Methods for avoiding pressure oscillations in a hydraulic vehicle braking system, hydraulic vehicle braking system and use of the vehicle braking system

Abstract

Method for avoiding pressure fluctuations in a hydraulic vehicle brake system (301), in which a fluid pressure is built up by means of a stroke-operated hydraulic pump (313, 314) according to a predetermined target pressure value and in which an overflow control is carried out using at least one analogously controlling hydraulic valve (311, 312), which diverts fluid at the pressure fluctuation maxima exceeding the target pressure value, characterized in that the overflow control is initiated by a pre-control, wherein fluid is diverted during the pre-control when the pressure fluctuation maxima exceed a pre-control pressure value and wherein the pre-control pressure value is reduced compared to the target pressure value.

Description

[0001] The invention relates to a method for avoiding pressure oscillations in a hydraulic vehicle braking system according to the preamble of claim 1, a hydraulic vehicle braking system according to the preamble of claim 8 and a use of the vehicle braking system.

[0002] The most precise possible control and regulation of analog digital valves in hydraulic vehicle braking systems is essential for an increasingly large number of different vehicle comfort functions. Particularly at low vehicle speeds, inaccurate control is clearly perceptible both haptically and audibly and is therefore perceived as annoying by the driver. While the use of pressure sensors in each individual wheel brake cylinder allows for a highly accurate pressure measurement at all times, and consequently, a highly accurate adjustment of the necessary brake pressure, this leads to increased costs for the manufacturer of the braking system.

[0003] A known method for avoiding the need for additional pressure sensors and the associated additional costs can be achieved by measuring the opening and closing current in the form of a characteristic curve that correlates a pressure differential applied to a hydraulic valve with an excitation current. This allows for essentially exact pressure control using an analog hydraulic valve, even without additional pressure sensors. Such a method is disclosed, for example, in DE 102 24 059 A1. The characteristic curve is stored electronically in the control system, and a pressure differential can then be precisely set via the excitation current without having to rely on actual measured pressure data.

[0004] German patent DE 10 2008 060 622 A1 discloses a hydraulic motorcycle brake system comprising a continuously delivering hydraulic fluid pump. A specific pressure requirement can be regulated by means of an overflow control of the separating valve or the outlet valve. Since the pressure regulation depends significantly on the overflow behavior of the regulating valves, and the control characteristic alone provides no information about the flow rate of a valve, additional pressure sensors are used in the area of ​​the wheel brakes.

[0005] The unpublished German patent application DE 10 2011 080 227.4 describes a method for optimizing pressure control accuracy in a motor vehicle braking system. A hydraulic pump is used to first build up hydraulic pressure according to a pressure request. This pressure is then regulated to a setpoint by means of an overflow control system using one or more analogously controlled hydraulic valves and a known control characteristic curve. This prevents any pressure buildup exceeding the pressure request. To enable highly accurate overflow control, in addition to the control characteristic curve of the respective hydraulic valve, an overflow characteristic map of the respective hydraulic valve is also taken into account. This map represents the overflow behavior of a property-averaged hydraulic valve.

[0006] However, a disadvantage of the methods and braking systems known from the prior art is that, despite all technical efforts, it is often not possible to avoid acoustically and haptically perceptible control vibrations for the driver resulting from a braking intervention triggered by a vehicle comfort function, especially at low vehicle speeds and low brake pressures.

[0007] The object of the present invention is therefore to propose a method which avoids the disadvantages known from the prior art.

[0008] This problem is solved according to the invention by the method for avoiding pressure oscillations in a hydraulic vehicle braking system according to claim 1.

[0009] According to the inventive method for preventing pressure fluctuations in a hydraulic vehicle braking system, in which a fluid pressure is built up by means of a stroke-operated hydraulic pump according to a predetermined setpoint pressure, an overflow control is implemented using at least one analogously controlled hydraulic valve, which diverts fluid when pressure fluctuation maxima exceed the setpoint pressure. The method is characterized in that the overflow control is initiated by a pre-control, wherein fluid is diverted during the pre-control when the pressure fluctuation maxima exceed a pre-control pressure value, and wherein the pre-control pressure value is reduced compared to the setpoint pressure value.

