For almost 80 years, today's 2-circuit braking system with two brake circuits has become established for safety reasons and, depending on the vehicle design, is used in a brake circuit layout of
DE 10 20 2018 213 306 describes a system with detection of brake circuit failure due to leakage of the brake circuit by evaluating the pressure gradient.
Almost all vehicles have electronic brake control systems for all four vehicle wheels, which are usually braked hydraulically. Each wheel brake cylinder is connected to at least one or two electromagnetically controlled control valves, which are electrically controlled by an electrical control unit (ECU), e.g. to prevent the wheel from locking.
In today's standard brake systems with ABS/ESP function, an inlet and an outlet valve are usually assigned to each wheel brake cylinder, with the inlet valve usually having a check valve connected in parallel so that the inlet valve, which is often also referred to as the shift valve, does not close due to the back pressure during rapid pressure reduction.
If an inlet valve with its associated check valve fails and leaks, in today's dual-circuit brake systems an entire brake circuit usually fails when the wheel brake cylinder fails, so that the braking effect is reduced by at least 30%.
The task of the invention is to provide a very fail-safe braking system that requires as few valves as possible.
This task is advantageously solved with a braking system having the features of claim 1. Further advantageous embodiments of this braking system result from the features of the subclaims.
The invention is characterized by the fact that components that are as fail-safe as possible are used and/or appropriate safety valves, in particular in the form of separating valves, are provided between the pressure supply and the wheel brake cylinders and/or between wheel circuits or brake circuits.
A common inlet valve used for ABS/ESP has a parallel check valve, which is considered unsafe in tightness, therefore can no longer be used. As described above, the check valve was provided to prevent the inlet valve from closing due to back pressure during rapid pressure reduction.
It is therefore advantageous to use a switching valve instead of an inlet valve with a parallel check valve, which is designed to be tamper-proof at least in one flow direction even at high flow velocities or high pressure gradients.
The switching valve assigned to each wheel brake cylinder should also be designed to be as fail-safe as possible, so that in principle no further valves, in particular isolating valves, are required to isolate a wheel circuit or brake circuit that has become leaky. If safety should nevertheless be increased, at least one of the isolating valves described above can be provided in addition.
To increase fail-safety and braking efficiency in the event of a fault, switching valves for the wheel brake cylinders can also be advantageously used in which the electromagnetic drive or at least some of its components are provided or designed redundantly, i.e. at least twice. For example, the switching valve can have at least two coils and two coil actuators which can switch the switching valve separately from one another, so that if one coil or its actuator fails, the other can take over its function, so that the switching valve is significantly more fail-safe and thus the entire braking system is also advantageously more failsafe.
The coils can also be designed in such a way that they each alone switch the valve reliably up to a certain pressure of e.g. 100 bar and that higher pressures can only be switched by the joint energization or activation of both coils.
The valve according to the invention is understood to mean the valve assigned to each wheel brake cylinder, via which hydraulic medium flows to build up pressure in only this wheel brake cylinder. The term wheel circuit is used here to mean the wheel brake cylinder including the hydraulic connection from the valve to the wheel brake cylinder. Of course, the hydraulic medium can also flow from the associated wheel brake cylinder through valve SV2k back into brake circuit BK1 or BK2 for pressure reduction. An exhaust valve assigned to a wheel brake cylinder is also part of the respective wheel circuit.
For the braking system according to the invention, in order to avoid the problems described above, a switching valve of the “normally de-energized open” type can be used, the valve actuator of which is adjusted by means of a first electromagnetic drive from the open valve position to the closed valve position, in which the valve actuator is pressed against a valve seat. When the electromagnetic drive is not energized or not energized sufficiently, a valve spring presses the valve actuator into the initial position, i.e. into the open valve position. In an advantageous further development of the switching valve described above, it has an additional force-applying device that generates an additional force on the valve actuator, which is directed in the direction of the open valve position and thus supports or replaces the valve spring, resulting in an increased resultant force with which the valve actuator is force-loaded into the open valve position.
The additional force device can be switchable, e.g. formed by an additional electromagnet to the actual valve actuator. It can thus also be described as an active additional force device, since the additional force generated on the valve actuator can be switched on or off as desired and depending on the state of the braking system. However, it is equally possible for the additional force device to act passively, for example by using a permanent magnet. It is also in the spirit of the invention if the force-applying device has an electromagnet as well as a permanent magnet. In all of the above-described embodiments, a force supporting the valve spring is advantageously exerted on the valve actuator by means of the additional force device in order to hold the valve actuator in its open position so that the valve does not close unintentionally.
