Patent GB-938945-A (GB)
Title: Steering mechanism for industrial trucks
IPC: B62D5/06
Filed: 1961-12-18
Abstract: 938,945. Steering industrial lift trucks. YALE & TOWNE MANUFACTURING CO. Dec. 18, 1961 [Jan. 17, 1961], No. 45209/61. Class 79(5). The wheels 11, 12, 13, 14 are rotatably supported by mountings 15, 16, 17 and 18 in the frame 10 of an industrial fork lift truck, the wheel mountings 15 and 16 being secured to eccentric gears 21 and 22 meshing with racks 19 and 20 as described in Specification 824,590, the racks 19 and 20 being pivoted to levers 25 and 26 pivoted to the frame at 27 and to hydraulic rams 34 and 35. Stops 28 and 29 on the levers 25 and 26 may be urged into close contact by a ram 30 pivoted to brackets 31 and 32 fast with the two racks. The mountings of wheels 13 and 14 are pivoted to rams 40 and 53 and the mounting 17 of wheel 13 is pivoted to a rod 46 pivoted to a crank 47 pivoted to the frame 10 at 48 and connected by a hydraulic ram 49 to the bracket 31 of rack member 19. The ram 53 is provided with stops 55 and 59 and the rams 35 and 40 with stops 36 and 42 respectively. The pistons of rams 40 and 53 may be locked by fluid pressure against the stops 42 and 55 and the vehicle may be steered in the direction Y by the pair of wheels 11 and 12, the ram 34 supplying the operative pressure, the rams 35 and 49 being relieved of fluid pressure and allowed to float, and the levers 25 and 26 being locked together by ram 30, or alternatively, the rams 35 and 30 may be allowed to float and wheel 11 becomes the single steering wheel. The wheels 12 and 14 may be locked for steering in a direction at right angles to Y by holding the pistons of rams 35 and 53 against the stops 36 and 59 respectively, the rams 30 and 40 being allowed to float and the wheels 11 and 13 may be steered conjointly from ram 34 by locking ram 49, or by allowing the latter to float, wheel 11 is again the sole steering wheel. The hydraulic circuit for effecting the steering, Fig. 5, comprises a pump P supplying liquid to a line 60 from which liquid is supplied to a hydraulic accumulator A and a steering valve 72 supplying the steering ram 34, a pressure relief valve V being provided. The line 60 leads to a cross over valve 61 from which lines 44, 57 and 33 lead to rams 40, 53 and 30, through which pressure fluid is supplied in the position shown, which provides for steering in the direction Y. A line 62 from reservoir R leads to valve 61 and connects with the low pressure side of rams 40 and 53 through the lines 45 and 58, a line 63 from reservoir connecting with the low pressure side of ram 30 and also, through lines 65 and 66, with rams 35 and 49, the rams 35 and 49 also being connected to reservoir through lines 64 and 50, respectively, and valve 61 and line 62. The lines 50 and 45 incorporate change over valves 68 and 67. For changing to the steering direction transverse to the direction Y, the valve 61 is changed over, and fluid pressure passes through valve 67 and line 45 into ram 40, forcing it into the position whereby the wheel 13 is locked at right angles to the direction Y, and through mechanical connections 69 and 70 automatically changing over the positions of valves 67 and 68 to the dotted line positions, so that now, rams 35 and 53 are locked against stops 36 and 55 respectively, rams 30 and 40 are free and ram 49 is locked against stop 52 so that wheels 11 and 13 are steerable from ram 34. Separate valves may be provided in an alternative system for the independent operation of each ram.