Drive device

The invention concerns a drive device (7) with variable transmission ratio for driving an auxiliary aggregate of a motor vehicle. A belt pulley (11) of the drive device (7) has a chamber (38) connected to a reservoir (30) of a hydraulic medium. The centrifugal action of the hydraulic medium contained in the chamber (38) is used to change the speed of the driven shaft (13). By applying a supporting pressure to the chamber (38), it is possible additionally to vary the output speed of the drive device (7).

The invention concerns a drive device for transmitting torque between a 
drive shaft having a first belt pulley and a driven shaft having a second 
belt pulley. The first belt pulley has an axially fixed flange non-rotably 
connected with the drive shaft and a flange axially movable under the 
action of a pre-load apparatus. The second belt pulley is composed of an 
axially fixed flange non-rotably connected with the drive shaft and an 
axially movable flange, the axially movable flange forming, with a flange 
of the driven shaft, a chamber for carrying a hydraulic medium. 
A drive device constructed as described above is especially used in the 
driving of auxiliary aggregates in motor vehicles. Such a device can here 
be, for instance, a generator, an air-conditioning compressor, or an 
air-charge compressor. In the driving of auxiliary aggregates the problem 
of reaching a sufficiently high speed generally arises, even at low engine 
speeds; on the other hand, said speeds should not be too high in the upper 
range of the engine speeds. This requirement can be met by using a drive 
device having a non-linear characteristic line. By a characteristic line 
it is here to be understood the ratio of the speeds of the drive and of 
the driven shaft of the drive device. The use of centrifugal force to 
change the characteristic line for the controlled drive of an auxiliary 
aggregate has been disclosed (DE 32 42 448 A1). Even though an adaptation, 
in the sense explained, can be obtained with such regulating forces, the 
reproducibility of the speed ratios of the driven to the driven shaft of 
the drive device is subject to great divergences. Said circumstance also 
exists mainly with the use of a plate or coil spring. Small fluctuations 
of the controlling and restoring forces resulting from differing friction 
and leverage ratios can already produce great deviations from the desired 
speeds of the driven shaft. 
To adjust hydraulically the position of the flange of the belt pulleys has 
also been disclosed (DE 21 18 083 A1, DE 25 60 653 C2). In order that the 
pressures acting upon the belt pulleys not be tampered with by centrifugal 
force depending on the speed, special precautions have been taken to 
compensate the effect of the centrifugal force upon the hydraulic medium. 
In the construction according to DE 38 30 165 Al, the position of the fixed 
and axially movable belt pulleys, with respect to each other, has been 
determined, on one hand, by a pre-load apparatus and, on the other, by an 
apparatus acting in accordance with centrifugal force. The apparatus that 
acts in accordance with centrifugal force consists of small elements such 
as powdered steel, copper, etc. Said apparatus takes care that the force 
of the pre-load apparatus be reduced as the speeds increase. In other 
words, the distance from each other assumed by both belt pulleys is 
accordingly enlarged again as the speeds increase, that is, the belt 
pulley is opened. The consequence of this is a reduction of the speed of 
the driven shaft. 
Based on the arrangement of DE 25 60 653 C2, the problem to be solved by 
this invention is to improve a drive device, especially for the driving of 
auxiliary aggregates of a motor vehicle, in the sense that the speed 
ratios to be adjusted be reproducible with sufficient exactness. The drive 
device according to the invention must be specially distinguished by a 
small hysteresis. Adding to the stated problem, the speeds of the drive 
device must be precisely controllable within wide limits. 
The invention solves the stated problem by the fact that the chamber is 
connected to a reservoir of the hydraulic medium and the centrifugal 
action of the hydraulic medium contained in the chamber is used for 
increasing the speed of the driven shaft. While in the devices of the 
prior art, the effect of the centrifugal action upon the adjustment of the 
belt pulleys was regarded as an interference, the solution according to 
the invention makes use of the knowledge that the rotating portion of the 
hydraulic medium contained in the chamber builds up a pressure which 
exponentially increases with the radial distance from the axis of rotation 
and which--on account of this physical mathematical interrelationship--is 
especially suited to control very precisely the position of the belt 
pulleys with respect to each other. Practical tests have shown that the 
speed ratios are outstandingly reproducible. In the drive device according 
to the invention, three possible operation ranges basically result: 
1. Below a ceiling speed a rigid speed ratio with speed-increasing ratio 
exists. The force of the pre-load apparatus of the first belt pulley 
outbalances the centrifugal force. 
2. If a first ceiling speed is exceeded, the action of the centrifugal 
force out-balances the force of the pre-load apparatus of the first belt 
pulley. From here starts the governed range of the driven shaft (secondary 
speed). 
