FR2833895A1 - Method for starting vehicle with heat engine and automatic transmission controlled by computer is initiated by detection of start up requirement and ended by total closure of clutch - Google Patents

Abstract

The method for starting the vehicle fitted with an automatic transmission, an input clutch and a heat engine controlled by a computer is initiated by the detection (a) of the desire to start the vehicle and closed by the total closure (f) of the clutch. It comprises the servo-control of the engine to a speed instruction, the partial closure of the clutch whilst maintaining the engine servo-control, obtaining a desired acceleration, the progressive suppression of the clutch slipping until zero clutch slipping is obtained (3) and the total closure of the clutch.

Description

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METHOD FOR STARTING A VEHICLE EQUIPPED WITH A
THERMAL ENGINE AND TRANSMISSION
AUTOMATED
The present invention relates to automated transmissions, and more particularly to their behavior when starting a motor vehicle.

 The invention relates more specifically to a method of starting a vehicle equipped with an automated transmission, provided with an input clutch, and a heat engine respectively placed under the control of a computer, said method being initiated by the detection of the will to start the vehicle and closed by the total closure of the clutch.

 Starting a vehicle fitted with such a transmission can be judged on the basis of comfort criteria such as exceeding the engine speed with respect to its final value during starting the vehicle, the torque supplied to the wheels or the acceleration of the vehicle during start-up, the clutch slip time and the jerk experienced during and at the end of vehicle start-up.

primaire de boite n'est pas parfaite. La minimisation de cet à-coup est un 1 critère de jugement du démarrage d'un véhicule. It is known from the prior art a device in which the clutch and the heat engine are controlled in particular as a function of the depressing of the accelerator pedal. This depression is interpreted as a request concerning the acceleration or the speed of the vehicle. At the end of starting, when the sliding of the clutch is canceled, we typically observe a jerk when the synchronization of the motor shafts and

gearbox primer is not perfect. The minimization of this jerk is a 1 criterion for judging the starting of a vehicle.

 To this end, the publication BOSCH WO 98 58514 proposes to correct the setpoint of the driver's engine torque in order to connect the setpoint of torques without interruption before and after the cancellation of the

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 clutch slipping. Due to uncertainties in the dynamics of engine and / or clutch control as a function of various phenomena, in particular the aging or wear of the clutch, the torque correction provided for in this publication does not have the desired precision. and takes place at the expense of other comfort criteria, such as exceeding the engine speed in relation to its final value during starting the vehicle, the torque supplied to the wheels or the acceleration of the vehicle during starting and the duration of clutch slipping.

 A first objective of the present invention is to control the engine speed during the starting of the vehicle. It meets a criterion of acoustic comfort. Indeed, an evolution of the engine speed which presents a significant overshoot compared to the final value of said speed is very badly felt by the driver and his passengers. In order to avoid this inconvenience, the proposed solution consists in controlling the engine so as to control its speed to a speed setpoint.

 A second objective is to quickly restore the acceleration of the vehicle as soon as the computer detects the driver's will to start the vehicle, and this requires rapidly increasing the torque transmissible by the clutch because when the clutch is slippery, the wheels benefit from the torque transmitted by the clutch multiplied by the gearbox ratio.

 A third objective is the smooth cancellation of the clutch slip. In fact, when the slip is canceled, the torque at the clutch output suddenly changes from the torque transmissible by the clutch to the torque delivered by the engine. The difference between these two torques results in a drop in torque at the wheels when the slip followed is canceled. To eliminate this jerk, the invention provides to minimize the difference between the torque transmissible by the clutch and the engine torque when the slip is canceled.

 To achieve all of these objectives, the invention consists of a start-up strategy controlling the combustion engine and the clutch simultaneously.

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 This strategy makes it possible to control the engine speed in order to avoid exceeding the final speed of starting the vehicle, then quickly establish the acceleration of the vehicle, then to control the slip of the clutch so that the cancellation of the sliding be done smoothly.

 This process is characterized in that, during an initial phase, the engine is slaved to a speed setpoint, the clutch is partially closed during a second phase quickly while maintaining the engine control initiated in the initial phase, the sliding of the clutch is then gradually eliminated until a zero clutch slipping is obtained, and the clutch is finally closed completely.

