Method for controlling an electronically modulated power brake system with redundancy of brake pressure generation

Abstract

This invention relates to a method for controlling an electronically slip-adjustable power-assisted braking system (10) with redundant braking pressure generation. Depending on operation, a shift in the pressure-volume-characteristic curve toward higher pressures may occur in such a power-assisted braking system (10). If the actual change in the pressure-volume-characteristic curve deviates from the target change to an unacceptable degree, correction is required. For this purpose, the pressure medium volume must be discharged from the braking circuit (18a, 18b) into a reservoir (32) of the power-assisted braking system (10). This invention proposes a method by which pressure can be discharged into the reservoir (32) in a controlled manner. This method can be performed during the braking process without unwanted noise or unexpected deceleration changes. This method can be implemented technically and thus at a particularly low cost.

Description

Technical Field

[0001] The present invention relates to a method for controlling an electronically slip-adjustable power-assisted braking system with redundant braking pressure generation, as described in the preamble of claim 1.

[0002] For vehicle braking systems, a distinction should, in principle, be made between the well-known manual braking system and the more modern power braking system. In a manual braking system, the driver manually participates in establishing braking pressure, while in a power-assisted braking system, the braking request is converted into braking pressure by an electrically driven brake pressure generator.

[0003] With the development of highly automated or fully automated driving vehicles, power-assisted braking systems have redundant braking pressure generation. Therefore, even if a malfunction occurs at one of the pressure medium delivery devices, the vehicle can still be automatically braked to a stop.

[0004] For safety reasons, power-assisted braking systems may have a hydraulic backup level in addition to their brake pressure supply. Even in the event of a voltage supply and / or electronic equipment failure, this hydraulic backup level allows the driver to manually establish brake pressure in a conventional manner. Background Technology

[0005] Figure 1 illustrates a hydraulic design known from the prior art for an electronically slip-adjustable power-assisted braking system with redundant brake pressure generation on which the following invention is based.

[0006] The known power-assisted braking system (10) includes, in particular, a brake request detection device through which the driver can specify a braking request. This brake request detection device is a master brake cylinder (14) operable via a pedal (12), which exemplarily has two pressure chambers (16a, 16b). These two pressure chambers are connected to a brake circuit (18a, 18b) respectively. In the event of a power supply failure or electronic equipment failure in the power-assisted braking system (10), braking pressure can be manually established via the master brake cylinder (14).

[0007] In addition, one of these pressure chambers (16a) is connected to a pedal feel simulator (20), which provides tactile feedback to the driver when the pedal (12) is operated.

[0008] The power-assisted braking system (10) also includes a brake pressure generator (22) having a first pressure medium delivery device (24) for establishing a brake pressure associated with a specified braking request. Furthermore, there is a brake pressure modulator (26) for individually adjusting the brake pressure for each wheel, having a second pressure medium delivery device (28).

[0009] These pressure medium delivery devices (24, 28) are arranged together with the assigned directional valves in hydraulic units (30a, 30b). In the illustrated embodiment variant, these hydraulic units are physically separated from each other, but are in hydraulic contact with each other.

[0010] Therefore, the brake pressure generator (22) and the brake pressure modulator (26) can be supplied with hydraulic pressure medium through the common reservoir (32) of the power-assisted braking system (10) located at the master brake cylinder (14).

[0011] The brake pressure generator (22) and the brake pressure modulator (26) are connected in parallel to each other to the two brake circuits (18a, 18b). Multiple wheel brakes (34a-d) are in contact with these brake circuits (18a, 18b), respectively.

[0012] To control the pressure medium connection between the components of the power-assisted braking system (10), multiple directional valves are provided. To control the connection between the master brake cylinder (14) and the pedal feel simulator (20), an electrically operable simulator valve (36) is provided, which is electrically operated and occupies the open or closed position under normal operating conditions of the power-assisted braking system (10).

[0013] There are also circuit disconnect valves (38a, 38b) that control the connection between the pressure chambers (16a, 16b) of the master brake cylinder (14) and the assigned brake circuits (18a, 18b). These circuit disconnect valves (38a, 38b) are normally open and disconnect the connection in the electrically operated state, i.e., in the normal state of the power-assisted braking system (10).

[0014] The provided plunger outlet valve (40) connects the first pressure medium delivery device (24) to the reservoir (32) of the power-assisted braking system (10) in a controllable manner. The plunger outlet valve (40) is closed in the basic position and opens the corresponding pressure medium connection in the electrically operated state.

[0015] Further provided plunger release valves (42a, 42b) are used to control the pressure medium connection from the first pressure medium delivery device (24) to one of these braking circuits (18a, 18b). These plunger release valves are open in the electrically operated state.

[0016] In addition, for each braking circuit (18a, 18b), a so-called circuit pressure regulating valve (44a, 44b) is provided. As the name suggests, the pressure in the braking circuit (18a, 18b) can be regulated using these valves. The valves are normally open valves, which can be electrically operated to close.

[0017] High-pressure switching valves (46a, 46b) are arranged in parallel with these circuit pressure regulating valves (44a, 44b). These high-pressure switching valves are used to control the supply of pressure medium from the reservoir (32) to the second pressure medium delivery device (28). These high-pressure switching valves are normally closed.

