The use of torque converters in connection with transmissions is well known in the prior art. In some vehicles, usually automobiles, the torque converter is part and parcel of the transmission, whereas in other vehicles, e.g., mining vehicles, the torque converter is a separate stand-alone system. That is, these latter kinds of torque converters are mounted directly to the engine casing and flywheel and they transmit the output torque to the transmission as a separate entity via a drive shaft.
In general, a torque converter input is mounted directly to the engine housing and connected to the engine flywheel. The output shaft is connected to the transmission by means of a drive shaft. The torque converter transmits the engine torque to the transmission and ultimately to the drive wheels. The role of a torque converter can be summarized as: (1) being able to multiply torque generated by the engine, (2) serving as an automatic clutch to transmit engine torque to the transmission; (3) absorbing torsional vibration of the engine and drive train; (4), smoothing out engine rotation, and (5) driving the oil pumps of the hydraulic system.
FIG. 1 shows a schematic drawing of a particular torque converter system, which is designated by the reference numeral 10. The system includes the torque converter 1, lockup clutch 3, a torque converter inlet designated by the reference numeral 5. The inlet 5 can include a charging inlet filter 6 and an inlet relief valve 7. The torque converter also includes an outlet relief valve 9. Other components include a torque converter outlet screen 11, water to oil cooler 13, a pump suction manifold 15, and a charging pump 17. A sump 19 is also provided that contains the pump suction manifold 15 and a circuit using a magnetic screen 21, whose outlet 23 is in communication with the pump suction manifold 15. The water to oil cooler 13 uses cooling water from source 25, e.g., a radiator of the vehicle having the torque converter. The cooling water passes through the radiator of the water to oil cooler 13 and returns to the cooling system of the vehicle via line 26.
In operation, charge oil is pumped out of the torque converter sump 19 and introduced to the impeller, turbine, and stator cavity of the torque converter 1. The impeller is an integral part of the torque converter casing and has many curved vanes that are radially mounted inside; a guide ring is installed on the inner edges of the vanes to provide a path for smooth fluid flow. The impeller rotates when the engine is running. The turbine is located inside the torque converter case and is not connected to it. The torque converter output shaft is attached by a spline hub to the turbine. Many cupped vanes are attached to the turbine. When the charge oil is introduced and thrust from the rotating impeller vanes, it is caught in the cupped vanes of the turbine and torque is transferred to the torque converter output shaft, turning it in the same direction as the engine crankshaft. The stator is located between the impeller and the turbine and catches the oil from the turbine and redirects it to the back side of the impeller; thus the torque output of the torque converter is multiplied. As these parts of a torque converter are well known, there is no need for their precise illustration to understand how the torque converter functions.
In a further description of the operation of the torque converter, the oil exiting the charging pump 17 passes through the inlet 5, i.e., the charging inlet filter 6 and inlet relief valve 7 to the torque converter 1. Oil exiting the torque converter as 27 passes through the outlet relief valve 9, through the outlet screen 11 and to the water to oil cooler 13. The cooled oil is then directed to the pump suction manifold 15, wherein it can be recirculated using the magnetic screen 21 and directed back to an inlet of the charging pump 17.
The torque converter also includes a lockup clutch 3. The lockup clutch directly links the output of the engine to the transmission, thus bypassing the torque converter. The system 10 includes a control valve 4 that receives a lockup signal from the transmission. This signal causes the lockup clutch to operate so that the vehicle is in lockup condition and the torque converter function is bypassed.
The action of redirecting the charge oil by the stator, while increasing torque output significantly at a lower speed also creates a significant loss component which manifests as heat added to the charge oil. The charge oil is expelled from the impeller and exits the torque converter to the water-oil cooler 13 which carries only part of this heat component to the engine radiator to be expelled. This heat release is adequate to provide a high torque start of short duration to assist initial vehicle motion, but continual operation of the vehicle in a high torque condition is not possible without over heating the charge oil and rendering the torque converter inoperative. This is particularly so when prime movers or mining vehicles are tasked to haul heavy equipment using a lowboy trailer.
Often times, the lowboy trailers are hauled to and from a particular site in a mining operation and experience grades during the hauling. As the speed of the lowboy trailers is very low due to the weight of the equipment being hauled and a grade that the vehicle traverses, a prime mover would have to operate for an extended period of time along such a grade and current systems do not permit this kind of low speed continual operation for the torque converter. The safe time on grade allowed, depends on the speed range of the vehicle, and some vehicles will go to a lock up condition at approximately 5 mph. The slower the speed of the torque converter output shaft and hence the vehicle, the greater the heat component produced in during torque converter operation.
Therefore, there is a need in the industry, particularly when hauling equipment using lowboy trailers, to improve the performance of the prime movers in these applications. That is, the design of torque converters in these types of vehicle does not allow the for hauling lowboy trailers over steep grades as too much heat is generated during the torque converter operation and the vehicles will just stall out. These prior art torque converters just cannot operate for a continual and extended period of time.
Therefore, a need exists to improve vehicles that encounter the conditions described above, especially prime movers hauling heavy mining equipment.