JP7569625B2 - Brake force generator and method of operation - Google Patents

Description

The apparatus described herein and the method described herein include hardware protection measures in pedal-isolated or pedal-less redundant braking systems. The apparatus described herein and the method described herein are particularly relevant for so-called "by-wire" braking systems. The method and the apparatus in particular represent hardware protection measures, which are achieved by pressure control.

More and more people are interested in driving vehicles without having to control them themselves. From the user's point of view, autonomous passenger transport allows for much more flexibility than buses and trains. At the same time, autonomous passenger transport promises the potential for significant cost savings compared to taxis.

However, autonomous passenger transport poses new challenges for vehicle manufacturers when it comes to designing braking systems. Today's automotive braking systems are designed to be controlled by the vehicle operator, who constantly applies hydraulic pressure to the wheels to generate braking force. However, in the event of a braking system failure, the driver ensures that they can still apply sufficient braking force to the vehicle's wheels by operating the brake pedal.

When designing automatic or autonomous or semi-autonomous braking systems, but also in the case of braking systems that are only electrically controlled ("by wire"), the challenge is that these often have braking characteristics that are usually very unnatural from the point of view of the average user. Such braking characteristics arise in particular because automatic braking systems are not able to react at all to unexpected increases in brake pressure, unlike normal or normal braking systems. An unexpected increase in brake pressure can also mean, for example, an excessive increase in brake pressure as a result of a request for brake pressure (brake request). In the case of manual brakes, which can be operated by the user, for example by means of the brake pedal, a direct reaction to an unexpected or unexpectedly strong increase in brake pressure is usually achieved by the user slightly releasing the brake pedal, completely unconsciously. Such an unconscious action is usually not possible or requires a lot of effort to achieve in an automatic or autonomous braking system.

Against this background, a particularly advantageous automatic brake force generator and a particularly advantageous operating method for a brake system are described herein.

A brake force generator as described herein for automatically generating hydraulic brake pressure for a braking system of a motor vehicle comprises a plunger system having at least one chamber for receiving and pressurizing hydraulic fluid and a brake drive. The component unit including the associated secondary components is referred to herein as a "brake force generator". The term "plunger system" refers primarily to the hydraulic components of the brake force generator. The brake drive is configured to vary the volume of at least one chamber of the plunger system, thereby causing a pressure increase. The brake pressure generator further comprises at least one pressure sensor arranged in the at least one chamber for measuring the pressure increase in the at least one chamber and for emitting a pressure value signal. Furthermore, the brake pressure generator comprises a control unit configured to control the brake drive to increase the pressure in response to an electronic brake request and in response to the actual pressure measured by the pressure sensor.

So-called "linked" or "auxiliary" brake systems are known. Separate or power brake systems are also known. In auxiliary brake systems, the clamping force required for braking is applied to the wheel brakes by the driver's foot force assisted by a brake booster. In power brake systems, the required clamping force is applied to the wheel brakes by stored compressed air, which is generated by a compressor or hydraulically. Such power brake systems are widely used, for example, in trucks (LKW).

The power brake system is configured to be regularly decoupled. This means that the brake pedal is decoupled from the actual brakes and there is no direct (especially mechanical) power transmission from the brake pedal to the wheel brakes. A decoupled brake system is also called a "by-wire" configured brake system. "By-wire" means "telegraphed" or "wired." This allows the information that it is desirable to apply the brakes when the brake system is decoupled to be transmitted from the brake pedal to the wheel brakes, decoupled from the braking force. The braking force is generated based on this information.

In such decoupled braking systems, so-called "pedal feel simulators" are regularly used, which simulate the actual pedal feel for the brake pedal and give the user feedback on the generated braking action in the usual way. In cases where the braking system is decoupled, variants with only one pedal feel simulator and variants with multiple pedal feel simulators are possible and common.

However, in particular in variations of well-known designs, separate braking systems (also referred to as "by-wire" braking systems as discussed above) are also implemented, still providing hydraulic backup. In the event of a system failure, such embodiments operate like a conventional pedal-coupled braking system. For these reasons, such braking systems often omit the redundancy of separate/"by-wire" components.

