Patent Application
20210162966
The present disclosure relates to the field of motor vehicle brake systems in general. Specifically, the operation of a motor vehicle brake system in the event of failure of a driving dynamics regulation system is described.
Known hydraulic motor vehicle brake systems, which are configured as brake-by-wire (BBW) systems or are equipped with an electric brake boost (EBB) system, comprise an electrically controllable actuator which, in service brake mode, generates a hydraulic pressure on the wheel brakes of the motor vehicle or boosts a hydraulic pressure generated by the driver. To this end, deceleration of a vehicle, requested by the driver via a brake pedal, is sensor-detected and converted into a control signal for the electrically controllable actuator.
Brake systems of this type normally also comprise a master cylinder which can be mechanically actuated by means of the brake pedal and via which hydraulic fluid can likewise be delivered to the wheel brakes. The master cylinder, which can be actuated by means of the brake pedal, produces a redundancy in relation to the electrically controllable hydraulic pressure generator of the BBW or EBB system, which is vital for reasons of operational safety. Motor vehicle brake systems for autonomous or partially autonomous driving are designed with redundancy, especially since the driver is not necessarily located inside the vehicle (e.g. in remote-controlled parking—RCP—mode).
Modern brake systems furthermore comprise a driving dynamics regulation system (also known as electronic stability control, ESC), which comprises, for example, one or more functions such as anti-slip regulation (ASR), an anti-lock brake system (ABS) or an electronic stability program (ESP). There are demands for the driving dynamics regulation system to be designed with redundancy. In other words, at least rudimentary driving dynamics regulation should still be possible in the event of a loss of function of the driving dynamics regulation system to enable the vehicle stability or the deceleration capacity to be at least partially maintained.
The present disclosure is based on the object of specifying a motor vehicle brake system which has a redundancy in the event of a loss of function of the driving dynamics regulation system.
According to a first aspect, a motor vehicle brake system is specified. The brake system comprises a driving dynamics regulation system, which is designed to carry out a wheel-specific regulating intervention on each of a plurality of vehicle wheels, and an electrically controllable actuator, which is designed to generate or boost a service brake force. The brake system further comprises a control, which is designed, in the event of an identified loss of function of the driving dynamics regulation system, to select one of at least two vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required in each case and to electrically control the actuator on the basis of a regulating intervention determined for the selected vehicle wheel.
The brake system can be a hydraulic, a pneumatic, a mechanical or a regenerative brake system. Combinations thereof are also conceivable (e.g. a hydraulic regenerative brake system).
The electrically controllable actuator can be part of an EBB system (for brake boosting) or a BBW system (for brake force generation). The actuator can comprise an electric motor and a transmission connected downstream of the electric motor. In a hydraulic brake system, a cylinder-piston arrangement or other device for hydraulic pressure generation can be connected downstream of the transmission.
In one realization, the brake system is configured as a BBW system, which comprises the actuator, and/or is equipped with an EBB system, which comprises the actuator. In one design, the brake system is provided with an electrically controllable vacuum brake booster, which functions as the actuator.
The BBW system can provide a constant mechanical decoupling of a brake pedal from a master cylinder of the brake system. This mechanical decoupling can be overridden in favor of mechanical push-through (PT) in the event of an error in the BBW system.
The EBB system (including the electrically controllable vacuum brake booster) cannot provide such a mechanical decoupling, or can only provide it in certain cases (e.g. with regenerative braking), wherein, in the case of the mechanical coupling, a force acting on the master cylinder by means of the brake pedal is boosted using the actuator.
The service brake force can be requested by a driver via a brake pedal. The service brake force can also be requested by a system for autonomous or partially autonomous driving. The service brake force is conventionally used for braking the moving vehicle and therefore differs functionally from the brake force generated by an emergency brake (e.g. an electric parking brake, EPB), for example.
