Method for estimating the torque of a heat engine

Abstract

A method estimates a torque of a heat engine in a vehicle hybrid transmission including at least a heat engine and an electric machine together or separately supplying a heat engine torque and heat engine torque intended for wheels of the vehicle. The method uses a measurement of a speed of the heat engine, a value of the heat engine torque reference, and a value of the electric machine torque. The method also sums an estimate of a total torque supplied by the transmission to the wheels and of an estimate of an equivalent resistive torque of the transmission to determine the estimated heat engine torque.

Claims

1. A method for controlling a torque of a heat engine of a vehicle hybrid transmission including at least the heat engine and an electric machine supplying a torque of the heat engine and the electric machine to wheels of the vehicle, comprising: measuring a speed of the heat engine, a reference torque of the heat engine, and the torque of the electric machine; estimating a total torque supplied by the transmission; estimating an equivalent resistive torque of the transmission to obtain an estimated equivalent resistive torque of the transmission, wherein the estimated equivalent resistive torque of the transmission is obtained by assigning a gain M.sub.1 a sign of an integration x.sub.1 and then multiplying by an inverse of a gain k.sub.2, then integrating, then multiplying by an inverse of an engine time constant , then integrating, then multiplying by a parameter , the parameter being dependent on stepdown gear ratios of a gearbox and an axle assembly of the vehicle; estimating the torque of the heat engine by summing the estimated total torque supplied by the transmission and the estimated equivalent resistive torque of the transmission; and controlling the torque of the heat engine based on the estimated torque of the heat engine and the reference torque of the heat engine.

2. The method for controlling the torque of the heat engine as claimed in claim 1, wherein a transmission equivalent inertia with respect to the heat engine is determined from a relationship of the type
J.sub.eq_th{dot over ()}.sub.th=T.sub.th+T.sub.emT.sub.eq.sup.res, where a parameter is dependent on stepdown gear ratios between a heat engine shaft and the wheels, T.sub.th is the torque of the heat engine, T.sub.em is the torque of the electric machine, .sub.th is the speed of the heat engine, T.sub.eq.sup.res is the equivalent resistive torque of the transmission, and J.sub.eq-th is the transmission equivalent inertia with respect to the heat engine.

3. The method for controlling the torque of the heat engine as claimed in claim 2, wherein an estimate of the speed of the heat engine is obtained from an integrated term, the integrated term being an integration of the torque of the electric machine multiplied by the parameter , and a drift compensation being assigned a sign of a difference of the measurement of the speed of the heat engine and the estimate of the speed of the heat engine.

4. The method for controlling the torque of the heat engine as claimed in claim 3, wherein the integrated term is corrected in a loop by an inverse of the transmission equivalent inertia with respect to the heat engine.

5. The method for controlling the torque of the heat engine as claimed in claim 3, wherein the drift compensation assigned the sign of the difference of the measurement of the speed of the heat engine and the estimate of the speed of the heat engine is multiplied by the inverse of a gain k.sub.1, and corrected with a result of the integration x.sub.1.

6. The method for controlling the torque of the heat engine as claimed in claim 5, wherein the estimate of the total torque is obtained by integrating the reference torque of the heat engine and the gain M.sub.1 assigned the sign of the integration x.sub.1.

7. A method for controlling a torque of a heat engine of a vehicle hybrid transmission, comprising: measuring a speed of the heat engine, a reference torque of the heat engine, and a torque of an electric machine; estimating a total torque supplied by the transmission, an equivalent resistive torque of the transmission, and a speed of the heat engine, wherein the estimated speed of the heat engine is corrected in a loop by an inverse of a transmission equivalent inertia with respect to the heat engine, and wherein the estimated equivalent resistive torque of the transmission is obtained by assigning a gain M.sub.1 a sign of an integration x.sub.1 and then multiplying by an inverse of a gain k.sub.2 then integrating, then multiplying by an inverse of an engine time constant , then integrating, then multiplying by a parameter , the parameter being dependent on stepdown gear ratios of a gearbox and an axle assembly of the vehicle; estimating the torque of the heat engine by summing the estimated total torque supplied by the transmission and the estimated equivalent resistive torque of the transmission; and controlling the torque of the heat engine based on the estimated torque of the heat engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from reading the following description of one nonlimiting embodiment thereof and by referring to the attached drawing, the single FIGURE of which illustrates the key steps in the method.

