EP2513470B1 - Method for determining the displacement of a radial piston machine - Google Patents

Description

The invention relates to a method for determining the absorption volume of a radial piston machine according to the preamble of claim 1.

EP 1 624 185 describes the closest prior art.

It is known that the delivery rate of a radial piston machine, ie a radial piston motor or a radial piston pump is directly dependent on the displacement, which is variable by adjusting the eccentricity. For a regulation of the delivery rate, the current intake volume would be suitable as a reference variable - however, neither the intake volume nor the currently set eccentricity can be measured.

By the DE 10 2007 003 800 B3 a method for controlling a hydrostatic drive has been known, wherein the current displacement of a hydraulic motor is derived from the current electrical adjustment by means of a Verstellstromkennlinie.

By the DE 10 2004 048 174 A1 the applicant has a device for determining the intake volume of an adjustable radial piston engine is known, which has pivotally mounted cylinder. To determine the absorption volume, a rotary encoder is provided, which measures the tilt angle of the cylinder, which is proportional to the current displacement.

By the DE 10 2006 043 291 A1 The applicant has been known a non-contact angle sensor for an adjustable radial piston motor. The rotational angle sensor is intended to detect the current rotational or swivel angle of a cylinder of the radial piston motor, wherein the rotational angle is proportional to the currently set absorption volume of the radial piston motor.

It is an object of the present invention to improve a method of the type mentioned in that the current absorption volume of the radial piston machine can be determined as simple and accurate.

The object of the invention is solved by the features of claim 1. Advantageous embodiments emerge from the subclaims.

According to the invention, the direction of rotation of the drive shaft from the functional curve of the pivot angle β, d. H. determined from the relative position of the swivel angle maxima and minima against π / 2 and 3 π / 2: If the increase of the swivel angle β from minimum to maximum steeper than the drop from maximum to minimum, the direction of rotation is considered to be dextrorotatory. In other cases, the direction of rotation is left-turning. The knowledge of the direction of rotation is essential for the calculation of the swallow volume.

According to the invention, the pivoting angle β of the cylinder is also measured while the radial piston engine is running, from which the eccentricity and, moreover, the displacement are calculated. The currently determined absorption volume can thus be used as a reference variable in a control process for regulating the delivery rate of the radial piston machine. This results in a fast and accurate control. The invention is based on the idea that there is a mathematical link between the swivel angle β, the angle of rotation α of the drive shaft and the respectively set eccentricity e. Since the displacement itself and also the eccentricity during operation of the radial piston machine are not or only very badly measurable, according to the invention, only the pivot angle is measured and calculated using this using the mathematical relationship, the displacement. For the function of the pivoting angle β as a function of the respective rotation angle α, a function similar to a sine curve results in which the maxima and minima are shifted relative to the sinusoid. The zero points of the pivot angle β are achieved in each case in the upper and in the bottom dead center of the radial piston.

According to an advantageous variant of the method, the swivel angle β is measured at defined times t _n , with an angle of rotation α _{n being} assigned to the drive shaft at each point in time t _n . By assigning the angle of rotation at the time of measurement and thus to the measured pivot angle β _n , the eccentricity e can be calculated.

In accordance with a further preferred variant of the method, a number z of pulses per revolution of the drive shaft is generated for determining the times t _n . The occurrence of the pulses triggers the measurement of the swivel angle β _n . Thus, one obtains for each revolution of the drive shaft a sufficient number z of measured values for the swivel angle β and thus calculated values of the current absorption volume.

According to a further advantageous variant of the method, the drive shaft is assigned a zero position which corresponds to the top dead center of the eccentric and which after each passage, i. H. a rotation angle of 360 ° is determined anew.

Fig. 1

eine schematische Darstellung eines verstellbaren Radialkolbenmotors,

Fig. 2

eine schematische Darstellung der geometrischen Verhältnisse für einen Zylinder eines Radialkolbenmotors und

Fig. 3

den Funktionsverlauf des Schwenkwinkels β in Abhängigkeit vom Drehwinkel α.

