Optimization design of structural parameters of duplex geared pump in hydraulic automatic transmission

A small gear pump, which can compress low viscosity fluid up to high pressure, is necessary for some systems such as an electric braking system. However, designing a high-efficiency small gear pump is difficult because leakage due to clearance is relatively larger than that in a normal-sized gear pump. Therefore, to design a high-efficiency small gear pump for high pressure, we are developing an external gear pump having an L-shaped block made of resin. This L-shaped block is the biggest difference from other gear pumps. First, we show the structure and characteristics of this gear pump with an L-shaped block, and we explain its advantages. Second, we explain a method to predict the clearances that are needed for designing high-efficiency gear pumps. Clearances in a gear pump are made by deformations of the inner parts during high-pressure operation. Thus, we applied structural analysis to design the high-efficiency gear pumps. Using this analysis, we can understand the deformation of each part during the pump operation. Moreover, we can design parts taking deformations into consideration. The analysis examples, such as the deformation in the vertical direction to the gear rotational axis and the deformation of the sliding surface with the side of the gears, are shown in this paper. As a result of these analyses, we could design the structure and shape of the inner pump parts to achieve high sealing performance. Finally, the results of an experimental evaluation for the developed gear pump are described in this paper. We measured the volumetric efficiency of a prototyped pump and evaluated the performance using experimental equipment. The results of the evaluation show that the developed gear pump has high volumetric efficiency under high temperature and low viscosity fluid.

Aiming at the problems of the general involute external gear pump, a gear pump with double circular arc helical gear as motion pair is proposed. Based on the comparison and analysis of their meshing characteristics, the advantages of contact strength, bending strength, and transmission stability are significant with the double circular arc helical gear as motion pair. Taking the sine curve as the transition curve and on the basis of the conjugate principle of gear meshing, the surface tooth profile equation of double circular arc helical gear is given out by coordinate transformation. The equal area method is used to deduce the displacement of double circular arc gear pump, then the maximum and the minimum instantaneous displacement of the double helical gear pump are solved, thus the theoretical pulsation tends to 0. Using Fluent three-dimensional dynamic mesh technique, by comparing and simulating the flow pulsation of double circular arc helical gear pump and ordinary involute helical gear pump of the same gear parameters, it is concluded that the flow pulsation of the double circular helical gear pump is much smaller than that of the involute helical gear pump. In summary, this article provides reference for design of high-performance gear pump.

To address the issue of large volumetric efficiency calculation error and neglect of cavitation effect in current gear pump research, this paper proposes a method combining theoretical and fluid analysis for accurate calculation of gear pump volumetric efficiency, providing guidance for gear pump development. Taking the microsegment gear pump (MSGP) as an example, a leakage model is established based on the flat-plate laminar flow principle and the Navier-Stokes equation. The impact of cavitation on volumetric efficiency is analyzed, and based on the proposed non-equilibrium cavitation model by authors, the effect of cavitation on gear pump oil viscosity is examined. On the basis of the above models, a comprehensive volumetric efficiency model of the MSGPs considering cavitation is established and validated through fluid analysis and experiments, with the error from experimental data within 2%. In addition, the total gas volume fraction in the pump and the volumetric efficiency follow the same trend, but in the opposite direction.

Gear pump is the most commonly used hydraulic component in hydraulic drive system.Volumetric efficiency of the traditional gear pump is low, big flow ripple causes large pressure fluctuations, makes pipes and valves vibration, noisy. The imbalance pressure on gear pump’s gears, shafts and bearings and the large radial load limits its pressure increased. Planetary gear transmission compared with ordinary gear transmission, it has many unique advantages. So the writer on the basis of the combination of proposed non-circular planetary gear pumps and gear pump works discussed the structure and working principle of the pump. The non-circular planetary gear pump with many advantages such as big flow, uniform flow, low noise and so on. It can be widely used in various hydraulic transmission systems.

In order to obtain as large a delivery as possible without changing the inner space VC of a gear pump casing, the authors introduced a method of designing and producing gear pumps with the number of teeth from Z1 = Z2 = 2 to 5. They presented a new tooth profile of helical gears suitable for pumps producing no fluctuations in delivery. Equations were derived for calculating the theoretical delivery Vth of the gear pumps and also the thrust which occurs on the gears. Experiments were conducted using four kinds of trial gear pumps with Z1 = Z2 = 3 or 4. In the case of the gear pumps with Z = 3 and a transverse module of 15.65 mm, the volumetric efficiency was about 98% and the total efticiency was about 90% when the pump was operated at about 1.5 MPa using a machine oil as the pumping fluid. The volume ratio Vth/Vc of the trial gear pump was about 0.5, while it was about 0.2 in the case of a conventional gear pump with almost the same delivery.