3. The regulating distance of the second belt pulley is used up so that the 
axially movable belt pulley assumes its greatest distance from the axially 
fixed belt pulley. There again exists a fixed speed ratio with a speed 
reducing ratio. 
To make use of the centrifugal action of the hydraulic medium contained in 
the chamber for increasing the speed of the driven shaft, it suffices to 
connect pressurelessly the chamber with the reservoir. 
According to an advantageous feature of the invention, the governed range 
of the drive device can be enlarged in a simple manner by additionally 
applying supporting pressure to the chamber. With the added supporting 
pressure the drive device can be moved at high speeds along a 
characteristic line. Said characteristic line extends with almost the same 
inclination as the characteristic line in which the centrifugal action is 
exclusively used. When driving an auxiliary aggregate of a motor vehicle, 
the supporting pressure can be diverted without special expense from the 
feed pressure of a lubricant pump or it can correspond to said pressure. 
The chamber for carrying the hydraulic medium can be formed in a 
structurally simple manner by slidingly and tightly passing a piston of 
the axially movable flange into an internal cylinder of the flange of the 
driven shaft. This type of construction makes possible also a simple 
adaptation of the governing characteristic of the drive device by a 
diameter of different size of the piston. By adequately selecting the 
diameter, the hydraulic medium contained in the chamber can easily be 
quantitatively varied. 
In a preferred embodiment of the drive device of the invention, 
semicircular slots, diametrically opposite to each other by their axially 
oriented openings, have been provided in the axially movable flange and in 
the flange of the driven shaft. The openings form separate hollow bodies 
in which cylindrical bodies are inserted to produce a non-rotable 
connection between the axially movable flange and the flange of the driven 
shaft. This feature per se has been disclosed in DE 12 84 779 B2. 
It is advantageous to design the driven shaft as a hollow shaft. The hollow 
shaft can be non-rotably connected or become connected with an output 
shaft directly or indirectly via a shiftable clutch. The output shaft can 
be the drive shaft of the auxiliary aggregate such as an air compressor. 
The shiftable clutch is preferably constructed as an electromagnetically 
actuatable clutch. 
In a simple and easy to assemble construction of the chamber, a bottom is 
provided which abuts against the hollow shaft by an outer seal. Said 
bottom can be provided with a central bore through which the output shaft 
passes. Together with the outer seal, an inner seal is then to be 
provided. In this solution, the feed or discharge pipe passes through the 
output shaft into the chamber. 
In order to fix the axially movable belt pulley exactly in its most open 
position of the pulley, the axially movable flange abuts in its end 
position against a stop of the flange of the driven shaft. 
The feed or discharge pipe for the hydraulic medium can also be situated 
concentrically with respect to the flange of the driven shaft. In this 
case, the pipe is tightly passed through a bore of the flange of the 
driven shaft in such a manner that the flange of the driven shaft can 
rotate about the pipe. 
In connection with the drive of an air compressor, it is advantageous to 
regulate the supporting pressure according to the performance 
characteristic of the internal combustion engine. This is done, in 
particular, by monitoring the engine speed dependent on the performance 
characteristic and/or the load pressure of the internal combustion engine 
and varying the transmission ratio of the drive device corresponding to 
said speed and/or said pressure. For this purpose, together with the 
change of the centrifugal action of the hydraulic medium, the supporting 
pressure is varied, connected or disconnected until a desired engine speed 
and/or loading pressure is measured. 
It is also advantageous to design the flange of the driven shaft as drive 
pulley for another auxiliary aggregate. This can be, for instance, an 
air-conditioning compressor.

The diagrammatic representation of FIG. 1 shows a drive device for 
operating an auxiliary aggregate in combination with an internal 
combustion engine of a motor vehicle. 
A suction pipe 1 leads to an air distributor 2 of an internal combustion 
engine 3. Said internal combustion engine is an otto engine. But this 
arrangement, according to the invention, can in principle be also embodied 
in a diesel engine. An exhaust gas collector 4 is coordinated with the 
internal combustion engine 3. 
An output shaft 5 is operatively connected with a transmission, itself not 
show. On the opposite side of the internal combustion engine is a drive 
shaft 6 of a drive device 7. Also derived from this shaft is the drive for 
a lubricant pump 8. When necessary, for reasons of space, the drive device 
7 and the lubricant pump 8 can also be driven via an intermediate shaft. 
A first belt pulley 9 of the drive device 7 drives a second belt pulley 11 
via a belt 10. 
