GB2345102A

GB2345102A - Change-speed gearbox with two parallel component transmissions

Info

Publication number: GB2345102A
Application number: GB9930421A
Authority: GB
Inventors: Ralf Sperber; Gunter Worner
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 1998-12-24
Filing date: 1999-12-22
Publication date: 2000-06-28
Anticipated expiration: 2019-12-22
Also published as: ITRM990770A1; DE19860250C1; GB2345102B; ITRM990770A0; FR2787852A1; IT1308033B1; GB9930421D0

Abstract

A change-speed gearbox. comprises an input shaft 10 connected to an output shaft 11 by two component transmissions 12, 13 each having a concentric intermediate shaft 14, 15 connected to the input shaft 10 by a power-shift clutch K1, K2. The intermediate shaft 14 of component transmission 12 is, on the one hand, connected to the output shaft 11 by a direct clutch 17 and, on the other hand, connected to a layshaft 16 via selectively engageable gear stage C1. The intermediate shaft 15 of component transmission 13 is connected to a layshaft 18, which is coaxial with layshaft 16, via a gear stage C2 that is permanently engaged. A gearwheel stage having gears 19, 20 is engaged, via gear clutches 21, 22, to either the layshaft 16 or layshaft 18, this allows double downshifts, eg skipping gears, since the component transmissions 12, 13 are provided with a gearwheel stage having equal transmission ratios. Several methods of changing gear involving overlap control of the power-shift clutches are also disclosed.

Description

Change-speed gearbox with two component transmissions arranged in parallel in the power flow The present inventions relate to change-speed gearboxes in which an input shaft is connected to a coaxial output shaft by two component transmissions which are arranged in parallel in the power flow and have gearwheel stages, each associated by virtue of their transmission ratio with one gearbox gear, and respective intermediate shafts, and in which the intermediate shafts are arranged concentrically to one another and are connected to the coaxial input shaft by respective frictional power-shift clutches, and in which the intermediate shaft of the one component transmission can be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and in which a layshaft arranged parallel to the input shaft can be brought into selective drive connection with the output shaft by means of the gearwheel stages associated with the other component transmission and is in permanent drive connection with one of the other mutually coaxial shafts by means of a gearbox constant, and in which the output shaft is connected to the intermediate shaft of the one component transmission by an engageable and disengageable direct clutch to form a direct gearbox gear, and to methods for changing gear in change-speed gearboxes of this kind.

US 4,658,663 has disclosed a change-speed gearbox in which the gearwheel stages for forward gears I, III and IV and for reverse gear belong to the one component transmission, fourth gear being designed as a direct gear-and consequently can be selected by engaging a direct clutch between the output shaft and the intermediate shaft of this one component transmission.

The other component transmission includes the gearwheel stages of forward gears II and V and an additional gearwheel stage, the transmission ratio of which is equal to the transmission ratio of third gear, the gearwheel stage of which belongs to the one component transmission with the direct clutch for the direct fourth gear. In this one component transmission, the gearwheel clutch for third gear and the direct clutch for fourth gear are combined to give a changing clutch with a common sliding selector sleeve which can be coupled to the free gear of the gearwheel stage of third gear or to the output shaft.

In the known change-speed gearbox, a common layshaft which is in continuous drive connection with the output shaft through a permanent gearbox constant is used for the two component transmissions.

Although this configuration allows all double downshifts in the known change-speed gearbox, i. e. downshifts which involve skipping a gear, the importantbecause frequent-gear changes between the direct fourth gear and those gears I and III, the gearwheel stages of which belong to the one component transmission like the direct gear, require the temporary selection of the additional gearwheel stage of third gear if they are to be performed without interrupting torque transmission-i. e. as power shifts.

The present invention seeks essentially to enable gear changes between the direct gear and the gears which likewise belong, by virtue of their gearwheel stages, to the one component transmission having the direct clutch to be performed as power shifts without interrupting the power flow and without the need to select an additional gearwheel stage for this purpose.

