Electro-hydraulic Unit Research Articles

A novel electro-hydraulic unit design based on a shaftless integration of an internal gear machine and a permanent magnet electric machine

In recent years, increasingly stringent emission regulations have spurred an electrification trend in off-highway vehicle technology. To address challenges such as the high cost of power electronics components, limited battery capacity, and the substantial modifications required for the vehicles, there is a pressing need to develop high-speed, cost-effective, compact, and efficient electro-hydraulic units capable of powering vehicle functions. In response to these demands, this paper introduces an innovative morphology for an electro-hydraulic unit and outlines the integration method for a crescent-type internal gear machine with a permanent magnet synchronous electric machine. The proposed morphology aims to minimize component count through a shaftless solution while incorporating a cooling system that utilizes the same working fluid as the hydraulic machine. The design approach utilizes a genetic algorithm optimization process to maximize overall energy efficiency and compactness. Insights gained from the optimization results shed light on the relationship between key design parameters and unit performance, enhancing the understanding of this electro-hydraulic unit. A prototype of the unit was manufactured and tested, demonstrating a volumetric efficiency ranging from 81 % to 97 % at a maximum rotational velocity of the pinion of 6000 rpm. These results validate both the morphology and the design approach, indicating the feasibility of designing compact electro-hydraulic units that leverage hydraulic machines with higher maximum rotational velocities than commercially available counterparts as a mean to enhance efficiency and compactness.

Инновационный способ утилизации отходов монолитных строительных конструкций

Introduction. During the reconstruction and technical re-equipment of various mining facilities, there is a need for the processing of concrete and reinforced concrete products that require environmental protection. The article analyzes innovative methods of destruction of hard rocks based on the use of electrohydraulic effect. The possibility of their use as an alternative environmentally friendly method of recycling reinforced concrete products is evaluated. A schematic diagram of an electrohydraulic installation for use for these purposes is presented. Based on the analysis of the mechanism of destruction of concrete and reinforced concrete products, the main electrical parameters that ensure the effectiveness of its application are substantiated. An assessment of the effectiveness of the implementation of the proposed technology in the process of recycling reinforced concrete structures was carried out. Materials and methods. After the main dismantling activities, the issue of removal and utilization of construction waste is solved, which requires its shredding. When using electrohydraulic technology for demolition of reinforced concrete, this production process includes: prior to processing – segmentation of structures by means of excavator hydraulic shears into fragments up to 1 m3 in size; placing them on the support grid of the EGU bath filled with water; grounding of the fittings; installation of working arresters in the bath and energizing of the EGU; after treatment – removal of the reinforcement cleaned from concrete from the bathtub; removal of the basket with concrete rubble from the EGU; storage of treatment products; installation of the released basket in place. Results and discussion. As a result of the research the organization of the production process of recycling of reinforced concrete fragments of building structure during their disposal using the technology of electrohydraulic crushing of concrete blocks at the site of their dismantling is proposed. Rational values of parameters of the organization of the destruction process in the EGU have been established: the distance from the arrester axis to the point of reinforced concrete blocks in the liquid volume; capacitance of the capacitor block; voltage at the moment of breakdown; inductance of the discharge circuit; cyclic frequency of oscillations. When using water as a working fluid, it is reasonable to vary the frequency of discharge pulses within 0.5...2.0 Hz. It has been established that the productivity of the single-electrode unit at the destruction of reinforced concrete to the final coarseness of 20 mm reaches 100 kg/h at a specific energy consumption of 120 kW/t. The use of 4-electrode EGU can ensure the crushing of one ton of reinforced concrete to a fraction of 20 mm in 2.5 hours. Increasing the overall environmental friendliness of the whole process of utilization of reinforced concrete products can be ensured by replacing the mechanical destruction of products by hydraulic shears with dust-free destruction by means of generation of a high-voltage current pulse by an electrode in a borehole filled with water. Сonclusion. According to the results of the conducted research, it is clearly seen that the proposed technology of electrohydraulic crushing of concrete blocks is a promising solution for effective utilization of reinforced concrete structures in the mining industry. Organization of the production process of recycling at the site of dismantling using this technology not only reduces the cost of transportation of materials, but also contributes to reducing the negative impact on the environment. The established rational parameters of the destruction process in the electrohydraulic unit provide the basis for optimization of the technology, which, in turn, provides precise regulation of the recycling process and increases its efficiency. Thus, the research results indicate that the proposed electrohydraulic shredding technology is a promising direction for the development of effective and environmentally friendly methods of construction waste utilization.

