Patent GB-979781-A (GB)
Title: Mobile mixers and agitatorsí¬more particularly concrete mixers and agitators
Inventor: PULLIN CYRIL GEORGE
IPC: B28C5/42
Filed: 1960-06-21
Abstract: 979,781. Hydraulic transmissions. WINGET Ltd. April 17, 1961 [Jan. 21, 1960; June 7, 1960; Jan. 11, 1961], Nos. 2271/60, 19990/60 and 1231/61. Heading F2C. [Also in Divisions B1 and G3] In a vehicle mounted rotary drum concrete mixer the vehicle engine drives through an auxiliary bevel gear-box a vehicle engine cooling water pump, a variable stroke, axial cylinder swash-plate hydraulic pump and a boost pump for making up leakage in the main circuit and reducing cavitation at the inlet of the main pump. The main pump is in circuit with a radial cylinder hydraulic motor which drives the mixer drum through reduction gearing. A single manual control member adjusts the angle of the pump swash plate to control the direction and speed of rotation of the motor. Fig. 4 shows a closed hydraulic circuit in which the main pump 40 is connected to the motor 43 by pipes 41, 42 which incorporate heat exchangers 44, 45. The boost pump 46 draws oil from the make-up tank 47 and supplies it through an oil cooler 48 and filter 49 to a flow divider 62, whence part of the oil passes through the cooling jacket 50 of the main pump 40, a heat exchanger 51 and a non-return valve 52, while the other part passes through the cooling jacket 63 of the motor 43. The flows then recombine and return to the make-up tank through the boost pressure relief valve 53. Oil in the main circuit is made up through the non-return valves 56, 57; excess pressure in the pipes 41, 42 is prevented by the high pressure relief valves 58, 59. The working pressure in the circuit is determined by the boost pressure relief valve 53. If the motor is not required to be cooled the flow divider 62 and pipe 62A may be omitted and leakage in the motor drained through a pipe 66. In an alternative arrangement, Fig. 5, the cooling jackets 70A, 71A of the pump and motor 70, 71 are on the suction side of the boost pump 72, thus reducing the pressure in the pump-cooling jacket 70A which might interfere with control of the pump. A high-pressure relief valve 77 may be fitted across the pipes 80, 81 as a preferable alternative to the relief valves 78, 79 which are the counterpart, of the valves 58, 59 of Fig. 4. In an application, Fig. 11, of the arrangement of Fig. 5, the boost pump 126 draws oil from the make-up tank 131 through the cooling jacket of the main pump 125, and discharges through pipe 139, oil cooler 132 and filter 133 into the relief valve manifold 134 at the boost inlet 154 (see also Fig. 12); a boost pressure relief valve 159 or spill-off valve communicates with the make-up tank through pipe 141. The main pump and motor circuit passes through the passages 146, 147 in the relief valve manifold. The pump is controlled by the levers 187, 188 of the hydraulic actuators situated in and to the rear of the cab respectively and connected to an actuator 183 which varies the pump swashplate angle by means of rods 190, 301. The speed of the drum is maintained constant by a governor valve 200 through which fluid is passed by a governor pump 204 rotated by the hydraulic pump or vehicle engine. Alteration in the flow causes the valve 200 to act on the pump swash plate through the linkage 201, 202, 301 to vary the drum speed. When the pump 125 is set to rotate the drum and the governor pump in reverse, the governor valve is inoperative and fluid is recirculated through the side-return valve 208. The relief valve manifold 134 (see Figs. 12 and 13, comprises in addition to the boost pressure relief valve 159 a balanced highpressure relief valve situated between the flow and return pipes to the motor and controlled by a pilot valve. In Fig. 13, the flow and return of oil to the motor passes through the passages 146, 147; either may be at the higher pressure according to the direction of flow. Assuming 147 is at the higher pressure, fluid passes the non-return valve 153 into the passage 151 (see also Fig. 12), and thence into chamber 161, through the bore 172 in the piston 165, and the passage 173; the pilot relief valve 175 is normally closed and fluid pressure is equal on both sides of the piston 165, the valve 160 being retained on its seat 162 by the spring 170. If now the pressure in passage 147 rises, due to excessive load on the motor, above a predetermined limit, the pilot valve 175 lifts and fluid passes down the axial bore 171 to the passage 148; pressure on the upper side of the piston 165 is reduced and the main valve is lifted to place passage 151 in direct communication with passage 148 and thence via the non-return valve 156 with the suction passage 146, by-passing the overloaded motor. The pressure at which the valve lifts may be adjusted by means of the hand wheel 177; a needle valve 144, Fig. 11, is attached to the pipe 143 to enable the device to be unbalanced manually.