EP0401408A1 - Radial-piston machine - Google Patents

Abstract

Radial piston machine, in particular radial piston pump for automobiles, with a radially inner control mirror pin (2), an outer cam ring (35) and a cylinder star (14) with pistons (20) arranged in between, which are inclined during rotation. The displacement can be constant or changeable. The control mirror pin (2) has a web widening in order to achieve pre-compression. In the case of variable displacement, the sinusoidal piston travel curve is adjusted by adding a constant eccentricity (c) by a variable lead angle (ε), so that the separation angle (τ) with large delivery volumes more towards the extreme value of the piston travel curve and with small delivery volumes more towards the flank of the piston travel curve is shifted so that a sufficiently large pre-compression path is achieved with small delivery volumes.

Description

The invention relates to a radial piston machine and in particular radial piston pump for automobiles.

In automotive engineering, the demands for small construction volumes and low production prices have to be reconciled. Another requirement is the low noise level of the pump. Since automobile pumps are driven from the main engine, strongly fluctuating drive speeds between 700 and 7000 rpm, for example, have to be managed. In positive displacement pumps, this leads to a strongly fluctuating pump flow, whereas a constant pump flow or a constant fluid pressure would be desirable from the consumer system.

The invention has for its object to provide a radial piston machine (pump or motor) which is small compared to known radial piston machines of the same power, can be easily manufactured and works quietly. Furthermore, the construction principle should open up the possibility of changing the displacement volume of the machine with additional components.

The object is achieved in a radial piston machine with the features of claim 1.

In the design according to the invention, the length of the respective cylinder bore is only slightly larger than the stroke of the associated piston. Furthermore, the supply and discharge of the fluid can save space through the central arranged control mirror pin take place, ie you can avoid inflow and outflow channels in radially outer housing parts. The manufacture is inexpensive insofar as it is essentially a matter of rotationally symmetrical components, the pistons have a simple design and there are also no high demands on the manufacturing accuracy of the cylinder bores.

A special feature of the new radial piston machine is that the pistons are inclined when the cylinder star rotates. This means that pressure in the torque (and vice versa) is converted directly, so that the pistons are relieved of the lateral force. The largest inclination angle α occurs at a piston position of 90 ° if the zero position in the main eccentricity plane is assumed. The size of this inclination angle α depends on the extent of the eccentricity of the cam ring, which in turn is related to the cylinder length. With the construction according to the invention, maximum inclination angles α of approximately 10 ° can be achieved. In a preferred embodiment of the invention, the inclination angle is α = 7.75 °.

Because of the changing inclination of the pistons, a line seal by means of a piston ring is preferred, which can adapt to the changing shape between the ellipse and the circle and does not lead to excessive edge pressures. For this purpose, the piston ring groove with its neck-side edge is arranged on the largest diameter of the piston head and the piston ring has a conical-spherical outer surface. The basic shape of the piston ring is therefore conical, with the piston ring being revised spherically at the largest diameter.

The piston shoe, which is preferably made in one piece with the piston neck and piston head, has a cylindrical bearing surface in order to engage with the

Support the inner race of the cam ring. In the case of pure hydrodynamic bearing lubrication, the cylindrical wing is connected asymmetrically to the piston head above the piston neck, the front wing part in the running direction being larger than the rear wing part. If the wings of the piston shoes are lubricated from the respective pump chamber via a hole in the piston, a symmetrical arrangement of the piston shoe and piston head can also be carried out. This type of lubrication also leads to hydrostatic relief of the pistons.

In order to reduce the structure-borne noise excitation, the fluid enclosed between the separating web and the cylinder space can be pre-compressed before it is connected to the actual pressure space. If the pre-compression at the time of connection corresponds exactly to the pressure in the pressure chamber, there is no structure-borne noise excitation. Therefore, the separator between low pressure and high pressure is widened in the direction of rotation of the pump by an amount that is suitable for producing a suitable pre-compression of the enclosed pressure fluid. Adjustments to different operating pressures can be made using pilot control notches.

