GB2180020A - Continuously variable transmission combining chain and V-belt drives with hydrokinetic torque converter - Google Patents

Abstract

The turbine (18) of a torque converter (12) is connectable to the input sprocket of a chain drive (62,66) for drive through the torque converter at low speeds whereafter drive is transmitted through infinitely variable V-belt gearing (26,28,32,34), the two drives having a common driven shaft (68). A friction brake (80) is selectively actuated for torque multiplication through the chain drive at low speeds. <IMAGE>

Description

SPECIFICATION Continuously variable transmission with hydrokinetic torque converter The invention relates generally to automotive vehicle powertransmission mechanisms having a continuously variable beltdrivefor use during a high speed driving mode and a hydrokinetictorque converterfor use during the initial acceleration mode.

Ahydrokinetictorqueconverterin an automotive vehicle driveline is useful during acceleration from a standing start because it is capable of providing high torque multiplication as well as a smooth variation in torque multiplication ratio as the speed ratio ofthe converterchanges. It also acts as a fluid damperthat eliminates harshness and vibration in the driveline.

After the hydrokinetic torque converter enters its coupling phase, it is characterized by a continuous slippage since, of necessity, the impeller speed must exceed the turbine speed to effect a torquetransfer from the engine to the input elements ofthe transmission. The slip in the hydrokinetic unit gives rise to hydrokinetic losses which reduces fuel consumption efficiency. It is conventional practice to modify the geometry ofthe bladed elements ofthe converter to improve the efficiency ofthe converter during operation in the coupling phase, but this invariably results in a reduction in the'stall torque ratio which reduces the available wheel torque for acceleration purposes.

The mechanical efficiency of positive drive infinitely variable transmissions,that employ variable pitch diameter pulleys and drive belts is higherthantheefficiencyofa hydrokinetic driveline, but it is characterized usually by harshness in the initial start upphase of the acceleration period and by undesirable slippage in the belt and pulley arrangement. An example of an infinitely variable belt and sheave type transmission may be seen by referring to U.S. patent 4,294,137.

It is an object ofthe present invention to combine the most desirable features of a variable pitch diameter belt and sheave transmission with the best features of a hydrokinetic torque converter transmission while eliminating the undesirable features of each.

According to the invention there is provided a powertransmission mechanism for an automotive vehicle comprising a torque converter having an impeller, a statorand aturbine arranged in toroidal flow relationship, means for connecting the impeller to an engine, an infinitelyvariablebeltandsheave assembly a positive drive chain and sprocket assembly, said chain and sprocket assembly and said infinitely variable belt and sheave assembly having a common driven shaft, a dinal drive means for connecting said driven shaft to vehicle traction wheels, said positive drive chain and sprocket assembly including atorqueinputsprocketandsaid belt and sheave assembly including a torque input sheave of variable pitch diameter, a first clutch means forconnecting said turbine to said torque input sprocket during low speed ratio operation whereby hydrokinetictorque is distributed from said converterthrough said clutch and through said chain and sprocket assembly to said driven shaft, and friction brake means for anchoring said statorto effect hydrokinetic torque multiplication in said converter.

The torque converter in the improved driveline provides adequate torque ratio and functions reliably during fast orslow idlewhile dampening driveline vibration and reducing harshness.

The converter may be designed for maximum torque multiplication during acceleration. For example, a stall torque ratio of about 2.5:1 may be achieved using a bladed hydrokinetictorque converter and the output torque ofthe converter is transferred by a drive chaintothe output shaft axis. If the drive chain ratio is 2:1 and the final drive and axle system is 4:1, a total torque multiplaction during acceleration from a standing start is 20:1.Afterthe torque converter reaches its coupling phase when the ratio in the hydrokinetic unit is 1:1 the overall ratio for the driveline is reduced to 8:1. At that time the variable ratio belt is activated and the hydrokinetictorque converter is removed from the driveline.Upon further acceleration of the vehicle, the overall transmission ratio may be controlled from 8:1 down to 2:1 This range is capable of providing effective downhill braking for all driving situations.

Since the torque converter is removed or bypassed during normal driving operations,the blading ofthe converter may be designed without the requirement that the blading provide low slip during the coupling phase ofthe converter. Thus it is possible to achieve maximum hydrokinetictorque multiplication since the converter is removed from the driveline during cruising, and in this way the hydrokinetic losses normally associated with hydrokinetictorque convertertransmissionsduring cruising are eliminated. The stall speed ofthetorque converter may be designed to provide sufficiently high engine speed so that the engine during initial acceleration may operate at its maximumtorquevalue.

