Hydraulic control for operating an automatic gearbox, especially a continuosly variable transmission

A hydraulic control for operating an automatic transmission, especially a continuously variable transmission, has at least one first and one second switching component (1, 2) for forward or reverse drive from a neutral position (N) to a drive (D) or reverse (R) position and vice versa. The switching components (1, 2) can be actuated by pressure via pressure lines (24, 25) by a selector slide (15) and by a switching device (26) between the selector slide (15) and the switching components (1, 2) which has a switching valve (27, 28) and a damper, switching and vent valve (29, 30) for a switching component (1, 2). The switching device (26) has a safety and vent device designed in a manner such that when one of the switching components (1, 2) is actuated, the other switching component(s) is/are automatically disengaged.

The invention relates to a hydraulic control for operating an automatic 
transmission including a CVT, having at least one first and one second 
switching component for forward or reverse drive from a neutral position 
to a forward drive position or a reverse drive position and vice versa. 
BACKGROUND OF THE INVENTION 
As generally known from the practice, in automatic transmissions with 
hydraulically actuated switching components, which usually have a 
switching piston installed in a piston space on a disc set to carry out a 
gearshift, the switching component is first filled with oil before the 
switching piston is placed on the disc set. If the switching component is 
disengaged, the pressurized medium is removed from the switching component 
and the disc set is again relaxed. The filling and installation of a 
switching component has a rapid filling phase in which the switching 
component that is almost full or running partly empty is filled with oil, 
there follows a filling equalizing phase during which a switching piston 
is placed on the disc set. At the end of the filling equalizing phase 
follows a pressure increasing phase which can be reproduced as pressure 
ramp increasing in the course of time. During this pressure increasing 
phase or pressure ramp the discs are adequately pressed together and can 
transmit or receive a torque. 
It also is generally known that in a first range up to the beginning of the 
pressure ramp a turbine belonging to a hydraulic start component of the 
transmission rotates at the idling speed of an engine connected with the 
transmission. When the pressure ramp has been climbed, the speed of the 
turbine goes back to zero and a torque is passed, for example, to the 
wheels of a motor vehicle wherein a jerky process generally occurs which, 
as a rule, is felt as disturbing. 
After the end of the pressure ramp, the pressure can be further raised, to 
increase torque transmission, by the switching components. The rise in 
pressure is effected according to what is needed. 
On the other hand, when the switching component is opened, for example, the 
turbine begins to rotate until it reaches the engine idle speed. As a 
rule, the turbine can then take up in a manner such that this, in turn, is 
noticed by the driver as light jolt. 
There have become known from testing that the gearshift operation can be 
made more comfortable by using switching times which are as brief as 
possible. 
However, this raises questions, relative to safety, since in a change that 
is too quick, under certain circumstances, two switching components are 
simultaneously loaded with pressure and work against each other, causing a 
lock up of the transmission. This can bring about a situation critical to 
safety in addition to the operating comfort being greatly reduced. 
SUMMARY OF THE INVENTION 
Therefore, the problem to be solved by the invention is to provide a 
control for operating an automatic transmission from a neutral position to 
a forward drive position or a reverse drive position and vice versa, the 
same as reversal shifts forward drive position--reverse drive position and 
vice versa with which a more comfortable, almost jolt-free, quicker and 
safer gearshift is obtained. 
The control according to the invention makes it possible that the change 
between the neutral position and the forward drive position or reverse 
drive position and back, the reversal shifts to forward drive 
position--reverse drive position and vice versa be so comfortable that as 
a rule the occupants of a motor vehicle will not notice the gearshift 
either by a switching jolt or by a noise. 
In addition, it is possible with the control, according to the invention, 
to keep the starting point of a pressure ramp constant during pressure 
loading by the damper, switching and vent valve. 
The control, according to the invention, offers the added advantage that it 
is very quickly possible to make shifts between forward drive position and 
reverse drive position wherein the switching components are reciprocally 
blocked in a manner such that, upon actuation of a switching component, 
other switching components are automatically disengaged. 
A quick vent of the unactuated switching components can advantageously 
prevent the occurrence of an operating state in which two switching 
components are simultaneously actuated, that is, there cannot occur any 
transmission stress or head-on blockage of the switching components which 
would cause a torque impact. 
The control, according to the invention, contributes considerably to an 
increase of the operating safety of a vehicle. 
The quick vent of the switching components upon reversals is ensured by a 
very advantageous quick vent of the damper space of the switching valves, 
via the damper, switching and vent valve. 
