EP2104624A2

EP2104624A2 - Method for braking a hybrid vehicle and method for improving a hybrid vehicle implementing said method

Info

Publication number: EP2104624A2
Application number: EP07871963A
Authority: EP
Inventors: Joseph Krasznai; Armand Boatas; Vincent Mulot; Rémy Delplace; Olivier Mechin
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2006-12-18
Filing date: 2007-12-18
Publication date: 2009-09-30
Also published as: FR2909957A1; US20100106386A1; WO2008087322A3; JP2010513130A; WO2008087322A2

Abstract

The invention relates to a method for braking a hybrid vehicle (1) including a thermal engine and an electric machine (3) defining a traction chain. According to this method, when the depression of the brake pedal is detected, an additional electric braking torque is added (Cf_recup), and the additional electric braking torque is modulated according to the position of the brake pedal as measured by a pedal stroke sensor (42) and/or to the braking hydraulic pressure as measured by a braking pressure sensor (43).

Description

Braking method for a hybrid vehicle and method for improving a hybrid vehicle for implementing this method

The invention relates to a braking process for hybrid vehicles in which a regenerative braking torque and a dissipative braking torque are applied to the wheels. The invention is in particular to increase the regenerative braking torque applied to the wheels by the electric machine while ensuring good control of the vehicle.

Braking systems in which a regenerative braking torque and a dissipative braking torque are applied to the wheels are known. The regenerative braking torque is applied to the wheels by the action of an electric machine acting as a generator to recharge a battery to which it is connected. The dissipative braking torque is applied to the wheels by means of disk or drum brakes which apply a frictional force on a mobile element rotating with the wheels.

Two types of regenerative braking exist and are distinguished by the European braking legislation. The first type is a category A recovery system exerting a braking torque to the wheels without action of the driver on the brake pedal. A representation of the braking characteristic of such a system is shown in FIG.

It can be seen that the recuperative CmeM torque applied by the electric machine to the wheels as a function of the depression of the brake pedal (lower left dial) is constant regardless of the depression of the brake pedal. The sum of the torque applied by the Chydri brakes and the CmeM electric machine to the wheels increases with the depression of the brake pedal. For its implementation, the category A system does not a priori require any adaptation of the hybrid vehicle's drivetrain.

The second type is a category B recovery system exerting a braking torque controlled by the brake pedal. The invention finds an advantageous application in this type of system. These systems make it possible in particular to decouple the brake pedal action from the torque produced by the conventional dissipative braking system. Thus, they offer the possibility of controlling the distribution between the recuperative brake achieved by the electric traction chain and the dissipative brake realized by the conventional hydraulic braking system.

The disadvantages of these devices are that they add a significant cost to the vehicle as well as risks in dependability and quality in use due to their intrinsic complexity.

Thus, document JP2003-284202 describes a distribution management method between the conventional braking system and the regenerative braking of the electric machine. This method comprises a step of increasing the regenerative braking while the brake pedal is actuated. However, this process involves an intrinsic modification of the hydraulic braking system.

The regenerative braking device according to the invention proposes to solve the aforementioned drawbacks.

To this end, it relies on minor modifications of the existing braking hardware architecture. Thus, by adding a pressure sensor and / or pedal stroke to a category A system, it optimizes the energy recovery during the braking phases. The addition of the sensors is performed in a "non-intrusive" manner, that is to say without intrinsically modifying the elements of the system. In addition to the deceleration performed by a foot lift, the invention uses the steps of:

- add additional electric braking torque (as far as the condition of the electric machine permits) when a brake pedal is detected. The brake pedal support can be detected by an inductive sensor of the BLS type, and / or by the pedal travel sensor, and / or by the hydraulic brake pressure sensor, and

modulating and controlling this additional electrical braking torque as a function of the brake pedal position measured by the pedal travel sensor and / or the hydraulic brake pressure measured by the brake pressure sensor.

In one implementation, the brake system supervisor, which is an ABS or ESP calculator, detects the braking life situation and controls the application of the additional electric braking torque according to this life situation. The living situation depends in particular on the vehicle speed, course of the road (curved or straight line), and tire grip on the road (dry or wet grip).

The brake supervisor also controls the modulation of the regenerative braking torque as a function of the position of the brake pedal measured by the pedal stroke sensor and / or the hydraulic brake pressure measured by the pressure sensor. The brake supervisor also controls the modulation of the regenerative braking torque as a function of the vehicle speed and the engaged gear ratio. The brake supervisor additionally modulates the regenerative braking torque so as to never exceed a limit "acceptable" by the driver in terms of approval.