[0010] The invention therefore initially starts with an overflow control system that diverts fluid by means of suitable control of the at least one hydraulic valve when the fluid pressure built up by the hydraulic pump exceeds the set pressure value. According to the invention, this overflow control system, which is known per se, is preceded by a pre-control system.

[0011] According to the invention, the term "pressure oscillation maxima" does not exclusively refer to the actual maximum values ​​of an amplitude in the pressure ripple profile, but rather, depending on requirements or application, to a predefinable amplitude range that extends the actual maximum value to lower values. An extreme example would therefore be to understand any pressure value deviating from the minimum value of an amplitude as a pressure oscillation maximum.

[0012] The method according to the invention offers the advantage that the pressure build-up is comparatively slow and therefore more uniform, so that frequent readjustment interventions at the at least one hydraulic valve or at the hydraulic pump to reduce and rebuild the fluid pressure can be largely avoided. Instead, the fluid pressure is effectively prevented from exceeding the setpoint value from the outset by means of the pre-regulation pressure value, which is lower than the setpoint value. The pre-regulation pressure value is selected such that even strong pressure fluctuations and, in particular, strong pressure oscillation maxima cannot exceed the setpoint value.

[0013] Since hydraulic pumps operating in strokes inherently generate an unavoidable pressure ripple profile in the built-up fluid pressure, this profile can be smoothed by deriving the pressure ripple maxima. By using the inventive pre-regulation to a pre-regulation pressure value reduced compared to the setpoint value, the pressure ripple profile can be almost completely smoothed.

[0014] Even at low vehicle speeds, where even slight pressure ripples become clearly noticeable, a braking force can thus be built up evenly without the driver perceiving longitudinal oscillations in the vehicle speed.

[0015] The hydraulic pump preferably remains unaffected during the pre-control phase, i.e., the hydraulic pump is preferably controlled during the pre-control phase in the same way as it will be controlled during the subsequent overflow control phase.

[0016] The hydraulic pump is preferably designed as a piston pump with two pump pistons operating with a 180° phase shift. However, according to the invention, hydraulic pumps with more than two pump pistons or with only a single pump piston are also possible for use in the described method.

[0017] Preferably, the pre-control pressure value is gradually increased over time, particularly continuously, to approach the setpoint pressure value. Thus, the pre-control pressure value is increased over time until the setpoint pressure value is reached, at which point the pre-control phase is complete and the system transitions to overflow control. The transition from pre-control to overflow control is preferably seamless and without interruption of the control process. By gradually increasing the pre-control pressure value to the setpoint pressure value over time, the advantage is that the setpoint pressure value can generally be reached uniformly and without the need for readjustment. In particular, this avoids the pressure fluctuations in the fluid pressure that occur during readjustment due to the reduction and restoration of fluid pressure.The pre-regulation pressure value does not necessarily have to be continuously increased to the target pressure value over time; an exponentially time-dependent increase is also possible.

[0018] Alternatively, the pre-pressure value is to be adjusted to the setpoint value depending on the pump speed, and in particular continuously depending on the pump speed. This has the advantage that the pump speed, a parameter directly contributing to pressure generation, is used to adjust the pre-pressure value to the setpoint value. This can improve the accuracy of the fluid pressure control. Here, "pump speed" refers to the number of pump revolutions, not a pump rotational speed in the sense of a pump revolution per unit of time.

[0019] Furthermore, it is stipulated that the overflow control is only initiated by a pre-control system if the target pressure build-up gradient does not exceed 10 bar / s, and in particular 5 bar / s. Since the pre-control system, due to its reduced pre-control pressure value compared to the target pressure, would counteract a rapid pressure build-up, it is advantageously only used in situations where a rapid pressure build-up is not necessary.

