Powertrain for a motor vehicle and method of controlling the same

Abstract

A powertrain (1) comprising an internal combustion engine (2) provided with an accessory drive arrangement (19), the accessory drive arrangement (19) comprising a first pulley (21) connected to a crankshaft (3) of the internal combustion engine (2), a second pulley (22) connected to a shaft (33) of a second electric machine (23), and a belt (26) connecting the first and second pulleys to each other for rotation in the same rotational direction (R), wherein the second electric machine (23) is operated to provide an effective torque to the second pulley (22) by means of a starter motor during starting of the internal combustion engine.

Description

[0001] Cross-reference of related applications

[0002] This patent application claims priority to Italian patent application No. 102019000023805, filed on December 12, 2019, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a powertrain for a motor vehicle and a method for controlling said powertrain.

[0004] This invention is preferably, but not exclusively, applied to hybrid powertrains, and without loss of generality, will be referred to in the following text as a hybrid powertrain. Background Technology

[0005] As is well known, hybrid traction vehicles include an internal combustion engine and at least one electric motor, which can be used as a generator or as a motor to deliver torque in combination with (or in place of) the internal combustion engine, depending on the vehicle's operating conditions.

[0006] The configuration that uses an electric motor connected between the internal combustion engine and the vehicle's transmission is conventionally referred to as "P2". It is known that the modular unit is designed to be inserted between the vehicle's internal combustion engine and transmission (hence the current term "P2 module"). In addition to the electric motor, the modular unit also includes one or more clutches that selectively connect the internal combustion engine and / or the electric motor, as well as associated actuators and transmission components, to the transmission.

[0007] Also known are powertrains for motor vehicles, which include an accessory drive unit located at the end of the internal combustion engine opposite to the transmission (typically denoted by "front end" or "PO"). The accessory drive unit, typically a belt drive, connects one or more accessories to the crankshaft. These accessories typically include electric motors operating as alternators and / or motors, and compressors for air conditioning systems. The accessory drive unit includes corresponding pulleys connected to the crankshaft and each accessory, a belt cooperating with the pulleys, and a tensioner designed to ensure minimum belt tension.

[0008] If the motor is specifically used as an alternator (generator), it is common practice to insert a one-way coupling or free wheel between the motor and the associated pulley. The purpose is to transfer torque from the pulley to the motor when it is driven by the engine, but to allow the motor to override the pulley under brief operating conditions where this might occur (e.g., in the event of sudden crankshaft deceleration). This prevents the high inertia of the motor from subjecting the belt to unwanted tension spikes.

[0009] On the other hand, if, as is happening more and more frequently, the electric motor is also used as a motor, then the use of freewheels as described above is impossible, because the electric motor must be able to receive torque or transmit torque to the relevant pulleys depending on the operating conditions.

[0010] In this case, to ensure minimum belt tension under all operating conditions, a double tensioner is used, which has a first tensioner pulley acting on the belt span upstream of the motor and a second tensioner pulley acting on the belt span downstream of the motor, since both spans can be slack spans depending on the operating conditions.

[0011] The known solutions described above can be combined to produce a hybrid power system with a motor at position P0 (hereinafter: motor P0) and a motor at position P2 (hereinafter: motor P2); the two motors can use different control strategies (e.g., one as a motor only, and the other in a reversible manner).

[0012] In addition, internal combustion engines can be started by means of electric motors P0, P2, or a first electric motor (a conventional starter motor) associated with the engine flywheel.

[0013] For example, if motor P0 is used only as a motor, and the internal combustion engine is started by means of motor P2 or a starter motor, the tension of the accessory drive belt can reach an unacceptable minimum, such as... Figure 3 As shown, this can help determine belt noise and premature wear. Summary of the Invention

[0014] The purpose of this invention is to produce a power system that solves the above-mentioned problems.

[0015] The above objective is achieved by the accessory drive device according to the present invention.

[0016] This invention also relates to a control method for a power system. Attached Figure Description

[0017] To better understand the invention, preferred embodiments are described by way of non-limiting examples and with reference to the accompanying drawings, wherein:

[0018] Figure 1 This is a schematic plan view of the power system according to the present invention;

[0019] Figure 2 This is a schematic front view of the power system according to the present invention;

[0020] Figure 3 This is a graph showing the tension variation in the accessory drive unit of a conventional power system; and

[0021] Figure 4This is a graph showing the belt tension variation in the accessory drive device of the power system according to the present invention. Detailed Implementation

[0022] refer to Figure 1 The number 1 generally represents the power system of a motor vehicle.

