Drive arrangement for a hybrid vehicle

A drive apparatus for a hybrid electric/combustion powered vehicle having an internal combustion engine and a gear-shifting transmission unit. The drive apparatus includes a rotatable crank shaft operatively connectable to the internal combustion engine, and a rotatable transmission shaft operatively connectable to the gear-shifting transmission unit. The drive apparatus further comprises a movable annular rotor disposed annularly about the transmission shaft, the rotor including a permanent magnet for generating a magnetic field and an attachment mechanism for attaching the rotor to the transmission shaft so that torque can be transmitted between the rotor and the transmission shaft. The stationary annular stator is attachable to at least one of the internal combustion engine and the gear-shifting transmission unit and is disposed concentrically about and proximate the rotor in an electromagnetically interactive relation. The stator includes a conductive winding for electromagnetically interacting with the magnetic field of the rotor, the stator defining a continuous axial recess annularly therewithin. The drive apparatus includes only one clutch disposed at least partially within the continuous axial recess of the stator, the clutch including 2 coupling mechanism for selectively and frictionally coupling the crank shaft to the transmission shaft for torque transmission therebetween so that the clutch is switchable between an engaged position in which torque can be transmitted between the crankshaft and the transmission shaft and a disengaged position in which torque transmission between the crankshaft and the transmission shaft can be discontinued.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to a drive arrangement for a hybrid vehicle and, 
in particular, to a drive arrangement having only one switchable clutch 
for engaging and disengaging the crankshaft of an internal combustion 
engine. 
2. Description of the Prior Art 
A hybrid drive for a motor vehicle driven by an internal combustion engine 
and an electric motor which is constructed as an asynchronous machine is 
known from DE 37 37 192 A1. The rotor of the electric motor can be 
connected with the crankshaft of the internal combustion engine through a 
first disengaging clutch (dry clutch) and with the input shaft of the 
transmission through a second disengaging clutch. The internal combustion 
engine does not possess its own flywheel. Instead, the rotor of the 
electric motor can be used as a flywheel mass for the internal combustion 
engine when the first clutch is closed. The rotor of the electric motor 
which is arranged inside the stator has a hub body disposed at the side 
facing the transmission and is supported on the transmission input shaft. 
The hub body construction possesses considerable mass and accordingly 
makes up a large part of the flywheel mass. The hub body forms an abutment 
for the clutch plate of the second disengaging clutch which produces the 
frictional engagement between the rotor and the transmission input shaft. 
The first disengaging clutch is arranged at the end of the electric motor 
facing the internal combustion engine. Its clutch plate is connected with 
the crankshaft so as to be fixed with respect to rotation relative 
thereto. In order to produce the frictional connection in the engaged 
state, it has its own annular abutment which is likewise constructed so as 
to have considerable mass and is rigidly connected with the rotor. Thus, 
both disengaging clutches are arranged one beside the other on the same 
side of the hub body. The electric motor works as a generator when the 
hybrid vehicle is driven exclusively by the internal combustion engine 
(i.e., when both disengaging clutches are closed). The output of the 
electric motor supplied to the vehicle battery and other electrical 
components amounts to only a relatively small fraction of the output of 
the internal combustion engine, e.g., 7 kW. Thus, drive outputs are 
correspondingly modest during exclusive electric motor operation (i.e., 
when the first disengaging clutch between the rotor and crankshaft is open 
and the second disengaging clutch is closed). In this hybrid vehicle, the 
electric motor should also be able to take over the function of the 
starter for the internal combustion engine. However, because of the low 
output and relatively low torque of the electric motor, direct starting by 
the electric motor is not possible when the electric motor is at rest. 
