KR102721888B1 - Brake system for a motor vehicle, having two electromechanical brake pressure generating devices - Google Patents

Abstract

The present invention relates to a brake system for a motor vehicle comprising two electromechanical brake pressure generating devices for generating hydraulic braking pressure in at least two wheel brake cylinders, wherein the first brake pressure generating device is formed as a hydraulic system including a first electric actuator for operating at least one pump and is configured to enable driving dynamics control of the motor vehicle by means of an intended wheel-specific pressure modulation in the at least two wheel brake cylinders, and the second brake pressure generating device is formed as a piston-cylinder device including at least one piston defining a hydraulic pressure chamber and which can be adjusted to vary the volume of the hydraulic pressure chamber by operation of the second electric actuator, wherein the first brake pressure generating device and the second brake pressure generating device are arranged in series with one another, and the first brake pressure generating device is connected to at least two wheel brake cylinders in each case by one direct hydraulic connection.

Description

{BRAKE SYSTEM FOR A MOTOR VEHICLE, HAVING TWO ELECTROMECHANICAL BRAKE PRESSURE GENERATING DEVICES}

The present invention relates to a brake system for a motor vehicle comprising two electromechanical brake pressure generating devices for generating hydraulic braking pressure in at least two wheel brake cylinders, the first brake pressure generating device being formed as a hydraulic system including a first electric actuator for actuating at least one pump and being configured to enable driving dynamics control of the motor vehicle by means of an intended wheel-specific pressure modulation in the at least two wheel brake cylinders, the second brake pressure generating device being formed as a piston-cylinder device including at least one piston which delimits a hydraulic pressure chamber and which can be adjusted in such a way as to vary the volume of the hydraulic pressure chamber by actuation of the second electric actuator, the first brake pressure generating device and the second brake pressure generating device being arranged in series with one another, the first brake pressure generating device being connected to at least two wheel brake cylinders in each case by means of one direct hydraulic connection.

Modern automotive braking systems are designed to provide driver control over the continuous hydraulic action of braking force generation at the wheels. As a result, in the event of a brake system failure, it is ensured that sufficient braking force is provided to the wheels of the vehicle by the driver operating the brake pedal.

Today, so-called coupled brake systems or auxiliary power brake systems, such as for example the iBooster and ESP, are known. Furthermore, decoupled brake systems or power brake systems, such as the IPB from Robert Bosch GmbH, are known. Decoupled brake systems are operated by-wire in full function mode, i.e. the driver does not directly exert any action (the driver is involved in a pedal feel simulator). However, these systems are also implemented so that a hydraulic action is still provided in backup mode. Current power brake systems, such as the IPB, are not electrically redundant. Therefore, in order to use these power brake systems in highly and fully autonomous vehicles, an additional hydraulic unit, such as a Redundant Brake Unit (RBU), must be integrated. In vehicles with a high degree of automation (i.e. highly automated and autonomous vehicles), the driver cannot be involved for at least a certain reaction time as a fallback state. Therefore, all safety-related systems (such as brakes, steering systems, etc.) must be redundant.

The task of the present invention is to provide a brake system that enables a modular brake system architecture suitable for providing low brake system cost and a high level of safety for the entire vehicle platform.

Unlike prior art, the brake system according to the present invention enables a modular brake system architecture that is suitable for providing a high level of safety, preventing peripheral measures of the brake system, such as a redundant vehicle electrical system, while allowing for lower brake system costs for the entire vehicle platform, not only for partially automated and highly automated vehicles but also for the transition towards electric vehicles.

This is made possible, according to the invention, by the features set out in the independent claims. Further embodiments of the invention are the subject of the dependent claims.

A brake system according to the present invention is a brake system for a motor vehicle comprising two brake pressure generating devices independent of the driver's force for generating hydraulic braking pressure in at least two wheel brake cylinders, wherein the first brake pressure generating device is formed as a hydraulic system including a first electric actuator for actuating at least one pump and is configured to enable driving dynamics control of the motor vehicle by means of an intended wheel-specific pressure modulation in the at least two wheel brake cylinders, and the second brake pressure generating device is formed as a piston-cylinder device including at least one piston which defines a hydraulic pressure chamber and which can be adjusted to vary the volume of the hydraulic pressure chamber by actuation of the second electric actuator, and wherein the first brake pressure generating device and the second brake pressure generating device are arranged in series with one another, and wherein the first brake pressure generating device is connected to at least two wheel brake cylinders in each case by means of one direct hydraulic connection.

