GB2120324A - Variable-displacement rotary pump or motor - Google Patents

Abstract

A trochoidal-type pump (or motor) has outer rotor elements (14 and 16) arranged in tandem, a common inner rotor (6), and means permitting phase adjustment of the outer rotor elements relative to each other. Variable displacement is thus accomplished with a constant shaft speed, the net output being proportional to the phasing of the outer rotor elements. The phase adjustment means may comprise an eccentric mounting element (22) for the uppermost outer rotor element and a lever (26) to turn the mounting element about the axis of a drive shaft (8), the lowermost outer rotor element being lodged directly in the main body (10). <IMAGE>

Description

SPECIFICATION Variable-displacement double-rotor trochoidal pump or motor This invention relates to variable-displacement double-rotor trochoidal pumps and motors.

Double-rotor trochoidal machines are widely employed as hydraulic pumps or motors. These machines may be classified as positivedisplacement rotary devices and, whereas arrangements for reversibility have been made, they are constant-displacement machines having outputs which are proportional to shaft speed.

Where such machines are used as pumps, the pumping action arises from the engagement of the two rotors the inner one of which is driven by the pump shaft. As the two rotors move, pumping chambers are formed between their respective profiles which change in volume as the engagement proceeds. By providing suitably proportioned ports in one or both end walls of the pump housing, a pump is formed which requires no external valves.

Equations describing a modified epitrochoidal form of the inner and outer rotor elements of these pumps have been published in "An Analysis of Epitrochoidal Profiles Suitable for Rotary Expanders and Pumps", F. J. Robinson and J. R.

Lyon, ASME 75-WA/DE-10, 1976, while techniques for their manufacture by numericallycontrolled machining are described in "Machining Trochoidal Profiles by Numerical Control", F. J.

Robinson and J. R. Lyon, "Machinery, November 6th, 1974, and "Trochoidal Oil Pump Machined by Numerical Control", F. J. Robinson and W.

Whiting, "Machinery", December 7to, 1977. In addition, equations describing the volume changes which result from the meshing of two epitrochoidal profiles have been published in "The Variation of Chamber Volume with Rotor Angle in Trochoidal Machines with Cuspal Sealing", F. J.

Robinson and D. N. Maclean, "Mechanism s Machine Theory", Vol.15, 1980, pp.171-178.

These equations, with suitable coefficients, may be taken to accurately represent the output from such a pump at 100% volumetric efficiency.

The present invention represents an important development of the machines described in these prior publications, and according to the invention a variable-displacement trochoidal pump or motor comprises double rotor trochoidal pumping elements arranged in tandem, with a common inner rotor and phase adjustment provision between the outer rotor elements. In this way variable displacement is accomplished at constant shaft speed by the combined effect of two pumping chambers, the net output from which is proportional to the phasing of the eccentric bores of the outer rotors.

Although specific trochoidal profiles are illustrated herein for the pump design, the technique is equally applicable to all double-rotor trochoidal pump configurations. Moreover, phase adjustment may be provided for either automatically or manually, according to choice.

By arranging for an actuator, sensitive to delivery pressure, to control the phasing of the adjustable eccentric, the pump may be designed to adjust its flowrate automatically according to delivery pressure. In this way constant output pressure could be maintained at a range of delivery flowrates.

Among the advantages given by the design are the following (1) Compactness and light weight.

(2) Simplicity and hence low manufacturing costs; the pump can have as few as 7 major components.

(3) Wide range of output flowrates which may be selected during running.

(4) Facility for automatic operation, as mentioned above.

The invention is illustrated, by way of example, in the accompanying drawings, wherein:- Figures 1 and 2 show conventional singlepiston and double-piston crank-operated pumps; Figure 3 shows sections through a typical pump in accordance with the invention; Figure 4 illustrates the effective swept volume for various phase angles in the pump of Figure 3; and Figure 5 is a graph of a computer simulation of output from the pump shown in Figure 3.

Whereas positive displacement pumps have outputs which are generally proportional to shaft speed, variable delivery is assumed to mean that the pump output may be changed at constant shaft speed. Various arrangements for achieving this aim are possible, including the provision of a by-pass passage or the use of complicated mechanisms which provide for variable stroke.

