Method for reducing the energy of the acceleration-boosting torque of a hybrid vehicle

Abstract

A method for reducing energy of torque for electrically boosting acceleration of a hybrid vehicle including a power train, a heat engine, an electric machine capable of jointly or separately outputting a torque to a wheel in accordance with management laws optimizing energy consumption of the vehicle, and a traction battery which is capable of recovering all or part of kinetic energy of a decelerating vehicle in a form of electric energy, and rechargeable via the heat engine. In the method electric boost torque available for the torque boost is reduced by a reduction coefficient of 0 to 1 according to an amount of energy remaining in an energy range of the battery reserved for the torque boost.

Claims

1. A method for limiting energy of torque for electrically boosting acceleration of a hybrid vehicle including a power train, at least one heat engine, and at least one electric machine configured to jointly or separately supply torque to a wheel under control of management laws optimizing energy consumption of the hybrid vehicle, and a traction battery configured to recover at least a part of kinetic energy of the hybrid vehicle in deceleration in a form of electrical energy, and be recharged via the at least one heat engine, the method comprising: defining the traction battery according to a first hypothetical battery and a second hypothetical battery, the first hypothetical battery defining a first energy band not reserved for electrical torque boost, and the second hypothetical battery defining a second energy band reserved for electrical torque boost; and reducing electrical boosting torque available for torque boost by a limiting coefficient having a value between 0 and 1, according to a quantity of energy remaining within the second energy band of the traction battery reserved for electrical torque boost, wherein energy stored in the traction battery is distributed based on the first and second energy bands, reserved respectively for application of an energy management law of the power train without reservation of the electrical torque boost, and with reservation of the electrical torque boost, wherein a quantity of energy assigned to the second energy band reserved for electrical torque boost is computed by integrating electrical power supplied by the at least one electric machine in a torque boost mode, wherein the electrical power supplied by the at least one electric machine in the torque boost mode is computed based on a difference between electrical power effectively consumed in the torque boost mode and electrical power recovered in deceleration or by recharging via the at least one heat engine, wherein the electrical power recovered in deceleration or by recharging via the at least one heat engine is weighted by a weighting coefficient computed as a function of a state of charge of the traction battery, and wherein the limiting coefficient is obtained by mapping, from the value of the integral obtained by the integrating of the electrical power supplied by the at least one electric machine in the torque boost mode.

2. The energy limiting method as claimed in claim 1, wherein the limiting coefficient is computed as a function of the quantity of energy remaining within the second energy band of the traction battery reserved for the electrical torque boost.

3. The energy limiting method as claimed in claim 1, wherein the weighting coefficient is 0 below a first threshold of a percentage of charge of the traction battery.

4. The energy limiting method as claimed in claim 3, wherein the weighting coefficient increases from the value 0 to the value 1, between the first threshold and a second threshold greater than the first threshold.

5. The energy limiting method as claimed in claim 1, wherein the limiting coefficient is returned in a loop as an electrical boost torque setpoint.

Description

(1) Other features and advantages of the present invention will become clearly apparent on reading the following description of a non limiting embodiment thereof, by referring to the attached drawings, in which:

(2) FIG. 1 shows the extra torque from the electrical torque boost over the maximum torque from the heat engine,

(3) FIG. 2 illustrates the proposed energy management mode,

(4) FIG. 3 illustrates the calculation of distribution of the recovered energy on which this management mode is based,

(5) FIG. 4 is a scheme for computing the integral limiting the electrical torque boost, and

(6) FIG. 5 illustrates the reduction of the torque obtained compared to FIG. 1.

(7) In a hybrid vehicle equipped with a power train comprising at least one heat engine and one electrical machine, capable of jointly or separately supplying a torque to the wheel, these two sources of energy are placed under the control of management laws (LGE) optimizing the energy consumption of the vehicle. A traction battery, generally capable of recovering, in electrical energy form, at least a part of the kinetic energy of the vehicle in deceleration, and that can be recharged via the heat engine, powers the electrical machine.

(8) A hybrid vehicle therefore has at least two actuators capable of supplying torque to the wheel: the torque demand from the driver can thus be satisfied by the sum of the torques supplied by the electrical machine and the heat engine. As indicated above, it is possible to improve the overall consumption of a hybrid power train by optimizing the distribution of torque between the two actuators, by virtue of an appropriate energy management law (LGE). However, for this law to be able to fully play its part, the traction battery must permanently have a reserve of energy sufficient to apply the optimal distribution.

(9) The maximum torque of the power train is defined on the basis of the maximum torque supplied by the heat engine, to which is added the overtorque supplied by the electrical machine. The curves C.sub.1, C.sub.2 of FIG. 1 respectively show the trend of the maximum torque of the heat engine as a function of its speed , and the maximum torque envelope available to the wheel with the addition of the electrical torque boost. The difference between the two curves C.sub.1 and C.sub.2 represents the available electrical torque boost. In order to control the energy expenditure of the driver in strong acceleration phases, it is proposed to limit the electrical boost torque available, by applying to it a limiting coefficient C, lying between 0 and 1. The electrical boost torque available for the torque boost is thus reduced by the limiting coefficient C, according to the quantity remaining within an energy band of the battery, which is reserved for the torque boost. The limiting coefficient C is calculated as a function of the energy remaining, within an energy band reserved for the torque boost. In the proposed method, it is in fact considered that the energy stored in the traction battery B is distributed between two energy bands (B.sub.1, B.sub.2), reserved respectively for the application of the energy management law of the power train outwith the electrical torque boost, and with the electrical torque boost.

