Patent GB-819873-A (GB)
Title: Improvements in and relating to hydraulic control devices for changing speeds in drive transmission systems, mainly applicable to drive transmission systems, of automobile vehicles
IPC: F15B13/04
Filed: 1956-02-15
Abstract: 819,873. Change-speed control. CITROEN S.A., A. Feb. 15, 1956 [Feb. 15, 1955; Oct. 6, 1955; Feb. 9, 1956], No. 4784/56. Class 80 (2). [Also in Group XXIX] An hydraulic ratio establishing servo-control device, for motor vehicle transmissions including a friction clutch and a changespeed gear, comprises a servocontrolled valve operating during a change of ratio to disengage the clutch, engage a selected ratio, reengage the clutch and return the device to its normal inoperative position, and a selector operable manually or automatically to initiate changes in ratio. As shown, the control svstem is applied to a constant-mesh change ratio gear having friction synchronized positive clutches, but it may also be applied to non- synchronized change ratio gearing and to planetary gearing. An engine driven pump 2 draws oil from a reservoir 1 and supplies it through a by-pass valve 4 to an hydraulic accumulator 3. A conduit 5 connects the accumulator through a conduit 45 to a space 46 between the two piston-shaped ends of a slide valve 9. This slide valve is normally biased to the left of Fig. 1 by a spring 11 acting on a disc 10 at its end. On starting the engine of the vehicle, the pump 2 builds up the pressure of the oil in the space 46 and thus increases the pressure of the oil in a conduit 19 connected to a servomotor cylinder 18 and acting on a piston 17 to disengage a main clutch 20 between the vehicle engine and its change-speed gear. As a modification, the clutch 20 may be electromagnetically controlled, the servo mechanism operating switches and relays (not further described) instead of the piston 17- &c. When the main clutch has been disengaged, pressure continues to build up in the space 46, which is also connected through a conduit 47 with a space 49 at the end of the slide valve 9. Ultimately, the slide valve 9 is moved rightwards against the bias of the spring 11 to uncover a conduit 48 connecting with the space 46, so that oil under pressure is then supplied through a coiled passage 59 in a sleeve 7 to a ring groove 50 and a radial passage 51 in the sleeve, the coiled passage 59 restricting the flow of oil under pressure. The desired ratio in the changespeed gearing is selected either directly by the driver, or automatically by means not further described, on operation of a slide valve 8 having an annular groove 52 connecting with the radial passage 51. The annular groove 52 is connected by a passage 39 with a central supply duct 37 in the slide valve 8. A radial passage 40 in the slide valve 8 can connect with a desired one of a number of radial passages 42, corresponding in number to the number of ratios in the changespeed gear, each passage 42 connecting with an annular groove 41 in the sleeve 7. Having posi. tioned the slide valve 8 opposite the desired passage 42, oil under pressure is then supplied through the annular groove 41 to a conduit 25 leading to a piston 31 in a servomotor which establishes the desired ratio. The servomotor piston 31 acts on a rod 27 carrying a clutch fork 28 moved axially of the gearing to establish the selected ratio. Two disc-like members 33, 331 surround a reduced portion 34 of the fork rod, and are biased by a precompressed spring 32 to engage shoulders thereon and also shoulders 35, 36 on the gear-case 26. The action of the spring 32 is to bias the selector fork to the neutral position. Admission of oil under pressure through the slide valve 8, the groove 41 and the conduit 25 to the selected servomotor piston 31, simultaneously builds up pressure in an associated conduit 44 leading to a space between a number of free pistons 13, the end one of which abuts a disc 14 biased to the right by a spring 15. The initial build-up of pressure against the piston 31 does not cause movement of the selector fork 28, the usual spring-biased ball detent preventing movement of the clutch member 29. As the oil pressure increases, the disc 14 is moved leftwards against the bias of the spring 15 until it engages a shoulder 58. The oil pressure is then sufficient to force the positive clutch member 29 out of engagement with its spring-biased ball detent, and snap the synchromesh clutch rapidly into engagement, the disc 14 returning to the position shown in Fig. 1. The pressure in the conduit 25 meanwhile is built up again, the disc 14 is again moved to the left to abut the shoulder 58, and on still further increase in pressure, oil in the annular groove 41 passes through a conduit 43 to the end of one of a number of free pistons 12 thereby moved rightwards to engage the end of the sleeve valve 9, which is then moved as far to the right as its disc 10 will permit. In this position the slide valve 9 connects the conduit 47 and the conduit 19 to an exhaust conduit 16 leading to the oil reservoir 1, so that the main clutch 20 is reengaged by its spring, and drive is commenced from the engine through the main clutch and the selected ratio in the change-speed gear. To disengage the selected ratio and return to neutral, the slide valve 8 is moved so that the radial passages 42 &c. connect the conduit 25 to cutaway portions 55 in turn connected to the exhaust conduit 16. This causes the slide valve 9 to move leftwards, and thereby supply oil under pressure to the conduit 19 to disengage the main clutch 20. The selector fork 28 is then restored to its neutral position by the spring 32. To engage another ratio, the selector valve 8 is again moved to position the radial passage 40 against the desired passage 42, and the process described recommences. As a modification, the spiral passage 59 may be replaced by a helically wound tube by-passed by a spring-loaded ball valve, Figs. 5, 6 (not shown). As a further modification, the helical bore 59 may be replaced by a flow control valve between conduits 75, 76, Fig. 7, at opposite ends of a cylinder 74.containing a piston 71 formed by a number of spaced discs 72 each provided at its centre with a small hole 73. The piston 71 is biased to the right of the Figure by a spring 77. On increase of pressure at the inlet conduit 75, the pressure drop across the piston causes it to be moved leftwards against the bias of its spring 77 until ultimately, should the pressure be sufficient, the edge of the piston takes up the dotted position shown at 79, and partially closes the outlet conduit 76. The rate of flow through the device is thereby limited, any further increase in pressure at the inlet conduit 75 serving to move the piston 71 still further to the left and further close the outlet conduit. In a similar modification, a cylinder 80, Fig. 8, containing a number of discs 82 each having a small hole at its centre, by-passes a cylinder 81 containing a piston 84 biased rightwards by a spring 83. When the system is applied to the control of change ratio gearing in which change of mesh of gearing members is not synchronized, or to the control of planetary gearing, the pistons 13, spring 15, &c., are omitted.