Therefore, it is proposed that the electric motor be brought up to a 
relatively high speed first while the disengaging clutches are open so 
that considerable energy is already stored in the rotating flywheel mass 
of the rotor. Only at this point is the first disengaging clutch between 
the rotor and crankshaft engaged in a jolting or sudden manner so that the 
internal combustion engine can be revved up beyond the starting speed and 
can then continue to run by itself. In addition to drive operation by 
either electric motor alone or by internal combustion engine alone, both 
motors can also be used for a simultaneous drive operation when the two 
disengaging clutches are closed so that the electric machine is operated 
as an electric driving motor rather than as a generator. 
A disadvantage in this known drive arrangement consists in the need for two 
separate disengaging clutches with their accompanying actuating devices. 
This results not only in added construction (production costs), but also 
in a greater space requirement, particularly in the axial direction. 
SUMMARY OF THE INVENTION 
Therefore, the object of the present invention is to provide a simplified 
drive arrangement which is compact and which nevertheless provides the 
three different types of operation of a hybrid drive mentioned above 
(e.g., internal combustion engine operation, electric motor operation, or 
combined operation) and reliable starting of the internal combustion 
engine. 
The present invention is directed to a drive apparatus for a hybrid 
electric/combustion powered vehicle having an internal combustion engine 
and a gear-shifting transmission unit. The drive apparatus includes a 
rotatable crank shaft having an end operatively connectable to the 
internal combustion engine for torque transmission, and a rotatable 
transmission shaft axially spaced from the end of the crank shaft 
operatively connectable to the gear-shifting transmission unit. The drive 
apparatus further comprises a movable annular rotor disposed annularly 
about the transmission shaft, the rotor including magnetic means for 
generating a magnetic field and attaching means for attaching the rotor to 
the transmission shaft so that torque can be transmitted between the rotor 
and the transmission shaft. The stationary annular stator is attachable to 
at least one of the internal combustion engine and the gear-shifting 
transmission unit and is disposed concentrically about and proximate the 
rotor in an electromagnetically interactive relation. The stator includes 
electromagnetic means for electromagnetically interacting with the 
magnetic field of the rotor, the stator defining a continuous axial recess 
annularly therewithin. The drive apparatus also includes only one clutch 
disposed at least partially within the continuous axial recess of the 
stator, the clutch including coupling means for selectively and 
frictionally coupling the crank shaft to the transmission shaft for torque 
transmission therebetween so that the clutch is switchable between an 
engaged position in which torque can be transmitted between the crankshaft 
and the transmission shaft and a disengaged position in which torque 
transmission between the crankshaft and the transmission shaft can be 
discontinued. 
In an embodiment, the stator of the drive apparatus is disposed 
concentrically within the rotor. In another embodiment, the drive 
apparatus further comprises an electronic control unit for commutation of 
electrical current in the stator, and wherein the rotor magnetic means 
comprises a plurality of permanent magnets. In still another embodiment, 
the clutch of the drive apparatus is one of a single-plate dry clutch and 
a multiple-plate dry clutch. In yet another embodiment, the clutch 
connecting means includes at least one of a torsional vibration damping 
element and an overload protection device such as, for example, a safety 
clutch. 
In accordance with an aspect of the present invention, the rotor attaching 
means includes a torsional vibration damping element. In accordance with 
another aspect of the invention, the transmission shaft has a bore defined 
axially therewithin, and further including a pushrod guidedly received 
within the bore of the transmission shaft for switching said clutch 
between the engaged and disengaged positions. In accordance with still 
another aspect of the invention, the clutch coupling means includes a 
clutch release mechanism disposed between the crank shaft and the 
transmission shaft for switching the clutch between the engaged and 
disengaged positions, the clutch release mechanism being actuatable, for 
example, by one of hydraulic and electric mechanism. In accordance with 
yet another aspect of the invention, a diaphragm spring is operatively 
connected to the clutch for resiliently urging the clutch to its engaged 
position. In still yet another aspect of the invention, the electronic 
control unit includes means for automatically switching the clutch between 
its engaged and disengaged positions. 
