Patent Application
20100143169
The present invention relates generally to engine cooling fans and more particularly to engine cooling fans having a one-way clutch bearing.
Engine cooling fans are common in the engine compartments of automotive vehicles. Some engine cooling fans are now driven by electric motors rather than mechanically driven off of the engine. These engine cooling fans have torsional resonance that can be excited on start-up, shut down, or steady state fan operation by the axial or torsional cogging of the electric motors used to drive them. This may occur at multiple RPM levels of fan blade rotational speed. This resonance may create objectionable noise inside the passenger compartment over a broad range of the fan start-up or shut-down process. The concern is particularly pronounced for engine cooling fans having a diameter of forty-five centimeters and larger because the torsional resonance for these relatively larger fans tends to have a higher amplitude. Some have attempted to overcome this concern by modifying the cooling fan hub, but this may compromise the strength of the fan. Also, material may be removed to reduce the torsional stiffness of the blades, but this may compromise the structure of the blades.
An embodiment contemplates a cooling fan assembly for use in an engine compartment of a vehicle including an electric motor having a motor shaft extending therefrom, a one-way clutch bearing mounted on and rotating with the motor shaft, and a cooling fan. The cooling fan includes a central hub with fan blades extending from the central hub. The central hub engages the one-way clutch bearing such that torque is transmitted from the motor shaft to the central hub in a first direction of rotation and torque is not transmitted from the motor shaft to the central hub in an opposed direction of rotation.
An embodiment contemplates a method of providing torque from an electric motor to a cooling fan in an engine compartment of a vehicle, the method comprising the steps of: activating the electric motor with an electric current to provide torque to a motor shaft in a first rotational direction; providing torque in the first rotational direction from the motor shaft, through a one-way clutch bearing, to the cooling fan to cause rotation of the cooling fan in the first rotational direction; and preventing torque from being transmitted in an opposed rotational direction from the motor shaft, through the one-way clutch bearing, to the cooling fan.
An advantage of an embodiment is that the electric motor torsional input oscillations are decoupled from the torsional mode of the cooling fan, which results in a reduction of start-up and shut-down noise that would otherwise occur due to motor windings exciting the torsional resonance of the cooling fan. This also assures that the structural integrity of the cooling fan is not compromised.
Referring to
The operation of the cooling fan assembly 32 and electric motor 34 will now be discussed. When cooling fan operation is needed, the electric motor 34 is activated. The motor 34 drives the motor shaft 36, which in turn provides a driving torque to the one-way clutch bearing 44. The bearing 44 allows torque in the direction of motor rotation to be transmitted to the cooling fan 37 while preventing torque in the opposite direction to be transmitted. Thus, the motor 34 can drive the fan 37 even though the torque output of the electric motor 34 is partially decoupled from the cooling fan 37. This results in a decoupling of the input forcing function of the cogging of the motor 34 from the torsional resonance of the cooling fan 37. The end result, then, is that the amplitude of the torsional resonance of the cooling fan 37 is reduced, which results in reduced noise transmitted to the passenger compartment 22.
While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
