Hydrostatic Transmission Research Articles

ANALYTICITY OF NON-STATIONARY PROCESSES OF CHANGE OF DIAGNOSTIC PARAMETERS OF HYDROSTATIC TRANSMISSIONS OF HARVESTERS

In this article, based on the Lagrange principle, the fundamental elements of the mechanics of continuous media with moving boundaries in relation to hydraulic drive systems of hydrostatic transmissions of combine harvesters are developed, which allows to expand the field of research and modeling diagnostics of these systems. The elements of the theory, the method of calculation of nonstationary processes of one - dimensional motions of uncompressed liquid media with moving media boundaries in hydraulic channels of complex geometric shapes of hydrostatic transmissions of combine harvesters are developed in the article. The analysis of methods of numerical solution of systems of ordinary differential equations with discontinuous coefficients is performed. It is shown that the Bless method is a more effective method of numerical solution of such systems of equations in the studied area. It is shown that for one-dimensional motions of uncompressed liquid media moving in the channel and bounded by moving boundaries, the calculation is reduced to solving the equation a a(x,t)ẍ= b(x, t)ẋ 2 + c(x, t). Here x = x (t) is the coordinate of the front or rear boundary of the liquid medium moving in the channel. It is shown that this equation is a generalized Bernoulli equation in the case of the motion of incompressible liquid media with moving boundaries. This equation is similar to the equation of motion of bodies with variable mass, and is convenient for use in CAD. The theory and method of calculation of processes of incomplete hydraulic shock arising at filling of liquid or gas-liquid environments of channels with local hydraulic support of difficult geometrical forms, for example, the centrifugal pump of hydrostatic transmissions of combine harvesters are created.The method of engineering calculation is obtained, which allows to determine the coefficient ε of compression of the liquid jet and the value of ∆p̅ = (p1 − p0 )/p0 relative shock pressure increase with incomplete hydraulic impact on local hydraulic resistance of complex geometric shape of hydrostatic transmissions of combine harvesters. Thus, the elements of the theory are created, as well as the method of calculating non-stationary processes of movement of uncompressed liquid media in the channels of complex geometric shapes of hydrostatic transmissions of combine harvesters. The method is used in the calculation of the dynamics of the start of the ampouled hydraulic system of the drive of hydrostatic transmissions of combine harvesters with minimum volumes of 1...10% of gas cavities for storage of the working fluid of the drive. The elements of the theory described above and the created calculation methods allow to expand the field of research of dynamic modes of operation of hydraulic systems of power drive of hydrostatic transmissions of combine harvesters in the process of filling working fluid channels of hydraulic systems with branches and hydraulic supports. Their application has allowed to increase the accuracy and reliability of diagnosing real processes characteristic of hydraulic drive systems of hydrostatic transmissions of combine harvesters, especially in difficult conditions of their amputation

LPV Control of Wind Turbine with Hydrostatic Transmission Under Inaccurate Wind Speed Measurement

LPV Control of Wind Turbine with Hydrostatic Transmission Under Inaccurate Wind Speed Measurement

Dynamics and Control of an Energy-Efficient, Power-Regenerative, Hydrostatic Wind Turbine Dynamometer

Dynamometers are used to evaluate the real-world performances of drivetrains in various loading conditions. Due to its superior power density, high bandwidth, and design flexibility, a hydrostatic power-regenerative dynamometer is an ideal candidate for hydrostatic wind turbine transmission testing. A dynamometer can emulate the wind turbine rotor dynamics and allow the investigation of the performance of a unique hydrostatic drivetrain without actually building the physical system. The proposed dynamometer is an energy-efficient system with counter-intuitive control challenges. This paper presents the dynamics, control synthesis, and experimental validation of a power-regenerative hydrostatic dynamometer. A fourth-order non-linear model with three inputs was formulated for the dynamometer. The strength of input–output couplings was identified, and two different decoupling controllers were designed and implemented. During wind turbine testing, the synchronous generator turns at a constant speed and the system model is linear. A steady-state decoupling controller was developed for independent control of the drive and transmission. The implemented decoupling controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure, but a 20 bar pressure spike for a 4 rpm step change in rotor speed. However, during starting and stopping, the synchronous generator speed is not constant, and the system model is nonlinear. Therefore, a steady-state decoupling controller will not work. Thus, a decentralized controller with feed-forward control and gain scheduling was designed and implemented. A reference command was designed to avoid cavitation, pressure spikes, and power flow reversal during start-up. The experimental results show precise tracking in steady-state and transient operations. The decentralized controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure but a 100 bar pressure spike for a 4 rpm step increase in rotor speed. The pressure spike was reduced by 80 bar with the implementation of feed-forward gain. The proposed electro-hydro-mechanical system requires less power and has the potential to reduce energy expenditure by 50%.

