Method for adjusting a pressure position in a brake system

Abstract

The invention relates to a method for regulating a pressure setting in a brake system (1) having a pressure application device (3) and a relief valve (7), comprising the following steps: receiving (10) a pressure demand (30) and determining (11) a pressure demand gradient (32) from the pressure demand (30), determining (12) a volume flow requirement (33) from the pressure demand gradient (32), generating a hydraulic pressure (13) by means of the pressure application device (3), determining an actual volume flow (14) of the pressure application device (3), adjusting the relief valve (7) on the basis of the pressure demand (30) and on the basis of a difference between the actual volume flow (14) and the volume flow requirement (33, 34, 35), wherein a special mode is activated (36) when the pressure demand gradient (32) exceeds a gradient limit value, a minimum value (22) of the volume flow requirement (33, 34, 35) is set in the special mode on the basis of a last maximum value (21) of the volume flow requirement (33, 34, 35), and the special mode is deactivated (37) when a difference between the pressure demand (30) and a system pressure (31) is below a first limit value (39).

Description

Technical Field

[0001] The present invention relates to a method for adjusting pressure settings in a braking system having a pressure application device and an overflow valve, wherein a pressure demand is received, particularly a control unit for pressure setting and for adjusting the overflow valve, and a pressure demand gradient is determined based on the pressure demand and used for adjustment. Background Technology

[0002] In known cases where pressure settings in a braking system are adjusted to achieve comfort and continuous, short-duration pressure build-up, pump actuation, independent of the driver's pressure build-up, is based solely on the pressure demand gradient. This adjustment is advantageous under slow pressure demands but problematic under rapid, high pressure demands. In such cases, the pressure demand gradient has a very high value, and if the pressure demand remains constant, it will very quickly drop back to zero. One problem here is that the calculated volumetric flow rate requirement is reduced to an unacceptable level, even though the target pressure has not yet been reached. Another problem is the calculation of the overflow volume via the relief valve, which is determined by the volumetric flow rate of the pressure application device and the volumetric flow rate requirement. When the overflow volume does not physically exist but is incorrectly used in the calculation, an excessively high correction value is calculated for the electric valve current, thus significantly degrading the actuation accuracy of the relief valve. Summary of the Invention

[0003] Therefore, the object of the present invention is to adjust the pressure setting in the braking system, which ensures that the pressure requirement is met quickly and accurately even under rapid high pressure demand.

[0004] This objective is achieved by the method described below, wherein a control unit for pressure setting, and particularly for regulating the relief valve, receives, for example, a pressure demand from an ESC control unit and determines a pressure demand gradient based on the pressure demand. For this purpose, the pressure demand can be differentiated with respect to time, and optionally filtering and smoothing measures can be performed. A volumetric flow rate requirement is determined based on the pressure demand gradient. For this purpose, corresponding characteristic curves or transformation variables, such as multiplication factors, can be stored in the control unit. A pressure application device is actuated to establish hydraulic pressure, thereby generating a volumetric flow rate. The pressure application device may include a hydraulic pump that is activated to generate a volumetric flow rate of hydraulic fluid for the braking system. Since the pressure application device is typically not adjustable with very high precision, the actual volumetric flow rate it provides may not perfectly match the demand; therefore, the actual volumetric flow rate of the pressure application device must be determined. A volumetric flow rate greater than the calculated volumetric flow rate requirement may also be required. Additionally, the electric valve current of the relief valve is calculated and provided to it. The electric valve current depends primarily on the differential pressure required by the relief valve, and therefore on the pressure demand. Furthermore, the valve flow rate must be adapted to the overflow volume passing through the relief valve because the Venturi effect causes a force to act on the valve tappet in the relief valve and move the tappet. Therefore, the relief valve is adjusted based on the pressure demand and the difference between the actual volumetric flow rate and the required volumetric flow rate.