The electrical control of the actuator on the basis of a regulating intervention determined for the selected vehicle wheel can comprise regulation on the basis of a parameter measured at the selected vehicle wheel. The measured parameter can also be used as a regulating variable. Such a parameter can be, for example, a wheel speed or a wheel velocity. Further or other parameters can be analyzed within the framework of the regulating intervention.
In one implementation, the control is designed to control the actuator on the basis of an anti-slip regulation intervention determined for the selected vehicle wheel. In the case of a hydraulic brake system, brake pressure regulation can take place for this purpose, which comprises, for example, pressure-decrease, pressure-build-up and pressure-holding phases.
According to one variant, the control is designed to select the vehicle wheel with the greatest slip. According to a further development, the control is designed to select the wheel with the (e.g. relatively) greatest slip, for which one or more further conditions are fulfilled. The further condition can refer, for example, to a particular vehicle side or a particular vehicle axle (e.g. front axle or rear axle). The further condition can additionally or alternatively refer to wheel-related roadway coefficients of friction. In such a further development, of all the vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required, it is not necessarily the wheel with the greatest absolute slip which is selected.
The control can be designed to analyze the roadway coefficients of friction associated with the vehicle wheels and to select the vehicle wheel on the basis of the roadway coefficient-of-friction analysis. The roadway coefficient of friction is also denoted by the Greek letter μ.
The control can therefore be designed to determine a high coefficient-of-friction side of the vehicle on the basis of the roadway coefficient-of-friction analysis and to select the vehicle wheel with the greatest slip on the high coefficient-of-friction side. The control can also be designed, when the roadway coefficients of friction at all vehicle wheels are each below a threshold value, to select the vehicle wheel with the greatest slip. The control can further be designed, when the roadway coefficients of friction at all vehicle wheels are each above a threshold value, to select a rear wheel. In the latter case, the control can be designed to carry out the regulating intervention on the selected rear wheel in such a way that, for the selected rear wheel, a coefficient-of-friction limit is prevented from being exceeded.
In general, the control can be designed to determine a yaw rate (e.g. by receiving a parameter indicating the yaw rate). In this case, the control can further be designed to carry out at least one of the following steps: select the vehicle wheel on the basis of the determined yaw rate and/or carry out the regulating intervention on the basis of the determined yaw rate.
In one variant, the control is designed to recognize oversteering on the basis of the yaw rate and to select a wheel on the inside of the turn or a rear wheel. The control can also be designed to determine understeering on the basis of the yaw rate and to select a wheel on the outside of the turn or a front wheel.
The control is, for example, further designed to also carry out the regulating intervention determined for the selected vehicle wheel on at least one non-selected vehicle wheel. In this case, the control can be designed, when carrying out the regulating intervention determined for the selected vehicle wheel on the at least one non-selected vehicle wheel, to permit locking of the at least one non-selected vehicle wheel.
In one implementation, the control is designed to identify a requirement for a regulating intervention on each of the at least two vehicle wheels. In this connection, the control can analyze one or more sensor-measured parameters and, on the basis of this analysis, identify whether or not a regulating intervention is required on a particular vehicle wheel. The regulating intervention can then be carried out with continued analysis of the one or more parameters (which then serve e.g. as regulating variable(s)).
The control can be designed to identify the regulating-intervention requirement on the basis of slip recognition for the respective vehicle wheel. In general, the control can be designed to identify the regulating-intervention requirement on the basis of at least one parameter measured at the respective vehicle wheel (e.g. wheel speed or wheel velocity). Additionally or alternatively, the control can be designed to identify the regulating-intervention requirement on the basis of at least one of the following parameters: yaw rate, steering angle, lateral acceleration, longitudinal acceleration, wheel speed, wheel velocity.
The control can further be designed to identify the loss of function of the driving dynamics regulation system. The loss of function can be identified by receiving an error signal or (alternatively) monitoring the driving dynamics regulation system. The loss of function can be caused, for example, by failure of a hydraulic, mechanical or electrical component of the driving dynamics regulation system. This includes a pump, valves etc.