A non-rotatable connection between the second belt pulley 11 and a driven 
shaft 13 with an output shaft 14 is produced by actuating an 
electromagnetic clutch 12. The output shaft 14 drives a high-driver 
planetary transmission 15. To increase the speed, a suitable transmission 
of a different type of construction can be used instead of a planetary 
transmission. A sun-wheel shaft 16 serves to drive a centrifugal 
compressor 17 which is within the suction pipe 1. 
During idling speed and at low engine speeds, the second belt pulley 11 
rotates slower than the first belt pulley 9. At maximum speed of the 
internal combustion engine 3, the system reaches a transmission ratio 
where the speed of the output shaft 14 is, as a rule, lower than the speed 
of the internal combustion engine. Since the output speed of the second 
belt pulley 11 for operating the centrifugal compressor 17 would not be 
sufficient, the high-driver planetary transmission has a high speed 
increasing ratio. 
In the suction pipe 1 is an air meter 18. A throttle valve 20 is actuatable 
from its closed position up to a maximum opening angle. 
The first belt pulley 9 of the drive shaft 6 consists of an axially fixed 
flange 22 non-rotably connected with the drive shaft 6 and a flange 24 
axially movable under the action of a pre-load apparatus such as a 
compression spring. 
The construction of the second belt pulley is explained herebelow with 
reference to FIG. 2. 
The second belt pulley 11 is composed of an axially fixed flange 25 and an 
axially movable flange 26. The axially fixed flange 25 is non-rotably 
connected with the driven shaft 13 by suitable connecting means such as 
screws 27. In the shown embodiment, the driven shaft 13 is designed as 
hollow shaft and rotatably situated on the output shaft 14 via two 
bearings 28. The clutch 12 is designed as electromagnetically actuatable 
clutch. When the clutch 12 is engaged, a non-rotable connection is 
produced between the axially fixed flange 25 and the output shaft 14. As 
already mentioned, the output shaft 14 drives the high-driver planetary 
transmission 15 and the latter, in turn, drives the centrifugal compressor 
17. 
The outline of the centrifugal compressor 17 is shown diagrammatically in 
FIG. 2. The interior 28 of a housing 29 is provided as reservoir 30 for a 
hydraulic medium. The reservoir can easily be situated also outside the 
housing 29. 
The axially movable flange 26 is opposite the axially fixed flange 25. 
The driven shaft 13 has a flange 31 which is non-rotably connected by 
screwed connections 32 with the driven shaft 13. Other suitable 
non-rotable connections can be chosen instead of the screw connections. 
The flange 31 of the driven shaft 13 has an axially oriented edge 33 which 
overlaps, in the manner of a cover, a piston 34 of the axially movable 
flange. The piston 34 is slidingly passed into an internal cylinder 35 of 
the flange 31. A seal 36 assumes the sealing of the piston 34 with respect 
to the internal cylinder 35. 
It is advantageous, as shown in the drawings, to design the flange 31 as 
drive pulley for another auxiliary aggregate such as an air-condition 
compressor. 
The axially movable flange 26 rests on the driven shaft 13 via sliding and 
sealing rings 37. 
As mentioned already, the flange 26 is axially displaceable with respect to 
the driven shaft 13 and has a non-rotable connection to the driven shaft 
13 in order to transmit the proportionate torque which results from the 
abutment of the belt 10 on said flange 26. The axial displacement and the 
non-rotable connection of the flange 26 are obtained by constructional 
steps explained herebelow: 
The flange 31 is a component part of a chamber 38 which is provided to 
carry hydraulic medium and, for said purpose, is connected with a 
reservoir 30 via a feed and discharge pipe 39. An annular bottom 40, which 
is sealed with respect to the driven shaft 13 and the output shaft 14, 
forms the boundary of the chamber 38 which is opposite the flange 31. The 
hydraulic medium comes into contact with the operative flange of the 
piston 34 of the flange 26 via a radially orient duct 41. 
The non-rotable connection between the flange 26 and the flange 31 of the 
driven shaft 13 results via cylindrical bodies 44, two of which are 
reproduced in the drawings. The cylindrical bodies 44 are inserted in 
semicircular grooves 45 of the flange 26 and semicircular grooves 46 of 
the flange 31. The semicircular grooves 45 and 46 face each other by their 
axially oriented openings so that the cylindrical bodies 44 can be easily 
accommodated. For production reasons, the semicircular grooves 46 of the 
flange 31 are situated in a separate swivel member 47 which is inserted 
when the flange 31 is connected with the driven shaft 13. It can be easily 
seen from the drawings, in relation to the foregoing explanation, that the 
flange 26 can perform an axial displacement movement with respect to the 
driven shaft 13. There exists a non-rotable connection of the flange 26 
with the driven shaft 13. The cylindrical bodies 44 serve to transmit the 
torque. 