[0005] To respond specifically to rapid, high-pressure demands, the pressure demand gradient is monitored to determine if it exceeds a gradient limit. In this case, a special mode is activated, which predefines a minimum volumetric flow rate requirement that cannot be lowered. That is, if the calculated volumetric flow rate requirement is less than the minimum, that requirement is set to the minimum. The minimum is calculated based on the last maximum volumetric flow rate requirement. For this purpose, if the gradient limit is exceeded, the largest possible volumetric flow rate requirement can be stored as the maximum value.

[0006] When the difference between the pressure demand and the system pressure is lower than the first limit value, that is, when the hydraulic pressure in the system is still less than the predefined difference to reach the pressure demand, the special mode is deactivated again.

[0007] In a preferred embodiment of the invention, the system pressure is determined based on calculations performed using a vehicle-specific model. This eliminates the need for additional pressure sensors, thus saving costs.

[0008] Vehicle-specific model calculations can be based on real measurement data from system pressure and the volume consumption of the braking system.

[0009] In another preferred embodiment of the invention, the pressure application device is actuated based on a volumetric flow rate requirement. The pressure application device may be, for example, a hydraulic pump whose flow rate is adjusted according to or greater than the volumetric flow rate requirement. Furthermore, a predefined operating time can be set for the pump.

[0010] In another preferred embodiment of the invention, the actual volumetric flow rate is determined based on the rotational speed of the pressure application device. This is a particularly simple way to determine the actual volumetric flow rate because the pump's rotational speed can be easily determined based on an assessment of the corresponding signal or supply voltage.

[0011] In another preferred embodiment of the invention, in a particular mode, the minimum volumetric flow rate requirement is set to a value between 100% and 60% of the final maximum volumetric flow rate requirement, preferably between 90% and 70%. A consistently high volumetric flow rate requirement means reaching the received pressure demand particularly quickly. However, it will not remain at the maximum value to produce overshoot, i.e., excessively high system pressure, which could lead to excessive braking pressure and thus over-braking.

[0012] In another preferred embodiment of the invention, the pressure demand gradient is monitored for a maximum value, and when a maximum value is detected, the current volumetric flow rate requirement is used as the final maximum value of the volumetric flow rate requirement. For this purpose, for example, the values ​​of the pressure demand gradient greater than the limit value can be stored as possible maximum values, and each new value of the pressure demand gradient can be checked to see if it is larger. The associated volumetric flow rate requirement is calculated based on the maximum value. Features or transformation variables (e.g., multiplication factors) stored in the control unit can be used again for this purpose. Alternatively, the pressure demand can be differentiated twice to find the maximum value of the pressure demand gradient where the second derivative is zero.

[0013] In another preferred embodiment of the invention, when the special mode is deactivated, a transition mode is switched to, in which the minimum required volumetric flow rate is reduced, particularly linearly. The minimum is preferably reduced to 0. This avoids a sudden transition and thus avoids potential overshoot where the system pressure exceeds the pressure requirement, as the system pressure reaches the pressure requirement slowly through the linear reduction of the volumetric flow rate requirement. For this purpose, the minimum can be proportionally adapted to the difference between the pressure requirement and the system pressure.

[0014] In another preferred embodiment of the invention, the first limit value is between 25 bar and 2 bar, preferably between 12 bar and 4 bar, and particularly preferably between 6 bar and 10 bar. This limit value allows the system pressure to be adjusted to the pressure requirement particularly quickly and accurately.

[0015] In another preferred embodiment of the invention, the gradient limit value is greater than 100 bar / second, preferably greater than 150 bar / second, and particularly preferably greater than 200 bar / second.

[0016] The present invention also employs a hydraulic braking system having at least one hydraulic wheel brake, a pressure application device, and a relief valve. The pressure application device is connected to the wheel brake and is designed to transmit a volumetric flow rate toward the at least one wheel brake. The relief valve is connected to the wheel brake in such a way that the volumetric flow rate can flow out from the wheel brake via the relief valve to regulate the hydraulic pressure at the at least one wheel brake. According to the invention, a control unit is provided, which is designed to perform the above-described method. Attached Figure Description

[0017] Other features, advantages, and possible applications of the invention will also be apparent from the following description of exemplary embodiments and the accompanying drawings. All features described and / or illustrated are individually and in any combination to be part of the subject matter of this invention.