An embodiment of the invention is illustrated in the drawing and will be explained in more detail below, which may result from the drawing / or the description of further features and / or other advantages. Show it

Fig. 1

a schematic representation of an adjustable radial piston engine,

Fig. 2

a schematic representation of the geometric relationships for a cylinder of a radial piston engine and

Fig. 3

the function of the swing angle β as a function of the rotation angle α.

Fig. 1 shows a designed as a radial piston engine 1 radial piston machine according to the prior art. Five cylinders 2 are arranged in a star shape and pivotally mounted (which is not shown). Each cylinder 2 is associated with a piston 3 which is slidably supported by a shoe on a lifting ring 4. The cam 4 is driven by an eccentric 5 and thus causes the different Hubphasen shown in the drawing. In the Fig. 1 not shown pivotable mounting of the cylinder goes from the aforementioned DE 10 2004 048 174 A1 which is hereby incorporated in full in the disclosure of the present application.

Fig. 2 shows a schematic representation of a cylinder 2 Fig. 1 , where like reference numerals are used for like parts. The cylinder 2 is pivotally mounted about a passing through the point S axis in a housing, not shown. The slidingly arranged in the cylinder 2 piston 3 is supported with its shoe 3a slidably on the cam 4, which is driven by the eccentric 5. The eccentric 5 has a pivot point D, through which the axis of a not shown, the eccentric 5 driving drive shaft extends. The cam ring 4 has a center M; the distance of the pivot point D from the pivot point S is denoted by A. The distance of the center M from the pivot point D is referred to as deflection or eccentricity e. The deflection e is adjustable for the purpose of changing the lift or displacement volume of the radial piston motor. The pivoting angle of the cylinder 2 is β and the angle of rotation of the drive shaft about the pivot point D, starting from the top dead center of the piston 3, is denoted by α. For the indicated rotational angle α results in a position designated by the point E of the eccentric, in which the cylinder 2 has been pivoted by the angle β. The following relationship can be derived from the triangle DSE: $$\mathrm{tan\beta }=\mathrm{e}\cdot \mathrm{sin\; \alpha }/\left(\mathrm{A}+\mathrm{e}\cdot \cos \right)$$

It can be seen from this relationship that the pivot angle β on the one hand depends on the rotation angle α and on the other hand on the set eccentricity e.

The function of the swivel angle β is in Fig. 3 plotted and shown in solid lines, on the one hand for a maximum eccentricity e and on the other hand for half the maximum eccentricity (e / 2). For comparison, corresponding sinusoids are shown in dashed lines. It can be seen that the zero crossings are identical, but not the maxima and minima. The maximum for the swivel angle β occurs before π / 2, the minimum for β occurs after the minimum of the sinusoid.

The diagram shows the maximum with β _max and the minimum with β _min . From the illustrated function curve, ie from the relative position of β _max and β _min with respect to π / 2 and 3 π / 2, the direction of rotation of the drive shaft can be determined derive as follows: the direction of rotation is considered to be dextrorotatory if the increase in the swivel angle β from the minimum to the maximum is steeper than the decrease from the maximum to the minimum; in all other cases the direction of rotation is left-turning. Clockwise is defined as d = 1 and counterclockwise as d = -1.

sodass die Kenntnis des Wertes der Auslenkung e äquivalent zur Kenntnis des Schluckvolumens v ist.From the thus determined values for β and α, the deflection or eccentricity e can be calculated according to the abovementioned tan function. For the displacement v of the radial piston engine 1 and the displacement e, there is a unique relationship: $$\mathrm{v}=\mathrm{f}\left(\mathrm{e}\right).$$

so that the knowledge of the value of the deflection e is equivalent to the knowledge of the swallow volume v.