A Novel Algorithm for Hydrostatic-Mechanical Mobile Machines with a Dual-Clutch Transmission

Mobile machines using a hydrostatic transmission is highly efficient under lower working-speed condition but less capable at higher transport velocities. To enhance overall efficiency, we have improved the powertrain design by combining a hydrostatic transmission with a dual-clutch transmission (DCT). Compared with other mechanical gearboxes, the DCT avoids the interruption of torque transmission in the process of shifting without sacrificing more transmission efficiency. However, there are some problems of unstable torque transmission during the shifting process, and an excessive torque drop occurring at the end of the gear shift, which result in a poor drive comfort. To enhance the performance of the novel structural possibility of powertrain design, we designed a novel control strategy, which maintains the sliding in the torque phase and reduces the difference before and after the engagement, for the motor torque and the clutch torques during the shifting process, and then validated the control effect with model-based simulation. As a result, the control strategy employing clutch and motor torque control achieve a smooth shifting process since the drive torque is well tracked, and highly dynamical actuators are not required. As another benefit, only two calibration parameters are designed and actually needed to adjust the control performance systematically, even for any different sizes machines. Our research indicates the possibility to adopt dual-clutch in the field of construction machines.

A Case Study of Open- and Closed-Loop Control of Hydrostatic Transmission with Proportional Valve Start-Up Process

This paper concerns the start-up process of a hydrostatic transmission with a fixed displacement pump, with particular emphasis on dynamic surplus pressure. A numerically controlled transmission using a proportional directional valve was analysed by simulation and experimental verification. The transmission is controlled by the throttle method, and the variable resistance is the throttling gap of the proportional spool valve. A mathematical description of the gear start-up process was obtained using a lumped-parameters model based on ordinary differential equations. The proportional spool valve was described using a modified model, which significantly improved the performance of the model in the closed-loop control process. After assuming the initial conditions and parameterization of the equation coefficients, a simulation of the transition start-up was performed in the MATLAB–Simulink environment. Simulations and experimental studies were carried out for control signals of various shapes and for various feedback from the hydraulic system. The pressure at the pump discharge port and the inlet port of the hydraulic motor, as well as the rotational speed of the hydraulic motor, were analysed in detail as functions of time. In the experimental verification, complete measuring lines for pressure, speed of the hydraulic motor, flow rate, and temperature of the working liquid were used.

Energy efficiency improvement of battery powered wheel loader with an electric-hydrostatic hybrid powertrain

An electric-hydrostatic hybrid powertrain is proposed for the wheel loader propulsion system. The powertrain is constituted from an electric hydrostatic powertrain by adding a hydraulic accumulator as the second power source. It not only reduces energy consumption through regenerative braking, but also improves the power performance of the machine. A thermostat control strategy is developed for electric hydrostatic hybrid wheel loader and a speed-displacement compound control is developed for the electric hydrostatic wheel loader. The energy flow, losses analysis, and energy efficiency in the two powertrains are studied. The energy consumption reduction of the electric hydrostatic hybrid powertrain over the electric hydrostatic powertrain is identified in the wheel loader loading cycle. Results show the hydraulic accumulator in the hybrid powertrain increases the hydrostatic transmission efficiency and overall system efficiency. The energy efficiency in the electric hydrostatic powertrain is 45.64% and 51.66% in the electric hydrostatic hybrid powertrain. The total battery energy consumption is 14.20 kWh in the EH wheel loader and 12.48 kWh in the EH-hybrid wheel loader (50 cycles). The total energy consumption saving by using hybrid powertrain is 12.11%.

