FR3003515A1 - POWERTRAIN AND METHOD FOR PROTECTING SECONDARY TRANSMISSION - Google Patents

Abstract

The invention relates to a powertrain and a method of protecting the secondary transmission during a sudden start. According to the invention the method comprises monitoring (3) the steering angle of the wheels of the vehicle and the driving situation to activate a clamping of the engine speed (5) in case of a situation at risk for transmission. The invention applies to any type of motor vehicle and powertrain control methods.

Description

The field of the invention relates to a powertrain of a motor vehicle and more specifically to a method of protecting the secondary transmission of such a powertrain. A power train of a motor vehicle comprises drive means for driving the vehicle wheels and transmission means for transmitting a driving torque generated by the drive means to the wheels of the vehicle. The transmission means comprise a main transmission between the engine and the gearbox of the vehicle and secondary transmissions between the gearbox and the wheels of the vehicle. During a maneuver in the parking lot, starting at a red light, a stop or a hill start, it is common for a sudden start to occur, ie when the driver unintentionally drops his foot. by accelerating. In such a situation, a large torque may appear in the secondary transmissions of the powertrain because of the high engine speed, this also inducing a significant inertia of the powertrain.

However, a high inertia of the powertrain can cause damage to the secondary transmissions when coupling the engine with the transmission if the wheels of the vehicle are positioned at a high steering angle. In this situation the secondary transmissions are particularly exposed to a break. This rupture usually occurs at the inner cage of the wheel-side seal of the secondary transmission. Several techniques are known in the state of the art which make it possible to limit the forces to secondary transmissions. A first solution is to introduce a limitation of the speed of opening and closing of the clutch by acting on the control of the clutch. The torque at the wheel is thus limited during a sudden start of the vehicle. The disadvantage of this solution is the introduction of a degradation of the performance of reassembly of the clutch pedal and therefore the feeling of inconvenience for the driver who sees his clutch pedal back in time of his order of foot. Moreover, this phenomenon is amplified by cold weather.

A second solution may be a limitation of the engine performance. The torque at the wheel is thus limited in certain situations of rolling life to improve the fatigue resistance of the transmissions. Patent application US20110066338 is known which limits the engine torque relative to the steering angle of the wheels. This solution degrades the performance of the powertrain while in a situation of brutal starting life, the limitation of the engine torque has no impact on the secondary transmission. Indeed, the limitation of the engine torque does not affect the exceptional torque to the transmission since it is the phenomena of inertia and gear ratios that are order 1. A third solution is a limitation of the engine speed in order to limit the influences of the motor inertia on the wheel. This third solution degrades the performance of the powertrain of the vehicle for a sloping start or for a service type 400 meters in a standing start.

There is therefore a need to improve the protection of powertrain secondary transmissions during a rough start and when the vehicle is configured with a large steering angle of the wheels while maintaining powertrain performance in the majority of aircraft situations. running life.

More specifically, the invention relates to a method for protecting a secondary transmission of a powertrain of a motor vehicle comprising the following steps: a step of acquiring the data of the steering angle of the wheels, the speed of the vehicle and the gear ratio engaged by a gearbox of the powertrain, - a step of detecting a risky operating state, - a step of controlling the powertrain so that it operates in a bridled state when the Dangerous operating state is detected. According to the invention, the step of detecting a risk operating state comprises monitoring the acquired data of the steering angle and the speed with respect to predetermined thresholds, respectively a threshold of steering angle of the wheels. and a vehicle speed threshold, as well as the gear ratio engaged with respect to a predetermined gear ratio position at risk.

