disk Axial piston pump with oblique disk

2000-02-17

2001-11-06

Tyler, Cheryl J. (Department: 3746)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

C417S269000, C091S504000, C091S499000, C092S012200

Reexamination Certificate

active

06312231

ABSTRACT:

RELATED APPLICATIONS
The present application claims priority to German Patent Application No. DE 199 06 540.3 filed Feb. 17, 1999, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention relates to axial piston pumps having oblique disks. One known type of axial piston pump has a piston drum that is rotatably displaceable by way of a rotatable drive shaft and that has a number of bore holes disposed therein.
Pistons are disposed in the piston bore holes and are displaceable between a lower dead-center point and an upper dead-center point. The pistons are each driven by an articulated piston rod that is reciprocably displaceable by way of an oblique disk. The disk is adjustable in its inclination with respect to the piston drum. A holder is provided to guide the piston rods. The holder is always oriented in parallel with respect to the oblique disk. The drive shaft is supported by way of a ball-type formation in a central receiving bore of the holder.
An axial piston pump with the aforementioned features is known from Delivery Catalog 2500 D of Parker Hannifin GmbH, Hydraulic Controls Division, 41564 Kaarst, 3rd edition (1997), page 1-64. The drive shaft, which rotationally displaces the piston drum via a toothed engagement, and which itself is driven, is supported by way of its forward, ball-type end on the central receiving bore of a holder. The holder is adjustable by way of the oblique disk and, in that connection, is always oriented in parallel to the oblique disk. The piston rods that connect to the pistons extend through the holder in corresponding bore holes. The end of each piston is coupled to a travel shoe that, during rotation of the piston drum relative to the fixed oblique disk, will run along the oblique disk so that the piston rods are displaced reciprocally, and thereby drive the pistons. The holder holds the travel shoes (that run along the oblique disk when the piston drum rotates) in place on the oblique disk with a predetermined bias and rotates synchronously with the piston drum.
In known axial piston pumps, as long as the driving of the piston drum takes place by way of the drive shaft coupled with it in form-fit fashion, a torque will be transferred from the piston drum through the pistons that reciprocate in the piston bore holes and the piston rods that extend through the holder. One disadvantage of this structure is that, for pistons resting in the lower dead-center point in the piston bore hole, a minimal axial covering of the piston must be provided by the wall of the piston bore hole in order to guarantee an adequate transfer of torque between the piston drum and the piston. When the piston is in that position, the angle of engagement of the oblique disk is limited, which limits the output of the axial piston pump.
With oblique disk pumps known in the art, the maximum angle of engagement, as a rule, is about 18 degrees. If the output of the pump is increased by way of a greater angle of engagement of the oblique disk, this will necessarily lead to the structural size of the piston drum being increased in the axial direction since, in addition to the longer piston travel achieved with a greater angle of engagement, one will need to account for the necessary minimal covering of the piston with the piston bore hole. With a zero-degree angle of engagement of the oblique disk with respect to the drive shaft, the extension of the piston rods through the holder must correspond exactly to the piston bore holes in the piston drum because of the task of transmitting torque to the holder that is accorded the pistons. An increase in the angle of engagement will lead to an undesirable increase in the structural size of the pump in the radial direction, since otherwise the travel shoes would displace too closely to the drive shaft.
The object of the invention is thus to improve upon an axial piston pump, that has the features mentioned above, in such a way that the angle of engagement of the oblique disk can be made greater without changing the structural size of the pump.
The solution to this objective encompasses advantageous developments and modifications associated with the invention in accordance with the content of the claims appended to this specification.
SUMMARY OF THE INVENTION
The invention provides that, in order to support the drive shaft on the holder, a ball head is provided that is connected to the drive shaft. The ball head has a sphere-shaped adjustment surface inserted in the receiving bore of the holder. Further, on the outer side of the spherical adjustment surface there are at least two glide blocks that are rotatable about a rotational mount and that exhibit an axial extent with respect to the drive shaft axis. For the purpose of transmitting torque from the drive shaft to the holder, the glide blocks are engaged with grooves in the holder. The grooves are preferably provided in the wall of the holder that circumscribes the receiving bore.
The basic concept of the invention resides in transmitting the torque needed for rotationally driving the holder directly from the drive shaft to the holder, yet the holder is positionally adjustable with respect to the drive shaft. With the arrangement according to the invention, the form-fit engagement between the adjustment surface (fixed with respect to the shaft) and the holder is retained, which serves to transmit torque. The holder can advantageously be altered in terms of its angle of engagement with respect to the shaft axis without regard for the axial length of the piston drum. The glide blocks, that are engaged in the grooves of the holder and are mounted on the spherical adjustment surface of the ball head that is connected with the drive shaft, will follow along with relative changes in position because of their rotatable formation. In each angular position of the holder with respect to the drive shaft, the guide blocks will remain in engagement with the corresponding grooves of the holder.
In this connection, the radial depth of a corresponding groove is dimensioned so that, for each maximal angle of engagement of the holder with respect to the drive shaft axis, the glide block can assume a skewed position in the groove that depends on the positioning of the glide block on the spherical adjustment surface and on its structural height.
Pursuant to a specific aspect of the invention, the piston rods are held in the holder, at their free ends, by way of an articulated connection. The holder, when it rotates, runs freely along the oblique disk. On its running surface, the holder has recesses oriented towards the oblique disk. These recesses are connected with the work chamber of the piston bore hole via bores that are formed in the holder and in the piston rods connected therewith. The travel shoes used in the prior art are not necessary. Since the recesses in the running surface of the holder are filled with oil on account of their connection with the work chamber of the corresponding piston bore, the holder will run along the oblique disk on a film of oil. This reduces friction and curtails corrosion of the components. Since the piston rods no longer extend through the holder, but are actually held in it, the mechanics of aligning the holder and piston drum to one another are simplified.
According to one embodiment of the invention, several glide blocks are distributed about the circumference of the spherical adjustment surface in symmetrical fashion and are arranged in grooves associated with the holder.
Since the overall construction of the piston drum with the pistons and the holder connected therewith can, at any given time, only be realized in one position of the holder and piston drum with respect to one another in order to establish the needed synchronization of the rotational movement of the piston drum and the holder, the piston drum and holder are designed for mutual and matching alignment with respect to the drive shaft during mounting. As far as one embodiment according to the invention contemplates that the ball head supported on t

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