METHOD FOR CONTROLLING A DCT TRANSMISSION IN ENERGY RECOVERY

Abstract

The invention relates to a method for controlling a DCT transmission of a motor vehicle comprising a powertrain (1) including an internal combustion engine (3) and a DCT-type transmission device (4) comprising an electric machine (5), a gearbox (41, 42) having a primary shaft (6), a coupling clutch (K0) between the internal combustion engine and the primary shaft 6, a gear train (65) kinematically linking the primary shaft to an input of the electric machine, wherein, with the hybrid motor vehicle decelerating and the electric machine (5) in generator mode, the method comprises the steps of: If the rotational speed of the primary shaft (6) falls below a threshold value RAP, changing the gear ratio of the gearbox (41, 42) to a slightly lower gear ratio, if possible. Figure 1.

Description

Title of the invention: METHOD FOR CONTROLLING A DCT TRANSMISSION IN ENERGY RECOVERY TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates, in general, to the technical field of the management of the control of a traction chain of a motor vehicle equipped with a hybrid powertrain associated with a DCT type transmission.

[0002] More specifically, the invention controls the DCT type transmission, in particular e-DCT, in energy recovery when the speed of a gearbox primary shaft is lower than an idle speed of a thermal engine. STATE OF PRIOR ART

[0003] In the remainder of the description, the example of implementation of the invention described is a hybrid motor vehicle whose motive power is alternately or cumulatively provided by a heat engine and an electric machine supplied with electrical energy by batteries. The heat engine and the electric machine form a motor assembly whose motive energy is transmitted by a DCT type transmission device to a front or rear wheel set. This example of implementation of the invention has been chosen to facilitate the description of the invention, without it being limited thereto. Indeed, the invention can also, for example, be applied to a motor vehicle in which the motive energy is transmitted to more than one wheel set.

[0004] In known DCT type transmission devices for hybrid motor vehicles, a control device makes it possible to ensure the transmission to the drive wheel set of an engine torque generated by the thermal engine, the electric machine or both. This control device manages a first clutch connecting the engine assembly to a first gearbox comprising odd transmission ratios, and a second clutch connecting the engine assembly to a second gearbox comprising even transmission ratios.

[0005] During a low-speed driving phase of the hybrid motor vehicle, the rotational speed of the wheels of the drive train returned to a primary shaft of the gearbox may be lower than a rotational speed of the thermal engine of the hybrid motor vehicle. Indeed, the thermal engine has a minimum rotational speed, called idle speed, below which it cannot fall. Typically, this idle speed is of the order of 900 rpm.

[0006] Consequently, in order to allow driving at low speed in a comfortable manner for a user of the hybrid motor vehicle, the control device is programmed to slip the clutch between the combustion engine and the gearbox input shaft. In the event of deceleration, there is a loss of braking energy which cannot be recovered by the electric machine in order to charge the batteries.

[0007] There is therefore a need for DCT type transmission control allowing optimal recovery of braking energy during deceleration when driving at low speed. Statement of the invention

[0008] The invention aims to remedy all or part of the drawbacks of the state of the art by proposing in particular a solution allowing control of the DCT type transmission allowing efficient recovery of braking energy when driving at low speed.

[0009] To do this, according to a first aspect of the invention, a method is proposed for controlling a DCT transmission of a motor vehicle comprising a powertrain comprising a heat engine and a DCT type transmission device comprising an electric machine, a gearbox having a primary shaft, a coupling clutch between the heat engine and the primary shaft 6, a gear train kinematically connecting the primary shaft to an input of the electric machine; the hybrid motor vehicle decelerating and the electric machine being in generator mode, the method comprises steps of: • If the rotation speed of the primary shaft falls below a threshold value RAP, change from a transmission ratio then engaged in the gearbox to a transmission ratio just lower, if possible.

[0010] According to one embodiment, the method prior to the change step, the method comprises a step of: • If the rotation speed of the primary shaft is lower than the idle speed value of the thermal engine, the coupling clutch opens and the thermal engine stops.