If the radial piston machine is designed with a variable displacement volume, this means that the respective piston strokes are reduced and thus the achievable pre-compression pressure is also reduced with a decreasing displacement volume. According to the invention, the stroke ring of the radial piston machine is adjusted tangentially along a specially aligned guide, as a result of which the eccentricity of the stroke ring is spatially aligned in a certain way, which is noticeable like an adjustment of the advance angle between pump star and control pin. Specifically, the cam ring is tangential along a guide by a first amount of eccentricity adjustable, and the vertical distance of the guide from the axis of rotation of the cylindrical star is smaller by a second amount of eccentricity than the diameter of the cam ring. These measures surprisingly achieve an approximately constant pre-compression path regardless of the displacement setting of the machine.

If radial piston machines are involved in which the dead volume changes during the displacement adjustment, the second amount of eccentricity can be varied depending on the stroke, if necessary, by giving the guide ring of the stroke ring an inclined contact surface. The novel radial piston machine can be constructed with one or more disks, i. H. two or more cylinder stars arranged next to one another can be provided, which run on the same control mirror journal and are connected to one another via entrainment means.

• Fig. 1 einen Längsschnitt durch eine Radialkolbenpumpe,
• Fig. 2 einen schematischen Querschnitt,
• Fig. 3 eine vergrößerte Einzelheit, nämlich einen Kolbenschuh,
• Fig. 4 eine Seitenansicht eines Kolbens,
• Fig. 5 die Ansicht eines weiteren Kolbenschuhs,
• Fig. 6 einen Querschnitt durch einen Kolben,
• Fig. 7 einen Querschnitt durch einen Kolbenring in vergrößerter Darstellung,
• Fig. 8 eine schematische Darstellung einer Hubringführung,
• Fig. 9 ein Diagramm des Kolbenweges und des erzeugten Druckes über dem Drehwinkel für einen einzelnen Zylinder bei großem Fördervolumen,
• Fig. 10 ein entsprechendes Diagramm, jedoch bei kleinem Fördervolumen,
• Fig. 11 einen Längsschnitt durch eine Radialkolbenpumpe mit zwei Zylindersternen und
• Fig. 12 einen schematischen Querschnitt der Pumpe nach Fig. 11.

The invention is described with reference to the drawing. It shows:

• 1 shows a longitudinal section through a radial piston pump,
• 2 shows a schematic cross section,
• 3 is an enlarged detail, namely a piston shoe,
• 4 is a side view of a piston,
• 5 shows the view of a further piston shoe,
• 6 shows a cross section through a piston,
• 7 is a cross section through a piston ring in an enlarged view,
• 8 is a schematic representation of a cam ring guide,
• 9 is a diagram of the piston travel and the pressure generated over the angle of rotation for a single cylinder with a large delivery volume,
• 10 shows a corresponding diagram, but with a small delivery volume,
• Fig. 11 is a longitudinal section through a radial piston pump with two cylinder stars and
• 12 shows a schematic cross section of the pump according to FIG. 11.

1 and 2. A control mirror pin 2 is inserted in a sealed manner in a housing 1. Inlet channels 3 and outlet channels 4 each lead to inlet grooves 5 and outlet grooves 6. The grooves 5 and 6 are separated from one another by separating webs 7 and 8. The control mirror pin 2 also has a central bore 9 through which a shaft 10 is passed in order to drive a further unit, not shown. The shaft 10 is supported by bearings 11 in the housing 1 and drives a drive disk 12 via a spline 13 or the like. The drive pulley 12 is connected to a cylindrical star 14, which is provided with a number of radially extending cylinder bores 15, which are each provided with a passage opening 17 on their base 16. The number of cylinder bores 15 can be freely selected within a certain range, i. H. both even and odd numbered cylinders can be used. A number of cylinders Z = 8 is preferred because it forms a good compromise between the requirements for small size and low volume flow pulsation and also offers enough space for the control mirror journal 2.

In each cylinder bore 15, a one-piece piston 20 is guided, which has a spherical piston head 21, a piston groove 22, a piston neck 23 and one Piston shoe 24 has. The groove 22 is made along the largest diameter of the spherical piston head 21, namely the neck-side edge of the piston groove 22 coincides with the equator of the piston head 21.

3 and 4, the piston shoe 24 has a rectangular outline and a cylindrical wing, in which a front wing part 25 and a rear wing part 26 can be distinguished. The areas of these two wing parts are 58 and 42%, respectively. The shoe 24 is connected asymmetrically to the piston neck 23 and piston head 22. This design is used for hydrodynamic lubrication since the lift on the rear wing part 26 is somewhat greater than on the front wing part 25.