A further method for the provision of variable output is to use two pumping units which may be operated with a changeabie phase relationship between the pumping elements. In order to explain this latter technique, it is useful to consider the action of a double-piston crank-operated pump as illustrated in Figure 1 and Figure 2. In these diagrams it may be seen that the provision of a mechanism, whereby the phase relationship between the driving cranks may be adjusted during operation of the pump, will provide for variable output from the combined unit. When the two cranks are set to run in phase (i.e., phase = 0), the combined output is double the output from each half of the pump. During intermediate phase settings, such as the illustrated value of 1 50 degrees in Figure 2, the outputs sum to provide a total output which is considerably lower.Setting the cranks to run in quadrature (phase = 1 80 degrees) would provide for no output although the pump shaft would continue to run.

In a variable-displacement double-trochoid design of pump, use is made of the fact that the phasing of the pumping action may be controlled by the positioning of the outer rotor element in relation to the inner rotor. Furthermore, the positioning of the outer rotor element is governed by the bore in which it runs which must be eccentric to the axis of the innter rotor. If, now, two such pumps are provided which use a common inner rotor but in which the outer rotor elements run in separate eccentric bores, variable phasing may be achieved by altering the relative positioning of the eccentric bores.

As shown in Figure 3, the pump of the present invention employs modified trochoidal profiles with, in this particular case, the following geometric parameters: Winding number 5 Inner Rotor width 20 mm Outer Rotor width 10 mm Eccentricity 2.54 mm Radius Vector 25.4 mm Modification -12.7 mm Max. Obliquity 30 degrees The pump body is bored eccentrically to provide location for one of the two outer rotor elements, and the end wall of this bore is provided with the necessary intake and delivery ports. The bore for the second outer rotor element is provided in an adjustable eccentric element which is located by a cover plate.In this particular case the adjustable eccentric is fitted with a simple lever whereby the eccentric bore may be moved during operation of the pump to bring it to the desired phase relationship with the eccentric bore of the pump body. It is, however, equally possible for the lever to be replaced by automatic means.

In this way it becomes possible for the two pumping units to be operated in any desired phase relationship to each other. When the units are operated in phase, the pump acts like a normal trochoidal pump with a 20 mm rotor width.

Movement of the adjustable eccentric results in the operation of the pumping elements at differing phases and their combined output is the sum of the output from each unit. Since only one unit is provided with ports and the other is directly connected to it, the actual displacement from the pumping chambers is given by the net chamber volume change of the two units.

Using the equation published in "Mechanism 8 Machine Theory", Vol. 15,1980, pp. 171-178, modified to account for double trochoidal profiles with variable phase relationship and adjusted to fit the above pump profiles, a digital computer simulation of the pump operation at 1000 rev/min has been carried out. Figure 4 shows the effective chamber displacement from both pumping units at phase angles of 0,90 and 1 80 degrees. Figure 5 is a graph of the computer output showing the pump delivery as a function of the phase relationship between the two pumping units at 1000 rev/min.

In this simulation the volumetric efficiency of the pump has been set at 100% and, as a result, this curve represents the theoretical maximum to be expected.

Pump flowrate values for a range of eccentric phase angles produced by the simulation and used to plot Figure 5 are listed below: Phase Angle deg. Flowrate cc/min 0 7600 30 7339 60 6575 90 5361 120 3778 150 1936 180 499 It wiil therefore be seen that, by using double rotor trochoidal pumping elements in tandem with a common inner rotor and phase adjustment provision between the two outer rotor elements, variable displacement is accomplished at constant shaft speed by the combined effect of two pumping chambers.

Claims (6)

1. A variable-displacement, double-rotor, trochoidal pump or motor comprising (a) two trochoidal pumping rotor elements arranged for rotation in two respective pumping chambers, the rotor elements being arranged in tandem to form two outer rotor elements; (b) an inner rotor element common to the two outer rotor elements and disposed inwardly thereof; and (c) phase adjustment means for adjusting the phase between the two outer rotor elements so that variable-displacement is accomplished by the combined effect of the two pumping chambers, the net output from the chambers being dependent on the phasing of the two outer rotor elements.

2. A trochoidal pump or motor according to claim 1, in which one of the trochoidal rotor elements rotates in a phase-adjustable eccentric.

3. A trochoidal pump or motor according to claim 2 having an actuator sensitive to delivery pressure to control the phasing of the adjustable eccentric automatically.

4. A trochoidal pump or motor according to claim 2 or claim 3, in which the other trochoidal rotor element rotates in a fixed eccentric.

5. A trochoidal pump or motor according to any preceding claim having a main body bored eccentrically to provide location for one of the trochoidal rotor elements and bored to receive a phase-adjustable eccentric for the other trochoidal rotor element.

6. A trochoidal pump or motor substantially as described herein with reference to Figures 3-5 of the accompanying drawings.