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Hybrid transmission: design of the electric oil pump
2006 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Hybrid vehicles are a step towards more environmentally friendly way of transportation. This type of vehicles will play an important role in the foreseeable future to decrease the overall dependence on oil reserves but also to reduce the combustion engine's negative impact on e.g. pollution and noise in urban areas. Hybrid propulsion systems can be accomplished in several different ways, but the common idea is to add an electrical motor for additional tractive power. This also gives possibility to recuperate the kinetic energy which is otherwise lost when braking. The hybrid transmission under development uses pressurized oil for gear shifting operations, clutch activation and cooling. Conventional automatic transmissions usually have a hydraulic pump driven by the combustion engine for pressurizing the oil. In the hybrid transmission, oil pressure is necessary also when the combustion engine is not running. In this Master's Thesis a design proposal for an electric oil pump for the transmission are developed. The goal has been to design a pump concept able to operate in all possible driving modes for a hybrid vehicle. The concept was designed considering capacity and pressure requirements, winter temperature performance, efficiency and package space. Three different hydraulic pump concepts has been developed and analyzed. A current transmission oil pump has also been analyzed for reference purposes. The different concepts have been extensively evaluated by methods described by Pahl & Beitz [5]. The chosen concept is a single stage spur gear pump driven by an electric motor. The volume displaced at each revolution is 5cm3 and the output flow can be varied by altering the rotational speed of the electric machine. The output produced by the pump can by an intelligent control system be precisely matched to the flow demanded by the hydraulic system in the transmission. Compared to a conventional transmission pump where the output is constrained to the engine speed, less power is needed because of the demand oriented flow production. A reduction in driving power of up to 46% for a highway cruise cycle can be achieved by incorporating the electro- hydraulic pump concept into a transmission. This corresponds to a total fuel saving of approximately 1.8%. The overall efficiency for the pump concept developed is 85% under optimal operation conditions, for the reference pump, overall efficiency is 64% under the same conditions. Packing size of the proposed design is strongly dependent on electric motor size since the motor is 5 times larger than the actual pump unit. This is due to the cold operation performance of the pump where low temperatures increase viscous friction dramatically and increases torque loss. If the cold operation performance was irrelevant and the motor could be designed for optimum operation conditions, the size of the motor could be reduced by 40%. The complete package including pump and electric motor is however substantially larger than the reference pump design, even if designing for optimum operation conditions.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Automotive transmission, Hybrid, Hydraulics, Oil pumps, Powershift
Keyword [sv]
URN: urn:nbn:se:ltu:diva-45658ISRN: LTU-EX--06/212--SELocal ID: 355e13d1-99c6-48da-964b-4f74706d26b7OAI: diva2:1018955
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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