[0018] In addition, to allow for individual setting of braking pressure for each wheel, each wheel brake (34a-d) is equipped with a controllable pressure boosting valve (48a-d) and a similar pressure reducing valve (50a-d). The pressure boosting valve (48a-d) is normally open, unlike the pressure reducing valve (50a-d), which is normally closed.

[0019] The valves mentioned are designed as either switching or regulating valves. Switching valves occupy one or both valve positions, while regulating valves can also be placed in an intermediate position to throttle the flow of the pressurized medium when needed. The adjustability of the directional control valves can be seen in the symbolic representation of the valves in Figure 1, indicated by the valve actuators equipped with diagonal arrows. The circuit pressure regulating valves (44a, 44b) and booster valves (48a-d) are designed as regulating valves, while the remaining valves are switching valves.

[0020] Finally, the power-assisted braking system (10) according to Figure 1 also includes electronic control devices (52a, 52b) assigned to the brake pressure generator (22) or brake pressure modulator (26). These electronic control devices operate the corresponding pressure medium delivery device and / or the valves described as needed, and for this purpose detect signals from sensors that detect the vehicle's driving state, current traffic conditions, and / or measurement parameters within the power-assisted braking system (10). In this regard, the path measurement sensor (64) of the power-assisted braking system (10) should be mentioned exemplarily, which detects the actuation path of the pedal (12), and pressure sensors (61a, 61b) should also be mentioned exemplarily, for detecting pressure generated by the master brake cylinder (14) or by the first pressure medium delivery device (24).

[0021] The two control devices (52a, 52b) communicate with each other electronically. These two control devices can also be combined to form an electronic control unit.

[0022] The first pressure medium delivery device (24) of the brake pressure generator (22) is a plunger piston (54) or squeezer, which is movably housed in and axially guided within a plunger cylinder (56). The plunger piston (54) can be moved within the plunger cylinder (56) in a pressurizing direction or in the opposite depressurizing direction by an electric drive (58). Alternatively, the plunger cylinder (56) can be moved relative to the plunger piston (54).

[0023] The movement of the extruder ends at the so-called external reversal point in the pressurization direction and at the so-called internal reversal point in the depressurization direction. As the plunger piston moves, the volume of the working chamber (60) surrounded by the plunger piston (54) and the plunger cylinder (56) changes. When the plunger piston (54) moves in the pressurization direction, the volume of the working chamber (60) decreases; conversely, when the plunger piston (54) moves in the depressurization direction, the volume of the working chamber increases.

[0024] The pressure-volume characteristic curve of the power-assisted braking system (10) illustrates the pressure variation in the connected braking circuits (18a, 18b) depending on the volume of the pressure medium extruded by the first pressure medium delivery device (24). This characteristic curve is largely defined by the design of the braking circuits (18a, 18b) and the dimensions of the plunger piston (54) or plunger cylinder (56) of the first pressure medium delivery device (24), and is digitally stored in the electronic control device (52).

[0025] Correspondingly, the second pressure medium delivery device (28) is a pump that continuously or cyclically delivers the pressure medium. Therefore, the pump can be, for example, a piston pump or a gear pump, which is also driven by an electrically controllable motor (62).

[0026] Under the operating conditions of the power-assisted braking system (10), for example, the following situation may occur: a braking request requires setting a braking pressure that is higher than the maximum pressure p(max) that can be provided by the braking pressure generator alone. This maximum pressure is defined by the power of the drive device (58) of the squeezer and the volume of the working chamber (60). Therefore, if the braking request is higher than the maximum pressure that can be set by the first pressure medium delivery device (24), the second pressure medium delivery device (28) of the braking pressure modulator (26) is used to enhance the existing braking pressure. For this purpose, in response to the corresponding request signal from the control device (52a) of the braking pressure generator (22) to the control device (52b) of the braking pressure modulator (26), the second pressure medium delivery device (28) is put into operation or driven.

[0027] However, the volume of pressure medium additionally extruded into the braking circuits (18a, 18b) by the second pressure medium delivery device (28) causes a shift in the described pressure-volume-characteristic curve toward higher pressures. Therefore, the actual change in the pressure-volume-characteristic curve deviates from the target change specified in the design.

[0028] Furthermore, in the event of a decrease in braking pressure at the end of the braking process, the additional volume of pressure medium squeezed into the braking circuits (18a, 18b) cannot be completely removed from the braking circuits (18a, 18b) by the first pressure medium delivery device (24) of the brake pressure generator (22) because the maximum capacity of the working chamber (60) is exhausted as the plunger piston (54) of the first pressure medium delivery device (24) reaches its inward reversal point. Therefore, residual pressure remains in the braking circuits (18a, 18b), which cannot be reduced in a controlled manner toward the reservoir (32) by the plunger outlet valve (40), as mentioned, because the plunger outlet valve (40) is designed as a switching valve and correspondingly allows only a gradual reduction in braking pressure. Alternatively, a discharge line can be provided that connects the working chamber (60) of the plunger cylinder (56) to the reservoir (32), and that the discharge line is opened by the plunger piston (54) once the plunger piston (54) has reached or passed its internal reversal point. However, this will then result in a sudden drop in braking pressure, which will cause an uncomfortable decrease in vehicle deceleration and unwanted operating noise. Summary of the Invention

[0029] Therefore, this invention proposes a method for controlling the reduction of residual pressure in the braking circuits (18a, 18b) using existing components. This avoids potential operational noise without requiring additional components for controlling the pressure medium or modifications to existing components. The proposed method is implemented technically and thus can be demonstrated at a particularly low cost.

