Air intake plenum for attenuating sound from a marine engine
An intake plenum is for a marine engine, the marine engine having first and second throttle devices for controlling flow of intake air to the marine engine. The intake plenum has an airbox providing an expansion volume, first and second inlets that convey the intake air in parallel to the expansion volume, first and second outlets that convey the intake air in parallel from the expansion volume to the first and second throttle devices, and first and second Helmholtz-style attenuator devices located at the first and second outlets, respectively. Together the first and second inlets, expansion volume, and first and second Helmholtz-style attenuator devices are configured to attenuate different frequencies of sound emanating from the marine engine via the first and second outlets.
1. An intake plenum for a marine engine, the marine engine having first and second throttle devices for controlling flow of intake air to the marine engine, the intake plenum comprising an airbox providing an expansion volume; first and second inlets that convey the intake air in parallel to the expansion volume; first and second outlets that convey the intake air in parallel from the expansion volume to the first and second throttle devices; and first and second Helmholtz-style attenuator devices located at the first and second outlets, respectively, wherein together the first and second inlets, expansion volume, and first and second Helmholtz-style attenuator devices are configured to attenuate different frequencies of sound emanating from the marine engine via the first and second outlets.
2. The intake plenum according to claim 1 , wherein each of the first and second Helmholtz-style attenuator devices comprises an air duct that conveys the intake air, first and second attenuation chambers located alongside the air duct, and first and second pluralities of attenuation holes in the air duct which connect the air duct to the first and second attenuation chambers, respectively.
3. The intake plenum according to claim 2 , wherein the first attenuation chamber has a larger volume than the second attenuation chamber.
4. The intake plenum according to claim 3 , wherein the first plurality of attenuation holes comprises thirteen attenuator holes and wherein the second plurality of attenuation holes comprises four attenuator holes.
5. The intake plenum according to claim 4 , wherein the thirteen attenuator holes are arranged in three columns of attenuator holes and wherein the four attenuator holes are arranged in two columns of attenuator holes.
6. The intake plenum according to claim 2 , wherein the air duct is cylindrical.
7. The intake plenum according to claim 2 , wherein the first and second attenuation chambers are next to each other and share a common wall radially extending from the air duct.
8. The intake chamber according to claim 7 , wherein the first and second attenuation chambers are located on only one side of the air duct.
9. The intake plenum according to claim 2 , further comprising a cover that encloses the first and second attenuation chambers.
10. The intake plenum according to claim 2 , wherein the first and second attenuation chambers of the first Helmholtz-style attenuator device are located next to the first and second attenuation chambers of the second Helmholtz attenuator device.
11. The intake plenum according to claim 10 , further comprising a cover that encloses the first and second attenuation chambers of the first and second Helmholtz-style attenuator devices.
12. The intake plenum according to claim 2 , further comprising a bell mouth that extends from the Helmholtz-style attenuator devices into the expansion volume and funnels the intake air from the expansion volume to the first and second Helmholtz-style attenuator devices.
13. The intake plenum according to claim 12 , wherein the bell mouth comprises a rounded outer perimeter and a sunken inner transition portion having opposing rounded sides that together with the rounded outer perimeter funnel the intake air inwardly towards the first and second Helmholtz-style attenuator devices, respectively.
14. The intake plenum according to claim 1 , wherein the first and second inlets are transversely oriented relative to the first and second outlets.
15. The intake plenum according to claim 14 , further comprising first and second air ducts that extend from the first and second inlets, respectively, into the expansion volume.
16. The intake plenum according to claim 15 , wherein the first and second air ducts are rectangular having rounded corners.
17. The intake plenum according to claim 15 , wherein each of the first and second air ducts has and inlet end that receives the intake air, an outlet end that discharges the intake air to the expansion volume, and an elongated body that extends from the inlet end to the outlet end.
18. The intake plenum according to claim 15 , wherein the airbox has a first elongated portion extending generally parallel to the first and second air ducts and a second elongated portion that depends from the first elongated portion and extends generally transversely to the first elongated portion.
19. The intake plenum according to claim 18 , wherein the first elongated portion narrows inwardly from the first and second air ducts to the second elongated portion.
20. The intake plenum according to claim 18 , wherein the first and second Helmholtz-style attenuator devices are located in the second elongated portion, and further comprising a bell mouth that funnels the intake air from the expansion volume to both of the first and second Helmholtz-style attenuator devices, wherein the bell mouth facilitates transitioning of the intake air from the first elongated portion to the second elongated portion.