Hydromechanical transmission having a continuously variable transmission ratio

Description

The present invention relates to a hydromechanical transmission having a continuously variable transmission ratio.

One object of the invention is to provide an improved transmission which allows the continuous variation of the transmission ratio over a wide range, both for positive values and for negative values of this ratio.

This and other objects are achieved according to the invention with a hydromechanical transmission having a continuously variable ratio the salient characteristics of which are defined in the annexed claim

1

.

Further characteristics and advantages of the invention will become apparent from the following detailed description given purely by way of non-limitative example, with reference to the attached drawings, in which:

FIG. 1

shows a transmission according to the invention;

FIG. 2

is a graph which shows the operating characteristics which can be achieved with the transmission according to

FIG. 1

;

FIG. 3

shows a further transmission according to the invention;

FIG. 4

is a graph which shows the operating characteristics which can be achieved with the transmission of

FIG. 3

;

FIG. 5

shows a further transmission according to the invention, and

FIGS. 6 and 7

are graphs which show operating characteristics which can be achieved with the transmission of FIG.

5

.

In

FIG. 1

the reference numeral T generally indicates a transmission according to the invention.

The transmission T has an input shaft IS connectable to a motor E by means of a clutch C

0

. The output shaft of the transmission is indicated OS.

The transmission T includes an epicyclic reduction unit EG including an input sun wheel A

1

fixed to a drive shaft S

0

, an output sun wheel A

2

fixed to a hollow shaft S

1

, an outer ring gear B with two sets of teeth B

1

and B

2

, and a planet carrier C which carries planets C

1

and C

2

which mesh between the wheels A

1

and A

2

and the sets of teeth B

1

and B

2

respectively.

The planet carrier C is fixed to a shaft S

2

coaxial with the shaft S

1

.

The input shaft IS is connectable by means of a clutch CF to a toothed wheel G

1

which is coaxial with the said shaft IS and which meshes with a toothed wheel G

2

fixed to a hollow shaft S

3

which is fixed to the ring B of the epicyclic reduction gear EG, and coaxial with the shaft S

0

.

The toothed wheels G

1

and G

2

provide a transmission ratio which is, for example, substantially equal to 1.

The shafts S

3

and S

0

, and therefore the ring B and the input sun wheel A

1

, can be connected for rotation by means of a clutch CL.

Downstream from the clutch CF the shaft IS is coupled by means of a further clutch CT to a toothed wheel G

3

which meshes with a toothed wheel G

4

carried by the input shaft S

4

of a hydraulic variator unit V. This unit comprises, for example, a variable flow rate pump P coupled to a hydraulic motor M. Said motor has a fixed displacement volume or capacity, but it can also have a variable capacity.

The clutch CT has the purpose of decoupling the hydrostatic group, for eliminating the consumption of rotation power in conditions such as, in a tractor, the static work at the power takeoff or the starting of the engine.

The output shaft S

5

of the variator V carries a toothed wheel G

5

which meshes with a toothed wheel G

6

, in turn coupled to a toothed wheel G

7

fixed Lo Lhe input shaft S

0

of tho epicyclic reduction gear EG.

Upstream of the clutch CF a toothed wheel G

8

is fixed to the shaft IS, which meshes with a toothed wheel G

9

which, via a clutch CR, can be coupled for rotation with a toothed wheel G

10

. This latter meshes with the toothed wheel G

2

with a transmission ratio which is, for example, substantially equal to 1.

The shaft S

1

of the epicyclic gear unit EG carries a sun wheel A

3

coupled to planets C

4

carried by a planet carrier C

3

which is fixed to a hollow shaft S

6

also coaxial with the shaft S

2

. The planets C

4

mesh with an outer ring B

3

which, by means of a clutch CB, can be locked to the body or casing G of the transmission.

A clutch CHH makes it possible, when engaged, to couple the shaft S

6

for rotation with the shaft S

1

via the planet carrier C

3

.

