WO2020079267A1

WO2020079267A1 - A hybrid drive module, and a method for improving performance of such hybrid drive module

Info

Publication number: WO2020079267A1
Application number: PCT/EP2019/078452
Authority: WO
Inventors: Hans AULIN
Original assignee: Borgwarner Sweden Ab
Priority date: 2018-10-18
Filing date: 2019-10-18
Publication date: 2020-04-23
Also published as: EP3867119A1

Abstract

A method (200) for reducing acceleration variations of an output shaft (102) of a hybrid drive module (100), said hybrid drive module (100) comprising an electrical motor (110) being connected to the output shaft (102), wherein a crankshaft (22) of an associated internal combustion engine (20) is connected to an input shaft (101) of the hybrid drive module, and wherein the input shaft (101) is connected to the output shaft (102) via a clutch (130), said method comprising: - determining (201) a target RPM difference between the crankshaft (22) and the output shaft (102), - calculating (202) an actual RPM difference between the crankshaft (22) and the output shaft (102), and - determining (203) a pressure to be applied by actuation of the clutch (130) based on the target RPM difference, the actual RPM difference and/or on a current torque output from the internal combustion engine (20) to achieve an actual RPM difference essentially matching the target RPM difference.

Description

A HYBRID DRIVE MODULE, AND A METHOD FOR IMPROVING

PERFORMANCE OF SUCH HYBRID DRIVE MODULE

Technical Field

The present invention relates to a hybrid drive module and aspects of methods for improving operating performance of such hybrid drive module, in particular for reducing angular acceleration of mass. It also relates to a hybrid vehicle comprising a hybrid drive module. Background

Vibration and noise are common problems in combustion engine-based vehicles due to the crankshaft being accelerated/decelerated during combustion in the cylinder. This may result in large alternating torque pulsations during rotation of the crankshaft. The torque pulsations can be dampened in various ways, e.g. by extending the piston rod, by providing a large flywheel or by increasing the number of cylinders to provide a more continuous torque on the crankshaft. In addition, mass forces arise due to the internal masses being accelerated back and forth causing oscillating forces; these can typically be balanced by means of increasing the cylinder count.

In the modern hybrid drive trains of today, it is common to use combustion engines with fewer cylinders. Hybrid systems are therefore susceptible to issues with vibrations. One way of dealing with such issues is using complex and expensive vibration dampeners, such as dual mass flywheels and centrifugal pendulum absorbers. These are not only costly, but also space consuming as well as heavy so it is desired to find a way to reduce the need for such components or at least allow use of smaller, less complex mechanical vibration dampeners.

As hybrid drivelines for passenger cars are gaining interest, so does the number of solutions for such applications that are being proposed. One such proposal is to provide the hybrid functionality as a separate module, which is added to the existing driveline. An example of an existing hybrid drive module includes a first sprocket which is intended to be connected to the crankshaft of the internal combustion engine indirectly via a dual mass flywheel and a disconnect clutch, and an electrical motor being drivingly connected to a second sprocket. The sprockets are connected by means of a belt or chain in order to allow for various driving modes such as pure electrical driving, recuperation, traction mode, and boost. The electric motor may also in other examples be arranged directly on a shaft in the driveline, with the rotor of the electric motor being fixedly connected and providing power directly to the shaft without having to use any belt or chain.

In the prior art hybrid module there is limited means for reducing the vibrations of the associated internal combustion engine due to the shortage of space in these types of applications. As such, there exists a need for a method of reducing the acceleration variations.

Summary

It is thus an object of the teachings herein to provide an improved hybrid drive module overcoming the disadvantages of prior art solutions.

An idea of the present invention is to provide a hybrid drive module, as well as a method for such hybrid drive module, utilizing the built-in clutch to provide active dampening.