[0018] Figure 1 The hydraulic circuit of the braking system is schematically shown.

[0019] Figure 2 The method sequence according to the present invention is illustrated schematically.

[0020] Figure 3 A chart showing method data is presented. Detailed Implementation

[0021] Figure 1 The braking system 1 shown is based on principles known from the prior art. Braking system 1 has four wheel brakes 2, which are connected to a tandem master cylinder (not shown) and pressurized by the driver using the brake pedal during normal operation. Braking system 1 has two substantially identical brake circuits, each connected to the chamber of the tandem master cylinder and actuating two wheel brakes 2. During normal operation, the inserted master cylinder valve 7 (MCI) opens when de-energized, and the pump valve 8 closes. Each wheel brake 2 also has an inlet valve 4 and an outlet valve 5 through which hydraulic fluid enters the wheel brake and exits from the wheel brake 2 into a low-pressure accumulator 6.

[0022] In order to establish braking pressure in wheel brake 2 independently of the driver, pump valve 8 can be opened and hydraulic pump 3 can be started so that hydraulic fluid can be pumped to wheel brake 2 through inlet valve 4.

[0023] Because the pressure in wheel brake 2 cannot be precisely regulated by hydraulic pump 3, master cylinder valve 7 is not fully closed but functions as relief valve 7. For this purpose, hydraulic pump 3 pumps slightly more hydraulic fluid than required to build up braking pressure at the wheel brake 2. The excess volume is discharged as overflow volume through relief valve 7. For this purpose, relief valve 7 is set to the required braking pressure in wheel brake 2 to precisely regulate the braking pressure. The required electric valve current depends on the pressure differential set on relief valve 7. Because there is virtually no pressure on the side of relief valve 7 connected to the master cylinder when the braking pressure is built up independently of the driver, the pressure differential on relief valve 7 corresponds to the pressure of the wheel brake. The electric valve current required for relief valve 7 also depends on the overflow volume through relief valve 7.

[0024] Figure 2 The method sequence is now shown in simplified form. In step 10, a pressure demand p(t) is received, for example, from the ESC control unit. In step 11, the pressure demand gradient is determined by differentiating from the pressure demand p(t). In addition, filtering and smoothing measures can be implemented.

[0025] To ensure that the change in pressure demand p(t) is sufficiently slow, in step 12, based on the pressure demand gradient... Determine the volumetric flow rate requirement The method is a pressure demand gradient. Vehicle-specific value multiplied by the relationship between pressure change and volume change .

[0026]

[0027] In step 13, hydraulic pump 3 is started and operated at a rate that achieves a volumetric flow rate higher than the calculated volumetric flow rate requirement. It can be a predefined value.

[0028] In step 14, the actual volumetric flow rate of hydraulic pump 3 is determined. For this purpose, the speed of hydraulic pump 3 is determined, and the volumetric flow rate is determined based on the characteristics of hydraulic pump 3. .

[0029] In step 15, based on the actual volumetric flow rate of hydraulic pump 3... and volumetric flow rate requirements Determine the required overflow volume through overflow valve 7 .

[0030]

[0031] In step 16, the characteristics of the relief valve 7 (pressure demand p(t), such as pressure difference Δp, and determined relief volume) are defined. Determine the required electric valve current and supply the current to the relief valve 7.

[0032] To ensure that pressure demand can be met quickly and safely even under conditions of rapid high pressure (i.e., when pressure demand p(t) rises rapidly, especially in stages), it is further proposed, as shown in step 20, to monitor the pressure demand gradient. To determine whether the latter exceeds a predefined limit value. If this is the case, then the special mode is activated, and in step 21, the maximum volumetric flow rate requirement is determined. For this purpose, vehicle-specific values ​​can be used specifically based on the pressure demand gradient. The maximum volumetric flow rate requirement is calculated from the maximum value.

[0033]

[0034] Based on the maximum volumetric flow rate requirement Specify a minimum value for volumetric flow rate. In the illustrated embodiment, this minimum value was selected as being greater than the maximum volumetric flow rate requirement. 20% less.