With the control, according to the invention, it is in addition possible 
advantageously to regulate, according to the torque to be transmitted, the 
pressure on a switching component even in operating state. The control, 
according to the invention, is further advantageous in that tolerances in 
the pressure loading of the switching components can be compensated. 
Other advantages and advantageous developments of the invention result from 
the sub-claims and the description that follows of an embodiment with 
reference to the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawing, it shows a hydraulic control of an automatic 
transmission in a motor vehicle, the individual components of which are, 
to a great extent, of known design for which reason only the essential 
features will be discussed in detail. 
To operate a switching component 1 and another switching component 2 which 
are symbolically indicated in the drawing, system pressure is fed by a 
pump 3 to a hydraulic system. The system pressure is first set by a first 
pressure-limiting valve 4 which is controlled by an electronically 
controlled pressure regulator. The pressure-limiting valve 4 is connected 
by a pressure line 5 with a hydraulically starting component 6, only 
symbolically indicated, the oil supply of which is thereby ensured. 
Together with the hydraulic starting component 6, consumers 7, indicated 
only symbolically, are supplied with system pressure, via pressure lines 8 
and 9. 
The system pressure to operate the switching components 1 and 2 of the 
hydraulic system is fed, via other pressure lines 10, 11, 12, there being 
situated in each line 10 and 11 a pressure-reducing valve 13, 14 which 
reduces the system pressure to a constantly remaining output value which 
is always lower than a minimum pressure adjustable by the 
pressure-limiting valve 4. In the instant embodiment, the output pressures 
of the pressure-reducing valves 13 and 14 are equal but in another 
embodiment they can also be different. 
In the pressure line 12, which leads to a selector slide 15, is situated a 
clutch pressure valve 16 which regulates the pressure level on the 
switching components 1 and 2. The clutch pressure valve 16 regulates the 
pressure loading of the switching components 1 and 2 in accordance with 
the torque. Thus, it is possible to preset a torque-dependent pressure, 
via the clutch pressure valve 16, in the operation with a closed switching 
component 1, 2. The clutch pressure valve 16 is controlled by an 
electromagnetically adjustable pressure regulator 17 with which the clutch 
pressure valve 16 is connected by a pressure line 18. The pressure 
regulator 17 is a proportional valve which is actuated by a current 
supplement in a manner such that for each change of current, a change of 
the output pressure of the pressure regulator 17 also linearly occurs. 
During a pressure buildup in one of the switching components 1, 2 which is 
along an adjustable pressure ramp having a ramp gradient and a ramp 
operating time, the clutch pressure valve 16 remains unchanged. This 
applies as long as no change of torque occurs on the engine during the 
gearshift operation. 
During travel, the clutch pressure valve 16 takes over, in addition, the 
task of a reverse drive lock, for which advantageously no other components 
are needed. To this end, the clutch pressure is disengaged when changing 
the forward drive above a specific velocity of the vehicle. 
To regulate a load valve 19 on which is applied, via the pressure line 10, 
the output pressure of the pressure-reducing valve 13, the latter is 
connected by a pressure line 20 with a pressure regulator 21 having a 
constructional configuration identical to the pressure regulator 17 which 
is coordinated with the clutch pressure valve 16. 
From the pressure line 20, which connects the pressure regulator 21 with 
the load valve 19, branches off another pressure line 22 for pressure 
supply of other functions, not shown, such as for maintaining a certain 
pressure level in other hydraulic circuits of the transmission. The 
connecting pressure line 20 between the load valve 19 and the pressure 
regulator 21 and the connecting line 18 between the clutch pressure valve 
16 and the pressure regulator 17 are each connected, via a pressure line 
57, with the pressure-reducing valve 14, the constant output pressure of 
which is fed, via feed-in nozzles 55, 56, to the pressure lines 18, 20. 
Depending on the position of the selector slide 15, five switching 
positions can be selected, namely, the switching positions D, L for 
forward drive, a switching position R for reverse drive, a switching 
position N for neutral position and a switching position P for parking 
position. The selector slide 15 is manually actuatable by a selector lever 
23. In the drawing the selector slide 15 is shown in neutral position N 
which hydraulically considered is equivalent to the parking position P, 
since in both switching positions N and P the switching components 1 and 2 
are vented. 