In the case of a merely active additional force device, the actuator of the switching valve thus only has to act against the force of the valve spring, which can be dimensioned smaller due to the switchable additional force device, so that the switching valve closes reliably and tightness is ensured by a high pressure force.
In the case of a purely passive additional force device, the actual actuator of the switching valve only has to apply an increased force at the start of the stroke movement from the open to the closed position in order to overcome the passive and thus permanently acting additional force. As the air gap becomes increasingly larger, the force of the passive additional force device will quickly decrease and have less of an effect in the closed position of the valve.
This is because the switching valve is the safety gate for the brake circuits BK to the wheel brake cylinder RZ. If one of the four hydraulic connections from the hydraulic control unit to a wheel brake cylinder fails in the brake system according to the invention, or if there is a leak in the wheel brake cylinder, the switching valve according to the invention can disconnect the faulty hydraulic connection or the faulty wheel brake cylinder from the rest of the brake system with a high degree of safety.
The additional force device only needs to be switched on or act when a rapid reduction in pressure is required. In all other operating states of the braking system, the additional holding or supporting force of the power boosting device is not required, so that energy can be saved to advantage. Thus, in the braking system according to the invention, in the event of failure of one wheel circuit, only the braking effect of this one failed wheel circuit is lost, while the braking effect of the remaining three wheel circuits continues to be available. This means that the braking effect is only reduced from four to three intact wheel circuits, so that in the event of the failure of one wheel circuit on the front axle, there is only a loss of braking effect of approx. 35%, as opposed to 70%, as described above for a black/white brake circuit distribution, if one entire brake circuit and therefore two wheel circuits always fail.
The possible embodiments of the switching valve described above may, but need not, be used in the braking system according to the invention.
It is therefore quite possible that only the isolating valves described need to be used in braking systems.
The braking system according to the invention generally has four wheel circuits, in which either two wheel circuits are assigned to each braking circuit or three wheel circuits are assigned to a first braking circuit and a fourth wheel circuit forms a separate braking circuit. If one wheel circuit fails, the three remaining wheel circuits are advantageously still available for the braking effect.
The functional reliability of the brake system according to the invention can be additionally increased in the case of dirt particles in the brake fluid by installing at least one filter with a small mesh size at the inlet and/or outlet of the valve. The mesh size should be selected so small that these small dirt particles generate only small leaks and thus only small flow rates when the switching valve is closed, which can be compensated by the pressure supply, but which can be detected by the diagnostics both via the delivery rate of the pressure supply and via the level in the reservoir.
In order to check the function of the switching valve according to the invention, for example, a measurement of the volume absorption and the time curve of the pressure in the respective wheel circuit and a comparison with the previously determined pressure-volume characteristic curve of the wheel circuit can be carried out during diagnosis. The diagnosis can be carried out during each braking operation and/or also at standstill or during servicing.
The preferred switching valve, as described above, does not require a check valve, but still meets a wide range of requirements. For example, it must remain reliably open in both directions even at high flow rates, i.e. the weak point typical of today's valves, i.e. that a force acts on the valve plug and valve spring at high flow rates due to effects on the valve seat and the valve closes automatically, must not occur.
Advantageously, the shift valve can be optimized by appropriate design of the sealing cone, the dimensions of the return spring and the valve tappet, in addition to the force-applying device. In the closed position of the valve, which can also be called an inlet valve but via which the pressure in the wheel brake cylinder can also be relieved, the press-on force should be significantly smaller than when a progressive spring is used, which has a higher force in this position than in the open position, which is unfavorable for the dimensioning of the solenoid circuit due to correspondingly higher force requirements.
The braking system according to the invention can have different valve circuits:
When using an outlet valve for a wheel circuit, it is possible to control the pressure buildup Pauf and pressure reduction Pab individually for each wheel. If a leak occurs in a wheel circuit, a diagnostic circuit can advantageously identify the faulty wheel circuit both during braking and parking and close the switching valve belonging to the wheel circuit, so that in the case of this single fault three wheel circuits continue to be available and in the case of a double fault, i.e. if two wheel circuits fail at the same time, two wheel circuits are available in the “worst case”. With conventional braking systems, on the other hand, a total failure of the brake follows in the “worst case”.
In summary, it can be said that a high safety gain can be achieved by making minor changes to the inlet valve and eliminating the check valve with the switching valve. If the switching valve is designed accordingly, a cost reduction is possible in addition to the safety gain.
The braking system according to the invention can also be designed in such a way that instead of four hydraulic wheel circuits, a mixed hydraulic-electric braking system is provided with, for example, hydraulic lines to the hydraulically operating front-wheel brakes and only electrical connections to the electromotively operating brakes (EMB) on the rear axle, the design of which is known. Here, too, the same advantages result if the hydraulic wheel circuits are designed in accordance with the designs described above.
