Patent GB-365344-A (GB)
Title: Improvements in and relating to differential speed indicating devices
IPC: G01P3/04
Filed: 1931-02-04
Abstract: 365,344. Differential or comparison speed indicators. PRATT, F., Abbeyview, Navan Gate, Trim, Co. Meath, Ireland. Feb. 4, 1931, No. 3539. [Class 106 (iii).] A single pointer is provided which is actuated by the two shafts the speed of which is to be compared in such a manner that one e shaft is only capable o f rotating the pointer in one direction and the other in the opposite direction the single pointer indicating the ratio of the two speeds. The spindle 1 is driven from the engine and drives a wheel 5 loose on a boss 6 mounted on the base 3. Secured to the wheel 5 is a ratchet wheel 7 provided with h a number of fine teeth. A shaft 11 is driven through a one-way drive from and at the same speed as the drive shaft. A member 12 having an arm 13 is loose on the shaft 11 while a member 14 having an arm 15 is keyed to it. The end of the shaft 11 is reduced and has a bearing in the frame 16 in which bearing also is the lower end of a spindle 18 having a disc part 19 to which is attached a pointer 20. The other end of the spindle 18 carries a pointer 24. The spindle is friction held in any position reached. The arm 13 is provided with a pawl 31 which depends therefrom and is pressed by a spring 33 to engage the teeth of the wheel 7. A projection 34 on the arm 13 is adapted to engage the face 35 of a stop 36 on the underside of the plate 16. On the arm 15 is pivotally mounted a member 42 provided with a hook portion 43 adapted to engage the pointer 20 and is pressed out by a spring 44 to a position limited by engagement of a tail engaging the member 14. A cam surface 46 is adapted to engage the projection 34 to press back the hook 43 to release the pointer 20 the hook 43 then engaging the projection 34. The hook 43 is disengaged from the projection 34 when a projection 47 meets the cam 48. At the same time as the cam 46 meets the projection 34, a cam 50 on the arm 15 engages the tail pieces 32 and disengages the pawl 31 from the wheel 7. In order that the engine operating member may not travel around too far, a catch 51 is provided to lift the pawl 31 away from wheel 7. A speedometer may be operated from the shaft 11. In operation the gear wheel 5 is driven anticlockwise, Fig. 2, from the engine and the engineoperating member 13 is driven through the ratchet device so that the recess 40 moves forward the pointer 20 and with it the needle 24. The drive spindle 11 moves the drive shaft operating member 42 clockwise until it meets the engine operating member when the hook 43 is released and also the pawl 31. The continued movement of the member 42 bring back the engine-operating member 13 until the projection 34 meets the stop 36 and then projection 47 engages the face 48 of the stop and releases the hook 43 from the projection 34. The engine-operating member then starts off anticlockwise again. Should the recess 40 the next revolution not meet the pointer 20 before the hook 43 meets it, the latter will carry the pointer round until it meets the recess when the pointer will again be released and left. The pointer is left in a different position when the drive shaft spindle is operated at a different gear ratio and the several positions are marked with the gear ratio, or 1st, 2nd, 3rd, &c.