A clutch CH, when engaged, makes it possible to couple the shafts S

2

and S

6

for rotation together.

The unit A

3

-C

4

-B

3

-C

3

is such that when the clutch CB is engaged, and therefore the ring B

3

is locked, and the clutches CH and CHH are disengaged, the planet carrier C

3

and the shaft S

6

turn at a low speed reduced by a divisor τ (for example equal to 4) with respect to the speed of rotation of the output shaft S

1

of the epicyclic reduction gear EG.

When, on the other hand, the clutches CB and CH are disengaged and the clutch CHH is engaged, the planet carrier C

3

and the shaft S

6

rotate at the same speed as the output shaft S

1

of the epicyclic reduction gear EG.

The shaft S

6

carries a toothed wheel G

11

which meshes with a toothed wheel G

12

which is coaxial with the output shaft OS. The wheels G

11

and G

12

together provide a speed reduction of a ratio α>1.

The toothed wheel G

12

can be coupled with the output shaft OS of the transmission by means of the clutch CW.

Transmission T described above is for example formed in such a way that if the shaft of the motor E rotates at a speed ω

E

and the clutch CF is engaged:

the speed ω

V

of the output shaft S

5

of the variator V is variable between a maximum value and a minimum value equal to ω

E

and −ω

E

respectively, upon variation of the flow rate and direction of the flow of the hydraulic fluid in the pump P of the variator; and

the speed ω

S1

of the shaft S

1

and the speed ω

S2

of the shaft S

2

at the output of the epicyclic reduction gear unit EG vary between ω

E

and 2ω

E

, and between ω

E

and 0.5ω

E

respectively upon variation of ω

V

between ω

E

and −ω

E

.

The above explanation is summarised in the following Table 1.

TABLE 1

ω

V

ω

B1

ω

E2

ω

E

ω

E

ω

E

−ω

E

2ω

E

½ω

E

If, as in the numerical example which will be described below, the speed of rotation ω

E

of the motor shaft E is equal to 2300 revolutions per minute, the speeds shown in the preceding Table assume the following values (in revolutions per minute):

TABLE 2

ω

V

ω

B1

ω

B2

2300

2300

2300

−2300

4600

1150

The mode of operation of the transmission T described above will now be described with reference to the graph of

FIG. 2

in which the speed values indicated correspond to the exemplary values of the speeds shown in Table 2.

In

FIG. 2

there is shown an operating characteristic which can be achieved with the transmission according to the invention.

In this Figure, the speed ω

V

of the output shaft S

5

of the variator V is plotted along the ordinate, and the speed ω

0

of the output shaft OS of the transmission, divided by the reduction ratio α achieved by the toothed wheels G

11

and G

12

is plotted along the ordinate.

The characteristic shown in

FIG. 2

presents a symmetrical variation with respect to the origin O and comprises a linear central section

1

passing through the origin, an upper portion comprising three linear sections

2

,

3

and

4

, and a lower portion comprising three linear sections

2

′,

3

′ and

4

′.

In operation the central section

1

of the characteristic is achieved in the following manner. The clutches C

0

, CT and CW are engaged so that the shaft of the motor E is coupled to the variator V by means of the gearing G

3

, G

4

.

The clutches CF and CR are disengaged.

The clutch CL is engaged so that the ring B of the epicyclic unit EG is coupled for rotation with the shaft S

0

and the input sun wheel A

1

, and the input shaft S

0

of the said unit is coupled to the output shaft of the variator V by means of the gears G

5

, G

6

, G

7

.

In these conditions the output shaft S

1

of the epicyclic reduction gear EG rotates at the same speed as the input shaft S

0

, which is driven by the output shaft S

5

of the variator V.

The clutch CB is engaged and the clutch CHH is disengaged. The clutch CH is also disengaged.

The shaft S

6

now rotates at a speed equal to the speed of the shaft S

1

of the epicyclic reduction gear EG divided by the ratio τ achieved by the unit A

3

, C

4

, B

3

, C

3

.