However, when braking control functions such as ABS (Anti-lock Braking System) or ESP (Electronic Stability Program) are activated, which are implemented when the vehicle loses the adhesion or does not follow the desired trajectory, the regulations and control laws specific to these functions (located in the control unit) take control and control the additional electrical braking torque.

The additional regenerative braking torque setpoint thus determined by the brake supervisor is then transmitted to the computer which controls the electric machine. This controls the electric machine so that it achieves this regenerative torque.

The invention therefore relates to a braking process for a hybrid vehicle comprising a heat engine and an electric machine forming a power train, this traction chain being connected to wheels of the vehicle, this vehicle comprising a brake pedal which controls the braking of the vehicle, this method comprising the following steps:

- when a brake pedal is pressed on the vehicle,

a dissipative braking torque is applied to the wheels by means of brakes connected to a hydraulic braking circuit, these brakes rubbing on elements rotating with the wheels, and

an additional braking torque is applied to the wheels by means of the electric machine,

this additional braking torque being modulated according to the travel of the brake pedal and / or the hydraulic brake pressure, this braking torque also depending on the gear ratio engaged. In one implementation, to modulate the braking torque to modulate this additional braking torque, it further comprises the following steps: - measuring the maximum braking torque of the electric machine,

weighting this maximum braking torque by a corrective gain dependent on the gear engaged, this corrective gain also depending on the speed of the vehicle for a given gear ratio and on at least one parameter among the braking pressure and the stroke. of the brake pedal, and - control the electric machine so that the electric braking torque applied to the wheels in addition to the dissipative braking is substantially equal to the maximum braking torque weighted.

The invention furthermore relates to a method for improving a hybrid vehicle comprising a heat engine and an electric machine forming a traction chain, this traction chain being connected to wheels of the vehicle, in which:

a pedal and / or pressure sensor is added, so that

the additional braking torque applied by the electric machine to the wheels when the brake pedal is depressed is modulated according to the stroke of the brake pedal and / or the hydraulic brake pressure.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given for illustrative but not limiting of the invention. They show :

- Figure 1 (already described): a curve representing the torque applied to the wheels according to a depression of the brake pedal for a regenerative braking process according to the state of the art;

- Figure 2: a schematic representation of a hybrid vehicle implementing the regenerative braking process according to the invention;

FIGS. 3-5: schematic representations of the control management according to the invention of the recuperative torque applied by the electric machine in the case of a braking system according to the invention comprising a driving sensor and / or a sensor hydraulic pressure; - Figure 6: a curve representing the torque applied to the wheels according to a depression of the brake pedal for a regenerative braking process according to the invention;

- Figure 7: a table indicating the value of a corrective gain F (i) depending on the engaged gear ratio used to calculate the regenerative braking torque.

Identical elements retain the same reference from one figure to another.

Figure 2 shows a braking control system according to the invention applied to a hybrid vehicle 1. The vehicle wheels are represented by their respective associated brake disks. Front wheels 2.1, 2.2 of this vehicle which function as drive wheels are driven by an electric machine 3 and a heat engine (not shown). This machine 3 and this motor can for example be connected to each other by means of a clutch and they can be accompanied by a controlled gearbox or a CVT (Continuously Variable Transmission).

The electric machine 3 is connected to the shaft of these wheels via a differential assembly 4. This machine 3 is also connected to a battery 7 via a power circuit.

The electric machine 3 transmits to the wheels 2.1-2.4 a regenerative braking torque when operating in generator mode to recharge the battery 7 and that its shaft is driven by the wheels. This charging phase occurs during deceleration or braking. A supervisor 8 controls the torque applied by the traction chain formed of the heat engine and the electric machine 3. In particular, the supervisor 8 controls the braking torque applied by the machine 3 to the wheels 2.1-2.4.

In addition, the vehicle 1 comprises a hydraulic braking system. This system 10 comprises a vacuum braking assistance device 11 which amplifies the force supplied by the driver on the pedal 20. For this purpose, the device 11 is connected to a source 13 of vacuum which allows to have pressures different on the piston that it comprises (not shown). This device 11 is connected to a master cylinder 12 fed with This master cylinder 12 is connected to the brakes 16.1-16.4 via a network 17 of pipes.

Thus, when the driver presses the pedal 20 to brake, the amplifier 11 and master cylinder 12 transforms the mechanical force provided by the driver when the pedal is pressed into hydraulic pressure. The pipes then transmit this hydraulic pressure to the brakes 16.1-16.4. These brakes turn this pressure into a force capable of driving the pads against the 4 discs 2.1-2.4.

