Device for stabilizing the temperature of the transmission oil of a motor vehicle

In order to control the temperature of the transmission oil of a motor vehicle driven by a liquid-cooled engine, a coolant/transmission oil heat exchanger is provided. The coolant stream supplied to the heat exchanger is miscible in a thermostatic valve from recooled and non-recooled coolant in order to achieve a desired temperature. Preferably the thermostatic valve is controlled by the temperature of the transmission oil, but it is also possible to have two expanding material elements as control pistons of the thermostatic valve, with one control piston being provided in the oil chamber of the thermostatic valve and the other control piston being provided in the coolant mixing chamber of the thermostatic valve. It is also possible, for purposes of precontrol, to electrically heat at least one of the control pistons.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to a device for stabilizing the temperature of the 
transmission oil of a motor vehicle with a liquid-cooled engine, whose 
coolant, recoolable in a radiator, can be conducted as a function of 
temperature through a heat exchanger that can likewise be traversed by the 
transmission oil. 
If it is necessary in motor vehicles to cool the oil of a transmission 
provided in the vehicle drive train (manual transmission, automatic 
transmission with hydraulic torque converter, or axle drive), an air/oil 
heat exchanger is usually provided for that purpose. In addition, it is 
known from German Patent document DE 32 01 443 A1 to heat the transmission 
oil more rapidly following a cold start of the vehicle by guiding the oil 
through an oil/coolant heat exchanger that is also traversed by the 
coolant of the engine that drives the vehicle. Since the coolant of a 
liquid-cooled engine, following a cold start of the motor vehicle, is 
heated more rapidly than the transmission oil, the transmission oil can 
thus be brought more rapidly to its optimum operating temperature. If 
these two systems were combined with one another, so that the transmission 
oil would be warmed more rapidly and the transmission oil could be 
recooled if necessary, this would involve a considerable expense since at 
least two heat exchangers would be required for the transmission oil. A 
high regulating cost is also required for this purpose if a desired oil 
temperature is to be reached or set. 
The goal of the present invention is to describe improvements in this 
regard. 
To achieve this goal, provision is made such that the coolant flow supplied 
to the transmission oil/coolant heat exchanger is miscible in a 
thermostatic valve from recooled as well as non-recooled coolant. 
Advantageous embodiments and improvements are further described herein. 
According to the present invention, a single heat exchanger suffices for 
the transmission oil in order to control the temperature of the latter if 
required, in other words to heat it more rapidly following a cold start 
and to recool it later, with the engine coolant also being conducted 
through this heat exchanger at a temperature that can be controlled. For 
this reason, a thermostatic valve is provided that sets the temperature of 
the coolant stream flowing through the heat exchanger. This temperature 
adjustment is performed by controlled mixing of recooled and non-recooled 
coolant from the engine. As already mentioned above, coolants with 
different intrinsic temperatures are available. Firstly, the coolant 
derived from the engine can be used, said coolant being relatively warm, 
and secondly the coolant recooled in the vehicle radiator can be used, 
said coolant having an even lower temperature. By suitable mixing of these 
two coolant volumes, in other words by suitable mixing of the recooled and 
non-recooled coolant, a desired coolant temperature can be set in the 
coolant/transmission oil heat exchanger that allows for the desired 
transmission oil temperature control. 
Preferably, provision can be made such that the thermostatic valve for 
mixing the recooled and non-cooled coolant is controlled by the 
temperature of the transmission oil. This ensures the fastest possible 
regulation, as well as the most reliable, since the temperature of the 
medium that controls the temperature of the transmission oil, namely the 
temperature of the coolant, is set as a function of the result of the 
temperature control, i.e. by the temperature of the transmission oil. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIG. 1, the reference numeral 1 designates a liquid/liquid 
exchanger through which firstly the transmission oil of a motor vehicle 
whose temperature is to be controlled and secondly a coolant stream from 
the engine driving the vehicle can be conducted. Accordingly, a supply 
line tube 2a and a drain line 2b for the transmission oil as well as a 
supply line 3a and a drain line 3b for the coolant are provided. The 
cooling liquid stream supplied through supply line 3a can be mixed in a 
thermostatic valve 4 from two coolant streams that have different 
temperatures. 