[0030] Other advantages or advantageous extensions of the invention can be derived from the dependent claims or from the following description. Attached Figure Description

[0031] The present invention is illustrated with reference to the accompanying drawings and is described in detail in the following description.

[0032] The attached diagrams consist of a total of 4 images, among which...

[0033] Figure 1 shows the hydraulic circuit diagram of the power-assisted braking system (10) on which the present invention is based, which has been described at the beginning of the initial position;

[0034] Figure 2 shows different charts 2a-2d in which the process parameters of the power-assisted braking system (10) are recorded synchronously with each other during the process of the proposed method.

[0035] · Figure 3 The flowchart illustrates the preparatory steps for performing this method; and

[0036] Figure 4 is based on Figures 4a-4d The diagrams in the figure illustrate the alternative methods according to the method in Figure 2. Detailed Implementation

[0037] The power-assisted braking system (10) shown in Figure 1 forms the basis of the method according to the invention described below. The structure and function of this power-assisted braking system have been discussed in the references to the specification. To understand the invention, one should start from the following initial state of the components of the power-assisted braking system (10):

[0038] The power-assisted braking system (10) is in active mode, meaning the voltage supply is intact and there are no mechanical faults in these components. Therefore, the directional valves occupy the positions shown in Figure 1. Thus, the simulator valve (36), i.e., the valve in the pressure medium connection from the pressure chambers (16a, 16b) of the master brake cylinder (14) to the pedal feel simulator (20), is open. The circuit disconnect valves (38a, 38b) for controlling the pressure medium connection between the pressure medium chambers (18a, 18b) of the master brake cylinder (14) and the brake circuit (18a, 18b) are in the blocked position. Therefore, the driver is no longer subject to braking pressure generation in the wheel brakes (34a-d) and only specifies the braking request by manipulating the pedal (12). The braking request is determined by means of a path measurement sensor (64), which detects the path traversed by the pedal (12), converts the path into an electronic signal, and transmits the electronic signal to the electronic control device (52a).

[0039] The plunger outlet valve (40) is closed, thereby blocking the pressure medium connection between the first pressure medium delivery device (24) and the reservoir (32), while the plunger separation valves (42a, 42b) are opened and the circuit pressure regulating valves (44a, 44b) are closed. Braking pressure is applied to at least one of these wheel brakes (34a-34d).

[0040] In order to establish the braking pressure corresponding to the specified braking request, the plunger piston (54) of the brake pressure generator (22) has been actuated in the pressure-increasing direction by its drive device (58), and is therefore at its external reversal point in the plunger cylinder (56). Thus, the working chamber (60) has a minimum volume.

[0041] It should also be assumed that, in order to increase the braking pressure, the second braking pressure delivery device (28) of the braking pressure modulator (26) draws in an additional volume from the reservoir (32) and delivers it to at least one braking circuit (18a, 18b). This is achieved through an existing pressure medium connection that runs from the reservoir (32) via a check valve (66) located downstream of the reservoir and via electrically operated and thereby opened high-pressure switching valves (46a, 46b) to the suction side of the second pressure medium delivery device (28).

[0042] The pressure boosting valve (48a-d) assigned to the wheel brakes (34a-d) is opened, and the pressure reducing valve (50a-d) is closed.

[0043] For example, additional pressure medium can be delivered via a second pressure medium delivery device (28) because during the braking process, it is necessary to adapt the braking pressure in the wheel brakes (32a-d) to the slip condition at one or more wheels of the vehicle, and / or because the brake pressure generator (22) has squeezed out the maximum possible volume of pressure medium, making it impossible to set the braking pressure corresponding to the braking request. That is, as stated above, this situation itself has resulted in the pressure-volume characteristic curve of the power-assisted braking system (10) being shifted towards higher pressures. This characteristic curve shift can be canceled in a controlled manner using the method described below.

[0044] Therefore, the method for controlling a power-assisted braking system (10) with redundant pressure supply, on which the present invention is based, is illustrated graphically with reference to FIG2. For this purpose, FIG2 includes a total of four overlapping graphs 2a-2d, which respectively represent the changes in parameters related to the method in time.

[0045] Therefore, the topmost graph 2a of Figure 2 represents the pressure change process. This graph shows a total of two characteristic curves. The first pressure-characteristic curve (68a) illustrates the change of pressure over time in the working chamber (60) of the first pressure medium delivery device (24), i.e., the brake pressure generator (22), while the second pressure-characteristic curve (68b) illustrates the change of brake pressure in one of the wheel brakes (34a-d) and thereby symbolically clarifies the specified braking request.

[0046] In the second graph 2b above, the change in volume of the pressure medium extruded from the corresponding pressure medium delivery devices (24, 28) over time is plotted. Here, the first volume-characteristic curve (70a) illustrates the volume extruded from the first pressure medium delivery device (24), i.e., the brake pressure generator (22), and the second volume-characteristic curve (70b) reflects the volume of the pressure medium extruded from the second pressure medium delivery device (28), i.e., the brake pressure modulator (26). In addition, graph 2b also illustrates the electrical control of the plunger outlet valve (40) in the pressure medium connection between the first pressure medium delivery device (24) and the reservoir (32) with a signal characteristic curve (72). Since the plunger outlet valve is a normally closed switching valve, the signal characteristic curve (72) indicates when the plunger outlet valve (40) is electrically controlled and thereby opened.

