Browsing by Subject "Schlepper"

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Adaptive operator systems in tractors : analysis of potentials and methods for specification and evaluation
(2024) Schempp, Timo Thomas
Der Ackerschlepper wird in der Landwirtschaft, auf dem Bau, im Forst und im Kommunalbereich als Universalmaschine eingesetzt. Dazu wird er wechselnd mit einer Vielzahl von Maschinen gekoppelt, um diese zu betreiben. Es ergeben sich wechselnde Bedienszenarien mit unterschiedlichen Anforderungen an die Bedienung der gekoppelten Maschinen. Heutige Bediensysteme sind statisch und müssen daher als Kompromisslösung für diese unterschiedlichen Anforderungen an die Bedienung eingeordnet werden. Adaptive Bediensysteme können sich hingegen an wechselnde Bedienszenarien anpassen. Diese Arbeit beleuchtet den Stand der Technik der Bediensysteme in Ackerschleppern allgemein und explizit an drei ausgewählten Beispielen. Ferner werden zwei Methoden beschrieben, mit denen ein adaptives Bediensystem spezifiziert werden kann. Für die Bewertung der kognitiven und physischen Ergonomie von Bediensystemen allgemein werden zwei weitere Methoden vorgestellt. Alle Methoden sind für einen auf dem V-Modell basierenden Entwicklungsprozess geeignet. Die beschriebenen Ergebnisse einer theoretischen und praktischen Potentialanalyse motivieren den Einsatz adaptiver Bediensysteme im Ackerschlepper. Die theoretische Potentialanalyse stützt sich auf die Grundlagen der Ergonomie und auf die Art und Weise wie die Funktionen in einem Ackerschlepper genutzt werden. Die praktische Potentialanalyse stützt sich auf die Auswertung und Analyse von Messdaten aus dem Feld mit fast 500 Arbeitsstunden aus 14 Bedienszenarien. Ferner beschreibt diese Arbeit die Anwendung der Methoden zur Spezifikation, das entwickelte und funktionsfähige adaptive Bediensystem und die Anwendung der Bewertungsmethoden, die für das adaptive Bediensystem eine signifikante Verbesserungen der physischen und kognitiven Ergonomie zeigen.
Dynamisches Verhalten von Ackerschlepperreifen in Vertikal- und Längsrichtung auf fester Fahrbahn
(1997) Plesser, Joachim
Der Anteil von Transportfahrten von Ackerschleppern nimmt durch betriebsbedingte Veränderungen der landwirtschaftlichen Betriebe immer mehr zu. Zur schnellen Durchführung der Transporte stiegen deswegen die Höchstgeschwindigkeiten der Schlepper in den letzten Jahren immer mehr an. Die Fahrsicherheit und der Fahrkomfort der Ackerschlepper wird dabei insbesondere im oberen Geschwindigkeitsbereich maßgeblich vom Schwingungsverhalten der großvolumigen Niederdruckreifen bestimmt. Da der Standardschlepper in der Regel keine Aufbaufederung besitzt, sind es vor allem die Reifen, die die Fahreigenschaften beeinflussen. Um das Fahrverhalten verbessern zu können, sind zunächst die Federungs- und Dämpfungscharakteristiken für die vorliegenden Betriebsbedingungen zu ermitteln. An einem Bandlaufprüfstand werden an drei Versuchsreifen umfangreiche Reifenuntersuchungen bei Variation des Reifendrucks, der Radlast, der Reifentemperatur und der Fahrgeschwindigkeit durchgeführt. Das Fahrverhalten wird dabei durch ein von Langenbeck für die Vertikalrichtung vorgeschlagenes nicht-lineares Reifenmodell beschrieben. Dieses Modell wird weiterentwickelt und auf die Reifenlängsrichtung übertragen. Wesentliche Aussagen des Modells sind die nicht-lineare Federkennlinie und die degressiv abfallende Dämpfung bei zunehmender Geschwindigkeit. Das nicht-lineare Federverhalten sowie der degressive Abfall der Dämpfung läßt sich sowohl für die Vertikal- als auch für die Längsrichtung feststellen. Aus den Meßergebnissen werden die die Federungs- und Dämpfungseigenschaften beschreibenden Modellparameter ermittelt.