According to a first aspect, a method for reducing acceleration variations of an output shaft of a hybrid drive module is provided. The hybrid drive module comprising an electrical motor being connected to the output shaft, and a crankshaft of an associated internal combustion engine is connected to an input shaft of the hybrid drive module. The input shaft is connected to the output shaft via a clutch. The method comprises determining a target RPM difference between the crankshaft and the output shaft, calculating an actual RPM difference between the crankshaft and the output shaft, and determining a pressure to be applied by actuation of the clutch based on the target RPM difference, the actual RPM difference and/or on a current torque output from the internal combustion engine to achieve an actual RPM difference essentially matching the target RPM difference. By determining a target RPM difference between the crankshaft and the output shaft by adjusting the pressure in the clutch can at least some of the vibrations from the internal combustion engine be absorbed. This is beneficial as it allows the use of a simpler, more lightweight flywheel while still reducing the amount of vibrations transferred from the engine through the hybrid drive module.

In one embodiment, the actual RPM difference between the crankshaft and the output shaft is always maintained such that it is zero or that the crankshaft rotates faster than the output shaft. Situations where the crankshaft rotates slower than the output shaft of the hybrid drive, for longer periods or briefly in an oscillating manner will restrict the dampening functionality. Keeping a minimum differential speed over the clutch while still having enough differential speed to reach the angular acceleration targets is therefore important, also for efficiency purposes.

The pressure may be determined based on an RPM difference error calculated between the actual RPM difference and the target RPM difference and/or on a current torque output from the internal combustion engine. Using the error, either or in combination its magnitude, derivate or integral, as a control parameter allows accurate and smooth regulation of the clutch to achieve an actual RPM difference closely following the target RPM difference.

In one embodiment, the pressure applied by the clutch and the

corresponding current torque output of the internal combustion engine at time intervals where the actual RPM difference is essentially constant are stored in a memory.

The pressure applied by the clutch may further be determined based on the current torque output from the internal combustion engine, which is used to retrieve a corresponding clutch pressure stored in the memory. Also taking into account the current torque output provides an even closer regulation of the clutch and the actual RPM difference in dynamic situations. By having stored torque outputs along with corresponding required clutch pressures for achieving a certain slip, the actuation of the clutch can be controlled more rapidly by monitoring the torque output and choosing a corresponding clutch pressure stored in the memory.

Further still, the target RPM difference may be determined further based on the internal combustion engine RPM and the current load on the internal combustion engine. As the engine RPM and the load on the internal combustion engine are important parameters in the characteristics of the vibrations it produces is may also be important to take this into account when determining a target RPM difference. The target RPM difference is the main source of vibration reduction in the hybrid drive module, and matching this to the operating conditions of the associated engine are beneficial for achieving efficient reduction of vibrations. The matching of the target RPM difference with the engine operating conditions may be done beforehand for each engine type in a controlled test where the optimal target RPM difference for each running condition is determined. It may also be performed continuously during operation of the engine, or a combination of both.

In one embodiment, the target RPM difference is determined based on

RPM variations on the output shaft of the hybrid drive module. As it is the vibrations transmitted by the output shaft of the hybrid drive module that is to be reduced, actually measuring these and using this as feedback into the control of the clutch will provide an even better reduction of vibrations in the drivetrain.

In a second aspect is a hybrid drive module provided. The hybrid drive module comprising a housing enclosing an electrical motor, the electrical motor being connected to an output shaft of the hybrid drive module. A crankshaft of an associated internal combustion engine is connected to an input shaft of the hybrid drive module. The input shaft is connected to the output shaft via a clutch also enclosed within the housing, the hybrid drive module further comprising a control unit and a memory. The hybrid drive module being configured to perform the method of the first aspect. The hybrid drive module according to the second aspect provides improved reduction of the vibrations that are produced by the internal combustion engine, while allowing the associated mechanical vibration dampers (e.g. the flywheel) to be made less complex and heavy.

In an embodiment of the teachings herein, the electrical motor is arranged in a coaxial manner on the output shaft downstream of the clutch.

In yet another embodiment, the electrical motor is arranged in an off-axis manner in relation to the output shaft of the hybrid drive module. The electrical motor being connected via a continuous member drive to a second sprocket on the output shaft of the hybrid drive module.

In one embodiment is a dual mass flywheel arranged between the input shaft and the clutch. Having the clutch downstream of the flywheel allows the clutch to reduce the vibrations that are transmitted through the flywheel.