Such widely known brake systems are therefore only of limited suitability for use in highly autonomous and fully autonomous vehicles (highly automated vehicles) since the additional safety features provided by the functional form of conventional auxiliary brake systems are not operational in highly or fully autonomous driving. Therefore, in today's vehicles with highly or fully autonomous capabilities, it is often necessary to incorporate further hydraulic brake units.

In some variants of vehicles with a high automation level (i.e. highly automated autonomous vehicles), the driver can consider applying the brakes manually in an emergency (when the autonomous driving functions of the vehicle fail or partially fail) at least with some reaction time. This is the case, for example, when the automation level of the vehicle is set in such a way that the driver always has to be ready to react and can also apply emergency braking. If the automation level is too high and the driver no longer considers applying emergency braking, in particular because the reaction time required for the driver to intervene is too short, all safety-relevant systems (e.g. braking, steering, etc.) can be executed redundantly (i.e. across the entire action chain). This is important since the vehicle must always be brought into a safe state in the event of an individual failure of a (braking) system.

Brake systems for vehicles with a high level of automation often pose special challenges to the designers due to the extremely high pressures and high pressure gradients that occur in such brake systems. High pressures and high pressure gradients mean high loads on the brake system.

These high loads are typically caused by the automatic operation of the valves for autonomous operation of the brake system, which significantly increases the stiffness of the brake system. This problem is solved by the brake pressure generator described herein.

The problem of increased brake system stiffness also already occurs in the area of ABS systems (antilock braking systems) and ESP systems (systems for electronic stability control) in brake systems coupled to the pedal, but is however reduced, since such systems generally also perform electronic braking, switching the valves without significant delay and thus also resulting in abrupt changes in the stiffness of the brake system. The resulting pressure increase/change is accommodated almost unconsciously by the driver concerned, who corresponds with a constant pedal force and slightly reduces/adapts the operation.

The increased stiffness caused by the switching of these valves has an effect, especially in relation to the fact that the volume discharged into the storage chamber during ABS control is directed back towards the plunger chamber again.

In this situation, improper adjustment of the brake pressure generator plungers and mass inertia act to push the plungers further forward, since the plungers do not know that the ABS/ESP has closed their valves. This related information can be provided by the ABS/ESP, but it is only provided to the plunger system with a time delay due to the latency caused by transmission over the bus system, and therefore cannot be used for optimal adjustment.

The brake pressure generator described here is in particular a module connected to a hydraulic unit, which delivers power to wheel brakes that are individually operated by a brake force generator. The brake force generator is also called a brake pressure generator or a pressure generator. The brake force generator (as already expressed) is an automated or autonomous brake force generator that can be integrated into an autonomous system or a "by-wire" system for driving a motor vehicle.

A plunger system having at least one chamber is generally a piston system in which a piston can be moved in the chamber to increase or decrease the volume of the chamber. Multiple chambers can be arranged one behind the other along an axis and can be operated (especially pressed) together in the plunger system. The plunger system generally has a push rod extending through at least one of the chambers. In this case, there is preferably at least one chamber partition that limits the multiple chambers from each other, and the push rod is movably sealed within the chamber partition. The chamber through which the push rod passes can also be called the "push rod chamber". The pressure circuit of the brake system connected to such a chamber can also be called the "push rod circuit".

The brake drive is preferably an electric drive motor, which typically generates rotary motion and converts it to linear motion via a spindle drive.

The control device is a type of controller that receives a brake request from a higher-level controller or pedal and generates a specifically suitable control signal for the brake actuation, taking into account the actual pressure recorded by the pressure sensor. The brake request can be provided in the form of an (electronic) braking signal.

The brake force generator is particularly advantageous if the pressure sensor has a time resolution of less than 1 ms [millisecond], preferably less than 0.2 ms, particularly preferably less than 0.1 ms.

Using such a pressure sensor with a very fine time resolution, particularly rapid adjustments are possible by the control device. The control device is preferably configured so that it can also process the corresponding signals from the pressure sensor at a correspondingly rapid rate.

It is also advantageous if the brake force generator has at least two chambers and at least one pressure sensor is arranged in each chamber.

In another advantageous embodiment, the brake force generator has at least two chambers and the pressure sensor is located in only one of these chambers.

