Note: Descriptions are shown in the official language in which they were submitted.
7513
The invention relates to a hydraulic control for
automatic vehic]e transmissions and more specifically, to
such transmissions having shifting valves which actuate the
clutches/brakes by means of an operating pressure. A
comparable hydraulic control in which the shifting points are
determined as a function of engine load and speed, is described
in ADZ, year 77, volume 9/1975, on pages 246 to 249. The
main pressure valve is followed by a throttle pressure valve
which produces a pressure dependent upon engine load
independently of the selector lever position. A cam, which
is rotated by an accelerator control cable according to the
accelerator pedal setting, displaces the valve piston so that
the spring is preloaded according to the required engine load
whexeby the load dependent pressure, the throttle pressure, is
produced. Arranged in parallel with the throttle pressure
valve is a modulating valve, to which operating pressure and
throttle pressure are also fed in the same way. In accordance
with the valve and piston area ratio, the modulating pressure
is usually higher than the throttle pressure and varies the
operating pressure, as a function of engine load, in order to
influence the shift pressure systems which determines the
pressure in the servo piston during the shifting process.
The pressure dependent upon the driving speed of the
vehicle is produced by the regulator arranged upon the output
shaft and, in shift position 1, ~ or 3, for example, non
return valves are provided to prevent shifting down to lower
gears above a predetermined speed. Shifting up to gears
above the selected position is also prevented.
Hydraulic controls of this and similar types have
been found satisEactory for vehicles equipped with naturally
1'~77~;13
aspirated engines in conjunction with automatic transmissions
because, by means of the throttle pressure valve and regulator,
dependence upon engine load and driving speed is achieved
with sufficient accuracy to determine the shifting points and
to engage and disengage the shift elements, and is transferred
to the shifting pressure system as throttle and regulator
pressure. Necessary overlapping shifts, when one clutch or
brake is released and a second is engaged, are effected with
the aid of the above mentioned pressures by means of shifting
and time control valves in such a manner as to avoid any
appreciable gear shifting jolt which is unpleasant for the
driver and occupants of a vehicle.
In the case of vehicles equipped with supercharged
engines, however, a control of this kind is unsatisfactory
since engine torque cannot be determined accurately from
accelerator pedal setting.
It is therefore the purpose of the invention to
develop still further a hydraulic control so that it may also
be used for super charged engines in this way, which has
been found satisfactory in principle. At the same time,
structural and equipment expense is to be kept to a minimum.
This purpose is accomplished as set forth in the
characterizing portion of claim 1.
Feeding intake pressure to at least one shifting
valve makes it possible to influence the operation, at least
of this shifting valve, as a function of intake pressure.
In order to maintain adequate pressure in a clutch or brake
to be released for a downshift, use is made of the 4/3 downshift
valve for example. The piston or pistons of this downshift
valve, which operates as a modulating valve, is influenced
1~2775~3
by driving speed dependent regulator pressure and/or by a
spring adapted to this operating pressure. The level of the
operating pressure during the shift is also influenced by
the intake pressure, since engine torque may vary before and
during the shift as a function of engine r.p.m. and throttle
valve opening, accelerator pedal setting.
If the intake pressure is fed dire~tly, i.e., without
conversion, to the pressure valve spring chamber, the`design
is particularly simple since no pressure boxes are required
for converting the pressure. Any sealing problems arising
may be solved quite simply by the provision of relatively
long sealing surfaces and sleeves.
In the drawing attached hereto:
Figures 1 and lA are schematic diagrams showing the
control mechanism of the present
invention;
Figure 2 is a graph showing pressure against
time of an overlapping shift;
Figure 3 is a schematic view of simplified
control for an overlapping shift;
Figure 4 is a cross-sectional view of a
4/3 down shifting valvei and
Figure 5 is a cross-sectional view of another
embodiment of a 4/3 shi~ting valve.