The hybrid drive module may further comprise a centrifugal pendulum absorber, achieving a further reduction of the vibrations from the internal combustion engine.

In a third aspect is a hybrid vehicle provided, comprising the hybrid drive module of the second aspect.

Further advantages and embodiments are disclosed below and in the appended claims.

Brief Description of the Drawings

Embodiments of the teachings herein will be described in further detail in the following with reference to the accompanying drawings which illustrate non-limiting examples on how the embodiments can be reduced into practice and in which:

Fig. la shows a schematic outline of a hybrid drive module according to an embodiment; Fig. lb shows a schematic outline of a hybrid drive module according to an embodiment;

Fig. 2a is a cross-sectional view of an exemplary dual mass flywheel according to an embodiment of the hybrid drive module shown in Fig. 1;

Fig. 2b is a cross-sectional view of an exemplary dual mass flywheel according to an embodiment of the hybrid drive module shown in Fig. 1;

Fig. 3 shows two diagrams representing operation of the hybrid drive module;

Fig. 4 shows three diagrams representing operation of the hybrid drive module; and

Fig. 5 is a schematic view of a method according to an embodiment. Detailed description

With reference to Fig. la, a schematic outline of an engine/hybrid assembly 10 of a vehicle is shown, comprising a hybrid drive module 100 according to an embodiment. The associated vehicle is typically a passenger car, and the engine/hybrid assembly 10 used for propulsion of the vehicle comprises an internal combustion engine 20 and the hybrid drive module 100. As will be explained in the following the hybrid drive module 100 is mechanically connected to a crankshaft 22 of the internal combustion engine 20 in order to provide additional drive torque to a transmission 160 arranged in series with the hybrid drive module 100. Hence, the transmission is also connected to the crankshaft 22 as is evident from Fig. la.

The hybrid drive module 100 thus comprises an input shaft 101 that is connected to the crankshaft 22 of the internal combustion engine 20, and an output shaft 102 that is connected to downstream driveline components such as the transmission 160.

The hybrid drive module 100 comprises an electrical motor 110 and a continuous member drive 120, here in the form of a chain drive, connecting the electrical motor 110 with the crankshaft 22. The electrical motor 110 is for this purpose driving a first sprocket 122 of the chain drive 120, whereby upon activation of the electrical motor 110 rotational movement of the first sprocket 122 is transmitted to a second sprocket 124 of the chain drive 120 via a chain 126.

The second sprocket 124 is drivingly connected to the output shaft 102, which is indirectly connected to the crankshaft 22 via one or more couplings. In the embodiment shown in Fig. la, the second sprocket 124 is connected to the output shaft 102 which is connected to a disconnect clutch 130 receiving driving torque from a dual mass flywheel 140. The dual mass flywheel 140 has a primary mass 142 and a secondary mass 144, typically rotationally connected to each other via one or more springs. For serial two-clutch systems, commonly denoted hybrid P2 systems, the disconnect clutch 130 is often referred to as the K0 clutch. The dual mass flywheel 140 (which could be replaced by another torsional damping/absorption device), receives input torque directly from the crankshaft 22 via the input shaft 101. The dual mass flywheel 140 may also be connected directly or indirectly via for instance the clutch 130 to a centrifugal pendulum absorber (CPA) 148.

Also illustrated in Fig. la is a further optional clutch 150, here representing a launch clutch 150. Again referring to P2 systems, the launch clutch 150 is often referred to as the Kl clutch. The launch clutch 150 is arranged downstream, i.e. on the output side of the hybrid drive module 100 upstream a transmission 160. It should be realized that the launch clutch 150 could be replaced by a torque converter or similar.

As is also shown in Fig. la the electrical motor 110, and the clutch 130, is connected to a control unit 170 being configured to control the operation of the electrical motor 110 and the clutch 130 as will be further explained below. The control unit 170 is further connected to a read/write memory 180 for storing and accessing data associated with the vehicle, the driveline, the hybrid drive module 100 and the associated internal combustion engine 20.