 Advantageously, so that the engine speed does not reach a value causing an auditory inconvenience for the driver, the speed setpoint corresponds to the minimum engine speed necessary for the engine to provide a torque equivalent to the clutch torque to be produced.

 According to another characteristic of the invention, the speed setpoint is obtained by first defining for each pedal position value a torque at the wheels or a clutch torque to be produced. The speed reference is then defined from the clutch torque and the torque = f (speed) characteristics of the engine.

 The present invention also provides that the transmission computer dialogues with the engine control computer and controls the clutch to control the slip of the clutch or the engine speed during starting.

 Other characteristics of the invention will appear on reading the detailed description which follows, for the understanding of which reference will be made to the following appended drawings: FIG. 1 is a schematic breakdown of a starting of a motor vehicle according to the invention .

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- Figure 2 is an example of determining the speed setpoint, characteristic of the starting process according to the invention.

Figure 1 details a motor vehicle start and its breakdown into several distinct phases.

An initial control phase 1 begins upon detection (a) of the will to start the vehicle, when either the first gear, the second gear or the reverse gear is engaged and when the driver presses the pedal. accelerator. From the start of phase 1, the transmission computer sends torque or speed instructions to the engine computer to control the engine at speed reference 11, corresponding to the minimum engine speed necessary for the engine to provide an engine torque equal to clutch torque 12 to be produced.

FIG. 2 describes a means of determining this speed setpoint 11. The bell curves represent the torque characteristics as a function of the speed for an engine according to different values of the position of the accelerator pedal. On this map, after having previously defined the clutch torque 12 to be produced as a function of the position of the accelerator pedal, the equation line is drawn (Engine torque = Clutch torque 12 to be produced), which has at least one intersection Pi (Engine torque i, Engine speed i) with the characteristic curves of the engine. This makes it possible to determine the conditions under which the engine can supply a torque equivalent to the clutch torque 12 to be produced. The engine speed setpoint chosen 11 is then the minimum value of the speeds corresponding to the intersection points obtained Pi.

A phase 2 of rapid clutch closure follows, as soon as a predetermined threshold is reached (b), the initial phase 1 until the clutch torque setpoint or the acceleration defined above is reached. above (c). This clutch torque must be such as to provide torque to the wheels or

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 an acceleration of the vehicle close to that which will be obtained after the clutch is closed. During this entire phase 2, the automated transmission computer continues to slave the engine to the speed setpoint 11.

The engine speed control can take account of the torque transmitted by the clutch to better ensure the control. The servo-control of the engine speed makes it possible to maintain clutch slip and to quickly establish the acceleration of the vehicle by increasing the torque transmitted by the clutch without this causing jolts. The speed at which the clutch closes can be varied depending on the driving style of the driver.

The torque transmitted by the clutch is made to increase rapidly to an intermediate level from which the growth of the torque is attenuated, a level which may depend on the operating point, on variables originating from the vehicle (vehicle speed, engine torque, etc.). and variables from an analysis of driving style (sportiness, ...).

 The vehicle start control then goes to phase 3. During this phase, the clutch torque setpoint and the motor control are kept constant. This phase increases the acceleration of the vehicle from a zero value to a value corresponding to the will of the driver materialized by the position of the accelerator pedal. The primary gearbox mode increases during this phase following a slope or an acceleration corresponding to the torque transmitted by the clutch. This phase lasts as long as the clutch slip is greater than a predefined slip threshold (d).

 The next phase 4 of controlling the clutch slip then makes it possible to nullify this slip (e). The slip of the clutch is controlled by an action on the torques supplied by the engine and transmitted by the clutch: simultaneously, the engine torque setpoint is given to the torque requested by the driver according to a law depending on the slip, from variables of the vehicle (vehicle speed, engine torque, etc.) and of variables

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 from an analysis of the driving style (sportiness, ...). This phase is used to maintain the traction torque of the vehicle by imposing the clutch torque and to modulate the engine speed to limit the dissipation of energy in the clutch.

