Abstract: The invention relates to a method of control fan speed in a fan speed control system having a cooling fan driven by a motor, a motor driver for driving the motor at a speed corresponding to a fan speed control signal, and an electronic control unit (ECU) for generating the fan speed control signal. The method includes generating a fan speed control signal and communicating the fan speed control signal to the motor driver so that the motor driver drives the motor at a speed corresponding to the fan speed control signal. If the fan speed control signal is at a level below a noisy fan speed range, then the ECU maintains the fan speed control signal below the noisy fan speed range until the ECU commands a fan speed above the noisy fan speed range. If the fan speed control signal is at a level above the noisy fan speed range, then the ECU maintains the fan speed control signal at a level above the noisy fan speed range until the ECU commands a fan speed below the noisy fan speed range.

Abstract: A resonator attenuates sound waves at first and second frequencies. The resonator includes a first tube, and a second tube received within the first tube. Both tubes have an open end and a closed end. The first tube has an axial length which is longer than the axial length of the second tube. The first tube attenuates sound waves at the first frequency and the second tube attenuates sound waves at the second frequency. The second tube has an outer wall which engages an inner wall of the first tube. The open end of the second tube is surrounded by the open end of the first tube. The open end of the first tube is attached to an engine air intake conduit. The conduit communicates air from a charge air cooler to an engine intake manifold.

Abstract: A vehicle cab noise suppressing system includes a cab interior panel having an opening exposed to acoustic noise in the cab, an acoustic resonator chamber, and a conduit communicating the resonator chamber to the opening. The resonator chamber is formed by a plurality of walls which are spaced apart from the interior panel and which are formed by a second panel. A third panel cooperates with the walls to enclose the resonator chamber. The chamber volume and the diameter and length of the conduit are chosen so as to acoustically tune the chamber to a noise frequency in the cab and thereby reduce noise in the cab.