The brake system can further comprise a control device, which is associated with the driving dynamics regulation system, and a second control device, which is associated with the electrically controllable actuator, wherein the control is implemented in the second control device. The second control device can be a control device for an electric brake booster or for a brake-by-wire system or for autonomous or partially autonomous driving.
A second aspect relates to a method for operating a motor vehicle brake system having a driving dynamics regulation system, which is designed for carrying out a wheel-specific regulating intervention on each of a plurality of vehicle wheels, and an electrically controllable actuator, which is designed to generate or boost a brake force. The method comprises, in the event of an identified loss of function of the driving dynamics regulation system, selecting one of at least two vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required in each case, and electrically controlling the actuator on the basis of a regulating intervention determined for the selected vehicle wheel.
The method can further comprise method steps which correspond to the functions of the control described here.
Likewise described control device or system made up of a plurality of control devices, comprising at least one processor and at least one memory, wherein the at least one memory contains program code for carrying out the method presented here when it is run on the at least one processor. The control device or system made up of a plurality of control devices is an exemplary implementation of the control described here.
Further aspects, details and advantages of the present disclosure are revealed in the description below of exemplary embodiments with reference to the figures, which show:
The hydraulic circuit diagram of an exemplary embodiment of a hydraulic motor vehicle brake system 100 is shown in
The brake system 100 comprises an assembly 110 for hydraulic pressure generation, which can be coupled to a brake pedal (not shown), and a hydraulic control assembly 120 (also known as a hydraulic control unit, HCU) with two separate brake circuits I. and II. The brake system 100 further comprises four wheel brakes. Two of the four wheel brakes 130 are associated with the brake circuit I., whilst the two wheel brakes 130 are associated with the brake circuit II. The association of the wheel brakes 130 with the brake circuits I. and II. takes place according to a diagonal allocation in such a way that the wheel brakes 130A and 130B at the right rear wheel (HR) and at the left front wheel (VL) are associated with the brake circuit I., whilst the wheel brakes 130C and 130D at the left rear wheel (HL) and at the right front wheel (VR) are associated with the brake circuit II. Any other allocation of the wheel brakes 130 to the brake circuit I. and II. would be likewise conceivable.
In the present exemplary embodiment, the brake system 100 further comprises an optional electric parking brake (EPB) with two electromechanical actuators 140A, 140B which can be electrically controlled separately from one another. In
The two actuators 140A, 140B are associated with different wheel brakes of the four wheel brakes 130. Specifically, the actuator 140A is associated with the wheel brake 130A of the right rear wheel (HR), whilst the actuator 140B is associated with the wheel brake 130C of the left rear wheel (HL). Of course, in other variants, the two actuators can also be associated with the wheel brakes 130B, 130D of the right front wheel (VR) and the left front wheel (VL).
The assembly 110 for hydraulic pressure generation comprises a master cylinder 110A and can be operated according to the EBB and/or the BBW principle. This means that, incorporated in the assembly 110, there is an electrically controllable actuator in the form of a hydraulic pressure generator 110B which is designed to boost or generate a hydraulic pressure for at least one of the two brake circuits I. and II. This hydraulic pressure generator 110B comprises an electric motor, which acts directly or indirectly on the master cylinder 110A for hydraulic pressure generation via a mechanical transmission (not shown). Indirect action can take place for example hydraulically (for instance, in that the transmission acts on a plunger arrangement whereof the output is hydraulically coupled to an input of the master cylinder 110A).
The HCU 120 comprises a driving dynamics regulation system (also referred to as an ESC system) for carrying out regulating interventions on the wheel brakes 130, which, in the present example, is designed with two circuits. In other exemplary embodiments, the driving dynamics regulation system can also be designed in a known manner, with one circuit.