The construction of the second belt pulley illustrated in FIG. 3 
corresponds fundamentally to the belt pulley of FIG. 2. But differing 
therefrom, the feed and discharge pipe 39 is situated in a separate 
connecting piece 48. Said connecting piece 48 is stationary placed and 
concentrically traverses the flange 31 so that the latter can rotate about 
the connecting piece 48. The illustration of FIG. 3 shows for the rest the 
belt pulley 11 in a position in which the flanges 25 and 26 assume their 
smallest distance from each other. In this position the piston 34 is 
farthest removed from the flange 31. 
The second belt pulley 11 is adjusted as follows: 
Since the internal cylinder unit 34-36 of the piston rotates with the 
driven shaft 13, the hydraulic medium contained in the chamber 38 is 
exposed to a centrifugal action. The rotating portion of hydraulic medium 
builds up a pressure which exponentially increases with the radial 
distance from the axis of rotation (longitudinal axis of the output shaft 
14). The pressure built up by the centrifugal action exerts a contact 
pressure upon the end face of the piston 34 of the axially movable flange 
26. Said contact pressure is speed dependent and changes with the second 
power of the speed. Below a certain ceiling speed, the pre-load force of 
the pre-load apparatus 23 of the first belt pulley 9 prevails. A fixed 
speed ratio exists between the first and second belt pulleys 9 and 11, 
specifically with a speed increasing ratio. If the ceiling speed of the 
driven shaft 13 is exceeded, the centrifugal action becomes increasingly 
noticeable. The speed ration between the first and second belt pulleys 9 
and 11 is variable, as is to be deduced from the course of the 
characteristic line A in the illustration of FIG. 4. In said illustration 
are diagrammatically shown, over the engine speed, to the left the 
compressor speed and to the right the speed of the driven shaft 13. The 
course of the curve reproduces the governing characteristic which 
distinguishes itself mainly in that already in the range of low engine 
speeds there are relatively high speeds of the driven shaft 13. Said 
governing characteristic particularly meets the auxiliary aggregates to be 
driven of a motor vehicle. 
When the regulating distance of the axially movable flange 26 has been used 
up, that is, the flanges 25 and 26 have assumed their smallest distance 
from each other, there results again a fixed speed ratio between the first 
and second belt pulleys 9 and 11 with a reducing speed ratio. 
In FIG. 4 is plotted a characteristic line B which results when an 
additional supporting pressure is superposed on the contact pressure 
resulting from the centrifugal action. Said supporting pressure can be 
branched off, or correspond to, the lubricant pump 8 which is all the same 
present. A pipe leading away from the lubricant pump 8 (see FIG. 1) is 
connected by a fitting 49 to the housing 29 and a connecting pipe not 
shown is connected to the chamber 38 or the feed and discharge pipe 39. 
In FIG. 4 the dashed line reproduces a linear speed course between the 
first and second belt pulleys 9 and 11 which results when the belt pulley 
is invariably closed. By virtue of the design according to the invention 
of the drive device 7, it is possible to adjust any desired speed ratio 
lying in the surface enclosed between the dashed line and the curve A or 
the curve B. This transmission ratio (curve A) of the drive device 7 can 
be adjusted according to the performance characteristic of the engine. For 
this purpose, the value of the supporting pressure can be varied when 
there is a deviation of a given desired value of the load pressure. 
The use of the drive device 7 according to the invention is not limited to 
the driving of an air-charge compressor. The device can rather be used 
wherever it generally matters advantageously to use the explained 
governing characteristic deviating from linear ratios. This is 
particularly the case when auxiliary aggregates of a motor vehicle are 
driven. 
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Reference numerals 
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1 suction pipe 
2 air distributor 
3 internal combustion engine 
4 exhaust collector 
5 output shaft 
6 drive shaft 
7 drive device 
8 lubricant pump 
9 first belt pulley 
10 belts 
11 second belt pulley 
12 clutch 
13 driven shaft 
14 output shaft 
15 high-driver planetary transmission 
16 sun-wheel shaft 
17 centrifugal compressor 
18 air meter 
19 -- 
20 throttle valve 
21 air filter 
22 flange 
23 pre-load apparatus 
24 flange 
25 flange 
26 flange 
27 screws 
28 interior space 
29 housing 
30 reservoir 
31 flange 
32 screws 
33 edge 
34 piston 
35 internal cylinder 
36 seal ring 
37 seal and sliding ring 
38 chamber 
39 feed and discharge pipe 
40 bottom 
41 duct 
42 -- 
43 -- 
44 cylinder body 
45 semicircular grooves 
46 semicircular grooves 
47 swivel 
48 connecting piece 
49 fitting 
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