Einfluss dynamischer Radlastschwankungen und Schräglaufwinkeländerungen auf die horizontale Kraftübertragung von Ackerschlepperreifen
(2006) Schlotter, Volkmar
Given the large variation of application conditions of tractors and agricultural machinery, the force transmission between tyre and ground is of particular importance for the efficiency in agricultural use. For a proper assessment of the tyre the exact knowledge of the tyre force behaviour in vertical, longitudinal and lateral direction is required as well as their inter-dependences. Besides the steady-state behaviour the dynamic behaviour of the force transmis-sion is of high relevance. This thesis centres on the investigation of the lateral-force behaviour which is highly important for cornering, for driving on slopes, and also for vehicle roll. The steady-state and transient behaviour of the lateral force has been investigated using the Single Wheel Tester of Hohenheim University. Comparative tests for the longitudinal force transmission have been carried out. The focus was the assessment of dynamic behaviour under the influence of transient parameters particularly on rigid surfaces. The investigations for the steady-state lateral-force transmission show higher lateral forces for wider tyres especially in case of small slip angles. Tyre load has a strong influence on the cornering stiffness. A large increase in tyre load can lead to doubling the cornering stiffness. For small slip angles the lateral force tends to a maximum or even declines with increasing tyre load, so that for the same lateral force larger slip angles are required. The test results with non-steady-state slip angle excitation reveal a time delay in the lateral-force generation. This behaviour can be described by a time constant. An increase of the tyre inflation pressure from 0.5 bar to 1.6 bar leads to a decrease of the time constant by more than one third. A hyper-bolic decrease of the time constant with increasing driving speed confirms a stroke-dependency and leads in consequence to the introduction of a relaxation length. The relaxa-tion length derived from the measurements shows an increase with reduced tyre inflation pressure and rising tyre load. The values for the relaxation length are in a range of approx. 0.5 m to 1.6 m. A strong dependence on the respective method of measurement was found this means that measured values should always be reported in connection with the employed measurement method. With longitudinal force measurements the longitudinal stiffness, analogous to the cornering stiffness, was determined. For the longitudinal stiffness of the traction force values nearly twice as high are determined compared to the longitudinal stiffness of the braking force. For both parameters a nearly linear increase with the tyre load was found. The comparison of lug-excited and surface-excited tyre load fluctuations indicates a dominant influence of the lug excitation and the radial run-out of the wheel compared to stochastic excitations on road surfaces. For stochastic excitations in form of a bump the tyre load fluc-tuations are strengthened. A different behaviour of the lateral force with positive and negative gradient of the tyre load can be seen. Therefore the mean lateral forces are decreased for stochastic excitations. With low frequency excitations of the tyre load up to 2 Hz realised with the Single Wheel Tester the mean lateral force decreases by up to around 6%. The transient response of the lateral force has been determined using sinusoidal excitation of the tyre load. The relaxation length of 0.40 m to 0.75 m for tyre load excitation is lower than the relaxation length for slip angle excitation. Here as well a decrease with increasing tyre inflation pressure can be observed. Comparison with the results for the longitudinal force transmission under the influence of tyre load fluctuations shows that the time constant of the traction force amounts to only approx. one third of the time constant of the lateral force: the traction-force transmission reacts faster to tyre-load fluctuations than the lateral force transmission. Simulation of stationary lateral forces with various models shows good accordance with the measured results. For interdependent longitudinal and lateral forces the Slip-Drift-Model with appropriate adaptation of the input parameters shows good results. For modelling the non-steady-state lateral force transmission the Maxwell model was used. The spring and damping parameters have been determined with the results of measurements. An increase of the lateral tyre stiffness due to increasing tyre inflation pressure or reduced tyre load can be seen. The damping constant is strongly reduced with increasing driving speed, whereas the tyre load and the tyre inflation pressure have only a slight influence. The lateral damping constant is considerably higher than the vertical damping constant.