[0047] Figure 2c The graph in the figure illustrates the change of pressure difference over time at the circuit pressure regulating valves (44a, 44b) attached to the braking circuit (18a, 18b) using pressure difference-characteristic curves (74).

[0048] This pressure difference corresponds to the pressure difference between the pressure at the pressure medium inlet and the pressure medium outlet of the pressure regulating valves (44a, 44b) in the circuit, wherein the pressure medium inlet is directed toward the wheel brakes (34a-d) due to the flow direction of the pressure medium, and the pressure medium outlet is directed toward the first pressure medium delivery device (24). If the displayed pressure difference is high, the pressure regulating valves (44a, 44b) have a relatively small throttling cross-section or even no throttling cross-section, and if the pressure difference is zero, the pressure regulating valves (44a, 44b) are in the open position.

[0049] Finally, based on Figure 2d In the bottom chart, the rotational speed of the motor (62) of the second pressure medium conveying device (28) is also plotted over time using the speed-characteristic curve (76).

[0050] The time axis in Figure 2 is divided into a total of 6 time periods, which are numbered t1 to t6.

[0051] If it can be based on Figure 2a The diagram shows that, in the first time phase t1, pressure is built up in at least one wheel brake (34a-d) of the braking circuit (18a, 18b). This pressure buildup occurs continuously and uniformly, i.e., along a straight ramp that rises from the lower left to the upper right.

[0052] Therefore, according to Figure 2bThe diagram shows that the pressure medium volume is delivered from the first pressure medium delivery device (24), i.e., the brake pressure generator (22), to the wheel brakes (34a-d). The circuit pressure regulating valves (44a, 44b) are not electrically operated and are thereby open, so that according to Figure 2c There is no pressure differential at this reversing valve.

[0053] During the first time phase t1, the second pressure medium delivery device (28) of the braking pressure modulator (26) is not required. The drive device (58) of the second pressure medium delivery device is not electrically controlled, and the rotational speed of the drive device is according to... Figure 2d , is zero.

[0054] During the subsequent second time phase t2, the braking pressure already present in the wheel brakes (34a-d) increases. The required pressure medium can no longer be supplied by the first pressure medium delivery device (24) of the brake pressure generator (22) because the squeezer of the brake pressure generator has reached its outer reversal point or is near it. Therefore, the electronic control device (52a) of the brake pressure generator (22) sends a corresponding request signal to the electronic control device (52b) of the brake pressure modulator (26). This electronic control device then operates the motor (62) of the second pressure medium delivery device (28). Figure 2d The motor (62) rotates at a constant speed, and correspondingly drives the second pressure medium delivery device (28). The second pressure medium delivery device delivers an increasing volume of pressure medium to the associated wheel brakes (34a-d) (Figure 2b), and the pressure in the wheel brakes (34a-d) continuously rises to a maximum value (Figure 2a).

[0055] Pressure regulation in the re-braking circuit (18a, 18b) or in the connected wheel brakes (34a-d) is achieved by electrically controlling the circuit pressure regulating valves (44a, 44b). For this purpose, the circuit pressure regulating valves continuously reduce the throttling cross-section until zero, thereby, as from... Figure 2c As can be seen, the pressure drop between its pressure medium inlet and its pressure medium outlet increases uniformly until it reaches its maximum value. During this second time phase t2, the pressure in the working chamber (60) of the first pressure medium delivery device (24) drops to the level of atmospheric pressure (Fig. 2a). This is because the second pressure medium delivery device (28), i.e., the brake pressure modulator (26), draws in the pressure medium required for pressure establishment from the reservoir (32), and the corresponding draw-in path is connected to the first pressure medium delivery device (24) via the open plunger separation valves (42a, 42b). Atmospheric pressure exists in the reservoir (32).

[0056] Because the pressure medium is delivered to the wheel brakes (34a-d) via the second pressure medium delivery device (28), the pressure-volume characteristic curve of the power-assisted braking system (10) no longer matches the pressure-volume characteristic curve specified in the design of the first pressure medium delivery device (24). As mentioned above, the latter has been shifted toward higher pressure. This state can be identified by the electronic control devices (52a, 52b) of the power-assisted braking system (10) within the framework of periodically performed characteristic curve checks. For this purpose, the actual value of the braking pressure that can be detected by measurement technology and the actual value of the delivered pressure medium volume calculated based on the operating parameters of the brake pressure generator (22) are compared with the known target value of the pressure-volume characteristic curve specified in the design of the first pressure medium delivery device (24). If the identified deviation is greater than the specified limit value, the deviation is intolerable and must be corrected. A little more explanation is given here.

[0057] During time phase t3.1, when the pressure in the wheel brakes (34a-d) remains constant and none of the pressure medium delivery devices (24, 28) are delivering, the electrical control of the circuit pressure regulating valves (44a, 44b) is gradually withdrawn. This causes the circuit pressure regulating valves (44a, 44b) to open and increase the throttling cross-section. Consequently, the pressure differential at the circuit pressure regulating valves (44a, 44b) decreases, and pressure is re-established in the chamber (60) of the first pressure medium delivery device (24) via the pressure medium path to the brake pressure generator (22) controlled by the circuit pressure regulating valves (44a, 44b). The throttling effect of the circuit pressure regulating valves (44a, 44b) is adjusted during time phase t3.2, resulting in a pressure level in the chamber (60) that, according to the diagram, corresponds to the maximum pressure p(max) that the first pressure medium delivery device (24) can fully establish in the brake circuit (18a, 18b) by design. Figure 2a In the diagram, P(max) is plotted as a horizontal line. Instead of p(max), any arbitrarily lower pressure can be set as p(max).