According to a feature of the invention, the electronic control unit of the 
drive apparatus includes means for regulating the clutch so that the 
clutch can be substantially engaged without jerking motion and with low 
wear. According to another feature of the invention, the drive apparatus 
further includes a resolver system operatively connected to the electronic 
control unit for supplying at least one of angle and speed information of 
the rotor to the electronic control unit, and wherein the electronic 
control unit selectively varies electrical current in the stator so as to 
influence motion of the rotor for torsional vibration damping of the 
transmission shaft. According to still another feature of the invention, 
the transmission shaft is a gear-shifting transmission input shaft, and 
the electronic control unit selectively changes the rotor's speed for 
transmission synchronization during gear shifting. According to yet 
another feature of the invention, the drive apparatus further comprises 
means for detecting the gear-shifting transmission unit output speed. 
According to still yet another feature of the invention, the drive 
apparatus further comprises an accelerator pedal movable from one position 
to another and is operatively connected to the electronic control unit, 
wherein the electronic control unit detects a desired gear-shifting by 
receiving information that includes at least one of change of the 
accelerator pedal's position over time and change of the rotor's speed 
over time. 
The present invention proceeds from the drive arrangement known from E 37 
37 192 A1. In a particularly preferred embodiment, the electric machine is 
designed as an external-rotor machine, in particular as a synchronous 
machine with electronic communication and with a plurality of permanent 
magnets with alternating polarity (especially made of FeNdB or SmCo alloys 
or similar alloys with the highest possible magnetic field strength). This 
construction enables considerably higher torques so that the internal 
combustion engine can be started more reliably proceeding from the rest 
state of the electric machine. Its stator is connected in a stationary 
manner with the housing of the internal combustion engine and/or with the 
housing of the associated gearbox or transmission, while the rotor is 
coupled with the driven shaft of the drive unit (transmission input shaft) 
for transmitting torque (e.g., so as to be permanently fixed with respect 
to rotation thereto). In this connection, "fixed with respect to rotation" 
does not necessarily mean a rigid connection. Rather, a limited change in 
the relative angular displacement between the rotor and driven shaft such 
as that provided for example, by the installation of torsional dampers, is 
permissible. Devices for overload protection such as a safety clutch can 
also be provided. Another important feature of the invention consists in 
the use of only one individual switchable clutch (i.e., an engaging and 
disengaging clutch) which allows switching of the connection between the 
crankshaft of the internal combustion engine and the driven shaft of the 
drive arrangement. For example, the driven shaft can be part of an 
automatic gear unit or torque converter. However, it is preferably the 
input shaft of a shift transmission. In this respect, the invention offers 
the advantage that the drive arrangement can, in general be easily 
accommodated within the space provided by a conventional transmission 
housing, but will at least not substantially exceed this space. 
