Browse Topic: Hydrostatic transmissions
This SAE Aerospace Information Report presents the following factors that affect hydraulic pump life and performance: a The need to supply hydraulic fluid at the correct pressure and quality to the pump inlet port b Considerations for the pump output c Factors to be considered for the pump case drain lines d The mounting of the hydraulic pump e Hydraulic fluid properties, including cleanliness
In a modern world, the tractor customer demands are increasing for more comfortable, new technology, fuel efficient and quieter vehicle. The customer’s expectation for NVH refinement often challenges the limitations for tractor designs. For smaller tractors Hydrostatic Transmission (HST) is need due to higher demand for fuel efficiency, lightweight powertrain, and the operation will become easy in the farm field. With the Hydrostatic Transmission (HST) tractor without damper, there is a technical challenge like withstanding of the sudden impacts from the implements which are connected to PTO during field operations. The NVH behavior in driveline is critical phenomena which can cause the discomfort to end users and structural failure of driveline parts. During gear engagement due to sudden variation in torque the driveline parts are tends to clash each other because of lashes which will create high level of angular acceleration and noise.
ABSTRACT
The traction-drive integrated drive generator (T-IDG®) has been developed since 1999 to replace current hydrostatic transmission drive generators mounted on Japanese military aircraft. The T-IDG® consists of a generator and a half-toroidal traction-drive continuously variable transmission (CVT), which maintains a constant output speed of 24000 rpm, that is, a 400 Hz AC power supply. To cope with recent trends of more electric aircraft (MEA) and the need for weight reduction, a high-speed traction-drive CVT is advantageous over other transmissions. The torque on the half-toroidal variator is transmitted through multiple power rollers. The equal load sharing among power rollers is typically controlled by a mechanical hydraulic feedback system, whose stability is one of the main issues for the high-speed traction-drive CVT. Previous studies have shown that insufficient damping and stiffness of the mechanical hydraulic feedback system cause self-induced vibration. We found that the support stiffness of the variator also affects the stability of the feedback system when it is driven at a high speed. This paper describes the theoretical criteria to maintain the stability of the load-sharing system of the power rollers of the high-speed CVT. A test to validate the theory is also conducted with a prototype traction-drive CVT at speeds of up to 20000 rpm with a peripheral speed of the traction contact of 70 m/s. The test results show that the vibration is excited at high rotational speeds when the variator is supported with a low-stiffness bearing support. We conclude that a high-stiffness support is necessary to transmit the power stably with a high-speed traction-drive CVT.
An increase in the number of vehicles per capita coupled with stricter emission regulations have made the development of newer and better hybrid vehicle architectures indispensable. Although electric hybrids have more visibility and are now commercially available, hydraulic hybrids, with their higher power densities and cheaper components, have been rigorously explored as the alternative. Several architectures have been proposed and implemented for both on and off highway applications. The most commonly used architecture is the series hybrid, which requires an energy conversion from the primary source (engine) to the secondary domain. From he re, the power flows either into the secondary source (high-pressure accumulator) or to the wheels depending upon the state of charge of the accumulator. A mode-switching hydraulic hybrid, which is a combination of a hydrostatic transmission and a series hybrid, was recently developed in the author’s research group. This paper focuses on the development of a new controller for the mode-switching hydraulic hybrid prototype. A uniform torque-based control strategy is proposed, which, along-with a supervisory controller decides on the usage of the high-pressure accumulator, thereby switching the vehicle mode from hydrostatic to series hybrid, among others. The supervisory controller analyzes the driving scenario, the system states and the user power demand to select the optimum vehicle-driving mode. This improved control strategy allows the vehicle to operate in higher efficiencies and the uniform control type results in a better “driver-feel”. The development of the control strategies, their implementation on the prototype vehicle and the test results are discussed in this paper.