[0023] The powertrain 1 includes an internal combustion engine 2 with a crankshaft 3 and a hybrid power module (hereinafter referred to as "thermal engine 2" for simplicity).

[0024] In use, the hybrid power module is inserted between the vehicle's thermal engine 2 and the transmission T, and is connected to one end 5 of the crankshaft 3 facing the transmission T.

[0025] The hybrid module includes an additional motor 6 and a disengagement clutch 7 designed to selectively connect the additional motor 6 to the crankshaft 3 and the transmission T.

[0026] The disengagement clutch 7 includes at least a clutch disc 8 and a plate 10. The clutch disc 8 is axially fixed and rotatably integrated with a flywheel 9 connected to the end 5 of the crankshaft 3. The plate 10 is axially movable and rotatably integrated with the intermediate shaft 11 of the hybrid power module. The disengagement clutch 7 also includes a hydraulic actuator 12 acting on the plate 10 for controlling the clutch.

[0027] The intermediate shaft 11 is connected to the pulley 14 by means of a known type of torsional vibration damper (not shown) housed in the pulley.

[0028] Pulley 14 is connected to pulley 16, which is connected to an additional motor 6, via belt 15.

[0029] A flexible plate 17 is fixed to a pulley 14, the plate constituting an output component of the hybrid power module, the output component being designed to connect to a torque converter 18 constituting an input component of the transmission T.

[0030] The powertrain 1 also includes an accessory drive 19 connected to an end 20 opposite to end 5 of the crankshaft 3.

[0031] Accessory drive device 19 ( Figure 2 The crankshaft 3 includes a first pulley 21 fixed to end 20, a second pulley 22 associated with a second motor 23, and a third pulley 24 for driving an accessory 25 (e.g., a compressor) of the regulating system. The first pulley 21, second pulley 22, and third pulley 24 are interconnected by a belt 26. A conventional tensioner 28 acts on the span 26a of the belt 26 between the second pulley 22 and the third pulley 24. The first pulley 21, second pulley 22, and third pulley 24 are connected to each other along a belt 26. Figure 2The same rotational direction R indicated by the middle arrow rotates, and is consistent with the rotational direction of crankshaft 3.

[0032] The power system 1 includes a first motor 30 that operates as a starter motor, the first motor 30 being provided with an output pinion that meshes with the flywheel 9. Conveniently, the first motor 30 is a brushless motor capable of quickly starting the heat engine 2.

[0033] The powertrain 1 also includes a programmable control unit 34, which controls the motor in response to input signals representing operating conditions of the powertrain 1 and the drive control device.

[0034] The operation of Power System 1 is as follows.

[0035] When the disengagement clutch 7 is engaged, the intermediate shaft 11 is connected to the thermal engine 2, the additional electric motor 6, and the vehicle transmission T.

[0036] In this configuration, depending on the operating conditions, the programmable control unit 34 can operate the additional motor 6 as a generator (to charge the battery during hot traction, or as a regenerative braking device) and as a motor combined with the second motor 23 to deliver additional torque (boost). The specific control logic of the motors is not described herein, as it is not part of this invention.

[0037] When the disengagement clutch 7 is open, the additional motor 6 can be used for electric traction, electric braking, and coasting when the thermal engine is off.

[0038] The thermal engine 2 is started by means of the first electric motor 30 (cold start and start under electric traction conditions). At this stage, the disengagement clutch 7 is disengaged.

[0039] During the start-up of the thermal engine 2, the first motor 30 drives the crankshaft 3 and the first pulley 21 connected to the crankshaft 3.

[0040] According to the present invention, in order to prevent the tension in the span 26c of the belt 26 (immediately downstream of the first pulley 21 in the direction of belt movement) from dropping below a predetermined level, the second motor 23 is operated by the programmable control unit 34 to provide effective torque to the second pulley 22. This additional torque causes an increase in the tension in the span 26c of the belt 26, thus eliminating the apparent technical problem.

