Drive assembly

[0002] The invention relates to a drive assembly, for motor vehicles in particular, as specified in the preamble of claim 1, and also to a process for operating a motor vehicle with such a drive assembly.

[0003] A generic drive assembly is disclosed in DE 29 43 532 A1; it has an internal combustion engine as first drive source, an electric motor, as second drive source, and a belt contact transmission as infinitely variable transmission. In the process of operation the internal combustion engine activates, by way of a coupling, the first converter element and respectively the drive wheel pair of the, belt contact transmission, while the driven wheel pair driven by way of belt contact means is connected to the driven shaft as second converter element. The electric motor is also connected directly to the drive wheel pair for the purpose of propulsion. With this drive assembly, for example, the vehicle may be set in motion and driven in the low-speed range by the electric motor by utilizing the transmission spread. If the coupling is closed on the internal combustion engine side, the internal combustion engine may be additionally engaged, and if desired the electric motor may be converted to operation as a generator. The transmission spread may also be suitably passed through by way of the internal combustion engine.

[0004] The object of this invention is to develop the generic drive assembly at low additional cost and so as to be much more versatile and favorable with respect to the transmission spread.

[0005] It is claimed for the invention that this object is obtained with the characteristic features presented in claim 1. Advantageous developments of the invention are to be found in the additional claims. In addition, claims 8 to 12 propose an advantageous process for operation of a motor vehicle with the drive assembly claimed for the invention, whereby favorable drive shaft efficiency can be achieved and emission of noxious exhaust gases may be reduced in local traffic areas, and accordingly in urban traffic.

[0006] Application of the measures claimed for the invention as presented in claim 1 yields the special advantage that the infinitely variable speed-change gear (e.g., a toroidal or belt-contact transmission) is passed through when the force flow from the first or second drive force hereafter referred to as internal combustion engine and electric motor, is reversed, the following functions being possible by means of simple switching of couplings:

[0007] 1. Propulsion by way of the electric motor only for starting both forward and reverse driving in urban areas;

[0008] 2. Propulsion by way of the internal combustion engine only, at higher speeds only, but if desired also for starting (emergency operation);

[0009] 3. Propulsion by way of both drive sources in extreme acceleration;

[0010] 4. Starting of the internal combustion engine by means of the electric motor;

[0011] 5. Engagement of the electric motor as generator to supply the electric network of the motor vehicle during internal combustion engine operation and if desired in braking of the motor vehicle; and

[0012] 6. Propulsion of the motor vehicle by the internal combustion engine or the electric motor without infinitely variable transmission (emergency operation).

[0013] It is also particularly advantageous if propulsive connections, such as gears, chains, etc., are provided which differ with respect to their transmission ratios. In this instance the connection switching on the electric motor, preferably a first set of spur pinions, may be designed for a higher starting torque and a lower speed range, while the connection switching on the internal combustion engine to effect propulsion, and accordingly the pertinent gear set, may be optimally designed for high speeds of the motor vehicle up to fuel-conserving overdrive operation. This propulsive connection is regularly superimposed in each instance on the spread of the infinitely variable transmission.

[0014] Smooth switching of the drive sources accompanied by low clutch wear is also achieved if reversal of the force flow is effected in the infinitely variable transmission when the speed of the elements to be coupled is synchronous. Such synchronous speed is present as a function of the given transmission ratios for the propulsive connections with a specific transmission ratio assigned to the infinitely variable transmission and can be determined more or less precisely, for example, by means of engine speed sensors on the drive shafts.

[0015] The switchable couplings may be positive claw clutches, synchronized clutches, and/or friction clutches, mounted as determined by structural relationships on the driven shaft and/or the other two transmission shafts. In the force flow on the side of the internal combustion engine in particular a clutch (single-plate dry clutch or multiplate clutch) which may also be used as starting clutch should be provided in order to make driving of the motor vehicle by the internal combustion engine possible at least in emergency operation.

[0016] Claim 8 and following claims propose operation as follows of the drive assembly described:

[0017] When the gas pedal is depressed, first the electric motor is activated by an electronic control unit with an assigned performance-value transmitter as a function of speed and/or performance and the starting torque and speed are controlled by appropriate current control. Starting at a specific speed or higher required performance (full gas or kick-down actuation if desired), the internal combustion engine is connected and activated (ignited) and its performance set at a high value, if desired with simultaneous switching from electric motor operation to internal combustion engine operation (switching of the connectable propulsive connections accompanied by reversal of force flow in the infinitely variable transmission. In the process the electric motor may feed in additional power to advantage, or again, if performance required is lower, the electric motor may be switched to generator operation to supply the electric network of the motor vehicle.