An electrified boom actuation system with energy regeneration capability driven by a novel electro-hydraulic unit

This paper presents a novel electrified solution for linear actuation systems, which has undergone a successful in-vehicle demonstration, marking a significant advancement in this field. Aligned with the growing trend towards electrification, this solution holds promise for a wide range of off-road applications. The showcased electro-hydraulic actuation architecture enables efficient four-quadrant operation and incorporates energy recovery capabilities. At the core of the system lies a distinctive electro-hydraulic unit, integrating a fixed hydraulic pump and a variable-speed electric motor into a compact and powerful entity. A specialized hydraulic system is designed to efficiently transform electrical energy from the electro-hydraulic unit into boom cylinder actuation. The sizing of the system is determined by the boom operation of a commercial compact loader. The maximum power output of the electro-hydraulic system is approximately 15 kW. The components of the proposed system are integrated into the reference vehicle, and comprehensive performance tests are conducted. The results of the tests performed on the vehicle with the boom lifting and lowering cycle indicate an overall system efficiency of 60%. The electrified solution consumes only about one-third of the energy used by the conventional boom actuation system on the reference machine, while exhibiting energy savings exceeding 75% during specific work phases. The energy savings come mainly from energy regeneration and minimal loss from throttling through the specialized hydraulic circuit design. The successful demonstration on the reference vehicle underscores the practicality and effectiveness of the proposed electrified solution in current mobile hydraulic applications.

Design methodology for an integrated axial piston-type electrohydraulic unit

This paper proposes a design methodology for power-dense and high-efficient electrohydraulic units (EHUs) that can be used to select design specifications for the electric machine (EM) for a given hydraulic machine (HM) architecture. The proposed method evaluates EHU performance considering both electric and hydraulic power losses. The compactness of the EHU is achieved by integrating an axial piston unit as HM inside a permanent magnet EM. The paper provides a sensitivity analysis for important EHU design specifications and discusses the best choices for reducing total mass and energy loss. The study finds that greater aspect ratios promote power-to-weight ratio, while high voltage promotes energy efficiency. The paper also discusses the choice of fixed versus variable displacement HMs, with the finding that a variable displacement unit helps address low efficiency limits of low-speed operation, particularly for low voltage electric machines. Additionally, variable displacement can also be used to reduce EM losses when meeting a flow-pressure demand. The proposed methodology has applications in fields such as off-road vehicles.

Experimental Verification of An Electro-Hydraulic Actuation System Driven by An Integrated Electro-Hydraulic Unit

This paper proposes an electro-hydraulic actuator (EHA) system, and a novel-designed electro-hydraulic unit (EHU) consisting of a fixed-displacement hydraulic gear machine and a variable-speed electric machine. The novel EHU design integrates an electric machine and a hydraulic machine in a single housing, targeting optimal compactness, power density, and component reduction. The EHA system features an open circuit design, where hydraulic hoses connect the EHU with a tank, a valve manifold, and the hydraulic cylinder. In this way, the proposed EHA technology can be used to implement distributed hydraulic actuation in a vehicle without requiring changes to the hydraulic actuators or at the overall layout of the hydraulic components with respect to the original vehicle design. A dedicated test rig is developed to verify the performance of the proposed EHA system. The efficiency of the EHA is measured in a steady state and under a realistic duty cycle of a commercial compact loader. The efficiency of the EHA system based on the measurements on the test rig can reach 54% with up to 20 kN load and 6 kW power level. Furthermore, the EHU is implemented on the reference machine to drive the boom function. Preliminary results on the performance of the EHU show an efficiency of up to 68% under different loading conditions.

Time-Driven Adaptive Control of Switched Systems With Application to Electro-Hydraulic Unit.