With the additional use of a circuit isolating valve between the two brake circuits or additional circuit isolating valves between the brake circuit and the pressure supply, even in the event of failure of a wheel circuit, this can be isolated via the circuit isolating valve so that the remaining wheel circuit of the respective brake circuit is still effective. Thus, double fault safety is achieved with a vehicle deceleration of 0.65 g.
In addition to the valve concepts described, different pressure supply concepts are also possible, e.g. a single pressure supply for level 2 of automated driving or two pressure supplies for level 3 to level 5 of automated driving, whereby the second, redundant, pressure supply can contain a piston pump or a rotary pump. The rotary pumps have a significant cost advantage. With the piston pump, a simple check valve can be used at the outlet of the pressure supply instead of the solenoid valve, which has the same advantages in the event of a pressure supply failure and is less expensive. In this braking system, pressure reduction during normal braking can be accomplished by controlling the exhaust valves using the pressure transducer signal from the pressure transducer, rather than by controlling the piston of the pressure supply. Since at least two exhaust valves are used, redundant pressure reduction is also provided. Depending on the requirement of the pressure reduction speed and on the number of outlet valves, one, two or more outlet valves can be opened.
Solenoid valves can be provided to isolate the pressure supply from the brake circuits. However, it is also possible to dispense with such isolation valves if the pressure supply is provided with a drive with redundant winding circuitry, e.g. 2×3 phases and/or redundant control, such that no further valves are provided between the switching valves assigned to the wheel circuits and the pressure supply. To prevent a failure of the braking system, e.g. due to a leaky piston seal or small piston clearance, compensation is provided by subsequent delivery.
Advantageously, the usual vehicle tuning in various areas such as logistics, service and homologation can be omitted for the brake systems described above.
The braking system according to the invention thus has four wheel circuits that are controlled individually. As described above, two wheel circuits can be assigned to each brake circuit. Other allocations to the brake circuits, as described above, are also possible.
However, the 4-wheel circuit braking system can also be controlled by the control system as a 2-circuit braking system. Thus, the 4-wheel circuit braking system can be combined with 2-circuit braking systems with four hydraulically braked wheels and thus even achieves double fault safety, by which is meant that even a leakage of a wheel brake cylinder and the failure of the control of the associated switching valve does not lead to a total failure of the braking system, whereby this double fault occurs with the low failure probability of approx. 10−19/J, which is still significantly better than core force safety. Even with this double failure, the braking system according to the invention would still achieve a braking effect of a conventional 2-circuit braking system.
This means that the braking system can be described as failsafe and fail-safe.
Advantageously, a diagnosis of the respective leakage of the individual wheel circuits is carried out at intervals or permanently, whereby depending on the diagnosis result the electronic control and regulating device of the braking system decides whether a wheel circuit is switched off by permanently closing the associated switching valve or continues to be operated for the generation of a braking effect. When the system continues to operate, the leakage detected is used to calculate and carry out an appropriate additional supply or replenishment of brake fluid so that the required braking effect of the respective wheel brake cylinder is achieved.
In order to move from the known braking systems to the braking system according to the invention, it is only necessary to replace the known inlet valves with check valves by the modified switching valve, whereby almost no additional costs are incurred.
The switching valve has another potential, which is used in the event of failure of the exhaust valve assigned to the respective wheel circuit. If, for example, the control of the exhaust valve fails, ABS pressure reduction via the exhaust valve is no longer possible, i.e. the corresponding wheel locks with a loss of braking distance and lateral stability. However, since the shift valve can be used in both directions for pressure buildup and depressurization, as it is resistant to tightening, it can also be used for depressurization if, for example, the pressure supply can absorb the necessary volume for depressurization. Since the switching valves do not contain a check valve, the pressure reduction in one wheel brake cylinder, e.g. RZ1 via the SV2k1, does not simultaneously reduce the pressure in the other wheel brake cylinders, e.g. wheel brake cylinders RZ2, RZ3 and RZ4 when the valves SV2k2, SV2k3, SV2k4 are closed. Advantageously, this can be realized with volume control of the piston of the pressure supply or also a rotary pump, as described in earlier patent applications. For the ABS control, there is only a small disadvantage due to a small time delay of the pump for volume pickup for pressure release, likewise for volume supply for pressure buildup. This is extremely rare, however, as it only occurs when the exhaust valve fails. However, the locking of a wheel during the ABS function must be avoided at all costs, especially in braking systems for automated driving at level >3.