The configuration shown in Fig. la is an off-axis configuration, where the electrical motor 110 is arranged in parallel but offset in relation to the longitudinal axis of the input shaft 101 and the output shaft 102 of the hybrid drive module 100, as well as in relation to the crankshaft 22 of the engine 20.

In Fig. lb however, the electrical drive module 100 is arranged in an on- axis configuration. Here, the electrical motor 110 is arranged in coaxially on the output shaft 102 of the hybrid drive module 100 and is thus preferably also coaxial with the input shaft 101 of the hybrid drive module 100 and the crank shaft 22 of the internal combustion engine 20. With the rotor of the electrical motor 110 arranged directly connected to the output shaft 102 is the need for a continuous member drive 120 removed. Both on-axis and off-axis configurations are commonly used in hybrid drive applications, and the application at hand dictates whether on- or off-axis is the best choice. With the exception of the arrangement of the electrical motor 110, the embodiment shown in Fig. lb is identical to that of Fig. la and therefore is the detailed description of the components and features of Fig. la applicable also to Fig. lb.

Fig. 2a is a cross sectional view of an exemplary dual mass flywheel (DMF) 140, to form part of the hybrid drive module 100 of Fig. la. The hybrid drive module 100 being arranged in an off-axis configuration, with the electrical motor 110 connected to the second sprocket 124. The dual mass flywheel 140 comprises the primary mass 142, which is connected to the crankshaft 22 via the input shaft 101, and the secondary mass 144, which transmits torque from the primary mass 142 further downstream. For the purpose of explaining the concepts of vibration damping herein, the secondary mass 144 is considered to also include the masses of the clutch 130, the second sprocket 124 (in

embodiments with off-axis configuration) as well as the CPA 148 (in

embodiments where a CPA is used) and the other thereto connected downstream components of the driveline such as the output shaft 102. However, the secondary mass 144 can also be divided into two separate masses l44a, l44b that are separated by the clutch 130. A first secondary mass component l44a is formed by the output 144 of the dual mass flywheel 140 and the input shaft l30a of the clutch 130 with the thereto-connected discs. A second secondary mass component l44b is formed by the output shaft 130b of the clutch 130, along with the CPA 148 (where applicable), the second sprocket 124 (where applicable) and the other downstream components of the driveline.

Fig. 2b shows a cross sectional view of the dual mass flywheel 140 in an on-axis configuration. As can be seen, the clutch output shaft l30b is now connected to the CPA 148, which is optional, and to the output shaft 102. The electrical motor 110 (not shown in Fig. 2b) is then connected directly onto the output shaft 102 via for instance a spline connection or by any other suitable connection type. The remaining features are shared with the embodiment shown in Fig. 2a and will thus not be described further in relation to Fig. 2b.

Fig. 3 a shows two graphical representations of how the hybrid drive module 100, together with the engine 20, perform during operation. The upper diagram represents actual speeds/velocities of the primary mass 142 (i.e. the RPM of the crankshaft 22, or the thereto connected input shaft 101) of the dual mass flywheel 140, the first secondary mass component l44a (as measured on the clutch input shaft l30a), and the second secondary mass component l44b (as measured on the output shaft 102), as a respective function of time.

The lower diagram is an acceleration diagram depicting the acceleration of the primary mass 142 (as measured on the input shaft 101) and the second secondary mass component l44b (as measured on the output shaft 102) as a function of time.

Both diagrams of Fig. 3 are aligned in time and thus showing

simultaneous measurements of velocities and acceleration of parts of the hybrid module 100. Thus, Fig. 3 illustrates in graphical form, some of the technical effects and advantages of the present invention as described herein.

Referring to the left hand side of the two diagrams; ranging from time mark zero and up to time mark three seconds, i.e. on the left side of the dashed line OP, there is no active dampening of the vibrations.