According to the present invention there is provided a change-speed gearbox in which an input shaft is connected to a coaxial output shaft by two component transmissions which are arranged in parallel in the power flow and have gearwheel stages, each associated by virtue of their transmission ratio with one gearbox gear, and respective intermediate shafts, and in which the intermediate shafts are arranged concentrically to one another and are connected to the coaxial input shaft by respective frictional power-shift clutches, and in which the intermediate shaft of the one component transmission can be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and in which a layshaft arranged parallel to the input shaft can be brought into selective drive connection with the output shaft by means of the gearwheel stages associated with the other component transmission and is in permanent drive connection with one of the other mutually coaxial shafts by means of a gearbox constant, and in which the output shaft is connected to the intermediate shaft of the one component transmission by an engageable and disengageable direct clutch to form a direct gearbox gear, wherein the gearbox constant is connected to the intermediate shaft of the other component transmission, the intermediate shaft of the one component transmission is connected by way of a gearbox constant which is adapted to be connected selectively into the power flow to a further layshaft, which is parallel to the input shaft and adapted to be brought into selective operative drive connection with the output shaft by means of the gearwheel stages associated with the one component transmission, and the gearbox constant connected to the layshaft of the one component transmission is adapted to be brought selectively into connection with one or both intermediate shafts.

In the change-speed gearbox according to the invention, the selectable layshaft provides a third torque path between the input and the output shaft and this torque path can be used in alternation with the torque path of the direct clutch by means of the two power-shift clutches for the power shifts between the direct gear and the gears which likewise belong to the one component transmission by virtue of their gearwheel stages. If the gearbox gears are distributed between the two component, all simple up-and downshifts can be carried out by directly changing the two power-shift clutches-i. e. directly. This applies also to the gear or gears adjacent in terms of their transmission ratio to the direct gear, even if the direct gear in the change-speed gearbox according to this invention is designed as the second-highest gear.

In the change-speed gearbox according to this invention, double upshifts and double downshifts between the direct gear and the gears or gearwheel stages which belong to the one component transmission, which has the intermediate shaft connected to the direct clutch, are made possible.

In the change-speed gearbox according to this invention, double upshifts and double downshifts between the gears or gearwheel stages which belong to the other component transmission are made possible by the configuration in Claim 4 or 5.

In the change-speed gearbox according to this invention, the two layshafts of the component transmissions can, for example, be arranged parallel to one another. If there is insufficient space in the directions normal to the axis, the arrangement can be that in Claim 7.

In the known change-speed gearbox, a respective mainshaft gearwheel connected to the respective intermediate shaft and a respective layshaft gearwheel connected to the common layshaft-i. e. a total of four gearwheels-are used for the gearwheel stages of two gears adjacent in terms of their transmission ratio, of which the gearwheel stage for third gear belongs to the one component transmission, which has the intermediate shaft connected to the direct clutch, and the gearwheel stage for second gear belongs to the other component transmission.

According to a second aspect of the invention there is provided a changespeed gearbox in which an input shaft is connected to a coaxial output shaft by two component transmissions which are arranged in parallel in the power flow and have gearwheel stages, each associated by virtue of their transmission ratio with one gearbox gear, and respective intermediate shafts, and in which the intermediate shafts are arranged concentrically to one another and are connected to the coaxial input shaft by respective frictional power-shift clutches, and in which the intermediate shaft of the one component transmission can be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and in which a layshaft arranged parallel to the input shaft can be brought into selective drive connection with the output shaft by means of the gearwheel stages associated with the other component transmission and is in permanent drive connection with one of the other mutually coaxial shafts by means of a gearbox constant, wherein the gearbox constant is connected continuously to the intermediate shaft of the other component transmission, the intermediate shaft of the one component transmission is connected by a further gearbox constant to a further layshaft parallel to the input shaft, the layshaft of the one component transmission is adapted to be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and two gearwheel stages, which are associated with adjacent gearbox gears and of which one gearwheel stage belongs to the one component transmission and the other gearwheel stage belongs to the other component transmission, have both a common mainshaft gearwheel, the latter being arranged coaxially and in rotationally fixed position relative to the output shaft, and also respective gearwheel clutches connected respectively to one of the two layshafts and an associated layshaft gearwheel.

