Expansion chamber for a brake boost vacuum pump

An expansion chamber for a rotary vane vacuum pump is provided. The expansion chamber is in fluid communication with the discharge side of the rotary vane vacuum pump, such that the expansion chamber attenuates sound as a Helmholtz resonator. The expansion chamber includes an internal volume of between 80 cubic centimeters and 100 cubic centimeters, inclusive, and includes a curved sidewall that extends partially around, and generally conforms to, the exterior of the rotary vane vacuum pump. The expansion chamber also includes a downward extending port, open to the atmosphere, for attachment to a hose in applications in which the expansion chamber is below a water line.

FIELD OF THE INVENTION

The present invention relates to an expansion chamber for attenuating noise from operation of a brake boost vacuum pump.

BACKGROUND OF THE INVENTION

Most modern brake systems include a brake booster to multiply the driver's pedal effort as the brake pedal is depressed. When the brake pedal is depressed, low air pressure within a brake booster assists in depressing a master brake cylinder. More specifically, low air pressure within a vacuum chamber relative to a supply chamber causes forward movement of a diaphragm which, in addition to the brake pedal, pushes forward a brake cylinder piston.

Brake boosters require a source of negative pressure for the vacuum chamber. For gasoline engines, engine manifold airflow is typically used to generate negative pressure. However, many compact vehicles have somewhat smaller engines that lack the additional capacity to provide sufficient negative pressure for a brake booster. In these vehicles, it becomes necessary to provide a dedicated vacuum pump for the brake booster vacuum chamber.

Rotary vane pumps are a known category of vacuum pumps for brake boosters. Rotary vane pumps include rotating vane chambers between adjacent vanes. As the vanes rotate, the vane chambers vary in size to draw air from the inlet side of the pump to the discharge side of the pump, creating a source of negative pressure at the inlet side. The vanes are typically rotated by an electric motor within a pump housing.

Despite the advantages of rotary vane pumps, in some instances rotary vane pumps may generate a perceptible noise at specific frequencies. Accordingly, there remains a continued need to reduce the acoustic output of rotary vane pumps for use with brake boosters and potentially other applications.

SUMMARY OF THE INVENTION

An expansion chamber for reducing the noise output of a rotary vane pump for a brake booster is provided. The expansion chamber generally includes an internal expansion volume in fluid communication with the output of the rotary vane pump, such that a flow path is defined through the expansion chamber, to thereby attenuate sounds caused by high frequency pulsations of the rotary vane pump. The expansion chamber is well suited for use in compact vehicles, including battery electric vehicles, however the expansion chamber can be used in other vehicles as desired.

In accordance with one embodiment, an expansion chamber for an electrically-driven rotary vane vacuum pump is provided. The expansion chamber is in fluid communication with an outlet side of the rotary vane pump, such that the expansion chamber attenuates sound as a Helmholtz resonator. The expansion chamber includes an internal volume of between 80 cubic centimeters and 100 cubic centimeters, inclusive, which was found to significantly attenuate the acoustic output of a rotary vane pump. The expansion chamber includes a curved sidewall that extends partially around, and generally conforms to, the exterior of the rotary vane pump. The expansion chamber includes a downward extending port, open to the atmosphere, for attachment to a hose in applications in which the expansion chamber is below a water line.

In accordance with another embodiment, a brake booster system is provided. The brake booster system includes a rotary vane pump driven by operation of an electric motor, a brake booster coupled to an input side of the rotary vane pump, and an expansion chamber coupled to an output side of the rotary vane pump. The expansion chamber includes an inlet port, an outlet port, and a cavity portion therebetween, the cavity portion being curved to extend partially around the rotary vane pump and defining expansion volume being between 80 cubic centimeters and 100 cubic centimeters, inclusive. The expansion chamber further includes a mounting plate for supporting the rotary vane pump thereon, wherein a cross-sectional area of the expansion volume is greater than a cross-sectional area of the inlet port and a cross-sectional area of the outlet port to attenuate sound from operation of the rotary vane pump. The cavity portion is curved about an axis that is orthogonal to the mounting plate, and the mounting plate extends orthogonally from the cavity portion along a lower portion thereof.