The wing parts 25 and 26 can also be arranged symmetrically, as shown in FIGS. 5 and 6, which is particularly considered when a lubrication channel 27 leads from the pump chamber 17 to the wings 25, 26. The wing parts 25, 26 can also be interrupted by an annular groove 28 which delimit a surface corresponding to the head 21 and are connected via a relief bore 29 with low pressure in order to provide hydrostatic relief.

A slotted piston ring 30 is inserted in the piston groove 22, the slot 31 of which can be seen in FIG. 2 and which enables a certain elastic change in shape of the piston ring 30, which is necessary because the piston head 21 can be inclined in the cylinder bore 15. The piston ring 30 must therefore temporarily change from the circular shape to a weak elliptical shape, which also leads to displacements and swivels of the outer piston ring surface 32 to the cylinder wall. In addition, the fluid pressure acts on the piston ring 30 from the outside and also from the inside, the piston groove 22, forth and in order to balance the fluid pressure on the piston ring, a trapezoidal cross-sectional shape of the piston ring 30 would be preferred. However, in order to reduce the wear due to the pivoting movements mentioned and to enable hydrodynamic lubrication of the piston ring 30, the piston ring 30 is designed spherical in the region of its largest diameter 33, as can best be seen from FIG. 7 at 34. For manufacturing reasons, the crowning radius can also be continued up to the smaller diameter of the piston ring.

The piston shoes 24 work together with a cam ring 35 (FIGS. 1 and 2) which has an inner running surface 36 and an outer surface 37. The inner running surface 36 is arranged eccentrically to the cylinder star 14 and therefore transmits a stroke movement to the pistons 20 when the cylinder star rotates. The return stroke is provided by hold-down rings 38 which engage on the inside of the piston shoes 24 in edge grooves formed there, so that overall positive guidance is achieved becomes. The pump chamber 18 enclosed between the piston head 20 and the cylinder bore 15 widens at the inlet grooves 5 and narrows at the outlet grooves 6. As a result, the fluid is sucked in on the side 5 and displaced on the side 6, which results in the pump flow.

If a maximum delivery volume of V = 12 cm³ per revolution is to be achieved with a number of pistons Z = 8, then a piston diameter of D = 16 mm and an eccentricity of e = 3.7 mm are required. In such a radial piston machine, the pistons must allow 20 inclinations up to α = 7.75 °. If you go for an even higher eccentricity and thus a larger piston stroke, the maximum inclinations increase. It is assumed that the system described tolerates a maximum inclination angle α of 10 °.

As can be seen from FIG. 2, the separating webs 7 and 8 are each wider than the passage openings 17, namely that widening points in the angular range τ are offset at least in each case in the direction of rotation of the cylindrical star 14. Accordingly, if the pumping spaces 18 move over the web 7 during their circulation, then the piston 20 already begins to compress the enclosed fluid before it comes into contact with the groove 6, in which the high pressure prevails. If this pre-compression corresponds exactly to the fluid pressure in the groove 6, there is no pressure release and thus no sound excitation. The aim is therefore to design the amount of pre-compression so that it corresponds to the desired pump pressure. Deviations can be compensated for by pre-tax notches in the range τ as long as these deviations are not too large.

The dividers 7, 8 can also be arranged symmetrically to the plane 40-40, the widening points then being on both sides.

The radial piston pump described can also be designed as a control pump, as shown in FIG. 2. The actuating system acts along an actuating plane 40 and has a small cylinder 41 with a small actuating piston 42 and a large actuating cylinder 43 with a large actuating piston 44 and a spring 45. The small actuating piston 42 is constantly pressurized with the pump pressure and the large actuating piston 44 with control pressure which is less than the pump pressure. It can be regulated to a constant delivery volume or to a constant delivery pressure, which need not be described further. In general, however, this leads to adjusting movements of the cam ring 35 and thus to changed eccentricities e and changed pre-compression amounts, which would thus be mismatched with the system.