In the change-speed gearbox according to the second invention, the transmission ratio of the two gearwheel stages operating with a common mainshaft gearwheel can in each case be determined by the centre distance of the layshafts relative to the output shaft.

In an advantageous embodiment of the change-speed gearbox according to the second invention, the transmission ratio of the two said gearwheel stages is determined by the transmission ratio of the two gearbox constants with an equal centre distance of the layshafts relative to the output shaft. This embodiment allows both parallel and coaxial arrangement of the layshafts relative to one another.

In another advantageous embodiment of the change-speed gearbox according to the second invention, both the structural and the spatial outlay are significantly reduced by the features of Claim 10 since only two gearwheels in total are then required for the two said gearwheel stages.

The two embodiments according to Claims 9 and 10 of the change-speed gearbox according to the second invention can be used separately or together with the first invention according to one of Claims 1 to 7.

Claims 11 and 12 each relate to an advantageous method for a double upshift or downshift between the direct gear and a further gear, the gearwheel stage of which likewise belongs to that one component transmission, the intermediate shaft of which is connected to the direct clutch, in each case while skipping a gear, in a change-speed gearbox in accordance with one or both inventions and forming the subject-matter of one of Claims 1 to 10.

Claims 13 and 14 relate to advantageous methods for a double upshift and a double downshift, on the one hand into and on the other hand out of that gear, the gearwheel stage of which belongs to the other component transmission and has the same transmission ratio as the additional gearwheel stage of the one component transmission, the intermediate shaft of which is connected to the direct clutch, in each case while skipping a gear, in a change-speed gearbox in accordance with one or both inventions and forming the subjectmatter of one of Claims 4 to 10.

Claims 15 and 16 relate to advantageous methods for a double upshift and a double downshift, on the one hand out of and on the other hand into that gear, the gearwheel stage of which belongs to the other component transmission and has the same transmission ratio as the additional gearwheel stage of the one component transmission, the intermediate shaft of which is connected to the direct clutch, in each case while skipping a gear, in a change-speed gearbox in accordance with one or both inventions and forming the subjectmatter of one of Claims 4 to 10.

The inventions are, for example, used jointly in a change-speed gearbox which is illustrated schematically in the drawing and described below.

In the drawing, Fig. 1 shows a longitudinal section through a change-speed gearbox in accordance with the two inventions according to Claims 1 and 8, Fig. 2 shows a signal flowchart for a method in accordance with Claim 11 for changing gear in the change-speed gearbox of Fig. 1, Fig. 3 shows a signal flowchart for a method in accordance with Claim 12 for changing gear in the change-speed gearbox of Fig. 1, Fig. 4 shows a signal flowchart for a method in accordance with Claim 13 for changing gear in the change-speed gearbox of Fig. 1, Fig. 5 shows a signal flowchart for a method in accordance with Claim 14 for changing gear in the change-speed gearbox of Fig. 1, Fig. 6 shows a signal flowchart for a method in accordance with Claim 15 for changing gear in the change-speed gearbox of Fig. 1 and Fig. 7 shows a signal flowchart for a method in accordance with Claim 16 for changing gar in the change-speed gearbox of Fig. 1.

Referring, first of all, to Figure 1, an input shaft 10 and a coaxial output shaft 11 are connected to one another by two component transmissions 12 and 13 arranged in parallel in the power flow.

The component transmissions 12 and 13 have respective intermediate shafts 14 and 15, which are arranged concentrically to one another and coaxially with the input shaft 10 and are connected to the said input shaft via respective engageable and disengageable frictional power-shift clutches Kl and K2.

The intermediate shaft 14 of the one component transmission 12 is, on the one hand, connected to the output shaft 11 by an engageable and disengageable direct clutch 17 to form a direct fifth gear V and, on the other hand, is connected to a layshaft 16, which is parallel to the output shaft 11 and is designed as a hollow shaft, by an engageable and disengageable gearbox constant C1.

