METHOD FOR CONTROLLING THE TORQUE AVAILABLE IN A HYBRID VEHICLE DURING GEAR CHANGES

Description

[0001] The present invention relates to the control of the torque available on a hybrid vehicle during gear changes.

[0002] More specifically, it relates to a method for controlling the torque available during gear changes of a powertrain composed of a heat engine connected to a first gearbox input shaft which can transmit its torque to the wheels on different transmission ratios, a first electric machine connected to a second input shaft thereof, and a second electric machine connected alternately to the first or second input shaft of the gearbox.

[0003] Publication WO 2014 / 207332 describes a hybrid transmission of this type, having several electric, thermal and hybrid ratios, where the torques of the thermal engine and at least one electric machine are added together towards the wheels. The thermal torque is transmitted to the wheels in a "thermal" transmission ratio, and that of the torque of the main electric machine in an "electric" ratio. When changing thermal transmission ratios in hybrid mode, the torque of the thermal engine is interrupted. The torque of the main electric machine is then controlled to synchronize the thermal engine to its new ratio, while providing torque to the wheel.

[0004] Document FR 2 847 638 A1 discloses a hybrid transmission in which, during torque break phases due to a gear change, the two electric machines operate in "series" mode.

[0005] In practice, the vehicle's electrical architecture, particularly the power available from the main electrical engine, limits its contribution during thermal gear changes. If the thermal torque interruption is poorly compensated, the driver and passengers of the vehicle feel these changes, like those of a robotic gearbox with torque loss.

[0006] It is therefore desirable to manage to reduce the torque break felt by the driver and vehicle users during gear changes.

[0007] A reduction in available torque around the shift theoretically addresses this problem. However, such a measure is unacceptable, due to its negative impact on performance. The solution is therefore to be sought in an increase in wheel torque during shifts. Any provision consisting of temporarily increasing the voltage of the on-board network is of interest in this regard. Some battery systems, which have the ability to modulate their output voltage by relays placing cells in series or in parallel, could notably help to mitigate the power loss felt during shifts. However, these systems have the disadvantage of increasing, or even compromising, the vehicle's architecture.

[0008] The present invention aims to increase the torque available during thermal transmission gear changes, particularly at high speed, in order to reduce their "power gap", without any particular adaptation of the components or the electrical architecture of the vehicle.

[0009] For this purpose, it proposes a control method according to claim 1.

[0010] The present invention will be better understood from reading the following description of a particular embodiment thereof, with reference to the appended drawings in which: there figure 1 is a hybrid architecture scheme, the figure 2 groups its passage curves, the figure 3 identifies the requested ratios in relation to these curves, and the figure 4 is the electrical diagram of the power network of this box.

[0011] Gearbox 1 of the figure 1 is for example of the "robotic" type, that is to say that its operation is that of a manual gearbox, but that the gear changes are automated. On the diagram, an electric machine, called HSG (for high voltage alternator-starter) 2, a thermal engine 3 on a solid primary shaft 4 is shown. Another electric machine 5 called ME, more powerful than the first, is mounted on a hollow primary shaft 6. The secondary shaft of the gearbox 7 is connected to the differential (not shown), then to the wheels of the vehicle.

[0012] The first dog clutch 8 located on the secondary shaft 7 makes it possible to modify the ratio of the electric machine ME 5, independently of the rest of the gearbox, to have two electric ratios EV1 and EV2. The second dog clutch 9, located on the solid primary shaft 4, makes it possible to modify the ratio of the thermal engine 3 independently of the electrical ratios, to establish two thermal ratios Th2 and Th4, independently of the electrical ratio. The third dog clutch 11, located on the transfer shaft 10, makes it possible to establish a third thermal ratio Th3, when it moves to the right in the diagram. It is possible to choose independently at any time, the desired ratio on the first electric machine ME and that desired on the thermal engine group Mth and the second electric machine HSG 2.The combinations of thermal ratios and electrical ratios make it possible to create hybrid ratios, denoted HEVxy, where x denotes the ratio of the thermal engine, and y the ratio of the ME.

[0013] The gearbox's gear change curves are grouped on the figure 2 . Box 1 allows two electric ratios ZE1 and ZE2 to be established, and four hybrid ratios Hyb21, Hyb22, Hyb32, Hyb42, depending on the "thermal ratio" and the "electric ratio". The curves plot the maximum achievable forces (wheel force in Newton) on the electric and hybrid ratios as a function of speed.