Einsatzmöglichkeiten elektrischer Antriebe für landwirtschaftliche Maschinenkombinationen
(2011) Hahn, Klaus; Böttinger, Stefan
Tractor-Implement-Systems are a vital component of agricultural mechanization. Their replacement by self propelled machines seems unlikely in the foreseeable future. At the same time, rising needs for food, high cost of energy, and a limited workforce require continuing increases in productivity. However, this should not have a negative impact on the environment. Technological progress is therefore of outstanding importance. Looking for trends in neighboring domains an increase in the utilization of electric drives can be observed. The research presented in this thesis shows that electric drives offer various benefits for agricultural tractors and implements ? the most important advantages being efficiency, controllability, and the possibility to distribute components. Yet, to fully utilize what electric drives have to offer it is necessary to pay close attention to system architecture as well as operator control concepts to make them work in the special environment of agricultural machinery. A concept was developed that is building on the ISOBUSidea of distributed control systems. For instance, the controller (i.e. the inverter) was placed on the tractor whereas the actuator (i.e. the motor) is on the implement. Given the frequent reconfiguration of the machines the inverter thus becomes a multi-purpose component. Easy, safe, comfortable, and profitable use is achieved by a high degree of standardization of the connector ? which includes automatic identification and configuration. Analytical models as well as prototype machinery of a fertilizer spreader, a sprayer, and a trailer with a propelled axle yielded a multitude of benefits. These include reduced fuel consumption for the spreader, less residual volume for the sprayer and better traction and vehicle dynamics for the propelled trailer. The good controllability of electric drives proved to be especially beneficial for those implements usually associated with precision farming: spreader and sprayer. Unproductive times for coupling and filling can be reduced. A propelled trailer helps to reduce soil compaction. The systems presented here are, however, in an early phase of development. The benefits of decoupling implement drivelines form the tractor?s engine speed could be proven. Due to their superior efficiency under partial loads electric drives are especially advantageous in applications that come with a wide range of loads. As far as complexity and ease of use are concerned, all three implements profited from the implementation of electric drives. In all cases safety and comfort of coupling the implement did increase. However, the systems are still limited both in functionality as well as level of automation. But given the good controllability, which is independent of most external influences, it is fair to assume that there is a high potential for improvements in this regard. When it comes to system control, a high degree of integration will be mandatory for the operator to fully utilize this increasing functionality. The required standardization is yet to be achieved. A mere substitution of a given drive by an electric drive is not always sensible. The use of electric drives necessitates a revision of rotational speed levels ? or more generally speaking ? of the working principle. It is vital to include the overload capability of electric drives into these considerations. The propelled trailer has a clear advantage in traction in the field whereas driving dynamics have a higher importance on the road. Whether it is a traction-assist or a drive that can be utilized over the entire speed range drives the power required and hence cost, weight, and space. In the end, this is an economical question but it may also be significantly influenced by legislation.
Entwicklung der Zufriedenheit der Landmaschinenhändler mit den Herstellern
(2015) Becker, Tilman; Semenenko, Ksenia
Bereits im April/Mai 2006 und im April/Mai 2008 wurde die Zufriedenheit der Landmaschinenhändler mit ihren Herstellern im Rahmen einer schriftlichen Befragung abgefragt. Eine Online-Befragung erfolgte dann im April/Mai 2015. Insgesamt nahmen 160 Händler an der Befragung teil. Wie 2006 und 2008 wurde auch 2015 die Bewertung der Händler zu fünf unterschiedlichen Kategorien abgefragt: - Traktoren - Mähdrescher - Futtererntetechnik - Bodenbearbeitung und Saat - Technik für Pflanzenschutz und Düngung. Abgefragt wurden z.B.: - Gesamtzufriedenheit mit jeweiligem Hauptlieferanten - Zufriedenheit mit einzelnen Marketingmaßnahmen im Detail Die Marketingmaßnahmen umfassen z.B. die Bereiche: - Produktprogramm - Zukunft der Lieferanten im Wettbewerb - Beziehung zu Lieferanten. Die Gesamtzufriedenheit setzt sich aus der Zufriedenheit in den einzelnen Bereichen zusammen. Um die Bedeutung einzelner Bereiche für die Gesamtzufriedenheit zu bewerten, wurde der Korrelationskoeffizient zwischen der Gesamtzufriedenheit und dem jeweiligen Bereich berechnet. Zusammenfassend kann man einen zumindest leichten Anstieg bei der Gesamtzufriedenheit feststellen. Lediglich in der Produktgruppe der Mähdrescher kam es zu einer insgesamt schlechteren Bewertung als 2006. Bezogen auf alle Beurteilungen konnte die Futtererntetechnik wie schon in den Vorjahren am besten abschneiden.
