Motor vehicle drive device

Abstract

Motor vehicle drive device for connecting an internal combustion engine (1) to an electromechanical energy converter (2), wherein this energy converter is configured for starting the internal combustion engine, and with a starter-generator transmission (5) comprising a first drive train (3) which is configured for transmitting a torque from the electromechanical energy converter (2) to the internal combustion engine (1) when starting the internal combustion engine and wherein this transmission (5) has a reduction gear ratio in the direction from the electromechanical energy converter (2) to the internal combustion engine (1) and comprising a second drive train (4) which is configured for transmitting a torque at least temporarily in the direction from the internal combustion engine (1) to the electromechanical energy converter (2) and wherein the second drive train (4) is arranged parallel to the first drive train (3) with respect to the torque transmission between the electromechanical energy converter (2) and the internal combustion engine (1), characterized by the fact that the first drive train (3) has a one-way coupling which is arranged such that a torque can be transmitted from the electromechanical energy converter (2) to the internal combustion engine (1) via this drive train (3) when the internal combustion engine (1) is started and that the second drive train (4) has a speed-sensitive clutch (6) which is open until a first speed threshold is reached, so that in this state no torque can be transferred from the internal combustion engine (1) to the electromechanical energy converter (2) via the second drive train (4) and that the speed-sensitive clutch (6) is closed from the moment this first speed threshold is exceeded and that the one-way clutch makes it possible, during the phases in which the internal combustion engine alone or together with the starter generator provides drive power for the propulsion of the motor vehicle, that the starter generator gearbox is only running freely, meaning no power can be transmitted through it.

Description

[0001] The invention relates to a motor vehicle drive device comprising an internal combustion engine and an electromechanical energy converter; a motor vehicle drive device according to the preamble of the first claim is known from DE 199 41 705 A1.

[0002] The invention is described below using a motor vehicle powertrain for a passenger car; this is not to be understood as limiting the invention to such an application. Motor vehicles frequently use a combination of an internal combustion engine and an electromechanical energy converter in the form of a so-called hybrid drive. If the electromechanical energy converter is designed to be "large," meaning it can continuously provide more than 35 kW of power, the functional design (starting, driving, recuperation, etc.) is simplified; that is, this large electromechanical energy converter can easily be used to start the internal combustion engine and to propel the vehicle. However, a disadvantage of such a configuration is that such a large electromechanical energy converter requires a large amount of installation space, which is generally disadvantageous because the available installation space is limited.A “small” electromechanical energy converter, i.e. an energy converter with which no more than 35 kW of power can be continuously provided, can be used with a corresponding gear ratio to start the internal combustion engine, but is limited due to this gear ratio and due to speed limits when driving the motor vehicle.

[0003] From JP 2004-278367 A, an internal combustion engine control system is known in which a drive motor also starts an internal combustion engine in a hybrid vehicle.

[0004] The object of the invention is to provide an improved motor vehicle drive system based on the known prior art. This object is achieved by a motor vehicle drive system according to the first claim; preferred embodiments of the invention are the subject of the dependent claims.

[0005] A fundamental aspect of the invention is to connect the output shaft of an internal combustion engine with the output shaft of an electromechanical energy converter, a so-called starter-generator. Two parallel drive trains are provided for this connection, with "parallel" referring to the torque transmission of these two drive trains. Furthermore, each of these two drive trains has a torque transmission device for interrupting the torque transmission. The first of these two drive trains has a starter-generator gearbox with a reduction gear ratio in the direction of power transmission from the output shaft of the electromechanical energy converter to the output shaft of the internal combustion engine. The second drive train, i.e., the drive train parallel to the first, has a 1:1 gear ratio, particularly for torque transmission.

[0006] Furthermore, the torque transmission device incorporated in the first drive train is designed as a clutch, preferably as a one-way clutch or a so-called starter freewheel. This one-way clutch has a locking direction, whereby torque transmission is enabled in the locking direction and torque transmission is not enabled, at least temporarily or permanently, in the opposite direction. A one-way clutch as such is known from the prior art, in particular as a freewheel, and preferably the one-way clutch is designed as a switchable freewheel, a switchable freewheel as such being also known from the prior art.

