Abstract:
A fluid control system providing a backup system for activating a pair of brakes on a vehicle includes a pair of double check valves with cross bleed located near the brakes. Each double check valve is connected at one end to a brake control valve which is in turn connected to a main pump and reservoir. The second ends of the double check valves are commonly connected to a secondary brake control valve which is connected to an accumulator which is fluid pressurized from the main pump. The center connections between the two ends of each of the double check valves are connected to one of the pair of brakes. The double check valves respond to pressure differentials to connect the main pump or the accumulator, whichever is supplying the greater pressure, to the brakes.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to secondary or emergency brake systems and more particularly to a simplified secondary braking control system. 
     In the past, agricultural vehicles generally relied on mechanical secondary brakes which required separate braking surfaces from the primary braking system. Due to the energy loss associated with the separate braking systems and the desire to increase the efficiency of the overall braking system, a secondary actuation system for the primary braking surfaces has long been desired. However, most of the systems developed have made use of an entirely separate control system requiring a multiplicity of control lines and hydraulic accumulators. 
     SUMMARY OF THE INVENTION 
     The present invention provides a secondary braking system which requires only a single fluid line from the accumulator and secondary brake control valve to the transmission case in which the brakes are located. A double check valve allows each brake to be operated either from the primary or secondary brake control valve even if the brake line from the other is broken. 
     The present invention further provides a secondary control system which may easily be interposed in the design of existing primary brake control systems. 
     The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawing. 
    
    
     DESCRIPTION OF THE DRAWING 
     The drawing is a schematic illustration of the fluid control system of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, therein is shown a fluid control system for an agricultural vehicle designated by the numeral 10. The fluid control system contains a primary braking system generally designated by the numeral 12 and a secondary braking system generally designated by the numeral 14. 
     The primary braking system 12 includes a main hydraulic supply pump 16 drawing hydraulic fluid from a hydraulic reservoir 18 and supplying it to a main supply line 20. The main supply line 20 then provides pressurized fluid to left and right supply lines 22 and 24 and to a secondary supply line 26. 
     It should be noted that the terminology &#34;left&#34; and &#34;right&#34; is used strictly for purposes of convenience for distinguishing between the various primary braking system elements and are not intended as limitations. 
     The left and right supply lines 22 and 24 are respectively connected to inlet ports 27 and 28 on respective left and right brake control valves 30 and 32. The left and right brake control valves 30 and 32 are conventional manually operable, three-way, two-position, internally modulated, fluid control valves which have respectively provided therein reservoir ports 34 and 36 and respective left and right brake ports 38 and 40. The left and right brake control valves 30 and 32 have a normal position in which the left and right brake ports 38 and 40 are respectively connected to the reservoir ports 34 and 36. The valves are individually actuatable, generally by means of a foot pedal in the vehicle control cab 42, to provide internally modulated connection of the inlet port 27 to the left brake port 38 or the inlet port 28 to the right brake port 40. 
     The left and right brake ports 38 and 40 are respectively connected to left and right brake lines 44 and 46 which pass out of the control cab 42 and along the vehicle 10 to a transmission case 48. 
     Inside the transmission case, the left and right brake lines 44 and 46 are respectively connected to the left and right double check valves 50 and 52 which will be described in greater detail later. The left and right double check valves 50 and 52 are respectively connected to left and right brake passages 54 and 56 which are connected to the usual brake pistons of conventional left and right brakes 58 and 60. The left and right brakes 58 and 60 serve to respectively brake the input shaft to left and right planetary gears 62 and 64 which drive the left and right ground-engaging wheels 66 and 68 of the vehicle 10. 
     Returning now to the secondary braking system 14 which contains the secondary supply line 26, the secondary supply line 26 is connected to a check valve 70. The check valve 70 normally allows the flow of fluid therethrough to an accumulator line 72 and blocks reverse flow. A conventional two-way, two-position relief valve 74 is connected in parallel to the check valve 70. The relief valve 74 is normally closed and pilot-operated at a predetermined pressure to allow the flow of fluid from the accumulator line 72 to the secondary supply line 26. 
     A conventional gas charged accumulator 76 is connected to the accumulator line 72 and is fluidly pressurized from the main pump 16 through the check valve 70. 
     The accumulator line 72 is further connected to an inlet port 78 of a secondary brake control valve 80. The secondary brake valve 80 is a conventional manually operable, three-way, two-position, internally modulated, fluid control valve having a reservoir port 82 and a secondary brake port 84. The secondary brake valve 80 has a normal position connecting the secondary brake port 84 with the reservoir port 82 and is actuatable, generally by a hand lever, to provide internally modulated fluid communication between the inlet port 78 and the secondary brake port 84. 