In addition, the vehicle has an ABS type system. This system comprises a hydraulic unit 23 connected to the master cylinder 12 and the network 17 of pipe. This hydraulic unit 23 is provided with a pump 22 and is associated with a braking supervisor 24. This hydraulic unit 23 provides control of the hydraulic pressure applied by the brakes. In addition, the ABS system includes sensors 27.1-27.4 measuring the speed of the wheels which are connected to inputs 30-33 of the supervisor 24.

Thus, as soon as a wheel 2.1-2.4 of the vehicle has an abnormal rotation speed (slipping), the supervisor 24 acts on the hydraulic unit 23 so that the wheel is partially or completely released by a drop or overpressure of the hydraulic pressure depending on the type of brake used, in the brake concerned.

In FIG. 2, the dissipative brake torque is applied to the four wheels, while the electric braking torque is applied solely to the tractor or propellant axle. Nevertheless, the invention is also applicable in the case of an integral transmission. In addition, the vehicle 1 comprises a sensor 41 brake contactor type BLS (Brake Light Switch in English) which can detect the depression of the brake pedal. This sensor is connected to an input of the computer 24.

The vehicle 1 also includes sensors for estimating the braking intensity requested by the driver. Indeed, the vehicle comprises a sensor 42 of brake pedal travel or master cylinder displacement and / or a brake pressure sensor 43 measuring the pressure delivered by the master cylinder. These sensors 42, 43 are added with respect to a conventional ABS configuration. In one embodiment, the sensor 43 of the brake pressure is implanted either at the location of the master cylinder 12 or at the location of the hydraulic block 23.

As a variant, the block 24 also includes an ESP function that makes it possible to rectify the trajectory of the vehicle from the calculation of an expected trajectory. In this case, the pressure sensor 43 is already present on the hydraulic block 23 and it is not necessary to add it.

Depending on the input signals that it receives, and in particular the signals emitted by the sensors 42 and 43, the computer 24 controls the computer 8 of the traction chain which modulates the recuperative torque of the electric machine 3.

More precisely, FIGS. 3 to 5 describe the implementation of the control laws of the invention in the brake computer 24 (ABS or ESP) and the supervisor 8 which controls the various elements of the hybrid traction system, namely in particular the heat engine 52, the electric machine 3, and the gearbox 53.

Figure 3 shows the case where the sensor 42 of stroke of the brake pedal and the pressure sensor 43 are used. In this case, the signals 51,

"Course_pedale", and "pressionjmtc" emitted respectively by the sensors 41-43 are applied at the input of a module 57 which detects whether braking is in progress or not.

The information 58 produced at the output of the module 57 is transmitted to the module 59 with the values of the depression (or the travel) of the brake pedal "pedal stroke" and the brake pressure measured.

"Pressure" respectively by the sensors 42 and 43. Similarly the value of the speed of the vehicle "speed" (calculated from the signals transmitted by the speed sensors 27.1-27.4), the value of the gear ratio engaged "i" , and the value of the maximum electrical braking torque

"Cf_recup-max" achievable by the electrical machine are transmitted to the module 59. It should be noted that the values "i" and "Cf_recup max" are transmitted to the brake supervisor 24 by the traction chain supervisor 8.

The module 59 then calculates the reciprocating electric braking torque setpoint Cf_recup as a function of these received values. More precisely, in the case of FIG. 3, the module 59 calculates Cf_recup from the following relation: Cf_recup = Cf_recup_max x Fcp_i (pedal stroke, speed) x Fpmtc_i (pressure_mtc, speed),

"Fcp_i" is a function that returns a corrective gain between 0 and 1 depending on the pedal stroke of the brake "course_pedale" and the vehicle speed "speed". Typically, this function is a tab with 2 inputs ("pedal_stroke" and "speed") and an output (gain between 0 and 1). The setting of the tab depends on the ratio "i" of gearbox engaged. Thus there is a set of parameters, and a specific tabulation for each ratio of gearbox (i = neutral, 1, 2, 3, ...). "Fpmtc_i" is a function that returns a corrective gain between 0 and 1 depending on the brake pressure and the vehicle speed. Typically, this function is a tab with 2 inputs ("pressurejmtc" and "speed") and an output (gain between 0 and 1). The setting of the tab depends on the gearbox ratio engaged. There is thus a set of parameters and a specific tabulation for each transmission ratio (i = neutral, 1, 2, 3, ...).

In special life situations such as curve braking, emergency braking (AFU braking) or loss of grip, ABS or ESP control functions activate. In this case, a module 63 which comprises the control and regulation laws specific to the ABS and / or ESP functions, takes control of the calculation of the regenerative braking torque setpoint "Cf_récup" and adjusts the value of this setpoint to these particular life situations.