It can be derived from the top diagram that the magnitude of speed of the input shaft 101, i.e. the primary mass 142, shows a characteristic oscillation throughout the whole time interval. This is expected due to the fact that the input shaft 101 is connected to the crankshaft 22. It is further derivable that also the speed of the second secondary mass component l44b oscillates, however with much smaller amplitude than the primary mass 142. Nevertheless, these oscillations of the speed of the second secondary mass component l44b will to some extent transmit through the output shaft 102 and onwards to the gearbox 160. The oscillations may then affect the speed of the output shaft of the gearbox 160 and form correlating oscillations, which are then transferred throughout the remaining driveline.

Thus, the oscillating speed of the crankshaft 22 will at least to some extent translate to acceleration variations of the output shaft of the gearbox 160. These oscillations will transmit to the wheels of the vehicle causing undesired noise, vibrations and harshness (NVH) issues in the vehicle. It may also cause increased wear of the affected components.

In the bottom diagram, it can be seen that the actual acceleration of the primary mass 142 (i.e. the crankshaft 22) is evidently oscillating with great amplitude, in the range of approximately +/- 600-700 rad/sec². The acceleration of the second secondary mass component l44b, which also represent the acceleration of the input shaft of the gearbox 160, also shows an oscillating pattern, in the range of +/- 150 rad/sec².

According to the embodiments described herein, a target RPM difference between the input shaft 101 and the output shaft 102 that is required to at least to some extent reduce the actual acceleration variations of the second secondary mass component l44b (i.e. of the output shaft 102 of hybrid drive module 100) is determined. The target RPM difference is then compared with the actual RPM difference with the aim to subsequently adjust the actual RPM difference to match the target RPM difference, and this is achieved by means of control of the clutch 130.

The required target RPM difference may for example be determined from the speed curve and/or the acceleration curve of the output shaft of the gearbox 160 by means of reading, processing, calculating, or any combination thereof.

Suitable input for such determination may e.g. comprise measured values from speed sensors, position sensors, or the like. In other embodiments, the target RPM difference is determined from the speed curve and/or the acceleration curve of the output shaft 102 of the hybrid drive module, which corresponds or connects to the input shaft of the gearbox 160, by means of reading, processing, calculating, or any combination thereof. In one embodiment, the target RPM difference is tabulated from the speed and load of the ICE 20.

Still referring to the left hand side of the OP line in the two diagrams of Fig. 3, the method of dampening vibrations is inactivated. The clutch 130 is thereby in default engaged position whereby there is no slip (i.e. actual RPM difference is zero) between the primary mass 142, the first secondary mass component l44a and the second secondary mass component l44b (or between the input shaft 101 and the output shaft 102). Thus, the speed of the primary mass 142 oscillates in the upper diagram while the acceleration oscillates as expected in the lower diagram due to the primary mass 142 being coupled to the crankshaft 22 via the input shaft 101. This applies mutatis mutandis to the second secondary mass component l44b, which speed oscillates in synchronization.

Referring to the right hand side of the two graphs; i.e. on the right side of the OP line, the method of reducing vibrations is activated. From the upper diagram, it is realized that upon activation of the method, the speed/RPM oscillation amplitude of the second secondary mass component l44b is at least to some extent reduced. When the method is activated, an RPM difference is allowed in the clutch 130 between the input shaft 101 and the output shaft 102, or between the first secondary mass component l44a and the second secondary mass component l44b, or between the crankshaft 22 and the output shaft 102. This equates to on one hand a change of the natural turning frequency of the second secondary mass l44b, and on the other hand to a certain degree of quenching of vibrations in the clutch 130 itself. Both these factors weigh in to provide improved vibration dampening in the driveline, and reduces the amount of vibrations that are transferred through the hybrid drive module 100.

Thus, upon activation of micro slip, the clutch 130 is controlled such that the acceleration variations of the crankshaft 22 caused by the engine 20 are to some extent isolated. This effect may be observed also in the lower acceleration diagram where the amplitude of the acceleration variations is substantially reduced.