Non-recooled coolant 5a enters directly into thermostatic valve 4 from the 
engine (not shown), followed by re-cooled coolant 5b, which has previously 
passed through a radiator (vehicle radiator), in which, as is known to the 
individual skilled in the art, the coolant of the engine can be recooled. 
In thermostatic valve 4, coolant 5a can be mixed with coolant 5b in any 
desired amounts, with the temperature of the coolant flow that enters heat 
exchanger 1 through supply line 3a being capable of being deliberately set 
in order to achieve a desired transmission oil temperature in drain line 
2b through the heat exchanging process in heat exchanger 1. 
It should be expressly pointed out at this point that a mixture of recooled 
coolant 5b and non-recooled coolant 5a to achieve a desired temperature in 
the coolant supply line 3a is also to be understood as referring to the 
state in which only recooled coolant 5b or only non-recooled coolant 5a 
passes through thermostatic valve 4 into supply line 3a. In addition, this 
thermostatic valve 4 is designed as a conventional mixing thermostat, i.e. 
two valve plates 6a, 6b are provided that are assigned to the inflow cross 
sections 7a, 7b for coolants 5a and 5b into a mixing chamber 8 inside 
thermostat housing 9. 
Valve plates 6a, 6b mounted on a common piston rod 10 are positioned by a 
control piston 12 that displaces piston rod 10 in the direction of arrow 
11 and is designed as an element made of expanding material. This control 
piston 12 in the embodiment shown in FIG. 1 is located in supply line 2a 
and is therefore impacted by transmission oil whose temperature has not 
yet been controlled. This means that thermostatic valve 4 is controlled by 
the temperature of the transmission oil, which, as mentioned above, is 
especially advantageous from the regulation technology standpoint. 
Alternatively, however, it would also be possible to control thermostatic 
valve 4 by using the temperature of the transmission oil that leaves heat 
exchanger 1 through drain line 2b or by using the temperature of the 
coolant stream, i.e. the temperature of the essentially mixed coolant 
stream or in other words, by the coolant temperature in mixing chamber 8 
itself. 
However, it is especially advantageous when control is possible both as a 
function of the temperature of the transmission oil and of the current 
coolant temperature. A preferred embodiment of this is shown in FIG. 2, 
with only the thermostatic valve 4 being shown in principle. The parts 
that are the same as in FIG. 1 have been given the same reference numbers. 
Thus, we again have mixing chamber 8 located inside thermostatic housing 9 
with valve plates 6a, 6b that delimit inflow cross sections 7a and 7b, 
with a coolant supply line 3a running from the mixing chamber 8 to a heat 
exchanger 1 (not shown here--see FIG. 1). Here again, the two valve plates 
6a, 6b are located on a piston rod 10. The rod however, in this case, is 
not directly connected with a control piston that is impacted by the 
transmission oil. Instead, in this embodiment according to FIG. 2, piston 
rod 10 is part of a so-called mixing chamber control piston 10' provided 
in mixing chamber 8, said piston again being designed in the form of an 
expanding-material element. This means that valve plates 6a, 6b can be 
displaced as a function of the temperature of the coolant in mixing 
chamber 8 in the direction of arrow 11. 
However, in FIG. 2, a control piston 12 is again provided that is impacted 
by the transmission oil and is designed as an expanding material element. 
This piston 12 is located in a so-called oil chamber 13 of thermostatic 
valve 4 that is integrated into transmission oil supply line 2a and is 
therefore referred to as a so-called oil chamber control piston 12. A 
separate piston rod 12' is associated with this oil chamber control piston 
12, with piston rod 10 of mixing chamber control piston 10' abutting the 
free end of said rod. In this manner, with a suitable change in shape of 
oil chamber control piston 12, the two valve plates 6a, 6b can again be 
displaced in the direction of arrow 11, resulting in a change in free 
inflow cross sections 7a, 7b and thus influencing the temperature of the 
coolant stream located in mixing chamber 8. 