The layshaft 16 of the one component transmission 12 is connected to the output shaft 11 by a gearwheel stage ZI to form the lowest forward gear I, the free gear of this gearwheel stage ZI being seated concentrically and rotatably on the output shaft 11 and being connected to the latter by an engageable and disengageable gearwheel clutch 26.

The layshaft 16 of the one component gear 12 is furthermore connected to the output shaft 11 by an additional gearwheel stage ZIV*, the free gear of which is seated concentrically and rotatably on the layshaft 16 and can be coupled to the latter by an engageable and disengageable gearwheel clutch 23.

Finally, the layshaft 16 of the one component transmission 12 is furthermore connected to the output shaft 11 by a gearwheel stage ZIII/IV to form third gear III and fourth gear IV, the fixed gear 19 of this gearwheel stage ZIII/IV being arranged concentrically and in a rotationally fixed position on the output shaft 11, while the free gear 20 of this gearwheel stage ZIII/IV is seated concentrically and rotatably on another layshaft 18, which is parallel to the output shaft 11, and can be coupled to the latter by an engageable and disengageable gearwheel clutch 22 or to layshaft 16 by an engageable and disengageable gearwheel clutch 21.

The further layshaft 18 passes through the layshaft 16 of the first component transmission 12 with a clearance and it is connected to the intermediate shaft 15 of the other component transmission 13 by a permanently acting gearbox constant C2, the said intermediate shaft 15 being designed as a hollow shaft and being passed through with a clearance by the intermediate shaft 14 of the one component transmission 12. The further layshaft 18, which thus belongs to the other component transmission 13, is connected to the output shaft 11 by further gearwheel stages ZVI, ZII and ZR, which of course likewise belong to the other component transmission 13.

In this arrangement, the free gear of the gearwheel stage ZVI provided to form the transmission ratio of the highest forward gear VI is arranged concentrically and rotatably on layshaft 18 and can be coupled to the latter by an engageable and disengageable gearwheel clutch 25.

The free gear of the gearwheel stage ZII used to form the transmission ratio of the second-lowest forward gear II, on the other hand, is arranged concentrically and rotatably on the output shaft 11 and can be coupled to the latter by an engageable and disengageable gearwheel clutch 24.

While the fixed gear 8 of the gearwheel stage ZR for the formation of reverse gear R is arranged concentrically and in a rotationally fixed position on layshaft 18 and meshes with an intermediate gearwheel (not shown) to give the reversal in the direction of rotation, the free gear 9 of this gearwheel stage, the said free gear likewise meshing with the intermediate gearwheel, is seated concentrically and rotatably on the output shaft 11, to which it can be coupled by an engageable and disengageable gearwheel clutch 27.

The gearbox constant Cl has a fixed gear 28 which is arranged concentrically and in a rotationally fixed position relative to layshaft 16 and meshes with a free gear 29 which is seated concentrically and rotatably on the intermediate shaft 14 and can be connected to the intermediate shaft 14 by an engageable and disengageable gearwheel clutch s-Cl/Kl and thereby to the power-shift clutch K1 and can be connected to the intermediate shaft 15 by an engageable and disengageable gearwheel clutch s-C1/K2 and thereby to power-shift clutch K2.

The transmission ratios of gearwheel stage ZIII/IV and of the gearbox constants Cl and C2 are matched to one another in such a way that, on the one hand, the transmission ratio of third gear is obtained if the power flows from power-shift clutch K1, via gearbox constant Cl to gearwheel stage ZIII/IV and hence to the output shaft 11, while, on the other hand, the transmission ratio of fourth gear is obtained if the power flows from power-shift clutch K2, via gearbox constant C2, to gearwheel stage ZIII/IV and hence to the output shaft 11.

The transmission ratios of gearbox constant Cl and of the additional gearwheel stage ZIV* are matched to one another in such a way that the transmission ratio of fourth gear is likewise obtained if the power flows from power-shift clutch K1, via gearbox constant C1, to the additional gearwheel stage ZIV* and hence to the output shaft 11.

