| 1. |
- Holgerson, Mikael
(författare)
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Apparatus for measurement of engagement characteristics of a wet clutch
- 1997
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 213:1-2, s. 140-147
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Tidskriftsartikel (refereegranskat)abstract
- The problem of obtaining smooth gear changing whilst maintaining long life of wet clutches in automatic transmissions demands more knowledge about their behaviour. Experimental and theoretical studies on the engagement of a wet clutch have been carried out. A wet clutch test rig which can apply a drive torque during engagement was developed. The apparatus could also vary the sliding velocity, inertia, force rate, and lubrication. Measured output data included normal force, brake torque, sliding velocity and temperature over time. The input parameters and output characteristics obtained were similar to those in automatic transmissions used in cars. The friction characteristics as well as power and temperature were investigated. A simple model was developed to estimate the engagement performance which gave a good approximation of the performance measured in the tests. The friction is high in the beginning and end of the engagement cycle and lower inbetween. There is a torque peak just before the clutch stops owing to friction characteristics. The maximum developed power occurs at about half of the engagement time, while the maximum temperature is just before clutch stop
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| 2. |
- Holgerson, Mikael
(författare)
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Developments in tribological materials in the next millennium
- 2000
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Ingår i: TriboTest Journal. - : Wiley. - 1354-4063. ; 7:2, s. 155-165
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Tidskriftsartikel (refereegranskat)abstract
- The materials needed for tribological contact systems in the next millennium will depend on the trend and pace of technological development, and environmental policy. The latter will certainly demand lower pollution and energy consumption, so materials should preferably be light, and work in most friction systems without lubrication, but with low friction, and no wear. The following properties, or requirements, of future tribomaterials can be conceived of in such a scenario: it seems likely that micro-mechanical systems will achieve great importance, but silicon must be either surface protected or replaced by an optimised material; light metal alloys must be conditioned by surface treatment or coating; coatings must be improved, e.g., by nanomaterials; ceramic materials sintered at low temperatures from nano-powders will be ductile and machinable, but retain the other beneficial properties of ceramics; and ultra-precise surface finishing of materials may lead to nearly friction-free and wearproof tribocontacts.
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| 3. |
- Holgerson, Mikael, et al.
(författare)
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Engagement behaviour of a paper-based wet clutch Part 1: Influence of drive torque
- 1999
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Ingår i: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering. - : SAGE Publications. - 0954-4070 .- 2041-2991. ; 213:4, s. 341-348
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Tidskriftsartikel (refereegranskat)abstract
- Owing to increasing demands when designing wet clutches for automatic transmissions, more knowledge about their behaviour is needed. In cars with power shifting automatic transmissions, an engine torque is continuously transmitted through the gear box. Most experimental and theoretical work concerning investigations of wet clutches today uses the inertia type of test apparatus, e.g. the SAE test machine 2. However, this type of test machine has no possibility of investigating the influence of a drive torque from the power supply. In order to investigate the influence of drive torque on wet clutch engagements, a new type of apparatus was built, which can operate with different combinations of inertia and drive torque. This apparatus can perform engagements more similar to those in automatic transmissions. The aim of this paper was to compare experimental outputs obtained using these principles of testing, concerning the influence of drive torque. It was found that the friction characteristics of wet clutches are independent of how the input energy is produced. This means that friction can be investigated with both principles. It was also found that an apparatus using only inertia gives shorter engagement times and higher temperatures than an apparatus including a drive torque at the same level of input energy. This can be explained by different power characteristics. Therefore, when investigating temperatures of wet clutch engagements, one must be careful when translating the results into reality.
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| 4. |
- Holgerson, Mikael, et al.
(författare)
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Engagement behaviour of a paper-based wet clutch Part 2: Influence of temperature
- 1999
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Ingår i: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering. - : SAGE Publications. - 0954-4070 .- 2041-2991. ; 213:5, s. 449-455
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Tidskriftsartikel (refereegranskat)abstract
- To increase comfort, performance and fuel economy, a more careful optimization of automatic transmissions is needed. Of special interest is how the temperature influences the engagement characteristics. In order to increase the level of knowledge in this area, a wet clutch test rig including a drive torque and inertia was used. The temperature and the developed energy were varied in order to investigate their influence on the characteristics of an engagement. As a consequence the influence of instant temperature, maximum temperature and instant normal force was also studied. Some of the most important conclusions of the investigation are that both the dynamic and static friction coefficients slightly decrease and the engagement time increases with increasing temperature. It was also found that the static and dynamic friction coefficients are not influenced by energy if the instant temperature is the same. An important parameter that describes the risk of stick-slip is the quotient between the static and dynamic friction. It was found that this quotient decreases with increasing temperature, and thus the risk of stick-slip is also supposed to decrease.
