GB1590988A - Change-under-load gear transmission having a hydrodynamic unit and a hydrodynamic retarder - Google Patents

Description

(54) CHANGE-UNDER-LOAD GEAR TRANSMISSION HAVING A HYDRODYNAMIC UNIT AND A HYDRODYNAMIC RETARDER (71) We, ZAHNRADFABRIK FRIEDRICH SHAFEN AKTIENGESELLSCHAFT, of Friedrichshafen-on-the-Bodensee, Federal Republic of Germany, a Joint-Stock Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement This invention relates to a change-underload gear transmission of the kind comprising a hydrodynamic unit (hydrodynamic clutch or hydrodynamic torque converter), a change-speed gear unit connected to the output of the said hydrodynamic unit, and a hydrodynamic retarder mounted on the input side of the changespeed gear unit, wherein a first housing portion containing the change-speed gear unit and the retarder is delimited by a coverlike closure housing part, which forms a partition, in relation to a second housing portion containing the hydrodynamic unit, and wherein a pressure medium pump, serving to supply pressure medium to the pressure medium consuming elements of the transmission, a main pressure valve, and a plurality of pressure medium ducts connecting the pump, the pressure medium consuming elements, and the main pressure valve are disposed in the closure housing part disposed axially directly next to the hydrodynamic unit.

In a change-under-load gear transmission of this kind relatively large amounts of pressure medium and flow medium must be delivered particularly for the hydrodynamic unit (converter) and the retarder.

In the known change-under-load gear transmissions a partition or housing cover is incorporated as closure housing part between the first housing portion (gear unit chamber), which is regarded as a wet chamber, and the second housing portion (converter chamber), which must remain dry.

This closure housing part contains a pressure medium pump, which is usually axially offset in relation to the input shaft, while the control valves are accommodated in a control housing disposed under the changespeed gear unit in the first housing portion.

In an arrangement of this kind there are long flow medium ducts from the pump via the corresponding control valves to the converter and retarder, and these give rise to relatively great flow losses and, in the case of the retarder, to a disturbingly long filling time. Furthermore, a large number of points where the pressure medium ducts pass over from one housing portion to the other cannot be avoided. These disadvantages still persist if the main pressure valve is disposed in the closure housing part.

It is also known (German Auslegeschrift No. 1,134,903) for a hydrodynamic converter to be separated from a retarder, which is connected to its output, by a partition containing the drive for a pressure medium pump, the stator of the retarder immediately adjoining this partition. Since here again the control valves are disposed separately from the housing containing the converter and the retarder, in this known arrangement the disadvantages described above also arise.

The invention aims at obviating the foregoing drawbacks and at providing a changeunder-load gear transmission of the foregoing kind in such la manner that the flow and leakage losses of the flow paths from the pressure medium pump via the control valves to the hydrodynamic elements (converter or hydraulic clutch and retarder) are as low as possible, and that in addition a short filling time is made possible for the retarder.

To this end, the present invention consists in a change-under-load gear transmission of the kind hereinbefore set forth, wherein the retarder has its stator directly adjoining the closure housing part in which there are disposed a converter counterpressure valve, a lubrication pressure valve and other valves for controlling the pressure medium flows of the hydrodynamic unit and retarder.

In a change-under-load gear transmission of the foregoing kind it is essential that not only the pump and the main pressure valve but also all the control valves necessary for supplying flow medium to the converter and retarder-with the exception of a pneumatically operated retarder regulating valve should be disposed in the closure housing part, so that only the control valves associated with the friction clutches will be accommodated in the control housing (under the change-speed gear unit). In addition, the arrangement selected for the retarder is one in which its stator directly adjoins axially the closure housing part. It is thus possible to dispose the control valves centrally around the pump and thus to avoid long ducts, which would result in flow losses, and numerous transitions between the housing parts, which would lead to heavy leakage losses. In addition, short flow paths from the closure housing part to the directly axially adjoining retarder are also possible, so that short filling times are obtained and the retarder will in case of need be ready for braking within a short time.

The closure housing part generally does not need any additional axial space, since the axial region of a subsidiary power output, which usually has to be provided, can also be used for this purpose.

The development of the invention according to claim 4 permits inexpensive production of the closure housing part.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example, one embodiment thereof, and in which: Figure 1 is a section, taken parallel to the axis, of a change-under-load gear transmission; Figure 2 a diagram of the pressure medium circuit for the change-under-load gear transmission of Fig. 1; and Figure 3 shows a closure housing part of the change-under-load gear transmission in a section at right-angles to the axis, showing a pressure medium pump and control valves of the pressure medium circuit.

