WO2014006347A1

WO2014006347A1 - Method of use of a hybrid propulsion system of a vehicle

Info

Publication number: WO2014006347A1
Application number: PCT/FR2013/051611
Authority: WO
Inventors: Gérald PETERS; Yoann LEFEVRE
Original assignee: Renault S.A.S
Priority date: 2012-07-06
Filing date: 2013-07-05
Publication date: 2014-01-09
Also published as: FR2992930A1; FR2992930B1

Abstract

The invention concerns a method for using a hybrid propulsion system of a vehicle, comprising a compressed-air tank (3) and a heat engine (1) provided with at least one cylinder (2), each of said cylinders (2) being capable of being supplied with air by an inlet circuit provided with a regulating device (8) for regulating the air pressure and by the air tank (3). The main characteristic of a method of use according to the invention is that it comprises the following steps, - A step of setting a parameter representative of the operating point of the engine (1), - A step of adapting the air pressure inside the inlet circuit by means of the regulating device (8) in such a way as to minimise the consumption of air from the tank (3) in order to reach said operating point.

Description

METHOD OF USING A PROPULSION SYSTEM

HYBRID VEHICLE

The invention relates to a method of using a hybrid propulsion system of a vehicle. In the context of this invention, the hybrid propulsion system has a thermal component and a pneumatic component.

For the rest of the description, the terms "cylinder" and "combustion chamber" are equivalent. It is furthermore known that each cylinder comprises a displaceable piston, to ensure the different phases of compression and expansion of the gases during a motor cycle. Similarly, it is assumed that a heat engine is associated with an air intake circuit and an exhaust circuit or exhaust line.

Pollutant emission limitations are becoming more restrictive and the resulting fuel consumption and CO2 emissions C0 ₂ are becoming more and more penalizing for vehicle users. Vehicle traffic constraints are already being applied in some cities and will be increasingly applied in order to limit pollution and the emission of greenhouse gases in cities. Some cities already use "tolls" to force users to drive in certain areas, the amount of these tolls being proportional to C0 ₂ emissions and polluting emissions.

Hybrid vehicles, by their ability to combine two onboard energy sources, allow to use the heat engine preferentially in areas of high energy efficiency, and to use the other energy source in the lower yield areas, to reduce fuel consumption and pollutant emissions such as hydrocarbons, nitric oxide, nitrogen oxides and various particles. The most common configuration for hybrid vehicles currently operational is the combination of a heat engine with an electric motor powered by a battery. Depending on the power of the electric motor and the storage capacity of the battery, Hybridization can range from simple assistance to the engine during the acceleration phases, to the complete support of the traction of the vehicle by the electric motor over a more or less long distance. The other hybrid mode of operation is called optimization of the operating point of the engine, the operating point of an engine being characterized by the speed of rotation of the engines in revolutions per minute and by the torque transmitted by the engine in newtons by metre. In this case, the heat engine generates more torque to operate the electric motor in current generator mode. The battery thus recharged can be used subsequently to operate the electric motor in torque generating mode on the wheels.

Hybrid thermal / electric vehicles however have the disadvantage of integrating electrical and electrotechnical components, the cost is relatively important. This cost is a burden on the gain in the cost of use of the vehicle, achieved through a significant reduction in fuel consumption obtained through hybridization. The main components mentioned above, are the additional electric motor and its power electronics, the coupling to the transmission and the battery.

An alternative solution to thermal / electrical hybridization is thermal / pneumatic hybridization. The principle is to recover energy in pneumatic form during decelerations of the vehicle made with or without braking, and to reuse this energy in the other fundamental phases of operation of the vehicle, such as, for example, start-up, taxiing. compressed air, and assistance during acceleration. This type of hybridization requires the implementation of components of lower cost than the electrical and electrotechnical components, these components being essentially constituted by a compressed air reservoir, valves and solenoid valves.

