Power steering reservoir and cooler

Abstract: A combined power steering hydraulic fluid reservoir and cooling unit (12, 112) includes a housing (14, 114) having a reservoir tank (16, 116) for receiving and collecting hydraulic fluid from a power steering gear (18) and holding the hydraulic fluid in readiness for supply to a hydraulic pump (20). The housing has a heat exchanger (22, 122) with a cooling liquid flow path therethrough in heat transfer relation with the hydraulic fluid, eliminating a hydraulic fluid cooler otherwise connected in series between the power steering gear and the reservoir tank, and eliminating two extra hose connections therefor.

Description: BACKGROUND AND SUMMARY OF THE INVENTION The invention relates to power steering reservoirs, particularly on heavy duty trucks and busses, and the need to dissipate heat within the system, in reduced space and with lower cost. One function of power steering reservoirs on heavy duty trucks and busses is to dissipate heat generated within the system. A larger reservoir is used when additional cooling is required. In some cases, a hydraulic fluid cooler is also required to reduce the operating temperature to an acceptable level. The hydraulic fluid cooling device is typically connected to the return hose between the power steering gear and the reservoir, i.e. a series connection with two additional hose connections. Truck manufacturers have expressed a need for reducing system temperatures. High operating temperatures cause seals, hoses, and hydraulic fluid to break down and wear out more quickly. A standard off the shelf hydraulic oil cooler will significantly reduce system temperatures. However, the added cost and installation time is objectionable. Truck aerodynamic improvements are limiting the amount of air flow through the engine compartment. This reduction in air flow also reduces the cooling efficiency of the power steering reservoir. Sloping front hoods are reducing under hood space, which makes larger reservoirs impractical. US-A-4 809 745 discloses an oil container for the supply of hydraulic power circuits according to the preamble of claim 1 which includes means for cooling oil returned to the container. Embodiments of the present invention address and solve the above-noted need in a particularly simple and cost effective manner. The embodiments enable elimination of a hydraulic cooler otherwise connected in series between the power steering gear and the reservoir, and eliminate the two extra hose connections thereof. Aspects of the invention are set out in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of a power steering system. Fig. 2 is a side view partially in section of a combined power steering hydraulic fluid reservoir and cooling unit. Fig. 3 is a sectional view taken along line 3-3 of Fig. 2. Fig. 4 is a sectional view of a portion of the structure of Fig. 2. Fig. 5 is a sectional view taken along line 5-5 of Fig. 4. Fig. 6 is a view like Fig. 1 and shows a similar power steering system. Fig. 7 is a view like Fig. 2 and shows a similar unit, not claimed here. Fig. 8 is a sectional view taken along line 8-8 of Fig. 7. Fig. 9 is a sectional view taken along line 9-9 of Fig. 7. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a combined power steering hydraulic fluid reservoir and cooling unit 12 including a housing 14 having a reservoir tank 16 for receiving and collecting hydraulic fluid from a power steering gear 18 and holding the hydraulic fluid in readiness for supply to a hydraulic pump 20. The housing has a heat exchanger 22 with a cooling liquid flow path therethrough in heat transfer relation with the hydraulic fluid, eliminating a hydraulic fluid cooler otherwise connected in series between power steering gear 18 and tank 16, and eliminating the two extra hose connections therefor. Housing 14 has a first hose connection 24 providing a hydraulic fluid inlet, a second hose connection 26 providing a hydraulic fluid outlet, a third hose connection 28 providing a cooling liquid inlet, and a fourth hose connection 30 providing a cooling liquid outlet. The housing may include a further hydraulic fluid inlet 32 as a bypass receiving excess flow from pump 20. Fig. 2 shows reservoir tank 14, which is Nelson Industries Part No. 94131A, duly modified. The tank is a cylindrical canister extending axially along a vertical axis 34 between distally opposite lower and upper axial ends 36 and 38. Extending through lower axial end 36 is heat exchanger 22, provided by a Serck Part No. 31002-97-AA01. Heat exchanger 22 extends axially along axis 34 through axial end 36 of reservoir tank 16. The cooling liquid flow path