This article focuses on the H∞ adaptive tracking problem of uncertain switched systems. A key point of the study is to set up a multiple piecewise Lyapunov function framework which provides an effective tool for designing an adaptive switching controller consisting of a state-feedback and time-driven switching signal and a time-driven adaptive law. The proposed switching signal guarantees the solvability of the H∞ adaptive tracking problem for uncertain switched systems. Significantly, it provides plenty of adjusting time for the adaptive tracking control strategy to damp the transient caused by switching and avoids frequent switching. A novel time-driven adaptive switching controller is established such that the tracking error asymptotically converges to zero and all the signals in the error dynamic system are bounded under an achieved disturbance attenuation level. The solvability criterion ensuring an H∞ adaptive tracking performance is established for the uncertain switched systems, where the solvability of the H∞ adaptive tracking problem for individual subsystems is not required. Finally, the proposed method is applied to the electro-hydraulic unit.

Evaluation of compliance with the current standards requirements regarding the anti-lock braking system effectiveness of an electric vehicle with mixed braking support

Introduction (statement of the problem and relevance). In accordance to the current standards the requirements were assessed: for the braking process efficiency of M1vehicles category using an antilock braking system (ABS) and the combined possibility control of two actuators - electric machines installed in the vehicle driving wheels as well as the electro-hydraulic modulation pressure unit in the hydraulic circuit of the working brake cylinders.The purpose of the study was to evaluate the effectiveness of the newly developed ABS algorithm in accordance with current standards and additional requirements.Methodology and research methods. The braking process computer simulation of a M1 vehicle category equipped with four electric motors and an electro-hydraulic braking system was carried out. As a result of calculations, the obtained braking parameters were to be compared and evaluate according to the requirements of UN Regulation No. 13H, as well as evaluate the braking efficiency parameters.Scientific novelty and results. The effectiveness of the developed control algorithm for the ABS actuators (electro-hydraulic unit and electric machines in the drive wheels) has been proven in terms of meeting the requirements of UN Regulation No. 13H. Studies showed an efficiency improvement of the ABS operating due to the proposed algorithm, when compared to foreign-produced analogues.The practical significance of the work is the proof of the developed algorithm efficiency for M1 electric vehicles category.

Energy recovery from shock absorbers through a novel compact electro-hydraulic system architecture

Riding a road vehicle involves only 10-16% of the fuel energy to overcome the resistance from friction and air drag, while the rest contributes to a massive ecological and economic damage. From an energy balance point of view, a great amount of energy is dissipated as vibrations at the shock absorbers level. In this paper, a hydraulic regenerative shock absorber, able to recover and convert the vibration energy caused by road profiles is designed and manufactured by exploiting off-the-shelf components to reduce R&D costs, and its overall maximum efficiency is measured. The prototype is composed of a twin tube electronically controlled shock absorber and of an electro-hydraulic unit (also called regenerative valve) rigidly connected to it. The main relations ruling the dynamics of a regenerative damper are discussed and the main features of the regenerative valve are designed to comply with size, performance, and safety requirements. Parametric relations are illustrated and properly managed to justify the choice of a dedicated electric motor. Performances are assessed through simulations and experimental tests, while reliability is confirmed through a thermal analysis that reveals no thermal issues. The prototype reaches a maximum overall harvesting efficiency of 11.7% for an intermediate value of the external electric load at a 500mm/s rod speed and a maximum electric power in output of 75W for a high external electric load at 1000mm/s rod speed. Efficiency is strongly hindered at low values of rod speed because of predominant friction effects. It is also demonstrated the possibility to modify the damping curve by varying the electrical characteristics of the circuit connected to the electric machine. The compact design of the RSA, with a mass of only 5.8kg, allows its installation into the suspension of a B-class SUV with a minimum impact on the current damper structure.

Электрогидравлическая технология разрушения монолитных объектов

Currently there exists a problem of carrying out a safe and environmentally friendly breaking of solid objects located in confined spaces. The article presents the results of studying the possibility of solving this problem by replacing blasting of a solid structure with explosives with its breaking using the electrohydraulic shock effect. The physical nature of the electrohydraulic effect is described, the design diagrams and the method of calculating the optimum parameters of the breaking device are given. Electrohydraulic units can be used in the boulder storage areas prior to the first crushing stage in the mining industry. The results of laboratory experiments on electrohydraulic crushing of granite objects are presented. A conclusion is made that the proposed technology is potentially effective for crushing solid materials, e.g. oversized blocks of rock, boulders, frozen ground, ice, concrete and reinforced concrete structures. The results obtained during the study confirm the practical possibility of environmentally friendly and safe breaking of solid rocks using the effect of electrohydraulic impact.