The principle of the pneumatic hybrid engine is known and is now in the public domain. By way of example, with reference to FIG. 1, a hybrid propulsion system of a motor vehicle comprises a thermal component through a motor 1 having four combustion chambers 2, and a pneumatic component through a reservoir. 3 of air under pressure recovered during the deceleration phases of the vehicle. The different air flows in each combustion chamber 2 are managed by two intake valves 4, an exhaust valve 5 and a charge valve 6. Schematically, incident air is sent into each combustion chamber 2 of the heat engine 1 via an intake manifold 14, the pressure of this air being regulated by a motorized throttle body 8 located upstream of said manifold 14. The actuation of each intake valve 4 makes it possible to drive the flow rate of the incident air to be injected into each chamber 2. The opening of each exhaust valve 5 creates a leakage passage for the exhaust gases from the combustion in each of said chambers 2, said gases then being conveyed , by means of an exhaust manifold 15, towards an exhaust circuit 13. A bypass flap 10 is located in the exhaust line 13 of the engine 1, to reroute the gases, either directly to the engine outside of the vehicle by an outlet 11 of this line 13 by means of a bypass circuit 21, or to a catalytic converter 12 in order to treat them before rejecting them clean outside said vehicle via this outlet 11. The reservoir 3 is in communication with each of the combustion chambers 2, through a connecting pipe 16, which opens into a charge manifold 17 for distributing the air in each of said chambers 2. Each charge valve 6 manages the passage of air between each combustion chamber 2 and said reservoir 3. Thus, when the reservoir 3 has filled with air, each charge valve 6 can open to allow the passage of air from the tank 3 to each chamber 2 combustion, in particular to provide additional injection of air into said chambers 2.

Such a hybrid propulsion system operates in 3 modes:

at. A conventional mode, which is the standard operating mode of the burning engine 1. In this case, the charge valves 6 remain in the closed position and the air reservoir 3 is not involved.

b. A pump mode, which is activated during the deceleration and braking phases of the vehicle. The air tank 3 tablet is filled during this mode. Each charge valve 6 is then controlled to open and pass air from each cylinder 2 to the reservoir 3 during the compression phase.

vs. A pneumatic mode, which is activated during the starting phases of the engine 1 and driving the vehicle only with compressed air. Each charge valve 6 is controlled to open and pass the compressed air from the tank 3 to each cylinder 2 during the expansion phase.

The bypass flap 10 of the exhaust circuit 13 is used to prevent the gases evacuated during the pump and pneumatic modes from passing through the catalytic converter 12 and thus cooling its heat. This component 12 can occupy two positions:

at. A first position for which the gases evacuated by the exhaust valves of the combustion chambers 2 during the pump and pneumatic modes are diverted to the bypass circuit 21 to avoid the catalytic converter 12, before being rejected at the outside of the vehicle. They are only composed of compressed compressed air, at a low temperature between -10 ° C and 15 ° C. This thus preserves the thermal of the catalytic converter 12, necessary for the treatment of burnt gases from the combustion chambers 2.

b. A second position for which the gases evacuated by the exhaust valves of the combustion chambers 2, during the conventional mode, pass through the catalytic converter 12 to be cleaned before being discharged into the atmosphere. Indeed, for the conventional operating mode of the heat engine 1, the exhaust gases are heated to high temperature and are loaded with polluting particles. It is therefore a priority to treat them with the catalytic converter 12 before rejecting them clean in the atmosphere. However, despite the implementation of a compressed air tank, intended to replace a heat engine, the production of carbon dioxide (CO2) by the engine is still too high. It is therefore important to increase the autonomy of the vehicle in pneumatic mode, in order to reduce the use of the engine. This autonomy is particularly related to the stored air mass, and its specific consumption level. The stored air mass is dependent on the volume of the tank, the pressure and the temperature of the stored air. The volume of the tank is limited by the architecture of the vehicle and therefore can not be refitted easily. The maximum pressure is dictated by what the engine is capable of providing in pump mode, and therefore can not be changed without a radical change in the characteristics of said engine, including the size of the combustion chambers. These two improvement paths remaining difficult to achieve, if not impossible, it remains an optimization of the air consumption by the engine, to obtain the desired engine operating point.