The maximum of the swivel angle β _max occurs in Fig. 2 (left half) then, when the beam of the angle β, the circle with radius e to D at point E 'tangent. Then the right triangle DE'S and the simple relation arise: $${\mathrm{sin\beta }}_{\mathrm{Max}}=\mathrm{e}/\mathrm{A}$$

One of the cylinders 2 is equipped with an angle sensor, not shown, which measures the pivot angle β - as known from the aforementioned prior art. The zero point of the pivot angle β is achieved in each case in the upper and lower end position of the piston (top dead center, bottom dead center). For one complete revolution of the drive shaft, an unillustrated pulse generator generates a number of z pulses in a pulse detector. Z does not necessarily have to be an integer. This is z. B. then the case when the pulse is not arranged directly on the drive shaft, but is driven by a pinion gear with non-integer ratio. Each pulse n stores the time of its detection t _n . In addition, each pulse triggers a measurement of the pivot angle β. This measured value is assigned to the triggering time t _n : β _n = β (t _n ).

Since the pulses are generally not associated with a fixed angular position of the drive shaft, the zero position is determined anew during each revolution.

d. h. der maximale Schwenkwinkel β_max hängt nur von der Geometrie, d. h. der aktuellen Auslenkung e ab.In the vicinity of the zero crossings, the swivel angle β _{n is} too small for useful accuracy. This is exacerbated when the eccentric is only slightly deflected, ie when the deflection e assumes small values. This problem is solved according to the invention as follows: if the rotational speed of the drive shaft is large compared to the adjustment speed of the eccentric, one can only utilize the extreme values of β of the last revolution of the drive shaft and determine e via the unique relationship β _max (e). This relationship is, as mentioned above: $${\mathrm{sin\beta }}_{\mathrm{Max}}=\mathrm{e}/\mathrm{A}.$$

ie the maximum tilt angle β _max depends only on the geometry, ie the current deflection e.

reference numeral

1

Radial piston motor

2

cylinder

3

piston

3a

shoe

4

lifting ring

5

eccentric

S

Pivot point cylinder

D

Fulcrum eccentric

E, E '

eccentric position

M

Center of Hubring

A

distance

e

eccentricity

α

angle of rotation

β

swivel angle

β _max

maximum

β _min

minimum

Claims (7)

1. Method for determining the displacement volume of a radial piston machine (1) with adjustable eccentricity (e), with pivotably arranged cylinders (2) and with a driveshaft which drives an eccentric (5), wherein a pivoting angle (β) of the cylinders (2) is measured and the eccentricity (e) is calculated on the basis of the measured values for the pivoting angle (β), and the displacement volume (v) is calculated on the basis thereof,
   characterized in that the rotational direction of the driveshaft is determined from the functional profile (β = f(α)) of the pivoting angle (β) as a function of the rotational angle (α) of the driveshaft.
2. Method according to Claim 1, characterized in that the pivoting angle β is measured at defined times t_n, and in that a rotational angle α_n of the driveshaft is assigned to each time t_n.
3. Method according to Claim 2, characterized in that in order to define the times t_n a number z of pulses per rotation of the driveshaft is generated.
4. Method according to Claim 3, characterized in that a zero position is assigned to the driveshaft, which zero position corresponds to the top dead centre position of the eccentric (5), and in that the zero position is determined anew after each rotation.
5. Method according to Claim 1, characterized in that only the extreme values β_maX of the pivoting angle β of one rotation of the driveshaft are evaluated approximately.
6. Method according to Claim 5, characterized in that the current eccentricity (e) is calculated on the basis of the extreme values β_max.
7. Method according to Claim 1, characterized in that the rotational direction is defined as clockwise if the increase in the pivoting angle (β) from the minimum β_min to the maximum β_maX is steeper than the drop from the maximum β_maX to the minimum β_min, and in that the rotational direction is anticlockwise in the case of a deviating functional profile.

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