When only one pressure sensor is provided for two or more chambers, the chambers are preferably connected to each other so that pressure compensation can be performed between the chambers and a pressure signal representative of both chambers can be obtained using the value detected by only one pressure sensor.

A method of operating a brake force generator for automatically generating brake pressure for a braking system of a motor vehicle, comprising:
a) receiving a braking request;
b) receiving an actual pressure from at least one pressure sensor monitoring the pressure in at least one chamber of the plunger system;
c) calculating a control signal for controlling a brake actuator of the brake force generator taking into account the brake demand and the actual pressure; and d) outputting a control signal to the brake actuator for regulating the brake pressure in the chamber.
Includes.

As already mentioned above, the brake request in step a) is preferably received by a higher-level unit (higher-level controller and/or brake pedal). The actual pressure is received in step b) by the pressure sensor already mentioned above.

The method is particularly advantageous if in step b) in addition to the actual pressure, the gradient of the actual pressure over time is also received or determined.

Such an actual pressure gradient can be calculated from the change in actual pressure over time in the controller (and in units upstream of the controller, if necessary).

This method is also particularly advantageous if, in step c), the control signal is calculated such that an upper limit is set for the gradient of the actual pressure over time.

The setting of such an upper limit has a particularly technical reason, since it would normally not make sense for the control device for the brake drive to set the control signal in such a way that it would cause a change in the actual pressure that exceeds an acceptable level.

Furthermore, this method is particularly advantageous if the calculated control signal is calculated in step c) such that an upper limit for the actual pressure is set.

An actual pressure exceeding a threshold value is usually not possible or meaningful, since it would necessarily result in the disconnection of the wheel brakes. Preferably, the system is designed so that such an actual pressure is not requested at all, i.e. no control signal that could request such an actual pressure is determined in step c).

The method is preferably carried out using a brake force generator as described above.

Here, particularly preferably, a brake system having the above-mentioned brake force generator is also shown.

The brake force generator described here, the control strategies possible with this brake force generator and the correspondingly configured brake system allow the pressure sensor with a high sampling frequency to recognize critical load changes independently of the data from the ESP and to adjust the electromechanical actuator based on the pressure to prevent further pressure fluctuations. This allows to avoid large vibrations that would be stressful on the hardware and allows for a more coordinated pressure adjustment for the ABS system. This prevents negative effects on the stopping distance.

Using the method and the brake force generator described above, it is possible to detect critical load changes early, independent of data from the ESP system. Pressure-based regulation of the electromechanical actuator avoids large vibration amplitudes that would load the hardware and ensures better ABS pressure control.

The brake force generator, the method and the braking system are particularly suitable for highly automated or purely autonomous braking systems. Such braking systems preferably completely eliminate the need for user operation of the brake pedal. However, the brake force generator and the method can also be operated by a brake pedal connected in a "by-wire" manner, i.e. a braking system operated by the user but with electronic "by-wire" signal transmission from the pedal to the brake force generator. The brake force generator, the method and the braking system may be part of a braking system allowing manual or conventional (e.g. via the brake pedal) operation. The pressure generator, the method and the braking system are particularly suitable for highly automated or even autonomous driving.

The above-mentioned brake force generator with pressure sensor and the above-mentioned method can be used to detect critical (and undesirable) load changes in the hydraulic system, at the point in time when the brake pressure at braking deviates from the actual pressure, especially independently of data from the ESP or ABS system. The data from the ESP or ABS system mainly take into account the effect of the brakes, i.e. in the case of an ESP system, usually the positive or negative acceleration of the vehicle (e.g. yaw rate), or in the case of an ABS system, the locking of the wheels of the vehicle. If further acceleration is required to further accelerate the control, the pressure gradient can be extrapolated from the most recent measurements available in order to detect the deviation earlier. This can also be achieved within the scope of the above-mentioned method.

The brake force generator described herein and the method described herein are particularly suitable for increased demands such as those occurring in the case of ABS control, where the stiffness of the brake system (of the entire hydraulic system) increases suddenly due to valve switching, resulting in pressure peaks in the plunger system chambers or very rapid and significant deviations from the target pressure, which are quickly detected by the pressure sensor.

The pressure generator, braking system, and method will now be described in more detail with reference to the drawings. It should be noted that the drawings show only preferred exemplary embodiments, and that the present disclosure is not limited to these preferred exemplary embodiments.

