RU105952U1 - SCREW GEROTOR PUMP WITH COMPENSATED TORSION - Google Patents

Abstract

 Compensated torsion screw gerotor pump, comprising a pump casing with stuffing box or mechanical seal, screw pump section, spindle, torque transmitting unit and receiving axial and radial loads located inside the spindle hollow drive shaft, made in the form of torsion connection with cones, tabs and sealing elements, characterized in that the torsion bar is rigidly sealed in the middle of a hollow balanced rotor and rigidly interfaced with an auxiliary elastic shaft placed by cial symmetrically with respect to the torsion bar and the center of the rotor, wherein the second end of the auxiliary shaft is fixed in the bearing assembly of the stator axis with the possibility of axial displacement.

Description

The invention relates to gerotor eccentric screw pumps of volumetric type, designed for pumping gas-liquid mixtures of a wide range of viscosity.

A known design of a screw pump (see US patent No. 3216768 from 11/09/1965), which we have chosen as an analogue, in which the node that receives the axial load and transmits torque, is made in the form of an articulated-finger drive shaft, located on the spindle side inside a hollow drive shaft with the coupling of the driveshaft coupling in the area of the bearing assembly of the drive shaft of the spindle. This layout of the propeller shaft allows you to reduce the length of the structure as a whole, significantly reduce the load on the end of the spindle drive shaft with stuffing box packing. However, this design has a significant limitation (up to 5 kW) in terms of transmitted hydraulic power, since all axial load is transmitted through thin-walled hinge bushings and fingers working for shear, bending, and subjected to cyclically varying loads.

This drawback was partially eliminated in the design of a screw gerotor pump (see Patent of the Russian Federation No. 58150 dated May 26, 2006), which we selected as a prototype, including a pump casing with a stuffing box or mechanical seal, a screw pump section, a spindle, and a unit, transmitting torque and perceiving axial and radial loads located inside the hollow spindle drive shaft and made in the form of a torsion or torsion-articulated connection with cones, tabs and sealing elements.

This design of the gerotor screw pump, having a relatively large hydraulic power (~ 40 kW), is convenient in operation, since it allows you to quickly replace the screw section and torsion bar.

However, a further increase in the hydraulic power of this design is accompanied by a sharp increase in the vibration level of the pump section, leading to rapid wear and destruction of the structural components.

The purpose of this utility model is to increase the hydraulic power of a screw gerotor pump, reduce the level of vibration, and increase its service life.

The goal is achieved due to the fact that the torsion bar with an auxiliary elastic shaft located symmetrically axially relative to it is rigidly sealed in the middle of a hollow balanced rotor, and the second end of the auxiliary shaft is fixed in a bearing assembly located on the stator axis. The length, diameter and material of the auxiliary shaft are selected so that the transverse moment of forces with which it acts on the rotor compensates for the moment of forces acting on the rotor from the torsion side, being equal to the latter in magnitude and opposite in sign. Since the transverse forces acting on the rotor are compensated by the elastic reaction from the rubber side of the stator, and the transverse moment of the force introduced by the torsion-auxiliary shaft system is zero, then with respect to the centrifugal forces arising from the rotation of the rotor, the latter is in a state of indifferent equilibrium making a calculated gerotor motion and not leading to an increase in the level of vibrations in excess of the calculated one.

The proposed utility model removes the limitations inherent in the analogue and prototype and can significantly increase hydraulic power and reduce the level of vibration of the gerotor screw pump.

Figure 1 shows a schematic diagram of the proposed gerotor screw pump with compensated torsion bar. Figure 2 shows a circuit for terminating a torsion bar and an auxiliary elastic shaft in the pump rotor. Figure 3 conditionally shows a diagram of the forces and moments of forces acting on a rotor located in an elastic medium with an offset by the amount of eccentricity.

The screw gerotor pump with compensated torsion, described in the utility model (Fig. 1), consists of a screw pump section with a stator 1, with a rubber lining 2, a rotor 3, an input manifold 4, coupled to a spindle 5 with a hollow drive shaft 6 and a screw pump section 1. The hollow spindle drive shaft is sealed from the input manifold by a mechanical seal or gland 7. The axial and radial loads acting on the drive shaft from the torsion bar 8 side are perceived by the spindle bearing unit 9. The torsion cone is fixed in a conical socket of the drive shaft in the area of the bearing assembly 9 due to friction, which is additionally amplified during operation of the pump by large axial loads perceived by the torsion bar. The second torsion cone 10 is also fixed by friction in a conical socket in the middle of the hollow rotor (Fig. 2) and the threaded connection 11 is connected to the auxiliary elastic shaft 12, the shank 13 (Fig. 1) of which is located in the blind socket of the shaft 14 of the bearing assembly 15 of the auxiliary shaft. The shank is fixed in the radial direction and has the ability to move axially. The bearing assembly of the auxiliary shaft is connected to the output manifold 16, which is connected to the pump section 1. The number of teeth of the stator lining is one more than that of the rotor, so that when the rotor rotates, cavities are formed that move from the input manifold to the output.