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| 5. |
- Holgerson, Mikael
(författare)
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Friction and temperature characteristics of wet clutch engagement
- 1997
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- För att erhålla mjukare växlingsförlopp och samtidigt få lång livslängd på våta kopplingar i automatväxellådor krävs förbättrad konstruktion. För att förbättra konstruktionen behövs mer kunskap om inkopplingsförloppet av våta kopplingar. En testrigg för att undersöka inkopplingsförloppet har byggts. Driftsparametrar och inkopplingskarakteristik efterliknar förhållanden i en verklig automatväxellåda. I apparaten kan hastighet, drivmoment, tröghet, pålastningshastighet och oljetillförsel varieras. Normalkraft, bromsmoment, glidhastighet och temperatur mäts som funktion av tiden. Experimentella studier av inkopplingsförloppet har utförts. Både friktionskarakteristik och effekt och temperatur har undersökts. Resultaten visar hur en lamellkoppling beter sig under ett inkopplingsförlopp. Inverkan av olika driftsparametrar på inkopplingstid, utvecklad energi, temperaturhöjning med mera har också undersökts. En enkel beräkningsmodell har utvecklats för att simulera inkopplingsförloppet. Modellen överensstämmer väl med mätningarna. Friktionskoefficienten vid inkopplingen av en våt lamell varierar över tiden men beror ej av driftsparametrarna. Förutom friktionen vid medelhastighet som minskar med glidhastighet, drivmoment och tröghet. Temperaturökningen är direkt proportionell mot den utvecklade energin och båda dessa ökas mest av glidhastighet. Drivmoment och pålastningshastighet har störst inverkan på inkopplingstiden.
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| 6. |
- Holgerson, Mikael
(författare)
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Influence of operating conditions on friction and temperature characteristics of a wet clutch engagement
- 2000
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Ingår i: TriboTest Journal. - : Wiley. - 1354-4063. ; 7:2, s. 99-114
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Tidskriftsartikel (refereegranskat)abstract
- To optimise the gear change in automatic transmissions, more knowledge is needed of the engagement behaviour of wet clutches. A factorial design investigation of the engagement of a wet clutch has been carried out. The friction and temperature characteristics have been studied. The experiments were carried out in an apparatus that can vary sliding velocity, drive torque, inertia, force rate, and lubricant flow. The results show how these parameters affect the response data: engagement time, developed energy, temperature rise, maximum torque, maximum power, static friction, dynamic friction, and initial friction. There are interaction effects between some of the input parameters, but they are relatively small. The friction coefficient varies over time but is independent of the input parameters, except for dynamic friction, which decreases with increasing sliding velocity, drive torque, and inertia. The temperature rise was found to be proportional to developed energy and both these were most affected by sliding velocity. The drive torque and force rate have the greatest effect on the engagement time.
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| 7. |
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| 8. |
- Holgerson, Mikael
(författare)
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Optimizing the smoothness and temperatures of a wet clutch engagement through control of the normal force and drive torque
- 2000
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 122:1, s. 119-123
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Tidskriftsartikel (refereegranskat)abstract
- Automatic transmission gear shifts are handled by wet clutches, which determine the smoothness. The clutch face temperatures during the engagements are often an important parameter for the total clutch life. A wet clutch test rig has been used to evaluate how a wet clutch engagement can be improved in terms of smoothness and temperature. This was performed with control based upon knowledge about friction characteristics and dynamic performance. The parameters used for control were the drive torque and the normal force on the clutch. By drive torque shut-off and reduced normal force the torque variations were greatly reduced and the temperature rise was decreased by 37%.
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| 9. |
- Holgerson, Mikael, et al.