Application of gear hydraulic machines in the composition of hydrostatic transmissions

Hydraulic machines serve either to impart energy to the fluid flowing through them, or to obtain energy from the fluid for its further useful use. The number of hydraulic machines used in the national economy is increasing annually, due to the fact that, in comparison with electric motors, they have smaller overall dimensions and weight, and also have a higher ratio of torque on the output shaft to the moment of inertia of the rotor. In agriculture, hydraulic machines are widely used in crop production. Through the use of hydraulics and automation, the development of complex mechanization of production processes is carried out, which provides for the development of machines of increased power and reliability. Also, the use of hydraulic machines allows you to relieve the structure of rigid mechanical connections and allows a wide range of adjustment of the unit operation. The most widely used today are two types of hydraulic machines - piston and gear. The use of hydraulic piston machines places high demands on the degree of purification and quality of transmission oil, as well as on the qualifications of technical personnel to ensure quality maintenance. Gear hydraulic machines are less demanding on the purity of the working fluid, as well as simplicity in design, are quite reliable, have a low cost price and a wide range of rotational speeds, in addition, they are able to create a relatively high pressure with low weight. The overall efficiency of gear hydraulic machines, which is 90%, is slightly inferior to that of piston hydraulic machines, which reaches 93%, respectively. The given characteristics of gear hydraulic machines allow us to consider them, taking into account modern design features, as a power basis for a hydrostatic transmission, with a limitation in power of application.

ОСОБЕННОСТИ ИСПОЛЬЗОВАНИЯ МЕТОДА ТЕПЛОВОЙ ДИАГНОСТИКИ ГИДРОСТАТИЧЕСКОЙ ТРАНСМИССИИ ЛЕСОЗАГОТОВИТЕЛЬНЫХ МАШИН

The extraction of timber in the territory of the Russian Federation is carried out mainly by logging technical complexes, made on the basis of machines with a hydraulic drive. In turn, of the currently known types of hydrodynamic transmission, the most advanced is the hydro-static transmission. Despite the exceptional reliability of such equipment, hydrodynamic transmission, including hydrostatic transmis-sion, has a large number of failures. The main hydrostatic transmission failures include mal-functions of the wheel drive hydraulic motor. Therefore, the purpose of this study is to use the method of thermal diagnostics to reduce the number of failures in hydrodynamic transmission, including hydrostatic transmis-sion.

Experimental Validation of a Hydrostatic Transmission for Community Wind Turbines

Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, for the first time, a validated dynamical model and controlled experiment have been used to analyze the performance of a hydrostatic transmission with a fixed-displacement pump and a variable-displacement motor for community wind turbines. From the dynamics of the HST, a pressure control strategy is designed to maximize the power capture. A hardware-in-the-loop simulation is developed to experimentally validate the performance and efficiency of the HST drive train control in a 60 kW virtual wind turbine environment. The HST turbine is extensively evaluated under steady and time-varying wind on a state-of-the-art power regenerative hydrostatic dynamometer. The proposed controller tracks the optimal tip-speed ratio to maximize power capture.

Цифровой двойник быстроходной гусеничной машины с бортовым гидрообъемным механизмом поворота

The article is devoted to the study of the processes occurring in the transmission and turning mechanism of the high-speed tractor with the original structure of the gear and turning mechanism (GTM). The traditional design of the gear-lever double-flow GTM is supplemented by three hydraulic machines connected by two hydraulic lines. This allowed the tractor to implement any turning radius from a straight line to a turn in place around the center of gravity. A mathematical model (digital twin) of a high-speed caterpillar tractor has been developed, with the help of which it was possible to select the parameters of the tractor automatic traffic control system, which ensures that the vehicle passes a serpentine-type track in fourth gear at a speed of 34 km/h, which is unattainable with the traditional GTM of this machine. The indicators of controllability of the tractor movement near the skid boundary are analyzed. It is shown that the turn of a high-speed tracked vehicle at the drift boundary is very attractive from an energy point of view. Turning due to inertial forces significantly unloads the internal combustion engine, and ultimately reduces fuel consumption. The difficulty lies in driving the car at the edge of the skid. The article shows that the servo control system successfully solves this problem. Information about the curvature of the track, which can be formed by GPS navigation or reference points on the ground, was used as a setting signal. The result of the study is graphs of changes in the hydrostatic transmission pump control parameter, pressure in the hydrostatic transmission lines, rotational speeds of the driving wheels, the displacement of the pole of rotation, which characterizes the degree of approach to the skid boundary, and the movement trajectory in Cartesian coordinates

MODERN TRENDS OF DESIGN, RESEARCH AND USE OF HYDRAULIC MACHINES IN DRIVES OF MECHANISMS AND TRANSMISSIONS (REVIEW ARTICLE)