[0058] Here, as based on Figure 2c As can be seen from the chart, at the circuit pressure regulating valves (44a, 44b), due to their relatively large throttling cross-section, there is only a correspondingly low pressure differential.

[0059] The pressure in the wheel brakes (34a-d) does not change during time phases t3.1 and t3.2 because the pressure medium is neither supplied to the wheel brakes (34a-d) nor flows out of the wheel brakes (34a-d) to a significant extent.

[0060] As time phase t4 now ends, the braking request is cancelled, and correspondingly, the braking pressure in the wheel brakes (34a-d) decreases. Here, the braking pressure is gradually released, such that the braking pressure change follows a straight slope from the upper left to the lower right. Figure 2a ).

[0061] During this pressure reduction phase, referred to for distinction as the pressure reduction phase controlled by the squeezer, the circuit pressure regulating valves (44a, 44b) are controlled to reach their open position, i.e., electrical control of the circuit pressure regulating valves ceases. Therefore, the pressure medium from the wheel brakes (34a-d) flows into the working chamber (60) of the first pressure medium delivery device (24). Simultaneously, the drive device (58) of the first pressure medium delivery device (24) is electrically controlled, thereby maneuvering the squeezer in the pressure reduction direction, i.e., towards its internal reversal point.

[0062] In the subsequent time phase t5, the pressure reduction phase controlled by the extruder continues by manipulating the drive device (58) of the first pressure medium delivery device (24) in the direction of the inward reversal point. The pressure reduction follows the aforementioned ramp function in a unchanged manner and can be based on... Figure 2a As can be seen from the chart.

[0063] Once the plunger piston (54) of the first pressure medium delivery device (24) is near its internal reversal point, the maximum capacity of the working chamber (60) is exhausted. Figure 2a This is illustrated: the volume of the pressure medium initially extruded into the braking circuit (18a, 18b) by the first pressure medium delivery device (24) now reaches zero again. With the cancellation of the electrical control of the drive device (58) of the first pressure medium delivery device (24) via the electronic control device (52a), the pressure reduction phase controlled by the extruder ends. Simultaneously, a corresponding signal is sent to the electronic control device (52b) of the braking pressure modulator (26).

[0064] At the start of the so-called valve-controlled reduction phase, the circuit pressure regulating valves (44a, 44b) are electrically reactivated based on the input electronic information. Through corresponding control signals, the circuit pressure regulating valves (44a, 44b) are brought to a throttling position, where the set throttling cross-section corresponds to the braking pressure allocated to the position of the plunger piston (54) in the plunger cylinder (56). Figure 2bSimultaneously, the plunger outlet valve (40) is operated, thereby moving it from its blocked position to its open position. Since atmospheric pressure exists in the reservoir (32) of the power-assisted braking system (10), this causes the pressure at the brake pressure generator (22) and consequently at the pressure medium outlet of the circuit pressure regulating valves (44a, 44b) to decrease to atmospheric pressure. The resulting pressure differential indicates the current braking request.

[0065] In principle, instead of controlling the pressure reduction by manipulating the plunger outlet valve (40), the pressure reduction could also be controlled by the movement of the plunger piston (54). However, this requires a discharge line (not shown) that runs from the working chamber (60) to the reservoir (32), and that the discharge line leads back to the working chamber (60) in the region of the inner reversal point of the plunger piston (54). The retracted plunger piston (54) passes through an opening, and the discharge line is only fully released when the plunger piston reaches the inner reversal point.

[0066] Now, this pressure differential is gradually reduced to zero or to the level required by the driver's current braking request through linear changes in the pressure regulating valves (44a, 44b) of this circuit, electrically controlled by the electronic control device (52b). See [link to relevant documentation]. Figure 2c Therefore, the pressure regulating valves (44a, 44b) in this circuit gradually release their maximum throttling section again until the residual pressure remaining in the braking circuit (18a, 18b) is adjusted according to... Figure 2a The graph has been completely eliminated. This reduction in braking pressure also occurs continuously or constantly, allowing the previous changes in braking pressure to continue in a transitional manner. Therefore, there is no noise or perceptible deceleration change for vehicle occupants.

[0067] Therefore, through the controlled opening of the circuit pressure regulating valves (44a, 44b) and the simultaneous opening of the plunger outlet valve (40), the pressure medium is discharged in a controlled manner from the wheel brakes (34a-d) via the first pressure medium delivery device (24) into the reservoir (32) of the power-assisted braking system (10) until atmospheric pressure is finally reached in the wheel brakes (34a-d) and the position of the plunger piston (54) of the first pressure medium delivery device (24) in the plunger cylinder (56) is related to it. Now, the pressure-volume-characteristic curve of the power-assisted braking system (10) is once again consistent with the pressure-volume-characteristic curve of the first pressure medium delivery device (24).

