Patent GB-709662-A (GB)
Title: Improvements in or relating to linkage, especially three-point linkage for connecting agricultural implements to tractors
Inventor: TOMIK GEORGE ALOIS
IPC: A01B61/00
Filed: 1951-12-10
Abstract: 709,662. Controlling tractors. INTERNATIONAL HARVESTER CO. OF GREAT BRITAIN, Ltd. April 25, 1952 [Dec. 19, 1951], No. 28873/51. Class 79(5) In a three-point linkage for connecting an agricultural implement to a tractor and comprising an upper link and two lower links, the lower links are provided with members adapted for connection to the implement and disengageable from the links by rearward displacement against the action of holding means which release the members on application of a load in excess of the maximum tractive effort required for operation of the implement, control means being actuated by rearward displacement of the members for disconnecting the driving mechanism of the tractor. As shown the linkage comprises the upper link 1 operated by hydraulic means (not shown) and the lower links 2. Each lower link 2, has a recess 11 engaged by a projection 12 on the displaceable member 5, the link and member being urged together by a spring 8 within a guide 7. Slidable on the link 2 is a friction clamp device 13 which is frictionally engaged with the member 5 by a screw 14. One of the devices 13 is connected by a cable 14a to an arm 15 on a cross shaft 16 mounted in the tractor. The other device 13 is cable connected to a plate 115 on the shaft 16. Connected to the plate 115 at 18 is a cranked part 19 of a spring 17 which is connected to a lever 20 pivoted to the tractor clutch pedal 21. The shaft 16 carries an arm 38 which is connected by a slack cable 37 to one of a pair of plates 30, which are interconnected bv bridge pieces 32, are pivoted at 33 to the walls 28 of a fitting 29 attached to the tractor and have hook shaped parts 34. The parts 34 co-operate with slots 27 in the walls 28 to retain trunnions 26 on the link 1, the plates 30 being held in such position by spring loaded plungers 35. The arrangement is such that when the implement which is coupled by balls and sockets 6 to the link 1 and members 5 encounters an obstruction, the members 5 and devices 13 move rearwardly relatively to the links 2, such movements through the cables 14 causing rotation of the shaft 16 and plate 115. Such movement of the plate 115 causes the crank part 19 to pass through a dead centre position and tension the spring 17. Such tension causes the lever 20 to pivot about a boss 23 on the pedal 21, thus depressing the pedal and disengaging the clutchto bring the tractor to a standstill. The operator can then fully depress the pedal 21, engage reverse gear, engage the clutch and allow the tractor to run back so that the parts 2 and 5 return to their original positions and the obstruction can then be negotiated. If the tractor does not come to a standstill before the devices 13 abut the guides 7, the members 5 and the link 1 become detached from the tractor, the members 5 detaching from the devices 13 and the link 1 being released from the fitting 29 by the plate 30 moving to the position shown in Fig. 3 under the action of the cable 38 on rotation of the cross shaft. The slack in the cable 38 is such that the plates 30 are moved just before the devices 13 and guides 7 abut.