| 1. |
- Fyhr, Pontus, et al.
(författare)
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An Experimental Study of Forced Vibration Influence on Disc Brake Drag Torque in Heavy Commercial Road Vehicles
- 2022
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Ingår i: Tribology in Industry. - : Faculty of Engineering, University of Kragujevac. - 0354-8996 .- 2217-7965. ; 44:1, s. 123-131
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Tidskriftsartikel (refereegranskat)abstract
- Drag torque in a disc brake is the residual torque when the brake is not activated. This torque can adversely influence the total energy consumption, life of the brake components, and level of airborne wear particles from vehicles. Drag torque is of special interest for long haul trucking since it could have an effect of the total energy consumption. Drag torque performance of a disc brake is usually evaluated with conventional inertia dynamometers. Vibrations induced by the wheel can help to retract the pads from the disc and decrease the drag torque. It is hard to study this phenomenon with conventional inertia dynamometers since there is usually no system to induce a forced vibration on the brake. Therefore, the aim of the paper is to investigate the effect of vibrations on the drag torque for a commercial vehicle disc brake with a novel test setup. This is done by comparing test run with and without pads, forced vibrations, and pad retraction springs. The results indicate that the forced vibrations strongly affect the level of measured drag torque. In addition, the introduction of a retraction spring can reduce drag torque with more than 50% when vibrations are induced.
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| 2. |
- Hjelm, Rikard, et al.
(författare)
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A method for calculating contact pressure and tip contact in spur gear sets with manufacturing errors
- 2018
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Ingår i: Conference Proceedings Volume I International Gear Conference 2018 Lyon Villeurbanne. - 9781911033424 ; 1, s. 488-497
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Konferensbidrag (refereegranskat)abstract
- To investigate how manufacturing errors affect the gear set, a method is developed to calculate the contact stress of a gear set with pitch and involute incline errors. The method is parametric, and a hybrid model is used to model the gear stiffness. Contact outside the line of action is considered.A numerical example is used to show how manufacturing errors can change the contact pressure and cause tip contact, in spite of tip relief, resulting in high contact pressure. A threshold for maximum allowable torque of the gear set due to the specified errors is found.
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| 3. |
- Hjelm, Rikard, et al.
(författare)
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A multi-perspective method for gear efficiency and contact analysis
- 2023
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Ingår i: Results in Engineering (RINENG). - : Elsevier BV. - 2590-1230. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Modern gearing applications, in particular electrification, impose new challenges in many different fields of engineering and research. In specific, new demands are imposed on gears, including higher rotational speed, lower noise acceptance, and increased efficiency, as well as increased resistance against pitting and scuffing. To meet these demands, a better understanding of gear contacts is needed. The Eurostars project Effigears proposes a novel multi-perspective methodology for assessment of gear efficiency and contact analysis. The methodology consists of using a novel surface treatment method, Triboconditioning (R), implemented in a streamfinishing process, surface measurements using a scattered light method, experimental testing using the standardized FZG test rig, and contact simulations using a novel thermal elasto-hydrodynamic lubrication tool. It is found, in preliminary tests, that enhanced gear performance may be enhanced due to Triboconditioning (R) surface treat-ment. Findings also include better understanding of how surface characteristics and lubricants affect scuffing and pitting, and the effect of load distribution on gearset behavior.
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| 4. |
- Hjelm, Rikard, et al.
(författare)
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Airborne Wear Particles from Dry Clutches
- 2022
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 13:10
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Tidskriftsartikel (refereegranskat)abstract
- A significant part of non-exhaust particle emissions in cities comes from the wear of vehicle components. Several studies on airborne particles from the wear of disc brakes and tires have been completed. However, few publications can be found in the scientific literature regarding airborne emissions from dry clutches used in road vehicles. With this in mind, this preliminary study designs a clutch tribometer for the generation of airborne wear particles in a controlled environment. The number concentration and the size distribution of airborne wear particles generated from a typical dry clutch used in passenger cars are investigated. The tests are run at a constant rotational speed, and normal load. The results show that the particle number concentration from dry clutches exhibits a running-in period and a steady state, similar to the particle emissions from disc brake contact. A significant number of nanoparticles (aerodynamic diameter < 100 nm) are emitted from the dry clutch contact.