moteur est régie par la relation suivante :

d d) mot Cmot-Cemb = Jmot *-----dt

Cemb= couple transmissible par l'embrayage, Cmot = couple moteur, comot = régime moteur, Jmot = inertie du moteur. The invention therefore provides during the cancellation of the slip, to limit the jolts, to minimize the difference between the torque transmitted by the clutch and the engine torque, which amounts to ensuring an acceleration of the engine speed close to zero when the slip is canceled. Indeed, at the instant when the slip is canceled, the torque transmitted by the clutch passes from the torque transmissible by the clutch Cemb, to the engine torque Cmot. The kinematic chain is therefore excited by a torque rung whose amplitude is equal to (Cemb-Cmot). Minimizing the jerk amounts to minimizing the derivative of the engine speed because the evolution of the speed

engine is governed by the following relation:

dd) word Cmot-Cemb = Jmot * ----- dt

Cemb = torque transmissible by the clutch, Cmot = engine torque, comot = engine speed, Jmot = engine inertia.

 The final phase 5 then consists in completely closing the clutch (see Figure 1 (f)). This phase begins when the engine and primary speeds are practically equal. The clutch can then be closed quickly without any jolts being felt. The engine torque setpoints remain equal to the torque that the engine would have delivered without the intervention of the automated transmission. It ends when the clutch is fully closed, that is to say when the torque transmitted by the clutch has reached its maximum value.

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 As indicated above, the solution proposed by the invention is applicable to any vehicle equipped with a petrol or diesel thermal engine and an automated transmission, provided with a computer controlling the actuation of the input clutch. The petrol or diesel combustion engine can be fitted with a motorized throttle unit, controlled by a computer. The present invention is not incompatible with the fact that the transmission computer sends requests, known as slow torques and fast torques depending on their incidence on the motorized throttle body for a petrol engine, or on the diesel flow for diesel engines, and on the ignition advance during vehicle starting to the engine control computer. The present invention is also applicable if the control exerted at the level of the gearbox only emits a single torque setpoint, which is the case for diesel engines in particular. Finally, the functions provided by the two engine control and automated transmission computers can be implemented in a single computer.

 In conclusion, the invention makes it possible to reduce the dead time consecutive to pressing the accelerator pedal which corresponds to the time during which the acceleration of the vehicle does not correspond to that requested by the driver. It also allows rapid acceleration of the vehicle smoothly. The desired speed is essential for a feeling of very short torque break time. Indeed, as soon as the vehicle reaches its acceleration after starting, the driver will have the feeling that the starting is finished even if the clutch is still slippery.

Claims (8)

 1. Method for starting a vehicle equipped with an automated transmission, fitted with an input clutch, and with a heat engine placed under the control of a computer, said method being initiated by detection (a) the will to start the vehicle and closed by the total closure (f) of the clutch, characterized in that it comprises the following stages: - the control of the heat engine to a speed setpoint (11), - the partial closing of the clutch quickly while maintaining the servo-control of the engine initiated in a previous phase, - obtaining an acceleration of the vehicle corresponding to the driver's will, - gradually eliminating the sliding of the clutch until on obtaining a zero clutch slip, - the total closure of the clutch. 2. Starting method according to claim 1, characterized in that the control of the engine to the speed setpoint (11) is initiated as soon as the driver's will to start the vehicle is detected (a). 3. Starting method according to claim 1 or 2, characterized in that the speed setpoint (11) corresponds to the minimum engine speed necessary for the engine to provide a torque equivalent to the clutch torque (12) to be produced. 4. Starting method according to claim 3, characterized in that the speed setpoint (11) is obtained by defining the clutch torque (12) to be produced as a function of the position of the accelerator pedal, a mapping, representing the characteristics for the torque motor in <Desc / Clms Page number 9>  speed function, used to define all the engine speeds for which the engine can achieve this clutch torque (12), the minimum value of these engine speeds then corresponding to the speed setpoint (11).  5. Starting method according to one of the preceding claims, characterized in that the clutch and the engine are controlled so as to cancel the sliding of the clutch smoothly at the end of starting.  6. The starting method according to claim 5, characterized in that the clutch and the engine are controlled so as to have an acceleration of the engine close to zero when the slip is canceled.  7. Starting method according to one of the preceding claims, characterized in that the transmission computer dialogues with the engine control computer and controls the clutch to control the slip of the clutch or the engine speed during starting. .  8. Starting method according to claim 7, characterized in that the transmission computer sends torque or speed instructions to the engine computer during startup.