ВЛИЯНИЕ ЭЛЕКТРОГИДРАВЛИЧЕСКОЙ ОБРАБОТКИ НА СОДЕРЖАНИЕ НИТРАТНОГО АЗОТА В ПОЛИВНОЙ ВОДЕ

The introduction of mineral fertilizers has a negative impact on the agrobiocenosis. An increase the concentration of nitrate nitrogen in irrigation water in order to use it as a nitrogen fertilizer that does not have a negative impact on the environment seems relevant. The change in the content of nitrate nitrogen was determined in irrigation water, which was used as the flowing water of the city water supply (Moscow); pond water (Moscow region); potassium nitrate solution with a concentration of 50.9 mg/l. Three types of irrigation water were processed using a high-voltage installation. The experimental electrohydraulic installation consisted of a TVI-50/70 transformer with a rectifier unit; DC electric energy storage systems (high-voltage pulse capacitors); arresters designed to generate pulsed spark discharges with a short rise time; controls that allow changing technological modes during experiments; working units. During the research, an ITAN pH meter/ionometer was used according to the RD 52.24.367-2010 method. The technological mode of operation of the electro-hydraulic unit provides for the following characteristics: operating voltage 42 kV; capacitance of capacitors 0.05 μF; number of spark discharges n = 1 ... 5 thousand pieces; forming the gap between the ball arresters FP = 14 mm; working gap between working high-voltage electrodes 10 mm. Electrohydraulic treatment of water increases the concentration of nitrate nitrogen compounds in the running water of city water supply by 3.7 times (from 2.9 to 10.9 mg/l), in pond water - by 7 times (from 1.2 to 8.4 mg/l), in a solution of potassium nitrate - 1.3 times (from 50.9 to 68.4 mg/l). In water treated electrohydraulically, the content of nitrate nitrogen increases, which expands the possibilities for its use when watering plants.

Electrohydraulic pretreatment method for the purpose of complex enrichment of fine clay ores of weathering crust

The paper substantiates the possibility of applying the technology based on the use of electrohydraulic effect for the preliminary preparation of clay ores with fine mineral phases. The technology was developed in the laboratory by conducting experimental studies on samples of several types of clay rocks and ores that differ in the composition of inclusions of solid fractions in them. Experiments have confirmed that with the optimal selection of operating modes of a specially created electrohydraulic unit, high selectivity is achieved for crushing and dispersing different strength minerals and mineral phases of sample materials, which ensures the destruction of the clay component while maintaining the integrity of solid fractions. Removal of water-soluble clay fraction with the pulp and washing of the resulting intermediate product provides a high degree of cleaning of solid inclusions from clay. This makes it possible to recommend the use of electrohydraulic technology for cleaning solid fractions of fine clay ores from clay at the initial stage of ore preparation, followed by the extraction of valuable minerals from the resulting intermediate product of enrichment by traditional methods.

Design of a Laboratory Electro-hydraulic Installation for Water Disinfection

Electrohydraulic effect is used in various fields of industry and agriculture: for cleaning metal casting forms, cleaning pipes of power boilers, treatment of heating radiators, soil treatment and water disinfection. Existing technical means for water disinfection with high-voltage discharges are expensive, cumbersome and untransportable. Currently used installations use an operating voltage of 10-50 kilovolts, capacitors designed for a voltage of no more than 100 kilovolts, with a capacity of 0.025 microfarads. Water disinfection according to the conducted research can be carried out with a voltage of 10 kilovolts. (Research purpose) The research purpose is in developing and manufacturing a laboratory electrohydraulic installation for water disinfection, which has a technical novelty in terms of mobility and compactness for implementing a method of water disinfection at a voltage of no more than 10 kilovolts. (Materials and methods) During the research, next materials, equipment and devices were used: power supply; transformer; capacitor; forming gap; working body; shunt resistance. (Results and discussion) The principle of the electrohydraulic effect, which is a consequence of the occurrence of electrohydraulic shocks between high-voltage electrodes placed in a liquid, is the basis for the development and manufacture of the installation. Authors developed a structural diagram of a laboratory electrohydraulic unit for water disinfection. The article presents an experimental sample of a laboratory installation for water disinfection, which has a technical novelty in terms of mobility and compactness for implementing a method for water disinfection at a voltage of no more than 10 kilovolts. The installation consists of a power supply unit FA-5-1/300W, a high-voltage step-up transformer TDKS32-04, a capacitor K75-29A (16 kilovolts, 1 microfarad), forming a gap of metal balls with a diameter of 18 millimeters, a plastic working body made of ABS material, a shunt resistance of 1 kilohm. (Conclusions) They article shows the scientific and practical significance of the research results: a technical means for water disinfection, providing the possibility of conducting experimental laboratory studies of the electrohydraulic effect at a voltage of no more than 10 kilovolts.