[0068] Thus, the proposed method ends, the brake pressure modulator (26) returns to its passive state, and the subsequent re-establishment of brake pressure may again be conventionally controlled by the adapted electrical control of the drive device (58) of the first pressure medium delivery device (24) or the brake pressure generator (22).

[0069] The described method should be performed at least whenever the shift described in the pressure-volume-characteristic curve occurs or reaches an unacceptable level. This check should be performed periodically in power-assisted braking systems, and is conducted in accordance with... Figure 3 As described, it shall proceed as follows:

[0070] First, in step (80), the deviation between the pressure-volume-target characteristic curve specified in the design and the pressure-volume-actual characteristic curve of the power-assisted braking system is determined. Various methods can be used for this purpose.

[0071] In the first variant, the actual value of the braking pressure is measured in the braking circuit (18b) by means of a pressure sensor (61), and this actual value is compared with a target braking pressure. This target braking pressure can be derived from the known pressure-volume characteristic curve of the power-assisted braking system (10) based on the braking request and thereby from the path signal of the path measurement sensing device (64) coupled to the pedal (12). If the comparison results in a deviation, the volume of the pressure medium, which is additionally extruded into the braking circuit (18a, 18b) by the second pressure medium delivery device (28), is determined based on the known pressure-volume characteristic curve according to the identified deviation.

[0072] Alternatively, the volume of pressure medium additionally extruded by the second pressure medium conveying device (28) can also be determined by multiplying the operating time of the motor (62) used to drive the second pressure medium conveying device (28) by the rotational speed of the motor (62) and the known value of the volume of pressure medium extruded per revolution of the motor (62). Information about when the second pressure medium conveying device (28) is operated and for how long can be derived from a request signal sent by the control device (52a) of the brake pressure generator (22) to the control device (52b) of the brake pressure modulator (26).

[0073] If the volume of pressure medium additionally extruded by the second pressure medium delivery device (28) to increase pressure has been determined accordingly, this value is compared with a predefined limit value (88) in the next second step (82). Below this limit value, the described method can be omitted because the effect of the subsequently additionally extruded pressure medium on the pressure-volume-characteristic curve is tolerable.

[0074] However, if the determined value corresponds to the limit value (88) or is even higher than the limit value (88), the above control method or an alternative control method described below is executed, wherein the execution is carried out within the framework of the ongoing braking process, more specifically, when the braking request is withdrawn during the braking process. Figure 3 The execution of the method is explained in accordance with the symbols marked with reference numerals (86).

[0075] in accordance with Figures 4a-4d The four charts in total illustrate the proposed alternative method for controlling the power-assisted braking system (10) with redundant braking pressure generation. Compared to the charts in Figure 2, these charts are recorded synchronously with each other, divided into multiple time periods and representing the same changing process parameters, plotted over time.

[0076] In the first time phase t1, braking pressure is also established here by manipulating the first pressure medium delivery device (24). Here, the plunger outlet valve (40) is closed, and the circuit pressure regulating valves (44a, 44b) are opened, so that there is no pressure difference across the circuit pressure regulating valves. Figure 4c The motor (62) of the second pressure medium conveying device (28) is not electrically controlled and therefore does not rotate.

[0077] During the second time phase t2, the existing braking pressure increases. The pressure medium required for this is supplied by a second pressure medium delivery device (28), such as from [the source / method / etc.]. Figure 4b The volume-property curve in the chart and according to Figure 4d The speed-characteristic curve of the motor (62) of the second pressure medium delivery device (28) is known. At the start of the second time phase t2, the plunger outlet valve (40) is electrically operated, and thus opens the pressure medium connection between the first pressure medium delivery device (24) and the reservoir (32). Then, the pressure in the working chamber (60) of the first pressure medium delivery device (24) and thereby at the pressure medium outlet of the circuit pressure regulating valves (44a, 44b) drops to atmospheric pressure. The pressure differential at these circuit pressure regulating valves (44a, 44b) is set by the adapted electrical operation of the circuit pressure regulating valves (44a, 44b). The value of this pressure differential depends on the braking pressure in the wheel brakes (34a-d) or on the pressure at the pressure medium inlet attached to the reversing valve.

[0078] An alternative control to the plunger outlet valve (40), which is not apparent from Figure 4, would be that the plunger outlet valve (40) is only opened when a pressure reduction is actually requested or executed via the loop pressure regulating valves (44a, 44b). In contrast, the plunger outlet valve (40) is closed during pressure build-up, and therefore flow through the plunger outlet valve (40) is only in one direction, i.e., toward the reservoir (32). The advantage of this alternative control is that the plunger outlet valve (40) can then be implemented more advantageously in the design, for example, because a filter used to remove contaminants from the pressurized medium flowing from the reservoir (32) into the plunger outlet valve (40) can be omitted.

[0079] During time phase t3, the braking pressure continuously increases until it exceeds the maximum pressure p(max), which is set entirely within the braking circuit (18a, 18b) by the first pressure medium delivery device (24) due to its design. Furthermore, the required volume of pressure medium for this purpose is provided by a second pressure medium delivery device (28), which is driven for this purpose (see [link to relevant documentation]). Figure 4b and 4d As the braking pressure increases, the pressure difference at the circuit pressure regulating valves (44a, 44b) also increases. Figure 4c ).