[0018] By preference the different transmission ratios of the propulsive connections are designed so that in traffic areas where speed is restricted to 30 km/hr, for example, as a rule only the electric motor is used in such areas. As a result, stages of operation of the internal combustion engine partial load ranges unfavorable to efficiency and generation of noise and exhaust gas pollution are prevented to the greatest possible extent.

[0019] Several exemplary embodiments of the invention are explained in greater detail below. In the schematic drawing,

[0020] FIG. 1 shows a drive assembly with an internal combustion engine, an electric motor, a belt-contact transmission, and the driven shaft with the propulsive connections connectable to the inlet or outlet of the belt-contact transmission,

[0021] FIG. 2 a drive assembly shown in FIG. 1, but with two gears as connectable propulsive connections mounted on the driven shaft,

[0022] FIG. 3 again a drive assembly as shown in FIG. 1 also with two gears mounted on the driven shaft as propulsive connections which may be connected by way of two multiple-disk clutches, and

[0023] FIG. 4 a drive assembly with an internal combustion engine, an electric motor, a toroidal transmission, and propulsive connections connectable to the inlet or outlet of the toroidal transmission.

[0024] In FIG. 1, 10 denotes an internal combustion engine, which is connected by a friction contact L₃to a first shaft 12 of the infinitely variable belt-contact gear 14.

[0025] The belt-contact gear 14 consists, as is known, of a first converter element or disk pair 16 on a shaft 12, a second converter element or disk pair 18 on a second shaft 20 mounted parallel to shaft 12, and belt contact means such as a chain 22 connecting the disk pairs 16, 18. The belt-contact radius of the chain 22 is appropriately adjustable, the conversion ratio i_Iconverting to “fast” with the force flow direction extending from shaft 12 to shaft 20, that is, shaft 20 rotates faster than shaft 12, which conversion ratio i_IIconverts to “slow” direction, shaft 12 rotating faster than shaft 20. Conversion is infinitely variable i_Iand i_II.

[0026] When the direction of force flow is from shaft 20 to shaft 12, conversion i_Iis to slow and i_IIto fast.

[0027] The rotor 24 of an electric motor 26, which may be a rotary-current motor, for example, acts directly on the second shaft 20 of the belt-contact gear 14.

[0028] In addition, there is mounted on shaft 12 a gear Z₁which may be coupled by way of a multi-plate clutch L₁and meshes with a gear Z₃on a driven shaft 28 mounted parallel to shafts 12, 20; a connectable propulsive connection with conversion ratio i_Iis thereby formed.

[0029] Similarly, there is mounted rotatably on shaft 20 a gear Z₂which also meshes with gear Z₃and which may be coupled with shaft 20 by way of a positive claw clutch K₂. The gear Z₂forms with gear Z₃a second propulsive connection with conversion ratio i₂.

[0030] The driven shaft 28 acts in conventional fashion on a differential of a motor vehicle not shown with a specified conversion ratio i_D. The aggregate conversion ratio of the motor vehicle is thus obtained from

[0031] i_I(i_II)×i₁×i₀

[0032] in the case of propulsion exclusively by the electric motor (direction of force flow from shaft 20 to shaft 12) and

[0033] i_II(i_I)×i₂×i_D

[0034] in the case of propulsion by the internal combustion engine and direction of force flow from shaft 12 to shaft 20.

[0035] The drive assembly described operates as follows:

[0036] If the motor vehicle is to be set in motion, coupling L₃and K₂are open and coupling L₁is closed. The couplings are controlled by suitable hydraulic actuators, by way of an electronic control unit not shown which also controls the performance electronics of the electric motor 26 and is also connected to the control unit of the internal combustion engine 10.

[0037] If the motor vehicle is set in motion by means of the gas pedal not shown and an electronic control value transmitter mounted on this pedal, the force flow proceeds from the rotor 24 of the electric motor, by way of shaft 20 to the belt contact transmission 14 and from the latter, by way of infinitely variable transmission ratio i_Ito i_II, to the shaft 12, and from the latter, by way of gear set Z₁and Z₃with transmission ratio i_I, to the driven shaft 28. Since the transmission ratio i_Iis relatively small, the drive torque of the electric motor 26 is appropriately increased.