Improve the Efficiency of the Service Process as a Result of the Muda Ideology

Abstract The aim of the paper was to improve service processes carried out by Knorr-Bremse Systemy Kolejowe Polska sp. z o.o. Particularly, emphasise unnecessary movements and physical efforts of employees. The indirect goal was to find a solution in the simplest possible way using the Muda ideology. In order to improve the service process at the beginning was executed the process mapping for the devices to be repaired, ie. brake callipers, electro-hydraulic units and auxiliary release units. The processes were assessed and shown as Pareto-Lorenz analysis. In order to determine the most time consuming process. Based on the obtained results use of a column crane with articulated arm was proposed to facilitate the transfer of heavy components between areas. The final step was to assess the effectiveness of the proposed solution in terms of time saving. From the company perspective results of the analysis are important. The proposed solution not only reduces total service time but also contributes to crew’s work comfort.

Low Intensity Extracorporeal Shock Wave Therapy Improves Erectile Function in a Model of Type II Diabetes Independently of NO/cGMP Pathway

Erectile dysfunction is highly prevalent in type II diabetes mellitus. Low intensity extracorporeal shock wave therapy improves erectile function in patients with erectile dysfunction of vasculogenic origin, including diabetes. However, its mode of action remains unknown. We investigated the effects of low intensity extracorporeal shock wave therapy compared to or combined with sildenafil on erectile dysfunction in a type II diabetes mellitus model. Our purpose was to test our hypothesis of a mode of action targeting the cavernous nitric oxide/cyclic guanosine monophosphate pathway. GK rats, a validated model of type II diabetes mellitus, and age matched Wistar rats were treated with low intensity extracorporeal shock wave therapy twice weekly for 3 weeks. Treatment was repeated after a 3-week no-treatment interval. The penis was stretched and dipped in a specifically designed water-filled cage. Shock waves were delivered by a calibrated probe yielding a controlled energy flux density (0.09 mJ/mm(2)). The probe was attached to an electrohydraulic unit with a focused shock wave source, allowing for accurate extrapolation to humans. Following a 4-week washout period erectile function was assessed as well as endothelium dependent and independent, and nitrergic relaxations of the corpus cavernosum of GK rats. Low intensity extracorporeal shock wave therapy significantly improved erectile function in GK rats to the same extent as sildenafil. Treatment effects were potentiated when combined with sildenafil. Shock wave effects were not associated with improved cavernous endothelium dependent or independent, or nitrergic reactivity. Low intensity extracorporeal shock wave therapy improved erectile function in GK rats. Unexpectedly, this was not mediated by a nitric oxide/cyclic guanosine monophosphate dependent mechanism. Sildenafil increased shock wave efficacy. This preclinical paradigm to deliver low intensity extracorporeal shock wave therapy to the rat penis should help further exploration of the mode of action of this therapy on erectile tissue.

Research on regenerative brake technology of electric vehicle based on direct-drive electric-hydraulic brake system

A novel brake-by-wire system based on a direct-drive electro-hydraulic unit, which is able to control braking force flexibly, was designed to improve braking performance and recovery efficiency in electric vehicles. The structure of the brake unit is discussed in detail as well as the composition of the brake system. Since this novel system is required to coordinate with the regenerative system because of flexibly controlled friction force, the regenerative strategy is discussed in detail. An experiment is completed to prove that this novel unit is technologically feasible, and an electric vehicle co-simulation model based on MATLAB/Simulink and AMESim is established to prove that the unit and recovery strategy are able to recover braking energy as much as possible in the premise of braking safety. The simulation result shows that this novel system is able to control friction force flexibly according to motor status, so the regenerative efficiency is significantly improved especially in light braking.