8 to 10 show how this problem is solved. A guide 46 is provided in the housing 1 for the cam ring 35, against which the cam ring rests and is guided between different eccentric positions. The vertical distance of the guide 46 from the axis of rotation 14a of the cylindrical star, that is to say the distance 46₀-14a, is smaller than the radius of the outer surface 37 of the cam ring 35 with which it is supported on the guide 46. In a position of the lifting ring 35, which is otherwise referred to as the zero lifting position, the center 35a of the lifting ring does not coincide with the axis of rotation 14a of the cylindrical star, but takes up a distance c which represents a "constant" eccentricity. In the zero stroke position there is an upper dead center OT₀ and a lower dead center UT₀, which deviate by 90 ° with respect to the positioning plane 40. In this position, of course, no fluid is pumped through the pump because the pistons 20 reciprocate symmetrically to the grooves 5 and 6, respectively.

If the cam ring 35 is now shifted to the right by a certain amount of eccentricity e1 in FIG. 8, the top and bottom dead centers shift into the positions OT1 and UT1 and a small delivery volume is pumped, as shown in FIG. 10.

If the cam ring 35 is moved even further, into its end position, the top and bottom dead center at OT₂ and UT₂. Starting from the main eccentricity plane 40-40, the circumferential angle of the cylindrical star is designated by Φ. The angular position of the bottom dead center before reaching the main eccentricity plane at Φ = 180 ° is referred to as the lead angle ε. The angle difference between the width of the web 7 and the width of the opening 17 is the separation angle τ. When a cylinder 15 passes this separation angle τ, the cylinder pressure P increases from low pressure ND to the high pressure HD. In order for this pressure increase to proceed evenly, pre-compression in the enclosed volume of the cylinder in the angular range τ is required. For this purpose, the piston 20 should cover a pre-compression path k when passing the angular range τ, although the radial speed of the pistons 20 depends on the delivery volume and therefore different pre-compression paths seem to be the inevitable result. The correction of the radial piston speed in the land area τ is actually only achieved by the interaction of the constant eccentricity c with the adjustable eccentricity e, where:
ε = arc tan c / e.
The lead angle ε is small for large delivery volumes and large for small delivery volumes. In the diagrams according to FIGS. 9 and 10, this means a shift of the sinusoidal piston path curve s to a greater or lesser extent to the left, namely a larger shift ε 1 with small delivery volumes and a smaller shift ε 2 with large delivery volumes. Accordingly, the piston travel curve s crosses the separation angle τ for large delivery volumes more in the range of an extreme value, while for small delivery volumes it is shifted more onto the flank of the piston travel curve s, as can be seen from the comparison of FIGS. 9 and 10. In other words: one uses the greater radial speed of the pistons away from the extreme points to achieve a sufficiently large pre-compression path k 1 despite the small delivery volume. You can ensure that the pre-compression paths k₁ and k₂ are approximately the same size, but it is also possible to make k₁ somewhat larger (as shown in Fig. 10) in order to compensate for the greater effect of the leakage oil loss with a smaller delivery volume.

In order to compensate for the effect of dead spaces, it may be expedient to vary the constant eccentricity c by means of an inclined contact surface (corresponding to the guide 46). Such an inclined contact surface can be a straight or a curved guide.

The amount of constant eccentricity c is otherwise very small. For a pre-compression pressure of 140 bar, a replacement compression module of oil of 14,000 bar, a dead volume of 1.5 cm³, a cylinder diameter of 1.6 cm and a separator web angle of 10 °, there is a constant eccentricity of c = 0.43 mm. It is conceivable to make the guide 46 adjustable by means of a fine thread in order to determine the optimal value of the constant eccentricity c from noise minimization measurements.

11 and 12 show that the radial piston pump can also be designed for two or more cylinder stars 14. The individual cylinder stars are coupled with one another in their rotational movement via driving claws 48 or the like, while a certain radial displacement between the cylinder stars remains possible. In the exemplary embodiment shown, two common suction connections 3 are provided, while the pressure connections 4a, 4b are separated for the two pump disks. It goes without saying that the bushing 9 is not absolutely required for the shaft 10 and this space could also be used for fluid channels.