Stationary (parking) brake is a very important and safety critical function in many classes of machines. The new transmissions and the “by wire” systems increase the criticality of the role of stationary brake, as it is also an emergency (secondary) brake, and it’s often used to hold the vehicle when the transmission is not locking the wheels. As an example, dual clutch and power-shift transmission gear systems, as well as hydrostatic transmissions under certain circumstances, are often unable to hold the vehicle stopped and this function is provided by the stationary brake. Due to the main need of having the brake actuated when vehicle is stopped, without any hydraulic and electric power, the brake configuration is normally a “negative” configuration, usually called “spring applied” because of the actuator configuration, but this configuration causes the brake actuation when de-energized, even in case of system failure. A thorough hazard analysis on fault cases, performed over the automatic stationary braking system of a big Agricultural machine, evidenced some fault cases, that could result in a unwanted actuation of the stationary brake, potentially causing serious damages. The paper deals with the electro-hydraulic braking system analysis and analyzes three different circuit architectures, that increase the Safety Performance Level of the solution, avoiding dangerous hazards and increasing the reliability of the entire system. The discussion will also be referred to Agricultural Tractors, due to the recent changes in homologation regulation within the European Union, introducing changes in brake and steer systems requirements.
With the need for improvement in the fuel economy along with reduction in emissions due to stringent regulations, powertrain hybridization has become the focal point of research for the automotive sector. Hydraulic hybrids have progressively gained acceptance due to their high power density and low component costs relative to their electric counterpart and many different architectures have been proposed and implemented on both on and off-highway applications. The most commonly used architecture is the series hybrid which offers great flexibility for implementation of power management strategies. But the direct connection of the high pressure accumulator to the system often results in operation of the hydraulic units in high pressure and low displacement mode. However, in this operating mode the hydraulic units are highly inefficient. Also, the accumulator renders the system highly compliant and makes the response of the transmission sluggish. In contrast, a hydrostatic transmission has a very stiff response which ensures a good drivability. However, it lacks energy storage. Keeping these in mind, the blended hybrid architecture was recently developed [1]. First realization of the hybrid architecture in Maha’s SUV showed that the complexity of the architecture results in difficulties while developing control strategies and results in poor drivability while transitioning between modes. This paper focuses on the development of a new mode-switching hybrid which is a novel combination of a hydrostatic transmission and a series hybrid. This architecture initially operates in hydrostatic mode offering a stiff response and later when the system demands higher pressure, the mode of operation can be switched to secondary control like in series hybrid using an on-off valve. In the secondary control mode, the accumulator energy is used as a power boost. This architecture helps to achieve better drivability along with improved efficiency. The development of control strategies and implementation of the architecture for an on-highway vehicle are also discussed.
Among the various types of hydrostatic transmissions, those based on radial piston multi-stroke machines are well-known solutions for off-road mobile machines. The balance between compactness, efficiency, control, comfort and price is the main reason for this. For the same reason, several car companies have tried to introduce hydrostatic transmissions into on-road applications. All such efforts have failed, mainly due to the whine noise produced by the hydrostatic machines. In particular, well-known standard solutions that aim to address the noise of radial piston multi-stroke machines, such as optimized relief grooves known as ‘notches’, are oriented toward reduction of the noise level. Unfortunately, the remaining whine noise, even with well-optimized notches, is unacceptable for automotive NVH standards. This article presents a new, inventive, scientifically based, successfully tested method aimed toward the suppression of the whine noise of radial piston multi-stroke hydrostatic machines. This method is based on the application of a Pseudo Random Binary Sequence (PRBS). This type of sequence is well-known in the domain of signal treatment as a basis for signal scrambling. In this case, a PRBS is used to scramble hydraulic noise. Accordingly, unpleasant whine noise can be altered, which can help merge the sound of a hydrostatic transmission with the sound of a thermal engine. Specifically, using the PRBS, the standard hydrostatic machine power spectrum is transformed toward the ‘white noise’ spectrum. In addition, by applying the PRBS, the frequency of the characteristic hydrostatic machine repetitive sound sequence is reduced, falling closer to the frequency of a characteristic thermal engine repetitive sound sequence. Due to the frequency reduction and transformed power spectrum, the sound of the hydrostatic machine will appear merged with the sound of the thermal engine. More precisely, overall noise will be increased, but it will be perceived more as that from the noisy thermal engine and not as the whine noise of a standard hydrostatic machine. With the hydrostatic machine sound merged with the sound of the thermal engine, a new powertrain concept based on the inclusion of a hydrostatic transmission can be successfully proposed for on-road applications. This concept, already proven with test vehicles, represents a significant achievement, as it will allow for new possibilities in powertrain design. It should be noted that this solution has a patent pending, so not all technical details can be reported currently. Therefore, the presentation of the methods and data herein may not be as clear as they would be once the patent is published. Nevertheless, enough technical details are given such that specialists in the field of hydrostatic transmission can grasp the novelty of the main idea behind the concept presented herein and start to evaluate potential impacts of the proposed new method against standard, known methods.