From the above description, it follows that the one component transmission 12 is assigned gear I (by means of the gearwheel clutch 26 of gearwheel stage ZI) and gear III (by means of the gearwheel clutch 21 of gearwheel stage ZIILTV) and gear V (by means of the direct clutch 17) and the other component transmission 13 is assigned gear II (by means of the gearwheel clutch 24 of gearwheel stage ZII) and gear IV (by means of the gearwheel clutch 22 of gearwheel stage ZIII/IV) and gear VI (by means of the gearwheel clutch 25 of gearwheel stage ZVI).

As a result, all single shifts (upshifts and downshifts between two adjacent forward gears) can be carried out in a known manner as power shifts, by respective overlap control of the two power-shift clutches Kl and K2, in such a way that the sum of the transmission capacities of both power-shift clutches is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch of the gear to be disengaged approaches zero. The single shifts III= > IV and IV > III are performed in such a way that both gearwheel clutches 21 and 22 of gearwheel stage ZIII/IV are in each case engaged during the overlap control operation.

With the assignent of the gearwheel stages to the two component transmissions 12 and 13 as described, all multiple shifts, i. e. upshifts or downshifts which involve skipping one or more gears, can of course also be carried out as power shifts between gears whose associated gearwheel stages do not belong to the same component transmission. These include the triple upshift I= > IV, the quintuple upshift I= > VI, the triple upshift IIrV, the triple upshift III= > VI, the triple downshift IV= > I, the triple downshift V=II, the quintuple downshift VI= > I and the triple downshift VI= > III.

The invention also makes possible multiple shifts between the direct gear V, which can be selected by means of the direct clutch 17, and one of the two other gears I or III, likewise belonging to the one component gear 12, in each case as a power shift.

Examples of this that will be described below are the shifts involving third gear in accordance with the methods according to Claims 11 and 12. The corresponding shifts involving first gear are performed analogously.

Double (2-fold) upshift III= > V in accordance with Fig. 2: In the steady state of third gear, power-shift clutch K1 and the gearwheel clutch 21 of gearwheel stage ZIII/IV and one gearwheel clutch s-Cl/Kl of the gearbox constant Cl are engaged.

When a gear-change signal 30 occurs, the other gearwheel clutch s-C1/K2 of gearbox constant Cl is first of all engaged in a first method step 31 and then, in a further method step 32, overlap control is carried out for K1= > 0.

I a subsequent method step 33, one gearwheel clutch s-Cl/Kl of gearbox constant C 1 is disengaged and the direct clutch 17 is engaged.

This is followed, in a further method step 34, by overlap control for K2= > 0, whereupon the gearwheel clutch 21 of gearwheel stage ZIII/IV and the other gearwheel clutch s-C1/K2 of gearbox constant Cl are disengaged in a final method step 35.

Double (2-fold) downshift vrm in accordance with Fig. 3: In the steady state of fifth gear, power-shift clutch K1 and the direct clutch 17 are engaged.

When a gear-change signal 36 occurs, the gearwheel clutch 21 of gearwheel stage ZIII/IV and the other gearwheel clutch s-C1/K2 of gearbox constant C1 are first of all engaged in a first method step 37, and overlap control for Kl= is then carried out in a further method step 38.

In a subsequent method step 39, the direct clutch 17 is disengaged and one gearwheel clutch s-Cl/Kl of gearbox constant C1 is engaged.

As a further method step 40, overlap control is performed for K2= with a final method step 41 to disengage the other gearwheel clutch s-C1/K2 of gearbox constant Cl, By virtue of the configuration according to Claim 4 or 5 of the invention in accordance with Claim 1, double (2-fold) shifts between that gear of the other component transmission 13 which corresponds in its transmission ratio to the additional gearwheel stage ZIV* of the one component transmission 12 and a further gear, likewise belonging to the other component transmission 13, are made possible in accordance with the methods of Claims 13 to 16, as described below.

Double (2-fold) upshift II= > IV in accordance with Fig. 4: In the steady state of second gear, the gearwheel clutch 24 of gearwheel stage ZII and power-shift clutch K2 are engaged.

