The above mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates an embodiment of the invention, in one form, the embodiment disclosed below is not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.
The pump 14 delivers high pressure hydraulic fluid through discharge line 18 to a flow-splitting valve 20 also known as a priority valve. The priority valve 20, in turn, selectively communicates with a first hydraulic application 22, a second hydraulic application 24, and the reservoir 16, depending on predetermined operating conditions of the system 10, as will be explained below.
The first and second hydraulic applications 22, 24 take the form of a hydraulic device or a hydraulic sub-circuit. In the illustrated embodiment, first application 22 is a hydraulic braking assist system or booster device, and the second application 24 is a hydraulic steering gear assist system or device.
The hydraulic brake booster device 22 communicates with a master cylinder 26 and brakes 28 of the braking system. Hydraulic booster device 22 is of a type well known in the art which is disposed in line between the hydraulic pump and the hydraulic master cylinder of a vehicular hydraulic brake system which acts to boost or amplify the force to the brake system in order to reduce brake pedal effort and pedal travel required to apply the brakes as compared with a manual braking system. Such systems are disclosed, for example, in U.S. Pat. Nos. 4,620,750 and 4,967,643, the disclosures of which are both incorporated herein by reference, and provide examples of a suitable booster device 22. Briefly, hydraulic fluid from the supply pump 14 is communicated to the booster device 22 through a booster inlet port and is directed through an open center spool valve slideable in a booster cavity (not shown). A power piston slides within an adjacent cylinder and is exposed to a fluid pressure on an input side of the piston and coupled to an output rod on the opposite side. An input reaction rod connected to the brake pedal extends into the housing and is linked to the spool valve via input levers or links. Movement of the input rod moves the spool valve, creating a restriction to the fluid flow and corresponding boost in pressure applied to the power piston. Steering pressure created by the steering gear assist system 24 is isolated from the boost cavity by the spool valve and does not affect braking but does create a steering assist backpressure to the pump 14. The priority valve 20 operates to manage the flow of hydraulic fluid from the pump 14 to each of the brake assist 22 and steering assist 24 systems in a manner that reduces the interdependence of the steering and braking systems on one another for operation.
With reference to
In the condition illustrated in
Turning now to
Priority valves having a different construction that divert hydraulic fluid flow such that the diverted fluid bypasses brake assist device 22 and is delivered to steering gear assist device 24 may also be employed with the present invention. For example, priority valves having a simplified construction that can be substituted for the illustrated priority valve 20 are described by Wong et al. in a U.S. Utility patent application (Ser. No. ______) entitled VEHICULAR HYDRAULIC SYSTEM WITH PRIORITY VALVE AND RELIEF VALVE having an Attorney Docket Number of DP-315726 and claiming priority from U.S. Provisional Application Ser. No. 60/845,911 filed Sep. 20, 2006; and by Wong et al. in a U.S. Utility patent application (Ser. No. ______) entitled VEHICULAR HYDRAULIC SYSTEM WITH PRIORITY VALVE having an Attorney Docket Number of DP-315727 and claiming priority from U.S. Provisional Application Ser. No. 60/845,892 filed Sep. 20, 2006, both of these utility patent applications having a common filing date with the present application, and wherein both of the utility applications and both of the provisional applications are assigned to the assignee of the present application and wherein each of these four utility and provisional applications are expressly incorporated herein by reference.