[0041] To better understand the effect of the additional torque according to the present invention Figure 3 and Figure 4 The tension trend of belt 26 in the accessory drive device of a conventional powertrain and the accessory drive device of the powertrain of the present invention is shown.

[0042] Specifically, tension was measured in three spans 26a, 26b, and 26c, respectively, between the second pulley 22 and the third pulley 24, between the third pulley 24 and the first pulley 21, and between the first pulley 21 and the second pulley 22, and is shown as a function of time in a graph. The tension trend was observed during the time interval from 0 to 2 seconds with the thermal engine off (driven by an additional motor 6); from 2 seconds onwards, the tension trend was observed during the start-up phase of the thermal engine 2 using the first motor 30.

[0043] from Figure 3 It can be easily seen that when the motor is driven, the average belt tension is approximately 350 N. Significant tension oscillations occur during startup in the belt span 26c, peak-to-peak at approximately 400 N, with the minimum peak value being approximately 20-30 N. Given the presence of torsional vibrations caused by combustion during startup, such low values, essentially due to the inertia of the second motor 23, can confirm slippage and noise.

[0044] Figure 4 This illustrates the tendency of the tension when starting with the first motor 30 while an additional torque is transmitted from the second motor 23 to the second pulley 22.

[0045] The effective torque to be transmitted to the second pulley 22 can be easily determined experimentally. For example, for a 1.0-liter three-cylinder engine, the required effective torque is only about 5 Nm. The effective torque must be maintained only during the engine's first ignition cycle; once stable combustion is achieved, the effective torque is no longer needed and can be interrupted.

[0046] from Figure 4 It can be seen that the effect of increasing the tension value in the 26c span of the 26 belt is obvious, with the minimum peak value being approximately 210N.

[0047] Finally, it is clear that modifications and variations can be made to the described power system 1 without departing from the scope defined by the claims.

Claims

1. A powertrain for a vehicle, the powertrain comprising: An internal combustion engine (2) is provided with a crankshaft (3); The first motor (30) operates at least as a starter motor and is located on the first side of the transmission (T) facing the vehicle during the use of the internal combustion engine (2); Accessory driving device (19), the accessory driving device (19) comprising: The first pulley (21) is connected to one end (20) of the crankshaft (3) on a second side opposite to the transmission (T) of the vehicle during the use of the internal combustion engine (2); The second motor (23) is located on the second side of the internal combustion engine (2); The second pulley (22) is connected to the second motor (23); At least a third pulley (24) is connected to an accessory (25) of the internal combustion engine (2); A belt (26) connects the first pulley (21), the second pulley (22) and the third pulley (24) together to rotate in the same direction of rotation (R) as the crankshaft (3); The first span (26a) of the belt (26) extends along the direction of rotation between the second pulley (22) and the third pulley (24), and the second span (26c) of the belt (26) extends along the direction of rotation between the first pulley (21) and the second pulley (22); and Tensioner (28), which acts on the first span (26a) of the belt (26); Programmable control unit (34), The powertrain is characterized in that the programmable control unit (34) is programmed to control the second motor (23) so as to transmit effective torque to the second pulley (22) by means of the first motor (30) during the start-up of the internal combustion engine (2) so as to maintain a predetermined minimum tension level in the second span (26c) of the belt (26) in the rotational direction.

2. The power system according to claim 1, characterized in that, The system includes a hybrid power module equipped with an additional motor (6) and a disengagement clutch (7) designed to selectively connect the additional motor (6) to the crankshaft (3).

3. The power system according to claim 2, characterized in that, The additional motor (6) is reversible and can operate as a motor or a generator depending on the operating conditions, and is characterized in that the second motor (23) is used as a motor.

4. A control method for a power system according to claim 1, characterized in that, Includes the following steps: During the start-up of the internal combustion engine (2), the second motor (23) is driven by the first motor (30) to transmit effective torque to the second pulley (22) so as to maintain a predetermined minimum tension level in the second span (26c) of the belt (26) in the direction of rotation.

5. The control method according to claim 4, wherein the powertrain includes a hybrid power module equipped with an additional motor (6) and a disengagement clutch (7) designed to selectively connect the additional motor (6) to the crankshaft (3), the method comprising the following steps: Depending on the operating conditions, the additional motor (6) may be operated as a motor or as a generator, and the second motor (23) may be operated as a motor.

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