Still referring to the right hand side of the OP line in Fig. 3, it may be derived that the angular velocity and RPM of the primary mass 142 and the second secondary mass component l44b, are increasing over a period of time. Thus, positive average accelerations may be determined on both sides of the clutch 130 and there is no change of sign over the clutch 130. The method may thus comprise ensuring that an average acceleration of the crankshaft 22 and the output shaft of the gearbox 160 both have equal signs; i.e. ensuring that there is no change of sign for the differential speed direction over the clutch. Put in other words, ensuring that the input shaft 101 rotates faster or with the same speed as the output shaft 102 and that acceleration of the input shaft 101 translates to essentially equal acceleration of the output shaft 102.

The control unit 170 controlling the clutch 130 may comprise a computer capable of carrying out the method according the embodiments of the disclosure and an associated readable medium, i.e. a memory 180, may contain associated logic.

Now referring to Fig. 4, where three separate time synchronized diagrams are shown. The diagrams shows actual measured values from a test vehicle fitted with a hybrid drive module 100 according to the teachings herein.

The upper diagram shows how the K0 torque (i.e. the torque applied by the clutch 130) is matched to that produced by the ICE 120. The torque output value from the ICE 20, which the K0 torque is to be matched to, is preferably an average value, a moving average value and/or a value where a low pass filter has been applied. The moving average may be defined such that the torque output is an average over the last 720° of rotation of the ICE 20 crankshaft 22. The dashed lines indicate between them where the vibration reduction method is switched on. The middle diagram shows the RPM that the primary mass 142 (i.e the input shaft 101) is turning with, as well as the RPM of the second secondary mass l44b (i.e. the output shaft 102). As can be seen, when vibration dampening is activated, the RPM of the second secondary mass l44b settles, after a brief initial oscillation, to a more or less constant RPM being slightly less than that of the primary mass 142, which is essentially the same as the RPM of the crankshaft 22 and the first secondary mass l44a. This RPM difference is set such that losses that occur due to the slip in the clutch 130 are kept as low as possible, vibrations are efficiently reduced and such that the risk that the second secondary mass l44b rotating faster than the primary mass 142 is reduced.

In the lower diagram is the acceleration of the second secondary mass l44b shown. What is desired is to reduce the amplitude of the acceleration variations that are transmitted to the second secondary mass l44b, or to the output shaft 102. It is clearly shown that this is achieved in the portion of the diagram between the dashed lines where the method is activated.

Turning now to Fig. 5 where the method for reducing vibrations is schematically illustrated.

In a first step, the target RPM difference is determined 201. The RPM difference is defined as between the primary mass 142 (or the first secondary mass 144a, or the input shaft 101, which both preferably turns with the same speed as the crankshaft 22 of the ICE 20) and the second secondary mass 144b (or the output shaft 102). I.e. over the clutch 130. As mentioned above, the target RPM difference is set such that the amount of vibrations transferred from the ICE 20 through the clutch 130 are reduced. Also taken into account is that the RPM difference should be small enough to minimize losses due to slippage in the clutch 130. This must also be weighed against the risk of the output shaft 102 rotating faster than the input shaft 101, which is undesired and can cause NVH issues.

The ideal target RPM difference may be tabulated from the current ICE 120 RPM and load, the values of which may be retrieved empirically for each application as mentioned earlier by measuring the characteristics of the engine 20. Additionally, or as an alternative, may the RPM variations on the output shaft 102 be monitored and used as feedback in determining the ideal target RPM difference.

The next step is to calculate 202 the actual RPM difference, this may be performed by subtracting the output shaft 102 RPM (or the RPM of any other component rotating therewith) from the ICE 20 RPM. From this is the error between the target RPM difference and the actual RPM difference calculated 203. The current RPM value from the ICE 20, which is used in the calculation, is preferably an average value, a moving average value and/or a value where a low pass filter has been applied. The moving average may be defined such that it is calculated over the last 720° of rotation of the ICE 20 crankshaft 22.

The clutch 130 is then controlled by means of the control unit 170 to apply a new clutch pressure, allowing the actual RPM difference to essentially match the target RPM difference. The clutch 130 may also/alternatively base the application of pressure on the current torque output from the ICE 20.

