Fluid-borne noise suppression in an automotive power steering system
A method of dampening fluid-borne noise in an automotive power steering system in accordance with a presently preferred embodiment of the invention contemplates provision of a power steering fluid hose having a laminated inner tube surrounded by a reinforcing outer tube. The inner tube has a resilient inner layer with a radial thickness T 1 and a resilient outer layer with a radial thickness T 2 . The inner layer is softer than the outer layer and is bonded by vulcanization to the outer layer. The radial thicknesses T 1 and T 2 have a ratio selected to dampen fluid-borne noise within a preselected frequency range by elastic expansion of the inner and outer layers.
1. A method of using a power steering fluid hose for dampening fluid-borne noise in automotive power steering system which comprises the steps of:
(a) directing power steering fluid through a power steering fluid hose having a laminated inner tube surrounded by a reinforcing outer tube,
(b) selecting the materials and radial thickness dimensions of said laminated inner tube to provide a resilient inner layer having good noise dampening properties with a radial thickness T 1 and a resilient outer layer with a radial thickness T 2 and having lesser noise dampening characteristics than said inner layer but capable of providing hoop strength reinforcement under adverse high temperature conditions,
(c) selecting said inner layer material to have a softer durometer value than said outer layer
(d) bonding said inner layer by vulcanization to said outer layer, and
(e) selecting by empirical determination a ratio of said radial thicknesses T 1 and T 2 found to maximize dampening of fluid-borne noise in said system within a preselected frequency range by elastic radial expansion of said inner and outer layers.
2. The method set forth in claim 1 wherein said ratio is in the range of 30:70 to 70:30.
3. The method of claim 2 wherein said inner layer has a hardness in the range of 70 to 80 durometer, wherein said preselected frequency range is 300 to 400 Hz and wherein said inner layer of said inner tube is of ethylene/acrylic elastomeric material and said outer layer of said inner tube is of peroxide-vulcanized acrylonitrile-butadiene copolymer rubber.
4. The method set forth in claim 1 wherein said inner layer has a hardness in the range of 70 to 80 diameter durometer.
5. The method set forth in claim 1 wherein said preselected frequency range is 300 to 400 Hz.
6. The method set forth in claim 1 wherein said inner layer of said inner tube is of ethylene/acrylic elastomeric material, and said outer layer of said inner tube is of peroxide-vulcanized acrylonitrile-butadiene copolymer rubber.
7. A method of making a power steering pressure hose having a predetermined fluid-borne noise dampening characteristics, which comprises the steps of:
(a) providing a laminated inner tube having an inner layer with a radial thickness T 1 and an outer layer with a radial thickness T 2 , said inner layer having a hardness in the range of about 70 to 80 durometer, and said radial thickness T 1 having a ratio to said outer thickness T 2 in the range of about 30:70 to 70:30,
(b) surrounding said inner tube with an outer reinforcing tube and
(c) selecting by empirical determination a ratio of said radial thicknesses within said range to maximize dampening of fluid-borne noise by elastic radial expansion of said inner and outer layers.