When a gear-change signal 42 occurs, the gearwheel clutch 23 of additional gearwheel stage ZIV* and one gearwheel clutch s-Cl/Kl of gearbox constant Cl are first of all engaged in a first method step 43, and overlap control for K2 > 0is carried out in a subsequent method step 44.

In a further method step 45, the gearwheel clutch 22 of gearwheel stage ZIII/IV is then engaged and, in a subsequent method step 46, overlap control for K1= > 0 is carried out.

In a final method step 47, the gearwheel clutch 24 of gearwheel stage ZII and the gearwheel clutch 23 of additional gearwheel stage ZIV* are disengaged.

Double (2-fold) downshift IV > II in accordance with Fig. 5: In the steady state of fourth gear, the gearwheel clutch 22 of gearwheel stage ZIII/IV and power-shift clutch K2 are engaged.

When a gear-change signal 48 occurs, the gearwheel clutch 23 of additional gearwheel stage ZIV* and one gearwheel clutch s-Cl/Kl of gearbox constant Cl are first of all engaged in a first method step 49, and overlap control for K2=0 is carried out in a subsequent method step 50.

In a further method step 51, the gearwheel clutch 24 of gearwheel stage ZII is then engaged and, in a subsequent method step 52, overlap control for KlrOis carried out.

In a final method step 53, the gearwheel clutch 23 of additional gearwheel stage ZIV* and the gearwheel clutch s-Cl/Kl of gearbox constant Cl are disengaged.

Double (2-fold) upshift IV > VI in accordance with Fig. 6: In the steady state of fourth gear, the gearwheel clutch 22 of gearwheel stage ZIIIJIV and power-shift clutch K2 are engaged.

When a gear-change signal 54 occurs, the gearwheel clutch 23 of additional gearwheel stage ZIV* and the gearwheel clutch s-Cl/Kl of gearbox constant Cl are first of all engaged in a first method step 55, and overlap control for K2= is carried out in a subsequent method step 56.

The gearwheel clutch 25 of gearwheel stage ZVI is then engaged in a further method step 57, and overlap control for Kl= > 0 is carried out in a subsequent method step 58.

In a final method step 59, the gearwheel clutch 23 of additional gearwheel stage ZIV* and the gearwheel clutch s-Cl/Kl of gearbox constant Cl are disengaged.

Double (2-fold) downshift VI= > IV in accordance with Fig. 7: In the steady state of sixth gear, the gearwheel clutch 25 of gearwheel stage ZVI and power-shift clutch K2 are engaged.

When a gear-change signal 60 occurs, the gearwheel clutch 23 of the additional gearwheel stage ZIV* and the gearwheel clutch s-Cl/Kl of gearbox constant Cl are first of all engaged in a first method step 61, and overlap control for K2= is carried out in a subsequent method step 62.

In a further method step 63, the gearwheel clutch 22 of gearwheel stage ZIII/IV is then engaged and, in a subsequent method step 64, overlap control for Kl= is carried out.

In a final method step 65, the gearwheel clutch 23 of additional gearwheel stage ZIV* and the gearwheel clutch s-C1/K1 of gearbox constant Cl are disengaged.

The gearwheel clutch s-Cl/Kl of gearbox constant Cl can remain engaged except in those gear-change operations in which a torque path parallel to the direct clutch 17 must be available in the one component transmission 12 by disengaging this clutch and engaging the other gearwheel clutch s-C 1/K2 of gearbox constant C 1.

Claims

1. A change-speed gearbox in which an input shaft is connected to a coaxial ',." ! output shaft by two component transmissions which are arranged in parallel in the power flow and have gearwheel stages, each associated by virtue of their transmission ratio with '. 5 one gearbox gear, and respective intermediate shafts, and in which the intermediate s are arranged concentrically to one another and are connected to the coaxial input shaft by '/. respective frictional power-shift clutches, and in which the intermediate shaft of the one component transmission can be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and in which a layshaft arranged parallel to the input shaft can be brought into selective drive connection with the output ' by means of the gearwheel stages associated with the other component transmission and is in permanent drive connection with one of the other mutually coaxial shafts by means of a Ct. gearbox constant, and in which the output shaft is connected to the intermediate shaft of the one component transmission by an engageable and disengageable direct clutch to form a c y direct gearbox gear, wherein the gearbox constant is connected to the intermediate shaft of '.-- the other component transmission, the intermediate shaft of the one component transmission is connected by way of a gearbox constant which is adapted to be connected selectively into //7 the power flow to a further layshaft, which is parallel to the input shaft and adapted to be brought into selective operative drive connection with the output shaft by means of the @ J,Z ~ ! z m gearwheel stages associated with the one component transmission, and the gearbox constant connected to the layshaft of the one component transmission is adapted to be brought selectively into connection with one or both intermediate shafts.'.