The invention will be explained more fully in the following with reference 
to exemplary embodiments shown in the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an axial longitudinal section of an embodiment of a drive 
arrangement of the invention. The drive arrangement is positioned between 
a crankshaft 3 of an internal combustion engine and a driven shaft 2 such 
as the input shaft of a shift transmission, not shown in more detail. The 
entire drive arrangement can be installed within the transmission housing 
22 as indicated by the dash-dot lines. A disengaging clutch 1 designed as 
a single-plate dry clutch produces a switchable torque-transmitting 
connection between the crankshaft 3 and the transmission or driven shaft 
2. For this purpose, the clutch part 15 is connected to the crankshaft 3 
in a stationary manner. The clutch plate 16 is connected with the 
transmission shaft 2 so as to be fixed with respect to rotation relative 
thereto through the hub body 19. However, this connection is not 
completely rigid since torsional dampers 10 are arranged in a known manner 
between the clutch hub 19 and the clutch plate 16. When the clutch 1 is 
not engaged, the diaphragm spring 13 presses a first pressure plate 17 
against a second pressure plate 17 which is connected with the clutch part 
15 in a stationary manner as an abutment. The frictional engagement for 
transmitting torque is effected in that the clutch plate 16 which is 
outfitted on both sides with friction linings is clamped between the two 
pressure plates 17. In order to cancel this frictional engagement, the 
release pushrod 12 which is guided through the driven shaft 2 is pushed 
toward the left so that the plate-shaped clutch release 11 and release 
bearing 18 act against the spring force of the diaphragm spring 13. The 
disengaging clutch 1 can be actuated in a purely mechanical manner, but is 
preferably designed to operate automatically (e.g., hydraulically, 
pneumatically or electromechanically). A suitably actuated clutch release 
is preferably arranged centrally between the internal combustion engine 
and the transmission. In order to transmit substantially greater torque, a 
two-plate dry clutch or other multiple-plate dry clutch can also be used 
as a disengaging clutch 1 instead of a single-plate dry clutch, as is 
shown in FIG. 2 (parts having the same function are designed with the same 
reference numbers as in FIG. 1). It is also conceivable to provide other 
types of clutch systems such as a magnetic-powder clutch to connect the 
crankshaft 3 and driven shaft 2, although a dry clutch is to be provided 
for purposes of shifting a shift transmission. 
The electric machine 4 has a rotor 8 as an external rotor which is 
preferably outfitted with permanent magnets of high field strength and a 
stator 5 disposed concentrically therein. The stator 5 of this electric 
machine 4 which is constructed as a synchronous machine, preferably with 
electronic commutation, and can be operated optionally as a motor or 
generator, is attached to the internal combustion engine and is formed of 
the stator windings 6 and stator laminations 7. The stator 5 has a 
continuous axial recess 9 which is substantially cylindrical and which 
extends to the vicinity of the stator windings 6. The disengaging clutch 1 
is arranged at least for the most part, but preferably completely, inside 
the space 9 enclosed by the annular stator 5 so that a short axial 
constructional length can be achieved. The crankshaft 3 can be made 
appreciably shorter than is depicted in the schematic views shown in FIGS. 
1 and 2 so that the clutch 1 can be displaced substantially farther toward 
the left and into the stator 5. This is not necessary in the present 
instance since the drive arrangement fits easily into the space provided 
by the (mass-produced) housing 22 of the shift transmission. The rotor 8 
which could also be constructed, e.g., as a short-circuited or 
squirrel-cage rotor, though less desirable, has a wheel body 21 which is, 
for example, diecast or made of deep-drawn sheet metal. The wheel body 21 
is connected to the driven shaft 2 so as to be fixed with respect to 
rotation relative thereto, preferably through torsional dampers 10 and a 
rotor hub 20. Thus the rotor 8 always rotates along with the driven shaft 
2 in a forced manner and thus can not be uncoupled. Angular displacements 
between the rotor 8 and the driven shaft 2 are possible with a narrow 
margin permitted by the optional torsional dampers 10. The electric 
connections to the stator windings 6 and an electronic control unit 30 (as 
shown in FIG. 3) with power electronics for commutation of current for the 
stator windings 6 are not shown. A resolver system 14 which supplies 
highly precise angle information and speed information which is derivable 
therefrom is preferably provided in order to supply the electronic control 
unit 30 at all times with information concerning the relative angular 
position between the permanent magnet poles of the rotor 8 and the magnet 
poles of the stator 5, which information is necessary for correctly 