Specifically, the two-circuit driving dynamics regulation system according to
The two electric motors 160A, 170A—and therefore the two hydraulic pressure generators 160, 170—can be controlled independently of one another. This means that each of the two hydraulic pressure generators 160 and 170 can build up a hydraulic pressure independently of the other hydraulic pressure generator 170 or 160 in the respective brake circuit I. or II. This redundancy is advantageous in relation to safety considerations.
The brake system 100 operates by means of a hydraulic fluid, which is partly stored in three reservoirs 110C, 190, 200. Whilst the reservoir 110C is an unpressurized reservoir, which forms part of the assembly 110, the other two reservoirs 190, 200 are each integrated as pressure accumulators (e.g. as low pressure accumulators, LPA) in one of the two brake circuits I., II. The two hydraulic pressure generators 160 and 170 are each capable of sucking hydraulic fluid out of the associated reservoir 190 or 200 or out of the central reservoir 110C.
The reservoir 110C has a greater capacity than each of the two reservoirs 190, 200. However, the volume of the hydraulic fluid stored in each of the two reservoirs 190, 200 is at least sufficient to enable a vehicle to also be brought safely to a stop in the event of a required brake pressure regulation on one or more of the wheel brakes 130 (e.g. in the event of ABS-assisted emergency braking).
The brake circuit I. comprises a hydraulic pressure sensor 180A, which is arranged on the input side of the brake circuit I. in the region of its interface with the assembly 110. The signal of the hydraulic pressure sensor 180A can be analyzed in association with a control of the hydraulic pressure generator 110B integrated in the assembly 110 and/or the hydraulic pressure generator 160 integrated in the brake circuit I. The analysis and control takes place by means of a control device system 300 shown merely schematically in
As shown in
In the brake circuit I., a plurality of valves which can be actuated by electromagnets are provided, which, in the unactuated, i.e. electrically non-controlled state, assume the basic positions illustrated in
The multiplicity of valves comprises two 2/2-way valves 210, 220, which permit an uncoupling of the two wheel brakes 130A and 130B from the assembly 110. Specifically, the valve 210 is provided to uncouple the wheel brakes 130A, 130B from the assembly 110 in the electrically controlled state when, by means of the hydraulic pressure generator 160, a regulating intervention is carried out on at least one of the two wheel brakes 130A, 130B. In its electrically controlled state, the valve 220 enables hydraulic fluid to be sucked or fed out of the reservoir 110C (e.g., in the case of a sustained regulating intervention, if the reservoir 190 is to be emptied completely). A decrease in pressure at the wheel brakes 130A, 130B is further possible in this electrically controlled state, in that a return flow of hydraulic fluid from the wheel brakes 130A, 130B into the unpressurized reservoir 110C is enabled.
The hydraulic connection of the wheel brakes 130A, 130B to the assembly 110 and the hydraulic pressure generator 160 is determined by four 2/2-way valves 230, 240, 250, 260 which, in the unactuated, i.e. electrically non-controlled state, assume the basic positions illustrated in
As explained below, the two valves 210 and 220, the two valve arrangements 230, 240 and 250, 260 and the hydraulic pressure generator 160 are each designed to be controlled for wheel brake pressure-regulating interventions on the respective wheel brake 130A, 130B. The control of the two valves 210 and 220, the two valve arrangements 230, 240 and 250, 260 and the hydraulic pressure generator 160 within the framework of the regulating interventions takes place by means of the control device system 300. The control device system 300 implements, for example, the wheel brake pressure-regulating interventions of driving dynamics regulation, wherein the driving dynamics regulation according to the present disclosure also includes an anti-lock brake system (ABS) and/or anti-slip regulation (ASR) and/or an electronic stability program (EPB) and/or brake pressure regulation for adaptive cruise control (ACC).