[0007] Furthermore, preferably the torque transmission device of the second drive train is designed as a speed-sensitive torque transmission device and preferably as a centrifugal clutch, which enables torque transmission from the output shaft of the internal combustion engine to the output shaft of the electromechanical energy converter above a predefinable first speed threshold (closed state) and prevents it below this first speed threshold (open state).

[0008] The proposed vehicle drive system thus enables torque transmission from the starter-generator to the internal combustion engine, particularly during engine start-up, via the first drivetrain, thereby increasing the torque from the starter-generator to the engine. Furthermore, the proposed vehicle drive system enables torque transmission from the engine to the starter-generator, or vice versa, via the second drivetrain, particularly after engine start-up, without any torque increase due to the 1:1 gear ratio of the second drivetrain. Investigations have shown that an efficient hybrid drive system can be implemented with such a system.

[0009] In other words, an objective of the invention is to provide a motor vehicle drive device for a hybrid powertrain, i.e., a motor vehicle powertrain with an internal combustion engine as the primary drive and an electromechanical energy converter as the secondary drive. The proposed motor vehicle drive device, and in particular the electromechanical energy converter, provides sufficient torque not only at low speeds, especially when starting the internal combustion engine, but also at high speeds, especially at output shaft speeds of more than 2000 rpm, for propelling a motor vehicle.

[0010] This torque provision is made possible despite the small size of the vehicle drive unit, particularly the starter generator. Preferably, the starter generator has a drive power of less than 35 kW, preferably less than 25 kW, more preferably less than 20 kW, and more preferably less than 12 kW. Particularly in connection with a passenger car, the starter generator has a drive power of preferably up to 35 kW, and more preferably, in connection with a motorcycle, the starter generator has a drive power of up to 20 kW.

[0011] Another key aspect of the proposed invention is the use of the so-called starter-generator transmission, which also includes the one-way clutch, or is connected to it for torque transmission. Preferably, the one-way clutch, with respect to torque transmission from the output shaft of the electromechanical energy converter to the output shaft of the internal combustion engine, is arranged upstream of the starter-generator transmission, or more preferably downstream of it. Furthermore, the vehicle drive system, in combination with this one-way clutch (first drivetrain), additionally includes the speed-sensitive clutch (second drivetrain), wherein the one-way clutch is arranged in the first drivetrain and the speed-sensitive clutch in the second drivetrain.The starter-generator transmission has an input shaft which can be connected to the output shaft of the electromechanical energy converter, at least temporarily, for torque transmission, or is permanently connected to it. Furthermore, the output shaft of the internal combustion engine, in particular a so-called crankshaft of the internal combustion engine, can be connected to an output shaft of the starter-generator transmission, at least temporarily, for torque transmission, or is preferably permanently connected to it.

[0012] Furthermore, the starter generator transmission, with regard to the torque transmission from the input shaft to the output shaft of this transmission, and in particular in the power transmission from the electromechanical energy converter to the internal combustion engine via the starter generator transmission, has a reduction in speed.

[0013] Furthermore, the speed-sensitive clutch can be connected to the output shaft of the electromechanical energy converter, at least temporarily, for torque transmission, or is permanently connected to it in a torque-conducting manner. The speed-sensitive clutch is designed such that it is open until the first speed threshold is reached and closed above this first speed threshold, meaning that no torque can be transmitted via the speed-sensitive clutch until this first speed threshold is reached. Structurally, the speed-sensitive clutch is preferably designed as a centrifugal clutch. More preferably, this first speed threshold is selected from a range that corresponds to the so-called idle speed of the internal combustion engine.For the purposes of the invention, this idle speed is understood to be the speed of the internal combustion engine at which the engine can be operated without a driving requirement, particularly when the vehicle is stationary, or without driver intervention. Preferably, this idle speed, depending on the engine design, especially in the case of a reciprocating internal combustion engine, lies in a range of 650 rpm to 1000 rpm.