controlling the electrical current with respect to phase during motor 
operation as well as during generator operation. The electronic control 
unit 30 is preferably so arranged that it varies the electric load or the 
generated torque of the electric machine 4 in a timely manner such that 
torque fluctuations at the driven shaft 2 are reduced by way of torsional 
vibration damping. In this case, the torsional dampers 10 can be omitted 
in part or entirely without sacrificing comfort to occupants of the 
vehicle. The electronic control unit 30 is preferably expanded in such a 
way that it initiates the actuation of the clutch so that the latter 
proceeds automatically. In so doing, the frictional engagement is to be 
produced sufficiently smoothly so that engagement of the clutch is free of 
jolts and induces minimal wear. Since the rotor 8 is in constant 
rotational connection with the transmission input shaft 2 of the shift 
transmission and represents a considerable flywheel mass (high WD.sup.2), 
it is preferable to arrange the electronic control unit 30 in such a way 
that it adjusts the required synchronizing speed of the rotor 8 by means 
of a suitable change in the speed of the electric machine 4 for changing 
gears. The transmission input shaft 2 is braked "electrically" (i.e., 
generator operation) in order to shift up the gear (higher gear) and is 
accelerated "electrically" (i.e., motor operation) in order to downshift 
(lower gear). v Since the electronic control unit 30 detects not only the 
previous gear but also the previous speed of the transmission input shaft 
2 (e.g., through the resolver system 14), it can determine the new 
reference speed of the transmission input shaft 2 for the actual speed of 
the hybrid vehicle with reference to the newly selected gear and can 
adjust it appropriately through the power electronics. In the absence of a 
separate device for detecting the gear selection (e.g., a sensor at the 
gearshift lever), the shifting direction can be detected by the electronic 
control unit 30 by means of the highly accurate detection of the change in 
rotor speed during the shifting process so that the acceleration or 
braking of the rotor 8 by means of the electric motor 4 actively supports 
the synchronizing process for relieving the synchronizing rings in the 
transmission. When changing gears and during the adjustment of the new 
rotor speed, the disengaging clutch 1 is, of course, open entirely or at 
least partially (i.e., dragging engagement). In order to carry out 
synchronization in a reliable manner also in the event of relatively sharp 
changes in the vehicle speed during the shifting process (e.g., shifting 
while climbing hills), additional means for detecting the rotational angle 
and speed can be provided which determine the actual speed of the driven 
shaft 2. Since a substantial portion of the flywheel mass (rotor) is 
uncoupled from the internal combustion engine during the shifting process, 
only the clutch housing which is connected in a stationary manner with the 
crankshaft 3 serves as flywheel mass. The electronic control unit 30 
therefore monitors the speed of the internal combustion engine and acts 
when appropriate (e.g., change in the amount of fuel injected or in the 
throttle valve angle) in order to prevent the speed from dropping below a 
defined value (e.g., idle speed). 
During exclusive electric motor operation, shifting is also carried out 
with support of the synchronizing process by an active change in the speed 
of the electric machine 4. In order to detect the gear shifting selection 
made by the operator in the absence of a sensor for detecting gearshift 
lever signals, the electronic control unit 30 can make use of the speed or 
the change in speed of the electric machine 4 and/or the change in the 
position of the accelerator pedal selected by the operator as input 
variables and can determine, e.g., on the basis of the value of the first 
or second derivative, whether or not a shifting process is to be 
initiated. This applies to electric operation as well as to internal 
combustion engine operation. 
The signal evaluation for the shifting processes is illustrated 
schematically in FIG. 3 by way of example. The electronic control unit 30 
receives actual information about the actuation of the accelerator pedal 
31, brake pedal 32, and gearshift lever 38, as well as speed information 
for the electric machine 33, internal combustion engine 34, and 
transmission input shaft 35 as input signals through suitable sensors. 
During internal combustion engine operation, evaluation of the signals 
leads to the following actions represented by block 36: 
a) detecting intended gear shifting; 
b) clutch opening; 
c) relieving transmission of torque by actively controlling the speed of 
the electric machine (if required); 
d) releasing gear; 
e) actively supporting the synchronizing process with the electric machine; 
f) engaging gear; 
g) proportioning engagement of clutch; and 
h) operating the internal combustion engine in accordance with signal from 
an accelerator pedal. 