     The secondary brake port 84 is connected to a secondary brake line 86 which passes out of the control cab 42 and along the vehicle 10 to the transmission case 48 where it is commonly connected to the left and right double check valves 50 and 52. 
     The left and right double check valves 50 and 52 are conventional double check valves with cross bleeds which permit reverse flow operation. The valves are integral with the transmission case 48 which is provided with left and right valve bores 88 and 90. First ends 92 and 94 of the left and right double check valves 50 and 52 are connected respectively to the left and right brake lines 44 and 46. Second ends 96 and 98 respectively opposite the first ends 92 and 94 are connected together and further connected to the secondary brake line 86. Midway between the ends, the left and right double check valves 50 and 52 are respectively connected to the left and right brake passages 54 and 56. 
     Check balls 100 and 102 are respectively disposed within the left and right valve bores 88 and 90 to shuttle between ball seats disposed proximate the ends 92 and 96 and ball seats disposed proximate the ends 94 and 98, respectively. 
     In normal operation, when the brakes are not applied, the main pump 16 provides pressurized hydraulic fluid to the left and right supply lines 22 and 24 and to the secondary supply line 26. Initially, fluid from the secondary supply line 26 passes the check valve 70 to the accumulator line 72 to fluidly pressurize the accumulator 76. 
     Upon activation of one or both of the left and right brake control valves 30 and 32 of the primary braking system 12, modulated hydraulic fluid is supplied through one or both of the left and right brake lines 44 and 46 to one or both of the left and right double check valves 50 and 52. Since there will be no pressure in the secondary brake line 86 because the secondary brake valve 80 would not be activated, the balls 100 and 102 will be forced by the pressure of incoming fluid against the second ends 96 and 98, respectively. This prevents fluid loss through the secondary brake line 86 and the secondary brake control valve 80 to the reservoir 18. Thus, the left and right brake lines 44 and 46 will be connected to the left and right brake passages 54 and 56 to cause actuation of one or both of the left and right brakes 58 and 60. 
     When the brake control valves 30 and 32 are released, fluid will return from the left and right brakes 58 and 60, the respective left and right double check valves 50 and 52, and the left and right brake control valves 30 and 32 to the reservoirs 18. 
     The above is normal operation of the primary braking system 12 and generally the secondary braking system 14 will only be called for if there is a break or a leak in either the left or right brake lines 44 or 46 or in both lines or if the main pump 16 does not provide pressurized fluid. 
     For example, if there is a break or leak in the left brake line 44, the left brake 58 will not be activated. At this point, the secondary brake control valve 80 will be activated causing the main pump 16 to provide pressurized fluid, modulated by the valve 80, to the secondary brake line 86. Since the pressure in the secondary brake line 86 will be greater than that in the left brake line 44, the ball 100 will be shifted to the first end 92 to prevent the loss of fluid from the secondary brake line 86 into the broken left brake line 44. With the ball 100 abutting the first end 92, fluid from the pump 16 will be modulated through the secondary brake valve 80 and will pass through the secondary brake line 86 into the left brake passage 54 to actuate the left brake 58. 
     Modulation is provided in the secondary brake control valve 80 for the same reason it is present in the primary brake control valves. Since sudden application of the brakes will cause skidding, modulation is required to cause gradual, controlled application of the brakes. 
     Similarly, the pressurized fluid in the secondary brake line 86 will cause both balls 100 and 102 to seal off the left and right brake lines 44 and 46 and allow the passage of fluid to the left and right brake passages 54 and 56 to actuate the left and right brakes 58 and 60 for full braking of the vehicle 10. 
     If the main pump 16 is inoperative, the effect on the brakes will be the same as a break in both brake lines. Under this condition, the accumulator 76 will provide the pressurized fluid in the secondary brake line 86. The accumulator 76 is fluidly pressurized by the main pump 16 and contains a sufficient gas charge for a large number of brake applications. 
     As would be evident, the check valve 70 will prevent the flow of fluid from the accumulator 76 into the secondary supply line 26 when the main pump 16 is not pumping or if the left and right brake lines 44 and 46 are broken while left and right brake control valves 30 and 32 are applied. The relief valve 74 is provided as a protective feature so that when the accumulator 76 is charged when cold and then heated later by the vehicle engine which is in close proximity to it, the accumulator 76 will not be damaged by the increase in pressure. 
     While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the appended claims.