The work is devoted to an overview of modern trends in the design, research and use of hydraulic machines in the drives of mechanisms and transmissions. The analysis of the use of hydromechanical transmissions has been carried out. The advantages and disadvantages of hydromechanical transmissions in comparison with mechanical ones are described. A brief overview of modern approaches to the design of new products, taking into account the existing information technologies, is carried out. We have analyzed modern software products designed to support the project at different stages of the product life cycle. It has been found that at the present time the appearance of individual variants of highly specialized software with a modern interface for synthesizing the structure of a designed product does not make it possible to solve the problems of synthesis and structural analysis of hydro-mechanical transmissions. A review of the analysis of operational factors affecting the fault tolerance and operating parameters of hydrostatic transmissions in general and hydromechanical transmission in particular is carried out. We have also considered the examples of technical solutions that allow to reduce the number of failures associated with the influence of one factor or another, as well as allow to reduce its influence on the parameters of the mechanism. The analysis of sources with information on the study of the parameters of hydrostatic transmissions using field tests or the mathematical apparatus developed by the authors is carried out. The ways of solving problems arising at the stages of design research are outlined. Keywords: design, hydrostatic transmission, hydromechanical transmission, influence of operational factors, synthesis

THE INFLUENCE OF LUBRICANTS BASED ON VEGETABLE OILS WITH FULLERENE COMPOSITIONS ON THE RELIABILITY OF HYDRAULIC MACHINES

The article analyzes the prospective use of vegetable oils as lubricating materials and working fluids with the addition of functional additives in the form of C60 fullerene nanocompounds, reliability of the main tribosystems of volumetric hydraulic transmission of the GST-90 type. For the most part, the reliability of hydraulic machines depends on the working fluids used, and additives as functional components that are added to their content. The possibility of improving the characteristics of working fluids using nano-additives was considered. It was established that when operating on working fluids of vegetable origin with the addition of C60 nano-additives to oils of vegetable origin, the wear rate is 11% lower than when using MGE-46B. The rate of wear of the in situ tribosystem attached bottom - distributor is non-linear and significantly differs from the plunger - bushing tribosystem. It can be seen that the operation of this tribosystem at high loads will significantly reduce its estimated resource. The obtained results of wear rates of tribosystems when using different types of working fluids and their analysis make it possible to calculate and forecast the resource of each of them, and of hydrostatic transmission of the GST-90 type as a whole. For calculations and forecasting of the resource of the hydrostatic transmission of the GST-90 type, the maximum allowable amount of wear of tribosystems was selected based on the analysis of literary sources. Cheaper working fluids based on RS and RR vegetable oils can be a good alternative. Compared with the most common working fluid of petroleum origin MGE-46B, working fluids RS and RR provide a fairly high calculated resource, which is higher on average by 15%, and this, in turn, is equal to 480 engine hours. It is known that during the working season the harvester is operated for approximately 250 engine hours, that is, the use of RS and RR working fluids instead of MGE-46B will make it possible to increase the operating time up to two years. Keywords: volumetric hydraulic drives, fullerene nanocompounds, GST-90.

Low-speed radial piston pump as an effective alternative power transmission for small hydropower plants

Low-head hydropower bears tremendous potential as a renewable energy source, especially in the context of the progressing global warming. In locations with a low head, for economic and environmental reasons, a small hydropower plant with a waterwheel and an asynchronous generator may provide the best solution for sustainable electricity production. The purpose of this study is to demonstrate a new type of low-speed radial piston pump intended to be part of the hydrostatic transmission of such a small hydropower plant. The advantage of the transmission is the possibility of stepless, automatic change of the gear ratio during operation. First, we describe a mathematical model of the proposed pump and subsequently demonstrate a test stand equipped with its prototype with three suction-pressure units. The pump flow rate characteristics calculated using the theoretical model were compared with those obtained from experiments, resulting in the determination and characterization of the pump's efficiency. Supplementary experiments with a hydraulic accumulator installed as part of the investigated system, demonstrated the possibility of flow rate pulsation dampening. The experimental results showed the validity of the developed mathematical model. In conclusion, the correct operation of the pump was corroborated, and its potential application confirmed by the efficiency results.