During exclusive electric motor operation, the actions symbolized by block 
37 are carried out with the clutch constantly open: 
a) detecting intended gear shifting; 
b) relieving transmission of torque by actively controlling the speed of 
the electric machine; 
c) releasing gear; 
d) actively supporting the synchronizing process with the electric machine; 
e) engaging gear; and 
f) operating the electric machine in accordance with signal from an 
accelerator pedal. 
In a drive arrangement according to the present invention, the internal 
combustion engine can be started in various ways. For example, when the 
vehicle is at rest and the shift transmission is in the neutral position, 
the crankshaft 3, together with the transmission input shaft 2, can be 
accelerated rapidly to starting speed and the internal combustion can be 
fired with the disengaging clutch 1 closed due to the high engine torque 
which can be generated by the electric machine 4. For another example, the 
starting process can also be carried out in that the disengaging clutch 1 
is first opened and the hybrid vehicle is then accelerated exclusively by 
the electric motor 4 to a suitable minimum speed (e.g., 5-20 km/h). When 
this minimum speed is reached, the disengaging clutch 1 is closed in a 
proportional manner (e.g., automatically by means of the electronic 
control unit) so that the internal combustion engine is accelerated to 
starting speed. The electronic control unit 30 preferably ensures that the 
disengaging clutch 1 is entirely or partially opened again temporarily 
during the ignition process in order to damp the transition of the 
internal combustion engine from the driven phase to the driving phase. The 
clutch is then engaged again automatically in a proportioned manner so 
that the hybrid vehicle is driven by the internal combustion engine. The 
electric motor 4 can then resume the driving function and can even be 
switched to generator operation for the purpose of charging an accumulator 
and/or to supply electricity to other electrical components. However, 
electric motor drive operation can also be maintained for a limited time 
(e.g., when passing) if the desired drive output exceeds the output of the 
internal combustion engine (e.g., booster operation). Of course, the 
internal combustion engine can be started at any time during exclusive 
electric motor operation from the current speed of the vehicle by 
proceeding in accordance with the second example of the aforementioned 
starting process. To prevent unwanted hesitation of the vehicle, the 
electronic control unit can provide a temporary increase in the drive 
output of the electric motor 4. In every case, as was already explained, 
the electric machine 4 can be operated through the electronic control unit 
in such a way that torsional vibration damping is achieved at the driven 
shaft 2. The highly precise detection of the speed of the electric machine 
4 and its first and second derivatives can be utilized as a control 
variable for this purpose. 
When braking the hybrid vehicle, the electric machine 4 preferably operates 
as a generator on instructions from the electronic control unit 30 and 
produces a braking torque while supplying usable electrical energy in this 
way. In order to recover as much energy as possible, e.g., during a thrust 
operation phaser, the internal combustion engine can be uncoupled 
temporarily depending on the required braking torque (e.g., depending on 
the path/time-dependent actuation of a brake pedal: s, s', s" whereby s is 
the path, s' is the speed and s" is the acceleration of the brake pedal 
during the actuation thereof) by releasing the disengaging clutch 1 so 
that braking is effected exclusively by generator operation. If a greater 
braking torque is required, the engine braking effect of the internal 
combustion engine can also be made use of by closing the disengaging 
clutch 1 and interrupting the supply of fuel to the internal combustion 
engine. Finally, for maximum braking power, conventional friction brakes 
(e.g., disk brakes) can also be used. 
The drive arrangement according to the invention, while fully operative 
with all forms of hybrid drives, has the advantage that it requires fewer 
structural component parts and accordingly reduces production costs. 
Moreover, it enables an appreciably more compact construction, in 
particular in the axial direction, especially in view of the fact that a 
second disengaging clutch including the accompanying actuating devices is 
dispensed with entirely. The high-torque external-rotor electric motor, 
especially when designed as a magnetoelectric generator, has a 
comparatively higher output (for improved driving performance) and a 
higher efficiency than previously used internal-rotor asynchronous 
machines and thus provides a vehicle with greater cruise range.