(författare)
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Plough and Stretch Losses for Rolling Ball in Grease
- 1997
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Ingår i: Proceedings of the fifth International Symposium on Cold Region Development, Anchorage, Alaska, USA, May 4-10, 1997. - : International Association of Cold Regions Development Studies. ; , s. 629-632
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Konferensbidrag (refereegranskat)
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| 10. |
- Holgerson, Mikael
(författare)
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Wet clutch engagement characteristics
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:3, s. 4-5
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Tidskriftsartikel (refereegranskat)abstract
- A wet clutch test rig has been built to examine the characteristics of engagements of wet clutch plates. Results show that the drive torque has a major effect on the engagement and should therefore be taken into consideration when investigating wet clutch characteristics. Furthermore, it was found that the temperature rise is approximately a linear function of the developed energy, and that the friction coefficient is mainly independent of the operating conditions
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| 11. |
- Holgerson, Mikael
(författare)
-
Wet clutch engagement characteristics
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A wet clutch test rig has been built to examine the engagement characteristics of wet clutch plates. The apparatus is specially designed to include a drive torque. Input and output characteristics of the apparatus are similar to those in automotive automatic transmissions. The research has clarified the effects of operating parameters on the engagement characteristics of a wet clutch. The drive torque has a major effect on the engagement, but the friction coefficient is mainly independent of the operating conditions. The temperature rise is approximately a linear function of the developed energy. Increased temperature extends the engagement time and lowers the torque capacity, due to decreased friction coefficient. A FEM model were developed that describes the dynamic and thermal behaviour of a wet clutch engagement, it includes a drive torque and a two-dimensional heat model. Experiments were made with control of wet clutch engagements to improve temperatures and smoothness.
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| 12. |
- Lingesten, Niklas
(författare)
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Wear behavior of wet clutches
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human civilization is largely based on the transformation of stored chemical energy in the form of fossil fuels into usable work through the use of the combustion engine. In recent years, the awareness of problems such as global warming due to emissions of greenhouse gases and the depletion of fossil fuel reserves has increased. New regulations have been put into place in order to limit these effects and as a result, the efforts made by the automotive industry to limit the emissions and fuel consumption of their products has taken a higher priority. Attempting to minimize power losses is one approach taken, where the knowledge of Tribology is often made use of to lower the fuel consumption. In heavy duty equipment such as wheel loaders and articulated haulers, a large portion of the mechanical power is lost in the transmission. One of the largest contributors to the transmission power losses is the viscous drag in disengaged wet clutches. While the method of reducing these losses are quite clear (e.g. a reduction in clutch size will yield lower losses), the effects of the subsequent increase in power and energy density in clutch engagements are less clear.In this thesis, the effects of increasing the load, i.e. increasing energy input density and power absorption density, on the clutch are investigated. The main concern with increased load on the clutch is the durability of the clutch. In particular, wear of the paper-based friction material lining of the friction discs has been evaluated, as well as the influence of friction material wear on the clutch performance. A new type of test rig has been developed to quantitatively measure the clutch wear throughout a durability test. The wear measured continuously in the test rig correlates well with verification measurements performed while the engagement behavior could be clearly distinguished through the measured torque transfer.At high energy densities and high power levels, a wear phenomenon was observed where the wear rate suddenly changed. During and after the change there was no significant change in engagement characteristics. However, if a clutch which experiences two different wear rates are to be used in a transmission, it is necessary to accurately model the wear so that a compensation can be implemented in the clutch control system. The model was derived in the form of a wear equation where the clutch pack thickness is described in terms of the number of clutch engagements, employing two different wear constants. Total clutch failure due to wear occurs once most of the friction lining has been removed from the friction discs. Up to that point, the clutch is still able to deliver the required torque transfer granted that the increased distance between discs can be compensated for by smart control of the clutch. Heavy duty wet clutches need to be designed in such a way that maximum power and energy density is achieved without reaching the point where the friction lining is totally removed within the required clutch life. The use of the proposed wear model can aid in the design of new wet clutch systems to minimize the clutch's size without compromising the length of its service life.
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| 13. |
- Mansouri, M., et al.
(författare)
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Thermal and dynamic characterization of wet clutch engagement with provision for drive torque
- 2001
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 123:2, s. 213-224
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Tidskriftsartikel (refereegranskat)abstract
- Wet clutches that handle the gearshifts in automatic transmission undergo severe thermal stresses due to the occurrence of large temperature gradients during engagement. To accurately design wet clutches, better models to simulate the engagement process are needed. This work presents a finite element model for simulating wet clutch engagements. The total friction coefficient was used to describe the different lubrication regimes that a wet clutch engagement undergoes. The model also includes provision for drive torque that realistically simulates the engine torque of a car. The results of the simulations are successfully verified by comparison with laboratory experiments on a testrig specially designed to accommodate the drive torque, covering a wide range of typical engagements. Excellent agreement between experiment and simulations is reported in terms of both the dynamics of the engagement and the thermal characteristics. The results are indicative of the utility of the model as a useful engineering tool.
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