In the diagram according to Figure 1, shift valve 2
is in setting D corresponding to an unrestricted automatic
driving mode. Pressure is built up by a pump 3 which draws
oil from gearbox sump 31 and delivers it to master valve
which operates as a modulating valve. The pressure is
dependent upon spring 320 and a shift throttle pressure line
341, and is produced in throttle valve 34 and modulating
valve 33 as a function of accelerator pedal setting. In
-- 3 --
~;~775~3
gears 1 to 3, this pressure is fed to downshift valve (4/3)
through line 11, so that the piston or pistons 12 are moved
to the right hand terminal position against the pressure
spring 13. This locks downshift valve (4/3) in these
gear positions. In the 4th gear, the main pressure is fed
only through line 14 to downshift valve (4/3) 1. A speed
dependent pressure is produced in regulator 35 and may also
be fed to downshift valve (4/3) 1 by line 35'. C' represents
the brake which releases in a shift from 4th to 3rd gear and
A is the clutch which is activated for this shift. srake
CI is also associated with the clutch valve plus damper C'l and
clutch A of damper A 1.
Figure 2 shows an overlapping shift, e.g., a pull
downshift from 4th to 3rd gear. In this case, PC' is the
pressure pattern in brake C' which is to be released, while
PA is the pressure pattern in clutch A to be engaged.
5 represents the pull-up release time delay of br~ke C'
and clutch A, while curve nMOt indicates engine r.p.m.
during the shift. Curve PL represents intake pressure.
The overlapping shift from 4th to 3rd gear operates
as follows when the vehicle is pulling a load:
When the accelerator pedal is fully depressed, i.e.,
in "kick down", and at a predetermined r.p.m. in the drive
train, the downshift from 4th to 3rd gear is initiated.
The pressure in brake C' drops, as shown in diagrammatical
curve PC', while over the same period of time, the pressure
in clutch A, to be engaged, is built up as shown in curve PA.
During pull-up release time delays 5, the pattern of curve PC',
unaffected by intake pressure, is according to 52 and, with
boost pressure, it is according to 51. In this connection,
curve 51, shown horizontal, may assume any shape according to
1'~77513
the actual intake pressure, but in this example, it is shown
as a straight line for the sake of simplicity. As far as
point 53 therefore, engine torque is transferred only
through brake C'. From point 54, it is transferred through
clutch A. Between these two points, during pull-up release
time delay 5, torque transfer takes place in brake C'. The
intake pressure in modulating the 4/2 downshift valve for the
main pressure of brake C' to be disengaged, produces a more
realistic adaptation of contact pressure to the torques to
be transferred which, in the case of supercharged engines, is
not provided merely by modulation according to accelerator
pedal setting and spring 13 arranged in downshift valve 1.
Figure 3 shows diagrammatically a carburetor 6, a
pressure box 7 and downshift valve (4/3) 10. In this case,
the intake pressure, at line 61, may be fed to the downshift
valve 10 either directly or through a pressure box 7 as
hydraulic pressure in line 71.
With direct feed in the form cf a gas, a sealing
element 16 is arranged in spring chamber 15 (Fig. 4), in such
a manner that a relatively large sealing surface 164 seals
spring chamber 15, which is acted upon by intake pressure,
from hydraulically acted upon piston chambers 18 of downshift
valve 10, by the sealing sleeve 16 against inner end 162 of
which spring 13 bears. Outer end 163 of sealing sleeve 16
bears against piston 12.
A second sealing arrangement may be seen in Figure 5.
Mounted in a groove 122 on shaft 121 of a piston 120-is the
bead 201 of a thin walled sleeve 200, secured by a retaining
element 210. The sleeve 200 is secured to valve housing 101
by means of a clamp 220 and spring chamber 150 is therefore
reliably sealed off from piston chambers 180. Retaining
-- 5 --
,
- .
1.~775~3
element 210 is also acted upon by spring 130 and carries out
the longitudinal movements of the piston in conjunction
with the pressure modulation. In contrast to this, clamp 220
is secured in the valve housing.
Since the absolute seal provided by the sleeve makes
it possible to design contact surfaces between the clamp body
220 and the retaining element to be easy running in view of
gap 214/222-, the modulation movement of piston 120 will not
be impeded by friction.