From the selector slide 15, a pressure line 24 leads to the switching 
component 1 and a pressure line 25 leading to the switching component 2, 
there being situated between the switching components 1 and 2 and the 
selector slide 15 a switching device 26 which has, for each one of the 
switching components 1 and 2, a respective switching valve 27 and 28 and a 
damper, switching and vent valve 29 and 30. The switching position of the 
switching components 1 and 2 is determined by the position of the selector 
slide 15, by the position of the switching valves 27, 28 and by the 
position of the clutch pressure valve 16. 
In addition, the selector slide 15 performs an emergency function in case 
of failure of the transmission control when the valves 17, 19 are no 
longer electrically controllable, since the switching components 1 and 2 
can be further actuated by the switching valves 27, 28, via a pressure 
ramp. The reciprocal interlocking is maintained here. In an emergency the 
pressure loading of the switching components 1, 2 with a maximum clutch 
pressure is provided by the pressure regulator 17 and the clutch pressure 
valve 16 interacting therewith. 
The switching valve 27 coordinated with the switching component 1 is in the 
pressure line 24 and the switching valve 28 coordinated with the switching 
component 2 is in the pressure line 25 intercalated between the switching 
component 1 or 2 and the selector slide 15. The switching valves 27, 28 
have in a respective valve housing 31, 31' a movable valve piston 33, 33', 
a damper piston 40, 40' and a compression spring 38, 38'. The damper 
pistons 40, 40' can be loaded here with a control pressure which , via a 
pressure line 34 or 35, reaches from the damper, switching and vent valve 
29 to the switching valve 27 or 28. 
The valve housing 31, 31' of the switching valves 27 and 28 have each a 
supply of pressurized medium via the lines 24, 25 and a tank connection 
37, 37'. 
In the valve housings 31, 31', between the valve pistons 33, 33' and the 
damper piston 40, 40', in a working space 39, 39', is situated axially 
movably supported a prestressable spring 38, 38'. 
A switching valve 27 or 28 is pressure loaded directly, via the 
appertaining damper, switching and vent valve 29 and 30 and at a moment 
when the appertaining switching component 1 or 2 is almost entirely filled 
with pressurized medium. The reversal point of the damper, switching and 
vent valve 29 and 30 is therefore slightly below a charge pressure of the 
appertaining switching component 1 or 2. A pressure ramp on the switching 
component begins after reversal of the appertaining damper, switching and 
vent valve 29, 30, for example, when the pressure of the switching 
component is substantially 0.2 to 0.3 bar below a final filling value. 
Thereby the pressure buildup is constant for all factors affecting an 
operating state such as temperature and oil viscosity. When disengaging 
the switching component 1 or 2 concerned, the oil volume cropping out 
behind the damper piston 40, 40' is directly removed, via the appertaining 
damper, switching and vent valve 29 or 30 directly to a tank 41, 41' 
whereby a quick vent is ensured. 
The damper, switching and vent valves 29, 30 are designed in the 
embodiment, according to the drawing, as 3/2 slide valves and each having 
a spring 42, 42' which determines the reversal value of the respective 
damper, switching and vent valve 29, 30 so as to counteract a pressure on 
the switching component 1, 2 which has been fed, via pressure lines 43, 
43' to the damper, switching and vent valve 29 or 30. The reversal value 
of the valve 29 or 30 is thereby function of the filling pressure of the 
coordinated switching component. In the embodiment shown the springs 42, 
42' have a different design and are adapted to the operating conditions. 
In another embodiment, similar springs obviously can be used. 
To prevent that two switching components from being simultaneously 
actuated, the switching device 26 has a safety and vent device which 
ensures that upon actuation of one of the switching components 1 or 2 the 
other switching component is automatically disengaged. To this end, there 
branches off from the pressure line 24, between the selector slide 15 and 
the switching valve 27 of the first switching component 1, a control 
pressure line 44 which introduces a control pressure on an active surface 
of the valve piston 33' which is coordinated with the not selected 
switching component 2 whereby the valve piston 33' of the switching valve 
28 is moved to the left far enough so that the tank outlet 37' of the 
switching valve 28 is opened. Thereby pressurized medium is directly 
removed to the tank 37' from the unactuated switching component 2. The 
pressure line 44, which branches off from the pressure line 24, is in 
addition connected with the damper, switching and vent valve 29, of the 
selected switching component 1 and via the component and the pressure line 
34 feeds pressurized medium to the switching valve 27 in a manner such 
that the damper piston 40 of the switching valve 27, within a time 
determined by the feed-in nozzle 46, moves to the right and thereby 
continuously prestresses the compression spring 38. From the continuously 
increasing spring compression upon the left side of the valve piston 33 
there is produced in the interplay with the reduced pressure of the 
switching component 1, which engages an active surface on the right side 
of the valve piston 33, the pressure ramp needed to operate the switching 
component. The switching component 2 is here automatically vented. 