The change-under-load gear transmission shown in Figure 1 consists of a changeunder-load change-speed gear unit 50 having an input shaft 51 and an output shaft 52, a hydrodynamic converter 17 disposed upstream of the change-speed gear unit, and a retarder 25 whose rotor and also the turbine wheel T of the converter 17 are connected to the input shaft 51 of the change-speed gear unit 50. A gear 53, by which an enginedependent change-under-load subsidiary output 54 is driven by way of a train of gears 55 and 56, is connected to the pump wheel P of the converter. The drive gear 57 of a pressure medium pump 12 for supplying pressure medium to the change-underload gear transmission is also driven by means of the gear 53.

The housing 58 consists of a first housing portion 58a which contains the change-speed gear unit 50 and the retarder 25, and a second housing portion 58b for the converter 17, this portion, unlike the first portion of the housing, having to remain dry.

The two housing portions 58a and 58b are separated from one another in a pressure medium-tight manner by a closure housing part 59 in the axial region of which the gear train 53, 55, 56 and the pressure medium pump are disposed. The retarder 25 is disposed directly next to the closure housing part 59, so that the stator blade wheel 25a of the retarder directly adjoins the closure housing part 59. In addition to the pressure medium pump 12 the closure housing part contains (see Fig. 3) a main pressure valve 14, a converter counter-pressure valve 19, a lubrication pressure valve 60, a cooler change-over valve 30, and numerous pressure medium ducts between the aforesaid valves, the associated pressure medium codsuming elements, and the pressure medium pump. The closure housing part is in the form of a pressure diecasting, while the pressure medium ducts are predominantly formed in the casting process.

The hydraulic function of the valves mentioned will be explained below with reference to the diagram of the pressure medium circuit shown in Figure 2.

From the bottom 10 of the first housing portion the pressure medium pump 12 delivers pressure medium through a filter 11 into a main pressure pipe 13 in which a constant pressure is set by a main pressure valve 14. From the main pressure pipe a pressure pipe 15 leads to the shift valves (not shown) of the shift clutches of the change-under-load gear. The excess flow medium which flows off from the main pressure valve 14, and which is not required for closing the clutches, is fed to the converter 17 through a feed pipe 16. A converter pressure limiting valve 18 limits the pressure which is possible in the feed pipe 16 to a value which is slightly higher than the pressure occurring in normal operation, which it does by opening the feed pipe 16 to the outlet when this pressure is exceeded. A converter counter-pressure valve 19 controls the pressure prevailing at the output of the converter 17 in the converter outlet pipe 20 to a value suitable for operation of the converter, and thus at the same time controls the pressure in the feed pipe 16. The flow medium flowing off from the converter counter-pressure valve 19 into a pipe 21 should under normal pulling conditions (normal operation without retarder) flour through a heat exchanger 22 and be fed via a lubrication pressure pipe 23, in wheb a lubrication pressure valve 60 sets a constant pressure, to lubrication points 24 in the transmission.

The retarder 25 is also fed from the abovedescribed supply circuit. From the feed pipe 16, upstream of the converter 17, a pressure pipe 26 leads to a control valve 27. The retarder is filled and emptied by the control valve 27 in conjunction with the change-over valve 30.

For filling purposes the pressure medium flows from the control valve 27 via the pipe portions 29a, 29b to the change-over valve 30 and from the latter via the pipe 28 to the retarder. The pipe 28 leads into the retarder in the radially inner region of the toroidal working chamber. On the outer diameter of the retarder working chamber, where the pressure medium during operation of the retarder has a higher pressure than that at the inner diameter, a retarder return pipe 29 is provided, which leads to the pipe portions 29a and 29b and during braking operation supplies the pressure medium via the change-over valve 30 to the heat exchanger 22, and for emptying purposes feeds it via the pipe portion 29a at the valve 27 to the sump or reservoir. The change-over valve 30 is a control valve in which one portion corresponds to pulling operation and the other to braking operation. The position assumed by the change-over valve 30 in the pressureless state (as shown in the drawing) is associated with braking operation.

The change-over valve 30 controls the connection pipes 31 and 32 of the heat exchanger 22, the pipe 21 coming from the converter, the lubrication pressure pipe 23, the pipe 28 leading to the retarder, and the return pipe 29 in such a manner that in the position of the valve which is associated with pulling operation the pipe 28 is closed, the connection pipe 32 of the heat exchanger is connected to the lubrication pressure pipe 23 and the pipe 21 coming from the converter is connected to the connection pipe 31 of the heat exchanger, while the return pipe 29 of the retarder is closed.

In the position of the change-over valve 30 which corresponds to braking operation, the pipe 28 leading to the retarder is connected to the connection pipe 32 of the heat exchanger, the connection pipe 31 of the heat exchanger to the return pipe 29, and the pipe 21 coming from the converter to the lubrication pressure pipe 23.