According to one embodiment, the flanged operating state comprises a step of controlling the powertrain so as to limit the engine speed to a predetermined ceiling speed. Preferably, the ceiling speed is variable and is between a maximum value and a minimum value, its value being calculated by a determination function having as input parameter the steering angle of the wheels. According to one embodiment, the at-risk operating state is detected when the steering angle is greater than the steering angle threshold, when the vehicle speed is below the speed threshold and when the gear ratio is engaged. is the first gear or reverse. According to one embodiment, in which the powertrain comprises a clutch for coupling the engine and the transmission, the control of the powertrain in the flanged state is active when the clutch is in a state of uncoupling of the transmission and the engine and a hazardous operating condition is detected. The invention also applies to a hybrid vehicle powertrain comprising control means for implementing any variant of the method for protecting a secondary transmission. Thanks to the invention it is possible to avoid the use of one of the solutions described in the state of the art and thus not to degrade the performance of the powertrain, including the rise of the clutch pedal and the performances in 400m start stopped. Moreover, it is possible to reduce the requirements relating to the stresses of certain parts of the secondary transmission and thus to reduce the production cost of a transmission and its mass. Other features and advantages of the present invention will appear more clearly on reading the following detailed description of embodiments of the invention given by way of non-limiting examples and illustrated by FIG. a secondary transmission of a motor vehicle according to the invention. The invention applies to any type of motor vehicle with a single engine or hybrid engine. The invention aims to protect the secondary transmissions of a motor vehicle may be damaged when a sudden start occurs and when the wheels have a high steering angle. A motor vehicle includes a power train to move the vehicle. Such a powertrain includes motorization means (thermal, electrical or compressed air for example), a gearbox, a transmission and a clutch for coupling the gearbox to the motorization means in particular to transmit the driving torque. generated by the motorization means to the wheels of the vehicle. The transmission comprises a main transmission between the gearbox and the drive means, and a secondary transmission between the gearbox and the wheels. According to one embodiment, a secondary transmission is constituted by the following successive elements, listed in the order of arrangement of the main transmission to the wheel side: a linkage shaft to the main transmission, a bellows fixed by clamps of tightening, a nut, a cage containing balls and the rocket wheel. When strong constraints are exerted on the secondary transmission, due to a high steering angle of the wheels, a high engine speed and a sudden coupling, the cage is the fuse element likely to break. The powertrain is controlled by control means. These control means comprise computers, data sensors and data transmission means (digital data bus type). The control means perform data acquisition functions between the computers and the elements of the engine (for example, the current speed of the engines, the steering angle of the wheels, the gear ratio engaged) and between the computers and the driver via the systems. on board (eg acceleration and braking setpoint, speed ratio setpoint, steering setpoint, clutch control). The control means also perform data transmission functions calculated from the acquired data and calculation functions. These data are then transmitted to the powertrain and aircraft systems. These calculated data can be in particular engine torque setpoints, engine speed instructions, actuator instructions or navigational information to the driver via the on-board systems.