Anti-lock regulation involves preventing the wheels from locking during braking. To this end, it is necessary to modulate the hydraulic pressure in the wheel brakes 130A, 130B individually. This takes place by adjusting successively alternating pressure-build-up, pressure-holding and pressure-decrease phases, which are realized by suitably controlling the valve arrangements 230, 240 and 250, 260 associated with the two wheel brakes 130B and 130A and possibly the hydraulic pressure generator 160.
During a pressure-build-up phase, the valve arrangements 230, 240 and 250, 260 each assume their basic position, so that an increase in the brake pressure in the wheel brakes 130A, 130B (as in the case of BBW braking) can take place by means of the hydraulic pressure generator 160. For a pressure-holding phase at one of the wheel brakes 130B and 130A, only the valve 230 or 260 is controlled, i.e. brought into its blocking position. Since control of the valve 240 or 250 does not take place in this case, it remains in its blocking position. The corresponding wheel brake 130B or 130A is thus hydraulically uncoupled so that a hydraulic pressure applied in the wheel brake 130B or 130A is held constant. In a pressure-decrease phase, both the valve 230 or 260 and the valve 240 or 250 are controlled, i.e. the valve 230 or 260 is brought into its blocking position and the valve 240 or 250 is brought into its throughflow position. Hydraulic fluid can therefore flow out of the wheel brake 130B or 130A in the direction of the reservoir 110C and 190 in order to lower a hydraulic pressure applied in the wheel brake 130A or 130B.
Other regulating interventions in normal braking mode take place in an automated manner and typically independently of an actuation of the brake pedal by the driver. Such automated regulations of the wheel brake pressure take place, for example, in association with anti-slip regulation, which prevents individual wheels from spinning during a starting procedure via targeted braking, driving dynamics regulation in a narrower sense, which adapts the vehicle behavior in the limit range to the driver request and the roadway conditions via targeted braking of individual wheels, or adaptive cruise control, which, amongst other things, maintains a distance between the vehicle in question and a vehicle in front via automatic braking.
When executing automatic hydraulic pressure regulation, a hydraulic pressure can be built up on at least one of the wheel brakes 130A or 130B by controlling the hydraulic pressure generator 160. In this case, the valve arrangements 230, 240 or 250, 260 associated with the wheel brakes 130B, 130A hydraulic pressure generator 160 firstly assume their basic positions shown in
The hydraulic pressure regulation takes place by means of the control device system 300 generally depending, on the one hand, on sensor-detected parameters (e.g. wheel speeds, yaw rate, lateral acceleration, etc.) describing the vehicle behavior and, on the other hand, sensor-detected parameters (e.g. actuation of the brake pedal, steering-wheel angle, etc.) describing the driver request, where present. A deceleration request by the driver can be identified, for example, by means of a position sensor, which is coupled to the brake pedal or an input element of the master cylinder 110A. As the measured variable describing the driver request, it is alternatively or additionally possible to use the brake pressure generated in the master cylinder 110A by the driver, which is then detected by means of the sensor 180A (and the corresponding sensor 180B associated with the brake circuit II.) and possibly plausibility-checked. The deceleration request can also be initiated by a system for autonomous or partially autonomous driving.
In the exemplary embodiment according to
The control device system 300 further comprises a third control device 310, which is designed to control the hydraulic pressure generator 110B integrated in the assembly 310 and therefore, in particular, the electric motor thereof. Depending on the configuration of the brake system 100, this control can take place according to the EBB principle or the BBW principle. The control device 310 can form a spatially cohesive control device unit with the two other control devices 302 and 304, or it can be provided at a spacing from these. In one realization, a housing of the control device 310 is integrated in the assembly 110. In a system for autonomous or partially autonomous driving, the control device system can comprise a further control device (not illustrated in
As shown in
Each of the three control devices 302, 304 and 310 (and an optional control device for autonomous or partially autonomous driving), is supplied redundantly both via the supply system K30-1 and via the supply system K30-2. To this end, each of the control devices 302, 304, 310 can be provided with two separate supply connections, which are each associated with one of the two supply systems K30-1 and K30-2.