2. A change-speed gearbox according to Claim 1, wherein the gearwheel stages are associated with the component transmissions in accordance with the alternating sequence of the gearbox gears.

3. A change-speed gearbox according to Claim 1 or 2, wherein the direct gearbox gear is the second-highest gearbox gear.

4. A change-speed gearbox according to any one of Claims 1 to 3, wherein the one component transmission has an additional gearwheel stage, the transmission ratio of which is equal to the transmission ratio of a gearwheel stage associated with a gearbox gear and belonging to the other component transmission.

5. A change-speed gearbox according to Claim 4, wherein the gearwheel stage of the other component transmission, the transmission ratio of which is equal to the transmission ratio of the additional gearwheel stage, is associated with the third-highest gearbox gear.

6. A change-speed gearbox according to any one of Claims 1 to 5, wherein the number of gearwheel stages provided (six) corresponds to the sum of the number (six) of the indirect forward gears and a reverse gear minus one.

7. A change-speed gearbox according to any one of Claims 1 to 6, wherein the layshafts are arranged coaxially to one another.

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8. A change-speed gearbox in which an input shaft is connected to a coaxial n., ' output shaft by two component transmissions which are arranged in parallel in the power flow and have gearwheel stages, each associated by virtue of their transmission ratio with ."-. one gearbox gear, and respective intermediate shafts, and in which the intermediate shafts are arranged concentrically to one another and are connected to the coaxial input shaft by :. . r - respective frictional power-shift clutches, and in which the intermediate shaft of the one component transmission can be brought into selective operative drive connection with the output shaft by means of the associated gearwheel stages, and in which a layshaft arranged parallel to the input shaft can be brought into selective drive connection with the output shaft by means of the gearwheel stages associated with the other component transmission and is in permanent drive connection with one of the other mutually coaxial shafts by means of a gearbox constant, wherein the gearbox constant is connected continuously to the intermediate shaft of the other component transmission, the intermediate shaft of the one , ~ component transmission is connected by a further gearbox constant@ to a further layshaft 9, parallel to the input shaft, the layshaft of the one component transmission is adapted to be brought into selective operative drive connection with the output shaft by means of the ---\ associated gearwheel stages, and two gearwheel stages, which are associated with adjacent gearbox gears and of which one gearwheel stage belongs to the one component transmission and the other gearwheel stage belongs to the other component transmission, have both a ly common mainshaft gearwheel, the latter being arranged coaxially and in rotationally fixed 2 , zZ position relative to the output shaft, and also respective gearwheel clutches connected zut respectively to one of the two layshafts and an associated layshaft

9. A change-speed gearbox according to Claim 8, wherein the layshafts have the same centre distance relative to the output shaft and the gearbox constants have different transmission ratios.

10. A change-speed gearbox according to Claim 9, wherein the layshafts are arranged coaxially to one another and the two gearwheel stages associated with adjacent gearbox gears and operating with a common mainshaft gearwheel also have a common layshaft gearwheel, which is connected to the two gearwheel clutches, each connected to one layshaft.

11. A method for changing gear in a change-speed gearbox according to any one of Claims 1 to 10, wherein in the case of an upshift to the direct gear from a lower gearbox gear, the associated gearwheel stage of which is associated with that one component transmission, the intermediate shaft of which is connected to the direct clutch, while skipping one gearbox gear, the selectively engageable gearbox constant of the one component transmission, is first of all connected additionally to the intermediate shaft of the other component transmission, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the direct clutch is engaged and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the connection between the selectively engageable gearbox constant and the intermediate shaft of the other component transmission is released and the gearwheel clutch of the gearwheel stage of the lower gearbox gear is disengaged.