The article "Pneumatic-combustion hybrid engine: a study of the effect of the valve train sophistication on pneumatic modes" (The Scientific Meeting of IFP, Advances in Hybrid Powertrains, 25-26 November 2008, P.Brejaud et al) discloses a step of forcing the closing of the intake valves when the engine is in pneumatic mode. A first drawback related to this solution is its additional cost, because it requires modifying the control means of the intake valves especially for operation in pneumatic mode. A second disadvantage is its poor performance at low load.

The operating methods of a hybrid propulsion system according to the invention make it possible to optimize the phases of use of the heat engine and the phases of use of the air coming from the tank, so as to reduce the production of C02, and while overcoming the aforementioned drawbacks.

The invention relates to a method of using a hybrid propulsion system of a vehicle, comprising a compressed air reservoir and a heat engine having at least one cylinder, each of said cylinders being able to be supplied with air by an intake circuit equipped with a regulation of the air pressure and by the air tank. The main characteristic of a method of use according to the invention is that it comprises the following steps:

A step of fixing a parameter representative of the operating point of the motor,

- A step of adjusting the pressure of the air from the intake circuit by means of the regulating device, so as to minimize the consumption of air from the tank to reach said operating point.

A hybrid propulsion system has a thermal component and a pneumatic component for supplying air to each of the engine cylinders by means of a conventional air supply circuit via a device for regulating the air pressure and intake valves, and by means of a self-contained air tank. These two sources of air supply are controlled independently of one another, and can therefore be triggered simultaneously or with a time shift, which may or may not cause recovery ranges. Thus, by wishing to privilege an air supply from the tank to the detriment of an air supply supplied by the supply circuit, in order to limit the C02 emissions, it has surprisingly been found by the applicant that it was possible to reduce the consumption of this air from the tank, to reach a given operating point of the engine, by varying the pressure of the air coming from said supply circuit. Thus, when a driver wishes to reach a specific operating point of the engine in pneumatic mode, by depressing the accelerator pedal, it is possible to adapt the air pressure in the intake circuit, so as to minimize the consumption of the air coming from the tank. A method of use according to the invention allows an economical use of the air from the tank, while obtaining the engine performance sought by the driver. It is assumed that the maximum air pressure in the tank is a fixed parameter.

Advantageously, the device for regulating the pressure is a motorized throttle body. The throttle body allows regulation of the intake air pressure, which is accurate and well controlled. The opening of this housing being variable, it can therefore provide a continuous range of air pressure in the intake circuit.

Preferably, the operating point of the engine is characterized by the torque and the engine speed. The engine speed is determined by the number of revolutions per minute of the engine, and the engine torque is evaluated in Newton. Meters.

Preferably, the parameter representative of the load of the operating point is an indicated average pressure. This parameter is known under the name PMI.

Preferably, the pressure level of the intake air is adjusted by the throttle body, so as to minimize the specific consumption of air Csair from the air tank, and which is the ratio of the flow Qres from of the tank on the indicated power Pind. By analogy with the indicated specific consumption (CSI) for comparing the yields in conventional thermal operation, it is the specific consumption of Csair air that is used in the context of a method of use according to the invention. This parameter is given by the following formula:

Csair = Qres / Pind

where Csair is the specific consumption of air coming from the tank in (g / kWh), Qres is the air flow coming from the tank (in g / h) and Pind is the indicated power in kW.

