Intake sound reduction device for internal combustion engine includes an elastic member formed into substantially cylindrical shape and having an open base end, a top end sealed by an end surface wall and a bellows circumferential wall; a base plate retaining base end of elastic member; and a communication pipe whose one end is connected to base plate so that a volume chamber formed inside elastic member communicates with an intake passage of the engine. Intake sound reduction device has first resonance system formed by expansion and contraction in axial direction of elastic member and second resonance system formed by film-vibration of end surface wall. When either one of resonance frequencies of the first and second resonance systems is primary resonance frequency and the other is secondary resonance frequency, the primary resonance frequency is set to 30200 Hz and the secondary resonance frequency is set to 50300 Hz.

Present embodiments provide a disruptive air flow assembly which connects to a vacuum line and utilizes a valve to open and close and thereby vary the vacuum pressure in the vacuum line. This affects air flow into the engine which is utilized for combustion and therefore causes the engine to vary the engine sound by running roughly at a preselected engine speed. A vacuum fitting may house the valve to vary air flow by opening and closing inlets in the fitting. A motor may be utilized to move the valve between the open and closed positions.

A variable noise attenuation element includes at least two tube sections that define an overall tube length that defines a first effective length and associated first peak frequency for noise attenuation, and a valve having a valve member. The valve joins the tube sections together and includes openings that permit communication between the tube sections when the valve is in an open configuration. The valve member operates to close the opening in response to a predetermined vacuum level within the tube sections to define a second tube effective length and associated second peak frequency for attenuation that is less than the overall length. A method of attenuating noise in a vehicle using a passive attenuation arrangement operates a valve disposed between two tube sections to change an effective length of the tube and associated peak frequencies for attenuation in response to an engine operating parameter.

An air cleaner for an internal combustion engine is arranged to reduce intake noise. The air cleaner includes an air cleaner element for cleaning an intake air, and an elastic member for reducing intake noise by utilizing an inside space of the air cleaner. An inside space of the elastic member is in communication with the inside space of the air cleaner through a communication passage. Preferably, a surrounding space formed between the elastic member and a case portion for receiving the elastic member is opened to the outside.

A variable air intake apparatus in accordance with the present invention includes an valve configured to open a through hole formed at a duct body when an engine is driven at a high output to change a path of air introduced into the engine depending on an engine RPM, in which a magnet is mounted on any one of the valve and the duct body and a steel member is mounted on the other one thereof to maintain a state in which the valve closes the through hole, and a buffering member is mounted on any one of the valve and the duct body to prevent generation of hitting sound that is generated when the valve hits the duct body.

Intake sound reduction device for internal combustion engine includes an elastic member formed into substantially cylindrical shape and having an open base end, a top end sealed by an end surface wall and a bellows circumferential wall; a base plate retaining base end of elastic member; and a communication pipe whose one end is connected to base plate so that a volume chamber formed inside elastic member communicates with an intake passage of the engine. Intake sound reduction device has first resonance system formed by expansion and contraction in axial direction of elastic member and second resonance system formed by film-vibration of end surface wall. When either one of resonance frequencies of the first and second resonance systems is primary resonance frequency and the other is secondary resonance frequency, the primary resonance frequency is set to 30200 Hz and the secondary resonance frequency is set to 50300 Hz.

Disclosed herein is an engine intake device for a forklift. The engine intake device for a forklift includes an intake flow path passing through a counterweight of the forklift, and an intake pipe connected to the intake flow path to provide intake air to an engine of the forklift.

Provided is an intake bypass recirculation structure capable of silencing, including: an intake bypass recirculation structure body and a structure-conducted silencing device. An intake bypass recirculation cavity is provided on the intake bypass recirculation structure body. An inlet of the intake bypass recirculation structure and an outlet of the intake bypass recirculation structure that are provided on the intake bypass recirculation structure body are each connected to the intake bypass recirculation cavity. The structure-conducted silencing device is disposed inside the intake bypass recirculation cavity. In this application, during working, noise generated by a compressor is transmitted into the intake bypass recirculation cavity via an inlet of the intake bypass recirculation structure, and transmitted outside via the outlet of the intake bypass recirculation structure.