FIG. 1 illustrates a conventional brake system. FIG. 1 illustrates a fully autonomous braking system. FIG. 1 illustrates a combined braking system. FIG. 1 is a diagram showing a typical brake pressure curve. FIG. FIG. 13 shows a brake pressure waveform improved by the method described.

Figures 1, 2 and 3 show different brake systems 31, which will be described together here to the extent that they have common components. Differences between the brake systems 31 shown in the individual figures will be pointed out in each case.

The brake systems 31 each have a brake force generator 12, 13 which serves to generate an initial brake force via which the braking process can finally be triggered. The initial brake force is fed as pressure into hydraulic lines and transmitted to the individual wheel brakes 9. The hydraulic fluid required for this is supplied from a fluid supply container 11 which holds a reservoir of hydraulic fluid for the brake systems 31.

In a conventional motor vehicle with the brake system 31 shown here, four wheel brakes 9 (one wheel brake 9 for each wheel) are provided, which are connected in pairs to the hydraulic unit 22, preferably with the wheel brakes 9 of diagonally opposite wheels connected to one hydraulic unit 22. Each hydraulic unit 22 includes a high-pressure switching valve 26, which can control the hydraulic fluid flowing to the wheel brake 9, and a pressure control valve 27, which can allow the hydraulic fluid to flow out of the wheel brake 9. The high-pressure switching valve 26 and the pump 29 allow the pressure of the wheel brake 9 to be increased. The pressure control valve 27 allows the pressure of the wheel brake 9 to be adjusted and reduced again. Between the hydraulic unit 22 and the wheel brake 9, controllable inlet valves 24 and outlet valves 25 for the individual wheel brakes 9 are respectively arranged. By means of the inlet valve 24, the pressure in the individual wheel brakes 9 can be limited individually and increased again to the system pressure. By means of the outlet valve 25, the pressure of the individual wheel brakes 9 can be reduced individually. The inlet valve 24 and the outlet valve 25 allow individual control of the individual wheel brakes 9, for example for ESP or ABS operation. The hydraulic units 22 each include a low-pressure accumulator 23 that can temporarily store hydraulic fluid discharged from the wheel brakes 9. The hydraulic fluid from the low-pressure accumulator 23 can be repressurized by a pump 29 driven by a pump drive 30 and then supplied again to the hydraulic unit 22 to generate brake pressure at the wheel brakes 9.

The embodiment shown in FIG. 1 shows a schematic representation of a conventional braking system 31 with a manual brake force generator 12. Brake pressure is generated by a brake pedal 16, shown here by way of example in a chamber 15 of a plunger system 14. A brake demand 1 (meaning a specific brake force setting) acts directly on the brake pedal.

2 shows a schematic representation of an automatically or automated brake system 31, in which the brake force is generated by means of an automatic brake force generator 13. This automatic brake force generator 13 likewise has a plunger system 14 with at least one chamber 15, preferably with several chambers 15 (particularly preferably with two chambers 15), for generating the brake pressure. However, the brake pressure is not generated by means of the brake pedal 16, but by means of a brake actuator 17 controlled by a control signal 33. According to the embodiment described here, the control signal 33 does not correspond directly to the brake request 1, as is typical when the brake actuator 17 is controlled similarly to the brake pedal 16 shown in FIG. 1, but is generated by a special control device 19 or a higher-level system. The brake request 1 is first transmitted to the control device 19, which in order to generate the control signal 33 also receives this brake request 1 and the actual pressure 2, which is determined by a pressure sensor 18 that records the pressure in the chamber 15 of the plunger system 14 of the automatic brake force generator 13. The brake system 31 shown in FIG. 3 is particularly designed for use in fully automated or fully autonomous vehicles, where there is no longer any manual intervention from the brake pedal into the brake system 31, but rather the brake request 1 is transmitted "only" as a signal and not mechanically. The brake system shown in FIG. 2 is atypical in that there is only one chamber 15. Here, to obtain redundancy, a plunger system 14 with two chambers 15 is generally required in the case of a vehicle without an additional brake force generator.