[0020] It is advantageous for the pre-regulation to be preceded by a base pressure setting of no more than 5 bar. This ensures that delays are avoided, especially at the beginning of the pressure build-up. At the same time, the base pressure setting of no more than 5 bar produces only a virtually imperceptible braking intervention. Since the base pressure setting is also only applied once before the start of the pre-regulation and transitions directly into it, it cannot generate any perceptible pressure fluctuations.

[0021] Furthermore, the pre-control is omitted when the target pressure value is requested by a safety-relevant vehicle system. Since the pre-control according to the invention counteracts a comparatively rapid pressure build-up, it prevents a potentially delayed braking intervention that serves vehicle safety. Moreover, comfort aspects, such as a uniform pressure build-up, play only a minor role in safety-relevant braking interventions. The method according to the invention is preferably used in comfort applications, such as autonomous distance or speed control.

[0022] Furthermore, it is advantageous that the control and / or regulation of the at least one hydraulic valve during pre-control and / or overflow control is based on the piston position of the hydraulic pump. This allows for control or regulation of the at least one hydraulic valve adapted to the pressure ripple, thereby enabling even better damping of pressure fluctuations, since these are known to be generated depending on the piston position.

[0023] Furthermore, it is preferred that the pre-regulation is omitted when a vehicle speed exceeds 30 km / h, particularly 20 km / h. At speeds above 30 km / h, and especially above 20 km / h, the pressure fluctuations in the fluid pressure of the vehicle's braking system, which typically occur with overflow control, are no longer perceptible or barely perceptible to the driver. Therefore, at such vehicle speeds, overflow control can be initiated immediately, thus ensuring that the target pressure value is not reached without delay.

[0024] The invention further relates to a hydraulic vehicle brake system comprising at least one master cylinder for fluid storage, at least one inlet valve for introducing fluid pressure into at least one wheel brake cylinder associated with a vehicle brake, and at least one outlet valve for releasing the fluid pressure from the at least one wheel brake cylinder associated with a vehicle brake, at least one stroke-operating hydraulic pump, at least one electronic control unit, and at least one analogously controlled isolating valve, wherein the hydraulic pump builds up a fluid pressure according to a target pressure value specified by the electronic control unit, and wherein, using the at least one analogously controlled isolating valve, an overflow control is carried out according to the electronic control unit, which diverts fluid into the master cylinder at pressure fluctuation maxima exceeding the target pressure value.The vehicle braking system according to the invention is characterized by the fact that it implements the method according to the invention. This results in the advantages already described with regard to improved pressure control.

[0025] The at least one analog-controlled separating valve, the at least one inlet valve and the at least one outlet valve are each designed as hydraulic valves.

[0026] The invention also relates to the use of the vehicle braking system according to the invention for distance and / or speed control in a motor vehicle.

[0027] Further preferred embodiments will become apparent from the dependent claims and the following description of an exemplary embodiment with reference to figures.

[0028] They show

[0029] Fig. 1 schematically the opening gap width of an analogously regulating separating valve during an embodiment of the method according to the invention,

[0030] Fig. 2 a possible sequence of the method according to the invention in the form of a flowchart and

[0031] Fig. 3 an exemplary construction of a hydraulic vehicle braking system according to the invention.

[0032] In Fig. 1 is curve 11 The diagram shows the opening gap width of an analogously controlled isolation valve during an embodiment of the inventive method versus the pump speed. The x-axis represents the opening gap width and the y-axis represents the pump speed. Here, the pump speed is the absolute speed since the start of the method and does not represent the rotational speed in the form of pump revolutions per unit of time. [In the pump speed range] 12The inventive pre-control takes place during the initial pump rotations. Through the corresponding control of the isolation valve, it initially has a comparatively large opening gap, which is further increased or decreased depending on the piston position of the hydraulic pump in order to dissipate any resulting pressure fluctuation maxima. This dependence of the control on the piston position leads to the modulation of the curve shown. 11 As can be seen, the modulation is in the pump speed range. 12 A continuously decreasing opening gap width is superimposed with the pump speed, which represents the adjustment of the pre-regulated pressure value to the setpoint value, since the fluid pressure increases with decreasing opening gap width because less fluid is discharged. This applies to the pump speed range. 12 subsequent pump speed range 13The pre-regulation is complete and overflow control is being implemented, meaning the pre-regulation pressure value has been fully adjusted to the setpoint pressure. Furthermore, it can be seen that – apart from the piston position-dependent modulation – the opening gap width remains constant throughout the pump speed range. 13 is constant, since a constant fluid pressure is to be maintained.