This means that the brake system comprises two pressure generators which can displace hydraulic fluid or build up pressure independently of the driver. In this case, the fluid displacement or pressure build-up is carried out in an automated manner. This is done, for example, by an electromechanical device, for example an electric actuator, for example an electric motor.

Pressure generation independent of the driver's force means, in particular, that there is no mechanical or hydraulic coupling with the driver. In other words, for example, the connected pressure generation in the pressure generator is not carried out via the electric motor and the brake pedal. In a practical implementation, for example, the second brake pressure generation device is designed so that there is no possibility of a mechanical action by the driver on the piston. In this case, the driver's braking demand is detected, for example, by a brake pedal travel sensor, and implemented by an electronic control of an electric actuator, which in turn adjusts the piston and displaces the fluid or builds up the pressure accordingly. In this sense, the pressure generation is carried out in response to the driver's braking demand, but is actually carried out independently of the pressure generated by the driver or independently of the driver's force. Furthermore, if the need for braking is identified, for example in an automated (partially automated) driving mode, the pressure generation can also be carried out in an automated manner and independently of the driver's braking demand.

For example, even in the case of the first brake pressure generator, there is no mechanical connection or mechanical action possibility for the driver. However, the first brake pressure generator is formed so that the braking pressure generated by the driver is transmitted to the wheel brake cylinders. In this case, the braking pressure can be modulated as required. When interpreted as pressure modulation, this is the formation, dissipation or maintenance of the braking pressure. By this pressure modulation, the driving dynamics are influenced in particular, and in particular the driving stability control (ESP) is implemented. This makes it possible to control the vehicle movement and prevent oversteer and/or understeer of the vehicle. As a result, brake slip control (ABS) can also be achieved. The hydraulic circuit of the first brake pressure generator can be formed so that there is an X-shaped division and a II-shaped division of the brake circuits. The expressions pressure formation unit, braking pressure generator, braking pressure generator and pressure generator are to be used interchangeably.

The second braking pressure generating device is formed as a main brake system and the first braking pressure generating device is formed as a secondary brake system. The main and auxiliary brake systems are arranged in series with one another or are thus hydraulically connected to one another. In this case, the first braking pressure generating device is connected to the wheel brake cylinders, i.e. hydraulically connected. The above-mentioned direct connection means that no additional pressure generating devices are connected in between. Furthermore, no valves are located between the first pressure generating device and the wheel brake cylinders. The pressure generation or pressure modulation by the first braking pressure generating device acts on all wheels of the vehicle via the hydraulic circuit of the first braking pressure generating device. In this case, the vehicle comprises in particular one wheel brake cylinder per wheel. The first braking pressure generating device and the second braking pressure generating device have at least one hydraulic connection possibility with one another. The connection can be hydraulically connected and disconnected, for example, by means of a separating valve. Thus, for example, the second braking pressure generating device can be disconnected from the wheel brake cylinders.

The second braking pressure generator (main brake system) is implemented as a so-called plunger system (piston-cylinder device). In this case, the plunger can preferably be formed as a single circuit, since the usual dual circuit is provided by the driver's dual-circuit mechanical action (dual-circuit tandem brake master cylinder) and the dual-circuit ESP in the event of a failure of the main brake system. This enables clear cost advantages compared to embodiments with a dual-circuit plunger due to the omission of a floating piston and the simple connection of the actuator. Alternatively, dual-circuit plunger systems are also possible to ensure high safety requirements. It should be noted here that the second braking pressure generator implemented as a dual-circuit plunger is also a braking pressure generator independent of the driver, i.e. does not have a mechanical connection to the brake pedal.

Furthermore, by using the plunger system as the primary brake system, optimum NVH performance of the full system can be achieved. Furthermore, this enables simple and precise monitoring and control, since not only position but also volume and pressure build-up information can be detected more simply and more precisely compared to other concepts (such as pumps). By combining and specific arrangement of two different braking pressure generating devices, so-called hot redundancy can also be achieved. The ESP system can assist the plunger system in certain functions, for example in HBB (hydraulic brake boost) or HBC (hydraulic booster failure compensation). Furthermore, in the event of a failure of the primary brake system, the full ESP functionality including longitudinal and lateral stabilization can be utilized.