The output shaft OS from the transmission T rotates at the speed of the shaft S

6

, reduced by the factor α by the gears G

11

, G

12

.

In the central section

1

of the characteristic of

FIG. 2

, with the numerical values indicated above, upon overall variation of the speed ω

V

of the variator from −2300 to 30 2300 revolutions per minute, the output shaft OS of the transmission T is made to rotate at a speed ω

0

which varies between (−ω

V

/τ) α and (+ω

V

/τ) α, that is to say between (−2300/4) α=−575α and (+2300/4) α=575 α. These speeds of the output shaft OS are reached at the points a and a′ of the characteristic of FIG.

2

.

The sections

2

,

3

and

4

of the characteristic are representative of forward gears, starting from the point a as follows.

At point a the speed ω

0

of the output shaft OS is, as mentioned, equal to +575 α.

If, in this condition, the clutch CL is disengaged and clutch CF engaged, leaving the conditions of the other clutches unchanged, the speed ω

0

of the output shaft OS is again (for ω

V

=+2300, that is to say at point a) equal to +575 α. In fact, the shaft S

1

of the epicyclic reduction gear, according to Table 2, rotates at a speed ω

S1

=2300 revolutions per minute. The shaft S

6

rotates at the speed of the shaft S

1

reduced by the dividing factor τ, and the output shaft OS is driven to rotate by the shaft S

6

via the reduction gearing G

11

, G

12

.

At point a, after commutation of the clutches CL and CF, the speed ω

0

of the output shaft from the transmission is therefore again equal to (+2300/τ) α=575 α.

If the speed ω

V

of the variator V is now caused to go from +2300 to −2300 revolutions per minute, the speed ω

0

of the output shaft OS varies according to the relation ω

0

equals (ω

S1

/τ) α. The speed ω

S1

of the output shaft S

1

of the epicyclic reduction gear EG varies (according to Table 2) from +2300 to +4600 revolutions per minute, and therefore between the points a and b (section

2

) of the characteristic of

FIG. 2

, the output speed ω

0

varies between (2300/4) α=575 α (at point a), and (+4600/4) α=1150 α (at point b).

At point b the planet carrier C and the output shaft S

2

of the epicyclic reduction gear EG rotate at a speed ω

S2

=+1150 revolutions per minute (Table 2) which is equal to the speed ω

S1

/τ=4600/4 of shaft S

6

.

At point b it is now possible to engage the clutch CH and disengage clutch CB and, having effected these operations, the output shaft OS of the transmission is coupled to the output shaft S

2

of the epicyclic reduction gear EG, still via the gearing G

11

, G

12

.

If the output speed ω

V

of the variator V is now made to pass from −2300 to +2300 revolutions per minute, the speed ω

0

of the output shaft OS of the transmission varies according to relation ω

0

=(ω

S2

) α. The speed ω

S2

varies from 1150 to 2300 revolutions per minute (Table 2) and therefore the speed ω

0

of the output shaft OS passes from 1150 α (at point b) to 2300 α revolutions per min. (at point c).

At point c the speeds ω

S2

and ω

S1

are equal to one another and to 2300 revolutions per minute (Table 2). It is now possible to disengage the clutch CH and engage the clutch CHH in such a way that the output shaft OS of the transmission is coupled to the output shaft S

1

of the epicyclic reduction gear EG, still via the gearing G

11

, G

12

. The clutch CB remains disengaged.

The output speed ω

V

of the variator V is now made to pass again from +2300 to −2300 revolutions per minute and the speed ω

0

of the output shaft OS of the transmission varies according to the relation ω

0

=(ω

S2

) α. The speed ω

S1

varies from 2300 to 4600 revolutions per minute (Table 2), and therefore the speed ω

0

of the output shaft OS passes correspondingly from 2300 α (at point c) to 4600 α (at point d).