The pump is driven by applying torque to the spindle drive shaft. Torsion transmits torque to the rotor, during rotation of which the formed cavities are filled with a pumped medium with its subsequent transfer to the output manifold. The auxiliary elastic shaft, compensating for the transverse elastic moment acting on the rotor from the torsion side, stabilizes the normal rotor motion of the rotor.

In order for the cavities to maintain tightness during the operation of the pump, the rotor in the stator lining is placed with some design tightness. The presence of interference leads to the appearance of an elastic radial component of the force acting on the rotor from the side of the stator lining, distributed along the axis of the rotor according to a harmonic law [Baldenko DF Single-screw hydraulic machines: monograph. In 2 volumes: T1: Single-screw pumps / D.F. Baldenko, F.D. Baldenko, A.N. Gnoev; IRC Gazprom. - M., 2005. - 488 p.]. It is known that the average value of the harmonic function on any interval of the argument that is a multiple of the period is zero. Therefore, by appropriately choosing the ratio between the rotor length, tooth pitch and the number of stator teeth (rotor), it is possible to exclude the appearance of a periodic (along the rotor axis and angle) radial force due to the interaction of the stator teeth and the rotor. The connection of the rotor with the drive shaft of the spindle by means of a torsion bar with a rigid termination of its end in the rotor leads to the appearance of additional radial force due to the elasticity of the torsion bar and the displacement of the rotor axis by the amount of eccentricity. In addition, an additional radial force is created by the decomposition of the axial force along the torsion axis into radial and axial components due to helical gearing of the rotor and stator and hydrostatic pressure on the rotor from the side of the output manifold and the eccentric arrangement of the end of the torsion bar during pump operation. Due to the tight termination, the torsion acts on the rotor with a certain moment of force M. An additional moment of force can also arise due to the elastic reaction of the stator lining during off-center termination of the torsion bar. Figure 3 conditionally shows the resultant force F and the moment of forces acting from the side of the torsion bar. The resultant force can be applied at any point on the rotor axis at a distance from the center of the rotor, where -1≤β≤1, l is the length of the rotor.

The presence of an off-center concentrated force acting from one end of the rotor leads to the fact that the rotor occupies a position different from the initial angle φ. We place the beginning of the Cartesian coordinate system at the intersection of the initial (stator axis) and new axes corresponding to the angle φ (Fig. 3). We direct the z axis along the new position of the rotor axis and assume that the concentrated force has one component f = -f _{x. We} represent the distributed reaction of the stator elastic sheath in the form g _x (z) = kφz, where k is a certain coefficient.

We assume that a concentrated force can be applied to any point on the rotor axis at a distance from the center of the rotor, where -1≤β≤1, l is the length of the rotor. The distance from the origin to the center of the rotor is denoted by the letter a .

Having written the balance of forces and moments of forces in the selected reference frame, we find that they correspond to it

,

.

The obtained values of a and φ correspond to the static position of the rotor in the elastic casing. In the dynamics, a will decrease, while φ will increase, which indicates an increase in vibrations in the pump section and deformation of the elastic stator lining beyond the calculated ones, especially at the edges of the stator. The calculated (design) position of the rotor corresponds to a = ∞ and φ = 0, whence

.

The above conditions will always be satisfied if M = 0 β = 0. Since the auxiliary shaft does not bear axial load, its dimensions can be optimized in order to reduce the size of the pump structure. It is known [Landau L.D., Lifshits E.M. Theoretical physics. - 5th edition, stereotyped. - 2007 T. VII. Theory of elasticity. - 264 p.] That the elastic moment of force created by a cylindrical rod of diameter d and length L is where E is the elastic modulus of the rod material; - moment of inertia of the rod section; R is the radius of curvature of the rod. It can be shown that for a torsion, taking into account eccentricity and tight termination .

Equating the elastic moments of the torsion bar and the auxiliary shaft, after simple transformations, we find:

,

where d _B , L _B , Е _B - respectively, the diameter, length and elastic modulus of the material of the auxiliary shaft; d _T , L _T , Е _T - the same for the torsion bar. Choosing the dimensions of the auxiliary shaft in accordance with this formula, we satisfy the condition M = 0, without significantly increasing the dimensions of the pump design.

Thus, the hinged termination of the torsion bar in the center of the rotor or the compensation of the elastic transverse moment of the torsion forces by means of an auxiliary elastic shaft are the only ones acceptable when creating gerotor screw pumps of increased hydraulic power. In the simplest case, the claimed technical result can be achieved by using an auxiliary elastic shaft made of the same material as the torsion bar and having the same diameter and length.

Claims (1)

Compensated torsion screw gerotor pump, comprising a pump casing with stuffing box or mechanical seal, screw pump section, spindle, torque transmitting unit and receiving axial and radial loads located inside the spindle hollow drive shaft, made in the form of torsion connection with cones, tabs and sealing elements, characterized in that the torsion bar is rigidly sealed in the middle of a hollow balanced rotor and rigidly interfaced with an auxiliary elastic shaft placed by cial symmetrically with respect to the torsion bar and the center of the rotor, wherein the second end of the auxiliary shaft is fixed in the bearing assembly of the stator axis with the possibility of axial displacement.