GB1599957A

GB1599957A - Transmission arrangement

Info

Publication number: GB1599957A
Application number: GB1628878A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-12-30
Filing date: 1978-04-25
Publication date: 1981-10-07
Also published as: DE2758905A1; JPS5496654A

Description

(54) A TRANSMISSION ARRANGEMENT (71) We, ROBERT BOSCH GMBH., a German company of 50, Postfach Stuttgart, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention provides a transmission arrangement for connecting a prime mover to a load to be driven which is particularly suitable for use in motor vehicles.

In order to provide a power connection between the driving side (prime mover) and the driven side in a motor vehicle, it is known to use either a step-by-step transmission providing a discrete number of fixed ratios or a stepless transmission providing a continuously variable transmission ratio.

Generally, step-by-step transmissions are formed as spur gear drives with traction force interruption or planet gear drives without traction force interruption; stepless transmissions use either belt drives provided with variable pulley separation or hydrostatic drives.

If it is desired to operate an engine in accordance with the required driving power always being on the minimum fuel consumption curve, wherein, according to the operating cycle, 20 to 25% fuel can be saved, it is necessary to use a stepless drive or a very finely graded change speed drive (step-by-step transmission) for matching the power between the driving side and the driven side. With such a fine variation of the transmission ratio, the speed adjustment or change speed operations must take place automatically since, with manual operation, too much attention would be required from the driver. In practice, a change speed range of at least 1:6 is necessary for this method of operation. Whereas with a stepless drive, the optimum consumption curve can always be followed, with a change speed drive it means that at least six speed ratios must be provided in order to achieve a useful gradation. As opposed to the advantage of the stepless drive, there are however the disadvantages that, with such a wide adjustment range, the efficiency becomes considerably worse compared to a selectable gear transmission or a direct drive between engine and load (i.e. 1:1 ratio). As opposed to the advantage of improvied efficiency with step-by-step transmissions, there are, on the other hand, the disadvantages that the optimum load curve cannot alwavs be followed due to the gear speed gradation, which leads to an over-consumption, especially in the low speed range, and that a considerable overpower input is necessary at the high speed ratio due to the then very complex planet gear drive and the requirement of changing ratio without interrupting the traction force.

It is furthermore known to operate a stepless drive by power division in series with different changeable gearwheel speed ratios but this require a considerable expenditure in gearwheels.

The present invention provides a transmission arrangement for connecting a prime mover to a load to be driven, comprising a continuously variable ratio transmission means and a fixed ratio transmission means, which means are alternatively selectable to provide one of two transmission paths between the prime mover and the load.

The preferred embodiment of the invention provides a transmission which combines a stepless belt drive with a direct drive, thereby providing a simple, cheap and operationally secure combination of a stepless drive and a change speed drive. In this manner, it is possible, without a nominal excess power input, to provide a method of operating a motor vehicle with an optimum consumption by following the curve of optimum consumption in the low speed range by means of the stepless drive and by following it in the upper speed range by means of the direct drive.

An especially simple construction is produced when the prime mover is coupled to a variable diameter pulley of a stepless belt; drive, if necessary through a set of planet gears providing a reverse gear, which belt drive can be selectively connected through a clutch to the driven side wherein a further variable diameter pulley drives a parallel shaft which can be likewise connected to the driven shaft through a further clutch and a pair of gearwheels.

Then the drive connection between the prime mover and the load can be provided either directly or through the stepless belt drive by a simple actuation of one or the other clutch, the direct drive being available in the higher speed range and the stepless belt drive in the lower speed range.

In order that the present invention may be more readily understood, two embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a family of curves for the output power from a motor vehicle drive against speed; Figure 2 is a representation showing the principle of a first embodiment of a transmission arrangement; and Figure 3 is a representation showing the principle of a second embodiment of a transmission arrangement.

The curves of the output power from a motor vehicle drive plotted against speed are illustrated in Figure 1. A family of curves is produced from the curves for 1st, 2nd, 3rd and 4th speed gears as well as a direct drive D. The intersection of the curve for the direct drive D with the resistance to motion parabola W provides for the maximum vehicle speed v x on the abscissa. In comparison to this, the curve of a stepless drive is illustrated by way of a dotted curve 7. Now if a stepless drive is combined with the direct drive, as is further described below, the thickly represented curve 8 is produced which can be rounded off in its transition region of the direct drive D into a dotted curve 9 by further measures described below.