through heat exchanger 22 is in heat transfer relation with hydraulic fluid in tank 16. Heat exchanger 22 has a side wall 40 extending axially between distally opposite lower and upper end walls 42 and 44. Cooling liquid inlet 28 and cooling liquid outlet 30 both extend axially through lower end wall 42. Hydraulic fluid inlet 24 extends radially through side wall 40. Side wall 40 of heat exchanger 22 extends axially through lower axial end 36 of reservoir tank 16. Side wall 40 of heat exchanger 22 has a first portion 46 exterior to reservoir tank 16, and a second portion 48 interior to reservoir tank 16. Hydraulic fluid inlet 24 extends radially through first portion 46 of side wall 40. Second portion 48 of side wall 40 has a pair of openings 50, 52, Figs. 2, 4 and 5, therethrough passing hydraulic fluid into lower portion 54 of tank 16 below divider wall 55. Coolant liquid flows from heat exchanger inlet 28 into lower entry plenum 56, Fig. 4, then upwardly through a plurality of transfer tubes 58 to upper plenum 60 then downwardly through a plurality of transfer tubes 62 to lower exit plenum 64 then to cooling liquid outlet 30. Entrance and exit plenums 56 and 64 are separated by dividing wall 66. Hydraulic fluid flows from hydraulic fluid inlet 24 into heat exchanger 22 and is directed around tubes 62, 58 in a tortuous flow path 68 by directional divider walls 70, 72, and then flows through openings 50, 52 into lower portion 54 of tank 16. The hydraulic fluid then flows upwardly as shown at arrow 74, Fig. 2, through central standpipe 76 and then radially outwardly through openings such as 78 therein, and then through filter 80 to hydraulic fluid outlet 26. If filter 80 becomes clogged, or the pressure drop thereacross otherwise exceeds a given threshold, the pressure build-up compresses bypass spring 82 axially upwardly to permit hydraulic fluid to bypass the filter as shown at flow arrow 84, as is known. Dipstick 86 in the housing permits checking of fluid level. A pair of mounting bands or straps 88, 90 extend around the housing and have ends such as 92, 94, Fig. 3, mountable to a vertical surface in the engine compartment, such as a fire wall, etc., and tightenable by a bolt 96. Fig. 6 is like Fig. 1 and shows a similar combined power steering hydraulic fluid reservoir and cooling unit 112 including a housing 114 having a reservoir tank 116 for receiving and collecting hydraulic fluid from power steering gear 18 and holding the hydraulic fluid in readiness for supply to hydraulic pump 20. The tank is provided by a cylindrical canister extending axially along vertical axis 34. The housing has a heat exchanger 122 with a cooling liquid flow path therethrough in heat transfer relation with the hydraulic fluid in tank 116. The heat exchanger is provided by an annular jacket around the canister. The jacket has upper and lower axially spaced annular chambers 124 and 126 separated by a circumferential divider wall or baffle 128 therebetween. Annular chamber 124 has a cooling liquid inlet 130, and annular chamber 126 has a cooling liquid outlet 132. Baffle 128 has a transfer passage 134 therethrough, Figs. 6-9, such that the cooling liquid flow path is through cooling liquid inlet 130, then through annular chamber 124, then through transfer passage 134, then through annular chamber 126, then through cooling liquid outlet 132. The hydraulic fluid flow path is from hydraulic fluid inlet 136, Figs. 6, 7, then upwardly through central standpipe 138, then radially outwardly through apertures 140 then through filter 142 against the side wall of tank 116, then to hydraulic fluid outlet 144. Bypass inlet 146 to the tank is provided for receiving excess flow from pump 20. If filter 142 becomes clogged, or the pressure drop thereacross otherwise exceeds a given threshold, such pressure build-up compresses bypass spring 148 axially upwardly to enable hydraulic fluid flow to bypass filter 142, as above described. Dipstick 150 enables checking of hydraulic fluid level. A pair of mounting bands or straps 152, 154 extend around jacket 122 and have ends such as 156, 158, Figs. 8 and 9, mountable to a vertical surface in the engine compartment such as a fire wall, etc., and tightenable by a bolt 160. Baffle 128 is C-shaped in radial cross section as shown at 162 in Fig. 8. The facing ends 164 and 166 of the C-shape 162 define transfer passage 134 in the circumferential arcuate gap 166 therebetween. Transfer passage 134 extends axially along canister 116 between annular chambers 124 and 126. Jacket 122 is an annular sleeve having a side wall 168 spaced radially outwardly of canister 116 to define an annular space