HYDRAULIC DISK BRAKE CIRCUIT FOR CRANE DRAW WORKS

Abstract: A disk brake circuit for the draw works of a crane having a first hoist drum and a pump, comprising a disk brake having a caliper engageable with a rotor attached to said drum, a brake valve capable of modulating pressure from said pump to said caliper in response to a control pressure, a displaceable spool for generating a control pressure for said brake valve, an accumulator connected to the charged by said pump, and means responsive to loss of pump pressure for directing accumulator pressure to said brake valve as a control pressure and as a modulated pressure to restrain said drum.

Description: The present invention relates to hydraulic disk brake circuits. In particular it relates to such circuits for the draw works of a mobile crane. It is common practice to include a motor driven pump in such circuits to ensure that there is at all times an adequate supply of fluid pressure. A prior art that is of interest in this respect is US-A-3 724 609. It discloses an hydraulic disk brake circuit in which the pistons of a pair of piston and cylinder members carry a brake disk that can be moved into engagement with a brake surface of a wheel. Spring means are used to add a biassing effect to the brake disk in the direction of the brake surface. A driven pump is included in a hydraulic circuit coupled to said piston and cylinder members via throttling means and pressure limiting valves controlled by a brake pedal. On depressing the brake pedal, high pressure fluid is directed in a controllable manner into the piston and cylinder members to assist said spring means, so causing the brake to be applied to a variably controlled degree. On releasing the pressure on the foot pedal the resulting circuitry is such that the high pressure fluid is directed to the piston and cylinder members such that the effect of the spring means is counter-acted and the brake is released. Coupled directly in parallel with the pump, with no shut-off means therebetween, is an accumulator for said pump pressure. This prior art is such that should the pump fail the accumulator then becomes a secondary source of pressure by means of which the brake pedal can continue to be used to release the brake. When this secondary source of pressure is exhausted the brake is then permanently applied via said springs since it is then impossible for the hydraulic disk brake circuit to release the brake via the foot pedal. For a motor vehicle this is a great disadvantage and so, to solve this problem, the prior art includes a manually operable valve member for switching the piston and cylinder members from the pedal operated brake releasing circuit to a hand operated pump system that can be actuated to supply sufficient pressure to the piston and cylinder members to release the braking effect of the springs. The present invention has as its object to provide an hydraulic disk brake circuit that functions in a different manner to this prior art should the pump fail to supply sufficient pressure for the operation of the brake. The invention is as defined in the accompnying Claim 1 which has been divided into a two-part form so that its inventive step over the aforesaid prior art is readily discernable. The sole figure of the drawing is a hydraulic and electrical schematic of a preferred embodiment of the present invention. Referring now to the drawing, the mobile crane has front and rear hoist drums 10 and 12 onto which separate wire ropes are wound and unwound to respectively raise and lower loads attached thereto suspended from the boom of the crane. Disk brakes 14 and 16 are provided to slow the rotation of or stop the drums 10 and 12 respectively. The front disk brake 14 has a pair of calipers 18 and 20 capable of frictionally engaging a rotor 22 attached to the front drum 10. Similarly, the rear disk brake 16 has a pair of calipers 24 and 26 for engaging a rotor 28 attached to the rear drum. The calipers 18 and 20 of the front brake 14 are supplied with fluid pressure for brake engagement through conduits 30 and 32 which connect respectively with variable pressure brake valves 34 and 36. Hydraulic fluid under pressure is supplied to the brake valves 34 and 36 through conduits 38 and 40 respectively from a pump 42 which is driven by an engine on the mobile crane; the pump pressure being modulated or reduced to the calipers 18 and 20 as an inverse function of a control pressure. An operator-controlled foot pedal 44 is connected to similtaneously stroke or displace a pair of spools or pistons 46 and 48 as the pedal is depressed. The hydraulic fluid displaced by the stroking of spools 46 and 48 generates the control pressure. As this pressure increases, the brake valves 34 and 36 reduce the hydraulic fluid pressure returned to the reservoir 114 through conduit 52 and hence increase the pressure directed to the calipers 18 and 20. Each of calipers 18 and 20 has sufficient capacity to restrain or hold the maximum line pull exerted on the wire rope wound on the front drum 10. Thus, either of the calipers 18 or 20 will be independently capable of stopping and holding the maximum anticipated load suspended from the boom and attached to the wire rope on the front drum. A failure of either caliper 18 or 20 and/or its associated hydraulic circuit will permit a controlled restraint of the load on the front drum 10. The calipers 24 and 26 of the rear disk brake 16 have a similar capacity or load capability. Conduits 54 and 56 separately and independently supply hydraulic fluid pressure to the calipers 24 