An embodiment of a transmission arrangement in accordance with the invention for achieving a curve 8 according to Figure 1 is illustrated in Figure 2a. A driving machine 10 is connected to a set of planet gears 12 through a clutch, in the illustrated example a centrifugal clutch 11.

The set of planet gears 12 has a sun wheel 121, planet wheels 122 and an internal gear 123. The web supporting the planel wheels 122 can be held fast by means of a fixed clutch Kl. A power connection can be provided to the sun wheel 121 through a clutch K2 located at the internal gear 123.

The output shaft 124 of the set of planet gears 12 connected to the internal gear 123 carries a pulley 131 of a stepless belt drive 13 and can be connected through a clutch K3 to a driven shaft 14. The driven shaft 14 acts on the driving side consisting of a differential 15 and wheels 16. A further pulley 132 of the stepless belt drive 13 is mounted on a parallel shaft 17 by means of which, through a clutch K4, a gearwheel 18 can be driven which is in engagement with a gearwheel 19 which once again meshes with a gear wheel 20 mounted on the driven shaft 14.

Figure 2b shows a variant of part of the transmission arrangement illustrated in Figure 2a. Instead of a centrifugal clutch 11 a torque converter 21 is provided which may include a bridging clutch K0 as shown.

Finally, Figure 2c shows the change speed condition of the clutches K,, Kl, K2, K3 and K4 for the different types of operation: I=starting (i.e. from rest in the case of a motor vehicle), II=low speed gear range, III=high speed gear range, R=reverse travel. Moreover, a distinction between the types of operation I and II, is only necessary with a transmission arrangement comprising a torque converter provided with a bridging clutch K0 according to Figure 2b. In all three types of operation, it is assumed that the prime mover (e.g. internal combustion engine) is already running.

The method of operation of the transmission arrangement illustrated in Figure 2 is as follows: In the low speed range, that is to say in the range in which travel is to be provided by the stepless drive, the clutches K2 and K4 are first of all engaged. This means that the set of planet wheels 12 rotates together with the driving shaft and the power connection to the driven shaft 14 is provided through the stepless belt drive 13, the coupling K4 and the gearwheel arrangement 18, 19, 20. After the starting from rest procedure has ended, if the bridging clutch K0 is provided, it is engaged and the transmission changes from type of operation I to II. Now if the vehicle enters the upper speed range (operation III) the clutch K4 is disengaged and the clutch K3 engaged. The condition of the clutch K2 is not altered. The power connection from the driving machine 10 then arrives at the driven shaft 14 directly through the output shaft 124 of the set of planet wheels 12 and the clutch K3. The reverse gear can be engaged by holding the planet wheel carrier for the set of planet wheels 12 by the fixed clutch Kl with the clutch K2 disengaged since the sense of rotation between the input and output shafts is then reversed in the set of planet wheels 12. Moreover, the further transmission of force to the driven shaft 14 takes place in a preferable manner through the stepless belt drive 13 and the clutch K4.

A further preferred embodiment of the transmission arrangement according to the invention is illustrated in Figure 3a. Once again, the driving machine 10 drives through a clutch 22 which can be formed as a centrifugal clutch or a torque converter (as previously described and shown), the output shaft 124 on which the pulley 131 of the stepless belt drive 13 is mounted and which can be connected furthermore through the clutch K3 to the driven shaft 14.

The driven shaft 14 carries an axially displaceable dog ring 23 from which a power connection to the gearwheels 24 or 25 can be provided selectively through the dog clutches K5 and K6. A parallel shaft 29 provided with gearwheels 27, 28 can be driven by the other pulley 132 of the stepless belt drive 13 through the clutch K4.

Moreover, the gearwheel 27 is in engagement through a further gearwheel 26 with the gearwheel 27 and the gearwheel 28 meshes with the gearwheel 25.