This can advantageously lead to a reduction in the brake system costs for modular platforms. Depending on the respective requirement characteristics for the respective vehicle version, the most advantageous brake system can be used. In particular for autonomous or partially autonomous vehicles, this type of system offers a wide range of advantages. For example, the active pedal disconnection can prevent driver errors from occurring and allows active braking to continue to be carried out without being affected by it. Furthermore, the brake booster can be replaced by the provided pedal disconnection and a separate pressure build-up unit (second brake pressure generator), while the ESP can continue to be used unchanged. Furthermore, the invention has a lower weight and volume compared to modern dual brake systems, especially with regard to the particularly package-critical components on the mudguard. Furthermore, no volume mixing is required during recuperation and, compared to fully pedal-connected systems, the pressure can be actively adjusted to zero during pure recuperation braking. As a result, residual pressures that reduce the recuperation efficiency are prevented.

In a preferred embodiment of the brake system of the present invention, the second brake pressure generating device is connected to at least two wheel brake cylinders via the first brake pressure generating device.

This means that the configuration and arrangement of the two pressure generators is such that the first pressure generator enables a pressure transmission from the second pressure generator to the wheel brakes. In this case, the first pressure generator forms (at least slightly) a hydraulic connection between the second pressure generator and the wheel brake cylinders. The plunger system pressurizes the brake fluid similarly to the ESP system. Of course, the ESP system can modulate the fluid flow.

In a possible embodiment, the first brake pressure generating device is formed as an ESP device comprising a plurality of valves, in particular twelve electromagnetic valves, and at least one storage chamber, in particular two storage chambers.

This means that the first brake pressure generator enables the full ESP functionality. For passenger cars, the ESP is configured as a dual-circuit system, for example, with one low-pressure accumulator, one re-sending pump, two inlet and outlet valves, one pressure maintenance valve and a pressure regulating valve (USV) and one high-pressure switching valve (HSV) per circuit. Preferably, a standard ESP module is used as the first brake pressure generator. The 1:1 takeover of the standard ESP module enables very low total system costs through the existing scale effect and avoids double or new application costs across all vehicle versions.

In a preferred embodiment, the brake system of the present invention comprises a driver brake pressure generating device, in particular the driver brake pressure generating device is connected to the first brake pressure generating device by at least one first separating valve.

When interpreted as a driver brake pressure generator, this is for example a master brake cylinder or a tandem brake master cylinder, or a vacuum booster (pneumatic auxiliary brake master cylinder), or an iBooster (electromechanically auxiliary/drive brake master cylinder). In this case, a direct driver action on the brake fluid exists. For example, a foot brake pedal enables a direct mechanical connection with a piston, which, by its movement, causes the brake fluid to be moved and the braking pressure to be generated. The driver brake pressure generator is hydraulically connected to the first brake pressure generator. Furthermore, the driver brake pressure generator is connected via the first brake pressure generator to at least two wheel brake cylinders.

The plunger system can generate a hydraulic fluid pressure independently of the brake master cylinder, which hydraulic fluid pressure is connected, in relation to the liquid, to the brake circuit of the first pressure generator via fluid lines, each of which has a switching valve arranged therein. Likewise, the brake master cylinder can generate a hydraulic fluid pressure independently of the plunger system, which hydraulic fluid pressure is connected, in relation to the liquid, to the brake circuit of the first pressure generator via fluid lines, each of which has a switching valve arranged therein. The two pressure generators are therefore arranged in parallel with one another. Due to the possibility of driver intervention on the wheel brake cylinders, a dual vehicle electrical system for controlling the actuators, for example, can be omitted.

By means of the separating valve, the hydraulic connection of the brake master cylinder to the wheel brake cylinders can be connected or disconnected. For this purpose, for example, a normally open separating valve can be used. The pressure circuit can be configured as a double circuit. Therefore, two separating valves are provided (one for each fluid line). The separating valves of the driver's braking pressure generation device prevent the pressure (or the displaced fluid) generated by the second pressure generator from reaching the hydraulic pressure chamber of the brake master cylinder, thereby making it possible for said pressure or fluid to actually be conducted to the wheel brake cylinders.