Entwicklung und Applikation eines instationären Reifenmodells zur Fahrdynamiksimulation von Ackerschleppern
(2009) Ferhadbegovic, Bojan
The driving speed of modern agricultural tractors increased continuously during the last years. Nowadays, a maximum driving speed of 50 km/h is standard for agricultural tractors in Germany. To be able to drive safely at such high speeds, the agricultural tractors are equipped with a suspended front axle. However, a rear axle suspension for standard tractors is still too expensive and has thus not prevailed yet. The increasing percentage of transportation duties and the efforts to increase the productivity generate a high demand for even faster agricultural tractors. Therefore, the first standard tractor with a maximum driving speed of 60 km/h was presented in 2005. This speed was achievable without a major change of the vehicle?s basic design. However, even higher driving speeds will require substantial modifications of the vehicle?s concept and are thus not expected very soon. Since the agricultural tractors are designed mainly for the field work, their driving dynamics characteristics on the road are not always perfect. The high vehicle masses, possible insufficiencies in the construction and interaction of various vehicle components together with the missing rear axle suspension can lead to critical behaviour of the vehicle, especially during high speed cornering. The entire suspension on the rear axle is accomplished by the tyres. Since the agricultural tyres are mainly designed for carrying high loads and generating high draft forces on soft soil, their driving dynamics properties on the road are rather insufficient. They usually have a radial run-out with an amplitude of 1-2 mm. Due to the rather low damping of the agricultural tyres, this rather small run-out can cause vibrations with a quite high amplitude, especially if the excitation is close to the eigenfrequency of the vehicle. Furthermore, the tyre inflation pressure varies between 0.8 and 2.0 bar - which is a relatively large span - making the vehicle setup more difficult. To analyse the driving dynamics of agricultural tractors and to identify possible problems and insufficiencies at an early stage of development simulation models are used. A very important part of a vehicle model is the tyre model. Being the link between the vehicle and the ground, the tyre has a high influence on the vehicle behaviour. It is therefore essential to use an accurate tyre model. Most of the commercially available tyre models today are optimized for passenger car tyres and are thus of limited use for soft and large agricultural tyres. In this doctoral thesis at the University of Hohenheim a dynamic model for agricultural tyres on rigid surfaces was developed ? the Hohenheim Tyre Model. It is a hybrid model since it needs physical parameters like spring and damper coefficients as well as empirically obtained data for the tyre-ground-characteristics. The Hohenheim Tyre Model uses the wheel speeds and the speed of the tyre tread to calculate the deflection velocity and the deflection of the tyre and subsequently uses both values as inputs for spring-damper-elements. The force calculated in these so-called Voigt-Kelvin-Elements is finally used to determine the slip and the slip angle of the wheel. The tyre model was created in MATLAB/Simulink and can be coupled to any multi-body-software. The model allows to calculate the transient tyre behaviour in three dimensions with a low computational effort, which makes it adequate for driving dynamics simulation. It takes the nonlinearities of the tyre into account and calculates the forces for pure longitudinal or lateral slip as well as for combined slip conditions.