In the context of the invention, for the implementation of the method of protecting the secondary transmissions of the powertrain, the control means comprise means for acquiring the steering angle of the wheels of the vehicle, ranging from an angle a minimum of 0 degrees when the wheels are in the right trajectory configuration at a maximum steering angle, referred to as a stop, of 45 degrees for the most common vehicles. Various means make it possible to record the steering angle information. Among these means, one can quote the physical flying angle sensor, data reconstructed from the direction or information obtained from a device of assistance to the direction. The control means also comprise means for acquiring the speed of the vehicle and the gear ratio engaged. In addition, the control means comprise means for detecting a risk situation for the secondary transmission. A risk situation is understood to mean a configuration in which strong stresses can be produced on the components of the secondary transmission that can cause premature wear or even breakage. From the steering angle data, the vehicle speed and the gear ratio engaged, computers can determine whether the power train is in a risky configuration for the secondary transmission. The control means perform a parameter monitoring function to detect the presence of this risky situation. When a risk configuration of the vehicle is detected the powertrain control means drive the powertrain so as to limit the speed of the engine or engines for a hybrid vehicle. The powertrain is then driven in a steady state operating state during the course of the risk situation to limit the inertia and torque on the secondary transmission. FIG. 1 describes the steps of the protection method implemented by the control means of the powertrain. According to the invention, following the starting of the vehicle 1, the protection method comprises a step 2 of acquiring vehicle steering angle data, the vehicle speed and the gear ratio engaged for the gearbox. speed of the transmission, a step 3 monitoring the operation of the powertrain to detect a risky driving situation for secondary transmissions. During this monitoring, the detection function determines whether the powertrain is in a risk configuration. If a risky configuration is detected then, during a step 5 the control means drive the powertrain in operation of clamping the engine speed by appropriate engine speed instructions. If a risky configuration is not detected then, during a step 4, the control means drive the powertrain in unstressed operation by appropriate engine speed instructions. Clutching operation of the power train of the powertrain is active from the start, when the clutch is in the uncoupled position and at least until the clutch is in the coupling position of the transmission with the engine. Thus, when the coupling of the transmission is achieved, it is protected from a sudden coupling, resulting from a foot drop for example. Preferably, the clamping of the engine speed is deactivated shortly after coupling of the clutch is executed and when the vehicle begins to roll. Indeed, when driving the vehicle secondary transmissions are not exposed. According to one embodiment of the invention, a risk configuration corresponds to a steering angle range between 35 degrees and 45 degrees, a vehicle speed of less than 3km / h and a committed gear ratio corresponding to the first gear or in reverse. Indeed, when the gearbox is positioned in first gear or reverse gear ratio is important. There is therefore a larger exceptional couple. In addition, a speed of less than 3 km / h reduces the impact on take-off and the delivery of 400m departure. Of course, the scope of the invention is not limited to this risk configuration. Other values of steering angle and vehicle speed can be chosen according to the type of vehicle and the performance of the powertrain used for the invention. In particular, the maximum steering angle can be selected so as to correspond to the steering angle of the stop and the gear ratio can be chosen according to the reduction achieved by the gearbox. Thanks to the invention, the powertrain control means calculate an engine speed limiting value as a function of the value of the steering angle of the wheels. For example, a minimum threshold and a maximum steering angle threshold may be defined and a engine speed limit calculation function defines a maximum engine speed limit value for the minimum threshold and a minimum engine speed limit value for the engine speed limit. maximum steering angle threshold. The speed limiting calculation function also defines intermediate engine speed values for the angle values in the steering angle range defined by the minimum threshold and the maximum threshold. Preferably, these intermediate values are defined by a linear calculation function. However, the scope of the invention is not limited to a linear function for determining the engine speed values. The engine speed limitation in this example can be set to values around 2750 rpm. However, the value of the engine speed restraint depends on the vehicle configuration and the steering angle value. In addition, once the drive means drive the wheels of the vehicle, the clamping of the engine speed is maintained only until the vehicle reaches 3km / h. This makes it possible not to degrade the performance of the vehicle during taxiing, while maintaining protection of the secondary transmission during the critical start-up situation. According to another embodiment, for an identical risk configuration and applied to a hybrid vehicle comprising a front electric machine and a rear electric machine, a motor speed limiting calculation function can be adapted to the hybrid architecture. Similarly, the ceiling motor speed values (minimum, maximum and intermediate) can be defined by the calculation function to adapt the clamping of the motor operation to this particular type of motorized architecture. For example, engine speed limiting values may be around 2750 rpm for the front electric machine and 2500 rpm for the rear electric machine. The invention applies to motor vehicle powertrains. It helps protect the life situations of brutal start of the vehicle.

Claims (6)

REVENDICATIONS1. A method of protecting a secondary transmission of a power unit of a motor vehicle comprising the steps of: - a step of acquiring (2) data of the steering angle of the wheels, the speed of the vehicle and the gear ratio. speed engaged by a gearbox of the powertrain, - a step of detecting (3) a dangerous operating state, - a driving step (5) of the powertrain so that it operates in a bridled state when the at-risk operating state is detected, the method being characterized in that the step of detecting a risk operating state includes monitoring the acquired data of the steering angle and speed against thresholds predetermined, respectively a threshold wheel angle and a speed threshold of the vehicle, and the gear ratio engaged with respect to a predetermined gear position risk. The method according to claim 1, wherein the flanged operating state comprises a step of driving the power train so as to limit the engine speed to a predetermined ceiling speed. 3. Method according to claim 2, wherein the ceiling speed is variable and is between a maximum value and a minimum value, its value being calculated by a determination function having as input parameter the steering angle of the wheels. A method according to any one of claims 1 to 3 wherein the at-risk operating state is detected when the steering angle is greater than the steering angle threshold, when the vehicle speed is below the threshold. speed and when the gear ratio engaged is the first gear or reverse gear. A method as claimed in any one of the preceding claims, wherein the power train comprises a clutch for coupling the engine and the transmission and wherein steering of the power train in the flanged state is active when the clutch is in a state of uncoupling. the transmission and the motor and that a hazardous operating condition is detected. 6. Hybrid vehicle power train characterized in that it comprises control means for carrying out the method according to any one of the preceding claims.