Advantageously, a method according to the invention comprises a mapping step, for a given engine and a given air tank, giving the percentage of opening of the throttle body as a function of the pressure in the reservoir of air, the torque requested by the driver, and the rotational speed of the engine, so as to minimize the consumption of air from said tank. In this way, for a particular operating point of the engine, characterized by a torque and an engine speed, it is easy to refer to the cartography thus developed, to read directly what should be the air pressure in the circuit d admission allowing a minimal consumption of the air coming from the tank. Preferably, the air supply of each cylinder through the intake circuit is provided by at least one intake valve, the air supply of each of said cylinders through the reservoir being provided by at least one charge valve . Each of these valves has its own actuating mechanism and can be triggered independently of each other.

The methods of using a hybrid propulsion system of a vehicle according to the invention have the advantage of not requiring any additional equipment or part removal, in order to achieve economical and efficient operation of said propulsion system . They also have the advantage of increasing the autonomy of the vehicle in pneumatic mode, not by involving an additional source of air under pressure, but by optimizing the use of the various components of the hybrid propulsion system.

The following is a detailed description of a method according to the invention, making it possible to use, under optimized conditions, a hybrid propulsion system comprising a heat engine and a pressurized air tank, with reference to FIGS. and 2.

FIG. 1 is a schematic view of an already existing hybrid propulsion system,

FIG. 2 is a diagram showing the specific consumption of Csair air as a function of the indicated average pressure PMI for different pressures in the air intake circuit and in the tank.

Figure 1 has already been described. A principle of the present invention is to control advantageously the throttle body 8 without modifying the control laws of the intake valves 4.

It is recalled that a hybrid propulsion system of a vehicle according to the invention is schematically represented in FIG. 1 and that it comprises a thermal component through a heat engine 1 and a pneumatic component thanks to a reservoir 3 of pressurized air. A method according to the invention for using such a hybrid propulsion system comprises the following steps:

- A step of setting a parameter representative of the operating point of the engine 1. This fixing step is performed by a user, who will depress the accelerator pedal to try to reach a point of operation of the engine 1 in mode pneumatic. An operating point of the engine 1 is essentially characterized by two parameters: the torque (in Nm) and the speed (in revolutions / min). It is therefore for this user to try to reach this point of operation of the engine 1, using only the air coming from the pressurized air tank (pneumatic mode). The parameter which is representative of the load of the operating point of the engine 1, is the indicated average pressure (PMI). In summary, this fixing step consists in assigning a value of PMI, which corresponds to what a user wishes to obtain by operating the accelerator pedal.

A step of adapting the air pressure in the intake circuit, by means of a regulation device placed on said circuit, so as to minimize the consumption of air coming from the tank 3 to reach said Working point. Indeed, it has been observed that the operating point selected in the first step through the allocation of a PMI value could be reached with a minimized specific consumption of the air coming from the tank 3, thanks to a value adapted to the pressure of the incident air circulating in the air intake circuit, said value being controlled by means of a motorized throttle body 8. This is particularly visible in the diagram of FIG. of this diagram gives the specific air consumption Csair according to the IMP to achieve, for a given value of the air pressure in the intake circuit and for a given value of the pressure in the tank 3 of pressurized air. For example, in this diagram, for a tank pressure of 15 bar and to achieve a PMI of 3 bar, it will be necessary to favor a pressure in the intake circuit which will be maximum, in this case 100Ombars, thanks to an opening percentage of the motorized throttle body 8 maximum. Indeed, by referring to the curve 20, which is representative of a pressure of 100Ombars in the intake circuit, the specific consumption of air Csair will be close to 24 g / kWh, while this consumption will increase to 26 or 27 g / kWh if the pressure in the intake circuit is only 500mbars as shown in curve 21. Still referring to these two curves 20,21, beyond a PMI of 4 bars to reach it will be preferable to close the motorized throttle body 8, to obtain a pressure of 500mbars in the intake circuit, and to minimize the Csair. It is important to emphasize that the method according to the invention is not limited to the single example illustrated in the diagram of FIG. 2. This example merely illustrates the possibility of limiting the specific consumption of air coming from the reservoir 3, to reach a given operating point of the engine, by varying the value of the air pressure, via the throttle body 8 motorized in the air supply system of the cylinders 2 of the engine.