Thus, the switching valve has multiple functions in the safety-related braking system according to the invention:
For these fault cases, it is appropriate to design the switching valve with redundant coils with connection, since the coil with electrical connection is the failure center.
Various possible embodiments of the braking system according to the invention and the valves used are explained in more detail below with the aid of drawings.
It show:
On the other hand, many influencing factors, such as electrical wire breakage, interference with the electrical connections EA (more than 4 connections) and with the ASIC, can occur. Since the SV2k switching valve is only relevant, for example, in the event of a double fault in the wheel circuit, a redundant design brings an enormous gain in safety, which is of great importance for Level 3 automated driving, e.g. system with electronic brake pedal.
This makes the SV2k switching valve double-fault-proof for various applications. To save installation space, the two coils have only 50% flow (i×n), so only both coils together can switch the maximum pressure load of >200 bar. I.e. in the normal case where the blocking limit is 100 bar, a single coil seems to be sufficient in the rare case of a fault. The valve actuator EM1 generates (see
The hydraulic force on the valve armature FH, which acts when volume flow Q flows through the valve, acts in each case in the open position of the valve. Therefore, the force of the additional force device FM2 should act primarily in this position and, due to the decreasing force of FM2 over the armature movement in the direction of valve closing, it can thus be dimensioned higher in the open position than when using a spring with increasing force FRF during the armature movement in the direction of valve closing.
The valve tappet 7 may also have a special shape that provides the counterforce by hydraulic flow forces and can reduce the tightening force.
The two brake circuits BK1 and BK2 are connected to the wheel brake cylinders RZ1-RZ4 via hydraulic lines HL1-HL4. Likewise, the reservoir is connected to the wheel brake cylinders RZ1-RZ4 via hydraulic lines HL1-HL4. The two brake circuits BK1 and BK2 are connected to the DV via the isolating valves DV/TV, and to the master brake cylinder THZ via the hydraulic line HL5 and the solenoid valves 9 and 9a.
A diagnostic system detects a leak and, if a wheel brake cylinder, e.g. RZ1, leaks, it closes the connection from the wheel brake cylinder, e.g. RZ1, to the corresponding brake circuit, e.g. BK2, via the corresponding solenoid valve SV2k, e.g. SV2k1 (so-called single fault). If a double fault occurs, e.g. additional switching fault SV2k1, the DV/TV valve assigned to the BK, e.g. BK2, closes. The pressure supply DV is driven by an EC motor. The individual functions are described in great detail in the corresponding patent application of
If, on the other hand, a pressure supply with two outputs is used, see
All system concepts considered here are to be assigned to the brake by wire systems, BBW, which have a pedal travel simulator with separating valve coupled to the THZ or SHZ, and belong to the state of the art and are therefore not described.
It is also possible to equip non-BBW systems, e.g. ABS/ESP, by replacing the inlet valve EV with the valve SV2k with 4-circuit function with a corresponding increase in safety.
The different brake circuits are shown here in different states:
This also applies to
Normally, the legislator only requires safety for single faults for braking requirements. These systems with redundant DP are at least safe against double faults, and in some cases even against triple faults, for the faults considered here. This is achieved in
If the pressure supply DV1 fails, the pressure supply DV2 is switched on via valve DV/TV (single fault safety). In the case of pressure supply DV1 with ECE motor and 2×3-phase winding and low failure probability of the ECE motor, almost double fault safety of pressure supply DV1 can be achieved here.
In case of failure of the pressure supply DV1 (4th fault), the redundant pressure supply DV2 with two electric motors and two pumps is switched on. Cost-effective brush motors are sufficient here. Thus, safety is achieved with the DV2 in the event of a quadruple fault.
The fault may be due to a leak in valve 9 (e.g.
Normally, when the driver applies the brakes, valve 9 is closed and the pressures in wheel brake cylinders RZ1-RZ4 are set to target pressures derived from the brake pedal travel using pressure supply DV. During braking by the driver (no recuperation, or the brake pressure in brake circuit BK2 is greater than the pressure in the master brake cylinder SHZ or THZ), brake fluid flows from brake circuit BK2 via the leaking valve 9 into the master brake cylinder SHZ or THZ as a result of the fault, pressing the brake pedal back, increasing the brake pedal force or the pressure in the master brake cylinder SHZ or THZ and reducing the brake pedal travel.
