Transmission having variable V-belt unit and hydrodynamic unit

A transmission includes a hydrodynamic transmission, such as a torque convertor or a fluid coupling, connectable to a drive source and driving an infinitely variable V-belt transmission having primary and secondary pulleys each constructed of two conical pulley discs. The drive ratio of the V-belt transmission is controlled by a pressure cylinder which adjusts the axial position of one of the pulley discs, and the hydrodynamic transmission is lockable in a direct drive mode in response to the pressure in the pressure cylinder.

This invention relates to a transmission, in particular for a motor 
vehicle, which includes an infinitely variable V-belt transmission unit 
and a hydrodynamic transmission unit, such as a torque converter or a 
fluid coupling, drivingly connected together. 
BACKGROUND OF THE INVENTION 
German Pat. No. 1630298 discloses a transmission of the general kind to 
which the present invention relates. The infinitely variable V-belt 
transmission, which is drivingly connected to the output of the 
hydrodynamic transmission unit, includes as is conventional a primary 
pulley and a secondary pulley. Each pulley is constructed of a pair of 
conical discs, and at least one disc of each pair is axially movable 
toward and away from the other disc of that pair. A primary fluid pressure 
cylinder controls the spacing between the discs of the primary pulley, and 
a secondary fluid pressure cylinder controls the spacing between the discs 
of the secondary pulley. The hydrodynamic transmission unit, in the system 
disclosed in the German patent is a torque converter, i.e. a transmission 
unit which on the one end serves as take-off clutch for driving away and 
on the other end for increasing the engine torque at low vehicle speeds, 
so that the range of ratios of the transmission can be increased. The 
hydrodynamic transmission unit, however, may also consist of a so-called 
fluid coupling, by which the engine torque is not increased and which only 
serves as take-off clutch. A general drawback of a hydrodynamic 
transmission unit is the continuous presence of a speed difference between 
the input and the output shaft, i.e. slip, which results in a loss of 
power. In order to eliminate this drawback, it is known to provide the 
hydrodynamic transmission unit with means for locking said transmission 
unit in a direct drive mode. The lock-up, for example in the form of a 
plate clutch, effects a direct, mechanical connection between the input 
and the output shift of the hydrodynamic transmission unit. 
A drawback of the transmission lock-up feature is the complexity of its 
control, i.e. the regulation of the locking of the clutch in a direct 
drive mode during the periods in which the hydrodynamic transmission unit 
is not used for take off or for torque increase. For example, when the 
clutch is hydraulically operated a special operating valve is required. 
SUMMARY OF THE INVENTION 
It is the principal object of the invention to provide a simplified control 
for a hydrodynamic transmission lock-up. This is accomplished, according 
to the invention, by a control means which is operable in response to 
fluid pressure in the primary operating cylinder of the V-belt 
transmission unit. In the preferred embodiment the fluid pressure in the 
primary operating cylinder acts on a piston which causes engagement of the 
lock-up clutch. This enables control, through the same fluid supply valve, 
of both the transmission ratio of the variable V-belt transmission unit 
and the engagement and disengagement of the lock-up in the hydrodynamic 
transmission unit. As long as the variable V-belt transmission unit has 
the maximum transmission ratio, i.e. is in the lowest gear, the driving 
belt runs in the primary pulley with minimal running diameter, whereby the 
conical discs have their maximum interspace and are pushed against stops 
by the tensile stress in the V-belt. At pressure values up to that at 
which the V-belt transmission unit is caused to shift toward a lower 
ratio, the fluid pressure in the primary cylinder may be varied without 
affecting the V-belt unit, and in this pressure range the fluid pressure 
variation may be used for operating the lock-up. As long as the variable 
V-belt transmission is in a higher gear, there is always sufficient fluid 
pressure in the primary cylinder to keep the lock-up closed, i.e. to keep 
the hydrodynamic transmission unit in a direct drive mode. By thus using 
the fluid pressure in the primary operating cylinder for operating the 
locking of the hydrodynamic transmission unit, there is achieved a simple 
construction, whereby either (1) a torque convertor or a fluid coupling 
functions in its normal manner (i.e. transmits power hydrodynamically) and 
the variable transmission is in the lowest gear, or (2) the torque 
converter or the fluid coupling is locked in direct drive and the variable 
transmission unit influences the transmission ratio of the overall 
transmission. The same fluid supply and discharge valve may thereby 
control the transmission ratio of the V-belt unit as well as operate the 
lock-up. 
In a preferred embodiment the lock-up comprises a clutch, such as a wet 
plate clutch, the plates of which are engaged by means of a hydraulic 
pressure cylinder, and conduit means is provided for placing the primary 
operating cylinder in fluid communication with the pressure cylinder of 
the clutch. The conduit means may include valve means, such as a pressure 
reducing valve. 
The mechanical locking of the hydrodynamic transmission unit may 
furthermore comprise a vibration damper in order to counteract the 
transmission of torsional vibrations.