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| 5. |
- Hjelm, Rikard, et al.
(författare)
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Influence of manufacturing error tolerances on contact pressure in gears
- 2021
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science. - : SAGE Publications. - 0954-4062 .- 2041-2983. ; 235:20, s. 5173-5185
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Tidskriftsartikel (refereegranskat)abstract
- Gear manufacturing always results in some degree of manufacturing errors, i.e. deviations from the desired gear geometry. These errors alter how the gears mesh, typically causing increased contact pressure which in turn shortens service life. It is therefore crucial to choose tolerances such that excessive contact pressure, and especially tip contact, is avoided. With increasing demands due to electrification, this becomes even more important. The aim of this paper is to study how pitch error and profile slope error affect the contact pressure in spur gears sets. The meshing is simulated using a novel simulation approach that uses a parametric description of the reference profile and gear geometry, and a hybrid model for the compliance. The method includes tooth modifications such as tip relief, and uses the true geometry to find contacts. Thus, it also handles contact outside the nominal line of action, including tip contact. The study includes cases where a gear is subjected to both pitch error and profile slope error simultaneously. Numerical examples, relevant to the automotive industry, show the outcome of the simulations. It is shown how simulation-based tolerances for relevant industrial applications can be used to improve manufacturing outcome.
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| 6. |
- Hjelm, Rikard, et al.
(författare)
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Influence of Manufacturing Error Tolerances on Thermal EHL Behavior of Gears
- 2022
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Ingår i: Lubricants. - : MDPI AG. - 2075-4442. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Due to the electrification of vehicles, new demands are being imposed on gears, which translates to the tolerances of manufacturing errors. However, not many studies treat the impact of manufacturing error combinations on the lubricant behavior of gear sets. Therefore, a simulation method is developed, including its derivation, discretization, and implementation. The method solves the thermal elasto-hydrodynamic lubrication (TEHL) problem, taking into account the varying temperature, viscosity, density, and cavitation of the lubricant. To account for manufacturing errors, the load distribution from a loaded tooth contact analysis (LTCA), developed by the authors, is used as input to the TEHL method. Comparison is made with a standard load distribution assumption, and a numerical example is used to show some preliminary results. The results show good agreement with results from other studies. It is shown that there is a great effect of manufacturing errors on the TEHL behavior, such as temperature, due to the change in load distribution such errors impose. It can be concluded that manufacturing errors of different tolerances have a great impact and that they should therefore be taken into consideration when analyzing gear set behavior and constructing gear sets for new applications.
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| 7. |
- Hjelm, Rikard
(författare)
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Modelling and Simulation of Gearset Behavior : Effects of Manufacturing Errors and Electrification
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to electrification, new demands are imposed on gears regarding e.g., quality, noise, lubrication, and gear ratio.Therefore, a better understanding of gearset meshing and operation is needed. Experiments are valuable tools, butalso tend to be cumbersome and time consuming. Moreover, contact pressure cannot be measured satisfactorily.Thus, a simulation tool is needed. In this thesis, an LTCA simulation tool is developed, which simulates meshingof gears with manufacturing errors (ME). Contact is found from common normal directions together with acompliance condition, instead of using a predetermined load distribution. The LTCA accounts for non-Hertzianpressure, contact outside the nominal line of action (LOA), and tip contact. Contact pressure of gearsets withdifferent combinations of ME tolerances is simulated, i.e., relating deviations in geometry caused by manufacturingto performance of the gearset.The transmission of motion should also be smooth. This is quantified by the transmission error (TE). TE issimulated together with contact pressure. Since they tend to counter-vary, optimization is performed. Designcurves are presented to show how to choose tolerances to simultaneously optimize TE and contact pressure.It is concluded that ME adversely impact gearsets. Too tight tolerances, however, increase the risk of unjustifiedscrapping, which increases production time and cost, material waste, and environmental impact. To avoid this, it issuggested to use tip contact threshold torque as a single metric to assess ME, i.e., basing assessment on performanceinstead of only geometry. The feasibility of the method is shown in a case study, where some scrapping is shownto be unjustified.To account for lubrication, a thermal elasto-hydrodynamic lubrication (TEHL) method is developed. It findslubricant pressure and temperature by solving the Reynolds equation and the heat equation, and considers varyingviscosity and density, as well as cavitation. Load distribution found from the LTCA is used as input to includeME. Results show that ME also cause an increase in temperature and a decrease in film thickness.Apart from the single gear pairs, a study of a two-stage gear reduction used in an electric vehicle is presented.Two stages open further possibilities for optimization. This is done by finding the optimum dog leg angle bymeans of the lowest reaction forces, which in turn allows for smaller bearings. The decreased enclosed volume ofthe gearset also results in a lower housing mass. Both propulsion and regenerative braking are accounted for
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| 8. |
- Hjelm, Rikard, et al.