[0011] According to another aspect of the invention, there is provided a powertrain for a motor vehicle comprising a heat engine and a DCT type transmission device comprising an electric machine, a gearbox having a primary shaft, a coupling clutch between the heat engine and the primary shaft, a gear train kinematically connecting the primary shaft to an input of the electric machine, as well as a computer arranged so as to implement the method having one of the preceding technical characteristics.

[0012] According to one aspect of the invention, in the powertrain, the transmission device comprises a first gearbox coupled to the primary shaft via a coupling clutch and a second gearbox coupled to the primary shaft via a coupling clutch.

[0013] According to yet another aspect of the invention, there is provided a motor vehicle comprising a powertrain having one of the preceding technical characteristics. BRIEF DESCRIPTION OF THE FIGURES

[0014] Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, which illustrate: • [Fig.l]: a diagram of a powertrain of a hybrid motor vehicle intended to be driven by a driving method according to the invention; • [Fig.2]: a graph of the evolution of the primary shaft speed and the driving speed for the first three gearbox ratios illustrating the operation of the control method according to the invention.

[0015] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION OF AN EMBODIMENT

[0016] [Fig.l] schematically illustrates a powertrain 1 of a hybrid motor vehicle within which a method for controlling a DCT transmission according to the invention will be implemented. The powertrain 1 drives a front or rear wheel set 2. Alternatively, the powertrain drives two or more wheel sets.

[0017] The powertrain 1 is here a hybrid powertrain. The latter comprises a heat engine 3, a DCT type transmission device 4. The DCT type transmission device is here an e-DCT type transmission device in that it comprises an electric machine 5.

[0018] On the other hand, the DCT type transmission device 4 comprises a primary shaft 6 and a coupling clutch KO between the thermal engine 3 and the primary shaft 6. The DCT type transmission device 4 also comprises a gear train 65 connecting the electric machine 5 to the primary shaft 6.

[0019] The DCT 4 type transmission device comprises, in a manner known per se, a first gearbox 41, comprising odd transmission ratios, a first coupling clutch K1 between the primary shaft 6 and that of the first gearbox 41, a second gearbox 42, comprising even transmission ratios, and a second coupling clutch K2 between the primary shaft 6 and that of the second gearbox 42.

[0020] The electric machine 5 is electrically connected to a battery 8. In traction mode, the battery 8 thus supplies the electric machine and, in recovery mode, the electric machine, controlled as a generator, thus supplies battery 8.

[0021] Finally, a control device or calculator 9 makes it possible to manage the operation of the hybrid powertrain 1, in particular the DCT type transmission device 4. In particular, the control device or calculator 9 is arranged so as to be able to implement the method for controlling a DCT transmission according to the invention which will now be described in more detail.

[0022] Overall, in the electrical energy recovery phase, a torque is provided by the wheel set 2 and the electric machine 5 is driven in generator mode in order to charge the battery 8. The electric machine 5 is driven here in full throttle. A deceleration braking phase can then induce a driving speed of the hybrid motor vehicle brought back, initially, to a rotation speed value of the primary shaft 6 (due to the gear reduction due to the transmission ratio then engaged within one of the first 41 and second 42 gearboxes) which is lower than the idling speed of the heat engine 3.

[0023] In this situation, the method for controlling a DCT transmission according to the invention comprises a step of opening the coupling clutch KO and stopping the heat engine 3. Thus, the primary shaft 6 is separated from the heat engine and remains only kinematically connected to the electric machine 5 via the gear train 65. The transmission ratio then engaged within one of the first 41 and second 42 gearboxes is retained.

[0024] Then, as the deceleration continues, the method for controlling a DCT transmission according to the invention determines whether a rotation speed value of the primary shaft 6 is lower than a threshold value RAP of the electric machine 5. This threshold value RAP is determined so that the electric machine 5 in generator mode can charge the battery 48. This threshold value RAP is lower than or equal to the idle speed of the heat engine 3.

[0025] If the rotation speed value of the primary shaft 6 is indeed, the method for controlling a DCT transmission according to the invention comprises a step of lowering the transmission ratio then engaged within one of the first 41 and second 42 gearboxes to a transmission ratio just lower. This is no longer possible when the transmission ratio then engaged is the 1st.