Engineers continue to master electronic controllers and software to help systems manage engine speeds and boost efficiency to the ultimate benefit of both OEMs and end users. Electrohydraulic controls continue to evolve rapidly, helping OEMS improve fuel efficiency and performance while also enhancing safety. Developers are tightening integration with engines, altering pump, valve, and networking schemes while also designing systems that meet functional safety requirements. Forging tighter links between the engine and hydraulics is a dominant trend. More electrohydraulic controllers are communicating with engines to increase efficiency and meet Tier 4 emissions and fuel consumption requirements.
A novel Blended Hydraulic Hybrid transmission architecture is presented in this paper with benefits over conventional designs. This novel configuration combines elements of a hydrostatic transmission, a parallel hybrid, and a selectively connectable high pressure accumulator using passive and actively controlled logic elements. Losses are reduced compared to existing series hybrid transmissions by enabling the units to operate efficiently at pressures below the current high pressure accumulator's pressure. A selective connection to the high pressure accumulator also allows for higher system precharge which increases regenerative braking torque and energy capture with little determent to system efficiency. Finally operating as a hydrostatic transmission increases transmission stiffness (i.e. driver response) and may improve driver feel in certain situations when compared to a conventional series hybrid transmission. To explore the novel blended hybrid architecture six transmissions were modeled and simulated. These included baseline manual and automatic transmissions, conventional series hybrid and series hybrid power split transmissions, and the novel blended hybrid and blended hybrid power split transmissions. All six transmissions were then optimally controlled on the UDDS cycle using dynamic programming to remove the influence of controller design on system efficiency. Ultimately the blended hybrid power split transmission improved fuel economy by 17.35% over a baseline automatic transmission while consuming 12.04% less energy than a conventional series hybrid power split transmission. The blended hybrid architecture was further explored by constructing a hardware-in-the-loop test rig and measuring the transmission over a defined drive cycle.
In this paper, the operating states of a wheel loader were studied for diagnostics purposes using a real time simulation model of an articulated-frame-steered wheel loader. Test drives were carried out to obtain measurement data, which were then analyzed. The measured time series data were analyzed to find the sequences of operating states using two different data sets, namely the variables of hydrostatic transmission and working hydraulics. A time series is defined as a collection of observations made sequentially in time. In our proposed method, the time series data were first segmented to find operating states. One or more segments build up an operating state. A state is defined as a combination of the patterns of the selected variables. The segments were then clustered and classified. The operating states were further analyzed using the quantization error method to detect anomalies. The recognized operating states define the operation of the machine so the analysis can be focused on specific sections and situations in time series and to identify which kinds of operating situations generate anomalies. Simulated leakages in the main hydraulic components of the hydrostatic transmission and the working hydraulics were used as anomalies to study the changes in the recognized operating states and the magnitude of the quantization error.
Having gained popularity in the automotive sector, many suppliers of hybrid drives are engineering their battery-electric offerings for the off-highway market. Customers, in turn, are experiencing major gains in efficiency and economy. As Innas BV's Peter Achten sees it, hybrids in recent years have not been considered a decent fit to off-highway applications. “Hybrid drivetrains are foremost developed for passenger cars where they can benefit from the recuperation of brake energy,” he said. “But for many off-highway vehicles, brake energy recuperation is not an option. Furthermore, hybrid-electric vehicles need sophisticated electric transmissions with delicate and expensive inverters, converters, and batteries. Taking the extreme power transients in mobile machinery and the rough operational conditions of off-road drivetrains into account, it is questionable whether the delicate hybrid-electric drivetrains can be considered a viable, inexpensive, and robust option for off-highway applications.” However, despite this view, there is a great deal of development effort being put into combining electrical power with traditional engines on a wide range of applications away from the highway.