12. A method for changing gear in a change-speed gearbox according to any one of Claims 1 to 10, wherein in the case of a downshift from the direct gear, while skipping one gearbox gear, into a lower gearbox gear, the associated gearwheel stage of which belongs to that one component transmission, the intermediate shaft of which is connected to the direct clutch, the gearwheel clutch of the gearwheel stage of the lower gearbox gear is first of all engaged and the selectively engageable gearbox constant is additionally connected to the intermediate shaft of the other component transmission, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the direct clutch is disengaged and the selectively engageable gearbox constant is additionally connected to the intermediate shaft of the one component transmission, and overlap control of the transmission capacities of both powershift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the powershift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and the connection between the selectively engageable gearbox constant and the intermediate shaft of the other component transmission is then released.

13. A method for changing gear in a change-speed gearbox according to any one of Claims 4 to 10, wherein, in the case of an upshift from a lower gearbox gear into that higher gearbox gear which is assigned that gearwheel stage of the other component transmission, the transmission ratio of which is equal to the transmission ratio of the additional gearwheel stage of the one component transmission, while skipping one gearbox gear, the gearwheel clutch of the additional gearwheel stage is first of all engaged, and overlap control of the transmission capacities of the two power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the gearwheel clutch of the gearwheel stage of the higher gearbox gear is engaged, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and the gearwheel clutches of the additional gearwheel stage and of the gearwheel stage of the lower forward gear are then disengaged.

14. A method for changing gear in a change-speed gearbox according to any one of Claims 4 to 10, wherein, in the case of a downshift from that higher gearbox gear, the associated gearwheel stage of which belongs to the other component transmission and has the same transmission ratio as the additional gearwheel stage of the one component transmission, into a lower gearbox gear, the associated gearwheel stage of which belongs to the other component transmission, while skipping one gearbox gear, the gearwheel clutch of the additional gearwheel stage is first of all engaged and then overlap control of the transmission capacities of both power-shift clutches is performed in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the gearwheel clutch of the gearwheel stage of the lower gearbox gear is engaged, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and the gearwheel clutches of the additional gearwheel stage and of the gearwheel stage of the higher gearbox gear are then disengaged.

15. A method for changing gear in a change-speed gearbox according to any one of Claims 4 to 10, wherein, in the case of an upshift from a lower gearbox gear, the associated gearwheel stage of which belongs to the other component transmission and has the same transmission ratio as the additional gearwheel stage of the one component transmission, into a higher gearbox gear, the associated gearwheel stage of which belongs to the other component transmission, while skipping one gearbox gear, the gearwheel clutch of the additional gearwheel stage is first of all engaged and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the gearwheel clutch of the gearwheel stage of the higher gearbox gear is engaged, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and the gearwheel clutch of the additional gearwheel stage is then disengaged.

16. A method for changing gear in a change-speed gearbox according to any one of Claims 4 to 10, wherein, in the case of a downshift from a higher gearbox gear, the associated gearwheel stage of which belongs to the other component transmission, to a lower gearbox gear, the associated gearwheel stage of which belongs to the other component transmission and has the same transmission ratio as the additional gearwheel stage of the one component transmission, while skipping a gearbox gear, the gearwheel clutch of the additional gearwheel stage is first of all engaged, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the other component transmission approaches zero, and, as the transmission capacity of this power-shift clutch approaches zero, the gearwheel clutch of the gearwheel stage of the lower gearbox gear is engaged, and overlap control of the transmission capacities of both power-shift clutches is then initiated in such a way that the sum of the transmission capacities is held approximately constant and, at the same time, the transmission capacity of the power-shift clutch which is connected to the intermediate shaft of the one component transmission approaches zero, and the gearwheel clutch of the additional gearwheel stage is then disengaged.

17 A change speed gearbox, substantially as described herein, with reference to, and as illustrated in the accompanying drawings.

18. A method of operating a gearbox according to claim 17.