Patent Application
20130288835
The invention relates to a traction drive of an internal combustion engine and to a method for operating same. The traction drive comprises an auxiliary unit drive, which extends in a first drive plane, a starter drive, which extends in a second drive plane parallel to the first drive plane, and:
A double belt drive of the type in question is disclosed by DE 10 2010 054 630 A1, which is not a prior publication. The electric machine proposed there is operated either as a driven generator or as a driving motor in the direction of rotation of the crankshaft. Here, the motor mode, in which the crankshaft is driven in the direction of rotation thereof, comprises a starting mode for starting the internal combustion engine and what is known as a “boost mode”, in which the crankshaft is driven not only by the internal combustion engine but also by the electric motor for the purpose of boosting the torque.
A further motor mode of the electric machine is used for what is known as “stationary air conditioning” for cooling the vehicle driven by the internal combustion engine. Here, the electric machine drives the air conditioning compressor, which is designed for a compression mode in both directions of rotation, in the opposite direction of rotation while the internal combustion engine is stationary.
It is the underlying object of the invention to simplify the design of a traction drive of the type stated at the outset and to indicate a method for operating a traction drive of this kind.
In terms of apparatus and method, the solution to this object is obtained from one or more features of the invention. Advantageous embodiments of the invention can be found below and in the claims.
Accordingly, the electric machine and the engine starter are separate electric units. In contrast to the situation in the cited prior art, therefore, there is no provision for an integrated unit in the form of a starter/generator machine which serves both as an electric machine that drives the crankshaft and a generator which is driven by the crankshaft. On the contrary, the invention provides two structurally separate individual machines which are designed in a technically specific and optimum manner for their respective purposes.
On the one hand, the electric engine starter can be either a high-grade machine with power electronics which also allows the abovementioned boost mode or, alternatively, a very low-cost machine without power electronics which is intended purely for starting the engine. The electric machine, which is separate therefrom, combines the functions of the generator, which supplies the vehicle electrical system with power, and of a motor, which does not drive the crankshaft but only the air conditioning compressor and, if required, further auxiliary units in “reverse” rotation. For this stationary air conditioning mode, it may be sufficient for the motor merely to be capable of being switched on and off, without complex control/regulation, in order to drive the air conditioning compressor at a constant speed of rotation, e.g. at 1500 rpm. Since the driving torque required for this purpose is significantly lower than that for starting or boosting the internal combustion engine, the motor can be of relatively simple dimensions, with corresponding cost advantages.
For operating the traction drive according to the invention, at least one of the following operating modes is provided:
Control/regulation of the individual operating modes is accomplished with the aid of various state variables, particularly those of the internal combustion engine, of the vehicle interior temperature and the operating state of the controllable clutch.
A nonpositively acting poly-V belt is provided as a preferred traction means for the auxiliary unit drive, and a positively acting toothed belt is provided as a preferred traction means for the starter drive. However, a traction drive according to the invention can also be a chain/chain drive or a belt/chain drive.
It is likewise possible for further auxiliary units, possibly also in further drive planes, to be provided. In particular, this concerns the coolant pump arranged in the auxiliary unit drive for the purpose of cooling the internal combustion engine. Thus, the coolant pump, like the air conditioning compressor, can be driven “in reverse” by the electric machine when the internal combustion engine is stationary in order to supply the heating heat exchanger of the vehicle with warm cooling water (stationary heating). The radial pumps that are now customary supply a volume flow in the same direction, even when the direction of rotation of the drive is reversed, but this is only about 30% of the volume flow in the normal operating mode. However, this may be sufficient to maintain the internal temperature of the vehicle.
Further features of the invention will emerge from the following description and from the single FIGURE, in which a traction drive according to the invention for a motor vehicle internal combustion engine (not shown) is disclosed schematically.
The traction drive is embodied as a double belt drive in two mutually parallel drive planes. The auxiliary unit drive 1, which extends in the first drive plane and is illustrated with a solid line, comprises a first crankshaft wheel 2, which is arranged on the crankshaft CR of the internal combustion engine, an electric machine A/M, which can be operated either as a generator A or, in the opposite direction of rotation, as a motor M and has a machine wheel 3, an air conditioning compressor A/C having a compressor wheel 4, a coolant pump WP having a pump wheel 5, a first traction means 6 in the form of a poly-V belt which revolves in an endless manner and is wrapped around wheels 2 to 5, and a first tensioning device BT1 in the form of a known spring-loaded belt tensioner, which pretensions the first traction means 6 in the slack side thereof, between the first crankshaft wheel 2 and the machine wheel 3.
The reverse direction of rotation in the motor mode M to that in the generator mode A prevents drive-induced swapping of the tight side and the slack side in the auxiliary unit drive 1, and therefore the first tensioning device BT1 is arranged in the slack side and hence always in a functionally optimum manner, both when the internal combustion engine is running, i.e. when the crankshaft CR is driving, and when the internal combustion engine is stationary, i.e. when the crankshaft CR is being driven.