[0014] Preferably, the first speed threshold is in a range that is greater than 0.75 times the idle speed of the internal combustion engine, more preferably 0.85 times and particularly preferably 0.95 times, and further preferably this range is less than or equal to 1.05 times the idle speed of the internal combustion engine, more preferably less than or equal to 1.0 times this idle speed, and more preferably less than or equal to 0.97 times this idle speed.

[0015] Functionally, the speed-sensitive clutch is designed as a so-called normally open clutch and is therefore open in the unactuated state, particularly below the first speed threshold. Specifically, the speed-sensitive clutch is open during the starting of the internal combustion engine via the electromechanical energy converter. In the open state of the speed-sensitive clutch, no torque transmission is possible through it and thus via the second drivetrain; in particular, there is no mechanical connection with a 1:1 transmission ratio from the electromechanical energy converter to the internal combustion engine. In the described situation of starting the internal combustion engine, the second drivetrain is open, and the first drivetrain transmits drive power.The drive power is therefore transferred from the starter generator via the starter generator gearbox when the internal combustion engine is started, and the selected reduction in speed increases the torque provided by the electromechanical energy converter and acting on the output shaft of the internal combustion engine.

[0016] When the first speed threshold is reached or exceeded, particularly during the starting process of the internal combustion engine, i.e., when the electromechanical energy converter has accelerated the output shaft of the internal combustion engine to a speed sufficient for starting the engine and the engine is brought into firing operation, the speed-sensitive clutch engages due to the resulting speed conditions on the second drive train. Preferably, the first speed threshold is selected as described above such that this engagement of the speed-sensitive clutch occurs at a speed "just" below the idle speed of the internal combustion engine at the so-called engagement point.

[0017] When the speed-sensitive clutch is engaged, torque can be transmitted from the internal combustion engine to the electromechanical energy converter via this clutch and thus via the second drivetrain. From this point onward (reaching the engagement point), torque from the electromechanical energy converter can preferably only be transmitted via the speed-sensitive clutch, resulting in a 1:1 speed ratio between the output shaft of the internal combustion engine and the output shaft of the electromechanical energy converter. This 1:1 speed ratio arises because the one-way clutch in the first drivetrain is open due to the speed ratios established in the second drivetrain when the speed-sensitive clutch is engaged, and power transmission therefore occurs via the second drivetrain.

[0018] In particular, the one-way clutch makes it possible for the starter-generator transmission to run freely during the phases in which the internal combustion engine alone or preferably together with the starter-generator provides drive power for the propulsion of the motor vehicle, i.e., no power can be transmitted with it.

[0019] Conversely, the torque transmission in the second drivetrain, with its speed-sensitive clutch, is bidirectional, particularly due to the direct coupling connection of this clutch. This allows torque from the starter-generator, especially for accelerating the vehicle, to be delivered to the internal combustion engine and thus to the vehicle's drive system. In the opposite direction of drive, i.e., from the internal combustion engine to the electromechanical energy converter, the proposed vehicle drive system enables energy recuperation.

[0020] Preferably, recuperation enables the charging of an electrochemical energy storage device, preferably a battery, whereby the electromechanical energy converter operates in generator mode during recuperation. When the internal combustion engine is brought to a standstill, particularly by means of a start-stop system as controlled by an engine control unit, or due to the vehicle being switched off normally, the speed-sensitive clutch opens upon reaching or falling below the first speed threshold, and no further torque transmission via the second drivetrain is possible. In this case, the internal combustion engine can be restarted via the first drivetrain, particularly from a standstill, using the starter-generator and the starter-generator transmission.

[0021] In a preferred embodiment, the starter-generator transmission is designed as a planetary gear with at least one planetary gear, and more preferably, the starter-generator transmission is designed as a spur gear with axes parallel to each other and offset from one another. Even more preferably, the starter-generator transmission is designed as a combination of a spur gear and a planetary gear. In particular, an embodiment in which the starter-generator transmission is designed completely or partially as a planetary gear (such gears are also frequently referred to as planetary gears) offers the advantage that the entire system can be mounted on a single shaft and requires less installation space.