(10) The distinction between the two energy bands is illustrated by FIG. 2: its top part corresponds to a physical representation of the traction battery B of the vehicle, whereas its bottom part introduces the proposed monitoring mode with the distinction of two hypothetical batteries: a first battery B.sub.1, the energy of which is involved without reserve in the energy management law in order to reduce the overall consumption of the power train, and a second battery B.sub.2, reserved for the torque boost.

(11) To calculate the quantity of energy available in the band B.sub.2, the power already supplied by the electrical machine in torque boost mode is integrated. The value of this integral, named I, is calculated as follows:
I=.sub.TP.sub.ElecOUT(P.sub.ElecRECUP*K),
in which:

(12) P.sub.ElecOUT=max((P.sub.GMPP.sub.MAXthermique)*n.sub.Elec;0) is the electrical power dissipated in torque boost mode,

(13) D.sub.Elec is an overall electrical efficiency, comprising the efficiency of the electrical machine, of the inverter, and of the battery, P.sub.GMP is the power demanded of the power train by the driver,

(14) P.sub.MAXthermique is the maximum power than the heat engine can supply,

(15) $P_{\mathrm{ElecRECUP}}=\min \left(\frac{P_{\mathrm{GMP}}}{n\mathrm{Elec}};0\right)$
is the electrical power recovered,

(16) K is a weighting coefficient calculated as a function of the state of charge of the physical battery, and

(17) T is the time spent in mission.

(18) The coefficient K makes it possible to assign the energy recovered by the electrical machine in generator mode, either in the battery B.sub.1, or in the battery B.sub.2.

(19) When the reserve of energy for the torque boost is full, I=0 [Wh]. When the reserve of energy is empty, I=E.sub.MAX [Wh], E.sub.MAX being the quantity of an energy made available to the driver, that is to say the capacity of the hypothetical battery B.sub.2.

(20) If the battery B.sub.1 contains enough energy to allow for the energy optimization, then K=1. All the energy recovered is then assigned to the battery B.sub.2. The driver can expend the recovered energy, in electrical torque boost mode.

(21) If the battery B.sub.1 does not contain enough energy to allow for the energy optimization then K=0. All the recovered energy is assigned to the battery B.sub.1: it is recharged with the energy recovered, without allocating energy to the hypothetical battery B.sub.2: the driver no longer benefits from the electrical boost in strong acceleration phases. Priority is thus given to reducing the consumption, rather than to the performance of the power train. The driver no longer has all the performance characteristics of the electrical boost since he or she has already expended all the energy allocated thereto.

(22) The weighting coefficient K defines the order of priority of the energy storage between the battery B.sub.1 and the battery B.sub.2, in order to improve either the performance, or the consumption. The scheme of FIG. 3 illustrates a non limiting way of determining K, as a function of the percentage charge of the battery, SOC %. Below a first threshold S.sub.1, K is 0. All the energy recovered in the battery is devoted to the energy management law LGE. Between S.sub.1 and a second threshold S.sub.2 higher than the latter, K has a linear growth. From S.sub.2, K=1, all the energy recovered in the battery is available for the torque boost.

(23) According to FIG. 4, the difference between the first and the second quantity of energy, weighted by the coefficient K that is a function of the state of charge of the battery SOC, is integrated. The quantity of energy I assigned to the energy band B.sub.2 is calculated by integrating the electrical power supplied by the electrical machine in torque boost mode. This power is calculated by the difference between the electrical power effectively consumed in torque boost mode and the electrical power recovered in deceleration or by recharging via the heat engine. The electrical power recovered is thus weighted by the weighting coefficient K, calculated as a function of the state of charge of the traction battery.

(24) The value of the integral I, corresponding to the reserve of energy reserved for the electrical boost, makes it possible to obtain, by mapping, the limiting coefficient C, limiting the electrical boost, which is returned in a loop on the available electrical power setpoint in torque boost mode.

(25) FIG. 5 introduces the limiting of the power available for the boost in FIG. 1. In this example, the envelope of maximum torque available to the wheel with the addition of the electrical torque boost without weighting (curve C.sub.2) and the electrical torque boost available with a limiting of the order of 20% (curve C.sub.3) are distinguished.

(26) As indicated above, when the integral I reaches E.sub.MAX, the electrical torque in torque boost mode becomes zero. The following example illustrates the implementation of the method on the basis of a number of examples.

(27) In a first situation, with an integral I (hypothetical battery B.sub.2) of 30 Wh, and a 30 Wh recharged physical battery B, its state of charge (SOC) is considered to be high, K=1. The energy management law (LGE) has enough energy to optimize the consumption. The 30 Wh recovered can be assigned to the hypothetical battery B.sub.2, to be expended fully in boost mode.

(28) In a second situation, with a same integral I value of 30 Wh of B.sub.2, there is a low physical battery state of charge, placing, for example, the coefficient K at 0.33. The LGE does not have enough energy to optimize the consumption. 20 Wh of the 30 Wh of the hypothetical battery are allocated to the LGE (battery B.sub.1) by discharging the hypothetical battery by only 10 Wh for the boost (battery B.sub.2).

(29) In a third situation, still with the same integral value of 30 Wh, the state of charge of the physical battery places the coefficient K at the value 0. The LGE does not have enough energy to optimize the consumption. All of the 30 Wh recovered will therefore be allocated to it (battery B.sub.1), without assigning energy to the battery B.sub.2 for the boost.

(30) The invention offers many advantages: it makes it possible to limit the electrical boost torque made available to the driver for strong accelerations, so as not to affect the energy management, particularly on hybrid vehicles with little on board energy, and it facilitates the typing of the electrical machine between targets of performance or of consumption.