and 26 respectively and connect with variable pressure brake valves 58 and 60. A supply of hydraulic fluid pressure from the pump 42 is directed to these valves through conduit 62 and 64 which connect respectively with supply conduits 38 and 40. The control pressure to the calipers 24 and 26 is generated by an operator-controlled, footpedal 66 which strokes a pair of spools 68 and 70, in the same manner as pedal 44 and its associated spools 46 and 48. Nitrogen precharged accumulators 74 and 76 are respectively connected to supply conduits 38 and 40, and are charged with hydraulic fluid by the pump 42. Should pressure from the pump 42 be lost, the charged accumulators will be available to furnish a supply of hydraulic fluid under pressure to the brake valves 34, 36, 58 and 60. A pair of check valves 78 and 80 in the conduits 38 and 40 respectively, upstream of the accumulator 74 and 76 permit flow only toward the accumulators and isolate the pump 42 from the brake circuits upon loss of pressure. A pilot line 82 senses pump pressure and connects with a pressure actuated electrical switch 84. The switch 84 is normally open and closes at a predetermined pressure to connect conductor or line 86 with an electrical source, such as battery 88. When momentary contact switch 89 is closed, the coil of relay 91 will be energized closing switch 93, which is then held closed by line 95 continuing to energize the coil of relay 91. The coil of relay 90 will thereby be energized closing switch 92. With switch 92 closed, the battery 88 will be connected with line 94, which connects with solenoids 96 and 98, and through a branch line 100, with solenoid 102. When energized, the solenoids 96, 98 and 102 cause their associated valves 95, 97 and 101 respectively to shift downwardly the positions shown in the drawing. The hydraulic conduit 104 extends between conduit 38 and 40 and has a shuttle valve 106 interposed therein. Conduit 108 connects between the shuttle valve 106 and valve 97. The conduit 110 is teed into the conduit 108 and communicates with the valve 101. A branch conduit 112 connects the conduit 110 with the valve 95. The valve 95 connects with the reservoir 114 through conduit 116. A conduit 120 provides power-beyond capability for actuation of other hydraulic equipment utilizing pump flow through conduits 38 and for 40, conduits 108, 110 and 112, valve 95 and conduit 120. The port 118 is blocked so that when solenoid 96 is deenergized, causing the valve 95 to shift upward in response to its spring bias, the conduit 112 will be blocked. Leakage points in the power-beyond circuit are thereby eliminated and the maximum amount of stored energy will be available from the accumulators 74 and 76 for actuation of the brakes as explained hereinafter. Pump pressure is also supplied through conduit 108 and valve 97 to conduit 122 which connects with a hydraulic cylinder 124, the rod of which is connected to pawl 126. Pawl 126 is capable of engaging a rachet (not shown) attached to the front drum 10. A compression spring 128 urges the pawl 126 into engagement with the rachet to lock the drum 10 from rotation. Hydraulic pressure extends the cylinder 124, against the bias of spring 128, to disengage pawl 126 from the ratchet. Similarly, pump pressure is supplied through conduits 108 and 110 and valve 101 to conduit 130, which conduit communicates with hydraulic cylinder 132 having a rod connected with a pawl 134 engageable with a rachet attached to the rear drum 12. spring 136 urges pawl 134 toward engagement with its associated rachet. When pump pressure, as sensed in pilot line 82, drops below a predetermined level, the switch 84 will open deenergizing the relay 91 and opening the switch 93, which in turn will deenergize relay 90 and open switch 92. The solenoids 96, 98 and 102 will be deenergized, permitting the springs of valves 95, 97 and 101 to urge the spools therein upward from their setting shown in the drawing. The conduit 112 will be blocked by the shifting of valve 95, sealing or isolating the brake circuit from the other hydraulic circuits. Simultaneously, the valve 97 will connect conduit 108 with conduit 138 and will connect conduit 122 with the reservoir 114. The spring 128 will urge the piston in cylinder 124 to the right, the rate of movement being determined by the orifice 140 which controls the flow of fluid out of the cylinder 124. Fluid pressure from accumulators 74 and 76 will be directed through conduit 108, valve 97 and conduit 138 to a spring biased, shuttle valve 142. The resulting pressure in the shuttle valve 142 will close the drain connection to the reservoir 114 valve 142 and direct pressure to a pair of differential area valves 144 and 146. These valve will shift to the right, as viewed in the drawing permitting accumulator pressure to be directed to the brake valves 34 and 36 as a control pressure, causing them to admit full accumulator pressure to the calipers 18 and 20. The disk brake 14 will then be applied automatically to gradually slow and stop the drum 10. An orifice 148 in the conduit 138 assures a gradual application of the disk brake, avoiding a shock load on the wire rope associated with the drum 10, as well as on other elements of the crane. The orifice 140 is sided so that the brake 14 is fully engaged and the drum 10 stopped before the pawl 126 engages the rachet on that drum. A second orifice 150 in conduit 122 controls the rate at which the cylinder 124 is filled so that there is not sudden unexpected release of the pawl 126. The brake 16 for the rear drum 12, is applied under