As further shown in
In the exemplary embodiment according to
An exemplary embodiment of a method for operating the brake system 100 according to
The method begins in step 402 with the identification of a loss of function of the driving dynamics regulation system. For example, a loss of function (including a failure) of one of the two control devices 302, 304 (or both control devices 302, 304) can therefore be identified. A loss of function (including a failure) of one of the two (or both) hydraulic pressure generators 160, 170 can also be identified in step 402. It goes without saying that, in the case of a one-circuit driving dynamics regulation system, only one control device 302 or 304 and only one hydraulic pressure generator 160 or 170 will be present, which means that a loss of function thereof is all the more serious. The loss of function can be identified, for example, in that the corresponding control device 302, 304 no longer communicates at all or in that the corresponding control device 302, 304 communicates an error message. The error message can be attributed, for example, to the loss of function of one of the hydraulic pressure generators 160, 170 or one of the valves shown in
After identifying the loss of function in step 402 (or previously or at the same time), it is identified in step 404 that a regulating intervention is required at two or more of the vehicle wheels VL, HR, VR, HL (c.f.
In step 404, a slip calculation is, in particular, carried out on the basis of the wheel signals. The slip calculation is based on the calculation of a deviation of an individual wheel velocity from the vehicle velocity. The vehicle velocity can be determined with the aid of the wheel velocity of a slip-free wheel or in another manner (e.g. on the basis of a satellite-based positioning system).
A roadway coefficient of friction for each wheel can further take place via the wheel velocities, the yaw rate or both in step 404 in order to identify a regulating-intervention requirement. It is thus possible, in particular, for different roadway coefficients of friction on different vehicle sides to be identified (i.e. a so-called split μ identification can be carried out). Vehicle stability identification (e.g. according to an ESP) can further be identified in step 404 based on the yaw rate (if available) in order to identify a regulating-intervention requirement.
As already mentioned, the steps 402 and 404 can be carried out in any order or also at the same time.
If, in step 404, a plurality of vehicle wheels are determined at which a regulating intervention is to be carried out (e.g. since it has been identified that a slip threshold value has been exceeded for a plurality of vehicle wheels), a selection of one of these vehicle wheels takes place in step 406. Specifically, the vehicle wheel selected is the one at which a regulating intervention promises the best results in terms of vehicle safety. The background to this selection is the fact that, with a loss of function of the driving dynamics regulation system, multi-channel regulating interventions are usually no longer possible. Multi-channel regulating interventions are understood to be those regulating interventions which take place at two or more vehicle wheels at the same time. However, the option of a one-channel regulating intervention by means of the actuator, which is conventionally used for (“one-channel”) service braking, is instead available. In the brake system according to
For more sustained regulation, the selection according to step 406 can be also be repeated once or a plurality of times in order to select different wheels in succession. However, it may also be that the selection in step 406 selects the same vehicle wheel a plurality of times.
After one of the affected vehicle wheels has been selected in step 406, control of the actuator, such as the hydraulic pressure generator 1006 according to
In the hydraulic brake system 100 according to
Several selection options according to step 406 and (one-channel) control options according to step 408 are listed in the table below. The slip and coefficient-of-friction recognition can be carried out on the basis of wheel signals. The regulating procedure can likewise be carried out on the basis of wheel signals. If one or more further parameters are available, for example the yaw rate, these can be taken into account both for the wheel selection and for the regulation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 008 948.5 | Sep 2017 | DE | national |
This application is a national stage of International Application No. PCT/EP2018/070015, filed Jul. 24, 2018, the disclosure of which is incorporated herein by reference in its entirety, and which claimed priority to German Patent Application No. 102017008948.5, filed Sep. 25, 2017, the disclosure of which is incorporated herein by reference in its entirety
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/070015 | 7/24/2018 | WO | 00 |