[0035]

[0036] When the special mode is activated, the volumetric flow rate requirement It cannot be lower than the minimum value As shown in step 22.

[0037] Once the difference between the pressure demand p(t) and the system pressure in the corresponding wheel brake 2 falls below the corresponding limit value, the special mode ends in step 23. For example... Figure 1 As shown, only a single pressure sensor 9 is used, which measures the pressure on the low-pressure side of the hydraulic pump 3 in the lower brake circuit. Therefore, the system pressure in the wheel brake 2 cannot be directly measured. Therefore, a vehicle-specific pressure model is calculated, based on which the system pressure can be determined. Once the system pressure determined according to the pressure model approaches the pressure requirement p(t) by a certain limit, the special mode ends, and the system changes to a transition mode in step 24. In the transition mode, the minimum volume requirement is... It decreases linearly to 0.

[0038] Figure 3The time curves of various variables under rapid high pressure demand (shown here as a jump) are illustrated by way of example. Pressure demand 30, for example, from an ESC control unit, is received as the first input variable. At time 36, this pressure demand has a level that changes from approximately p = 0 to a constant value p > 0. However, the actual system pressure does not follow such rapid high pressure demand, but rather has a curve 31 as shown by the dashed line. Since the actual system pressure cannot be directly measured, a vehicle-specific pressure model 31 is used to determine this curve.

[0039] The pressure demand gradient 32 roughly corresponds to the time derivative of pressure demand 30, and this pressure demand gradient has been time-domain filtered. Despite the time-domain filtering, the pressure demand gradient 32 still rises very rapidly to its maximum value and then drops very steeply to 0.

[0040] The volumetric flow rate requirement 33 is calculated based on the pressure demand gradient 32 by relating it to the specific volume consumption of the vehicle. Multiplying this, the specific volumetric consumption of the vehicle has been determined by pressure / volume consumption measurements and stored in the brake control unit. According to this calculation formula, the volumetric flow rate requirement 33 will follow the process shown by the dashed line, and therefore drop to 0 as quickly as the pressure demand gradient 32. At the point when the volumetric flow rate requirement has fallen back to 0, the system pressure 31 has not yet risen to the actual required pressure 30, but has only reached a small fraction of the pressure requirement. Since the volumetric flow rate requirement 33 is used as the basis for regulating the hydraulic pump 3 and the relief valve 7, the rapid decrease in the volumetric flow rate requirement 33 will prevent the actual brake pressure demand that can be provided.

[0041] Accordingly, the special mode begins at time 36 because the pressure demand gradient 32 exceeds the limit. For this purpose, the volumetric flow rate requirement is calculated at the time of the maximum pressure demand gradient 32 and stored as the maximum volumetric flow rate requirement. A minimum value 34 for the volumetric flow rate requirement is established based on this maximum volumetric flow rate requirement, and the value cannot fall below this minimum value during the duration of the special mode. Accordingly, the volumetric flow rate requirement does not correspond to the calculated dashed curve 33, but instead remains at the minimum value 34 until time 37, when the special mode ends, because the difference 39 between the pressure demand 30 and the pressure model 31 is below the limit.

[0042] At time 37, the special mode ends and transitions to transition mode 35. In transition mode 35, the minimum volumetric flow rate requirement decreases linearly to 0, and therefore the transition mode also ends at time 38. At this point, the system pressure from pressure model 31 roughly corresponds to pressure demand 30.

[0043] List of reference numerals in the attached diagram:

[0044] 1 Braking System

[0045] 2 wheel brakes

[0046] 3 hydraulic pumps

[0047] 4 Inlet Valves

[0048] 5. Outlet valve

[0049] 6 Low-voltage accumulators

[0050] 7. Overflow valve

[0051] 8 switching valves

[0052] 9-channel tandem master cylinder pressure sensor

[0053] 10. Pressure demand reception

[0054] 11 pressure gradient

[0055] 12 Volumetric Flow Rate Requirements

[0056] 13 Start pump

[0057] 14 Volumetric Flow Rate

[0058] 15 Overflow Volume

[0059] 16 valve flow

[0060] 20 Rapid high-pressure demand

[0061] 21 Maximum volumetric flow rate requirement

[0062] 22 Minimum required volumetric flow rate

[0063] 23 Transition Mode Start Conditions

[0064] 24 Volumetric Flow Equalization Transition Mode

[0065] 30 pressure demand

[0066] 31 System pressure from the pressure model

[0067] 32 Pressure Demand Gradient

[0068] 33 Calculated volumetric flow rate requirements

[0069] 34. Volumetric flow rate requirements for special modes

[0070] 35. Volumetric flow rate requirements for transition mode

[0071] Special mode starts at 36

[0072] 37 changed to transition mode

[0073] 38 End Transition Mode

[0074] 39 First limit value

Claims

1. A method for adjusting pressure settings in a braking system (1), the braking system having a pressure application device (3) and an overflow valve (7), the method comprising the steps of: - Receive pressure demand (30) and determine pressure demand gradient (32) based on pressure demand (30). - Determine the volumetric flow rate requirement based on the pressure demand gradient (32). - Hydraulic pressure is generated by the pressure application device (3), - Determine the actual volumetric flow rate of the pressure application device (3). - The relief valve (7) is adjusted based on the pressure requirement (30) and the difference between the actual volumetric flow rate and the required volumetric flow rate, wherein - When the pressure demand gradient (32) exceeds the gradient limit, a special mode is activated. -In this special mode, the minimum value of the volumetric flow rate requirement is set based on the final maximum value of the volumetric flow rate requirement. - And when the difference between the pressure demand (30) and the system pressure (31) is lower than the first limit value (39), the special mode is deactivated.

2. The method as described in claim 1, characterized in that, The system pressure is determined based on calculations using a vehicle-specific model (31).

3. The method as described in claim 1, characterized in that, The pressure application device (3) is actuated based on the required volumetric flow rate.

4. The method according to any one of claims 1 to 3, characterized in that, The actual volumetric flow rate is determined based on the rotational speed of the pressure application device (3).

5. The method according to any one of claims 1 to 3, characterized in that, In this special mode, the minimum value of the volumetric flow rate requirement is set to a value between 100% and 60% of the last maximum value of the volumetric flow rate requirement.

6. The method according to any one of claims 1 to 3, characterized in that, Monitor whether the pressure demand gradient (32) reaches a maximum value, and when a maximum value is detected, use the current volumetric flow rate requirement as the last maximum value of the volumetric flow rate requirement.

7. The method according to any one of claims 1 to 3, characterized in that, When this special mode is deactivated, it switches to a transition mode, in which the minimum required volumetric flow rate is reduced.

8. The method according to any one of claims 1 to 3, characterized in that, The first limit value (39) is between 2 bar and 25 bar.

9. The method according to any one of claims 1 to 3, characterized in that, The gradient limit is greater than 100 bar / second.

10. The method as described in claim 5, characterized in that, In this special mode, the minimum value of the volumetric flow rate requirement is set to a value between 90% and 70% of the last maximum value of the volumetric flow rate requirement.

11. The method as described in claim 7, characterized in that, The minimum required volumetric flow rate decreases linearly during this transition mode.

12. The method as described in claim 8, characterized in that, The first limit value (39) is between 4 bar and 12 bar.

13. The method as described in claim 12, characterized in that, The first limit value (39) is between 6 bar and 10 bar.

14. The method as described in claim 9, characterized in that, The gradient limit is greater than 150 bar / second.

15. The method as described in claim 14, characterized in that, The gradient limit is greater than 200 bar / second.

16. A hydraulic braking system having at least one wheel brake (2) and a pressure application device (3) and an overflow valve (7), the pressure application device being connected to the at least one wheel brake (2) and designed to transmit a volumetric flow rate in the direction of the at least one wheel brake (2), the overflow valve being connected to the at least one wheel brake (2) such that the volumetric flow rate can flow out of the at least one wheel brake via the overflow valve and being designed to regulate the hydraulic pressure at the at least one wheel brake (2), characterized in that, A control unit is provided, which is designed to perform the method as described in any one of claims 1 to 7.

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