High pressure, high flow pump prime valve

[0002] This invention relates generally to a pump valve for use in high pressure applications such as advanced controlled vehicle braking systems.

[0003] In conventional design of hydraulic modulators for controlled braking systems where brake self-apply is required, such as traction control, and vehicle stability enhancement systems, it is usual to incorporate a normally closed valve assembly between a main master cylinder port and an inlet of a recirculation pump. The valve functions to isolate flow from a master cylinder to the pump inlet when the pump is idle, and to provide a flow path to the pump inlet when the pump is running. Traditionally, a normally closed single poppet-type valve with a suitably designed poppet and seat is commonly employed for this function. This type of valve works well for all systems which permit valve actuation under very low braking pressures.

[0004] However, under high master cylinder pressures, the force requirements needed to open the single large poppet valve are high. These force requirements to open the valve are proportional to an area of a main control orifice valve seat of the valve assembly. In order to open the valve under high pressures an exceedingly large solenoid coil and a large amount of magnetic force as generated by an electrical current are required. In the newer type of controlled braking systems, such as vehicle stability enhancement, such high pressure requirements frequently occur. Failure of the valve to open during high pressure use is unacceptable. While the newer brake systems require operation under high pressures, traditional requirements such as operation during very low pressure, cold temperatures remain a requirement of the valve assembly.

[0005] Previous solutions to these requirements have utilized two separate valves, one for high pressure/low flow and one for low pressure/high flow situations. However, the two valve designs are more costly and require additional packaging space.

[0006] Thus, it is desired to design an efficient high flow pump valve which has the capability to function during all expected conditions including opening under high braking pressures.

[0007] The present invention is an efficient two-stage, two-poppet prime valve assembly. The valve assembly utilizes one valve and two poppets for allowing the valve assembly to open under high pressure while providing minimal internal flow restrictions to enhance cold temperature and low pressure operation. Such conditions are present in modern vehicle braking systems. The two-stage poppet design contains two separate flow paths, one being high pressure, relatively low flow comprising a stage one, and the other being relatively low pressure, high flow comprising a stage two. In addition, the valve incorporates a reverse flow bypass feature that is capable of checking flow at very high pressure yet allowing reverse flow with a very low pressure drop.

[0008] The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows:

[0009] FIG. 1 is a cross-sectional view of a valve assembly of the present invention;

[0010] FIG. 2 is a cross sectional view of the assembly showing in detail a two poppet design;

[0011] FIG. 3 is a cross sectional view of the assembly in a stage one of operation;

[0012] FIG. 4 is a cross sectional view of the assembly in a stage two of operation;

[0013] FIG. 5 is a cross sectional view of the assembly in a closed state.

[0014] Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, in FIG. 1, a cross sectional view of a dual poppet, two stage, high pressure valve assembly for use in vehicle braking systems is shown generally at 10. The valve assembly 10 is connected through a master cylinder inlet port 16 to a brake system main master cylinder line (not shown). The valve assembly is also connected to a recirculation pump(not shown) through a pump inlet port 18. The assembly 10 is shown with two poppets, a high pressure poppet 20 and a low pressure poppet 26 between a main orifice 28 and a primary plunger 22. The high pressure poppet 20 seals against a seat 24 formed at a top of secondary plunger 13. The low pressure poppet 26 seals against a seat 30 formed at the top of main orifice 28.

[0015] In FIG. 2, the two poppet valve assembly 10 is shown in closer detail. Under normal vehicle brake operation, a brake fluid flow path is blocked between the pump inlet port 18 and the master cylinder inlet port 16. Blockage to flow is caused by the high pressure poppet 20 formed by a nose 21 of the primary plunger 22 which seals at the high pressure valve seat 24 of the secondary plunger 13. In addition, a nose 26 of the secondary plunger 13 forming the low pressure poppet 26 seals the main orifice 28 at the main valve seat 30. The two poppets 20 and 26 and their corresponding valve seats 24 and 30 provide an economical means to seal master cylinder pressure from the master cylinder port 16 from the pump inlet port 18 under normal vehicle braking operation.

[0016] Referring again to FIGS. 1-2, a thin walled tube 70 has a first end 72 affixed to value housing 58 and a second end affixed to stator 34 defining a cavity 71 housing primary plunger 22, secondary plunger 13, and first stage return spring 52 thereby affixing the valve components within housing 12. Tube 70 includes a flared step 76 at a point intermdiate the length of tube 70 such that first end 72 has a diameter greater than second end 74. Housing 12 includes a shoulder 82 upon which is affixed flange 78. Flange 78 includes a bore for receiving therein second end 74 of tube 70 and further includes a chamfer 80 that bears against flared step 76. In this manner, flange 78 bears against and affixes tube 70 within housing 12 with out requiring the use of additional means to facilitate the retention of the valve components within housing 12.