Figure 3 shows a combined braking system 31 combining both a manual brake force generator 12 as shown in Figure 1 and an automatic brake force generator 13 as shown in Figure 2. Both brake force generators 12, 13 can be connected to the hydraulic unit 22 via a connecting valve 28, respectively, and can be separated from the hydraulic unit 22. This makes it possible to decide whether it is desired to generate the brake force by the manual brake force generator 12 or by the automatic brake force generator 13. A brake pressure simulator 21 is further shown here as an example, which can be used to simulate the brake force for a user of a vehicle having such a braking system 31. Such a brake pressure simulator 21 can be connected to the brake pedal 16 and serves to give the user a realistic braking sensation, in the case where the brake pressure is transmitted "only" as a signal and there is no direct mechanical interaction between the brake pedal and the generated brake pressure.

Embodiments of the present invention provide a hydraulically closed multi-circuit brake system without mechanical and/or hydraulic intervention by the driver, particularly for highly automated or autonomous vehicles, and a corresponding actuation method, in which a pressure generator is used in series in the hydraulic circuit, acting on all wheel brakes of the vehicle via a hydraulic unit.

The brake drive 17 shown in Figures 2 and 3 is generally a motor. The motor current and the motor rotation speed are the relevant variables for controlling this motor. In particular when operating the emergency brake, the brake drive 17 must have very high dynamic characteristics. This means that the brake drive 17 must be able to react very quickly to a brake force request. Therefore, the pressure sensor signal relating to the actual pressure 2 from the pressure sensor 18 is preferably read in frequently and evaluated frequently in the control device 19.

Figure 4 shows a typically occurring situation involving the above-mentioned brake force generator and the above-mentioned operating method. In this figure, the brake demand 1, which is typically set by a user (or a system for autonomous/automated driving), is plotted on the pressure axis 3 against the time axis 4. Also shown is the actual pressure 2, which follows exactly the brake demand 1 up to a first deviation 34 (defined, for example, by a predefined threshold). From this threshold, the actual pressure 2 typically rises too high relative to the brake pressure 1.

This phenomenon is countered by the control strategy shown in FIG. 5. The upper part of FIG. 5 shows a brake pressure setting unit 20 including an ABS controller 35 which sets a brake demand 1, typically a brake pressure model pressure 40 (ideal brake pressure determined by an electronic model) and determines the brake demand 1 from this brake pressure model pressure 40. This brake demand 1 is transmitted to a control device 19 shown in the lower part of the figure. The control device 19 serves to control the brake drive 17, which is also shown here in a schematic form. The core element of the control device is an adder 39, in which the actual pressure 2 measured by the pressure sensor 18 and the brake demand 1 can be added to each other (or subtracted from each other) in order to determine a control difference 41 which the control device 19 can use to control the brake drive 17. The control device 19 preferably comprises the sub-modules position control device 36 (for checking the current position of the brake drive 17), a speed check device 37 (for checking the current speed of the brake drive 17) and a current check device 38 (for checking the current drive current supplied to the brake drive 17). Each of these three units can receive (further) input variables from the brake drive 17, thereby achieving ideal control of the drive 17 so that the actual pressure 2 follows the braking demand 1 as accurately as possible.

During normal partial braking, the pressure sensor value (actual pressure 2 measured by pressure sensor 18) follows the nominal driver brake demand (waveform before deviation 35 shown in Figure 4).

Figure 6 shows the situation that arises with the above-described braking force generator and the above-described method when performing ABS control. The example shown in Figure 6 also applies to the case of ESP control.

Figure 6 illustrates the determination of the target pressure 43, which is a control variable during ABS operation, using the method described herein and the brake force generator described herein. Figure 6 illustrates three phases A, B, and C of the ABS braking process with the brake force generator described. At the start of phase A, the pressure is monitored and the actual pressure 2 measured by the pressure sensor corresponds to the braking demand. This is plotted on the pressure axis 3 against the time axis 4 in the upper part of the figure.

At or immediately before the transition from phase A to phase B, the control device detects a deviation 34 by means of the pressure sensor. Such deviation 34 may be caused, for example, by an intake valve, an exhaust valve, a high-pressure switching valve, or a pressure regulating valve of the brake system. Closing such a valve causes an abrupt change in the stiffness of the hydraulic system.

