FR3068942B1 - METHOD FOR STARTING A HYBRID VEHICLE WITH AN INCREASED BATTERY POWER - Google Patents

Abstract

The invention relates to a method of starting a hybrid motor vehicle comprising a heat engine (2) transmitting the torque by a clutch (4), an electric traction machine (10) powered by a battery (12) delivering its torque without passing through the clutch (4) to transmit this torque, a method of calculating the maximum authorized power delivered by the battery (12) according to its state of charge, and comprising a method of evaluating the torque transmissible by the clutch (4), this method being remarkable in that for a starting of the vehicle requiring a sliding of the clutch (4), for a detection of a torque transmissible by the clutch (4) less than a necessary torque to start this vehicle, and a maximum authorized power of the battery (12) lower than its maximum possible power, it allows a delivery by the battery (12) of a power greater than the maximum power allowed.

Description

The present invention relates to a method of starting a hybrid vehicle at a stop or below a speed threshold, equipped with a "hybrid" vehicle. thermal engine and an electric traction machine, and a hybrid vehicle comprising means implementing such a starting method.

[0002] A type of hybrid vehicle using electrical energy, called a parallel hybrid, comprises a first engine equipped with a heat engine, and a second engine comprising an electric traction machine powered by energy storage devices, which is connected to the driving wheels without passing through a coupling clutch of the engine. The storage of electrical energy, hereinafter called battery, can use all types of technologies, including electrochemical cells for energy storage, or electrical capabilities.

The heat engine is connected to the driving wheels by a transmission having several gear ratios, comprising an input clutch of this transmission, including a clutch working dry. When starting the vehicle on the first gear, the clutch has a slip to match the speed of the vehicle to that of the engine through this first report.

The sliding of the clutch transmitting a torque generates a thermal heating power which in a short time is little dissipated to the outside, and raises the temperature of the clutch mechanism.

Under certain conditions the clutch can rise significantly in temperature, particularly after a series of starts in hill, or with a very loaded vehicle. In this case the torque transmission capacity by the clutch decreases, which increases its sliding as well as its temperature. It is possible to obtain situations in which the engine can no longer start the vehicle at a standstill.

Furthermore, in the case of a strong torque demand for the traction of a hybrid vehicle comprising an electric machine connected to the engine, which can recharge the traction battery, a known method, presented in particular by the WO document -A1-201427152, torque limit absorbed by this machine to favor the transmission to the drive wheels of the torque delivered by the engine.

Another known method for the traction of the same type of hybrid vehicle, presented in particular by the document WO-A1-201427153, in the case of driving with an automatic system for controlling the speed of the vehicle, limit torque absorbed by the electric machine to meet the demand in traction torque.

However, the torque delivered by the electrical machine directly connected to the engine, can not help for the takeoff of the vehicle from the stop when the capacity of the clutch is limited in torque.

[0009] Moreover, certain hybrid vehicles comprise an electric machine connected to drive wheels without going through the clutch, which may in particular be linked to the transmission of the heat engine.

Generally speaking on hybrid vehicles, the power authorized by an energy management system that can deliver the traction battery, depends on its state of charge, called "SOC" (abbreviation of English terms "State Of Charge"). When the state of charge decreases, the authorized power also decreases, and the energy management laws privilege the engine to achieve traction of the vehicle.

In the case of a torque capacity of the greatly reduced clutch, there is then a torque contribution of the electric machine low or zero due to the state of charge of the traction battery, which can cause problems of impossibility of starting with the engine not transmitting enough torque by the clutch. The vehicle remains immobilized, which represents a serious problem perceived by the customer as a powertrain failure.

The present invention is intended to avoid these disadvantages of the prior art.

It proposes for this purpose a starting method of a hybrid motor vehicle comprising a heat engine transmitting torque by a clutch to drive wheels, an electric traction machine powered by a traction battery delivering torque to said drive wheels without going through the clutch to transmit this pair, the starting method using a method of calculating the maximum authorized power delivered by the battery according to a state of charge of said battery, and using a method of evaluation of a maximum torque value transmittable by the clutch, this method being remarkable in that for a starting of the vehicle requiring a sliding of the clutch, in the case of a detection of a torque transmittable by the clutch less than one torque required to start this vehicle, and a maximum authorized power of the battery lower than its power m as far as possible, the method allows the battery to deliver a power greater than the maximum power allowed to power the electrical machine that participates in starting the vehicle.