[0080] As the maximum pressure in the braking circuit (18a, 18b) is reached, the pressure medium delivery caused by the second pressure medium delivery device (28) ends (according to...). Figure 4d (Motor speed is zero); the plunger outlet valve (40) remains open.

[0081] The braking variation during time phase t3 is corrected by electrical control of the circuit pressure regulating valves (44a, 44b). Here, in conjunction with the plunger outlet valve (40) which is open as before, pressure medium is discharged from the wheel brakes (34a-d) via the first pressure medium delivery device (24) to the reservoir (32) of the power-assisted braking system (10) when the pressure decreases, or when the pressure builds up, pressure medium is drawn from the reservoir (32) and expelled from the wheel brakes (34a-d) via the open high-pressure switching valves (46a, 46b) by the second pressure medium delivery device (28). During this pressure build-up phase, the circuit pressure regulating valves (44a, 44b) are closed in an understandable manner.

[0082] Starting from time phase t4, braking pressure is reduced because the specified braking request is cancelled.

[0083] Here, as always, the pressure medium is first discharged from one or more wheel brakes (34a-d) to the reservoir (32) via an open or partially open circuit pressure regulating valve (44a, 44b), the working chamber (60) of the first pressure medium delivery device (24), and the similarly open plunger outlet valve (40). Regulation of the brake pressure reduction is achieved through continuous adaptation of the corresponding electrical controls of the circuit pressure regulating valves (44a, 44b), and is correspondingly referred to as the valve-controlled pressure reduction phase.

[0084] If, in this manner and method, the braking pressure of the wheel brakes (34a-d) drops to such a position that, due to the extension of the extruder of the first pressure medium delivery device (24) in the plunger cylinder (56), the volume of the working chamber (60) is sufficient to completely contain the volume of the pressure medium in the brake circuit (18a, 18b) to further reduce the braking pressure to zero, then at the end of time phase t4, the electrical control of the plunger outlet valve (40) is revoked.

[0085] In doing so, the plunger outlet valve (40) returns to its closed position, and the pressure medium connection between the first pressure medium delivery device (24) and the reservoir (32) is interrupted. Simultaneously, the electrical control of the circuit pressure regulating valves (44a, 44b) is canceled. These circuit pressure regulating valves return to their open position, and correspondingly, the pressure differential across them no longer decreases. Figure 4c With the opening of the circuit pressure regulating valves (44a, 44b), pressure is re-established in the working chamber (60) of the first pressure medium delivery device (24). The resulting pressure level corresponds to the pressure level assigned to the position of the plunger piston (54) in the plunger cylinder (56).

[0086] The further reduction in braking pressure is referred to as the pump-controlled pressure reduction phase, which is achieved at time t5 by manipulating the drive device (58) of the first pressure medium delivery device (24) or the drive plunger piston (54) in the direction of pressure reduction. If the squeezer has reached its internal reversal point, the braking pressure reaches zero, and the pressure-volume characteristic curve of the power-assisted braking system (10) again matches the pressure-volume characteristic curve of the first pressure medium delivery device (24).

[0087] Finally, it should be noted that the described method can be implemented even if the extruder of the first pressure medium conveying device (24) should not be located at the external reversal point at the start of the pump-controlled pressure reduction phase.

[0088] In this case, the braking pressure is reduced in a valve-controlled manner to a pressure level corresponding to the position of the plunger piston (54) in the plunger cylinder (56), according to the known pressure-volume characteristic curve of the power-assisted braking system (10). Then, the residual pressure still present in the braking circuit (18a, 18b) can be reduced to atmospheric pressure by further retracting the squeezer of the brake pressure generator (22) to its internal reversal point.

[0089] Furthermore, it should be clarified that the braking processes shown in Figures 2 and 4 involve braking pressures corresponding to braking requests that are higher than the maximum pressure p(max) that can be generated in the braking circuits (18a, 18b) by the first pressure medium delivery device (24). However, the latter is not a prerequisite for performing the described method, as braking processes may also occur in the power-assisted braking system (10) where the pressure medium has been delivered to the braking circuits (18a, 18b) by the second pressure medium delivery device (28), but the maximum pressure that can be provided by the first pressure medium delivery device (24) is not reached.

[0090] Therefore, the triggering factor for performing the method on which the present invention is based is not the braking pressure in the braking circuit (18a, 18b), but more precisely the volume of the pressure medium that has been delivered to the braking circuit (18a, 18b) by the second pressure medium delivery device (28) to generate the braking pressure.

[0091] If the volume has a value below the limit that can be specified in the electronic control devices (52a, 52b), the execution of this method can be omitted. In this case, the deviation between the pressure-volume characteristic curve of the power-assisted braking system (10) and the pressure-volume characteristic curve of the first pressure medium delivery device (24) is still tolerable.

[0092] Of course, other modifications and / or advantageous extensions to the described embodiments of the invention are conceivable without departing from the basic idea of ​​the invention as claimed in claim 1.

[0093] This basic idea is particularly evident in the fact that, as described in the specification, the reduction of braking pressure in the braking circuit (18a, 18b) of the power-assisted braking system (10) with redundant pressure supply includes a valve-controlled pressure reduction phase in which the pressure medium is discharged to the reservoir (32) in a controlled manner by electrical control of the circuit pressure regulating valves (44a, 44b). Here, the pressure medium connection to the reservoir (32) can be guided via a line containing a plunger outlet valve (40) or via a discharge line whose opening to the working chamber (60) is controlled by a plunger piston (54).