With their advantages of low-cost, high-reliability and simplicity, external gear pumps (EGPs) are popular choices in many applications, such as mobile hydraulic control system, fuel injection, and liquid transportation system, to name a few. Like other positive displacement machines, EGPs are characterized by a flow non-uniformity, which is given by the gear meshing and results in vibrations and noises. With increasing demands for low-noise components required by modern fluid-power systems, new designs of external gear machines with less noise emission and lower pulsation production are highly desired by the industry. To satisfy these demands, there are several new-generation gear pump designs that have been realized by the industry and already commercialized. However, the research from both academia on external gear pumps are still primarily focused traditional involute gear pumps, while state-of-the-art research on these new-generation external gear pumps are highly lacked. Also for the most novel designs recently released to the market, their designs still have large margin to improve, as some of the physics inside these gear machines are not well understood and formulated. The goal of this research is to fill in this gap, by gain understanding of the relations between design features and actual flow generated by such novel designs, and provide general methods of analysis and design for efficient and silent units. To achieve this goal, this PhD dissertation presents a comprehensive approach of analysis for external gear pumps, with the emphasis on the new-generation helical gear pumps. The discussion covers a large variety of aspects for gear pump design and analysis, including: the analysis on the gear profile design and meshing, the displacement-chamber geometric modeling, and the kinematic-flow analysis. They are followed by a dynamic simulation model covering the dynamics of fluids, forces, and micro-motions, together with simulation results that provides the insights into the physics of new-generation gear machines. Multiple experimental results are provided, which show the validity of the simulation models by matching the pressure ripple measurement and the volumetric efficiencies. Furthermore, a linearized analysis on the ripple source of gear pumps are described, in order to provide the connection and understanding of the pump-generated ripple to the higher-level system analysis, which is also missing from the past academia research. In addition, the some of the models are utilized in optimization studies. These optimization results show the potentials of using the proposed approach of analysis to improve the existing designs as well as development of more efficient and silent units.

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In view of the axial force produced in the working process of double arc helical gear hydraulic pump, the theory of differential equation of curve and curved surface was utilized so that the calculation formula of axial force was obtained and the relationship between the axial force and structure parameters of gears was clarified. In order to balance the axial force, the pressure oil in the high pressure area was introduced into the end face of the plunger to press the plunger against the gear shaft, and the hydrostatic bearing whose type is plunger at the end of the shaft was designed. In order to verify the balance effect of axial force, the leakage owing to end clearance and volume efficiency of gear hydraulic pump before and after the balancing process was analyzed. This paper provides a new analysis idea and balance scheme for the axial force produced in the working process of the double arc helical gear hydraulic pump, which can reduce the leakage owing to end clearance caused by the axial force and improve the volume efficiency of the gear hydraulic pump.

A water muffler is used for the noise control of a hydraulic pipeline with an external gear pump. An experimental system is established to investigate the acoustic performance of the water muffler, in which the gear pump is utilized as the sound source and power supply. Comparisons between the experimental results of the reference tube, rubber tube, and water mufflers with different inner structures have been made. Numerical simulations on the rubber tube and different water mufflers with various inner structures have been conducted. Simulation results have been compared with the experimental results. These comparison results show that the rubber tube with a compliant wall substantially contributes to the reduction of the noise generated by the gear pump, especially at the high frequency band and relatively low rotate speed of the gear pump. The water muffler results in the enhancement of the noise reduction effect on the rubber tube. With the speed of the gear pump increasing from 1172 r/min to 2344 r/min, the effect of the noise reduction becomes much weaker, since the flow-induced noise gets more intensified. For the rubber tube, in particular, the sound pressure level gets close to that of the reference tube at the speed of 2344 r/min. Moreover, it has been proven by another important experimental result that the length of the inner structure can play a critical role to the flow noise generation.