Research on Load Disturbance Based Variable Speed PID Control and a Novel Denoising Method Based Effect Evaluation of HST for Agricultural Machinery

This paper aims to realize and improve the constant speed control performance of tractors with HST (Hydrostatic Transmission) variable speed units. To achieve this, based on the HST test bench of the tractor, we perform a verification test of the adjustable speed characteristics, a denoising filter test of the response signal, a test on the influence of the load disturbance on the adjustable speed characteristics and a PID-based constant speed performance detection test. The results of the verification test of the adjustable speed characteristics show that the theoretical value and actual value of the adjustable speed transmission characteristics of the HST used are essentially consistent with each other. The results of the test of the load disturbance’s influence on the adjustable speed characteristics show that the increase in load torque inhibits the HST output response. Therefore, the paper proposes and designs a PID-based closed-loop constant speed control system. The paper uses a step response test and a load disturbance test to research the control result of the constant speed system. Collecting and analyzing all test results, we find that the constant speed control based on PID has a very good result. The average error between the average HST output speed and the target speed set was 0.37%, and the average standard deviation of output speed was 1.18 rpm. In addition, the paper proposes a denoising method combing the empirical mode decomposition method and the Gaussian distribution determination. The method shows that the first two orders of the components of the HST response signal should be removed as noise. The paper uses the denoised signal and the partial least squares method to analyze the influencing factors of the constant speed control result. The analysis results show that the rate of change of load torque has the biggest influence on the stability of HST output speed, followed by the target value.

Advanced Design and Optimal Sizing of Hydrostatic Transmission Systems

This paper presents a novel method for designing and sizing high-efficient hydrostatic transmissions (HTs) for heavy duty propulsion applications such as agricultural and construction machinery. The proposed method consists in providing cost effective HT architectures that maximizes efficiency at the most frequent operating conditions of the transmission, as opposed to the traditional HT design methods based on the most demanding requirements of the system. The sizing method is based on a genetic optimization algorithm for calculating the optimal displacement of the main units of the HT to maximizes the efficiency in the most frequent operating conditions of the vehicle. A simulation model for HTs is built in MATLAB/Simulink® environment to test three different circuit alternatives for basic HTs. Considering a particular 250 kW heavy-duty application for which drive cycle data were available, this study shows great improvement in energy efficiency (14%) and power saving (20.1%) at frequent operating conditions while still achieving the corner power condition.

Research on the FM control for hydraulic wind turbine based on virtual inertia compensation control method

Wind has been admitted as one of the most promising renewable energy resources in multinational regionalization policies. However, the intermittent wind energy volatility and the weak coupling between traditional wind generators and the power grid all influence the electrical grid frequency stability. The hydrostatic transmission wind turbine (HWT) is taken as the research object, and the hydraulic energy storage system (HESS) is introduced into HWT to improve the frequency regulation capability. First, the mathematical models of rotor, hydraulic power main transmission system, and the excitation synchronous generator are established. Then, the HWT frequency modulation characteristics are analyzed under different amplitude of load frequency fluctuation. In view of the HWT limited frequency modulation capability, the frequency modulation control strategy based on virtual inertia compensation is proposed with the HESS. Under the condition of maximum power point tracking, the effectiveness is verified. The simulation and experimental results show that the control strategy has a good control effect, and the HESS dynamic response characteristic satisfies the wind power–frequency regulation. The research results will be helpful to make wind power become grid-friendly power and solve the problem of electrical grid low frequency stability.

Optimal Control of Hydrostatic Drive Wind Turbines for Improved Power Output in Low Wind-Speed Regions

World wind energy output is steadily increasing in both production scale and capacity of harvesting wind. Hydrostatic transmission systems (HTSs) have been used mostly in offshore wind turbine applications. However, their potential has not been fully utilized in onshore wind turbines, partially due to concerns related to hydraulic losses. In our prior work, it was shown that the annual energy production from a hydrostatic wind turbine can match or exceed that of a mechanical drive wind turbine with appropriate optimal control techniques. In this paper, we present an optimal control technique that can further improve energy production of a hydrostatic wind turbine, particularly in low speed regions. Here, the overall loss equation of the HTS is developed and used as a cost function to be minimized with respect to system model dynamics. The overall loss function includes the losses due to both the aerodynamic efficiencies and the hydrostatic efficiencies of the motor and pump. A nonlinear model of HST is considered for the drive train. Optimal control law was derived by minimizing the overall loss. Both unconstrained and constrained optimization using Pontryagin’s minimum principle were utilized to derive two distinct control laws for the motor displacement. Simulation results showed that both the controllers were able to increase power output with the unconstrained optimization offering better results for the HTS wind turbine in the low speed regions (3–8 m/s).

