Browse Topic: Clutches
ABSTRACT
As embedded electronic control systems are increasingly penetrating vehicle subsystems, the designers are faced with a dilemma of providing state of art vehicle features on one hand and ensuring frugal implementation of the same to meet competitive pressures on the other. For embedded software and hardware systems this means adoption of judicious and innovative design choices with reusable building blocks. This paper dwells upon various design aspects of control and monitoring which are frequently used for automotive applications such as feed-forward and proportional integral control, diagnostics for sensor boundary conditions, handling of intermittent faults without causing nuisance to the vehicle users etc.
This paper develops a lumped-parameter multi-plates wet clutch Offset Compound Gear (OCG) transmission dynamics and its thermal model for dual-speed rotorcraft applications with an active clutch slip-speed control. This model includes the Reynolds equation for the clutch oil film thickness, the clutch thermal model, the clutch transferred torques (viscous and asperity torque) and the clutch disengagement model. The wet clutch/OCG transmission system is implemented in Matlab® Simulink™ to manage the upshift clutch temperature rise, which is a main issue need to handle for a dual-speed helicopter transmission. Here, the clutch temperature rise is treated by injecting a certain amount of coolant during engagement so that the temperature rise for the wet clutch is much lower than that of an dry clutch. In order to transfer a required torque using the available power, the sizing of the wet clutch could be evaluated via the developed wet clutch/OCG transmission model. This study shows that the temperature rise drops as the wet clutch oil flow rate increases adding extra weights compared with the dry clutch. The simulation also captures a phenomenon that a larger clutch engagement pressure might be required for the wet clutch to transfer the same torque since the wet clutch oil viscosity drops as the oil temperature increases during the clutch engagement.
This paper explores the effects of maneuvering and gust loads on the drive system and flight dynamic response of a single main rotor helicopter equipped with a two speed dual clutch transmission. The authors demonstrate that performing upshifts during certain maneuvers can significantly reduce the transmitted clutch frictional torques and the resulting clutch pack temperature rise during gear changes. For example, compared with an upshift in level flight, performing a 8° pitch-up maneuver reduced peak clutch frictional power dissipation by 63% (from 455 Hp down to 169 Hp) and reduced total upshift time by 37% (from 5 seconds down to 3 seconds). This results in an 83% reduction in total heat energy dissipated by the clutch during the upshift. Since the design of the clutch pack mass is directly proportional to the heat dissipation requirements, this new (Maneuver Assisted Shifting) MAS technique could enable significant weight savings and clutch wear reduction in helicopter two-speed transmissions.
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