Claims

1. A method for controlling an electronically slip-adjustable power-assisted braking system (10) with redundant braking pressure generation, The power-assisted braking system (10) is equipped with: Braking request detection device (12) is used to specify a braking request; A brake pressure generator (22) is used to supply pressure medium to wheel brakes (34a-d) in at least one connected brake circuit (18a, 18b) at a brake pressure corresponding to the brake request. The brake pressure generator (22) is equipped with a first pressure medium delivery device (24) that is controllably drivable. The first pressure medium delivery device includes a squeezer (54) that can be driven in the pressurization direction within a cylinder (56) to build up brake pressure until an outward reversal point and to reduce brake pressure in the direction opposite to the brake pressure build-up direction until an inward reversal point. The squeezer, together with the cylinder (56), defines a chamber (60) that is variable in volume. Brake pressure modulator (26) is used to individually set the braking pressure in each of the wheel brakes (34a-d) in the brake circuit (18a, 18b). The brake pressure modulator (26) is connected in parallel with the brake pressure generator (22) to the brake circuit (18a, 18b), and It has a second pressure medium delivery device (28) that can be driven in a controllable manner; Storage container (32) for pressure medium; An electrically operable plunger outlet valve (40) is used to control the first pressure medium connection from the first pressure medium delivery device (24) to the reservoir (32) of the power-assisted braking system (10); Electrically operable pressure regulating valves (44a, 44b) are used to regulate the braking pressure in the braking circuit (18a, 18b); and At least one electronic control device (52a, 52b) is used to electrically operate the corresponding assigned pressure medium delivery device and directional valve as needed. Its features are, Determine how much volume of pressure medium will be delivered to the braking circuit (18a, 18b) by the second pressure medium delivery device (28) in order to establish braking pressure; The determined volume of the pressure medium is compared with a limit value (88), which indicates the maximum volume of the pressure medium to be extruded; and The braking pressure reduction includes a valve-controlled pressure reduction phase during which a pressure medium connection is provided to discharge the pressure medium supplied by the second pressure medium delivery device (28) from the braking circuit (18a, 18b) into the reservoir (32) of the power-assisted braking system (10). Where the volume of the determined pressure medium is equal to or greater than the limit value (88). The volume of the pressure medium discharged into the reservoir (32) is controlled by adapting the electrical operation of the pressure regulating valves (44a, 44b). If the braking pressure in the braking circuit (18a, 18b) is higher than the maximum pressure that can be applied to the braking circuit (18a, 18b) by the first pressure medium delivery device (24), then the method is performed, and A third pressure reduction phase is performed, in which a controllable pressure medium connection is provided between the working chamber (60) of the first pressure medium delivery device (24) and the braking circuit (18a, 18b) by electrically controlling the pressure regulating valves (44a, 44b), and the pressure regulating valves (44a, 44b) are controlled during the third pressure reduction phase so that the pressure in the working chamber (60) is reduced to the maximum pressure that can be applied to the braking circuit (18a, 18b) by the first pressure medium delivery device (24).

2. The method according to claim 1, Its features are, By simultaneously electrically controlling the plunger outlet valve (40) and the pressure regulating valves (44a, 44b), or The positioning of the plunger piston (54) at the internal reversal point and the simultaneous electrical control of the pressure regulating valves (44a, 44b) A pressure medium connection is provided between the braking circuit (18a, 18b) and the reservoir (32).

3. The method according to claim 1, Its features are, The braking pressure reduction includes another, pressure reduction phase controlled by the squeezer, in which the pressure medium connection to the reservoir (32) is closed, and in which the squeezer (54) of the first pressure medium delivery device (24) is moved in the pressure reduction direction by electrical control of the drive device (58).

4. The method according to any one of claims 1 to 3, Its features are, If the braking pressure in the braking circuit (18a, 18b) is related to the braking pressure generated in the braking circuit (18a, 18b) by the extruder (54) of the first pressure medium delivery device (24) in the current position of the extruder (54) in the cylinder (56) taking into account the pressure-volume-characteristic curve on which the power-assisted braking system (10) is based, then the pressure reduction phase ends.

5. The method according to any one of claims 1 to 3, Its features are, The reduction in braking pressure is controlled to result in a continuously decreasing process.

6. The method according to any one of claims 1 to 3, Its features are, If the squeezer (54) of the first pressure medium delivery device (24) reaches its internal reversal point, the braking pressure reduction ends.

7. The method according to any one of claims 1 to 3, Its features are, The volume of the pressure medium extruded by the second pressure medium delivery device (28) is determined by comparing the known pressure-volume-characteristic curve of the power-assisted braking system (10) with the pressure in the braking circuit (18a, 18b) and the position of the extruder (54) of the first pressure medium delivery device (24) in the cylinder (56) where the pressure is assigned.

8. The method according to any one of claims 1 to 3, Its features are, The volume of the pressure medium extruded by the second pressure medium conveying device (28) is determined by multiplying the operating time of the motor (62) of the second pressure medium conveying device (28) by the rotational speed of the motor (62) and the known volume of the pressure medium extruded by the second pressure medium conveying device (28) per revolution of the motor (62).

9. The method according to any one of claims 1 to 3, Its features are, The third pressure reduction phase is performed when the braking pressure reduction begins.

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