These and other features and advantages of the present invention will become apparent from the following description of an embodiment of the invention, when viewed in accordance with the accompanying drawings and appended claim.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENT

The embodiment disclosed herein includes an expansion chamber coupled to the output of a rotary vane pump for reducing its noise output. As set forth below, the expansion chamber includes an internal expansion volume adapted to function as a Helmholtz resonator. The expansion chamber also includes a mounting plate for the rotary vane pump and includes compact construction that extends partially around the rotary vane pump. Though described herein in connection with compact vehicles, the expansion chamber can be used in other vehicles as desired.

Referring toFIGS. 1 and 2, an expansion chamber for use with a rotary vane vacuum pump in accordance with one embodiment is illustrated and generally designated10. The expansion chamber10includes an inlet port12, a cavity portion14, and an outlet port16. The inlet port12is configured for attachment to the discharge side of a rotary vane vacuum pump. The cavity portion14includes a cross-sectional area that is greater than the cross-sectional area of the inlet port12, such that the cavity portion14is an expansion volume. The expansion volume is optionally 70 cc to 110 cc, inclusive, further optionally 80 cc to 100 cc, inclusive. The outlet port16is open to the atmosphere and includes a rigid tube for optional attachment to an outlet hose. The outlet port16includes a cross-sectional area that is less than the cross-sectional area of the cavity portion14.

More specifically, the cavity portion14is defined by first and second spaced apart curved sidewalls18,20, a top surface19, and a bottom surface21. The first sidewall18includes a concave surface, visible inFIG. 1, and the second sidewall20includes a convex surface, visible inFIG. 2. The internal expansion volume is resultantly curved, following an arc of a circle, optionally between 45 degrees and 90 degrees, inclusive. As also shown inFIG. 2, the second sidewall20can include a plurality of ribs22to improve the structural integrity of the expansion chamber10. A mounting plate24extends orthogonally from the base of the cavity portion14for attachment to a rotary vane vacuum pump (not shown). The expansion volume is curved about an axis Y that is orthogonal to a mounting plate24, the mounting plate24being cantilevered from the cavity portion14for attachment to a rotary vane pump.

In the illustrated embodiment, the expansion chamber10includes a two-piece molded construction. The two-piece construction includes a casing body comprising a lower portion26joined to an upper portion28along an air-tight interface. First and second snap clips30secure the lower portion26to the upper portion28at opposing sides of the cavity portion14. The mounting plate24is integrally joined to the cavity portion14in the current embodiment, being co-molded with the lower portion16. The inlet port12is integrally joined to, and protrudes from, the upper portion28of the casing body, and the outlet port16is integrally joined to, and protrudes from, the lower portion26of the casing body. The outlet portion16is axially offset from the inlet port12, such that the outlet port16is not vertically aligned with the inlet port12. In addition, the outlet port16is sized for attachment to an outlet hose, particularly in embodiments in which the expansion chamber10may be below a water line.

As noted above, the expansion chamber10provides a flow channel for the discharge of compressed air from the discharge side of a rotary vane pump. Referring now toFIG. 3, the inlet side of a rotary vane pump32is in fluid communication with a brake booster34, such that the rotary vane pump32is connected between the brake booster34and the expansion chamber10. The rotary vane pump32includes rotary vanes33and an electrical motor35which receives power from a suitable power supply36. In the current embodiment, the electrical motor35is a DC motor coupled to a DC power supply. During operation, the electrical motor causes the rotary vane pump32to rotate at high speeds, thereby providing a source of negative pressure for the brake booster34and a source of positive pressure for the expansion chamber10.

EXAMPLE

Expansion chambers were developed and tested in accordance with the following example of the present invention, which is intended to be non-limiting.

During operation of a rotary vane pump, pulsations of the internal vanes in combination with the internal motor created a perceptible noise. The noise was detected within the range of 550 Hz to 650 Hz. At a nominal 13V DC voltage, the internal motor operated at 4800 rpm. For a rotary vane pump having eight vanes, each motor revolution was accompanied by eight vane pulsations. The vane pulsations per minute were determined by multiplying the number of vanes (8) by the motor speed (4800 rpm), corresponding to 640 vane pulsations per second or 640 Hz. Using the Helmholtz principle of noise reduction by expanding air in a volume, an internal volume of between 80 cc and 100 cc (inclusive) was found to achieve the desired noise reduction. In particular, favorable noise reductions were achieved with internal volumes of about 92 cc and about 100 cc.

The above description is that of current embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of any claims to the specific elements illustrated or described in connection with this embodiment. Any reference to elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.