[0022] In a preferred embodiment of the invention, the motor vehicle drive device, in particular the device comprising the components: - Centrifugal clutch, - One-way coupling and - Starter-generator transmission, connected to the internal combustion engine or to the electromechanical energy converter or to both, by a traction device, preferably a belt drive or preferably a chain drive, or preferably a gear drive, or preferably directly. Preferably, such a transmission for connecting the internal combustion engine or the electromechanical energy converter has a fixed gear ratio; more preferably, such a transmission is switchable in at least two stages. In particular, by means of such a transmission, the internal combustion engine or the electromechanical energy converter can be adapted to the respective load requirement.

[0023] In a further preferred embodiment of the invention, at least the starter-generator transmission and the internal combustion engine or the electromechanical energy converter, or all three, share a common oil supply. More preferably, at least the starter-generator transmission is structurally integrated into the electromechanical energy converter or the internal combustion engine. In particular, the proposed measures allow for a small installation space requirement for the vehicle drive system. Furthermore, the above-described design of the vehicle drive system makes it possible to cover the entire or at least a large part of the speed range for propelling the vehicle (starting the internal combustion engine, driving) with electrical assistance from the starter-generator, despite the use of a "small" electromechanical energy converter.

[0024] In a preferred embodiment of the invention, the starter generator transmission for power transmission from the input shaft of the starter generator transmission to its output shaft, i.e., power transmission from the electromechanical energy converter to the internal combustion engine, has a gear ratio from a range in which the reduction ratio is greater than 1:6, preferably greater than 1:4, and more preferably greater than or equal to 1:3, and further preferably this gear ratio is less than 1:2, more preferably less than 1:2.5, and particularly preferably less than 1:2.75.Investigations have shown that a motor vehicle drive device can be represented with a translation from the proposed range, which, with a small installation space requirement, can provide on the one hand sufficient drive power, in particular sufficient drive torque to accelerate the internal combustion engine from standstill (starting process) and on the other hand to drive the motor vehicle while driving.

[0025] An embodiment of the invention is explained in more detail below with reference to a schematic figure, showing: Fig. 1: a schematic representation of a motor vehicle drive system with a motor vehicle drive device.

[0026] The vehicle drive system connects the internal combustion engine 1, which is designed as a reciprocating internal combustion engine with several cylinders, to an electromechanical energy converter 2 designed as a starter-generator. The vehicle drive system comprises the first drive train 3 and the second drive train 4.

[0027] The first drive train 3 incorporates the starter-generator transmission 5 with a one-way clutch. This transmission 5 has a reduced gear ratio in the torque transmission direction 7 from the electromechanical starter-generator 2 to the internal combustion engine 1. This reduced torque transmission direction 7 is determined by the one-way clutch, which can also be considered a reversing clutch. This gear ratio of the starter-generator transmission 5 increases the torque for starting the internal combustion engine 1, which is provided by the electromechanical starter-generator 2. The one-way clutch is integrated into the first drive train 3 in such a way that the torque can be transmitted in the torque transmission direction 7.

[0028] When the internal combustion engine 1 is started, it is pulled up to starting speed by the electromechanical starter generator 2 via the first drive train 3. Once starting speed is reached, the internal combustion engine 1 is switched to firing operation. When the internal combustion engine reaches the first speed threshold, which is set as a speed slightly below the engine's idle speed, the speed-sensitive clutch 6 located in the second drive train 4 engages the torque and thus also the speed transmission in the second drive train 4.

[0029] The second drivetrain 4 has a 1:1 gear ratio, meaning it is designed as a direct drive. The speed-sensitive clutch 6, when engaged (first speed threshold exceeded), directly couples the internal combustion engine 1 to the electromechanical energy converter 2. This enables bidirectional torque transmission 8 between the internal combustion engine 1 and the electromechanical starter-generator 2 via the second drivetrain 4. In recuperation mode, the electromechanical starter-generator 2 can be driven by power from the vehicle's drivetrain 9, for example, during coasting. Furthermore, with the speed-sensitive clutch 6 engaged, power can also be transferred from the internal combustion engine 1 to the electromechanical starter-generator 2. In another operating mode, e.g.,When the motor vehicle is powered by the internal combustion engine 1, the starter generator 2 can provide additional power and thus be used in addition to the drive; a drive of the motor vehicle is therefore possible either purely electric, purely internal combustion engine or combined.

