DE20014160U1 - Powertrain for motor vehicles - Google Patents

Description

Martin Strobel, graduate designer

Schwanengasse 10

64823 Gross-Umstadt, DE

Powertrain for motor vehicles

Description

The invention relates to a drive train for motor vehicles, in particular compact cars, which provides for an underfloor installation of a longitudinally mounted, horizontal reciprocating piston engine with a transaxle drive acting on the front wheels, which is preferably equipped with a transversely mounted CVT belt transmission. The layout is suitable for optional equipment with additional electromechanical converters as a parallel hybrid drive in various configurations, for which cylinder deactivation and electromechanical compensation of the imbalances are proposed.

State of the art and task

Vehicles with transaxle drive have so far only been known with rear-wheel drive. They have relatively acceptable traction due to the load on the driven axle, and also good space economy, since the transmission is located below the trunk or the rear seat. Front-wheel drive with a transverse engine is now standard for small and compact cars; passive safety is more difficult to achieve in these cars than in longer vehicles. Two-seater city vehicles with a length of 2.5 m have recently been produced with rear engines and rear-wheel drive. The package is suitable for a single-volume design of compact vehicles for reasons of interior use (i.e. with a silhouette without a vehicle nose) and also has advantages in terms of passive safety, since with this length the engine would otherwise be pushed into the passenger compartment in the event of a frontal impact. However, there is a conflict of objectives because with short wheelbases the torque of the driven wheels relieves the load on the front axle when starting and accelerating. This is critical on slippery roads and when starting on a hill and impairs driving stability. Rear-wheel drive vehicles generally tend to break out at the rear in extreme situations; this naturally applies particularly to rear-engine and transaxle vehicles. Conventional rear-wheel drive trains with longitudinally installed engines therefore require complex rear axle kinematics and have poorer traction than front-wheel drive vehicles. Above all, however, they find their limits in terms of space utilization.

So-called "sandwich floors" with parallel floor panels to create higher structural impact safety have already been implemented in car construction, as have platform concepts with standardized floor assemblies and standardized drives that allow greater variability of the superstructures. Platform concepts that use "sandwich floors" have not yet been implemented, although they are obviously advantageous. However, "sandwich floors" could offer advantages in terms of safety, lightweight construction and production costs, particularly in conjunction with a space frame structure of the body made of formed semi-finished products, which as a lightweight load-bearing structure represents a departure from the self-supporting shell construction and allows paneling with non-load-bearing (possibly plastic) add-on parts.

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Against the background of the prior art, the invention sets itself the task of proposing a drive train that enables a space-efficient, variable and structurally impact-proof design of a compact car and ensures a high level of active safety. In addition, possibilities are to be shown for optionally equipping this drive train as an energy-efficient hybrid drive, which arise from the arrangement of the components.

Description

The drive train is explained below using the drawing Fig. 1, which shows a front view and a shortened top view. The horizontal reciprocating piston engine (1) in the rear of the vehicle, which is shown as a longitudinally installed three-cylinder, is located between the rear wheels (2a, 2b). The pistons therefore move parallel to the vehicle's transverse axis. Such engines can be built very flat. Narrower designs of the cylinder heads are to be expected in the future, as mechatronic, electromagnetic valve actuators are being developed, which also potentially enable simple cylinder deactivation because camshafts and thus their partial decoupling become superfluous. In contrast to transversely installed front engines, the length of the in-line engine is hardly limited in terms of space. The cardan shaft (3) does not run centrally, but is offset to the side towards the front and drives a transmission, which is shown here as a CVT belt transmission (4); this is also the preferred design. The CVT transmission (4) is installed parallel to the vehicle's transverse axis, as seen in the direction of travel of the transmission chain (5). The separating clutch (6) is arranged on the transmission (4) or on the reciprocating piston engine (1). The output of the CVT transmission (4) drives the differential (7) via bevel gears (8). The differential (7) is arranged behind the transmission in the direction of travel, as shown here, or in front of it. In the first case, the cardan shaft (3) and a half shaft (9a) run crosswise, for which the CVT transmission (4), as shown in the front view, is positioned at an angle to the vertical axis, so that the height of the shafts is offset. This design ensures sufficient foot space. The drive shafts (9a, 9b) drive the front wheels (10a, 10b) via joints (11a, 11b). A central route of the cardan shaft (3) can be produced with boxer engines, although this is more complex. The cardan shaft can be lowered using universal joints or gears (e.g. with an output via a ring gear; this is not shown in the drawing). When using gear drives, the speed of the cardan shaft (3) can be reduced in front of the CVT transmission (4). In a preferred design, the cardan shaft runs within a double vehicle floor (12). This design also offers space for an impact-proof arrangement of the fuel tank (13) or additional accumulators below the vehicle seats, which have a slightly higher seating position. With a double floor, a cutout reinforced by a frame can be made in the area of the engine so that the engine (1) can still be removed downwards. The spark plugs can be made accessible from the trunk using a flap. The oil filler neck, oil dipstick and filler neck for hydraulic oil can be made accessible from the outside via a service flap; a fold-down license plate in the bumper is ideal for this. In the event of a rear-end collision, the flat engine (1) can be installed in such a way that it is pushed under the vehicle. In another version, the engine can be arranged as a mid-engine under the seats. The components not shown in the drawing, such as heat exchanger, heating and air conditioning, are installed in the front of the vehicle, and the spare wheel can be stowed there under a flap. At the same time, energy-consuming deformable honeycomb structures, hard foam blocks, hydraulic impact absorbers, etc. can be installed there.