In an alternative improved example, in a first state a hydraulic connection is formed between the driver braking pressure generating device and at least two wheel brake cylinders, and in a second state a hydraulic connection is formed between the driver braking pressure generating device and the braking feel simulator.

This means that the system can hydraulically involve or disconnect the driver from the braking process. In the involved (first) state, there is a possibility of mechanical-hydraulic driver action on the wheel brake cylinders. In the disconnected (second) state, the driver does not perform any action, but only participates in the braking feel simulator. In this case, the driver is actively disconnected from the braking system via the valves, and the required pedal feel is generated via the simulator. Therefore, the system can be referred to as an active pedal disconnect system.

In a preferred embodiment, the second brake pressure generating device is connected to the first brake pressure generating device by at least one second separating valve.

This means that the second pressure generator can be separated from the first pressure generator by means of a separating valve. Therefore, in the case of a dual-circuit system, two separating valves are provided. The separating valves are assigned to the second pressure generator. That is to say, the separating valves are not the same separating valves as in the driver brake pressure generator. However, the separating valves of the second pressure generator prevent the pressure (or the displaced fluid) generated by the driver in a similar manner from reaching the hydraulic pressure chamber of the second pressure generator, thereby making it possible for the pressure or fluid to actually be conducted to the wheel brake cylinders.

In a possible embodiment, the brake system of the present invention is formed as a closed brake system.

This means that the entire brake system is implemented as a closed system. In other words, the brake fluid is discharged via the outlet valves in the case of the ABS into a low-pressure accumulator or storage chamber and is recirculated into the brake circuit above the inlet valves via the replenishment pump of the auxiliary system. Accordingly, replenishment of the main brake system (plunger system) is preferably not necessary in a closed system. Thus, due to the omission of the pressure holding phase in the case of replenishment, a functional reduction and a performance gain can be achieved.

In a preferred improved embodiment, the first and second brake pressure generating devices are each controlled by separate control devices.

This means that the electric actuators of each pressure generator are each controlled by one control unit, the two control units being preferably connected to the vehicle electrical system.

In an alternative embodiment, the control devices are connected to different vehicle electrical systems. This results in increased system safety.

In an alternative embodiment, the brake system of the present invention comprises a plurality of structural units, a first structural unit comprising a first braking pressure generating device, a second structural unit comprising a second braking pressure generating device, at least a second separating valve, a driver braking pressure generating device, at least the first separating valve and a braking feel simulator.

Preferably, the so-called 2-box design allows for high modularity and flexibility in geometric integration into the overall vehicle.

In a preferred embodiment, the brake system of the present invention comprises a plurality of structural units, a first structural unit comprises a first braking pressure generating device, a second structural unit comprises a second braking pressure generating device and at least a second separating valve, and a third structural unit comprises a driver braking pressure generating device, at least the first separating valve, and a braking feel simulator.

The so-called 3-box design further increases modularity and flexibility when it comes to geometric integration into the overall vehicle. As a result, not only packaging advantages are achieved (since the relatively smaller box is positioned on the mudguard and the box of the second pressure generator can be positioned arbitrarily), but also NVH advantages (since the box of the second pressure generator with its motor is no longer positioned on the mudguard and thus an optimized (more suitable/attenuated/longer) sound transmission path can be achieved).

Furthermore, according to the present invention, a method for operating the aforementioned brake system of a vehicle is proposed, wherein the brake system is operated at least temporarily in one of the following modes:

- In the first mode, the brake master cylinder is hydraulically separated from the wheel brake cylinders, the braking pressure within the wheel brake cylinders is generated by at least a second braking pressure generating device, the first braking pressure generating device performing wheel-individual braking pressure modulation;

- In the second mode, the brake master cylinder is hydraulically separated from the wheel brake cylinders, the braking pressure within the wheel brake cylinders is generated by at least a first braking pressure generating device, the first braking pressure generating device performing wheel-specific braking pressure modulation;

- In the third mode, the brake master cylinder is hydraulically connected to the wheel brake cylinders, the braking pressure in the wheel brake cylinders is generated at least by the brake master cylinder, and the first braking pressure generating device performs wheel-specific braking pressure modulation and/or braking force enhancement (HBC).

It should be noted that the features described individually in this specification may be combined with each other in any technically meaningful manner and represent further embodiments of the present invention. Further features and effectiveness of the present invention are presented in the description of embodiments with reference to the attached drawings.