The "Cf_recup" electrical braking instruction is then sent by the braking supervisor 24 to the traction chain supervisor 8 which drives the machine 3 in order to achieve the requested electrical braking torque.

In the case of normal operation, the torque setpoint

"Cf_recup" is transmitted by the braking supervisor 24 to the supervisor

8) of the traction chain without being adapted by the module 63. In a variant, if the value "Cmel" of the actual torque applied by the electric machine to the wheels is available, the module 63 uses this value in order to adapt the control of the machine. . More specifically, the module 63 compares the setpoint torque "Cf_recup" with the value "Cmel", so that the module 63 can refine the setpoint value. "Cf_recup" sent to the supervisor 8. The "Cmel" value, which is measured or estimated, is supplied to the brake supervisor 24 by the supervisor 8.

FIG. 4 shows an alternative embodiment of the method according to the invention in which only a brake pedal stroke sensor 42 is used. In this case, the value "pressure_mtc", is not available and one has: Cf_récup = Cf_récup_max x Fcp_i (_alpale stroke, speed).

FIG. 5 shows an alternative embodiment of the method according to the invention in which only a brake pressure sensor 43 is used. In this case, the value "pedal_stroke" is not available and we have: Cf_récup = Cf_récup_max x Fpmtc_i (pressure_mtc, speed).

The vehicle 1 has a failure detection capability of the sensor 41 BLS, the brake pedal stroke sensor 42, the master cylinder pressure sensor 43, the information flow between the traction chain computer 8 and the engine. supervisor 24 braking. In case of failure of one of these elements, the function of adaptation of the recuperative torque of the electric machine according to the depression of the brake pedal ("pedal stroke") and / or the hydraulic brake pressure (" pressure ") is inhibited.

FIG. 6 shows a curve representing the recuperative torque Cf_recup applied by the electric machine to the wheels as a function of the depression of the brake pedal (bottom left dial). This torque Cf_recup increases substantially linearly with the depression of the brake pedal. The curve thus demonstrates that the regenerative braking method according to the invention makes it possible to obtain a braking torque applied to the wheels by the machine (Cf_recup) greater than with a method of the state of the art (see CMEM in Figure 1).

The second curve represents the sum of the torque applied by the brakes Chydr2 and the electric machine Cf_recup to the wheels. This curve is identical to that of FIG. 1. During braking, the torque applied by the brakes is therefore less important in the process according to the invention than in that of the state of the art. While optimizing the energy recovery in the braking phases, the method according to the invention also makes it possible to limit the wear of the brakes.

In a variant, the module 59 calculates the electric regenerative braking torque setpoint "Cf_recup" according to the following relation: Cf_recup = Cf_max_recover x Fcp (pedal_stroke) x Fpmtc (mtc_pressure) x F (i)

With F (i) = Cf_elec_max_acceptable / Cf_elec_max_roue_i

"Cf_elec_max_roue_i" is the maximum electrical braking torque value that the electric machine is able to supply to the wheels for each gear ratio i. This value corresponds to the torque saturation by construction of the electric machine. It corresponds to the maximum value of the electric braking torque to the wheels that can be achieved by the electric machine under nominal operating conditions. "Cf_recup_max" indicated by the engine ECU is the value of the maximum electrical torque achievable by the machine at time t, at the moment when braking is performed. "Cf_recup_max" therefore depends in particular on the state of the power train, the temperature of the electric machine, and the state of charge of the batteries. When the electric machine operates under nominal conditions "Cf_recup_max" is equal to

"Cf_elec_max_roue_i", otherwise "Cf_recup_max" is different from (lower than) "Cf_elec_max_roue_i".

"Cf_elec_max_acceptable" is the maximum acceptable electrical torque level with respect to the braking performance of the driver. It can be interesting that this level of electric braking torque is substantially constant regardless of the gear engaged. In one example,

"Cf_elec_max_acceptable" is worth 300 N. m

Furthermore, the corrective gain "Fcp" is between 0 and 1. In one example, the gain "Fcp" varies linearly between 0 and 1 depending on the depression of the brake pedal "pedal_stroke" on the first 20 millimeters of this depression, Fcp being 0 for a void and 1 for a depression of 20 millimeters.

The corrective gain "Fpmtc" is between 0 and 1. In one example, the gain "Fpmtc" varies linearly between 0 and 1 as a function of the pressure delivered "pressurejmtc" by the master cylinder between 0 and 10 bar, "Fpmtc 0 for a pressure of 0 bar and 1 for a pressure of 10 bar.