[0030] By closing the speed-sensitive clutch 6, the one-way clutch in the starter-generator transmission 5 opens due to the speed conditions established in the first drive train 3, and the starter-generator transmission 5 runs without torque transmission and thus with minimal losses. After the internal combustion engine 1 is switched off and the speed in the second drive train 4 has dropped, the speed-sensitive clutch 6 opens (first speed threshold undershot), and the internal combustion engine 1 can then be restarted by the electromechanical starter-generator 2 via the first drive train 3. Reference symbol list 1 internal combustion engine 2 electromechanical energy converters 3 first drivetrain 4 second drivetrain 5 Starter generator gearboxes with one-way clutch 6 Speed-sensitive clutch 7 possible torque transmission directions in the first drive train 8 possible torque transmission directions in the second drive train 9 Power transmission to the vehicle powertrain

Claims

[1] Motor vehicle drive device for connecting an internal combustion engine (1) to an electromechanical energy converter (2), wherein this energy converter is configured for starting the internal combustion engine, and with a starter-generator transmission (5) comprising a first drive train (3) which is configured for transmitting a torque from the electromechanical energy converter (2) to the internal combustion engine (1) when starting the internal combustion engine and wherein this transmission (5) has a reduction gear ratio in the direction from the electromechanical energy converter (2) to the internal combustion engine (1) and comprising a second drive train (4) which is configured for transmitting a torque at least temporarily in the direction from the internal combustion engine (1) to the electromechanical energy converter (2) and wherein the second drive train (4) is arranged parallel to the first drive train (3) with respect to the torque transmission between the electromechanical energy converter (2) and the internal combustion engine (1), characterized by , that the first drive train (3) has a one-way coupling which is arranged such that a torque can be transmitted from the electromechanical energy converter (2) to the internal combustion engine (1) via this drive train (3) when the internal combustion engine (1) is started and that the second drive train (4) has a speed-sensitive clutch (6) which is open until a first speed threshold is reached, so that in this state no torque can be transferred from the internal combustion engine (1) to the electromechanical energy converter (2) via the second drive train (4) and that the speed-sensitive clutch (6) is closed from the moment this first speed threshold is exceeded and that the one-way clutch makes it possible, during the phases in which the internal combustion engine alone or together with the starter generator provides drive power for the propulsion of the motor vehicle, that the starter generator gearbox is only running freely, meaning no power can be transmitted through it. [2] Motor vehicle drive device according to claim 1, characterized by , that the speed-sensitive clutch (6) is designed as a centrifugal clutch. [3] Motor vehicle drive device according to one of the preceding claims, characterized by that the one-way clutch is designed as a freewheel. [4] Motor vehicle drive device according to any of the preceding claims, characterized by , that the starter generator transmission (5) has a gear ratio in the direction from the electromechanical energy converter (2) to the internal combustion engine (1) between 1:6 and 1:

2. [5] Motor vehicle drive device according to any of the preceding claims, characterized by , that the first speed threshold is greater than 0.75 times the idle speed of the internal combustion engine and less than 1.05 times the idle speed. [6] Motor vehicle drive device according to any of the preceding claims, characterized by , that the starter generator transmission (5) has a planetary gear unit or consists of a planetary gear unit. [7] Motor vehicle propulsion system in which an internal combustion engine (1) and an electromechanical energy converter (2) are connected to the motor vehicle propulsion device according to one of the preceding claims for propelling a motor vehicle. [8] Motor vehicle drive system according to claim 8, characterized by, that the starter generator transmission (5) and at least the internal combustion engine (1) or the starter generator transmission (5) and at least the electromechanical energy converter (2) have a common oil supply. [9] Motor vehicle with a motor vehicle propulsion system according to one of claims 8 or 9.

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