[0014] In the intended application, it can be agreed that the target ratio is always (regardless of the travel speed) a ZEV electric ratio, as long as this ratio can meet the driver's torque demand. By default, the engaged ratio becomes the longest hybrid ratio, allowing the demand to be met. In this hypothesis, the requested ratios can be distributed on a graph, like that of the figure 3 . This figure allows us to identify the gear changes that may occur during a typical drive. For example, we see that when accelerating at full throttle, we go from HEV22 to HEV32 at around 125 km / h. For this change, the second thermal gear must be disconnected from the transmission to be synchronized with the new thermal gear. With a battery voltage of 270V, the first ME machine can provide, for example, a power of 35kW. The second HSG machine can provide a power of 25kW, while the Mth thermal engine provides 70kW. The overall power supplied by the gearbox to the wheel before the change is then 105kW. After the change, the gearbox provides roughly the same power (except for the variation in the power of the thermal engine). On the other hand, during the change, the thermal engine and HSG assembly is disconnected from the wheels. Only the ME then provides power to the wheel, i.e. 35kW.

[0015] The GMP (Powertrain) thus suffers from a " trou de puissance » during this gear change. At 125 km / h, the power absorbed by the vehicle's aerodynamics is around 25 kW. The power available for acceleration actually drops from 80 kW to 10 kW during the change. Such a drop in acceleration (of 87%), gives the driver the impression that his vehicle is no longer accelerating, despite the torque provided by the main electric machine ME. His feeling is that of a vehicle equipped with a robotized gearbox with torque break.

[0016] On the figure 4 , the battery 12 of the vehicle is shown, connected by two relays 13a 13b to the inverters 14, 16 of the two electrical machines, mounted in parallel on the electrical network, with an inverter capacity 17.

[0017] The proposed solution consists of increasing the power supplied by the first main electric machine ME during gear changes of the thermal engine (Mth), by operating the second electric machine (HSG) in regenerative mode. All the electrical power of the latter is then transmitted to the first, which uses it to compensate for the reduction in wheel torque caused by the temporary decoupling of the thermal engine. The supply voltage of the inverters is increased for this purpose. In the example described above, a 450V supply instead of an average voltage of 200V allows the ME to supply approximately 70kW and the HSG to supply approximately 50kW, using the usual components of the electrical network. The supply voltage of the inverters is therefore increased to increase the power achievable by the two electric machines during gear changes.The first electric machine (ME) thus provides the wheel with all the power transmitted to it by the second electric machine (HSG).

[0018] The proposed method is applicable to a box such as that of the figure 1 (where the couplers are preferably dog ​​or claw couplers, the architecture of which is shown diagrammatically on the figure 4 It consists of linking the following steps: 1. cancellation of the torques of the ME and the HSG, 2. opening of the battery relays, 3. switching the HSG to regenerative mode: the HSG regulates the voltage of the inverter capacity to 450V and then provides a negative torque on the shaft of the thermal engine (limited to the maximum power of the HSG at 450V, i.e. approximately 50kW) which is directly restored as positive torque to the wheel by the ME, 4. cancellation of the torque on the primary dog ​​clutch by reducing the torque of the thermal engine until the power of the thermal engine and the HSG is balanced: Power (Mth) - - Power (HSG), 5. de-clutching of the abandoned gear pinion on the primary shaft, 6. synchronization of the primary shaft on the target gear: if this is longer than the abandoned gear, the speed of the thermal engine is reduced by further reducing its torque (Mth torque), 7. clutching of the pinion of the new gear, and increase of the engine torque thermal up to its maximum power, 8.cancellation of the ME and HSG torques by canceling the HSG torque a little faster to decrease the inverter capacity voltage, 9. reconnection of the battery relays, 10. return of the ME and HSG torques in the overall satisfaction of the driver torque demand.

[0019] When the gearbox is a dog clutch or a clutch gearbox, the engine is decoupled by disengaging a gear from its input shaft. Its coupling to a new gear is achieved by dog-engaging a new gear on its input shaft.

[0020] The proposed method thus includes the following steps, before decoupling the thermal engine and its input shaft: cancellation of the torques of the two electric machines, opening of the battery relays, switching of the second electric machine to energy recovery mode, reduction of the torque of the thermal engine until the balance of its own power and the power recovered by the second electric machine.

[0021] Preferably, the torque of the second HSG electric machine is canceled more quickly than that of the first, to decrease the voltage of the inverters capacity.