Figure 7 shows a table showing the values of the corrective gain

F (i) between 0 and 1 as a function of the gear ratio engaged i, for a maximum acceptable torque "Cf_elec_max_acceptable" equal to 300N. m. The maximum electric braking torque values that the electric machine is capable of providing the wheels "Cf_elec_max_roue_i", which vary according to the gear ratio i engaged, are indicated for a given conventional gearbox. If the ratio Cf_elec_max_acceptable / Cf_elec_max_roue_i is higher than 1, F (i) takes the value 1.

In a variant, "Fcp" and "Fpmtc" also depend on the speed of the vehicle. As a variant, the corrective gains "Fcp" or "Fpmtc" can be chosen so that whatever the engaged ratio, the level of electric braking torque applied to the wheels "Cf_récup" is substantially equal to "Cf_elec_max_acceptable".

Claims

1 - Braking method for a hybrid vehicle (1) comprising a heat engine and an electric machine (3) forming a traction chain, this traction chain being connected to wheels (2.1-2.4) of the vehicle (1), this vehicle having a brake pedal (20) which controls the braking of the vehicle, said method comprising the following steps:

when a pressing on the brake pedal (20) of the vehicle is detected,

a dissipative braking torque is applied to the wheels by means of brakes (16.1-16.4) connected to a hydraulic braking circuit, these brakes rubbing on elements rotating with the wheels (2.1-2.4), and

an additional braking torque (Cf_recup) is applied to the wheels by means of the electric machine (3),

this additional braking torque (Cf_recup) being modulated according to the stroke of the brake pedal ("course_pedale") and / or the hydraulic braking pressure ("pressurejmtc"), this braking torque also depending on the ratio committed speed (i).

2. Method according to claim 1, characterized in that, to modulate this additional braking torque, it further comprises the following steps:

- measure the maximum braking torque (Cf_recup_max) of the electric machine (3),

weighting this maximum braking torque by a corrective gain (Fcp_i, Fpmtc_i) dependent on the engaged ratio (i), this corrective gain (Fcp_i, Fpmtc_i) depending moreover, for a given speed ratio (i), the speed of the vehicle and at least one parameter among the brake pressure and the brake pedal stroke, and

- Control the machine (2) electric so that the electric braking torque (Cf_recup) applied to the wheels in addition to the dissipative braking is substantially equal to the maximum braking torque weighted.

3 - Method according to one of claims 1 and 2, characterized in that: - the pressing on the brake pedal (20) is detected by means of a sensor (41) inductive type BLS and / or a sensor (42) of pedal stroke and / or a sensor (43). ) hydraulic pressure brake.

4 - Process according to one of claims 1 to 3, characterized in that:

- the stroke of the brake pedal ("course_pedale") is measured by means of a sensor (42) of pedal stroke.

5 - Method according to one of claims 1 to 4, characterized in that: - the hydraulic brake pressure ("pressionjmtc") is measured by means of a sensor (43) brake pressure positioned

- at the location of a hydraulic block (23) controlling the hydraulic pressure applied to the brakes (16.1-16.4),

- Or at the location of a master cylinder (12) ensuring the transformation of a support on the pedal (20) in a hydraulic pressure.

6 - Method according to one of claims 1 to 5, characterized in that for modulating the braking torque of the electric machine (Cf_recup), it comprises the following steps:

calculate a first correction gain (Fcp_i) which depends on the vehicle speed and the brake pedal stroke, and / or

calculate a second corrective gain (Fpmtc_i) which depends on the speed of the vehicle and the brake pressure, - multiply the maximum braking torque by the first (Fcp_i) and / or the second (Fpmtc_i) computed corrective gain, and

- Control the machine (2) electric so that the value of the electric braking torque (Cf_recup) applied to the wheels in addition to the dissipative braking is substantially equal to the result of the multiplication. 7 - Process according to claim 6, characterized in that:

the corrective gains (Fcp_i, Fpmtc_i) depend on the speed ratio (i) engaged.

8 - Process according to claim 6 or 7, characterized in that: - The maximum braking torque (Cf_recup_max) of the machine (3) is obtained by means of a computer (8) which controls the torque applied by the traction chain.

9 - Process for improving a hybrid vehicle comprising a heat engine and an electric machine (3) forming a traction chain, this traction chain being connected to wheels (2.1-2.4) of the vehicle (1), in which :

a sensor (42) for pedal travel and / or a pressure sensor (43) is added so that - the additional braking torque (Cf_recup) applied by the machine (3) to the wheels when the brake pedal (20) ) is depressed according to the stroke of the brake pedal ("stroke_pedale") and / or the hydraulic brake pressure ("pressurejmtc").