In FIG. 2, the two valve plates 6a, 6b in mixing chamber 8 are 
approximately at their middle positions. Thus, a coolant stream flows 
through heat exchanger 1 as shown in FIG. 1 that has an approximately 
medium temperature, so that in heat exchanger 1 the transmission oil 
likewise undergoes a slight cooling as it passes through. If the 
temperature of the transmission oil should increase for some reason 
relating to loading, this causes oil chamber control piston 12 to expand 
so that its piston rod 12' and hence piston rod 10 as well are displaced 
toward the right starting at the position shown. The inflow cross section 
7a for non-recooled coolant 5a is closed as a result, so that a larger 
amount of recooled coolant 5b flows through inflow cross section 7b into 
mixing chamber 8, and from there through coolant supply line 3a into heat 
exchanger 1. As a result, the transmission oil is recooled to a greater 
degree in heat exchanger 1. Finally, if the temperature of the 
transmission oil drops again, oil chamber control piston 12 changes its 
shape accordingly in such fashion that piston rod 12' as well as piston 
rod 10 are again displaced leftward and a greater amount of non-recooled 
coolant 5a can pass through coolant supply line 3a into heat exchanger 1. 
In addition to the above-described operation of the coolant flow 
temperature control as a function of the temperature of the transmission 
oil, thermostatic valve 4 also permits control as a function of the 
coolant temperature itself. Thus, immediately following a cold start of 
the engine, when the coolant is still cold, piston rod 10 assumes a 
position due to a suitable shape of mixing chamber control piston 10' such 
that inflow cross section 7b is closed and inflow cross section 7a is 
completely open. Beginning at the position shown in FIG. 2, valve plates 
6a, 6b are thus displaced leftward. If on the other hand the coolant is 
heated, for example by an extreme load on the engine, so that the 
transmission oil would be unnecessarily or inadmissibly heated in heat 
exchanger 1, inflow cross section 7a for non-recooled coolant is closed 
under the influence of mixing chamber control piston 10 and inflow cross 
section 7b for recooled coolant 5b is completely open. Then, piston rod 10 
with the two valve plates 6a, 6b, starting from the position shown, would 
be displaced against its right-hand stop. By suitable adjustment, it is 
therefore possible with thermostatic valve 4 described above, in all 
possible operating states, to set the desired coolant temperature in heat 
exchanger 1 in order to achieve the desired transmission oil temperature. 
With the goal of providing an especially advantageous improvement on the 
invention, at least one of the two control pistons 10', 12, in this case 
the oil chamber control piston 12 formed of a corresponding expanding 
material element, can be heated electrically. For this purpose, a heating 
element 14 is provided in control piston 12. The heating element 14, under 
the control of an electronic control unit (not shown) is connectable with 
an electrical power supply 15. As a result, a form of temperature 
precontrol is possible, as also described in German Patent application P 
195 12 783 (not previously published). If for example, due to some 
boundary conditions, it is determined that the transmission oil 
temperature is expected to rise sharply within a short time interval, oil 
chamber control piston 12 or the corresponding expanding material element 
can already be heated in a preventive manner so that it expands, 
displacing its piston rod 12' and hence the two valve plates 6a, 6b to the 
right. This is done so that the inflow cross section 7a for non-recooled 
coolant 5a is closed. Even before the transmission oil has actually 
reached the higher temperature, because of the high percentage of recooled 
coolant 5b in heat exchanger 1, greater recooling of this transmission oil 
takes place so that undesired temperature excesses are avoided. With 
electrical heating of at least one of the two control pistons 10' or 12, 
it is possible to set the transmission temperature not only for the 
purpose of precontrol but also in general for a desired temperature value. 
A number of the details, especially of a structural nature, can be made 
different from the embodiments shown without departing from the scope of 
the patent claims, as would be readily understood by one skilled in the 
art. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.