The arrangement of the components offers advantageous possibilities for equipping the drive train as a hybrid drive. Due to the space available, additional equipment for existing drive trains has not yet been possible.

so that additional hybrid components cannot currently be offered as an option. Instead, separate vehicles are manufactured in small series.

A first possibility is a parallel single-shaft hybrid drive, in which the electromechanical converter is installed coaxially on the shaft of the reciprocating piston engine (1). In this case, two separating clutches are required for dual-mode operation, in front of and behind the ε-converter. The electromechanical converter, which works both as a motor and as a generator, makes the starter and alternator superfluous in this configuration. It can be designed for inductive braking and support acceleration in such a way that leveled operation of the combustion engine is possible.

Fig. 1 shows a configuration in which the electromechanical converter (14) acts on the drive cone disk of the CVT transmission (4) via a constant ratio gear transmission (15), i.e. a parallel two-shaft hybrid drive. In this case, a starter is required, which is designed as a starter/generator unit (16) mounted coaxially on the engine shaft, which is shown here mounted at the rear, or can otherwise be installed behind the separating clutch. The system is also suitable for inductive braking and can avoid partial load operation of the combustion engine over large areas. With a shaft assembly without an intermediate transmission, the unit (16) is able to actively compensate for shaft imbalances electromechanically by means of a control system, by either alternately accelerating the converter (16) during motor operation, or alternately increasing the induction during generative operation. This makes cylinder deactivation and operation on one or two cylinders possible, especially when using electromechanical magnetic valve control. The control range of the CVT transmission (4) is also retained for the separately operated electromechanical converter (14), but is not required due to the constant torque curve of electric motors, but is used to produce the highest possible gear ratio in slow speeds. An advantage over the previously mentioned configuration of a coaxial single-shaft hybrid is that with separate electric motor operation and exhausted electrical storage, the reciprocating piston engine can briefly drive the starter/generator unit (16) to recharge it. The system therefore functions as a serial hybrid at slow driving speeds. The separating clutch can also be designed as a multi-disk clutch, so that driving is carried out with a "slipping clutch" and a portion of the torque is temporarily transmitted in parallel if the converter (14) is so small that its starting torque is no longer sufficient, and dual-mode operation is dispensed with in favor of a serial drive in slow driving mode. A design of the CVT transmission as an i ² transmission, in which the effective range of the transmission is passed through twice and in a "second gear" the chain drive (5) changes its direction of movement, is possible, although this is not necessary if the converter (14) is designed to be powerful or if cylinder deactivation is used. The three energy converters (1,14,16), the transmission (4) and, if applicable, the electro-hydraulic multi-disk clutch are controlled by a (fuzzy logic) process control.

Other possible solutions could be that the electromechanical converter acts on the output disk of the CVT transmission (4) or on the bevel gear of the differential gear (7). As an alternative to the functional scenario described above, a generative support of a motor-operated starter/generator unit (16) can be implemented by the E-converter (14) if inductive braking to compensate for the imbalance is not possible, e.g. if the storage capacity is exhausted. The system design depends on various factors, such as the design of the E-converter, and mainly on the question of whether dual-mode operation is desired at all, or whether the system is designed so that the combustion engine runs smoothly while recuperating and buffering the thrust and braking energy. In this case, the cylinder displacement is

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circuit with electromechanical momentum compensation is proposed. This minimizes fuel consumption by operating at the best point, or in the ideal range, of the respective displacement appropriate to the power requirement, as well as the need for expensive and weight-increasing electrical storage capacity, and the electromechanical converters are made smaller. The storage then only serves to buffer energy for leveling the thermal engine, and thus also to avoid switching the displacement sizes over as long a distance as possible.

Of course, a corresponding design of a hybrid drive with a transversely installed front engine and a longitudinally flanged CVT transmission is also according to the invention (deviating from the main claim 1 and in designs which correspond to claims 10 and/or 11).

Advantages

The drive train described has various advantages. The weight of the engine rests on the "right" end of the lever arm. This is particularly important for very short wheelbases and light vehicles. The longitudinal weight distribution and the low center of gravity promise balanced handling.