Experimental investigations on tractor tire vibration properties
(2017) Brinkmann, Christian
Vehicle vibrations have raised articulate awareness in agricultural industry during the last years. Especially, the legal basis with the EU directive 2002/44/EC and its implementation into national law with the corresponding ordinance have sensitized the manufacturers concerning the vibration behaviour of their vehicles accompanied with an increasing demand for ride comfort by the customers. Furthermore, vehicle components’ stress due to vibration and shock is also significantly dependent on the tire’s vibration characteristics. Only an optimized design and combination of the vehicle components can reduce vibrations and improve ride comfort and endurance strength. In this thesis mechanical vibrations in the ride comfort frequency range between 10 Hz and 80 Hz are regarded. For the investigations a new mechanical shaker device has been developed and single frequency force excitations in the mentioned frequency range can be applied to a rolling tire. From excitation and response of the system it is possible to identify the vibration modes of the rolling tire. The shaker is designed to be applied both to a flat-belt test stand and a research tractor. Additionally, uniformity and cleat tests have been conducted with the research tractor in order to compare shaker, tire and impact excitations.
Experimenteller Beitrag zum Schräglauf- und Lenkmomentverhalten rollender Reifen landwirtschaftlicher Fahrzeuge auf starrer und nachgiebiger Fahrbahn
(1991) Heine, Adolf
Beim Einsatz landwirtschaftlicher Fahrzeuge können zwei Fahrzustände mit schrägrollenden Reifen unterschieden werden. Die Spurhaltung beim Fahren am Hang oder beim Pflügen erfolgt durch konstant (stationär) schräglaufende Reifen, wohingegen Lenkvorgänge zur Änderung der Fahrtrichtung als instationäre Fahrzustände anzusehen sind, weil sich der Reifenschräglauf hierbei ständig ändert. Um das instationäre Schräglaufverhalten der Reifen landwirtschaftlicher Fahrzeuge auf starren und nachgiebigen Fahrbahnen untersuchen zu können, wurde als Versuchseinrichtung ein Einachsanhänger mit stufenlos gegeneinander einlenkbaren Versuchsreifen und einer Fünf-Komponenten-Kraft- und Momentmessnabe entwickelt.
Kraftstoffverbrauch beim Einsatz von Ackerschleppern im besonderen Hinblick auf die CO2-Emissionen
(2006) Schreiber, Matthias; Kutzbach, Heinz Dieter
Agricultural tractors are currently almost exclusively driven by diesel engines. By rising fuel prices and growing ecological awareness concerning CO2-emissions and preservation of fossil fuel resources the importance of fuel consumption has been increasing. Generally, the substitution of diesel by alternative fuel based on vegetable oil is possible, however the potential for the substitution is limited by the scarcity of agricultural farmland and categorized as low. The cost savings are not very big due to higher fuel consumption with bio fuel. Therefore, only the reduction of fuel consumption for different agricultural operations and if applicable the reorganisation of the production chains can contribute to a sustained reduction of fuel consumption and costs. In this thesis the basic influencing factors on fuel consumption of tractors are shown. Field tests are only of limited usefulness for the examination of single influencing variables. For those studies a model had to be developed. The presented model is based on the status of science concerning engine and transmission performances as well as tractive performance for agricultural tractors and is combined with the ASAE-Standard 497.4-model for the tractive force needed to pull the implement. As existing tyre-soil-models are only of limited use to predict tractive performance in the field and to deliver these values to the tractor model, an independent traction prediction model was developed. It is based on empirical equations, which were parameterized on the basis of numerous field tests. Furthermore, the influence of the fuel consumption for turning over in the headlands and for transportation work were investigated and considered in the model. The new model was implemented into the software Matlab to determine fuel consumption for different agricultural work and defined parameter variations. The calculated values were compared to the results of field tests with a special equipped tractor at the University of Hohenheim to validate the model. The model was used to investigate the influence of numerous influencing parameters, the effect on fuel consumption was shown and optimization strategies were developed. The saving potential by the optimization of the working process is up to 30 % for different implements, depending on the current state. For this purpose the tractive efficiency must be maximized by the correct weight of the tractor and the correct tyres, tractor and implement must be adjusted ideal, four wheel drive and differential locks must be used if necessary and the transmission ratio must be chosen to run the engine close to the optimum working point with the optimum engine load. Besides the process optimisation it is important to deliver standard values for the fuel consumption for different working operations and production chains for the practical use. For the presented model a large number of parameters has to be determined, thus it is of limited use to calculate standard values. Furthermore, it is too accurate for those calculations. Therefore, the model was used to obtain simplified equations for a quick and simple calculation of fuel consumption values, considering the major criteria of engine, transmission and tractive performance of the tractor as the drawbar pull and the needed PTO-power of the implement. On the basis of these equations, implemented into Microsoft Excel, the required standard values for fuel consumption can be calculated for different tractors with implements of different size and defined soil conditions. However, the required data of some implements are not complete. For the most