During operation ofthe driveline in reverse,the statortorque is relied upon to effect reverse torque delivery through the gearing. The drive chain, rather than the belt, is effective during reverse torque.

In the event of failure of the belt during operation, the torque converter and the chain still may be usable to effectforward driving as well as reverse driving.

The invention will now be further described byway of example with reference to the accompanying drawings in which: Figure lisa schematic representation of the improved driveline showing a hydrokinetic torque converter, a variable displacement belt drive and a positive displacement chain drive.

Figure2 is a chartthat shows the patter of engagement ofthe clutches and brakes ofthe mechanism shown in Figure 1 to effect a low speed ratio, a forward drive cruising ratio and a reverse drive ratio, and Figure 3 is a chart that shows the performance characteristics of the transmission mechanism illustrated schematically in Figure 1.

In Figure 1 reference numeral 10 designated the crankshaft of an internal combustion engine. A hydrokinetictorque converter 12 includes an impeller 14 connected drivably through a driveplate 16to the crankshaft 10. The impeller 14 is in fluid flow relationship with respect two a turbine 18 and a bladed stator 20.

The impeller 14 is connected drivablyto a sleeve shaft22 which serves as a torque input shaftfora positive displacement pump 24. This pump serves as a fluid pressure source foroperating servosforthe clutches and brakes to be described subsequently.

Shaft 22 is adapted to be connected to drive sheave 26 of an infinitely variable belt drive system 28. The connection between shaft 22 and the sheave 26 is established by selectively engageable friction clutch 30 located between the sheave 26 and thetorque converter 12. Provision is made for adjusting the spacing ofthe sheave portions to provide a variable pitch radiusfora drive belt 32. The sheave portions may be adjusted axially, one with respect to the other, as indicated in patent 4,294,137 so thatthe operating pitch diameter of the belt 32 is moved closer orfartherfrom the axis of rotation ofthe sheave depending upon the axial adjustment ofthe spacing ofthesheave portions.

The driven sheave assemblyforthe variable belt drive 28 is shown in 34. Like the sheave 26 it includes displaceable sheave portions that register, one with respect to the other, to define a "V" groove in which belt 32 is positioned. The edges of the belt have a cone angle resembling the cone developed by the sheave portions. As the belt 32 moves toward the axis ofthe sheave 26, it moves away from the axis of the sheave 34, and vice versa. Fluid pressure operated servor, such as that shown in patent'137, are used to effect axial displacement of the sheave portions in order to achieve a variation in pitch radius forthe belt.

The output sheave 34 is connected drivablyto sun gear 36 of a final drive gear unit 38. Gear unit 38 includes also a fixed ring gear 40, a planetary carrier 42 and planet pinions 44journalled on the carrier42.

Carrier42 is connected to the differential carrier of a differential gear mechanism 46 which includes carrier 42, pinions 48 and side gears 50 and 52. Side gear 50 is connected to the input side of a first universal joint 54 and side gear 52 is connected through a second U-joint 56 by means of drive shaft 58. The sheave 34 is journalled aboutthe axis of shaft 58. The output sides of universal joints 54 and 56 are connected to the vehicle traction wheels.

A positive drive chain 60 includes a drive sprocket 62 connected to sleeve shaft 64. It includes an output drive sprocket 66 connected to sleeve shaft 68, which is connected also to sun gear 36 and sheave 34. Drive chain 70 connects sprocket 62 with sprocket 66. A low speed ratio selectively engageable friction clutch 74 is adapted to connect the turbine shaft 72 with the sleeve shaft 64. Turbine shaft 72 is coaxial with the sheave 36 and sleeve shaft 22. Thus when the clutch 74 is applied by a fluid pressure operated servo, not shown, a direct mechanical connection is established between turbine shaft 72 and sleeve shaft68throughthechain70.

A stator sleeve shaft 76 is arranged concentrically with respect to the shaft 72 and 22. Stator 20 is adapted to distribute torque in the reverse direction to the sleeve shaft 76 through overrunning coupling 78. Shaft 76, during operation of the torque converter inthetorquemultiplication range, is braked buy a selectively engageable friction brake 80 thus providing a hydrokinetictorque reaction. During reverse drive a selectively engageable reverse clutch 82 is applied whereby the statortorque is distributed through the clutch 82 to the sprocket 62. Underthese reverse driving conditions turbine shaft 72 is braked by selectively engageable friction brake 84.Thus the hydrokinetictorque converter acts in a fashion similarto its mode ofoperation during operation at stall as reverse driving torque is distributed through the coupling 78 and through the clutch 82 to the sprocket 62.