If the switching component 2 is selected and must be actuated, it is 
similarly loaded with pressure and the switching component 1 is locked. 
The safety and vent device thus ensures a reciprocal locking since while 
loading with pressure one of the switching components 1 or 2, the 
switching valve of the unactuated switching component is loaded with 
pressure in opposite direction so that in a reversal a quick vent of the 
other switching component by force takes place. 
The supply of control pressure, via the control pressure lines 44 and 45 to 
the respective damper, switching and vent valve 29 or 30 is throttled by a 
nozzle 46 and 47 which determines the definite operating time of the ramp. 
In the working space 39, 39' of the spring 38, 38', the load pressure is 
fed, via a pressure line 48, by the load valve 19. 
From a balance of the forces on the switching valves 27, 28 can be 
detected, for example, that the pressure of the switching component 2 is 
momentarily proportional to the load pressure of the loading valve 19 
during the damper operating period. The pressure on the switching 
component 2 is likewise proportional to the spring tension of the spring 
38' in the switching valve 28 belonging to the switching component 2. This 
means that in consequence of a change in the prestress of the spring 38' 
an increase of the pressure in the coordinated switching component 2 
occurs, that is, a change of path on the spring constitutes a change of 
pressure or basic ramp. The spring prestress is increased, according to 
the volume flowing in, whereby the pressure increases on the switching 
component concerned. 
The pressure originating from the loading valve 19 depends on an engine 
load and is altered by the pressure regulator 21. The loading valve 19 
acts with its output pressure, via the pressure line 48, upon both 
switching valves 27, 28 or the valve piston 33, 33' thereof. Thereby the 
pressure ramps produced by said switching valves in the appertaining 
switching component 1 or 2, for example, can be changed in a manner such 
that the pressure ramp extends with equal gradient to a higher pressure 
level. In this manner, the switching components 1, 2 are supplied with 
pressurized medium according to the load. 
The vent of the switching components 1, 2 on the switching valves 27, 28 
takes place when reversing via the respective tank connection 37, 37' When 
switching back from forward position or reverse position after neutral or 
parking position, the corresponding switching components are vented via 
the selector slide 15 and the draining nozzles 53, 54 in the tank 51, 52. 
The beginning of the pressure ramp is determined by the pressure fed to the 
switching valve 27 or 28 by the respective damper, switching and vent 
valve 29 or 30 via the pressure line 34 or 35. On the other hand, the load 
pressure of the loading valve 19 serves for a change of the pressure 
loading of the valve piston 33, 33' in the switching valves 27, 28, for 
example, when the load change occurs by gas supply during the gearshift. 
By the load pressure of the loading valve 19, a comfortable gearshift 
course can be represented even when shifting from the neutral position N 
to the forward drive position D or L or to the reverse drive position R 
under an engine part load. 
If the selector slide 15 is in neutral position N or parking position P, 
both switching components 1 and 2 are vented by removing the pressurized 
medium from the switching components via the selector slide 15 and 
pressure lines 49 and 50 to a pressurized-medium tank 51 or 52. Between 
the selector slide 15 and the pressurized-medium tank 51 or 52 is placed a 
draining nozzle 53 or 54 which adjusts the cross section of the through 
flow for the drain of the pressurized medium in accordance with the 
temperature of the transmission. Corresponding to the higher oil viscosity 
at low temperatures or low oil viscosity at high temperatures, the 
draining nozzles 53, 54 change their cross section in such a manner that 
at low temperatures large drain cross sections and at high temperatures 
small drain cross sections are adjusted. By the temperature-dependent 
adjusting function, which is obtained by any temperature-dependent setting 
or adjustment members (not shown), the discharge time of the switching 
components 1, 2 can be maintained constant over the transmission 
temperature range. 
On the other hand, when shifting directly from forward drive to reverse 
drive, no delay of the pressure breakdown occurs in the switching 
components 1, 2 by the draining nozzles 53, 54, since this would cause a 
jolt which impairs the gearshift quality. The switching components 1, 2 
are drained here via the tank connections 37, 37' on the switching valves 
27 and 28.