Tumbling Multi-Chamber (TMC) gear pump is a generally unknown type of hydraulic device, which features a unique three-dimensional shape of the gears. The main benefits of such design over the conventional gear pumps are self-adapting tightness of the pump parts, the possibility to mold the parts from a polymer material and high volumetric efficiency, considering the simplicity of the design. The specific working principle of TMC pumps requires a slightly different approach to the numeric modeling and analysis process compared to the conventional gear pump types (e.g. external gear and gerotor pumps). One of the main contributions of the work is the development of an analysis procedure, which allows studying flow and pressure conditions in the TMC pump. This includes the influence of the positioning of the pump parts on spatial and temporal variations in sealing regions and the influence of pressure field propagation in relation to the valve plate position.

The inlet pressure of the gear pump is important factors affecting its volumetric efficiency. This paper taken a high-speed fuel gear pump as the research object, then carried out the numerical simulation of the gear pump flow field under different inlet pressure, axial clearance and radial clearance based on the CFD method. The experimental and the numerical simulation method were combined to expound the influence laws of axial clearance, radial clearance and inlet pressure on the volumetric efficiency. Based on the numerical simulation method, the theoretical model of minimum inlet pressure of gear pump was modified in the paper. The research work of this paper can provide a reference basis for the further optimization design of engine fuel gear pump.

Based on the analysis of the structural characteristics of the internal meshing gear pump with multi-output, the main leakage ways in the gear pump are summarized. By establishing the mathematical formula of leakage, the general formula of the total leakage of the gear pump under three working modes is obtained, and the volume efficiency of the pump is calculated. It is concluded that the volume efficiency of the internal meshing gear pump with multi output is the highest when the internal pump is used alone, and the volume efficiency of the external pump alone is the lowest. The structure of internal gear pump with multi output is improved to reduce the leakage and is verified via experiments. The experimental results show that the volumetric efficiency of the pump is consistent with the analysis results, that is, the volume efficiency decreases with the increasing of load pressure of pump.

In order to obtain as large a delivery as possible without changing the inner space Vc of a gear pump casing, the authors introduced a method to design and make gear pumps with teeth of Z1 =Z2 =2 to 5. They presented a new tooth profile of helical gears suitable for the pumps producing no fluctuations in delivery. Equations were derived for calculating the theoretical delivery Vth of the gear pumps and also the thrust which occurs on the gears. Experiments were conducted using four kinds of trial gear pumps with teeth of Z1 =Z2 =3 or 4. In the case of the gear pump with Z = 3 and a transverse module of 15.65, the volumetric efficiency was about 98% and the total efficiency was about 90% when the pump was operated at about 1.5 MPa using a machine oil as pumping fluid. The volume ratio Vth/Vc of the trial pump was about 0.5 while it was about 0.2 in the case of a conventional gear pump with almost the same delivery.

To investigate the effect of the number of teeth on the cavitation characteristics of the cavity at high speed, a simulation model of the flow field with six to nine teeth of the gear pump is created. To study the influence of the number of teeth on the internal cavitation characteristics of the circular arc spiral gear pump and its outlet flow characteristics under high-speed conditions. The results show that the gear pump cavitation characteristics are significantly affected by the number of teeth and the speed; as the number of teeth increases, the extent of the effect of cavitation on the outlet flow decreases significantly. The critical speeds at which the gas volume fraction of the six- to nine-teeth gear pump changes significantly are 9000 RPM, 9000 RPM, 10,000 RPM, and 10,000 RPM, respectively, and after exceeding these critical speeds, the volumetric efficiency begins to decrease while the gas content in the cavity increases abruptly, which seriously affects the continuity and stability of the outlet flow. In addition, when designing gear pumps, increasing the number of teeth helps to inhibit cavitation, improve volumetric efficiency, and reduce pulsating flow.

This paper presents a high-pressure and high-speed gear pump for aerospace application and introduces a circular-arc tooth profile that has no trapping feature and whose gears are in continuous one-point contact in the plane of rotation. Basic dimensions are determined and performance parameters of the gear pump are obtained by structural design of the gear pump. The performance parameters are discussed for different tooth profiles. A disc tool and hob are designed to generate the circular-arc tooth profile. A computer-aided design (CAD) system for the design of the circular-arc gear pump is developed with features of tooth profile design, tool design, and numerical control. The test gears were processed to verify the correctness of CAD system. A study of the outlet pressure of the circular-arc gear pump reveals that the developed high-pressure and high-speed gear pump has low outlet pressure fluctuations.