Active muffler with dynamic tuning

• US 5,060,271 A
• Filed: 05/04/1990
• Issued: 10/22/1991
• Est. Priority Date: 05/04/1990
• Status: Expired due to Fees

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Geddes, Earl R.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/519,389
• Time in Patent Office: 536 Days
• Field of Search: 381/71, 181/206, 181/207
• US Class Current: 381/71.5
• CPC Class Codes: F01N 1/065 by using an active noise source, e.g. speakers
• CPC Class Codes: F02B 27/04 in exhaust systems only, e.g. for sucking-off combustion gases
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A method and apparatus for muffling motor vehicle engine noise comprises conventional noise attenuation apparatus and techniques as well as a tuning circuit for delivering separate signal outputs to at least two transducers separated along the length of the exhaust conduit. A spacing between the transducers corresponds to the range of tuned exhaust lengths required at various engine speeds within the operating range of the motor vehicle engine. The tuning circuit varies the strength of the signal delivered to each of the transducers to vary the cancellation point within the conduit so as to vary the effective length of the conduit in a manner that maintains a minimum or negative pressure pulse at the valve exhaust port and aids in the exhaustion of combustion gases from the cylinder. As a result, engine performance is improved throughout the operating range of the motor vehicle engine.

Claims

1. A dynamically tuned exhaust system for a motor vehicle exhaust conduit having an inlet and an outlet, said system comprising:

a sensor for generating a signal representative of sound pressure pulses from a source through a conduit;

a first transducer fixed at a first position along said conduit;

a second transducer fixed at a second position spaced from said first position;

an electronic controller for selectively driving said first and second transducers in response to said sensor signal and producing an output pulse having a phase opposite to said sound pressure pulse at said first and second positions, and including means for variably driving said first transducer and second transducer to control the effective cancellation point along said conduit as the frequency of said sound pressure pulses changes with engine speed by inducing a minimum pressure at the conduit inlet throughout the engine speed range.

2. The invention as defined in claim 1 wherein said means for variably driving comprises means for proportionally varying the amplitude of the signals delivered to said first and second transducers.

3. The invention as defined in claim 1 wherein said means for variably driving comprises means for simulating a standing wave generated in a tuned exhaust conduit.

4. The invention as defined in claim 3 wherein said effective cancellation point is upstream of said first and second transducers.

5. The invention as defined in claim 1 wherein the source is a motor vehicle engine.

6. A method for dynamically tuning a motor vehicle exhaust conduit with an active attenuation system for sound pressure pulses, said conduit having an inlet and an outlet comprising:

actively attenuating said sound pressure pulses by generating a cancellation signal at a first effective conduit location along said conduit for a first predetermined sound frequency of said sound pressure pulses corresponding to a first engine RPM limit;

actively attenuating said sound pressure pulses by generating a cancellation signal at a second effective conduit location for a second predetermined sound frequency of said sound pressure pulses corresponding to a second engine RPM limit; and

actively attenuating said sound pressure pulses by controlling the effective conduit location between said first and second effective conduit locations by generating a first proportional cancellation signal at a first transducer location, and a second proportional cancellation signal at a second transducer location when said sound pressure pulses are at sound frequencies intermediate said first predetermined sound frequency and said second predetermined sound frequency, to induce a minimum pressure at the conduit inlet throughout the engine RPM range.

7. A method for dynamically tuning a combustion engine exhaust conduit comprising:

positioning first and second transducers downstream of a sound pressure input at a distance L2-L1 from each other, where L2-L1 is greater than one-sixteenth of the wavelength of a highest frequency of sound pressure related to engine speed and less than one-fourth the wavelength of a lowest frequency, where L2 is of sound pressure related to engine speed distance beyond a variable distance LT from the sound pressure input a upstream of said first transducer and L1 is the distance beyond said distance LT from the sound pressure input to said second transducer;

variably driving said first and second transducers with an active attenuation signal proportional to the amplitude of the sound pressure input to cancel the sound pressure pulses downstream of said transducers and tuning said signal to control distance LT as a function of engine speed to induce a minimum pressure pulse in a standing wave induced upstream of said transducers.