[0026] Thus, as illustrated in [Fig. 2], if the transmission ratio then engaged is 3rd, the method for controlling a DCT transmission according to the invention lowers the transmission ratio to 2nd when the value of the rotation speed of the primary shaft 6 falls below the threshold value RAP. From then on, the value of the rotation speed of the primary shaft 6 increases by “passing” from the speed curve of 3rd to the speed curve of 2nd. Then, as the driving speed continues to decrease, the value of the rotation speed of the primary shaft 6 again falls below the threshold value. RAP: the method for controlling a DCT transmission according to the invention then lowers the transmission ratio to 1st and the rotation speed value of the primary shaft increases by “passing” from the speed curve of 2nd to that of 1st.

[0027] Once the 1st gear is engaged, if the value of the rotation speed of the primary shaft falls again below the threshold value RAP, it is no longer possible to lower the engaged transmission ratio and said rotation value of the primary shaft 6 continues to follow the speed curve of the 1st gear if the deceleration continues.

[0028] The change in the value of the rotation speed of the primary shaft 6 due to the method of controlling a DCT transmission according to the invention is shown in thick lines in [Fig.2],

[0029] The fact of lowering the transmission ratio engaged within one of the first 41 and second 42 gearboxes makes it possible to maintain a rotational speed of the primary shaft 6, and therefore a rotational speed of the input of the electric machine 5 operating in generator mode, sufficient to efficiently charge the battery 8, in particular at low driving speed of the hybrid motor vehicle within which the method for controlling a DCT transmission according to the invention is implemented. “Low driving speed” is understood to mean a travel speed of less than 20 km / h, or even less than 15 km / h.

[0030] In addition, the implementation of the method for controlling a DCT transmission according to the invention makes it possible to avoid slippage of the coupling clutches KO, K1 and K2, sources of recovery energy losses, and therefore to have efficient charging of the battery 8 by the electric machine 5 in generator mode, in particular during decelerations at low driving speed of the hybrid motor vehicle.

[0031] Naturally, the invention is described in the foregoing by way of example. It is understood that the person skilled in the art is able to carry out different variant embodiments of the invention without departing from the scope of the invention.

[0032] It is emphasized that all features, as they emerge for a person skilled in the art from the present description, the drawings and the attached claims, even if they have been specifically described only in relation to other determined features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances make such combinations impossible or devoid of sense.

Claims

Claims

1. Method for controlling a DCT transmission of a motor vehicle comprising a powertrain (1) comprising a heat engine (3) and a DCT type transmission device (4) comprising an electric machine (5), a gearbox (41, 42) having a primary shaft (6), a coupling clutch (KO) between the heat engine and the primary shaft 6, a gear train (65) kinematically connecting the primary shaft to an input of the electric machine, characterized in that, the hybrid motor vehicle decelerating and the electric machine (5) being in generator mode, the method comprises steps of: • If a rotational speed of the primary shaft (6) falls below a threshold value RAP, changing a transmission ratio then engaged of the gearbox (41, 42) to a transmission ratio just lower, if this is possible.

2. Method according to claim 1, characterized in that, prior to the changing step, the method comprises a step of: • If a rotation speed of the primary shaft (6) is lower than an idle speed value of the thermal engine (3), opening of the coupling clutch (KO) and stopping of the thermal engine (3).

3. Powertrain for a motor vehicle comprising a heat engine (3) and a DCT type transmission device (4) comprising an electric machine (5), a gearbox (41, 42) having a primary shaft (6), a coupling clutch (KO) between the heat engine and the primary shaft (6), a gear train (65) kinematically connecting the primary shaft to an input of the electric machine, characterized in that it comprises a computer (9) arranged so as to implement the method according to one of claims 1 to 2.

4. Powertrain according to claim 3, characterized in that the transmission device comprises a first gearbox (41) coupled to the primary shaft via a coupling clutch (K1) and a second gearbox (42) coupled to the primary shaft (6) via a coupling clutch (K2).

5. Motor vehicle, characterized in that it comprises a powertrain according to claim 3 or 4.

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