[0033] In Fig. Figure 2 shows a possible sequence of the process according to the invention in the form of a flowchart. In process step 21 The electronic control unit generates a target pressure value to be achieved in the vehicle's braking system and a pre-regulation pressure value. In step 22 The hydraulic pump, which delivers in strokes, is controlled according to the target pressure value and in step 23An analog hydraulic valve is controlled according to the pre-control pressure value. Since the pre-control pressure value is lower than the set pressure value, most of the fluid pumped by the hydraulic pump is initially diverted through the analog hydraulic valve. This largely prevents pressure fluctuations. In process step 24 The hydraulic pump now begins pumping the fluid, while simultaneously a pump position sensor determines the respective piston position of the hydraulic pump. The piston position of the hydraulic pump is determined in step 25 This is used to control the hydraulic valve depending on the current piston position and to evenly dissipate the pressure fluctuation maxima that occur due to the stroke-like delivery method. In the next step 26The pump speed, which is also recorded by means of the pump position sensor, has been evaluated since the beginning of the execution of the method according to the invention and in step 27 The pre-regulation pressure value is continuously adjusted towards the target pressure value as the pump speed increases, according to the electronic control unit. In step 28 Finally, the preliminary control is terminated and the system immediately transitions to overflow control.

[0034] Fig. Figure 3 shows an example of a hydraulic brake system according to the invention. 301 , which pressure control device to be operated by the driver 302 , consisting of tandem master cylinder 303 , vacuum booster 304 and the brake pedal attached to it 305 includes tandem master cylinder 303 This includes a pressure sensor. 329 assigned via hydraulic lines 305 and 306 is pressure control device 302with hydraulic pressure control circuits 307 and 308 Hydraulically coupled. Hydraulic pressure control circuits. 307 and 308 are basically identical in structure and therefore in their representation of Fig. 3 also shown identically. Pressure control loops 307 and 308 Each hydraulic pressure control circuit is assigned to one of the wheel brakes of a brake circuit of a two-axle motor vehicle. 307 and 308 include normally closed electronic switching valves 309 and 310 , normally open, analog-controlled isolation valves 311 and 312 , stroke-operated hydraulic pumps 313 and 314 , normally open inlet valves 315 , 316 , 317 and 318 as well as normally closed exhaust valves 319 , 320 , 321 and 322 Furthermore, hydraulic pressure control circuits include 307 and 308Low-pressure storage tank 323 and 324 as well as wheel brake cylinders assigned to each vehicle wheel 325 , 326 , 327 and 328 . When carrying out the method according to the invention in a hydraulic brake system 301 First, hydraulic pumps will be used. 313 and 314 The valves are controlled to build up a fluid pressure according to a target pressure value specified by an electronic control unit. This requires switching valves. 309 and 310 Opened. Simultaneously, isolation valves are opened. 311 and 312 controlled in such a way as to a pre-control pressure value specified by an electronic control unit, such that pressure oscillation maxima exceeding the pre-control pressure value are in tandem master cylinders 303 can be derived. Since intake valves 315 , 316 , 317 and 318 are also open while exhaust valves 319 , 320 , 321and 322 are closed, in wheel brake cylinders 325 , 326 , 327 and 328 A fluid pressure builds up, which creates a braking effect. This pressure is contained in the wheel brake cylinders. 325 , 326 , 327 and 328 The fluid pressure setting is determined on the one hand by the delivery rate of hydraulic pumps. 313 and 314 , but also from the control of isolation valves 311 and 312 , which during the pre-regulation process directs most of the pumped fluid into tandem master cylinders 303 derive. This causes the fluid pressure in the wheel brake cylinders to decrease. 325 , 326 , 327 and 328 initially rises only slowly and pressure fluctuations, especially due to the stroke-like operating mode of hydraulic pumps 313 and 314 The resulting pressure oscillations are largely avoided. In wheel brake cylinders 325 , 326 ,327 and 328 This results in a substantially constant, increasing fluid pressure, which is not increased further once the target pressure value is reached. As soon as the target pressure value is reached, the pre-control according to the invention is terminated and an overflow control is initiated to maintain the fluid pressure. QUOTES INCLUDED IN THE DESCRIPTION

