Patent GB-691798-A (GB)
Title: Improvements relating to change speed gearing
IPC: F16H61/02
Filed: 1950-08-23
Abstract: 691,798. Change-speed gear; friction clutches. DAIMLER-BENZ AKT.-GES. Aug. 23, 1950 [aug. 23, 1949], No. 20888/50. Classes 80 (i) and 80 (ii). A two-speed planetary or other overdrive unit, between an input shaft 3 from a main change-speed gear and the rear-axle bevel pinion 7, or combined with the main gear on a motor-vehicle, &c., has a direct-drive friction cone-clutch 24 engaged mechanically, e.g., by one or more springs 28, and an overdrive reaction disc-brake 35 engaged by hydraulic, pneumatic or electric auxiliary power, which also effects release of the direct-drive clutch and may be controlled automatically by means responsive to output speed or torque. During a shift-interval (and at all other times) a forwardly arranged free-wheel 19 prevents forwarddrive ratio from falling below direct-drive, whilst a reversely-acting one-way detent 37 sets an upper limit of overrun ratio to overdrive, the detent being releasable automatically at low-speeds or reverse to permit reversing, or controllable to permit its use as a means for preventing backward running of a vehicle on a hill. The planetary train may be double, or, as shown, a single train having ring-gear 22, mounted on the output shaft 7, and integral with a doubly-coned axially-fixed clutch member 24, which is gripped between an axially-movable outer cone 32, fast to a sleeve 17 splined on a reaction sun 14, and an axially-slidable inner cone 31, when, in the absence of fluid-pressure, the spring 28 presses rightwards a piston 27 to thrust the inner cone 31 through pins 30 passing slidably through one end-wall 25 of an axially-slidable cylinder 26 fast to the outer cone 32 and the sun-connected sleeve 17. Oil pressure supplied through an inlet 43 to a cylinder-space 45 urges the piston 27 leftwards, compressing the spring 28 to release the directdrive clutch 24 and clamping against the other end-wall 34 of the sun-connected cylinder 26 a single, axially-fixed, 35, or multiple, 35', brakediscs splined on a fixed member 36, to hold the sun 14 and introduce overdrive. To permit a degree of radial movement, for planet-tooth accommodation, the sun 14 is integral with a long sleeve 15 centred only at its remote end on one-way clutch rollers 19, described below; and splines 23, pins or resilient means which connect the ring-gear 22 to the output shaft 7 permit similar suspension of the ring-gear on the planets. Secured by splines to, the sunsleeve 15 is a member 17, 18, forming the outer element of the forwardly-acting roller freewheel clutch 19, the inner element of which is fast to the input shaft, and also the inner element of the reversely-acting one-way roller detent 37, the outer element 38 of which is normally connected to the fixed casing by a spring-released brake-cone 39 thrust into engagement by hydraulic pressure applied at 46. The inner free-wheel 19 prevents relative forward rotation of the input shaft at a speed greater than that of the output shaft, whilst the detent 37, when effective, prevents backward rotation of the sun, thus preventing forward relative output speed from exceeding that corresponding to forward overdrive ratio on overrun. Thus the relative freedom of the input and output shafts during a "free" shift interval (and at any other time) is limited to a range between direct-drive and overdrive. To permit reverse drive the detent 37 must be released, for which purpose the hydraulic pressure supplied at 46 for holding it may be supplied by a pump having a low or zero output at low forward and all reverse speeds, so as to release automatically, or, where the locking is desirable, e.g., to prevent backward movement of a stationary vehicle on an upgrade, the pressure may be supplied by a separate pump or storage chamber and may be released manually for reversing. The oil pump supplying the overdriveactuating piston space 45 may be driven by a wheel 42 on the output shaft 7, and have a speed responsive output for automatic shift, or the supply may be controlled by speed- or torque-responsive governor. Scavenge and pressure pumps are used in Fig 6, (not shown). In Figs. 2 and 6, (not shown), the directdrive clutch comprises a double internally coned ring having slight positive radial and axial freedom in a cylindrical extension of the ring-gear and gripped between oppositely directed cones, one axially-fixed, the other axiallymovable when the latter is forced towards the former by springs, and released, for overdrive, by oil pressure acting against the springs as before. Fig. 6, (not shown), uses separate pistons for the release of the clutch and engagement of the brake, the former being rotary and of lesser radius than the non-rotary brake piston to reduce centrifugal oil pressure. Dashpot delay means may be incorporated in the pressure-fluid control to permit the overdrive brake to commence engagement after (and disengagement before) commencement of the release (or engagement) of the direct-drive clutch to permit a long shift interval (1 to 2 secs.) during which synchronisation, assisted by the one-way devices can occur. The forward free-wheel is, in this case, arranged directly between input and output shafts. Reference has been directed by the Comptroller to Specification 677,099.