A unified prediction method for smooth and micro-fin tube condensation performance
- Authors: Liebenberg, Leon
- Date: 2009-01-22T05:36:54Z
- Subjects: Heat transmission , Heat exchangers , Condensation , Refrigerants
- Type: Thesis
- Identifier: uj:14813 , http://hdl.handle.net/10210/1939
- Description: D.Ing.
- Full Text:
- Authors: Liebenberg, Leon
- Date: 2009-01-22T05:36:54Z
- Subjects: Heat transmission , Heat exchangers , Condensation , Refrigerants
- Type: Thesis
- Identifier: uj:14813 , http://hdl.handle.net/10210/1939
- Description: D.Ing.
- Full Text:
Dynamic hydromachine control
- Authors: Liebenberg, Leon
- Date: 1990
- Subjects: Machinery, Dynamics of. , Machine design.
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/16078 , uj:15736
- Description: Abstract: A Dynamic Hydromachine Control concept is presented here with specific application as a specialized transmission for a heavy vehicle, which would provide such a vehicle with good mobility and good ride and handling characteristics as well as the provision of a large torque/speed range which is essential for multi purpose vehicles. Dynamic Hydromachine Control is a term given to a hydrostatic transmission which is subjected to both primary unit dynamic pressure control and secondary unit dynamic speed control, so as to obtain an extremely versatile hydrostatic transmission with unique characteristics. The Dynamic Hydromachine Control concept is realized by a digital Transmission Control Computer and analogue controllers, which interpret the operator/driver inputs and generate control signals for the hydromachines according to a Control Law, which is petrol engine speed dependent. This control strategy ensures that the petrol engine cannot stall (nor overspeed for long periods) and it would also provide a vehicle with handling characteristics similar to those of a conventional vehicle with an automatic transmission. The Control Law may be operated in three main modes, namely those of normal differential action (with limited wheel slip control capability), differential lock action or forced steering action. The Dynamic Hydromachine Control concept has been evaluated on an experimental power train, the hydrostatic transmission of which is to be directly implemented in a technology demonstrator vehicle (at a later stage of the research program). The hydromachines have been dimensioned (in terms of torque and speed) so as to fulfil the functional requirements of the eventual technology demonstrator vehicle. No—load characterisation tests as well as vehicle traction simulation tests were performed on the experimental hydrostatic transmission. It is shown that the system pressure, the high pressure accumulator, and the inertial loads, all have significant influences on the overall dynamic response of the system. The high pressure accumulator which is normally included in a hydraulic circuit where secondary unit speed control is performed, has been found to be redundant due to the fast and effective dynamic pressure control which is exercised. It is however this controlled variation of system pressure together with the absorbing effect of the high pressure accumulator, which cause pressure oscillations and possible system instability, thus providing further motivation for the omission of the high pressure accumulator from the final hydraulic circuit which is to be implemented in the technology demonstrator vehicle. Apart from these findings, the experimental results prove that the different operational modes of the Control Law, operate successfully under various simulated traction load conditions, thus validating the use of the Dynamic Hydromachine Control concept for multi wheeled heavy vehicles. , M. Ing. (Meg)
- Full Text:
- Authors: Liebenberg, Leon
- Date: 1990
- Subjects: Machinery, Dynamics of. , Machine design.
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/16078 , uj:15736
- Description: Abstract: A Dynamic Hydromachine Control concept is presented here with specific application as a specialized transmission for a heavy vehicle, which would provide such a vehicle with good mobility and good ride and handling characteristics as well as the provision of a large torque/speed range which is essential for multi purpose vehicles. Dynamic Hydromachine Control is a term given to a hydrostatic transmission which is subjected to both primary unit dynamic pressure control and secondary unit dynamic speed control, so as to obtain an extremely versatile hydrostatic transmission with unique characteristics. The Dynamic Hydromachine Control concept is realized by a digital Transmission Control Computer and analogue controllers, which interpret the operator/driver inputs and generate control signals for the hydromachines according to a Control Law, which is petrol engine speed dependent. This control strategy ensures that the petrol engine cannot stall (nor overspeed for long periods) and it would also provide a vehicle with handling characteristics similar to those of a conventional vehicle with an automatic transmission. The Control Law may be operated in three main modes, namely those of normal differential action (with limited wheel slip control capability), differential lock action or forced steering action. The Dynamic Hydromachine Control concept has been evaluated on an experimental power train, the hydrostatic transmission of which is to be directly implemented in a technology demonstrator vehicle (at a later stage of the research program). The hydromachines have been dimensioned (in terms of torque and speed) so as to fulfil the functional requirements of the eventual technology demonstrator vehicle. No—load characterisation tests as well as vehicle traction simulation tests were performed on the experimental hydrostatic transmission. It is shown that the system pressure, the high pressure accumulator, and the inertial loads, all have significant influences on the overall dynamic response of the system. The high pressure accumulator which is normally included in a hydraulic circuit where secondary unit speed control is performed, has been found to be redundant due to the fast and effective dynamic pressure control which is exercised. It is however this controlled variation of system pressure together with the absorbing effect of the high pressure accumulator, which cause pressure oscillations and possible system instability, thus providing further motivation for the omission of the high pressure accumulator from the final hydraulic circuit which is to be implemented in the technology demonstrator vehicle. Apart from these findings, the experimental results prove that the different operational modes of the Control Law, operate successfully under various simulated traction load conditions, thus validating the use of the Dynamic Hydromachine Control concept for multi wheeled heavy vehicles. , M. Ing. (Meg)
- Full Text:
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