important agricultural implements these parameters were determined by measurements or collected from KTBL- or FAT-values. The results for different operations and production chains are correlating well with values measured in the field. The effect of the field size or the distance between field and the farm yard on fuel consumption can be shown as well. The saving potential by changing the whole production chain (like zero tillage) is enormous, however, there are horticultural and economical external effects. As those economical effects can hardly be estimated, the conversion of the production chain has to be reviewed for the individual case. In the future the importance of fuel consumption will increase. Different saving strategies will gain in importance in order to optimize agricultural operations with respect to fuel consumption. The approach of this thesis can be used to show saving potentials, to develop optimization strategies and to calculate values for the fuel consumption of different agricultural operations.
Load based evaluation of machines using the example of a tractor
(2018) Balbach, Florian; Böttinger, Stefan
The estimation of tractor value requires a lot of experience and knowledge and relies mainly on to-tal operation hours and manufacturing year. Today each tractor operation hour is considered to be equal because tractor meters operate time based only and do not consider the varying loads. But tractors face multiple applications within a year. Each application puts different loads on each tractor assembly such as engine, gearbox, axles or power take-off. A more precise method is introduced to evaluate tractor operation hours on basis of real applica-tion loads of each tractor assembly within the drivetrain separately. The method relates accumulat-ed tractor loads to standard operation loads which are defined by a reference load spectrum for the specific assembly. For the load evaluation a pseudo damage calculation similar to the Miner’s rule is used. A test tractor was equipped with strain gauge sensors to measure torque flow within the drivetrain. A variety of different tractor applications were measured and load spectra for different assemblies were generated. Based on different tractor application profiles lifetime load spectra for the differ-ent assemblies can be calculated. Further consolidation of the individual load factors can be done by weighting of the assemblies. The resulting load factor brings transparent information about in-tensity of tractor usage. Results show big differences between the assemblies and between the different application profiles. This supports the demand for a new method for tractor evaluation
Potential and prospects of a brand differentiation in the agricultural engineering, using the example of the multi-brand company CNH Industrial
(2023) Münd, Benjamin; Köller, Karlheinz
CNH Industrial unites three agricultural brands, Case IH, Steyr and New Holland. With miscellaneous mergers in the past, these former independent manufacturers of agricultural equipment were combined in one company. A lot of synergies were used and are still being used to maximize the profit of the parent company CNH Industrial and to reduce complexity. Through this harmonization process, the tractor models of the three brands became more and more similar with less distinctive features which leads to a high comparability of the brands Case IH, Steyr and New Holland and its tractor product line up above 55 hp. This results in a strong competition between these brands because in most countries the dealer network is separated for New Holland and Case IH/Steyr and every distribution partner is independent and strives for their own profitability. Due to this, the internal competition prevents external competition with tractors from other manufacturers, which generates cannibalization effects and reduces the profit of the three brands, CNH Industrial and the dealers. Structural changes in the European agriculture led to bigger farms with in total less tractor registrations per year what intensifies additionally the competition for tractor manufacturers. A survey with farmers and contractors from Germany, UK and France showed, that a brand and product differentiation would make sense and would bring a sustainable benefit for all three brands and their parent company CNH Industrial. Because of the history of all three brands and loyal long-term customers, a merger to one CNH Industrial brand is not efficient and expedient. It is important to identify the right customer group for each brand, to know the customers’ requirements and to offer the appropriate products and technical solutions. The network of distribution partners (dealers) is the key factor for an efficient market development. The professionalism of the dealers is mainly determining the success of a brand and its products in the market and the perception of the farmers and contractors. The professionalization of the dealer and collaboration between manufacturing company and dealer is essential. Also, the country of production of the tractors has a significant impact on the customer perception and appreciation. “Made in Germany” is still a quality characteristic and explains partially the high appreciation of Fendt and John Deere as premium tractors for professional farmers and contractors. Steyr as one brand of CNH Industrial AG which only produces tractors has a valid potential to establish to a premium tractor brand in Europe. Due to little negative connotations of customers and a straightforward history the brand has a good base for this development purpose. Bottom line, there are manifold possibilities to achieve a differentiation that is perceived by the customers as such. However, several actions are only feasible mid- or long-term. A product differentiation makes sense to reach a broad base of customers. Certainly, it is undisputed that a product differentiation is connected to high investment. If it is economically viable for the CNH Industrial group remains to be evaluated.