[0022] After decoupling, the input shaft 4 linked to the thermal engine is synchronized to the target ratio by controlling the torque of the thermal engine (Mth), before coupling the thermal engine to its input shaft in the new ratio. Preferably, the coupling of the thermal engine is followed by an increase in torque up to its maximum power.

[0023] During gear change, gearbox 1 adopts a series hybrid type operation, where the first electric machine ME can supply the wheel with exactly the power that the HSG supplies to the high-voltage network. The thermal engine maintains the speed of the HSG. Relays 13a, 13b of battery 12 are open during gear change. Their opening makes it possible to increase the voltage on the network in a simple way, preventing the battery from absorbing all the power supplied by the HSG. Disconnecting the battery thus makes it possible to increase the power achievable during the change.

[0024] There figure 5 illustrates the evolution of the power of each component, ME power, HSG power, Mth power and wheel power, during the shift, with the evolution of the thermal engine speed and the corresponding HT (High Voltage) network voltage from stage 1 to 10. These curves highlight the gain provided by the invention. Without compensation during the gear change, the wheel power would have fallen to 35kW. Thanks to the invention, the wheel power is maintained at 70kW for three stages, and at 50kW for one stage. The "power gap" thus remains below 50%. The loss of acceleration is reduced, so that the driver constantly feels the availability of power to accelerate.

[0025] It is also always possible to increase the network voltage to further reduce the power hole. However, this adaptation may require the resizing of certain system components, which is not the case with the simple control measures proposed by the invention.

[0026] In the case of a vehicle of the category known as “ mild hybrid » or the main electrical machine is mainly intended for a restart function (or « boost ”) , or when driving at low speed, you can choose to limit the power available at high speed to that of the combustion engine, especially when accelerating at full throttle, so as not to drain the battery too quickly. In the example described, the power loss during gear changes is only 20kW (difference between the maximum power of the Mth equal to 70kW). The minimum power during gear changes is equal to 50kW.

[0027] In conclusion, the invention results in a transient increase in the voltage of the high voltage (HV) network during gear changes. The major advantage of the invention is that it does not require any addition to the system, if we limit ourselves to a maximum of 450V on the network in the example described.

Claims

1. Method for controlling the torque available during gear changes of a powertrain made up of a combustion engine (Mth) connected to a first input shaft (4) of a gearbox which can transmit its torque to the wheels in different transmission ratios, of a first electric machine (ME) connected to a second input shaft (6) thereof, and of a second electric machine (HSG) connected to the first input shaft of the gearbox, the second electric machine (HSG), during the changes in combustion engine (Mth) transmission ratio, switching into regenerative mode before the combustion engine is uncoupled, so as to transmit all its electrical power to the first electric machine (ME) which uses it to compensate for the reduction in torque to the driven wheel which is brought about by the temporary uncoupling of the combustion engine, and said method comprising the following steps, before the uncoupling of the combustion engine and of its input shaft (4): - cancellation of the torques of the two electric machines (ME), (HSG), - switching of the second electric machine into energy recovery mode, - reduction of the torque of the combustion engine until its own power balances the power recovered by the second electric machine, characterized in that said method also comprises the following steps, before uncoupling of the combustion engine and of its input shaft (4): - increasing the supply voltage to the inverters in order to increase the power supplied by the two electric machines during gear change, and - opening the relays (13a, 13b) of the battery (12).

2. Torque control method according to Claim 1, characterized in that the first electric machine (ME) supplies the wheel with the power supplied to it by the second electric machine (HSG).

3. Control method according to one of the preceding claims, characterized in that the torque of the second electric machine (HSG) is cancelled more rapidly than that of the first (ME), so as to reduce the voltage of the inverters' capacitor.

4. Control method according to one of the preceding claims, characterized in that the uncoupling of the combustion engine is performed by disengaging a pinion of its input shaft (4).

5. Torque control method according to Claim 1 or 2, characterized in that, after it has been uncoupled, the input shaft connected to the combustion engine is synchronized with the target ratio by controlling the torque of the combustion engine (Mth).

6. Torque control method according to Claim 3, characterized in that the coupling of the combustion engine to its new transmission ratio is performed by engaging a new pinion on its input shaft (4).

7. Torque control method according to Claim 5 or 6, characterized in that the coupling of the combustion engine is followed by an increase in (Mth) torque up to its maximum power.