Application Study of Newton-Raphson-Type Nonlinear MPC for Hydrostatic Transmissions Under Disturbance and System Uncertainty

Model predictive control is well established and has a huge practical relevance in many industrial applications, especially for chemical or thermal plants. This paper presents the design and the implementation of a nonlinear model predictive control aiming at an accurate tracking control of desired output trajectories under disturbances and uncertainties for a nonlinear hydrostatic transmission system with multiple control inputs, which represents a fast mechatronic system. The benefit of this solution is that it can be easily adapted to either velocity tracking control or torque tracking control -- which is not the case with alternative model-based approaches. The control design is based on a numerical optimization within a moving horizon using the Newton-Raphson method in combination with the optimization-over-some variables technique. The unmeasurable system state variables as well as the system disturbances are reconstructed by an unscented Kalman filter which is well suited for nonlineaer systems subject to process and measurement noise. The proposed control scheme is investigated by simulations and experimentally validated on a test rig at the Chair of Mechatronics, University of Rostock. The results indicates the robustness of the proposed control structure by a high tracking accuracy despite system disturbances and uncertainties.

Design Matching and Dynamic Performance Test for an HST-Based Drive System of a Hillside Crawler Tractor

In recent years, research into and development of hillside tractors has become a popular topic in the field of agricultural engineering in China. To solve the main problems associated with a low adjustment range of the working speed, complex operation, and low safety for slope operation of medium-sized crawler tractors, a hydrostatic drive system that can be used for hillside crawler tractors was designed. According to the operation requirements of a hillside crawler tractor, the parameters of the three-cylinder diesel engine, hydrostatic transmission (HST), drive rear axle, and other key components of the drive system were matched after the force and motion analyses of the tractor, and then the main performance indicators, including the traction performance, system pressure and working speed of the drive system were verified. On this basis, a drive system performance test bench was built, and the traction performance and starting acceleration performance of the drive system was tested. The results of the traction bench test show that when the engine was at the maximum torque point of 1700 r/min, the maximum theoretical tractive force outputted by the tractor in Gear I was 114,563 N, and the maximum theoretical tractive force outputted by tractor in Gear II was 10,959.2 N, which were both larger than the traction resistance of 9550.6 N experienced by the hillside tractor ploughing on the slope. The results of the initial acceleration bench test show that the tractor driving speed can gradually increase with increasing output of the variable pump and can reach the maximum in 3 s. When the tractor was driving on flat ground, the maximum driving speeds of Gear I, Gear II, and Gear III were 4.65 km/h, 6.58 km/h, and 8.57 km/h, respectively, which are close to the theoretical values. When the tractor was driving on a 15° slope, the maximum driving speeds of Gear I, Gear II, and Gear III were 4.55 km/h, 6.25 km/h, and 8.28 km/h, respectively. It can be concluded that the design matching of the drive system is reasonable, the speed consistency is good and there is enough power reserve, which can meet the requirements for a large workload.

A Digital Displacement Hydrostatic Wind-turbine Transmission

In 1984 a hydrostatic wind-turbine transmission with ‘secondary control’ was proposed by Stephen Salter using the, then only conceptual, Digital Displacement® (DD) principle for controlling the flow of the primary, rotor-driven, ring-cam pump. This transmission ‘could achieve the correct ratio of tip-speed to wind-speed in conjunction with true synchronous generation’.
 In the following years DD machines were progressively developed. To start with they were relatively small in capacity but the power ratings were systematically increased, until it seemed that a high-power hydrostatic wind-turbine transmission might indeed be feasible. In 2006, Artemis Intelligent Power (Artemis), a company that had been formed from Salter's original university team, began working on a megawatt-scale, hydrostatic, wind-turbine transmission based on new pump and motor designs. In 2011 Artemis completed a 1.5 MW transmission and dynamometer test-rig. This was one of the largest hydraulic transmissions ever made and, with a shaft-to-shaft efficiency of 93%, one of the most efficient. Using secondary control to respond rapidly to gusting wind and to instantaneous grid faults, it was also the most controllable. This paper discusses the design of the transmission and test-rig and presents the results of steady-state efficiency tests. Subsequent papers will describe systematic experimental work to account for the various energy losses and to develop a comprehensive simulation model of the DD wind-transmission.