CONTINUOUSLY VARIABLE TRANSMISSION SYSTEM

Abstract: A two regime, continuously variable ratio transmission system having coaxial input and output shafts, comprises: a continuously variable ratio transmission unit (a variator) connected coaxially to the input shaft and having a coaxial output shaft; a mixing epicyclic gear train having a first input gear coupled to the system input shaft in 1:1 ratio, a second input gear, and an output gear coupled to the system output shaft in 1:1 ratio; a Low Regime epicyclic gear train disposed between the variator and the mixing epicyclic gear train and having an input gear coupled to the variator output shaft, a braked gear cooperating with a Low Regime brake, and an output gear coupled to the mixing epicyclic second input gear, whereby drive may be transmitted in Low Regime from the variator output to the mixing epicyclic in a non-unity ratio; and High Regime clutch means, connected so as to couple the variator output shaft to the system output shaft in 1:1 ratio when engaged.

Description: CONTINUOUSLY VARIABLE TRANSMISSION SYSTEM This invention relates to a continuously variable ratio transmission system suitable for use in motor vehicles, for example. In particular, it is concerned with transmissions of the two regime type, that is transmissions operable in either Low Regime with power recirculation or High Regime without it. Continuously variable ratio transmissions are well known, and one of the toroidal race-rolling traction type is described in UK Patent Application No 2108600A. Two regime continuously variable ratio transmission systems are also now known, and one using a toroidal race-rolling traction transmission unit is disclosed in UK Patent Application No 2100372A. It is an object of the present invention to provide a two regime system which is coaxial throughout, conveniently compact and simple in construction. The invention consists in a two regime, continuously variable ratio transmission system having coaxial input and output shafts, comprising: a continuously variable ratio transmission unit (a variator) connected coaxially to the input shaft and having a coaxial output shaft; a mixing epicyclic gear train having a first input gear coupled to the system input shaft in 1:1 ratio, a second input gear, and an output gear coupled to the system output shaft in 1:1 ratio; a Low Regime epicyclic gear train disposed between the variator and the mixing epicyclic gear train and having an input gear coupled to the variator output shaft, a braked gear cooperating with a Low Regime brake, and an output gear coupled to the mixing epicyclic second input gear, whereby drive may be transmitted in Low Regime from the variator output to the mixing epicyclic in a non-unity ratio; and High Regime clutch means, connected so as to couple the variator output shaft to the mixing epicyclic output gear when engaged. In the preferred form of the invention, the mixing epicyclic is a compound epicyclic with a positive basic ratio, enabling the first and second input gears to rotate in the same direction, and the Low Regime epicyclic is simple with a negative basic ratio. The basic ratio of an epicyclic gear train is defined here as the velocity of the sun gear divided by the velocity of the annulus, with the planet carrier stationary. Preferably, in the mixing epicyclic the sun gear is the first input, the annulus is the second input, and the planet carrier is the output which is connected to the High Regime clutch means and the system output, and in the Low Regime epicyclic the sun gear is the input gear, the annulus is the output, and the planet carrier is the braked gear. The basic ratios of the Low Regime epicyclic and of the mixing epicyclic are in one example approximately -3.7 and 2.9 respectively. The annuli of both epicyclic gear trains are conveniently integral. In order that the invention may be better understood, a preferred embodiment of a transmission system will now be described with reference to the accompanying drawings, wherein: Figure 1 is a schematic diagram of a transmission system according to the preferred embodiment; and Figure 2 is a view in cross-section of part of the transmission system of Figure 1, showing only a section above the centre axis of the transmission. Referring firstly to Figure 1, a toroidal race-rolling traction type continuously variable ratio transmission unit 10, hereafter known as variator 10, has an input shaft 11 coinciding with (and therefore in 1:1 ratio with) the system input shaft 11. The input shaft 11 drives a toroidally-recessed disc at each end of the variator unit. The upper part of the right-hand one of these discs is shown as 101 in Figure 2. A pair of similar discs, facing respective ones of these driven discs, is connected to a variator output shaft 12 which extends at 13 coaxially with the system input shaft 11. As described more fully in the Applications mentioned above, sets of rollers are mounted between opposing faces of these discs to transmit drive from input to output with a gear ratio which is variable by tilting the rollers. Depending on the Regime which is selected, drive from the variator output 12, 13 reaches a mixing compound epicyclic gear train 15 by way of either a Low Regime simple epicyclic gear train 14 or a High Regime multiplate clutch H. The sun gear of the mixing epicyclic 15 receives drive from the system input shaft 11. The summed output from the mixing epicyclic 15 is taken from the planet carrier to the system output shaft 16. For Low Regime, that is usually for a range of system output shaft speeds of between maximum reverse speed and slow forward speed, the clutch H is disengaged and a brake L is applied to anchor the planet carrier 18 of the Low Regime epicyclic 14 to the system casing (not shown). Drive is then taken from the input shaft 11 through a sun gear 17 and planet pinions 18A to the annulus 19. The basic gear ratio of the Low Regime epicyclic is in this example -3.665 (negative). The annulus 19 is integral with the annulus of the mixing epicyclic gear train 15, which sums drive from both input and output variator shafts and provides the system output to shaft 16, with a degree of power recirculation within the variator. For High Regime, that is usually for a range of system output shaft speeds of slow forward to maximum forward, the clutch H is engaged and the Low Regime brake released. Drive is then taken directly from variator output shaft 13, via the planet carrier 21 of the mixing epicyclic, to the system output shaft 16 in 1:1 ratio. The mixing epicyclic 15 runs freely, and no torque is transmitted by the sun gear 20. There is no power recirculation. The basic gear ratio of the mixing compound epicyclic is in this example 2.909 (positive). The High Regime clutch H is an hydraulically operable multiplate clutch operated automatically by a computer-controlled hydraulic control system. The same computer is responsible for operating the Low Regime brake L and for controlling the variator in response to external conditions. In particular, the computer effects a change between Low and High regimes. The design of this system especially allows for a synchronous change between the two regimes, i.e. the gear trains are such that their rotational velocities undergo no appreciable change at the point of change from Low to High regime or vice versa. In some applications also it will be desirable to operate in both regimes simultaneously, locking both the clutch H and the brake L. Figure 2 shows in cross-section the upper half of part of the system of Figure 1, of which the parts having identical numbers have already been described. The hydraulic control fluid for the clutch H enters through a passage 22 adjacent the output shaft 16, and is passed through the compound epicyclic gear train 15 by means of special axial channels 23 arranged between the two sets of planet pinions 21A, reaching an annular chamber 24 in which slides a piston for applying pressure to the clutch plates. A system according to the invention may be incorporated in any power driveline, it is especially useful in a motor vehicle between the vehicle engine and the final drive.