[0017] Whenever a controlled vehicle brake system is required to self-apply the brakes or to boost a pressure above that which a driver may be initiating through the main master cylinder line, it becomes necessary to open a passageway between the master cylinder inlet port 16 and the pump inlet port 18. In FIG. 3, the valve assembly 10 is shown in a stage one of operation with an open passageway or high pressure orifice 50 formed in the secondary plunger 13 between the primary plunger 22 and the poppet 20. Due to the high pressure valve seat 24 sealing on a relatively small diameter in comparison to the main valve seat 30, a minimal magnetic force is required in a main air gap 32 between the primary plunger 22 and a stator 34 to move primary plunger 22 and open the passageway. Primary plunger 22 is constructed of a magnetic material such as iron. The minimal magnetic force is generated by a small coil assembly shown generally at 36. The coil assembly 36 consists of a case 38, a bobbin 40, a top 42, and a pair of terminals 44. During Stage one as shown in FIG. 3 the primary plunger 22 moves until a plunger cage 46 contacts a positive stop 48 located on the secondary plunger 13. At this stage in the process, the main air gap 32 has been reduced and the high pressure poppet 20 as formed by nose 21 of the plunger 22 has moved far enough from the high pressure valve seat 24 that significant flow due to the high master cylinder pressure present inside the valve assembly 10 can feed the pump inlet 18 to maintain optimized pumping efficiencies even though the main valve seat 30 remains closed.

[0018] In FIG. 4, the valve assembly 10 is shown in a stage two position. If master cylinder pressures drop, flow through the high pressure orifice 50 will no longer be sufficient to maintain pumping efficiencies. Therefore, prior to reaching a crossover pressure which will initiate significant pump cavitation, it becomes necessary for the main valve seat 30 to be opened so that relatively unrestricted flow through the main orifice 28 will be available to feed the pump inlet 18. The coil assembly 36 is designed to be able to open the main valve seats 30 at a pressure slightly higher than a pump cavitation pressure. Additional magnetic force is required to move the plunger cage 46 and secondary plunger 13 in stage two, however, the magnetic force requirement is still reasonably low since the main air gap 32 has been significantly reduced by travel of the primary plunger 22 during stage one. After the nose 20 of the secondary plunger 13 opens the main valve seat 30, a first stage return spring 52 is able to move the low pressure poppet 26 back against the nose 20 of the primary plunger 22 to recover first stage travel loss. At the stage two position, the valve assembly 10 is fully opened with minimal flow restriction through the main orifice 28.

[0019] In FIGS. 2 and 5 the valve assembly 10 is shown in a fully closed condition. An additional feature contained within the valve assembly 10 is a reverse flow bypass valve shown generally at 54. It is beneficial in hydraulic modulators using valves of this type, that either air or brake fluid flow relatively unrestricted from the pump inlet port 18 to the master cylinder inlet port 16. This is accomplished in valve assembly 10 by a lip seal 56 which seals pressure in one direction only between a pair of bores 60 and 64 for fluid flow between housing 12 and a valve housing 58. The bore 62 in housing 12 is constructed of a tapered design at a bottom which fully supports the back end of the lip seal 56. Tip 57 of lip seal 56 interferes primarily with the tapered bore 62 to permit relatively unrestricted air or fluid flow through bore 60 in the unchecked (left to right as shown in FIGS. 2 and 5) flow direction. A suitable gap 68 exists between end 55 of lip seal 56 and flange 59 of valve housing 58 to permit axial displacement of lip seal 56. The axial displacement occurs when fluid flowing in the unchecked direction (left to right) and stops when the pressure in the master cylinder inlet port 16 is increased to exceed that of the pump inlet port 18. When such pressure reversal occurs, lip seal 56 is axially displaced to the left causing tip 57 of lip seal 56 to again interfere with tapered bore 62 and thus prevent a right to left fluid flow. The geometry of bores 60, 62, and 64 allows for repeated high pressure cycling as is typically found in a brake system while also allowing reverse flow of either air or brake fluid to be initiated at a very low pressure, for example, less than 140 millibar (2 psi). This is important when using the valve assembly 10 for reverse flow of air during a typical evacuation cycle when processing a brake system at a vehicle assembly plant, or when using the bypass feature to empty pump inlet accumulators at the end of a controlled braking event. Using the bypass feature eliminates the need to run the pump for an extra duration at the end of such a controlled braking event which reduces wear on the pump elements and also reduces noise that can be discerned by the driver of a vehicle.

[0020] The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.