DETAILED DESCRIPTION

(2) By applying the fundamental principle of mechanics to a hybrid powertrain comprising a heat engine and an electric machine, the following dynamic model is obtained: for the heat engine: J.sub.th{dot over ()}.sub.th=T.sub.thT.sub.th.sup.res for the electric motor: J.sub.em{dot over ()}.sub.em=T.sub.emT.sub.em.sup.res for the wheel: J.sub.r{dot over ()}.sub.r=T.sub.rT.sub.r.sup.res

(3) where: .sub.th: the speed of the heat engine, T.sub.th: the torque of the heat engine, T.sub.th.sup.res: the resistive torque of the heat engine, J.sub.th: the inertia of the heat engine, .sub.em: the speed of the electric motor, T.sub.em: the motor torque, T.sub.em.sup.res: the resistive torque of the electric motor, the inertia of the electric motor, .sub.r: the speed of the wheel, T.sub.r: the torque applied to the wheel, T.sub.r.sup.res: the resistive torque applied to the wheel (unknown input of external origin), J.sub.r: the inertia of the wheel.

(4) The torque of the heat engine T.sub.th is always a response to the driver's torque demand (reference) T.sub.th.sup.ref. If is the symbol used for a time constant of the heat engine ( (comprised between .sub.min and .sub.max) being indicative of the responsiveness of the heat engine to achieving its torque reference T.sub.th.sup.ref, this can be written:
{dot over (T)}.sub.th=T.sub.th.sup.refT.sub.th.

(5) Whatever the kinematic mode of the transmission, the overall inertia of the powertrain can be referenced to the heat engine by introducing the notions of equivalent inertia or inertia with respect to the heat engine J.sub.eq-em, and of equivalent resistive torque T.sub.eq.sup.res.

(6) The fundamental principle of dynamics, applied to the sum of the driving and resistive torques of the transmission, can be written as follows: J.sub.eq_th{dot over ()}.sub.th=T.sub.th+T.sub.emT.sub.eq.sup.res, where () and () are dependent on the stepdown gear ratios between the heat engine shaft and the wheels. is dependent in particular on the stepdown gear ratios of the gearbox and on the axle assembly of the vehicle.

(7) From a relationship of this type it is possible to determine the value of equivalent inertia of the transmission with respect to the heat engine J.sub.eq-th. The equivalent resistive torque may be the resistive torque applied to the wheel T.sub.r.sup.res or the resistive torque of the engine or motor. From this equation, the invention proposes constructing an observer that makes it possible to establish an estimate of the heat engine speed {circumflex over ()}.sub.th, an estimate {circumflex over (T)}.sub.th of the torque T.sub.h, applied by the heat engine, and an estimate {circumflex over (T)}.sub.eq.sup.res of the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res, guaranteeing the robustness of {circumflex over (T)}.sub.th.

(8) The method is illustrated in FIG. 1. It makes it possible to estimate the torque of a heat engine in a vehicle hybrid transmission comprising at least a heat engine and an electric machine together or separately supplying a heat engine torque T.sub.th and an electric torque T.sub.m intended for the wheels of the vehicle. The output signals {circumflex over ()}.sub.th, {circumflex over (T)}.sub.th, {circumflex over (T)}.sub.eq.sup.res may be seen in FIG. 1, together with the estimate of the total torque {circumflex over (T)}.sub.th.sup.tot. The estimated torque of the heat engine {circumflex over (T)}.sub.th is the algebraic sum of {circumflex over (T)}.sub.th.sup.tot and of {circumflex over (T)}.sub.eq.sup.res. These estimates are produced from just three inputs used by the observer: a measurement of the speed of the heat engine .sub.th, the value of the heat engine torque reference T.sub.th.sup.ref, and the value of the electric machine torque T.sub.em.