Figure 1 is a drawing showing a first possible implementation of a brake system according to the present invention.
Figure 2 is a drawing illustrating a possible alternative implementation of the brake system according to the present invention.
FIG. 3 is a drawing illustrating another possible alternative implementation of the brake system according to the present invention.
Figure 4 is a flowchart illustrating possible method steps.

In Fig. 1, a schematic diagram of a first possible implementation of a brake system (19) according to the invention is shown. In this case, the first pressure generating device (1) is formed as a hydraulic ESP system. The ESP system is formed as a structural unit (18a). In addition to the electric actuator (5), the unit comprises pumps (6) and valves (11) (high-pressure switching valves and switching valves, inlet valves, outlet valves) and storage chambers (12). This is a conventional ESP system whose operating principle is known. The ESP system has two hydraulic connections in the direction of the brake master cylinder (13) or the second braking pressure generating device (2) as well as four hydraulic connections in the direction of the wheel brake cylinders (4a, 4b, 4c, 4d).

The second braking pressure generator (2) is formed as a plunger system (7). In this case, the electric actuator (10) adjusts the piston (8) which delimits the hydraulic pressure chamber (9). By means of this adjustment, the hydraulic fluid is pushed out or sucked out of the pressure chamber. The separating valves (16) enable the connection and disconnection of the second braking pressure generator to the brake system of the first pressure generator.

The second braking pressure generation device (2) is formed together with the driver braking pressure generation device (3) in one structural unit (18b). The driver braking pressure generation device comprises a brake master cylinder (13) and a braking feel simulator (15). Separating valves (14) enable connection and disconnection of the driver braking pressure generation device to the brake system of the first pressure generator. Likewise, the brake master cylinder is connected to the braking feel simulator (15) via the separating valve. When the driver acts on the brake pedal, the two separating valves (14) in the driver path are closed by an electrical control in the main brake system (main system) shown above, and the separating valves (16) in the simulator and plunger path are opened. As a result, the driver is disconnected from the brake system and displaces the braking fluid volume only into the pedal feel simulator (15), whereby the driver experiences the travel and the force recoil that he knows. The main system sets the hydraulic pressure required for decelerating the vehicle in accordance with the driver braking request detected via the plunger system (7). The known vehicle stabilizing functions (ESP, TCS, ABS, etc.) and, if applicable, additional functions are implemented wheel-by-wheel by the ESP system of the first pressure generator (1), as is known. Two control devices (17a and 17b) are provided for controlling the actuators (5 and 10).

If the vehicle executes autonomous braking and the higher-level coordination system prohibits the implementation of driver braking requests (e.g. if children play in the autonomous vehicle and in some cases inadvertently actuate the brake pedal), pedal actuation by the “driver” does not lead to an increase in vehicle deceleration, and the brake system can continue to independently set the required braking pressure of the higher-level coordination system for vehicle deceleration based on active pedal disconnection. In the event of a failure of the pedal disconnection system, the driver is mechanically/hydraulically directly connected to the foundation via the de-energized position of the valves (14), the pedal feel simulator (15) and the plunger system (7) are disconnected, i.e. the driver can directly generate the braking force at the wheels of the vehicle by providing a pedal pressure with the existing hydraulic conversion ratio.

In Fig. 2, an alternative implementation of the brake system (19) according to the invention is shown. In contrast to the implementation described at the beginning, the plunger system here comprises a double-circuit plunger. In other words, two hydraulic pressure chambers (9) are formed. In addition, there are two pistons (8) which can be adjusted by an actuator (10).

In Fig. 3, a further alternative implementation of the brake system (19) according to the invention is illustrated. In contrast to the implementation in Fig. 1 initially described, there are now three structural units. The first structural unit (18a) comprises a first braking pressure generator (1) with an ESP system. The second structural unit (18b) comprises a second braking pressure generator (2) (illustrated as a single-circuit implementation of a plunger system, but a dual-circuit implementation is also possible). The structural unit (18c), on the other hand, comprises a driver braking pressure generator (3) with a brake master cylinder (13), a braking feel simulator and associated separating valves.

In Fig. 4, the method steps of one embodiment of the present invention are illustrated. In this case, the method of the present invention starts in the first step (S1). In the second step (S2), the operation of the brake system in the selected mode is performed. In the final step (S3), the method of the present invention ends.