In sections 2′, 3′ and 4′ the clutches CL and CF are disengaged whilst the clutch CR is engaged (starting from point a′) . In these sections the operation of the transmission T therefore follows an identical person to that described above with reference to sections

2

,

3

and

4

save for the fact that after engagement of the clutch CR between the drive shaft E and the shaft S

3

of the epicyclic reduction gear EG the transmission of drive takes place now through three toothed wheels G

8

, G

9

-G

10

and G

2

rather than through the two toothed wheels G

1

and G

2

which act in sections

2

,

3

,

4

when clutch CF is engaged and clutch CR is disengaged.

Therefore, in sections

2

′,

3

′ and

4

′ transmission of drive from the motor E to the shaft S

3

of the epicyclic reduction gear EG is reversed in sign with respect to the sections

2

,

3

,

4

. The sections

2

′,

3

′ and

4

′ are therefore symmetrical to the sections

2

,

3

and

4

with respect to the origin O, the management of the clutches CB, CH and CHH being the same in these sections as already described with reference to sections

2

,

3

and

4

.

The above explanation in relation to a fixed numerical example can be generalised in such a manner that when the speed ω

V

of the variator V varies from −ω

E

to +ω

E

, the speed ω

S1

of the output shaft S

1

of the epicyclic unit EG varies from +ω

E

to +kω

E

(k>1) and correspondingly the speed ω

S2

of the shaft S

2

varies from +ω

E

to ω

E

/k, with τ=1/k

2

.

In

FIG. 3

there is shown a similar embodiment to that previously described with reference to FIG.

1

. In

FIG. 3

the parts and elements which are the same as or correspond to parts and elements already described have again allocated the same alphanumeric reference symbols utilized previously.

The transmission of

FIG. 1

can be defined by 4 modes of operation:

A first mode, essentially of “hydrostatic” type, corresponds to section

1

of

FIG. 2

; there are then 3 forward gear modes (and

3

reverse gear modes) corresponding to the sections

2

,

3

and

4

(

2

′,

3

′ and

4

′) of FIG.

2

.

By contrast, as will be seen, the transmission of

FIG. 3

has five modes of operation, or rather— beyond the same four modes as the transmission of FIG.

1

— it has a fifth forward gear mode (and a corresponding fifth reverse gear mode). The operating characteristic for the transmission of

FIG. 3

is shown in FIG.

4

.

Briefly, in the transmission shown in

FIG. 3

the shaft S

2

can be coupled to the output shaft OS via a further clutch CVHH and a speed multiplier gear comprising two toothed wheels G

20

and G

21

. This gearing G

20

, G

21

multiplies the speed by a factor β=αk

2

.

The first four modes of operation of the transmission of

FIG. 3

are identical to those of the transmission of FIG.

1

. In the transmission of

FIG. 3

, when in the branch

4

(

4

′) it arrives at point d (d′) of

FIG. 2

or

4

, it is possible to engage the clutch CVHH (until now disengaged); in fact, in this condition the output shaft OS rotates at a speed

ω

0

=ω

S1

·α=2ω

E

·α(k=2)=4600·α

and this speed is the same as that to which the shaft S

2

tends to make the output shaft rotate via the multiplier G

20

, G

21

:

ω

S2

·β=ω

S2

·α·k

2

=ω

S2

·α·4=1150·α4=4600·α

Starting from point d (d′) the operation of the transmission of

FIG. 3

can thus continue following section 5 (5′) of

FIG. 4

up to the point e (e′) at which the speed ω

0

of the output shaft reaches the maximum value of 9200 ·α revolutions per minute.

In

FIG. 5

there is shown a further transmission according to the invention, of the type having 6 modes of operation. Although the layout of the transmission of

FIG. 5

is a little different from those of

FIGS. 1 and 3

, those parts and elements which are the same or essentially equivalent in

FIG. 5

to parts or elements already described have been allocated the same alphanumeric reference symbols utilised previously.