(9) M.sub.0, M.sub.1, k.sub.1 and k.sub.2 are the gains that need to be calibrated. A first gain M.sub.0 or drift compensation is assigned the sign of the difference (.sub.th{circumflex over ()}.sub.th) to be added to the product .Math.T.sub.em. This sum is integrated in order to give the estimate {circumflex over ()}.sub.th of the engine speed with loop correction by the product of the integration with the inverse of the equivalent inertia J.sub.eq-th. The term M.sub.0 assigned the sign of (.sub.th{circumflex over ()}.sub.th) is multiplied by the inverse of the gain k.sub.1. This product is integrated, then corrected with the result of the integration x.sub.1. To sum up, an estimate {circumflex over ()}.sub.th of the engine speed is obtained from its measurement .sub.m by integrating the sum of the product .Math.T.sub.em and of the calibrated gain M.sub.0 assigned the sign of the difference .sub.th{circumflex over ()}.sub.th.

(10) The sign of x.sub.1 is imposed on the second gain M.sub.1, used to calculate the torque estimates {circumflex over (T)}.sub.th.sup.tot, {circumflex over (T)}.sub.th and {circumflex over (T)}.sub.eq.sup.res in the subsequent steps. The term M.sub.1.Math.sign(x.sub.1) is added to the torque reference T.sub.th.sup.ref to give, through integration, the estimate of the total torque {circumflex over (T)}.sub.th.sup.tot. This undergoes double integration after having been multiplied in succession by the inverse of the gain k.sub.2 and by the inverse of the engine time constant . The estimate of the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res is obtained by multiplying the result by the inverse of the parameter mentioned above. As indicated in the figure, the estimate of the heat engine torque {circumflex over (T)}.sub.th is the sum of the estimate of the total torque {circumflex over (T)}.sub.th.sup.tot and of the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res.

(11) The proposed method for estimating the torque thus breaks down into two main phases: a first phase that involves estimating the speed of the heat engine {circumflex over ()}.sub.th, the total applied torque {circumflex over (T)}.sub.th.sup.tot and the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res, and a second phase that involves estimating the applied torque of the heat engine {circumflex over (T)}.sub.th from the total applied torque {circumflex over (T)}.sub.th.sup.tot and from the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res.

(12) In order to estimate the speed of the heat engine {circumflex over ()}.sub.th, the total applied torque {circumflex over (T)}.sub.th.sup.tot and the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res, the observer has available to it only the heat engine speed measurement .sub.th, the torque reference T.sub.th.sup.ref and the electric machine torque T.sub.em.

(13) In the second step, the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res is multiplied by the parameter .

(14) In conclusion, the invention proposes a robust method for estimating torque for a vehicle equipped with a heat engine or hybrid powertrain. The observer allows the applied torque of the heat engine {circumflex over (T)}.sub.th, the total applied torque {circumflex over (T)}.sub.th.sup.tot and the equivalent resistive torque {circumflex over (T)}.sub.eq.sup.res to be estimated. This estimation makes it possible for the next step, that of coupling the two shafts (reapplication of torque or torque switchover) to be rendered transparent, thereby considerably reducing the jerkiness of the torque curve. The method notably allows better control over how well the torque curve is followed while two shafts are being synchronized, by means of the heat engine. Finally, the convergence of the estimated speed {circumflex over ()}.sub.th onto the measured speed .sub.th is somewhat insensitive to variations in the parameters of the system, such as the inertia and response time of the actuator, or any lags there might be, so that this observer is particularly robust.