MP52-07 EXPRESSION AND DISTRIBUTION OF CANNABINOID RECEPTORS IN THE HUMAN SEMINAL VESICLES

water-filled cage. Shockwaves were delivered by a calibrated probe yielding a controlled energy flux density of 0.09mJ/mm2 attached to a compact electrohydraulic unit with a focused shockwave source (Omnispec ED1000, Medispec Ltd, USA). Following a 4-week wash-out period, erectile function was assessed by electrical stimulation of the cavernous nerve in anesthetized rats and the effects of Li-ESWT alone or in combination with acute iv sildenafil (0.3mg/kg) were evaluated. Subsequently, ex vivo isometric tension studies were performed on CC from the same rats. RESULTS: Erectile function in GK rats was markedly impaired compared to age-matched Wistar rats and associated with altered endothelium-dependent, -independent and nitrergic mediated relaxations in CC. Either acute sildenafil or Li-ESWT significantly improved erectile responses in GK rats. Ratios of intracavernosal pressure and area under the curve /mean arterial pressure were significantly increased by 18% (p<0.001), 17% (p<0.05) and 32% (p<0.001), 23% (p<0.01), respectively versus untreated GK. This proerectile facilitator effect of Li-ESWT was not associated to improved endothelium-dependent, -independent or nitrergic reactivity of CC. The combination of Li-ESWT with sildenafil significantly potentiated the effect of Li-ESWT alone. CONCLUSIONS: Li-ESWT improves the erectile function of diabetic GK rats. Surprisingly, this effect is not mediated by a NO/ cGMP-dependent mechanism. Furthermore, this study shows additive effects when Li-ESWT is combined with a single dose of sildenafil.

Comparison of the effectiveness and safety of MPL 9000 and Lithostar Modularis shockwave lithotriptors: treatment results of 263 children

In this study, we aimed to compare the treatment results of two different shock wave lithotripsy (SWL) machines used in the management of pediatric urolithiasis. Between January 1993 and October 2004, Dornier MPL 9000 (electrohydraulic) had been used, and since then Siemens Lithostar Modularis (electromagnetic) has been used. The last evaluation was done 3 months after SWL treatment in terms of the success rate, use of anesthesia and complications. A total of 263 children (171 boys and 92 girls), with an age range of 9 months-14 years (mean age 8.1 +/- 3.8 years) were included in this study. Of the patients treated with the Dornier MPL 9000, 60.1% (173/104) required general anesthesia and 69 needed sedation. In contrast, for all patients treated with the Lithostar Modularis necessitated only sedo-analgesia (90 children). The hospital stay was shorter for Siemens Lithostar Modularis than those of Dornier MPL 9000 (26.2 vs. 35.5 h, P = 0.03). The success rate for the electromagnetic unit (86.5%) was almost identical that achieved with the electrohydraulic unit (85.2%) in the stones for the different location. Success rates were compared for stone burden subsets, the differences were insignificant for both lithotriptors (P > 0.05, for all). The electromagnetic unit had a significantly higher success rate for distal ureteral calculi (86.2 vs. 54.5%, P = 0.034). The efficiency quotients (EQ) for distal ureteral calculi were significantly different in favor of electromagnetic machine (56 vs. 40%). The complication rates for SWL were not significantly different for electrohydraulic and electromagnetic lithotriptors (8.7 and 6.2%, respectively). This study showed that SWL treatment was effective and safe in pediatric urolithiasis using both electrohydraulic and electromagnetic machines. Electromagnetic machine was more effective than electrohydraulic one for distal ureteral calculi. Additionally, the electromagnetic lithotriptor has significant clinical advantages over the electrohydraulic lithotriptor in terms of anesthesia requirements, hospitalization duration and fluoroscopic targeting.