Reference symbol list

• 1 housing
• 2 steering mirror pins
• 3 inlet channels
• 4 outlet channels
• 5 inlet grooves
• 6 outlet grooves
• 7, 8 dividers
• 9 hole
• 10 wave
• 11 bearings
• 12 drive pulley
• 13 splines
• 14 cylinder star
• 15 cylinder bores
• 16 bottom
• 17 passage opening
• 18 pump room
• 20 pistons
• 21 piston head
• 22 piston groove
• 23 piston neck
• 24 piston shoe
• 25, 26 wing part
• 27 lubrication channel
• 28 ring groove
• 29 relief bore
• 30 piston ring
• 31 slot
• 32 piston ring surface
• 33 largest piston ring diameter
• 34 crowning
• 35 cam ring
• 36 inner tread
• 37 outer surface
• 38 hold-down ring
• 40 level
• 41 cylinders
• 42 actuating pistons
• 43 actuators
• 44 actuating pistons
• 45 spring
• 46 leadership
• 48 claws
• c constant eccentricity.
• e adjustable Eccentric.
• k pre-compression path
• s piston travel
• D piston diameter
• P cylinder pressure
• OT top dead center
• UT bottom dead center
• V funding volume
• Z number of cylinders
• α Piston slant angle.
• ε lead angle
• Φ angle of rotation
• τ separation angle
• 46₀ zero stroke position

Claims (10)

1. Radial piston machine, in particular radial piston pump for automobiles, with the following features:
a control mirror pin (2) is provided with inlet and outlet channels (3, 4) which lead to corresponding inlet and outlet grooves (5, 6), separated from one another by separating webs (7, 8), for the fluid flowing through the machine;
a cylindrical star (14) is rotatably mounted relative to the control mirror pin (2) and contains a number of cylinder bores (15), each of which has a passage opening (17) which, depending on the rotational position of the cylindrical star, with the inlet groove (5), the outlet groove (6) or one of the dividers (7, 8) cooperates;
A piston (20) is pivotably guided in each cylinder bore (15) and for this purpose has a spherical piston head (21), a piston groove (22) and at least one piston ring (30) inserted therein, each of which has a radially inward pump chamber (18) limit; each piston also has a piston neck (23) and a piston shoe (24) in order to achieve an overall length of the piston which is only slightly greater than the length of each cylinder bore (15);
the piston shoes (24) work together with a cam ring (35) which is arranged eccentrically to the cylinder star (14) and transmits a stroke movement to the piston (20) during the cylinder star revolution, so that the piston (20) is at a certain angle (α ) and incline the pump chamber (18) enclosed between the piston head (21) and the cylinder bore (15) the inlet grooves (5) increases and the outlet grooves (6) decrease. 2. Radial piston machine according to claim 1, characterized in
that the eccentricity of the cam ring (35) is limited to a value which leads to an inclined angle (α) of the pistons (20) of at most 10 °. 3. Radial piston machine according to claim 2, characterized in that
that the largest inclination angle (α) is about 7.75 °. 4. Radial piston machine according to one of claims 1 to 3, characterized in
that the piston groove (22) is arranged with its neck-side edge at the largest diameter of the piston head (21) and
that the piston ring (30) has a conical-spherical outer surface (32). 5. Radial piston machine according to one of claims 1 to 4, characterized in
that the piston shoe (24) has a cylindrical bearing surface (25, 26) which is connected asymmetrically to the piston head (21) via the piston neck (23), the front wing part (25) in the running direction being larger than the rear wing part (26) is. 6. Radial piston machine according to one of claims 1 to 5, characterized in that the supporting surface (25, 26) of the piston shoe (24) is connected via a channel (27) to the respective pump chamber (18). 7. Radial piston machine according to one of claims 1 to 6, characterized in
that the dividers (7, 8) are widened by an amount (τ). 8. Radial piston machine according to claim 7, characterized in
that the cam ring (35) is tangentially adjustable along a guide (46) by a first eccentricity amount (e) and
that the vertical distance of the guide (46) from the axis of rotation (14a) of the cylindrical star (14) is smaller by a second amount of eccentricity (c) than the radius of the cam ring (35). 9. Radial piston machine according to claim 8, characterized in
that the guide (46) is inclined to guide the center point (35a) of the cam ring (35) at a variable distance from the plane of symmetry (40) of the separating webs (7, 8). 10. Radial piston machine according to one of claims 1 to 9 with two or more cylinder stars (14) arranged next to one another, which run on the same control mirror pin (2) and are connected to one another via driving means (48).

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