The mode of operation of the structure of Figure 1 can be seen by referring to Figure 2. In the left hand column of Figure 21 have indicated the drive ranges. I have indicated also by "X" marks the clutches and brakes that are engaged to effect the various drive conditions. To achieve a low speed ratio forward drive mode, clutch 74 which carries the symbol Lc, is applied as well as the brake 80, which carries the symbol Lb. Underthese conditions hydrokinetic torque is distributed through the turbine shaft 72 and through the engaged clutch 74to the sprocket 62.

Torque then is transferred to the universal joints throughthedifferential assembly46.

A ratio change from the low speed ratio to the drive ratio is achieved by releasing clutch 74 and applying clutch 30, which carries the symbol "D". Under these conditions a direct connection is established between the impeller and the input sheave 26.

Torque is transferred through the sheave and belt assembly 28to the sun gear36and hencetothe differential assembly. The hydrokinetic portion ofthe torque flow path is eliminated and all ofthe driving torque is distributed mechanically through the infinitely variable belt drive assembly 28.

It may be seen in Figure 2thatthe initial overall reduction ratio may start at 20:1, but it is reduced to 2:1 as the transition from hydrokinetic drive to infinitely variable mechanical drive takes place.

Figure 2 also indicates that reverse drive is achieved by engaging reverse clutch 82, which carries the symbol Rc and reverse brake 84. In these circumstances reverse stator torque is distributed through the stator shaft 76 and through clutch 82to the chain drive which drives the sun gear36 in the reverse direction.

Figure 3 shows one method of controlling the clutches and brakes to achieve the desired relationship of engine speed to vehicle speed.

Engine speed is plotted on a vertical axis and vehicle speed is plotted in miles per hour on the horizontal axis. The accelerator pedal position determines a governed engine speed, and the throttle is controlled by a preset relationship with respect to enging speed.

The wide open throttle path indicated in Figure 3 results from moving the accelerator pedal to a position that calls for a governed engine speed of 4,800 RPM. Sincethetorque converter speed at wide open enginethrottle is about 2,500 RPM in atypical embodiment, thetorqueflow path isthroughthe chain until the vehicle accelerates to a speed of 30 miles per hour. Then as the engine attempts to exceed a speed of 4,800 RPM, the variable drive assembly 28 is clutched in and the chain is declutched. Thus the ratio is gradually decreased from 2:1 to prevent the engine from exceeding the governedvalue.Asimilarcontrol is availablefor part throttle acceleration, as indicated on the dotted line curve of Figure 3.

Claims (5)

1. Apowertransmission mechanismforan automotive vehicle comprising a torque converter having an impeller, a stator and a turbine arranged in toroidal flow relationship, means for connecting the impellerto an engine, an infinitely variable belt and sheave assembly, a positive drive chain and sprocket assembly, said chain and sprocket assembly and said infinitely variable belt and sheave assembly having a common driven shaft, a final drive means for connecting said driven shaft to vehicle traction wheels, said positive drive chain and sprocket assembly including a torque input sprocket and said belt and sheave assembly including a torque input sheave of variable pitch diameter, a first clutch meansforconnecting said turbine to said torque input sprocket during low speed ratio operation whereby hydrokinetictorque is distributed from said converterthrough said clutch and through said chain and sprocket assembly to said driven shaft, and friction brake means for anchoring said statorto effect hydrokinetictorque multiplication in said converter.

2. ThecombinationassetforthinClaim 1 wherein said converter, said belt and sheave assembly and said chain and sprocket assembly are arranged coaxially, said brake means being releasable during reverse drive and reverse drive clutch means for connecting said statorto said driving sprocket during reverse drive whereby torque is distributed from said stator and through said chain and sprocket assemblyto said driven shaft.

3. The combination assetforth in Claim 1 wherein said driven shaft is arranged in spaced parallel relationship with respect two the axis of said converter said final drive means comprises a final drive planetary gear and a differential assembly, said final drive gear including afixed ring gear, a sun gear connected to said drive shaft and a planetary carrier, said differential assembly including a differential converter connected to the carrier of said final drive planetary gear unit, and side gears adapted to be connected to said vehicle traction wheels.

4. The combination assetforth in Claim 1 wherein said driven shaft is arranged in spaced parallel relationship with respect to the axis ofsaid converter, said final drive means comprises a final drive planetary gear and a differential assembly, said final drive gear including a fixed ring gear, a sun gear connected to said driven shaft and a planetary carrier, said differential assembly including a differential carrier connected to the carrier of said final drive planetary gear unit, and side gears adapted to be connected to said vehicle traction wheels.

5. Apowertransmission mechanism substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.