Claims: CLAIMS 1. A two regime, continuously variable ratio transmission system having coaxial input and output shafts, comprising: a continuously variable ratio transmission unit (a variator) connected coaxially to the input shaft and having a coaxial output shaft; a mixing epicyclic gear train having a first input gear coupled to the system input shaft in 1:1 ratio, a second input gear, and an output gear coupled to the system output shaft in 1:1 ratio; a Low Regime epicyclic gear train disposed between the variator and the mixing epicyclic gear train and having an input gear coupled to the variator output shaft, a braked gear cooperating with a Low Regime brake, and an output gear coupled to the mixing epicyclic second input gear, whereby drive may be transmitted in Low Regime from the variator output to the mixing epicyclic in a non-unity ratio; and High Regime clutch means, connected so as to couple the variator output shaft to the system output shaft in 1:1 ratio when engaged. 2. A transmission system in accordance with Claim 1, wherein the mixing epicyclic has a positive basic ratio, and wherein the Low Regime epicyclic has a negative basic ratio. 3. A transmission system in accordance with Claim 2, wherein the mixing epicyclic is a compound epicyclic gear train whose sun gear is the first input, whose annulus is the second input, and whose planet carrier is the output, the output being connected to the High Regime clutch means and to the system output, and the positive basic ratio enabling the first and second input gears to rotate in the same direction when the planet carrier is stationary. 4. A transmission system in accordance with Claim 1,2 or 3, wherein the Low Regime epicyclic is a simple epicyclic gear train whose sun gear is the input gear, whose annulus is the output, and whose planet carrier is the braked gear. 5. A transmission system in accordance with Claim 4 as appendant to Claim 3, wherein the annuli of both epicyclic gear trains are integral. 6. A transmission system in accordance with any preceding claim, wherein the gear trains are such that their rotational velocities undergo no appreciable change at the point of change from Low to High regime or vice versa. 7. A transmission system in accordance with any preceding claim, wherein the variator is of the toroidal race-rolling traction type. 8. A transmission system in accordance with any preceding claim, wherein the High Regime clutch means is an hydraulically operable multiplate clutch having a fluid supply taken through the Low Regime mixing epicyclic gear train. 9. A transmission system in accordance with any preceding claim, wherein the basic ratios of the Low Regime epicyclic and of the mixing epicyclic are in the ranges -3 to -4, and 2.5 to 3.5, respectively. 10. A transmission system in accordance with Claim 9, wherein the basic ratios of the Low Regime epicyclic and of the mixing epicyclic are substantially -3.7 and 2.9 respectively. 11. A motor vehicle whose drive train from engine to final drive incorporates a transmission system according to any preceding claim.

Inventors: GREENWOOD, CHRISTOPHER J.
Applicants: TOROTRAK (DEVELOPMENT) LIMITED
Application year: 1984
Main classification: F16H37
IPC codes: F16H37, F16H3