Finally, Figure 3b shows the change speed condition of the clutches K3, K4, K5 and K5 for the operating conditions II, III and R with the transmission arrangement illustrated in Figure 3a. In this instance, a distinction between the operating conditions I and II has not been made for reasons of simplicity.

The method of operation of the transmission arrangement illustrated in Figure 3a is as follows: In the type of operation II the clutches K4 and K5 are engaged. Thus, a power connection from the driving machine 10 to the driven shaft 14 is provided through the stepless belt drive 13, the clutch K4, the gearwheels 27, 26, 24, the dog clutch K5 and the dog ring 23. On changing from the type of operation II to the type of operation III the clutch K4 is disengaged and the clutch K3 engaged.

Once more, a direct connection from the driving side to the driven side is produced thereby. Preferably, the clutch K, remains engaged in the type of operation III whereupon the parallel shaft 29 rotates therewith during changing back into the type of operation II, so that a shock-free engagement of the clutch K4 is made possible, the gearwheel 24 being already in engagement with the dog ring 23 through the dog clutch K5. Finally, the reverse gear is provided by engaging the clutches K4 and K6. In so doing, the power connection is provided through the stepless belt drive 13, the clutch K4, the gearwheels 28, 25, the dog clutch K6 to the dog ring 23 and thus to the driven shaft 14 whereby, at the same time, a reversal of the sense of rotation between the driving and driven shafts takes place.

Changing over from the type of operation I to the type II can take place in known manner by determining the speed ratio between the converter input and the converter output. Either a manual or an automatic electronic changeover can be provided for changing between the types of operation Il-Ill. Moreover, the type of operation II will be used substantially in the low speed range (town traffic) whilst the transmission arrangement is used in the type of operation III for long-distance travel or at high speeds. The fall in power during the transition from the type of operation II (stepless drive) to the type of operation III (direct speed gear) as is illustrated in the diagram according to Figure 1 by the thick line 8, can be reduced by a short disengagement of the bridging clutch K0 for the torque converter 21 during the transition, thereby providing a torque conversion effect. In this manner, the modified curve 9 is produced having a somewhat smoother transition from the stepless drive to the direct gear drive.

WHAT WE CLAIM IS: 1. A transmission arrangement for connecting a prime mover to a load to be driven, comprising a continuously variable ratio transmission means and a fixed ratio transmission means, which means are alternatively selectable to provide one of two transmission paths between the prime mover and the load.

2. A transmission arrangement according to claim 1 further including a centrifugal clutch arranged between the prime mover and the selectable transmission means.

3. A transmission arrangement according to claim 1 further including a torque converter arranged between the prime mover and the selectable transmission means.

4. A transmission arrangement according to claim 1, 2 or 3 wherein the fixed ratio transmission means provides a direct drive path.

S. A transmission arrangement according to any one of the preceding claims further including an input shaft arranged to be driven by the prime mover and an output shaft for driving the load, wherein the fixed ratio transmission means comprises a clutch for selectively providing drive from the input shaft to the output shaft, and wherein the continuously variable ratio transmission means comprises a first variable diameter pulley coupled to the input shaft, a second variable diameter pulley connected to the first pulley by means of an endless belt, and a further clutch for selectively allowing

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

further transmission of force to the driven shaft 14 takes place in a preferable manner through the stepless belt drive 13 and the clutch K4.

A further preferred embodiment of the transmission arrangement according to the invention is illustrated in Figure 3a. Once again, the driving machine 10 drives through a clutch 22 which can be formed as a centrifugal clutch or a torque converter (as previously described and shown), the output shaft 124 on which the pulley 131 of the stepless belt drive 13 is mounted and which can be connected furthermore through the clutch K3 to the driven shaft 14.

The driven shaft 14 carries an axially displaceable dog ring 23 from which a power connection to the gearwheels 24 or 25 can be provided selectively through the dog clutches K5 and K6. A parallel shaft 29 provided with gearwheels 27, 28 can be driven by the other pulley 132 of the stepless belt drive 13 through the clutch K4.

Moreover, the gearwheel 27 is in engagement through a further gearwheel 26 with the gearwheel 27 and the gearwheel 28 meshes with the gearwheel 25.