The driving dynamic advantages of front-wheel drive are combined with the advantages in space utilization resulting from the engine's location in the rear. The three- to six-cylinder engine is located under the trunk in a place where the spare wheel or storage compartments would otherwise be located, or where space would be wasted. With the seat back folded forward and the seat raised, a flat loading area is created. Compared to vehicles with front-mounted engines, the underfloor design saves 25 to 50 cm in length, or adds space to the interior. The acceptance of single-volume designs is likely to increase in the future due to the growing popularity of minivans; however, a design with a separate front volume is also possible. Despite the shortening of the length, kinetic absorption in the event of a frontal impact is better achieved with a rear-mounted engine than with a short front section, in which non-deformable engine components that can penetrate the vehicle in the event of an impact have to be accommodated. If a sandwich floor concept is used, which is an obvious option, passive safety is improved anyway. In this case, the variability of the superstructures is also very easy to implement, up to full convertibles that do not require any floor reinforcements, four-seater or as a roadster. Other useful variants include a compact pickup, a two-seater city vehicle with a shortened wheelbase and a minivan or station wagon with three rows of seats. Ideally, the body construction can be more cost-effective than with a self-supporting construction (- in the future, non-thermal assembly of the superstructures on standardized cowls may also be realistic).

The CVT transmission saves fuel, and this type of transmission can also be expected to gain increasing market acceptance in the future. It can also be optionally designed as a virtual (optionally switchable, optionally semi-automatic) manual transmission with defined gear ratios for customers who do not want an automatic transmission.

The arrangement of components directly results in possibilities for mounting electrical energy converters, which make it possible to offer a version with a parallel two-shaft hybrid drive as an option. In the future, this could become a popular equipment variant that cannot be implemented optionally, or only with difficulty, with the drive trains of the state of the art in small or compact cars. Certain novel features that are proposed here for the drive train according to the invention are generally adaptable and advantageous for hybrid drives.

Claims (13)

1. Drive train of a vehicle, characterized in that a longitudinally mounted, horizontal reciprocating piston engine ( 1 ), which is installed in the rear of the vehicle or in the middle of the vehicle, drives the front wheels via a transaxle drive which consists of a cardan shaft ( 3 ), separating clutch ( 6 ), manual or automatic transmission, differential gear ( 7 ) and axle shafts ( 9 a, 9 b). 2. Drive train of a vehicle according to claim 1, characterized in that the transmission is a CVT belt transmission ( 4 ) arranged transversely to the vehicle's longitudinal axis. 3. Drive train of a vehicle, characterized in that all drive components are installed as underfloor components in a double vehicle floor ( 12 ). 4. Drive train of a vehicle, characterized in that the drive train can optionally be equipped as a hybrid drive by an electromechanical converter ( 14 ) installed coaxially or by a gear transmission ( 15 ) constantly translated into slow gear on the drive shaft of the CVT transmission ( 4 ). 5. Drive train of a vehicle deviating from claim 4, characterized in that the drive train can optionally be equipped as a hybrid drive in that an electromechanical converter, constantly translated into slow speed by a gear transmission, engages the output shaft of the CVT transmission ( 4 ) or the bevel gear or a half-shaft of the differential gear ( 7 ). 6. Drive train of a vehicle, characterized in that the drive train can optionally be equipped as a hybrid drive by an electromechanical converter acting on the shaft of the internal combustion engine ( 1 ). 7. Drive train of a vehicle, in particular according to claim 6, characterized in that the electromechanical converter is installed coaxially on the cardan shaft ( 3 ) between two separating clutches. 8. Drive train of a vehicle, characterized in that the electromechanical converter according to claim 7 is designed as a starter/generator unit ( 16 ) and at the same time, in the alternative embodiments according to claim 4 or claim 5, supports the corresponding electromechanical converters generatively and/or motor-wise. 9. Drive train of a vehicle, in particular according to claim 8, characterized in that the electromechanical converter ( 16 ) according to claim 7 electromechanically compensates for shaft imbalances by the electromechanical converter (= the starter/generator unit 16 ) being alternately accelerated during motor operation or braked during inductive operation by an increased induction, and that the regulation is controlled by the ignition sequence and/or by an inertia sensor and/or torque sensor. 10. Drive train of a vehicle, in particular according to claim 9, characterized in that the internal combustion engine ( 1 ) is equipped with a cylinder deactivation and preferably an electromechanical magnetic valve control which regulates this cylinder deactivation without a mechanical camshaft control. 11. Drive train of a vehicle, in particular according to claim 10, characterized in that a partial, parallel, supporting power transmission to the transmission takes place at times via a mechatronically switched clutch, preferably a multi-disk clutch, namely when the electromechanical converter ( 14 ) does not have sufficient starting torque and the internal combustion engine with the cylinders switched off and disengaged in slow driving mode otherwise works as a constant, serial drive, wherein at the same time the induction of the starter/generator unit ( 16 ) can be reduced, or the unit ( 16 ) can be switched to motor operation in order to maintain a constant running of the internal combustion engine. 12. Drive train of a vehicle, in particular according to claims 8, 9, 10, 11, characterized in that the reciprocating piston engine, deviating from claim 1, is designed as a transversely installed, standing front engine to which the CVT transmission is mounted longitudinally in the direction of the vehicle. 13. Drive train of a vehicle according to the preceding claims, but deviating from claim 1 and claim 12, characterized in that the reciprocating piston engine is designed as a horizontal underfloor front engine and drives the rear axle.