FR3054988B1 - METHOD FOR BRAKING A VEHICLE IN AUTOMATIC PARKING MODE USING AN AUTOMATIC GEARBOX - Google Patents

Abstract

A method of braking a motor vehicle comprising an automatic gearbox driven by a heat engine, comprising planetary gear trains (10) delivering a plurality of gear ratios engaged by clamping clutches (6) and brakes (8); vehicle being equipped with an automatic parking mode which controls a rolling with a gear ratio engaged in order to perform a parking maneuver, and braking using an automatic brake control function of the vehicle wheels, characterized in that in the automatic parking mode during a braking request, in the event of a failure of the vehicle brake control function, it engages an additional gear ratio.

Description

METHOD FOR BRAKING A VEHICLE IN AUTOMATIC PARKING MODE USING AN AUTOMATIC GEARBOX

The present invention relates to a braking process of a motor vehicle equipped with an automatic gearbox, and a motor vehicle comprising means implementing such a braking method.

Some motor vehicles include an assistance system for parking the vehicle, including sensors for measuring the distance of surrounding obstacles, and a control of the rotation of the steering wheel.

The driver has indications to only advance or retreat the vehicle at a low speed, the steering is automatically rotated to take the optimal path to park the vehicle in a parking space.

An evolution of this system under development by some car manufacturers, presents a fully automated maneuver of the vehicle equipped with an automatic gearbox, including with the commitment of the transmission its advance and its decline at a low speed of up to 12km / h, and braking at the end of each maneuver. The driver can stay in the vehicle, or be outside to supervise the automatic maneuver.

The braking of the vehicle is then automatically ensured by an automatic braking function for the control of trajectory of the vehicle, including an electronic stability program called "ESP" (abbreviation of the English term "Electronic Stability Program"), which comprises a hydraulic pump generating a pressure transmitted individually to each wheel brake to correct its trajectory if necessary.

However, in the case of a failure of the automatic braking function of the vehicle, particularly if the driver is outside the vehicle, it can not intervene for example on the emergency brake to stop the vehicle, in order to ensure in particular the safety of pedestrians or passengers in the vehicle.

Furthermore, a method of stopping the vehicle, presented in particular by the document DE-A1-102012217704, comprises the use of parking blocking of the automatic gearbox to if necessary stop the vehicle during its automatic maneuvering at low speed, if the main braking is faulty.

However parking blocking automatic transmissions generally comprises a tilting finger which descends on a notched wheel linked to the output of this transmission, to engage in a notch to ensure the locking of the drive wheels. But this type of blockage is a problem because the rocker finger can not engage in the notch of the wheel beyond a very low speed of the vehicle, which is of the order of 2km / h.

Indeed the tilting finger provided to engage when the vehicle is stopped, causes a net lock of the toothed wheel and the vehicle, resulting in very significant constraints for vehicle speeds above 2km / h which could cause breakage of components.

The present invention is intended to avoid these disadvantages of the prior art.

It proposes for this purpose a braking process of a motor vehicle comprising an automatic gearbox driven by a heat engine, comprising planetary gearboxes delivering several gear ratios engaged by the clutch and brake clamping, this vehicle being equipped an automatic parking mode that controls a rolling with a gear ratio engaged to perform a parking maneuver, and braking using an automatic brake control function of the wheels of the vehicle, this method being remarkable in that in the automatic parking mode during a braking request, in the event of failure of the vehicle brake control function, it engages an additional gear ratio in addition to the gear ratio already engaged.

An advantage of this braking process is that by using the brakes and clutches of the automatic transmission, without adding a component to the vehicle, by simply controlling this transmission with software, it can still slow down quickly. vehicle in case of failure of the usual brake control function.

This method thus provides a simple and economical additional security to quickly stop the vehicle for sufficiently high speeds, up to 12km / h, using a completely independent braking means of the wheel brakes and their control.

The braking method according to the invention may further include one or more of the following features, which may be combined with each other.

The automatic transmission comprising a hydraulic pump driven by the heat engine, advantageously during the braking of the vehicle given by the engagement of the additional gear ratio, the method maintains the operation of this engine.

Advantageously after stopping the vehicle, the method automatically engages a parking blocking system of this vehicle integrated in the automatic transmission.

Advantageously, the method achieves a level of tightening of the clutches and brakes engaging the additional gear ratio, calculated according to a braking level of the desired vehicle depending on the speed of the vehicle. The invention also relates to a motor vehicle equipped with an automatic gearbox and an automatic parking mode, comprising means implementing a braking process of this vehicle comprising any one of the preceding features. The invention will be better understood and other features and advantages will appear more clearly on reading the following description given by way of example, with reference to the accompanying drawings in which: - Figure 1 shows an automatic gearbox implementing the braking method according to the invention; and FIG. 2 is a diagram of a planetary gear train for a gearbox of this type.

FIG. 1 shows a gearbox comprising, forwards, a hydrodynamic input torque converter 2 connected to the engine of the vehicle, equipped with a clutch 4 making it possible to block this converter in order to prevent it from slipping under certain driving conditions.

The gearbox comprises behind the torque converter 2, a set of planetary gear trains 10 arranged along the axis of the engine, clutches 6 each for securing two elements in rotation of the planetary gear, and brakes 8 each for locking an element.

An oil pump 16 is connected by a chain to the casing of the torque converter 2, permanently driven by the heat engine, in order to constantly deliver a pressure to the gearbox allowing the control of the different clutches 6 and brakes 8.

The gearbox comprising an output of the rear movement 12 also arranged in the axis of the motor installed longitudinally in the vehicle, is provided to drive a rear axle of the vehicle comprising a differential, connected to the rear wheels.