As the clutch pressure applied by the clutch 130 and the corresponding current torque output of the internal combustion engine 20 may be stored in the memory 180, this data can be retrieved to achieve a quicker application of a desired clutch pressure. The storing of data of the clutch pressure and the corresponding torque output from the ICE 20 is preferably only done at time intervals where the actual RPM difference is essentially constant.

This data is preferably regularly updated, as a given ICE torque output and a corresponding clutch pressure to achieve a stable RPM difference may change over time due to wear or other factors that may affect the hybrid drive module 100. It is therefore beneficial to not only base the clutch pressure on the torque output from the ICE 20, but to also simultaneously monitor the how the target RPM difference compares to the actual RPM difference and adjust the clutch pressure accordingly if necessary. Such a change is then, as explained above, stored in the memory 180 as a new value of ICE torque output and corresponding clutch pressure, which replaces the old values. The clutch 130 may also be used to start the engine 20, either by using the electric motor 110 and/or the momentum of a vehicle at speed to bump start the engine 20. This process is facilitated by the storing of clutch pressures along with corresponding torque outputs from the ICE 20, as the clutch 130 may quickly be set to apply a certain pressure corresponding to the expected torque required to start the engine 20.

The clutch control may further be based on the actual magnitude of the error between the actual RPM difference and the target RPM difference as well as the derivative and possibly also the integral of the error, i.e. using P, PD, PI or PID regulation.

For a given operating condition when the actual RPM difference has reached the target RPM difference and is constant, the torque transmitted through the clutch 130 should be essentially the same as that delivered by the ICE 20. During a change in target RPM difference when the clutch pressure changes is there however also a slight momentary difference in the torque transferred over the clutch 130 and the torque delivered by the ICE 20.

The steps of the method may naturally be performed in another order than that described above, and the entire sequence is iterated continuously when vibration reduction is desired. A preferred iteration rate is approximately 1 iteration/ lOOms or faster. In addition to what has been stated above, determining the RPMs may be done either by measurements or by estimations. The measurements and/or estimations of the angular velocities may simultaneously and continuously be communicated to the control unit 170 by which the speed is monitored and used as feedback for controlling the clutch 130.

To provide a more stable and less volatile regulation of the vibration reduction method may average values of the measured RPMs be used, as mentioned above. The average values may further be distributed as sequential samples, each sample forming an average value during a specific time period. Such a time period may e.g. be in the range of 1-100 ms.

As mentioned, the method may comprise using the derivative of the RPM of the primary mass 142 (or the input shaft 101, the crankshaft 22 or another component rotating therewith) and of the second secondary mass l44b (or the output shaft 102). This equates to the acceleration of these components, which should as mentioned preferably also follow each other. I.e. when the input shaft 101 is accelerating, the output shaft 102 should preferably also accelerate at the same rate. This is achieved by the iteration of the method, which strives to keep a certain RPM difference (although not necessarily constant during the entire RPM interval) at all times, and will require continuous adjustment of the pressure in the clutch 130 as the ICE 20 accelerates or decelerates.

Accordingly, the clutch 130 can be controlled to allow a small amount of slip, here denoted microslip. In some implementations of the invention, the microslip may comprise providing of a RPM difference continuously. In preferred embodiments, the clutch 130 is controlled according to the target value of RPM difference which may be calculated or tabulated, e.g. by the control unit 170 using feedback attained by means of sensors or the like which are arranged to monitor operation of the hybrid drive module 100.

The microslip facilitates that internal masses of the dual mass flywheel 140, in this case the primary mass 142 and the first secondary mass l44a rotate with the same angular velocity or RPM, which during vibration reduction may exceed the RPM of the second secondary mass component l44b, which is typically connected to the output shaft 102 of the hybrid drive module 100. The microslip of the clutch 130 thus allows the second secondary mass component l44b to a certain extent be isolated from the acceleration variations of the crankshaft 22. The vibrations of the output shaft 102 and in extension also of the output shaft of the gearbox 180 may thereby be substantially reduced or at least to some extent reduced. The clutch 130 may be controlled, selectively controlled or at least partially controlled based on feedback relating to the angular rotation speed of the crankshaft 22 and the speed of the output shaft of the associated gearbox 180.