In this manner the change-over valve when in its position associated with pulling operation passes the flow medium flowing off from the hydrodynamic unit 17 into the heat exchanger 22 and from the latter to the lubrication system, while the inlet 28 and uutlet 29 of the retarder are closed; in its position corresponding to braking operation the change-over valve passes only the flow medium flowing off from the retarder 25 into the heat exchanger 22 and, in a closed circuit, back to the retarder, while the flow medium flowing off from the converter bypasses the heat exchanger and is fed direct to the lubrication system 24.

The change-over valve 30 is changed over via the pipe 35 by a control pressure which is produced by the control valve 27 and which acts against a spring. In pulling operation (i.e. normal operation without retarder) the control valve 27 is in the position shown in the drawing. On the other hand, in consequence of the control pressure acting in the pipe 35 the change-over valve has assumed the other position, i.e. the position not shown in the drawing Thus the retarder connection pipes 28 and 29 are closed, while the flow medium flowing off from the converter is passed by way of the pipe 21, change-over valve 30, pipe 31, heat exchanger 22, pipe 32, and once more the change-over valve 30 to the lubrication pressure pipe 23 and the lubrication system 24.

On operation of the main brake of the vehicle the change-over valve 30 is switched over the "retarder operation" position. By means of the change-over valve 30 a by-pass circuit is freed between the retarder and the heat exchanger by way of the connecting pipes 31 and 32 and the pipes 28 and 29, this circuit being maintained by the retarder, which acts as a pump, and circulates the flow medium rapidly because of its relatively large cross-sections.

The closure housing part 59 shown in Figure 3 contains the pressure medium pump 12, which is axially offset in relation to the axis of the transmission, and which by way of a suction pipe 61 sucks pressure medium out of the housing through a filter 11 (not shown in Figure 3) and delivers it into the main pressure pipe 13. Directly next to the pressure outlet 62 of the pump, which outlet is connected to the main pressure pipe 13, is disposed the main pressure valve 14 whose control piston 63 adjusts a constant pressure in the main pressure pipe 13 through the action of the force of the spring 64, by opening a flow cross-section to the converter feed pipe 16. While the main pressure pipe 13 leads by way of a pressure duct 15 to the shift unit in the bottom part of the transmission housing, in which the control valves associated with the shift clutches are disposed, the pressure medium overflowing at the main pressure valve is passed to the converter by the shortest route by way of the pipe 16 and the opening 65, which leads through a hollow shaft (flanged on to the closure housing part) for the guide wheel T of the converter. By way of the hollow shaft of the guide wheel the pressure medium coming from the converter is passed back through the opening 66 into the closure housing part, in order to be able to be fed by the shortest route to the heat exchanger by way of the converter counter-pressure valve 19 and the pipe 21 in the closure housing part to the cooler change-over valve 30 lying axially parallel thereto and the pipe 31. The cooler changeover valve 30 is disposed on that side of the closure housing part on which connections 31, 32 to the heat exchanger and for return from the heat exchanger respectively are provided on the housing, so that here again the shortest possible path from the valve 30 to the heat exchanger is obtained.

During the braking operation of the retarder, the cooler change-over valve 30 changes over and the pressure medium is passed from the cooler change-over valve by way of a pipe 28 to the retarder, and flows through the closure housing part in the axial direction on the shortest possible route from the cooler change-over valve 30 through an opening 67 and by way of the retarder stator 25a, which directly adjoins the closure housing part, into the working chamber of the retarder 25 and from there back via an opening 68 and a pipe 29 to the cooler change-over valve, in order to be passed on the shortest route via the pipes 31 and 32 through the heat exchanger.

Axially parallel to the cooler change-over valve and-in this case-- coaxially with the converter counter-pressure valve 19 there is disposed in the closure housing part the lubrication pressure valve 60, by which the pressure medium is passed through the pipe 23 to the lubrication points of the transmission and excess pressure medium is returned through the vent E into the housing.

The retarder regulating valve 27 is disposed outside the closure housing part, because this control valve is operated with compressesl-air and a compressed air connection would unnecessarily complicate the closure housing part. Since the retarder regulating valve is already in communication by way of the pipe 26 with the portion 16 of the supply circuit which lies upstream of the converter, the converter pressure limiting valve 18 is also accommodated there, although it could also be disposed in the closure housing part.

In the change-under-load gear transmission with subsidiary output which is illustrated in the drawings the intermediate gears are mounted in the closure housing part and in a cover plate which is associated therewith on the converter side and which also covers the open ducts cast in the closure housing part. These ducts distribute the oil to the various valves. On the gear unit side the open ducts cast therein are covered by the stator of the retarder.

The unit thus formed, consisting of the closure housing part with cover plate and stator, contains the entire oil supply system and can be mounted as a complete unit.