For efficiency improvements, the desire to reduce the mass of vehicle subsystems is far greater than the ability. As a result, off-highway suppliers must seek innovation and technological advances through other means. Given their sheer size and resulting weight, it is easy to see why losing a few pounds from a combine, dump truck, or track loader would not really help the overall mass of the vehicle. Given this conundrum, while a lightweight, compact off-highway vehicle may be the dream, in reality, the road to efficiency gains is not as straightforward. “Building an axle is not like a recipe,” said Michele Lazzaro, Director at Dromos, the Italian manufacturer of transmissions, drive axles, and suspensions for numerous industrial markets. “Axles or associated components need to be developed harmonically, not through a modular concept. You need an optimized solution, and the key to optimizing the weight is making the best use of the material possible. This means that when you look at the lightest possible solution, it probably won't work for mass-production products.”
Carraro launches concept variable transmission transaxle Carraro DriveTech, the Italian-based manufacturer of axles, transmissions, and epicycloidal drives displayed a concept transaxle designed for agricultural and other off-highway applications at the recent Agritechnica. The transaxle, named VaryT, introduces a Torotrak toroidal transmission in place of a hydrostatic/shunted hydrostatic drive in a transaxle casing. “At the heart of any variable-speed transmission is the variator, and in the Carraro VaryT it's a very high efficiency mechanical unit across a wide speed range, which is unlike some of the hydrostatic options. It's a very power-dense solution, which means we can have a compact overall transmission, ideal for small tractors,” Roger Weyman, the Agricultural Director of Torotrak, told SOHE.
Case CE says new crawler dozer offers big performance, not weight Case Construction Equipment says its new 650L crawler dozer for residential job sites and confined commercial work areas retains the features of the Case crawler dozer line, such as hydrostatic drive, the operator compartment, and two undercarriage options. The 650L delivers 74 net hp (55 kW) through a four-cylinder, 4.5-L turbocharged Case Family IV engine with electronic fuel injection for maximum fuel efficiency and easier starts in cold weather. The Tier 3-certified engine is equipped with a high-pressure common-rail injection system and a charge air cooler that Case says reduces emissions and provides a cleaner, more efficient fuel burn.
In-wheel hydraulic motors, hydraulic transformers, and a common pressure rail with accumulators put new meaning in the word drivetrain. Hybrid-electric vehicles are compromises. The pure mechanical transmission is unparalleled when it comes to cost, weight, and efficiency. On the other hand, gear transmissions and even CVT's lack flexibility regarding energy management, energy transformation, and energy storage. Electric systems are in this respect much more convenient, but the power density and the efficiency are too poor to make a full electric drive feasible. However, Innas believes that if a flexible, nonmechanical transmission principle could be found with the same performance, cost, and efficiency as existing mechanical transmissions, there would be no reason for a hybrid configuration. And, the company claims that it has found it: a full hydrostatic all-wheel-drive system that eliminates the complete mechanical drivetrain between the engine and the wheels. The company refers to its hydraulic hybrid transmission as a “hybrid.”
Japan's leading companies have focused development on reducing size, mass, and cost. Japan is a predominantly automatic transmission country, with a small proportion of manual transmissions enjoyed by die-hard driving enthusiasts and accepted by economy-conscious utilitarian users. Accustomed to the automatic's smooth and less-arduous progression through narrow roads and congested traffic, the Japanese have not embraced automatically shifting manual transmissions. On the other hand, the continuously variable transmission (CVT) population is rapidly growing, with Nissan, Toyota, Honda, Mitsubishi, and Fuji Heavy Industries offering a large variety of cars equipped with CVT, from the Subaru R2/1 mini to the 3.5-L V6-propelled Murano SUV. These all employ the VDT (Dutch Van Doorne Transmissie) push-type steel belt and pulley system. Nissan's ambitious and extremely smooth and responsive Extroid toroidal CVT is still listed as a top option in the Skyline (Infiniti G35), but has been dormant, awaiting a second awakening.