[0035] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0036] DE 10224059 A1

[0003] DE 102008060622 A1

[0004] DE 102011080227

[0005]

Claims

[1] Method for avoiding pressure oscillations in a hydraulic vehicle braking system ( 301 ), in which a stroke-operating hydraulic pump ( 313 , 314 ) a fluid pressure is built up according to a predetermined target pressure value, using at least one analogously regulating hydraulic valve ( 311 , 312 ) an overflow control is implemented, which diverts fluid when pressure fluctuation maxima exceed the set pressure value, characterized by that the overflow control is initiated by a pre-control, wherein fluid is diverted during the pre-control when the pressure oscillation maxima exceed a pre-control pressure value and wherein the pre-control pressure value is reduced compared to the setpoint pressure value. [2] Method according to claim 1, characterized by that the pre-regulation pressure value is brought closer to the target pressure value in a time-dependent manner, in particular continuously time-dependently. [3] Method according to claim 1, characterized by that the pre-regulation pressure value is brought closer to the target pressure value depending on the pump speed, in particular continuously depending on the pump speed. [4] Method according to at least one of claims 1 to 3, characterized by that the overflow control is only initiated by a pre-control if a target pressure build-up gradient does not exceed a value of 10 bar / s, in particular 5 bar / s. [5] Method according to at least one of claims 1 to 4, characterized by that the pre-regulation is preceded by a base pressure setting of no more than 5 bar. [6] Method according to at least one of claims 1 to 5, characterized by that the pre-regulation is omitted when the target pressure value is requested by a safety-relevant vehicle device. [7] Method according to at least one of claims 1 to 6, characterized bythat a control and / or regulation of at least one hydraulic valve ( 313 , 314 ) during pre-control and / or during overflow control according to a piston position of the hydraulic pump ( 313 , 314 ). [8] Method according to at least one of claims 1 to 7, characterized by that the preliminary regulation does not apply if a vehicle speed of more than 30 km / h, in particular more than 20 km / h, is exceeded. [9] Hydraulic vehicle braking system ( 301 ), comprising at least one main cylinder ( 303 ) for fluid storage, at least one inlet valve ( 315 , 316 , 317 , 318 ) for introducing fluid pressure into at least one wheel brake cylinder assigned to a vehicle brake ( 325 , 326 , 327 , 328 ) and at least one exhaust valve ( 319 , 320 , 321 , 322) to release the fluid pressure from the at least one wheel brake cylinder assigned to a vehicle brake ( 325 , 326 , 327 , 328 ), at least one hydraulic pump delivering in strokes ( 313 , 314 ), at least one electronic control unit and at least one analog control separating valve ( 311 , 312 ), wherein the hydraulic pump ( 313 , 314 ) builds up a fluid pressure according to a target pressure value specified by the electronic control unit, using at least one analogously regulating isolation valve ( 311 , 312 ) according to the electronic control unit, an overflow control takes place, which directs fluid into the main cylinder when pressure fluctuation maxima exceed the set pressure value ( 303 ) derives, characterized by that the vehicle braking system ( 301 ) performs a method according to at least one of claims 1 to 8. [10] Use of the vehicle braking system ( 301 ) according to claim 9 for distance and / or speed control in a motor vehicle.

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