Claims (12)

In a brake system (19) for an automobile, comprising a first brake pressure generating device (1) independent of a driver's power for generating hydraulic braking pressure within at least two wheel brake cylinders (4a, 4b), and a second brake pressure generating device (2),
The above first braking pressure generating device (1) is formed as a hydraulic system including a first electric actuator (5) for operating at least one pump (6) and is configured to enable driving dynamics control of the vehicle by means of an intended wheel-specific pressure modulation within the at least two wheel brake cylinders (4a, 4b).
The second braking pressure generating device (2) is formed as a dual-circuit piston-cylinder device (7) comprising two pistons (8) which define two hydraulic pressure chambers (9) and can be adjusted to vary the volume of the corresponding hydraulic pressure chambers (9) by the operation of a second electric actuator (10), each hydraulic pressure chamber (9) being connected to the first braking pressure generating device (1) by a second separating valve (16),
The first braking pressure generating device (1) and the second braking pressure generating device (2) are arranged in series with each other, and the first braking pressure generating device (1) is connected to the at least two wheel brake cylinders (4a, 4b) by one direct hydraulic connection,
The above brake system (19) comprises a driver braking pressure generating device (3) connected to the first braking pressure generating device (1) by at least one first separating valve (14),
In the first state, a hydraulic connection is formed between the driver braking pressure generating device (3) and the at least two wheel brake cylinders (4a, 4b), and in the second state, a hydraulic connection is formed between the driver braking pressure generating device (3) and the braking feel simulator (15).
Brake system for automobiles. In paragraph 1,
A brake system for an automobile, wherein the second braking pressure generating device (2) is connected to at least two wheel brake cylinders (4a, 4b) via the first braking pressure generating device (1). In claim 1 or 2,
A brake system for an automobile, wherein the first braking pressure generating device (1) is formed as an ESP device including a plurality of valves (11) and at least one storage chamber (12). delete delete delete In claim 1 or 2,
The above brake system (19) is a brake system for an automobile, formed as a closed brake system. In claim 1 or 2,
A brake system for an automobile, wherein the first braking pressure generating device (1) and the second braking pressure generating device (2) are each controlled by separate control devices (17a, 17b). In Article 8,
A brake system for an automobile, wherein the above control devices (17a, 17b) are connected to different vehicle electrical systems. In paragraph 1,
A brake system for an automobile, wherein the brake system (19) comprises a plurality of structural units (18a, 18b), the first structural unit (18a) comprises the first braking pressure generating device (1), and the second structural unit (18b) comprises the second braking pressure generating device (2), a second separating valve (16), a driver braking pressure generating device (3), a first separating valve (14), and a braking feel simulator (15). In paragraph 1,
A brake system for an automobile, wherein the brake system (19) comprises a plurality of structural units (18a, 18b, 18c), the first structural unit (18a) comprises the first braking pressure generating device (1), the second structural unit (18b) comprises the second braking pressure generating device (2) and the second separating valve (16), and the third structural unit (18c) comprises the driver braking pressure generating device (3), the first separating valve (14), and the braking feel simulator (15). In a brake system operating method for operating a brake system (19) for an automobile according to claim 1 or 2,
The above brake system (19) operates at least temporarily in one of the following modes:
- In the first mode, the brake master cylinder (13) is hydraulically separated from at least two wheel brake cylinders (4a, 4b), the braking pressure in said wheel brake cylinders (4a, 4b) is generated by at least a second braking pressure generating device (2), and the first braking pressure generating device (1) performs wheel-individual braking pressure modulation;
- In the second mode, the brake master cylinder (13) is hydraulically separated from the at least two wheel brake cylinders (4a, 4b), the braking pressure within the wheel brake cylinders (4a, 4b) is generated at least by the first braking pressure generating device (1), the first braking pressure generating device (1) performs wheel-individual braking pressure modulation;
- A method of operating a brake system, wherein in a third mode, the brake master cylinder (13) is hydraulically connected to at least two wheel brake cylinders (4a, 4b), the braking pressure within the wheel brake cylinders (4a, 4b) is generated at least by the brake master cylinder (13), and the first braking pressure generating device (1) performs wheel-individual braking pressure modulation and/or braking force enhancement.

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