There is much potential for gain for everyone if OEMs and suppliers work together early in terms of hydraulic system design. Modern off-highway equipment is some of the most powerful, most productive, most impressive machinery ever built. The key to that success is fluid power. It seems, in fact, that the primary function of equipment is to deliver fluid power to the site so that buckets and blades can do their work. As such, it is imperative that OEMs work closely with fluid-power-component manufacturers, no matter how big the OEM, or how vast its knowledge of fluid power.
A new control concept was developed to minimize the power losses of a hydrostatic drive line for off-road vehicles. The drive line control concept is based on two separate closed loop controls, one for the hydrostatic transmission and another for the combustion engine. The command values for both control loops are calculated under consideration of the characteristic curves of the combustion engine and the losses within the hydrostatic transmission, using an on-line optimization procedure. This paper discusses the benefits of this control concept based on a comparison of typical realistic driving manoeuvres. Objective of the investigations for different output powers is the potential of fuel savings under different operating conditions. A hardware-in-the-loop test rig for the investigated hydrostatic propel drive is used for the experimental validation.
A continuously variable transmission can improve the fuel efficiency of heavy-duty diesels by matching the engine's torque/speed to the applied load through the smooth torque multiplication of the transmission. The need for significant fuel-economy improvements in off-highway vehicles has never been greater than it will be over the coming years, according to researchers at the Southwest Research Institute (SwRI). In a conventional vehicle, the engine is responsible for meeting most of the requirements for varying vehicle speed and acceleration, while the transmission intermittently shifts between fixed ratios. Most vehicle speed variation therefore results in internal-combustion (IC) engine speed variation. Heavy-duty vehicles, with lower-speed engines, compensate for the lack of engine speed range with a greater number of fixed transmission ratios. Although the speed-varying capabilities of IC engines vary widely, they all share a common trait in that their regions of best brake specific fuel consumption (BSFC) comprise a relatively small portion of their overall operational envelope.
In a world of shrinking margins, fierce competition, and increasing regulations, equipment owners want nothing less than stellar performance from their equipment. New technology helps off-highway OEMs respond to equipment-owner demands for faster, cheaper, and more reliable vehicles. So do new business practices: most OEMs are compelling suppliers to re-examine their technologies and practices. “OEMs are trying a purchase strategy much like that used by the automotive people where you have Tier 1 and Tier 2 suppliers,” said Joe Maher, Marketing Manager, Poclain Hydraulics. “The idea is that if they can consolidate their suppliers, those suppliers (will) have more volume, which should generate some cost reduction. And because you're dealing with fewer suppliers, you've saved some administration cost, as well.”
In this paper a simple technical solution is presented. This solution allows a significant reduction of a wear of parts in an integrated hydrostatic transmission as well as a great efficiency improvement. This solution is suitable for all types of integrated hydrostatic transmissions and it is easy in application.
Since 1974, KUBOTA “B-Series Compact Tractors” have gained a high reputation all over the world mainly for their compact body sizes and versatile performances in mowing, transporting and landscaping. Recently KUBOTA developed the new B-Series Tractors, which consists of five models with PTO power ranging from 9.3 to 16.4 kW (12.5 to 22 HP) as shown in Table 1. Recently, models equipped with hydrostatic transmissions (HST) account for the majority of the 9 to 16 kW (12 to 22 HP) range tractor sales, because of ease of operation and higher operating efficiency. Accordingly we have equipped all five models with HST, while making the manual transmission available on only one model. We have increased the PTO horsepower to more than 14.9 kW (20 HP), while maintaining the compact body size. At the same time, we have added new features to enhance performance of the tractors' three major uses, front loader, mid mount mower, and rear implement operations. This paper discusses the technologies incorporated in the development of the higher horsepower models, the B2710 and B2910, as well as new features added.
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