An advantage of this starting method is that the electrical machine can exceptionally deliver a high torque level from the maximum power that the battery can deliver, despite the usual laws of limitation of this power delivered by the battery to because of its low charge level.

It is considered in this case that the takeoff of the vehicle intervening in these conditions infrequently, may be authorized exceptionally to avoid a vehicle failure deemed severe by the user.

The starting method according to the invention may further comprise one or more of the following features, which may be combined with each other.

According to one embodiment, the method of evaluating the torque transmissible by the clutch uses a measurement or an estimate of the temperature of this clutch.

According to another embodiment, the method of evaluating the torque transmissible by the clutch uses a monitoring of the vehicle dynamics in previous uses of this clutch.

Advantageously, the starting method uses a speed threshold dependent on different operating parameters of the vehicle, to determine below this threshold the slip state of the clutch when starting the vehicle.

Advantageously, the starting method allows a power delivered by the battery that can reach the maximum power possible.

The invention also relates to a hybrid motor vehicle comprising a heat engine transmitting torque to a transmission by a clutch, and an electric traction machine powered by a battery delivering its torque on driving wheels without going through the clutch for transmitting this torque, this vehicle being remarkable in that it comprises means implementing a starting method comprising any one of the preceding features.

In particular, the electric machine can be connected to a primary shaft of the transmission driven by the clutch.

The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the explanatory description which follows, with reference to the accompanying drawings given solely by way of illustrative example. an embodiment of the invention, and in which: - Figure 1 is a diagram of a hybrid vehicle implementing a starting method according to the invention; and FIG. 2 is a graph showing, as a function of battery charge, powers that can be delivered by this battery.

Figure 1 shows a hybrid vehicle having a heat engine 2 driving by a clutch 4 automatically controlled, a transmission 6 having different speed ratios, connected to the front wheels 8 of this vehicle.

The input shaft of the transmission 6 receiving the movement of the clutch 4 comprises an electric traction machine 10 powered by a traction battery 12. In this way the electric machine 10 can deliver a torque on the driving wheels 8 without passing through the clutch 4 to transmit its torque, using the different gear ratios proposed by the transmission 6.

A powertrain calculator connected to a supervisor monitoring the vehicle, controls the operation of this powertrain to meet the demands of the driver while optimizing energy consumption and emissions of gaseous pollutants.

In particular, the hybrid vehicle can run only with the heat engine 2, the clutch 4 being closed to drive the transmission 6, the electric machine 10 not delivering torque.

When running in electric mode with the electric machine only 10, the clutch 4 is open and the engine 2 is stopped. The electric machine 10 delivers a motor torque to the driving wheels 8 by taking energy from the traction battery 12, or during braking the vehicle works as a generator by producing a charging current of this battery.

In hybrid mode running the heat engine 2 and the electric machine 10 deliver couples that complement each other, to meet the demand of the torque driver on the drive wheels 8.

The vehicle comprises a method of evaluating the torque transmissible by the clutch 4, which can be based in particular on a measurement or an estimate of the temperature of this clutch, or on a monitoring of the vehicle dynamics during previous uses of the clutch, to determine the maximum torque delivered by the engine 2 that can transmit this clutch.

Figure 2 shows according to the state of charge of the SOC battery expressed in percentage, a first curve representing the maximum possible power Pmax that can physically deliver the battery, which is constant.

A second curve represents the maximum power allowed Paut for the battery 12, calculated according to SOC state of charge by limiting this power for low battery loads to protect it. In particular, the maximum power allowed Paut is constantly equal to the maximum possible power Pmax for a charge state SOC greater than 40%, and decreases linearly below to reach a zero value at 0%.

The maximum possible power Pmax representing the product of the intensity by the voltage of the current delivered, is that which can deliver the battery 12 under given operating conditions, in particular temperature conditions. It should be noted that the maximum possible power Pmax is constant, it is independent of the charge level of the battery 12.