therebetween. Baffle 128 is provided by a recessed groove formed in side wall 168 of the sleeve and extending radially inwardly towards side wall 170 of the canister. The groove extends partially circumferentially around the canister and divides the annular space into the noted annular chambers 124 and 126 and provides the noted C-shaped baffle therebetween. Cooling liquid inlet 130 and cooling liquid outlet 132 are diametrically opposite gap 166 between facing ends 162 and 164 of the C-shape 162. Baffle groove 128 is V-shaped in axial cross-section, Fig. 7, with the apex 172 of the V engaging tank 116 at side wall 170. As above noted, transfer passage 134 through baffle 128 is diametrically opposite cooling liquid inlet 130 along the circumference of cylindrical canister 116 such that cooling liquid from cooling liquid inlet 130 splits into two paths in annular chamber 124, a path 174, Fig. 8, traversing 180° in a semi-circle to transfer passage 134, and.a path 176 traversing oppositely from first path 174 and 180° in a semi-circle to transfer passage 134, such that cooling liquid from cooling liquid inlet 130 splits into two paths 174, 176 and then rejoins at transfer passage 134. Transfer passage 134 is diametrically opposite cooling liquid outlet 132 along the circumference of cylindrical canister 116 such that cooling liquid from transfer passage 134 splits into two paths in annular chamber 126, a path traversing 180° in a semi-circle to cooling liquid outlet 132, and another path traversing oppositely and 180° in a semi-circle to cooling liquid outlet 132, such that cooling liquid from transfer passage 134 splits into two paths and then rejoins at cooling liquid outlet 132. Hydraulic fluid flows radially outwardly through filter 142 and against side wall portion 170 of canister 116. Jacket 122 is around portion 170 of the side wall of the canister and provides the noted cooling chamber thereat. Hydraulic fluid exiting from filter 142 flows against cooled portion 170 of the side wall of the canister and gives up heat to cooling liquid in cooling chambers 124, 126 provided by jacket 122, such that hydraulic fluid is filtered first and cooled second. This is preferred because there is then less pressure drop at the cooling interface, and because filtering of hot fluid reduces the chance of bypass spring 148 opening. It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims.

Claims: A combined power steering hydraulic fluid reservoir and cooling unit (12) comprising a housing (14) having a reservoir tank (16) for receiving and collecting hydraulic fluid from a power steering gear (18) and holding said hydraulic fluid in readiness for supply to a hydraulic pump (20), said reservoir tank (16) having a hydraulic fluid outlet (26), said housing ( 14) having a heat exchanger (22) with a cooling liquid flow path therethrough in heat transfer relation with said hydraulic fluid, characterised in that said reservoir tank (16) comprises a cylindrical canister extending axially along an axis (34) between distally opposite axial ends, said heat exchanger (22) extends axially through one of said axial ends of said reservoir tank (16) and said heat exchanger (22) has a hydraulic fluid inlet (24), a cooling liquid inlet (28) and a cooling liquid outlet (30). The unit according to claim 1 wherein said heat exchanger (22) extends axially along an axis (34) and has a side wall (40) extending axially between distally opposite end walls, said cooling liquid inlet (28) and said cooling liquid outlet (30) both extend axially through one of said end walls of said heat exchanger (22), said hydraulic fluid inlet (24) extends radially through said side wall (40) of said heat exchanger (22). The unit according to claim 2 wherein said side wall (40) of said heat exchanger extends axially through said one axial end of said reservoir tank (16), said side wall (40) of said heat exchanger (22) has a first portion (46) exterior to said reservoir tank (16), and a second portion (48) interior to said reservoir tank (16), said hydraulic fluid inlet (24) extending radially through said first portion (46) of said side wall (40) of said heat exchanger (22), said second portion (48) of said side wall (40) of said heat exchanger (22) having one or more openings (50, 52) therethrough passing hydraulic fluid into said reservoir tank (16). The unit according to claim 2 wherein said axis of said canister and said axis of said heat exchanger are coincident.

Inventors: SCHWARTZ SCOTT W, SCHWARTZ, SCOTT W.
Applicants: NELSON IND INC, NELSON INDUSTRIES, INC.
Application year: 1999
Main classification: B62D5
IPC codes: B62D5, F15B1, F15B21