GB602316A - Improvements in or relating to change-speed power transmission mechanism - Google Patents

Abstract

602,316. Change-speed gearing. HOBBS, H. F. Oct. 24, 1944, No. 20608. [Class 80 (ii)] Relates to change-speed gearing of the kind (e.g. as described in Specifications 549,988 and 560,379) wherein two concentric intermediate shafts 16, 17 are selectively driven either separately through nested friction clutches 10 or 12 on a driving (or driven) drum 13, or differentially together through differential gearing 21 and a third nested friction clutch 11, the shafts 16, 17 being connected to the driven (or driving) shaft 40 through further change-speed gearing, shown as being of the type having a countershaft 39 and two splined wheels 35, 37 slidable on the driven shaft 40. In such an arrangement in each of three settings of the countershaft gear three ratios are provided by the nested clutches 10, 11, 12, so that three series of three ratios are possible. According to this invention one ratio of each series provided by one setting of the countershaftgear is equal or nearly equal to one ratio provided by the adjacent series given by another setting of the countershaft gear, so that the change of setting of the 'countershaft-gear can be made between members running at the same speed and synchronizing means for the sliding-wheels 35, 37 and a jaw-clutch 41 are unnecessary. Synchronizing means may, however, be provided for one or more of the changes. Seven different ratios ranging from 4 to 1 to 0.5 to 1 are available. The first (lowest) series of three ratios is with the countershaft-gear set in the position shown, first-speed being through friction clutch 10 alone, intermediate shaft 16 and wheel pairs 31, 32 ; 38, 37. In second-speed the same final wheel pair 38, 37 is driven differentially through the clutch 11 alone, differential gear 21, both intermediate shafts 16, 17 and both wheel pairs 31, 32 ; 33, 34. In third speed the same pair 38, 37 is driven through clutch 12 alone, intermediate shaft 17 and wheel-pair 31, 32. For the second series of ratios, the setting of the countershaft-gear is changed by sliding the wheel 37 out of mesh and sliding the wheel 35 into mesh with a countershaftwheel 36, the first ratio being through clutch 12 alone, and wheel-pairs 33, 34 ; 36, 35. In order to produce the synchronous shift above referred to, the ratio of the wheel-pairs 31, 32 and 36, 35 are equal (both 1 to 1), as are also those of wheel-pairs 33, 34 and 38, 37 (both 2 to 1). Thus in the third ratio of the first series, the driven shaft 40 and wheels 35, 37 both rotate at half-engine speed. For the change to the first ratio of the second series the clutch 12 and wheel 37 are disengaged and the clutch 10 is engaged. Prior to mesh of the wheel-pair 36, 35, the driven shaft 40 and wheel 35 continue to run at half-engine speed by momentum, and, since the drive through clutch 10 and wheel-pair 33, 34 is at 2 to 1 ratio, the countershaft is driven at half-engine speed, so that the peripheral speeds of the wheels 35, 36 are equal and they can be engaged without shock, the new ratio being the same (2 to 1) as that just left. Two additional ratios are possible in this second series by use of the clutches 10, 11, the higher being 1 to 1 through wheel-pairs 31, 32 ; 36, 35, which is the same as that obtained by changing to the first ratio of the third series by engaging jaw-clutch 41 and driving directly through the clutch 10, so that a similar synchronised shift to the third series can be made. The third series provides two overdrive ratios, one through clutch 11, differential-gear 21, both intermediate shafts 16, 17, wheel-pairs 31, 32 ; 34, 33 and jawclutch 41, and the highest ratio (0.5 to 1) through clutch 12, intermediate shaft 17 and wheel-pairs 31, 32 ; 34, 33. Three reverse ratios are provided by sliding an idler (not shown) to mesh the wheels 37, 38 after the former has been disengaged from the wheel 38. One or more jaw-clutches may be arranged on the countershaft. Control may be effected by a single lever movable into three positions to control the three series of ratios, the lever carrying a three-position knob operating a valve which controls the friction clutches hydraulically, the valve being moved back as the lever moves to the next series. Control may be hydraulic or manual, or partly automatic, in which latter case the friction clutches are controlled by a centrifugal valve on the driving drum 13.