Reifenparameterermittlung aus Fahrversuchen mit einem Ackerschlepper unter besonderer Berücksichtigung des Hohenheimer Reifenmodells
(2017) Schulze Zumkley, Hendrik
Die Landwirtschaft weltweit strebt eine zunehmende Industrialisierung und Effizienzsteigerung an. Ein Ansatz dazu ist die Verkürzung der Transport- und Umsetzzeiten von Gütern und Maschinen durch Steigerung der Höchstgeschwindigkeit, insbesondere von Ackerschleppern und selbstfahrenden Landmaschinen. Unter Beibehaltung der notwendigen Sicherheit ist dieses Ziel jedoch nur mit aufwendigerer Technik möglich. Ein weiteres Ziel ist die Fahrzeugentwicklung zu beschleunigen und zu präzisieren, was mit Simulationswerkzeugen wie der Mehrkörpersimulation gelingen soll. Wesentliches Element der Gesamtfahrzeugsimulation ist die Modellierung des Reifenverhaltens. Kommerzielle Reifenmodelle sind zahlreich verfügbar. Die Eignung für Ackerschlepperreifen und besonders ihre Parametrierung ist jedoch stark eingeschränkt. Es gibt nur sehr wenige Prüfstände, die in der Lage sind, Reifen mit einem Durchmesser größer 2 m zu vermessen. In dieser Arbeit wird daher die Alternative geprüft, mit einem messtechnisch ausgestatteten Ackerschlepper aus Fahrversuchen einzelne Reifenparameter zu ermitteln. Das Hohenheimer Reifenmodell dient wegen der Verfügbarkeit des Codes und der weitgehenden Allgemeingültigkeit der verwendeten Parameter als Grundlage.
Untersuchungen der Kräfte an schräglaufenden angetriebenen Ackerschlepperrädern
(1991) Armbruster, Karlheinz
Mit einer Einzelradmesseinrichtung wurden an Ackerschlepper-Antriebsrädern bei Radschräglauf und Schlupf gleichzeitig auftretende Längs- und Seitenkräfte an Reifen unterschiedlicher Größe auf verschiedenen Fahrbahnen gemessen. Die Ergebnisse wurden dargestellt und unter Berücksichtigung des Einflusses von Fahrgeschwindigkeit und Schlupf auf die Bodeneigenschaften durch Modellrechnungen beschrieben. Steigender Schlupf führt zu größeren Triebkräften, eine Zunahme des Schräglaufwinkels zu einem degressiven Anstieg der Seitenkräfte. Die Radführungskräfte nehmen vor allem mit der Radlast zu. Größere Raddurchmesser führen zu höheren Triebkräften, breitere Reifen zu größeren Seitenkräften. Eine Zunahme der Längskräfte führt zu einem Rückgang der Seitenkräfte. Das Maximum der Seitenkräfte liegt im Bereich geringen negativen Schlupfes und geringer negativer Triebkräfte.