The starter drive 7, which extends in the second drive plane and is illustrated in dashed lines here, comprises a second crankshaft wheel 8, which is arranged on the crankshaft CR coaxially with the first crankshaft wheel 2, an electric engine starter S having a starter wheel 9, a second traction means 10 in the form of a toothed belt which revolves in an endless manner and is wrapped around wheels 8, 9, and a second tensioning device BT2, likewise in the form of a known belt tensioner, which pretensions the second traction means 10 in the slack side thereof, between the starter wheel 9 and the second crankshaft wheel 8. The power characteristic of the engine starter S, which can be operated purely in the positive direction of rotation M-CR and purely as a motor, is matched both to the torque requirement of the internal combustion engine to be started and—in combination with suitable power electronics—to the torque requirement of the running internal combustion engine in boost mode. The torque that can be transmitted to the crankshaft CR corresponds to the relatively large transmission ratio between the starter wheel 9 and the second crankshaft wheel 8.
The operational direction of rotation of the crankshaft CR corresponds to the direction of rotation indicated by a positive sign. The direction of rotation of the electric machine A/M is positive when the electric machine is in the generator mode A and is driven by the crankshaft CR. The direction of rotation of the electric machine A/M has a negative sign when the electric machine is in the motor mode M and, with the internal combustion engine stationary, drives the compressor wheel 4 and the pump wheel 5 in a correspondingly reversed direction of rotation for the purpose of cooling or heating the vehicle interior. The electric machine A/M has a significantly lower power consumption than known starter/generator machines and, in the motor mode M, is designed only to drive the air conditioning compressor A/C and the coolant pump WP at a constant speed of rotation of about 1500 rpm.
The air conditioning compressor A/C is a swashplate compressor, which is designed for a compression mode in both directions of rotation and is inserted into the refrigerant circuit of the vehicle air conditioning system with a corresponding freedom in terms of direction of rotation. The compressor wheel 4 can be connected for rotation to the air conditioning compressor A/C by means of a controllable magnetic clutch (not shown).
A reversal in the direction of rotation in accordance with the current operating mode is also provided in the case of the coolant pump WP, which is designed as a radial pump and, like the air conditioning compressor A/C, is designed for a pumping mode in both directions of rotation.
In the auxiliary unit drive 1, the machine wheel 3 is connected to the electric machine A/M for rotation by means of a one-way clutch 11 in the form of a one-way roller clutch, which allows overrunning of the electric machine A/M relative to the machine wheel 3 in the positive direction of rotation and hence relative to the crankshaft CR and locks up in the opposite, negative direction of rotation. The one-way roller clutch 11 is embodied as a one-way generator clutch known per se for the purpose of decoupling the generator A, wherein the inner ring thereof, which is provided with wedging ramps for the wedging rollers, rotates with the electric machine A/M and wherein the cylindrical outer ring thereof rotates with the machine wheel 3 (one-way clutch with profiled internal race).
As an alternative to a one-way clutch of this kind, spring decoupling with stops on both sides or, in principle, also a rigid connection between the machine wheel 3 and the electric machine A/M can be provided for the electric machine A/M.
The rotary connection between the first crankshaft wheel 2 and the crankshaft CR is accomplished by means of an electrically controllable magnetic clutch 12. This can be either open when deenergized or closed when deenergized. In the open state of the magnetic clutch 12, the auxiliary unit drive 1 is operationally decoupled from the crankshaft CR. Decoupling is required in order to be able to drive the air conditioning compressor A/C and the coolant pump WP in isolation when the internal combustion engine is stationary and, consequently, the crankshaft CR is stationary, and hence to be able to perform stationary air conditioning or stationary heating of the vehicle. Decoupling furthermore enables the auxiliary unit drive 1 to be stopped when the internal combustion engine is running, in order to minimize operational frictional losses.
In the starter mode 7, the rotary connection between the second crankshaft wheel 8 and the crankshaft CR is accomplished by means of a further one-way clutch 13 in the form of a one-way roller clutch, which allows overrunning of the crankshaft CR relative to the second crankshaft wheel 8 in the positive direction of rotation and locks up in the opposite direction of rotation. In terms of design, the one-way roller clutch 13 is arranged in such a way that the cylindrical inner ring thereof rotates with the second crankshaft wheel 8 and that the outer ring thereof, which is provided with wedging ramps for the wedging elements, rotates with the crankshaft CR (one-way clutch with profiled external race). As compared with pinion starters which mesh abruptly, this design embodiment allows start/stop operation of the internal combustion engine with “change-of-mind starting”, in which case the still-rotating crankshaft CR of the internal combustion engine, which has already been switched off, is driven until restarting.
The traction drive allows the following operating modes:
a) a starting mode, in which the engine starter S drives the crankshaft CR from the stationary condition until the internal combustion engine starts:
| Number | Date | Country | Kind |
|---|---|---|---|
| 102011003227.4 | Jan 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/068752 | 10/26/2011 | WO | 00 | 7/19/2013 |