Briefly, in the transmission according to

FIG. 5

the shafts S

6

and S

2

belong to a reduction unit A

3

′-C

4

′-B

3

′-C

3

′ similar to the unit A

3

-C

4

-B

3

-C

3

already described.

The planet carrier C

3

′ is fixed for rotation with the output shaft OS and can be selectively coupled to the shaft S

6

or the shaft S

2

by engaging a clutch CTR (analogous to the clutch CHH) or a clutch CBHH (analogous to the clutch CH). A clutch CB′, when engaged, locks the ring B

3

′, and then the planet carrier C

3

′ and the output shaft OS rotate at a speed reduced by a divisor τ′ (also equal to 4, for example) with respect to the speed of the shaft S

6

.

As the man skilled in this art will appreciate, a suitable management of the clutches of the transmission according to

FIG. 5

makes it possible to operate in six modes, in particular as shown in the following Table 3:

TABLE 3

MODE

C

F

C

R

C

L

CHH

CH

CVHH

CTR

CB

CB′

1

X

X

X

2 (2′)

X

(X)

X

X

3 (3′)

X

(X)

X

X

4 (4′)

X

(X)

X

X

5 (5′)

X

(X)

X*

X

6 (6′)

X

(X)

X

X

X = engage

*preferably engaged

It will be noted that this Table 3 is also valid for the transmissions of

FIGS. 1 and 3

, obviously up to the fourth and, respectively, the fifth mode and excluding column CB′.

With the transmission of

FIG. 5

it is therefore possible to achieve an operating characteristic ω

0

/ω

V

with

a first section (passing through the origin) in which the speed ω

0

of the output shaft varies according to the relationship ω

0

=ω

V

/(τ·τ′) where τ and τ′ are the reduction ratios achieved by the units A

3

-C

4

-B

3

-C

3

and A

3

′-C

4

′-B

3

′-C

3

′ when the clutches CB and CB′ are engaged,

a second section in which ω

0

−ω

S2

/τ′,

a third section in which ω

0

ω

S2

/τ′,

a fourth section in which ω

0

=ω

S1

/τ′,

a fifth section in which ω

0

=ω

S2

, and

a sixth section in which ω

0

=ω

S6

=ω

S1

Corresponding relations are valid in the reverse gear operation.

FIG. 6

shows the operating characteristic curve for the transmission of FIG.

5

. The portion of said characteristic curve relating to the first five modes has the same shape of the characteristic curve of

FIG. 4

, with the values of ω

0

/α reduced by τ′ (assumed equal to 4) in view of the presence, in the transmission of

FIG. 5

, of the further reduction unit A

3

′-C

4

′-B

3

′-C

3

′-CB′.

It is noted that the system of

FIG. 5

having six modes of operation, can be made to operate also in four modes only, i.e. in the following:

a first mode (or section of the characteristic curve ω

0

/ω

V

) in which ω

0

=ω

V

/τ′,

a second mode in which ω

0

=ω

S1

/τ′,

a third mode in which ω

0

=ω

S2

, and

a fourth mode in which ω

0

×ω

S1

, thus achieving a same overall speed range, by extending the first mode up to the speed achieved at the end of the third mode of the operation in six modes, as it is shown in the graph of the annexed FIG.

7

.

In the operation in four modes the clutches of

FIG. 5

are operated in accordance with the following Table 4:

TABLE 4

MODE

C

F

C

R

C

L

CHH

CH

CVHH

CTR

CB

CB′

I (I′)

X

X

X

II (II′)

X

(X)

X

X

III (III′)

X

(X)

X

X

IV (IV′)

X

(X)

X

X

The possibility of operating in four/six modes is particularly interesting for controlling the vehicle speed, permitting (in the operation in four modes) higher acceleration values at the start, when a high traction is not needed at the same time.

