Pumps – Three or more cylinders arranged in parallel – radial – or... – Radial cylinders
Reexamination Certificate
1999-05-17
2001-06-05
Tyler, Cheryl J. (Department: 3746)
Pumps
Three or more cylinders arranged in parallel, radial, or...
Radial cylinders
C417S366000
Reexamination Certificate
active
06241484
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a radial piston pump, with cylinders oriented radially to an axis of rotation of an eccentric shaft, and with pistons arranged radially movably in the cylinders against the force of a spring. The pistons are pressed radially outwards by the rotational movement of an eccentric and are pressed radially inwards by the spring. The pistons have an inlet opening connected to an inlet chamber of a pumping medium when the pistons are in the radially inner positions. The pumping medium is pressed into a pressure area during the radially outward movement of the pistons. The eccentric shaft is mounted in sliding bearings arranged on both sides of the eccentric and is drivable by a traction means.
Radial piston pumps of this type are known. The alternating radial inward and outward movements of the pistons in the cylinders pump a medium, for example oil, is conveyed in a known manner. Radial piston pumps of this type are used for levelling systems in motor vehicles for example. In that case, the radial piston pump is driven by a belt drive which is driven by an internal-combustion engine of the motor vehicle. The belt engages on a drive wheel of the radial piston pump in order to rotate the eccentric shaft of the radial piston pump. The arrangement of the radial piston pump applies a belt force having a radial direction vector upon the eccentric shaft by the belt drive. The direction vector and the amount of the belt force are substantially constant.
In addition, the eccentric shaft is loaded by hydraulic forces which are introduced by the pistons of the radial piston pump and which likewise have a radial direction vector. A resulting hydraulic force of the radial piston pump, formed from partial hydraulic forces, is produced in accordance with the number of pistons of the radial piston pump. In this case the level and the direction vector of the resulting hydraulic force vary during use of the radial piston pump for its intended purpose in accordance with a rotational speed of the eccentric shaft. The constant belt force is overlaid by the variable hydraulic force, causing the eccentric shaft to be acted upon with a varying radial force. The resulting hydraulic force (also referred to as the “bearing force” below) has to be removed by the sliding bearings in which the eccentric shaft is mounted.
With large volumes in the radial piston pump and high hydraulic pressures, the resulting hydraulic forces can have a greater total than the belt force and, depending upon their operative direction, the hydraulic forces can cause a change in direction of the resulting force acting upon the eccentric shaft. In this way, the eccentric shaft can be pressed onto the sliding bearing against the belt force by the hydraulic forces. In this case, the actual resulting hydraulic force determines the direction vector of the resulting bearing force of the eccentric shaft and thus specifies a position of the eccentric shaft in the sliding bearing.
A drawback of this is that the change in position of the eccentric shaft in the sliding bearings can generate noise, a so-called knocking, as well as increased wear. In particular, if the radial piston pump is suction-throttled and is operated heavily regulated, phases can occur in which none of the pistons of the radial piston pump conveys the pumping medium, so that the eccentric shaft is oriented exclusively by the belt force as a result of the absence of hydraulic forces. At the beginning and the end of this phase, the resulting bearing force changes abruptly with respect to its direction vector, so that a reciprocating movement of the eccentric shaft occurs in the sliding bearings.
In addition, the hydraulic force acting upon the eccentric shaft does not change continuously, but changes abruptly, with respect to both the amount and the direction vector. Depending upon whether a piston of the radial piston pump begins or ceases to convey, the hydraulic force and thus the resulting bearing force produced by the superimposition with the belt force suddenly change.
It is known to lubricate the sliding bearings of the eccentric shaft in radial piston pumps with the pumping medium, for example oil. This oil is generally heavily foamed, particularly in the case of suction-regulated radial piston pumps, so that mixed friction of the eccentric shaft in the sliding bearings occurs as a result of air inclusions in the pumping medium. The mixed friction is not sufficient to damp the above-mentioned knocking of the eccentric shaft in the sliding bearings.
SUMMARY OF THE INVENTION
The object of the invention is to provide a radial piston pump of the above type which is simple in design and which prevents an eccentric shaft in a sliding bearing from knocking as a result of varying hydraulic forces which act upon the eccentric shaft.
This object is attained through a pressure connection present between the pressure area of the radial piston pump and at least one of the sliding bearings. It is advantageously possible for a bearing gap between the sliding bearing and the eccentric shaft to be constantly supplied with a closed film of oil which has a damping effect upon the radial movements of the eccentric shaft. This prevents the production of noise due to mechanical contact of the eccentric shaft with the sliding bearing. The radial piston pump as a whole operates more quietly. In particular, it is possible to counteract knocking by the superimposition of the hydraulic force acting upon the eccentric shaft and the belt force.
In a preferred embodiment of the invention, the pressure connection is formed by a duct which is formed in a housing of the radial piston pump and which opens with at least one outlet opening into the sliding bearing. This makes it possible to build up a volume flow of the pumping medium from the pressure area of the radial piston pump to the sliding bearing, and that volume flow performs the lubrication and damping of the sliding bearing.
In particular, the pumping medium is preferably conveyed into a radially central region of the sliding bearing. This makes a satisfactory distribution over the entire bearing surface of the sliding bearing possible, so that particularly good damping and lubrication can be achieved.
In a further preferred embodiment of the invention, the pressure connection opens in a range of ±90°, preferably ±50°, and in particular ±30°, with respect to a direction vector of the force of a traction means, in particular a belt traction force, acting upon the eccentric shaft. This advantageously makes it possible for the pressure build-up to first occur in particular in the region of the sliding bearing in which the eccentric shaft can be pressed against the bearing shell by the belt traction force, so that particularly good damping of the sliding bearing is provided in the direction of the belt traction force.
In addition, in a preferred embodiment of the invention, the pressure connection opens into a plurality of openings arranged preferably symmetrically over the periphery of the sliding bearing. This advantageously makes it possible for a uniform film of oil to be built up in the bearing gap between the eccentric shaft and the sliding bearing, enabling a high degree of damping of the sliding bearing in all radial directions, particularly in the case of radial piston pumps with high hydraulic forces which can be superimposed on the belt traction forces in an opposite manner.
Other objects and features of the invention are explained below in embodiments with reference to the accompanying drawings.
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patent: 1074371
Luk Automobiltechnik GmbH & Co. KG
Ostrolenk Faber Gerb & Soffen, LLP
Tyler Cheryl J.
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