Principle of Oil Film Test on Port Pair of Axial Piston Pump and Control Characteristics

In order to study the lubrication characteristics of several key friction pairs in axial piston pump under oil or water medium, the principle of the specialized test system that adopts electrohydraulic units for active and passive control of the lubricating oil film is proposed. The principle and constitution of the simulation test system of the said test system that uses film thickness feedback to control the sealing gap of port plate pair is discussed. The action of micro gap flow on the electrohydraulic control system is simplified to the load on the damper in spring, the physical model of the valve-controlled cylinder of port plate pair in relation to the lubricating film thickness is established, and the precision cylinder displacement control equation is derived. The main control parameters affecting the lubrication performance and their interrelations are analyzed, and the dynamic characteristic of film thickness control is simulated. The preliminary test of planar port plate pair oil film is carried out by using the test system. The results show that the simulation of oil film equilibrium is basically consistent with the test, and oil supply pressure and friction torque have relatively great effect on the formation of lubricating oil film. The feedback control principle of servo proportional valve makes the system’s film thickness dynamic feedback performance tend to keep stable, but when the slope of oil supply pressure varies, the equilibrium value of film thickness has certain variation within the preset range.

EXTRACORPOREAL SHOCK-WAVE LITHOTRIPSY: A COMPARATIVE STUDY OF ELECTROHYDRAULIC AND ELECTROMAGNETIC UNITS

We determined the results of shock wave lithotripsy with a newer electromagnetic lithotriptor and compared them with those in a contemporary series of cases managed by an electrohydraulic lithotriptor using identical treatment and followup criteria at a single center. Between 1995 and 1999, 356 patients (375 renal units, 483 upper urinary tract stones) meeting study inclusion criteria were treated with an MFL 5000 electrohydraulic shock wave lithotripsy unit (Dornier Medical Systems, Inc., Marietta, Georgia). From 1999 to 2000, 173 patients (175 renal units; 218 upper urinary tract stones) meeting identical study inclusion criteria were treated using an electromagnetic Modulith SLX shock wave lithotripsy unit (Karl Storz Lithotripsy, Atlanta, Georgia). In each group stone-free results were determined by plain abdominal x-ray and renal ultrasound 1 month after lithotripsy and efficiency quotients were developed. Baseline patient and stone characteristics were compared by the Wilcoxon rank sum and Fisher exact tests. All variables significant at p <0.05 were included in subsequent outcome analysis using multivariate logistic regression. Baseline characteristics were equivalent, including patient age, gender, stone number and location, although patients treated with the electrohydraulic unit had a significantly larger median stone burden (103 versus 71 mm.2, p = 0.015). Multivariate regression analysis demonstrated a higher stone-free rate in the electrohydraulic group (77% versus 67%, p = 0.01) but also a higher rate of total adjunctive measures (56% versus 47%, p = 0.04). Consequently the efficiency quotients were comparable for the electrohydraulic and electromagnetic lithotripsy units (0.45 and 0.42, respectively, p = 0.43). Electrohydraulic lithotripsy resulted in a higher stone-free rate at 1 month, although it was associated with a higher rate of auxiliary measures. Ultimately the efficiency quotients were equivalent, implying that these 2 contemporary energy sources are acceptable. According to single center treatment and followup criteria they are equally efficacious.

PM—Power and Machinery: Prediction and Experimental Verification of the Hoe Path of a Rear-mounted Inter-row Weeder

Accurate lateral positioning of implements operated by tractors is important in field operations such as inter-row weeding and band spraying. However, this can be difficult to achieve in practice and consequently there is much interest in automating the steering task. To develop an effective integrated system of control, the dynamic lateral behaviour of the tractor and implement must be understood.In this paper, a mathematical model is developed to predict the path of the weeder mounted on a tractor three-point linkage with free lateral movement and supported on steerable wheels. Experiments were conducted with a unit which could be steered either mechanically or by an electro-hydraulic control system. The principal purpose of the experiments was to test model performance and assess the steering geometry needed to achieve the best weeding accuracy. Results show good agreement between the performance of the test machine and the mathematical model. The amplitude of the predicted path was accurate within 2% and the phase angle within 2° in all but extreme tractor steering errors. Results also indicate that the level of steering accuracy sufficient for a commercial inter-row weeder can be achieved with simple proportional control. An optimum steering gain of 2·9 is suggested for the electro-hydraulic unit.