CC BY
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Section 10. Transport
Section 10. Transport
Bondarenko Anatoliy Igorovich, National Technical University «Kharkiv Polytechnic Institute» Associate Professor of the Department of Machine and Tractor Building
E-mail: [email protected]
Scientific basis of the theory of vehicles braking with stepless hydrostatic mechanical transmissions
Abstract: This paper presents the results of studies of kinematic, power and energy parameters distribution of hydrostatic mechanical transmissions. The influence of ways to implement the service and emergency braking, operational conditions, the laws of pressing the brake pedal and the laws of parameters change for regulation of hydraulic machines of hydrostatic mechanical transmissions regulation on the basic parameters of hydrostatic mechanical transmissions of different structures, as well as the drivability and the braking performance are determined.
Keywords: hydrostatic manual transmission, braking, drivability, braking efficiency.
Introduction
With the emergence of new types of hydraulic machines of volume type, increase of wheeled tractors traffic speeds particularly acute the problem of safety maintaining in the braking mode. Unfortunately, so far there has not been detected and systemized the influence of ways to implement the service and emergency braking, operation conditions, the laws of pressing the brake pedal and the laws ofparameters change for regulation of hydraulic machines of the hydraustatic drive (HSD) on kinematic, power and energy parameters of hydrostatic mechanical transmissions (HSMT) of different structures, as well as the drivability and braking performance.
Analysis of recent achievements and publications
Works on improving the HSMT are strenuously carried out by such world-renowned multinational corporations as “SNH", which combines the companies «Case IH», «New Holland» (USA) and «Steyr» (Austria); «AGCO», which combines the companies «Fendt» (Germany), «Massey Ferguson», « Challenger» (USA) and «Valtra» (Finland); «SDF», which combines the companies «Same», «Lamborghini» (Italy) and «Deutz-Fahr» (Germany), and the two largest companies «John Deere» (USA) and «Claas» (Germany) [1].
In Ukraine, the problem of creation of tractors with stepless HSMT is dealt with by scientists of the National Technical University «Kharkiv Polytechnic Institute», JSC «Kharkiv Tractor Plant after S. Ordzhonikidze», by experts of the JSC «Ukrainian Industrial Energy Company» [2; 3].
Despite the numerous works of scientists to create and study HSMT for self-propelled machines [1-4], the problems of systematic analysis and control of braking of wheeled tractors with stepless HSMT has not been almost paid attention to. In addition, the issue of mental and physical stress of operators-wheeled tractors drivers with both HSMT and mechanical transmissions in the process of implementation of various manufacturing operations has not been studied.
Purpose and goal setting
The aim of this work is the development of applied scientific foundations of system analysis and control of braking of wheeled tractors with stepless HSMT for increasing the structural reliability of HSMT, as well as the drivability and braking efficiency of the tractor by improving the braking process control.
To achieve this goal there were identified the following tasks:
— Identify the trends of stepless HSMT development and the prospects for their use in tractors;
— By experimental studies of the degree of exhaustion of operators- drivers ofwheeled tractors with HSMT and various mechanical transmissions perform a quantitative assessment of the studied tractors ergonomics;
— Identify and systematize the impact of ways to implement the service and emergency braking, operation conditions, the laws of pressing the brake pedal and the laws of parameters change for controlling the hydraulic machines of HSD on kinematic, power and energy parameters of HSMT of different
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Scientific basis of the theory of vehicles braking with stepless hydrostatic mechanical transmissions
structures, as well as the drivability and braking performance.
Scientific basis of the theory of vehicles braking with stepless HSMT
In recent years, double-flow stepless transmissions have become more common. Moreover, in tractors with capacity of 110-192 kW, their share reached almost 46% in 2013, and in tractors with capacity of 192-295 kW — 50%.
Double-flow HSMTs are currently the only type of stepless transmissions, serially installed on agricultural tractors. The field of their application expands both in the number of tractor models, and the power transmitted.
HSMT design develops in the direction of power increase that is transmitted by mechanical means and reduction of the number of friction multidisc clutches, reduction of the number ofbands (sub-bands) and complex mechanical parts respectively.
As a result of experimental studies the degree of exhaustion of operators- drivers of wheeled tractors it was established [5] that by the end of the 12 hours working day the tractor operator driver of «Fendt 936 Vario » was less tired according to the heart rate revealed by the method of Akioshi Kitaoka and the lactate content (lactic acid) in the blood, a little more tired — by 2.7-13.3% (depending on the number of measurement, operations performed and the method of determining the degree of fatigue) was the tractor operator-driver of « Case IH Magnum 255, by 5.4-20.0% the operator-driver of «Deutz-Fahr Agrotron X720», and the most tired — by 31.1-44.1% was the operator-driver of «HTA-200 Slobozhanets».
The difference in the results of the degree of fatigue of operators-drivers of tractors «Fendt 936 Vario», «Case IH Magnum 255», «Deutz-Fahr Agrotron X720» and «HTA-200 Slobozhanets” is mainly explained by the type of transmissions, the operation system complexity and psychophysical efforts made by tractor drivers accordingly.