The feedback relating to the measured rotational speeds may preferably be processed by an on-board controller such as an integral controller or control unit 170 being capable of communicating with and controlling the clutch 130.

The clutch 130 is typically otherwise per default operated in a fully engaged state resulting in zero slip over the clutch under ideal conditions.

The invention as disclosed herein is not limited to the performing of the above described method steps in the consecutive order specified herein, one or more steps may be carried out simultaneously or in an order other than has been explained herein.

Claims

1. A method (200) for reducing acceleration variations of an output shaft (102) of a hybrid drive module (100), said hybrid drive module (100) comprising an electrical motor (110) being connected to the output shaft (102), wherein a crankshaft (22) of an associated internal combustion engine (20) is connected to an input shaft (101) of the hybrid drive module, and wherein the input shaft (101) is connected to the output shaft (102) via a clutch (130), said method comprising:

determining (201) a target RPM difference between the crankshaft (22) and the output shaft (102),

calculating (202) an actual RPM difference between the crankshaft (22) and the output shaft (102), and

determining (203) a pressure to be applied by actuation of the clutch (130) based on the target RPM difference, the actual RPM difference and/or on a current torque output from the internal combustion engine (20) to achieve an actual RPM difference essentially matching the target RPM difference.

2. The method (200) according to claim 1, wherein the actual RPM

difference between the crankshaft (22) and the output shaft (102) is always maintained such that it is zero or that the crankshaft (22) rotates faster than the output shaft (102).

3. The method (200) according to claim 1 or 2, wherein the determining (203) of pressure is based on an RPM difference error calculated between the actual RPM difference and the target RPM difference and/or on a current torque output from the internal combustion engine (20).

4. The method (200) according to any one of the preceding claims, wherein the pressure applied by the clutch (130) and the corresponding current torque output of the internal combustion engine (20) at time intervals where the actual RPM difference is essentially constant are stored in a memory (180).

5. The method (200) according to claim 4, wherein a pressure to be applied by the clutch (130) is determined (203) based on the current torque output from the internal combustion engine (20), which is used to retrieve a corresponding clutch pressure stored in the memory (180).

6. The method (200) according to any one of the preceding claims, wherein the target RPM difference is determined (201) further based on the internal combustion engine (20) RPM and the current load on the internal combustion engine (20).

7. The method (200) according to claim 1, wherein the target RPM difference is determined (201) based on RPM variations on the output shaft (102) of the hybrid drive module (100).

8. The method (200) according to claim 1, wherein the actual RPM

difference is calculated using a moving average value of the current internal combustion engine (20) RPM and/or by applying a low pass filter to the current RPM signal. 9. A hybrid drive module (100), said hybrid drive module (100) comprising a housing (100) enclosing an electrical motor (110), said electrical motor (110) being connected to an output shaft (102) of the hybrid drive module (100), wherein a crankshaft (22) of an associated internal combustion engine (20) is connected to an input shaft (101) of the hybrid drive module, and wherein the input shaft (101) is connected to the output shaft

(102) via a clutch (130) also enclosed within said housing (100), said hybrid drive module (100) further comprising a control unit (170) and a memory (180), said hybrid drive module (100) being configured to perform the method according to any one of claims 1 - 8.

10. The hybrid drive module (100) according to claim 9, wherein the electrical motor (110) is arranged in a coaxial manner on the output shaft (102) downstream of the clutch (130). 1 1. The hybrid drive module (100) according to claim 9, wherein the electrical motor (110) is arranged in an off axis manner in relation to the output shaft (102) of the hybrid drive module (100), said electrical motor (110) being connected via a continuous member drive (120) to a second sprocket (124) on the output shaft (102) of the hybrid drive module (100).

12. The hybrid drive module (100) according to any one of claims 9 to 11, wherein a dual mass flywheel (140) is arranged between the input shaft

(101) and the clutch (130).

13. The hybrid drive module (100) according to any one of claims 9 to 12, further comprising a centrifugal pendulum absorber (148).

14. A hybrid vehicle, comprising the hybrid drive module (100) according to claim 9.