[0038] When the motor vehicle reaches a specific speed, 30 km/hr for example (in forward drive), the difference in conversion ratio between i₁and i₂is offset by the transmission ratio I_IIof the contact-belt transmission in effect at this time, so that the speed difference between shaft 20 and accordingly coupling K₂and the gear Z₂meshing with the gear Z₃of the driven shaft 28 equals zero, that is, synchronous speed has been reached. Hence the coupling K₂may be closed almost without wear and with no switching jerk.

[0039] Before the coupling K₂is closed, however, the internal combustion engine is activated by ignition by closing of the coupling L₃and its drive output is switched smoothly to the shaft 12. If necessary, any uncomfortable speed-change jerk may be eliminated by suitable adjustment of the torque values by control engineering means in conjunction with the electric motor 26.

[0040] After the output of the internal combustion engine 10 has been received and coupling K₂has been closed, the multiple-disk coupling L₁is opened, so that now the drive output is transmitted from combustion engine 10 to the shaft 12 and by way of the belt-contact transmission 14 operating at transmission ratio i_IIto the shaft 20 and by way of gear Z₂, with transmission ratio I₂, now connected to the shaft 20, to the driven shaft 28. The internal combustion engine now propels the motor vehicle fuel efficiently by way of the transmission ratio now present, such that i₁<i₂at reduced speed and accordingly with more lengthy transmission, into the overdrive range, that is, transmission ratio i_Iof the contact-belt transmission 14.

[0041] If high performance is required, the electric motor may be engaged for a short period to increase output. The electric motor is otherwise connected conventionally as a generator and, at least when the internal combustion engine 10 delivers excess power (especially in efficiency promoting partial load operation), supplies appropriate current to the vehicle network, that is, the drive batteries of the motor vehicle.

[0042] FIGS. 2 and 3 present alternative embodiments of the drive assembly shown in FIG. 1. Functionally equal parts are identified by the same reference numbers.

[0043] Thus, in FIGS. 2 and 3 two gears Z₃₁and Z₃₂are mounted on driven shaft 28 in place of a gear Z₃; they operate separately together with gears Z₁or Z₂to form transmission ratios i₁and i₂. As a result, the different transmission ratios between i₁and i₂can be better realized by allowance for structural realities (shaft spacing, etc).

[0044] In addition, as is shown in FIG. 2 a form locking claw coupling K₁may be used in place of the multiple-disk coupling L₁, as shown in FIG. 1, and is for this purpose mounted on the driven shaft 28.

[0045] FIG. 3 shows that couplings K₁and K₂may be in the form of hydraulically actuated multiple-disk couplings L₁and L₂, both of which are for this purpose seated on the driven shaft 28. Hence this design is advantageous in that the hydraulic medium impinging on the multiple-disk clutches L₁and L₂may then be supplied by the driven shaft, while shafts 12, 20 may be used for supply of hydraulic fluid to disk pairs 16, 18.

[0046] FIG. 4 shows as a modification of that presented in FIG. 1 a conventional toroidal transmission 30 as an infinitely variable transmission one converter element 32 of which is propulsively connected to the internal combustion engine 10 by coupling L₃and shaft 34. The electric motor 26 acts directly on the other converter element 36 by way of shaft 38.

[0047] The transmission ratio i_Ior i_IIis controlled conventionally by rollers 40 which may be swung horizontally into position.

[0048] The gears Z₁and Z₂effecting the propulsive connections to driven shaft 28 mounted in parallel are mounted on shafts 34, 38, which mesh with the meshing gears Z₃₁and Z₃₂on the driven shaft 28 by ways of two form locking claw couplings K₁, K₂. The relation i₁<i₂again applies.

[0049] The operation of the drive assembly shown in FIG. 4 corresponds to that of the drive assembly shown in FIG. 1. While use of a belt-contact transmission 14 as infinitely variable transmission results in a three-shaft design with shafts 12, 20, and 28, in the case of the drive assembly shown in FIG. 4, as determined by the design in the form of the toroidal transmission 30, shafts 34, 38 are oriented coaxially and only the driven shaft 28 is oriented parallel to them.

[0050] The drive assemblies described in the foregoing are illustrated in the form of sketches. Housing, shaft bearings, etc., may be of conventional transmission design. Reverse gear operation of the motor vehicle may be controlled by suitable polarity reversal of the electric motor 26. The speed of travel of the motor vehicle in reverse gear may be limited by the electronic control unit, for example, to 15 km/hr.