Finally, Figure 3b shows the change speed condition of the clutches K3, K4, K5 and K5 for the operating conditions II, III and R with the transmission arrangement illustrated in Figure 3a. In this instance, a distinction between the operating conditions I and II has not been made for reasons of simplicity.

The method of operation of the transmission arrangement illustrated in Figure 3a is as follows: In the type of operation II the clutches K4 and K5 are engaged. Thus, a power connection from the driving machine 10 to the driven shaft 14 is provided through the stepless belt drive 13, the clutch K4, the gearwheels 27, 26, 24, the dog clutch K5 and the dog ring 23. On changing from the type of operation II to the type of operation III the clutch K4 is disengaged and the clutch K3 engaged.

Once more, a direct connection from the driving side to the driven side is produced thereby. Preferably, the clutch K, remains engaged in the type of operation III whereupon the parallel shaft 29 rotates therewith during changing back into the type of operation II, so that a shock-free engagement of the clutch K4 is made possible, the gearwheel 24 being already in engagement with the dog ring 23 through the dog clutch K5. Finally, the reverse gear is provided by engaging the clutches K4 and K6. In so doing, the power connection is provided through the stepless belt drive 13, the clutch K4, the gearwheels 28, 25, the dog clutch K6 to the dog ring 23 and thus to the driven shaft 14 whereby, at the same time, a reversal of the sense of rotation between the driving and driven shafts takes place.

Changing over from the type of operation I to the type II can take place in known manner by determining the speed ratio between the converter input and the converter output. Either a manual or an automatic electronic changeover can be provided for changing between the types of operation Il-Ill. Moreover, the type of operation II will be used substantially in the low speed range (town traffic) whilst the transmission arrangement is used in the type of operation III for long-distance travel or at high speeds. The fall in power during the transition from the type of operation II (stepless drive) to the type of operation III (direct speed gear) as is illustrated in the diagram according to Figure 1 by the thick line 8, can be reduced by a short disengagement of the bridging clutch K0 for the torque converter 21 during the transition, thereby providing a torque conversion effect. In this manner, the modified curve 9 is produced having a somewhat smoother transition from the stepless drive to the direct gear drive.

WHAT WE CLAIM IS:

1. A transmission arrangement for connecting a prime mover to a load to be driven, comprising a continuously variable ratio transmission means and a fixed ratio transmission means, which means are alternatively selectable to provide one of two transmission paths between the prime mover and the load.

2. A transmission arrangement according to claim 1 further including a centrifugal clutch arranged between the prime mover and the selectable transmission means.

3. A transmission arrangement according to claim 1 further including a torque converter arranged between the prime mover and the selectable transmission means.

4. A transmission arrangement according to claim 1, 2 or 3 wherein the fixed ratio transmission means provides a direct drive path.

S. A transmission arrangement according to any one of the preceding claims further including an input shaft arranged to be driven by the prime mover and an output shaft for driving the load, wherein the fixed ratio transmission means comprises a clutch for selectively providing drive from the input shaft to the output shaft, and wherein the continuously variable ratio transmission means comprises a first variable diameter pulley coupled to the input shaft, a second variable diameter pulley connected to the first pulley by means of an endless belt, and a further clutch for selectively allowing

drive from the second pulley to a means arranged to drive the output shaft.

6. A transmission arrangement according to claim 5 wherein the means arranged to drive the output shaft comprises three gearwheels forming a geartrain, one of the gearwheels being selectively drivable by the second pulley through the further clutch, another of the gearwheels being coupled to the output shaft, and the remaining gearwheel being intermediate the one and another of the gearwheels.

7. A transmission arrangement according to claim 5 wherein the means arranged to drive the output shaft comprises an axially displaceable dog ring provided on the output shaft, first and second gearwheels provided on an intermediate shaft parallel to the output shaft, the intermediate shaft being selectively drivable by the second pulley through the further clutch, a first dog clutch for selectively allowing drive from the first gearwheel to the dog ring, and a second dog clutch for selectively allowing drive from the second gearwheel via an intermediate gear to the dog ring.

8. A transmission arrangement for connecting a prime mover to a load to be driven, substantially as hereinbefore described with reference to Figure 2 or 3 of the accompanying drawings.