A pressure reducing valve 60 is located in hydraulic line 25 which conveys hydraulic fluid from brake assist device 22 and Port C to steering gear assist device 24. The illustrated pressure reducing valve 60 is a pilot operated, sliding spool valve and is placed in line 25 before steering gear assist device 24. Valve 60 includes a valve body 62 that defines a valve chamber 62 and Ports E (inlet port), F (outlet port) and G (pilot port) which open into valve chamber 62. Threaded plug or member 78 has a bore 80 that extends through its length and defines Port H (low pressure port). As can be seen in
Valve 60 also includes a double-headed spool valve member 64 located in valve chamber 62. Spool member 64 includes a first plunger head 66 and a second plunger head 68. The first and second plunger heads 66, 68 sealingly engage the sidewalls of valve chamber 62 and sealingly partition valve chamber 62 into a central portion 70, a pilot portion 72 and a low pressure portion 74. First plunger head 66 faces Port G while second plunger head 68 is engaged by biasing member 76 which takes the form of a helical spring in the illustrated embodiment. Threaded plug 78 is located in the open end of valve chamber 62 and engages the opposite end of spring 76.
Under low pressure conditions, as exemplified by
As evident from the description presented above, hydraulic circuit 10 includes, in series arrangement and serial order, hydraulic pump 14, flow-splitting valve 20, brake booster device 22, pressure-reducing valve 60, steering gear device 24 and reservoir 16. When flow splitter 20 is not diverting a portion of the fluid flow through Port C to bypass brake booster 22 as occurs when brake booster 22 is generating a relatively high back pressure, a substantial majority of the fluid flow discharged from pump 14 will flow along a primary flow path that extends from the outlet of pump 14, through discharge line 18, through valve 20 from Port A to Port B, to brake booster 22, to Port E of valve 60, through valve 60 from Port E to Port F, through line 56 to steering gear 24, to reservoir 16 and then to the inlet of pump 14 wherein the cycle is repeated. As described above, when the pressure upstream of brake booster 22 is elevated to first threshold value, flow-splitting valve 20 will split the fluid flow with a portion being communicated to Port B in the primary flow path upstream of brake booster 22 and another portion of the fluid flow being diverted through Port C to a point in the primary flow path downstream of brake booster 22 and upstream of valve 60.
It is noted that the reducing valve 60 illustrated in
While the present invention has been described above with reference to a hydraulic system that combines both a steering gear assist device and a brake assist device, it may also be employed with other hydraulic devices and systems. For example, it is known to employ a single hydraulic fluid pump to power the fluid motor of a steering assist device and a second fluid motor associated with a radiator cooling fan. U.S. Pat. No. 5,802,848, for example, discloses a system having a steering gear assist device and a radiator cooling fan with a fluid motor powered by a single hydraulic fluid pump and is incorporated herein by reference. In alternative embodiments of the present invention, the priority valve and pressure reducing valve arrangement disclosed herein could be employed to facilitate the use of a single hydraulic fluid pump to power the fluid motors of both a steering gear assist device and that of a radiator cooling fan.
Furthermore, the priority valve and pressure reducing valve arrangement of the present system could be used to control the fluid flow associated with two hydraulic devices (e.g., a brake assist device, a steering gear assist device, a radiator fan having a fluid motor, or other hydraulic device), or two hydraulic circuits, wherein the priority valve and relief valve arrangement and the two associated hydraulic devices or circuits, form one portion of a larger complex hydraulic circuit.
In still other embodiments, a pressure reducing valve could be used in a hydraulic circuit without a priority valve to limit the pressure of the fluid being provided to a steering gear assist device or other hydraulic device. For example, a pressure reducing valve could be used in an integrated hydraulic circuit having both a brake assist device and a steering gear assist device but not a priority valve to enable the use of a steering gear assist device having a lower pressure relief value than that of the brake assist device. Or, a pressure reducing valve could be employed as described herein in a conventional hydraulic circuit for a steering gear assist device that does not include any other hydraulic devices to limit the pressure of the hydraulic fluid at the inlet of the steering gear assist device.
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.
This application claims priority under 35 U.S.C. 119(e) of U.S. provisional patent application Ser. No. 60/846,004 filed on Sep. 20, 2006 entitled VEHICULAR HYDRAULIC SYSTEM WITH PRESSURE REDUCING VALVE the disclosure of which is hereby incorporated herein by reference.
Number | Date | Country | |
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60846004 | Sep 2006 | US |