DETAILED DESCRIPTION 
One embodiment of the transmission according to the invention will now be 
described, by way of example, with reference to the accompanying drawing 
which is a schematic sectional view of a transmission embodying the 
principles of the invention. The drawing diagrammatically shows a part of 
the transmission, viz. a fluid coupling 1 and a primary pulley 2 of a 
two-pulley, infinitely variable ratio V-belt transmission unit. The fluid 
coupling 1 comprises a pump impeller 3 which via an input shaft 4 is 
driven by an engine, not shown, and a turbine impeller, which is directly 
connected to the primary pulley 2 of the variable V-belt transmission 
unit. Only the primary pulley 2, and a part of V-belt 9 are shown. The 
primary pulley 2 comprises a conical disc 6 fixedly connected to a primary 
shaft 10, and a conical disc 7 axially movable over the primary shaft 10. 
The running diameter of the V-belt 9 in the primary pulley 2 is defined by 
the interspace of the discs 6 and 7. With the maximum interspace shown in 
the drawing, the V-belt 9 lines with a minimum running diameter in the 
pulley 2. Through the tensile stress in the V-belt 9 the side half 7 is 
urged against a stop 14 connected to the primary shaft 10. Disc 7 
functions as a piston in a fluid pressure operating cylinder 11, which is 
fixedly connected to the primary shaft 10 and by which a cylinder space 8 
is enclosed. By pressure fluid supply and discharge to and from the 
cylinder space 8, via a coaxial fluid conduit 12 in the primary shaft 10, 
the spacing between the discs 6, 7 may be varied, resulting in a change of 
the running diameter of the V-belt 9 in the primary pulley 2. Thereby an 
equilibrium may be adjusted between the fluid pressure in the cylinder 
space 8 and the tensile stress in the V-belt 9. Such a control is 
described in detail in Dutch patent application No. 7601286. 
The transmission ratio of the variable V-belt transmission is consequently 
adjusted by fluid supply and discharge to and from the cylinder space 8, 
while the fluid pressure should always be sufficiently large to achieve an 
equilibrium condition with the tensile stress in the V-belt. 
In the illustrated embodiment there is a plate clutch having plates 15 
carried by the input shaft 4 and plates 16 carried by the primary shaft 
10. A clutch-actuating piston 17 is exposed to the fluid pressure in the 
conduit 12, so that at a predetermined pressure in the conduit the piston 
17 presses the plates 15 and 16 against each other, to effect a direct, 
mechanical connection between the shafts 4 and 10. Thus the hydrodynamic 
transmission unit 1 can be locked in a direct drive mode depending on the 
fluid pressure prevailing in the cylinder space 8. By means of the 
construction shown in the drawing, it is possible, depending on the fluid 
pressure in conduit 12 (and cylinder space 8), to operate the direct-drive 
lock-up 15, 16, 17, and to adjust the transmission ratio of the V-belt 
transmission. Thereby lock-up takes place at a fluid pressure that is 
insufficient to displace the disc 7 against the tensile stress of V-belt 9 
and away from stop 14, while during displacement of the disc 7 such a 
large fluid pressure is always pesent that the direct-drive lock-up 
remains in effect. 
The drawing furthermore shows a part of a stationary wall 18 which 
separates the coupling unit of the transmission from the V-belt 
transmission. In the wall 18 there is accommodated a fluid conduit 19 for 
supplying fluid to the hydrodynamic fluid coupling 1. Moreover, a bore 20 
is disposed for discharging fluid leaking via bearing 21. The fluid 
pressure prevailing in the fluid coupling 1 ensures the release of the 
plate clutch 15, 16, 17, when the fluid pressure in the space 8 is 
insufficient to engage the clutch, so that no additional provisions are 
required for clutch release. 
The transmission is provided with seals 22, 23 and 24 for counter-acting 
fluid leakage in the respective places. Furthermore, restrictions may be 
optionally applied in the fluid lines which are not shown in the drawing. 
The drawing only shows a diagrammatic picture of one embodiment; it will 
be clear that modifications of the illustrated combination of the 
direct-drive lock-up and the V-belt transmission are possible within the 
scope of the invention.