It is also noted that in

FIGS. 1 and 5

two different input reversing arrangements are shown, the reversing function being achievable by a plurality of other per se known arrangements.

The group comprising the variable pump/the motor with fixed or variable capacity can be conveniently provided with a modulator valve X (

FIG. 5

) placed across the high pressure and the low pressure lines connecting said units. The purpose of said valve, which can be operated through the friction clutch or other means, is that of allowing to control, up to the reduction to zero, the pressure differential of the hydrostatic group, and thus the transmitted torque, when the transmission operates in the first mode.

This function is particularly useful for the manoeuvrability of the vehicle at low speeds and during the coupling of implements.

In a similar manner transmissions having even more than six modes of operation can be formed.

Naturally, the principle of the invention remaining the same, the embodiments and details of construction can be widely varied with respect to what has been described and illustrated purely by way of non-limitative example, without by this departing from the ambit of the invention as defined in the following claims.

Claims

1. A hydromechanical transmission having a continuously variable speed ratio, comprisingan input shaft intended to be coupled to a motor, an output shaft, an epicyclic reduction gear with an input sun wheel, a ring gear and first and second respectively fast and slow output shafts, a first clutch operable to couple the input sun wheel, the ring gear and the said reduction unit for rotation together, an hydraulic variator unit coupled between the input shaft of the transmission and the input sun wheel of the epicyclic reduction unit; second and third clutches operable to couple the input shaft of the transmission to the said ring gear of the epicyclic reduction unit with respective transmission ratios of opposite sign, respectively for forward and reverse gears; the arrangement being such that when the output speed of the variator varies over a predetermined range on either side of zero, and the said first clutch is disengaged and the said second or third clutch is engaged, the said first and second output shafts of the epicyclic reduction gear unit have respective speeds which vary over respective ranges of contiguous values; auxiliary clutch means being provided for coupling the output shaft of the transmission selectively to the first or second output shaft of the epicyclic reduction gear unit with predetermined speed ratios, in such a way that the transmission can operate in a first mode in which the said first clutch is engaged and the second and third clutches are disengaged, the output shaft of the transmission is coupled to an output shaft of the epicyclic reduction gear unit and its speed varies in a manner proportional to the output speed of the variator; a plurality of successive forward gear modes in which the said first clutch is disengaged, the said second clutch is engaged a plurality of successive reverse gear modes in which the said first clutch is disengaged, the said third clutch is engaged, and the output shaft of the transmission is selectively coupled to the first or the second output shaft of the epicyclic reduction gear unit via the said auxiliary clutch with the said predetermined speed ratios.
2. A hydromechanical transmission according to claim 1, in which the said hydraulic variator unit includes a pump of variable flow rate and an associated hydraulic motor, and is adapted to be disengaged by means of a clutch associated with it.
3. A hydromechanical transmission according to claim 2, wherein to said variator unit there is associated a modulating valve adapted to allow to control the pressure differential of said group in the above-said first mode of operation.
4. A hydromechanical transmission according to claim 1, comprising means which are selectively switchable to provide an operation according to a first or a second sequence of modes, selectively.

Priority Claims (1)

Number	Date	Country	Kind
TO20A0162	Feb 2000	IT

US Referenced Citations (9)

Number	Name	Date	Kind
5156577	Fredriksen et al.	Oct 1992	A
5531304	Ishino et al.	Jul 1996	A
5667452	Coutant	Sep 1997	A
5820508	Konig et al.	Oct 1998	A
5890981	Coutant et al.	Apr 1999	A
6007444	Kinokami	Dec 1999	A
6056657	Garnett	May 2000	A
6080074	Ulbrich et al.	Jun 2000	A
6203463	Casey et al.	Mar 2001	B1

Foreign Referenced Citations (2)

Number	Date	Country
WO 9609482	Mar 1996	WO
WO 9936285	Jul 1999	WO

Hydromechanical transmission having a continuously variable transmission ratio

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (9)

Foreign Referenced Citations (2)