From this point on, the wheel brakes tend to apply particularly high braking forces and the wheels tend to lock. This is based on the fact that the usual sensors for monitoring the braking characteristics in the ESP or ABS controller only provide a signal if a braking effect has already occurred on the acceleration characteristics of the vehicle or the braking action of the brakes. This is why the controller for the ESP or ABS only receives a usable signal at the transition from phase B to phase C. Only from this point on does it close the ESP or ABS control loop, because ABS and ESP respond much more slowly compared to the control device described here and also compared to the method described here. In phase B, the actual pressure is further increased with a predefined (maximum) gradient according to the driver's braking demand. However, this only occurs up to a defined upper limit (for example up to 180 bar). The predefined (maximum) gradient and the predefined upper limit are permanently stored in the control device for the method described here.

From the transition from phase B to phase C, typical repetitive fluctuations in the brake pressure occur. These fluctuations are caused by control actions by the ESP or ABS controller. The corresponding target pressure 43 and the brake pressure model pressure set by the ESP or ABS control unit are plotted against the time axis 4 in the middle part of FIG. 6. The lower part of FIG. 6 shows the piston position set by braking, which sets or influences the volume of the chamber in the plunger system.

Claims (8)

A brake force generator (13) for automatically generating hydraulic brake pressure for a braking system (31) of a motor vehicle, comprising :
a plunger system (14) having at least one chamber (15) for containing and pressurizing hydraulic fluid;
a brake actuator (17) configured to change the volume of at least one chamber (15) of the plunger system (14), thereby causing a pressure increase;
at least one pressure sensor (18) arranged in the at least one chamber (15) for measuring a pressure rise in the at least one chamber (15) and for delivering a pressure value signal;
a control device (19) configured to control the brake actuator (17) to increase pressure in response to an electronic brake request (1) and in response to an actual pressure (2) measured by a pressure sensor (18);
In a braking force generator (13) comprising:
The control device (19) controls the brake driving device (17),
a) receiving an electronic brake request (1);
b) receiving an actual pressure (2) from at least one pressure sensor (18) monitoring the pressure in at least one chamber (15) of the plunger system (14), where in addition to the actual pressure (2) also a gradient of the actual actual pressure (2) over time is received or measured;
c) calculating a control signal (33) for controlling the brake actuator (17) of the brake force generator (13) taking into account the electronic brake demand (1) and the actual pressure (2), the control signal (33) being calculated such that an upper limit is set for the gradient of the actual pressure (2) over time;
d) outputting a control signal to a brake driver (17) to regulate the brake pressure in the chamber (15);
Execute
Brake force generator (13) . A braking force generator (13) according to claim 1,
A brake force generator (13), wherein the pressure sensor (18) has a time resolution of less than 1 ms [millisecond] . A braking force generator (13) according to claim 2 ,
A brake force generator (13), wherein the pressure sensor (18) has a time resolution of less than 0.2 ms. A braking force generator (13) according to any one of claims 1 to 3 ,
A brake force generator (13) comprising at least two chambers (15) with at least one pressure sensor (18) disposed in each chamber (15). A braking force generator (13) according to any one of claims 1 to 3 ,
A brake force generator (13) having at least two chambers (15), with a pressure sensor (18) disposed in only one of the chambers (15). 1. A method of operating a brake force generator (13) for automatically generating brake pressure for a braking system (31) of a motor vehicle, comprising the steps of:
a) receiving an electronic brake request (1);
b) receiving an actual pressure (2) from at least one pressure sensor (18) monitoring the pressure in at least one chamber (15) of the plunger system (14) , where in addition to the actual pressure (2) also a gradient of the actual actual pressure (2) over time is received or measured ;
c) calculating a control signal (33) for controlling the brake actuator (17) of the brake force generator (13) taking into account the electronic brake demand (1) and the actual pressure (2), the control signal (33) being calculated such that an upper limit is set for the gradient of the actual pressure (2) over time;
d) outputting a control signal to a brake driver (17) to regulate the brake pressure in the chamber (15);
The method includes: A method for operating a brake force generator (13) according to claim 6, comprising the steps of :
In step c), the control signal (33) is calculated such that an upper limit for the actual pressure (2) is set. A brake system (31) for a motor vehicle, comprising a brake force generator (13) according to any one of claims 1 to 5 .

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