Experimentally under laboratory conditions there was completely proved the adequacy of mathematical models of HSMTs used for theoretical modeling of stand operation in the brake mode. This very approach [6] used for composing mathematical models is recommended to describe the HSMT when modeling the braking process of the tractor.
As a result of comparison of theoretical and experimental results, regardless of HSMT schemes, it was established that the largest error does not exceed 5.93% in determining the maximum working pressure drop in the HSB, 6.01% — for the torque on the induction motor
shaft 1, 12% — for the angular velocity of the hydraulic pump shaft, 2.71% — for the angular velocity of the hydraulic motor shaft, 4.93% — for the angular velocity of the powder brake mechanism shaft (the law of braking torque variation and the law of the induction motor shaft angular velocity variation depending on time, which were obtained by experimental studies, are inherent in the mathematical model as input data).
The adequacy of the brake process mathematical model was totally confirmed on example of the tractor «Fendt 936 Vario» by comparing the theoretical results with experimental ones [7]:
• Maximum error in determining the stopping distance in case of service braking is less than 9.65%, in case of an emergency one — 9.95%;
• Maximum error in determining the deviation from the planned trajectory in case of service braking is less than 9, 91%, in the case of an emergency one — 8, 33%.
As a result of comprehensive study of the braking process of wheeled tractors with HSMT of different structures it was established that there is no ideal way or law for controlling the process of braking at both service and emergency braking [8].
— The most appropriate way of service braking, in terms of the load on the operator-driver, is braking by changing the relative parameter of HSD adjustment while maintaining the kinematic connection with the engine;
— Based on the research findings of emergency braking of wheeled tractors with various HSMT schemes, which can be realized only when the engine is apart from the cinematic driving wheels, it was determined:
• there does not exist a universal optimal law of change of relative parameter of HSD adjustment for all HSMT schemes. This is primarily due to the fact that the minimum value of the operating pressure drop in HSD, satellite angular velocity, angular velocity of the hydraulic pump and hydraulic motor shaft do not always correspond to the minimum value of differences between the values of angular velocities of the driving and driven shafts of the clutch. In some cases the speed of the tractor decreased slower than the equivalent to it parameters for adjusting the hydraulic machines ofHST for reducing the extremely high value of differences between the values of the angular velocity of the driving and the driven shafts coupling, and sometimes faster — in this case the value of the operating pressure drop in HST, the value of the angular velocity of satellites, and the value of the angular velocity of the hydraulic pump and hydraulic motor shaft were determined as the minimum possible;
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Section 10. Transport
• the use of the law of changing the relative parameter for HSD adjustment during wheeled tractors braking with stepless HSMT under kinematic separation of the engine from the drive wheels, in which the values of parameters for regulating the hydraulic machines of HSD correspond to the real speed change of the tractor acceptable to all options of HSMT schemes that is also confirmed by theoretical studies;
• the transmission maintains its efficiency and all the parameters are within the recommended limits assuming that the wheels of the tractor are not locked.
In case of technical impossibility of implementing the change of parameters value for adjusting the hydraulic machines of the HSD relative to the real tractor speed under the emergency braking at kinematic separation of the engine from the drive wheels (due to the complication of transmission control system) the following requirements are mandatory: tractor braking till the full stop; the options for regulating the hydraulic machines of the HSD during braking remain unchanged and are relevant to the value they had at the start ofbraking; at the time offull stopping of the tractor the HSMT control system should automatically provide the parameters change for adjusting the hydraulic machines of the HSD to those values that correspond to the zero speed of the tractor movement.
Conclusions
1. Double-flow HSMT are currently the only type of stepless transmissions that are serially installed on agricultural tractors. The field of their use increases in both the number of tractor models, and the power transmitted.
2. Designs of HSMT develop in the direction of power increase transmitted by mechanical friction and reduction of the number of multi-disk clutch, reduction of the number of bands (sub-bands) and complex mechanical parts respectively.
3. As a result of experimental studies the degree of exhaustion ofoperators- drivers ofwheeled tractors it was established [5] that by the end of the 12 hours working day the tractor operator driver of «Fendt 936 Vario » was less tired according to the heart rate revealed by the method of Akioshi Kitaoka and the lactate content (lactic acid) in the blood, a little more tired — by 2.713.3% (depending on the number of measurement, operations performed and the method of determining the degree of fatigue) was the tractor operator-driver of « Case IH Magnum 255, by 5.4-20.0% the operator-driver of «Deutz-Fahr Agrotron X720», and the most tired — by 31.1-44.1% was the operator-driver of « HTA-200 Slobozhanets ».
4. The most appropriate way of service braking, in terms of the load on the operator-driver, is braking by changing the relative parameter of HSD adjustment while maintaining the kinematic connection with the engine.
5. The use of the law of changing the relative parameter for HSD adjustment during wheeled tractors braking with stepless HSMT under kinematic separation of the engine from the drive wheels, in which the values of parameters for regulating the hydraulic machines of HSD correspond to the real speed change of the tractor acceptable to all options of HSMT schemes.
References:
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7. Samorodov V. The Results of the Experimental Study of the Process of «Fendt 936 Vario» Wheeled Tractor Braking/V. Samorodov, A. Bondarenko//Technology Audit and Reserves of Production. - 2014. - № 3/2 (17). -P. 54-59.
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