FR3068942A1 - 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

“METHOD FOR STARTING A HYBRID VEHICLE WITH AN INCREASED BATTERY POWER” The present invention relates to a method for starting a hybrid vehicle when stationary or below a speed threshold, equipped with a heat engine and an electric traction machine, as well as a hybrid vehicle comprising means implementing such a starting process.

One type of hybrid vehicle using electrical energy, called a parallel hybrid, comprises a first motorization equipped with an internal combustion engine, and a second motorization comprising an electric traction machine powered by energy storage devices, which is connected to the driving wheels without going through a coupling clutch of the heat engine. Electric energy storage devices, hereafter called batteries, can use all types of technology, in particular electrochemical energy storage cells, or electrical capacities.

The heat engine is connected to the drive wheels by a transmission having several speed ratios, comprising an input clutch of this transmission, in particular a clutch working dry. When the vehicle starts on the first gear ratio, the clutch has a slip which makes it possible to adapt the speed of the vehicle to that of the engine by means of this first gear.

Slippage of the torque-transmitting clutch generates 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 sharply in temperature, in particular after a succession of hill starts, or with a heavily loaded vehicle. In this case the torque transmission capacity by the clutch decreases, which increases its slip as well as its temperature. We can obtain situations where the heat engine can no longer start the vehicle when stationary.

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

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

However, the torque delivered by the electric machine directly connected to the internal combustion engine cannot help take off of the vehicle from a standstill when the clutch capacity is limited in torque.

In addition, some hybrid vehicles include an electric machine connected to the drive wheels without passing through the clutch, which can in particular be linked to the transmission of the heat engine.

In general 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 favor the internal combustion engine to pull the vehicle.

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

The present invention aims in particular to avoid these drawbacks of the prior art.

To this end, it proposes a method for starting a hybrid motor vehicle comprising a heat engine transmitting torque by a clutch to the driving wheels, an electric traction machine powered by a traction battery delivering torque to said driving wheels. without going through the clutch to transmit this torque, the starting method using a method for calculating the maximum authorized power delivered by the battery as a function of a state of charge of said battery, and using a method for evaluating a maximum value of torque transmissible by the clutch, this method being remarkable in that for starting the vehicle requiring sliding of the clutch, in the case of detection of a torque transmissible by the clutch less than one torque required to start this vehicle, and a maximum authorized battery power lower than its power m aximum possible, the process allows a delivery by the battery of a power higher than the maximum authorized power to supply the electric machine which takes part in the starting of the vehicle.

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

It is considered in this case that the take-off of the vehicle intervening under these conditions infrequently, can be authorized exceptionally in order to avoid a failure of the vehicle judged as severe by the user.

The start-up method according to the invention may also include one or more of the following characteristics, which can be combined with one another.

According to one embodiment, the method for 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 during previous uses of this clutch.

Advantageously, the starting method uses a speed threshold depending 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 process allows a power delivered by the battery which can reach the maximum possible power.

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

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, characteristics, details and advantages thereof will appear more clearly in the explanatory description which follows, made with reference to the accompanying drawings given solely by way of example illustrating 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

- Figure 2 is a graph showing as a function of the battery charge, the powers that can be delivered by this battery.

Figure 1 shows a hybrid vehicle comprising a heat engine 2 driving by a clutch 4 controlled automatically, a transmission 6 having different speed ratios, connected to the front drive 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 drive wheels 8 without passing through the clutch 4 to transmit its torque, using the different speed ratios offered by the transmission 6.

A powertrain computer connected to a vehicle monitoring supervisor controls the operation of this powertrain to meet the driver's demands while optimizing energy consumption and polluting gas emissions.

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 driving 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 driving torque to the driving wheels 8 by taking energy from the traction battery 12, or during braking of the vehicle works as a generator by producing a charging current for this battery.

When driving in hybrid mode, the heat engine 2 and the electric machine 10 deliver complementary torques to meet the demand of the torque driver on the drive wheels 8.

The vehicle includes a method for 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 a function of the state of charge of the SOC battery expressed as a percentage, a first curve representing the maximum possible power Pmax that the battery can physically deliver, which is constant.

A second curve represents the maximum authorized power Paut for the battery 12, calculated as a function of the SOC state of charge by limiting this power for low battery charges in order to protect it. In particular, the maximum authorized power Paut is constantly equal to the maximum possible power Pmax for a SOC state of charge greater than 40%, and decreases linearly below it 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 the battery 12 can deliver under given operating conditions, in particular temperature conditions. It will 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 Paut too low, the power management laws of the powertrain favor the use of the heat engine 2 for the traction of the vehicle. In parallel, the battery 12 can be recharged if the heat engine 2 can supply additional energy for this recharging, in particular by using the electric machine 10.

When the vehicle takes off in difficult conditions, in particular a loaded vehicle or on a slope, and with a very hot clutch 4 which can transmit a limited torque less than the torque required for this start-up, in the case of a low state of charge of the SOC battery, while respecting the maximum authorized power Paut the electric machine 10 can deliver an additional torque adding to that delivered by the clutch which is insufficient to allow takeoff of the vehicle.

We then obtain a failure to start the vehicle, which is considered a serious failure by the driver. The method of starting 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 vehicle speed, depending on other operating parameters of this vehicle, in particular the driver's dynamic demand, is below 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 can be less than a required torque threshold, or an evaluation of its temperature, which can be greater than a maximum temperature threshold, to deduce a insufficient torque capacity deliverable by this clutch in order to start the vehicle.

In the example shown in Figure 2, the method calculates that the electric machine 10 must deliver a torque to supplement that delivered by the clutch 4, corresponding to a necessary power P1 coming from the battery 12 to obtain this torque. It is noted that for a state of charge SOC of less than 20%, the maximum authorized power Paut is less than the necessary power P1, the battery 12 cannot normally respond to this request.

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

Usually uncommon, which limits the risks for the traction battery 12, in as many cases as possible to avoid immobilization of the vehicle.

Claims (7)

1. Method for starting a hybrid motor vehicle comprising a heat engine (2) transmitting torque by a clutch (4) to driving 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 process using a process for calculating the maximum authorized power (Paut) delivered by the battery (12) in function of a state of charge (SOC) of said battery, and using a method for evaluating a maximum value of torque transmissible by the clutch (4), characterized in that for a starting of the vehicle 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 this vehicle, and of a maximum authorized power (Paut) of the battery ( 12) lower ure at its maximum possible power (Pmax), the method allows delivery by the battery (12) of a power greater than the maximum authorized power (Paut) to power the electric machine (10) which participates in the starting of the vehicle. 2. Starting method according to claim 1, characterized in that the method for evaluating the torque transmissible by the clutch (4) uses a measurement or an estimate of the temperature of this clutch (4). 3. Starting method according to claim 1 or 2, characterized in that the method for evaluating the torque transmissible by the clutch (4) uses a monitoring of the vehicle dynamics during 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. Starting 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 the torque to a transmission (6) by a clutch (4), and an electric traction machine (10) powered by a battery (12) delivering its torque to the wheels drive (8) without passing through the clutch (4) to transmit this torque, characterized in that it comprises means implementing a method of starting this vehicle according to any one of the preceding claims. 7. Hybrid motor 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).