(författare)
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Reducing scrapping of gears by assessment of tip contact threshold torque
- 2022
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 236:8, s. 1613-1622
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Tidskriftsartikel (refereegranskat)abstract
- While striving for more competitive products as well as reaching the Global Sustainable Development Goals, automotive powertrain manufacturers increase the demands on gears, which translates to decreased manufacturing error tolerances. Too tight tolerances may, however, counteract the goal if it leads to increased material and energy consumption due to unjustified scrapping. This paper presents a method to prevent unjustified scrapping by comparing the severity of different manufacturing error tolerances by means of the tip contact threshold torque. Curve fits are shown to be accurate and helpful to assess the outcome of a produced batch of gears. A case study is made where the method is used with measured data from the industry. It can be concluded from the investigation that considerable amounts of scrapping can be avoided by consideration of the threshold torque.
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| 9. |
- Hjelm, Rikard, et al.
(författare)
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Ultrafine particle emissions from dry clutches : number concentration, size distribution and chemical composition
- 2024
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 4:1, s. 35-42
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Tidskriftsartikel (refereegranskat)abstract
- Non-exhaust sources, such as brakes, tyres, roads, and clutches, emit a large portion of airborne particles in road transportation, from ultrafine to coarse sizes. While airborne wear particle emissions from brakes and road-tyre contacts have been studied extensively, emissions from clutches have been overlooked. A preliminary study using a novel test rig has indicated that dry clutches also emit airborne wear particles. This paper presents a multi-method for the assessment of ultrafine particles from dry clutches regarding the number concentration, size distribution and chemical composition. The results show that ultrafine particles are emitted both during run-in and at the steady state, featuring a bi-modal size distribution. Elementary analysis shows that the particles consist of several elements, predominately iron, silicon, and sulfur. It can be concluded from this study that ultrafine particles are always generated when the clutch is operated. Clutches in automobiles are shown to produce ultrafine particles, consisting of several metallic elements, which become airborne.
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| 10. |
- Radon, Anita, et al.
(författare)
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What happens when retail meets research? : Special session
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- special session InformationWe are witnessing the beginning of a seismic shift in retail due to digitalization. However, what is meant by digitalization is less clear. Sometimes it is understood as means for automatization and sometimes it is regarded as equal to e-commerce. Sometimes digitalization is considered being both automatization and e-commerce trough new technology. In recent years there has been an increase in Internet and mobile devise usage within the retail sector and e-commerce is growing, encompassing both large and small retailers. Digital tools such as, new applications are developing rapidly in order to search for information about products based on price, health, environmental and ethical considerations, and also to facilitate payments. Also the fixed store settings are changing due to digitalization and at an overall level; digitalization will lead to existing business models being reviewed, challenged and ultimately changed. More specifically, digitalization has consequences for all parts of the physical stores including customer interface, knowledge creation, sustainability performance and logistics. As with all major shifts, digitalization comprises both opportunities and challenges for retail firms and employees, and these needs to be empirically studied and systematically analysed. The Swedish Institute for Innovative Retailing at University of Borås is a research centre with the aim of identifying and analysing emerging trends that digitalization brings for the retail industry.
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