conditions of pressure loss in a similar way. The shifted valve 101 connects the conduit 110 with a conduit 152 connected with a spring-biased, shuttle valve 154, which directs accumulator pressure to the differential area valves 156 and 158 as a control pressure. These valves shift under this pressure to cause the brake valves 58 and 60 to direct the accumulator pressure to calipers 24 and 26. An orifice 160 assures a smooth application of the disk brake 16. The shifted valve 101 will also connect the conduit 130 with the reservoir 114 permitting the pawl 134 to engage a rachet attached to the drum 12. The orifice 162 assures a predetermined delay before engagement of the pawl 134, while orifice 164 provides the different delay before disengagement of the pawl. Check valves 170 and 172 in conduits 108 and 110 respectively prevent the pawls 126 from assuming a disengaged position until the valves 97 and 101 are shifted by deenergization of their respective solenoids. A proper nitrogen precharge in at least one of the accumulators 74 and 76 is necessary for operation of the circuit. In order to warn the operator when either of the accumulators does have a proper precharge, a pair of pressure switches 174 and 176, normally closed, are wired in parallel with battery 88 and an alarm device 178. If either of the accumulators 74 and 76 has a low nitrogen precharge, the switch 174 or 176 associated with that accumulator will close activating the alarm and alerting the operator. When the operators shuts down the crane the loss of pump pressure will permit switch 84 to open, which causes accumulator pressure to apply the brakes and allows the pawls to engage their respective ratchets. Once the relay 91 has been deenergized, the brakes are applied and the pawls engaged. The subsequent closing of switch 84 due to pump pressure appearing in pilot line 82 will not release the brakes and disengage the pawls. The operator must first close switch 89. This requirement minimizes the possibility of inadvertently dropping a load. The operator also can apply the brakes and set the pawls 126 and 134 for either the front and rear drums by opening the switches 180 and 182, which will individually deenergize the associated solenoid. It will be seen from the foregoing that the present invention provides a disk brake circuit which will automatically arrest and hold the load on either or both of the front and rear drums, thus obviating the need for quick operator reaction, or even knowledge of a malfunction. Since the present invention utilizies a narrow disk brake, the width of the upper may be minimized, and unlike band brake systems, requires little or no adjustment. Each of the disk brakes are applied by a split system, so that failure of either half of the system will automatically cause the other half of the system to stop the drum and insert the pawl. Suspended or freefalling loads can be brought to a halt regardless of pump failure, a single accumulator failure or a line breakage. While a preferred embodiment of the present invention has been shown and described herein, it will be appreciated that various changes and modification may be made therein without departing from the spirit of the invention as defined by the scope of the appended claims.

Claims: A disk brake circuit comprising: a disk brake (14) having a caliper (18,20) engageable with a rotor (22) attached to a drum (10); a brake valve (34, 36) capable of modulating pressure from a pump (42) to said caliper (18,20) in response to a control pressure; a displaceable spool (46,48) for generating a control pressure for said brake valve (34,36); an accumulator (74,76) connected to be charged by said pump (42); characterised in that said disc brake circuit is for the draw works of a crane and has a first hoist drum (10); and by pressure actuated means (84) for sensing loss of pump pressure; and means (86, 88 to 95, 97, 98, 104, 106, 108, 138) associated with said pressure actuated means (84) for automatically directing accumulator pressure to said brake valve (34, 36) as a control pressure and as a modulated pressure to actuate said caliper (18,20) to restrain said drum (10) on the sensing by the pressure actuated means (84) of loss of pump pressure. The invention according to Claim 1, and further comprising: a first orifice (148) for controlling the flow of fluid from the accumulator (74, 76) as a control pressure. The invention according to Claim 2, wherein the crane has a pawl (126) engageable with a rachet attached to the drum (10), and further comprising; a cylinder (124) having a piston connected to said pawl (126) the piston being biased to cause engagement of said pawl with said ratchet but movable to disengage said pawl when subjected to pressure; and said means for automatically directing pressure to said brake valve (34,36) also serving to exhaust pressure from said cylinder in response to loss of said pump pressure to permit said biassing means to cause the pawl to engage said ratchet. The invention according to Claim 3 further comprising: a second orifice (140) to control the flow of fluid from said cylinder (124) to delay the engagement of said pawl (126) until after application of said brake (14). The invention according to Claim 4 and further comprising: a check valve (78, 80) between said pump (42) and accumulator (74, 76) for isolating said circuit from said pump (42) upon loss of pressure.

Inventors: CUHEL, LEON L.
Applicants: LINK-BELT CONSTRUCTION EQUIPMENT COMPANY
Application year: 1984
Main classification: B66D5
IPC codes: B60T13, B60T17, B66D5