In an intact brake system, each brake pedal travel involves a defined pedal force or pressure in the master brake cylinder SHZ or THZ, which determines the pedal characteristic, and which is determined by the design of the travel simulator WS (see
In the following, the process after detection of the fault is described as an example using a DG-SHZ pressure sensor, which can measure the pressure in the SHZ master brake cylinder. The fault is detected by permanently comparing the actual pressure in the master brake cylinder SHZ, which is measured by the pressure sensor DG-SHZ, with the target pressure in the master brake cylinder SHZ, which is determined on the basis of the pedal characteristics and the measured brake pedal travel. In the fallback level, when the difference between the actual pressure measured and the target pressure exceeds a selectable upper limit, e.g. 1 bar, the pressure supply DV is stopped, and the valves SV2k1-SV2k4 to the wheel brake cylinders RZ1-RZ4 are closed. The control of valve 9 is switched off and the pressure in the pressure supply DV is reduced via the control of the pressure supply
DV. As a result, brake fluid flows from the master brake cylinder SHZ, through the open connection from the master brake cylinder SHZ to the brake circuit BK2, into the brake circuit BK2 and through the valve DV/TV into the pressure supply DV. When the difference between the actual pressure and the set pressure in the master brake cylinder SHZ falls below a selectable lower limit value, e.g. −1 bar, valve 9 is activated again, the switching valves SV2k1-SV2k4 to the wheel cylinders RZ1-RZ4 are opened again and the pressures in the wheel cylinders RZ1-RZ4 are set to the set pressures again with the pressure supply DV. As a result of the error, the actual pressure in the SHZ master brake cylinder is increased again, as already described, and the brake pedal travel is reduced again. If the difference between the actual pressure and the set pressure in the master brake cylinder
SHZ again exceeds the selectable upper limit value, then the switching valves SV2k1-SV2k4 to the wheel cylinders RZ1-RZ4 are closed, valve 9 in the brake circuit is opened, and the pressure in the master brake cylinder SHZ is reduced via the pressure supply DV, thus repeating the process. As a result, brake pedal feel remains largely normal. However, slight brake pedal vibrations may occur.
The error is also detected here by permanent comparison of the actual pressure with the set pressure in the master brake cylinder SHZ. In the fallback level, if the difference between the actual pressure and the set pressure falls below the selectable lower limit value, the pressure supply DV is stopped and the valves SV2k1-SV2k4 to the wheel brake cylinders RZ1-RZ4 are closed. The control of valve 9 is switched off and the pressure in pressure supply DV is increased via the control of pressure supply DV. As a result, brake fluid flows from the pressure supply DV, through the valve DV/TV into the brake circuit BK2, and through the opened connection from the brake circuit BK2 into the master brake cylinder SHZ. When the difference between the actual pressure and the set pressure in the master brake cylinder SHZ exceeds the selectable upper limit value, the pressure supply is stopped, valve 9 is activated again, the switching valves SV2k1-SV2k4 to the wheel cylinders RZ1-RZ4 are opened again and the pressures in the wheel cylinders RZ1-RZ4 are set to set pressures again with the pressure supply DV. As a result of the error, the actual pressure in the SHZ master brake cylinder is reduced again, as already described, and the brake pedal travel is increased again. If the difference between the actual pressure and the set pressure in the master brake cylinder SHZ again falls below the selectable lower limit value, then the switching valves SV2k1-SV2k4 to the wheel cylinders RZ1-RZ4 are closed, valve 9 in the brake circuit is opened, and the pressure in the master brake cylinder SHZ is increased via the pressure supply DV, thus repeating the process. As a result, brake pedal feel remains largely normal. However, slight brake pedal vibrations may occur.
A leak in the SHZ master brake cylinder or in the WS travel simulator leads to a failure of the actuation unit (combination of SHZ master brake cylinder and WS travel simulator). When the driver applies the brakes, brake fluid flows out of the SHZ master cylinder through the leak in the actuation unit due to the fault, causing the brake pedal to move forward, reducing the brake pedal force or the brake pressure in the SHZ master cylinder and increasing the brake pedal travel. Therefore, the faulty operation of the actuation unit is similar to that described in
Overview of the electrical valve circuit
Number | Date | Country | Kind |
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20 2021 105 880.3 | Apr 2021 | DE | national |
20 2021 105 878.1 | Sep 2021 | DE | national |
10 2022 102 036.3 | Jan 2022 | DE | national |
This application is a Section 371 of International Application No. PCT/EP2022/059069, filed Apr. 6, 2022, which was published in the German language on Oct. 13, 2022 under International Publication No. WO 2022/214521 A1, which claims priority under 35 U.S.C. § 119(b) to German Patent Application No. 20 2021 105 880.3, filed Apr. 7, 2021, German Patent Application No. 20 2021 105 878.1, filed Sep. 9, 2021, and German Patent Application No. 10 2022 102 036.3, filed Jan. 28, 2022, the disclosures of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2022/059069 | 4/6/2022 | WO |