It is recalled that in order to prevent gases stored in a cylinder 2 from passing to the tank 3, the charge valve 6 is only opened when the pressure in the cylinder 2 is close to the pressure in the tank 3. pressure in the intake circuit 14 is high, the pressure in the cylinder at top dead center (TDC) is high, which leads to waiting longer than the pressure in the cylinder 2 is close to the pressure in the tank 3, before opening the charging valve 6. Conversely, if the pressure in the intake manifold 14 is low, the cylinder pressure at the TDC is small, which leads to being able to open the valve earlier. load 6 and thus benefit from a greater relaxation stroke. At low load, the opening time of each charging valve 6 being low, the expansion stroke of the piston is sufficient to relax all the compressed air injected by each charging valve 6, even if the instant of The opening is delayed due to a high TDC cylinder pressure, when the pressure in the inlet manifold 14 is large. We take this opportunity to reduce the pumping on admission and therefore to reduce the low pressure PMI.

At high load, the opening times of each charging valve 6 are higher, which leads to position the opening slot of the charge valve 6 all the more late, as the pressure in the distributor 14 of admission is high. This niche may be so late, that the compressed air no longer has the piston stroke necessary to relax, which is detrimental from a performance point of view. To achieve the same PMI with a pressure in the low intake manifold 14, the opening slot of each load valve 6 will be positioned earlier in the engine cycle, to benefit from a greater relaxation stroke. This situation is beneficial for performance, despite the creation of a negative low pressure loop (LP). When the gain of PMI High Pressure by a better setting of the opening of the charge valve 6, compensates for the losses on the low pressure PMI, the specific consumption of Csair air from the tank 3, intersect.

In pneumatic mode, the opening percentage of the motorized throttle body 8 in the air intake circuit is therefore a function of the air pressure in the reservoir (near), the torque (C) requested by the user by depressing the accelerator pedal, and the rotation speed (N) of the engine 1. This opening percentage can be mapped according to these parameters, to allow instantaneous evaluation of the value of this percentage, depending on the operating point of the motor to be reached.

Claims

A method of using a hybrid propulsion system of a vehicle, comprising a reservoir (3) of compressed air and a heat engine (1) provided with at least one cylinder (2), each of said cylinders ( 2) can be supplied with air by an intake circuit provided with a device (8) for regulating the air pressure and by the air tank (3), said method being characterized in that includes the following steps,

A step of setting a parameter representative of the operating point of the motor (1),

- A step of adapting the air pressure from the intake circuit by means of the regulating device (8), so as to minimize the consumption of air from the tank (3) to reach said point Operating.

2. Method of use according to claim 1, characterized in that the pressure regulating device is a motorized throttle body (8).

3. Method of use according to claim 2, characterized in that the operating point of the engine (1) is characterized by the torque and the engine speed.

4. Method of use according to claim 3, characterized in that the parameter representative of the load of the operating point is an indicated average pressure (PMI).

5. Method of use according to any one of claims 2 to 4, characterized in that the pressure level of the intake air is adjusted by the throttle body (8), so as to minimize the specific fuel consumption. air (Csair) from the air tank (3), which is the ratio of the flow rate (Qres) from the tank (3) to the indicated power (Pind).

6. Method of use according to any one of claims 2 to 5, characterized in that it comprises a development step, for a motor (1) and a given air reservoir (3), a mapping showing the opening percentage of the throttle body (8) according to the pressure in the tank (3) of air, the torque demanded by the driver, and the rotational speed of the engine (1), so as to minimize the consumption of air from said tank (3).

7. Method of use according to any one of claims 1 to 6, characterized in that the air supply of each cylinder (2) through the intake circuit (14) is provided by at least one valve of admission (4), and in that the air supply of each of said cylinders (2) through the tank (3) is provided by at least one charge valve (6).