In the case of a maximum power allowed Paut too low, the energy management laws of the powertrain favor the use of the engine 2 for the traction of the vehicle. In parallel, the battery 12 can be recharged if the heat engine 2 can provide extra energy for this recharge, particularly by using the electric machine 10.

During a take-off of the vehicle in difficult conditions, in particular a loaded vehicle or on a slope, and with a very hot clutch 4 can transmit a limited torque less than the torque necessary for this start, in the case of a state of charge of the SOC low battery, while respecting the maximum power allowed The electric machine 10 can deliver an additional torque in addition to that delivered by the clutch which is insufficient to allow the vehicle to take off.

This results in a failure to start the vehicle, which is considered a serious fault by the driver. The starting method of the vehicle according to the invention represents an emergency situation comprising the following steps.

When starting or restarting the vehicle at very low speed, it checks whether the speed of the vehicle, according to other operating parameters of the vehicle, including the driver dynamics demand, is lower than a threshold requiring a sliding of the clutch 4. In this case it calculates the torque necessary to deliver on the transmission 6 to start the vehicle.

The method then performs an evaluation of the torque transmissible by the clutch 4, which may be less than a necessary torque threshold, or an evaluation of its temperature, which may be greater than a maximum temperature threshold, to deduce a insufficient torque capacity to be delivered by this clutch to start the vehicle.

In the example shown in Figure 2, the method calculates that the electrical machine 10 must deliver a torque to complete that delivered by the clutch 4, corresponding to a power P1 from the battery 12 to obtain this torque. It is found that for a state of charge SOC less than 20%, the maximum power allowed Paut is less than the necessary power P1, the battery 12 can not normally meet this demand.

In this case the method allows a delivery by the battery 12 of a power greater than the maximum power allowed Paut. In particular as shown by the arrows 24, the method can allow the delivery of the maximum possible power Pmax if necessary.

This is thus usually uncommon manner which limits the risks for the traction battery 12, in the greatest possible number of cases to avoid the immobilization of the vehicle.

Claims (2)

1. A method for starting a hybrid motor vehicle comprising a heat engine (2) transmitting torque by a clutch (4) to drive wheels (8), an electric traction machine (10) powered by a traction battery ( 12) delivering torque to said driving wheels (8) without passing through the clutch (4) to transmit this torque, this starting method using a method of calculating the maximum authorized power (Paut) delivered by the battery (12) in according to a state of charge (SOC) of said battery, and using a method of evaluating a maximum value of torque transmissible by the clutch (4), characterized in that for a vehicle starting requiring a sliding of the clutch (4), in the case of detection of a torque transmissible by the clutch (4) less than a torque necessary to start the vehicle, and a maximum authorized power (Paut) of the battery ( 12) inferiors ure at its maximum possible power (Pmax), the method allows a delivery by the battery (12) of a power greater than the maximum power allowed (Paut) to power the electrical machine (10) involved in starting the vehicle. 2. Starting method according to claim 1, characterized in that the method of evaluating the torque transmissible by the clutch (4) uses a measurement or estimate of the temperature of the clutch (4). 3. Starting method according to claim 1 or 2, characterized in that the method of evaluating the torque transmissible by the clutch (4) uses a monitoring of the vehicle dynamics in previous uses of this clutch (4). . 4. Starting method according to any one of the preceding claims, characterized in that it uses a speed threshold dependent on different operating parameters of the vehicle, to determine below this threshold the slip state of the clutch. (4) when starting the vehicle. 5. Start-up method according to any one of the preceding claims, characterized in that it allows a power delivered by the battery (12) which can reach the maximum possible power (Pmax). 6. Hybrid motor vehicle comprising a heat engine (2) transmitting torque to a transmission (6) by a clutch (4), and an electric traction machine (10) powered by a battery (12) delivering its torque on wheels motor (8) without passing through the clutch (4) to transmit this torque, characterized in that it comprises means implementing a starting method of this vehicle according to any one of the preceding claims. Hybrid automobile vehicle according to claim 6, characterized in that the electric machine (10) is connected to a primary shaft of the transmission (6) driven by the clutch (4).