The most important valves are accessible from the transmission housing without dismantling the closure housing parts.

WHAT WE CLAIM IS: 1. A change-under-load gear transmission of the kind hereinbefore set forth, wherein the retarder has its stator directly adjoining the closure housing part in which there are disposed a counter-pressure valve for the hydrodynamic unit, a lubrication pressure valve and other valves for controlling the pressure medium flows of the hydrodynamic unit and retarder.

2. A transmission as claimed in claim 1, wherein inside the closure housing part there is also disposed a converter pressure limiting valve.

3. A transmission as claimed in claim 1 or 2, wherein a cooler change-over valve which has two change-over positions and which in one of these positions establishes a self-contained flow circuit between the retarder and a heat exchanger, which circuit is maintained by the pump action of the retarder, is disposed inside the closure housing part in such a manner that the outlet and inlet apertures of the retarder and the connections leading to the outside to the heat exchanger and also the cooler changeover valve are disposed in the immediate proximity of one another.

4. A transbission as claimed in any of claims 1 to 3, wherein the closure housing part is in the form of a pressure diecasting and the pressure medium ducts leading to the valves are predominantly formed in the casting process.

5. A change-under-load gear transmission, substantially as herein described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. for the guide wheel T of the converter. By way of the hollow shaft of the guide wheel the pressure medium coming from the converter is passed back through the opening 66 into the closure housing part, in order to be able to be fed by the shortest route to the heat exchanger by way of the converter counter-pressure valve 19 and the pipe 21 in the closure housing part to the cooler change-over valve 30 lying axially parallel thereto and the pipe 31. The cooler changeover valve 30 is disposed on that side of the closure housing part on which connections 31, 32 to the heat exchanger and for return from the heat exchanger respectively are provided on the housing, so that here again the shortest possible path from the valve 30 to the heat exchanger is obtained. During the braking operation of the retarder, the cooler change-over valve 30 changes over and the pressure medium is passed from the cooler change-over valve by way of a pipe 28 to the retarder, and flows through the closure housing part in the axial direction on the shortest possible route from the cooler change-over valve 30 through an opening 67 and by way of the retarder stator 25a, which directly adjoins the closure housing part, into the working chamber of the retarder 25 and from there back via an opening 68 and a pipe 29 to the cooler change-over valve, in order to be passed on the shortest route via the pipes 31 and 32 through the heat exchanger. Axially parallel to the cooler change-over valve and-in this case-- coaxially with the converter counter-pressure valve 19 there is disposed in the closure housing part the lubrication pressure valve 60, by which the pressure medium is passed through the pipe 23 to the lubrication points of the transmission and excess pressure medium is returned through the vent E into the housing. The retarder regulating valve 27 is disposed outside the closure housing part, because this control valve is operated with compressesl-air and a compressed air connection would unnecessarily complicate the closure housing part. Since the retarder regulating valve is already in communication by way of the pipe 26 with the portion 16 of the supply circuit which lies upstream of the converter, the converter pressure limiting valve 18 is also accommodated there, although it could also be disposed in the closure housing part. In the change-under-load gear transmission with subsidiary output which is illustrated in the drawings the intermediate gears are mounted in the closure housing part and in a cover plate which is associated therewith on the converter side and which also covers the open ducts cast in the closure housing part. These ducts distribute the oil to the various valves. On the gear unit side the open ducts cast therein are covered by the stator of the retarder. The unit thus formed, consisting of the closure housing part with cover plate and stator, contains the entire oil supply system and can be mounted as a complete unit. The most important valves are accessible from the transmission housing without dismantling the closure housing parts. WHAT WE CLAIM IS:

1. A change-under-load gear transmission of the kind hereinbefore set forth, wherein the retarder has its stator directly adjoining the closure housing part in which there are disposed a counter-pressure valve for the hydrodynamic unit, a lubrication pressure valve and other valves for controlling the pressure medium flows of the hydrodynamic unit and retarder.

2. A transmission as claimed in claim 1, wherein inside the closure housing part there is also disposed a converter pressure limiting valve.

3. A transmission as claimed in claim 1 or 2, wherein a cooler change-over valve which has two change-over positions and which in one of these positions establishes a self-contained flow circuit between the retarder and a heat exchanger, which circuit is maintained by the pump action of the retarder, is disposed inside the closure housing part in such a manner that the outlet and inlet apertures of the retarder and the connections leading to the outside to the heat exchanger and also the cooler changeover valve are disposed in the immediate proximity of one another.

4. A transbission as claimed in any of claims 1 to 3, wherein the closure housing part is in the form of a pressure diecasting and the pressure medium ducts leading to the valves are predominantly formed in the casting process.

5. A change-under-load gear transmission, substantially as herein described with reference to and as shown in the accompanying drawings.