The gearbox comprises in front of the output, a notched wheel 14 connected to this output receiving a locking finger to achieve parking blocking of the vehicle.

The automatic transmissions provided for a heat engine arranged transversely to the front, likewise comprise a torque converter, planetary gear, clutches and brakes arranged in the axis of this engine, and a differential integrated in the gearbox to drive the front wheels of the vehicle.

With particular combinations of clutch actuation and brakes, we obtain different kinematics giving a neutral, at least a reverse gear, and different forward gears.

FIG. 2 shows an example of a planetary gear train 10 of an automatic gearbox, comprising on a main axis A a sun gear 22 maintained by a bearing 24 disposed along this axis, and a planet carrier 26 also maintained by a bearing 28. disposed along this axis to a front side.

The planet carrier 26 supports three satellites 30 arranged at 120 °, each comprising a first planet gear 32 meshing with the sun gear 22, and a second rearward gear 34 meshing with the internal toothing of a ring gear 36 held by a rear bearing 38 disposed along the main axis A.

Different clutches and brakes (not shown) make it possible to connect two elements together or to block an element of the planetary gear train 10 in order to produce several gear ratios.

In particular by braking the sun gear 22 and driving the planet carrier 26, a reduction of the speed on the ring gear 36 is obtained. By securing with a clutch 6 two elements between them among the sun gear 22, the planet carrier 26 and the crown 36, we obtain a complete attachment of the planetary gear 10 which gives a speed of the crown equal to that of the planet carrier 16.

By arranging several planetary gear trains 10 in the vehicle, which may have different configurations, for example with four elements in rotation instead of three, and by choosing the ratios of the different teeth meshing with one another, an automatic gearbox is obtained which Today usually has at least six forward gears and one reverse gear.

The vehicle implementing the method according to the invention, comprising an automatic gearbox with planetary gear, comprises an automatic parking mode which automatically controls the advance and the retreat of the vehicle to perform parking maneuvers.

During vehicle forward and reverse maneuvers at a speed of less than 12km / h, the first forward gear ratio or the reverse ratio of the automatic gearbox is engaged to drive this vehicle with the engine.

The automatic parking mode also normally controls the wheel brakes in order to stop each of these movements, using an automatic braking function, in particular of the ESP type. In the case of an unforeseen obstacle, for example if a pedestrian is approaching the path of the vehicle, the automatic parking mode may be required to suddenly brake the vehicle to avoid an accident. The vehicle can also arrive on a slope, where it must also brake to avoid being driven.

The first forward gear ratio or the reverse gear ratio being engaged when driving with the automatic parking mode, when a request is made to brake the vehicle by this mode, in the event of failure of the brake control function of the vehicle, the braking method according to the invention maintains the current ratio, and further engages a complementary gear ratio by tightening at least one clutch 6 or a brake 8 giving this complementary report.

This results in a blockage of the output 12 of the gearbox, given by the impossibility of rotating this gearbox with two different gear ratios simultaneously between the input torque converter 2 and the output. The vehicle is then in the same way braked by the clamping of the engaged friction elements, clutches 6 or brakes 8, giving the complementary report, in a very short time compatible with the safety requirements.

During the braking of the vehicle, the shutdown procedure of the engine is not engaged in order to maintain the rotation of the oil pump 16 for actuating the gearbox. Alternatively if the automatic transmission has an electric pump, the engine can be stopped immediately leaving this pump running to deliver the control pressure.

In particular, the engagement of the second gear ratio as a complementary ratio, close to the first gear used for the forward gear, gives a lower speed difference in the engaged friction elements and a higher torque, while the engagement the last gear ratio, for example the sixth, gives a higher speed difference and a lower torque in these engaged friction elements.

Depending on the speed of the vehicle, the tightening of the friction elements 6, 8 is controlled with a certain progressiveness to limit the braking level of the vehicle and the mechanical stresses in the transmission. It will be noted that the speed of the vehicle being reduced, the energy released by the clutch 6 and the brakes 8 depending on the kinetic energy of the vehicle is very low, which avoids deterioration.

Once the vehicle is stopped, the process can automatically engage the parking lock of the gearbox using the toothed wheel 14 to immobilize it completely to ensure high security, especially after the observation of the failure of the brake control function. The engine can then be stopped.

It is obtained by using existing elements, without increasing the cost of the vehicle, by adding only a programming implementing the braking process, a security of passengers and pedestrians of the vehicle

Claims (5)

1 - A method of braking a motor vehicle comprising an automatic gearbox driven by a heat engine, comprising planetary gear trains (10) delivering a plurality of gear ratios engaged by clamping clutches (6) and brakes (8) , this vehicle being equipped with an automatic parking mode which controls a rolling with a gear ratio engaged in order to perform a parking maneuver, and braking using an automatic brake control function of the vehicle wheels, characterized in that in the automatic parking mode when a braking request is made, in the event of a failure of the vehicle brake control function, it engages an additional gear ratio in addition to the gear ratio already engaged. 2 - A method of braking according to claim 1, with an automatic gearbox comprising a hydraulic pump (16) driven by the engine, characterized in that during the braking of the vehicle given by the commitment of the additional gear ratio, it maintains the operation of this engine. 3 - A method of braking according to claim 1 or 2, characterized in that after stopping the vehicle, it automatically engages a parking blocking system (14) of the vehicle integrated in the automatic transmission. 4 - A braking method according to any one of the preceding claims, characterized in that it achieves a level of clamping clutches (6) and brakes (8) engaging the additional gear ratio, depending on a level of braking of the desired vehicle depending on the speed of the vehicle. 5 - A motor vehicle equipped with an automatic gearbox and an automatic parking mode, characterized in that it comprises means implementing a braking process of this vehicle according to any one of the preceding claims.