DE19947757C1 - Automobile braking system with electro-hydraulic braking servo has independent brakes for same wheels and brake pressure modulator controlled by signals from sensor detecting brake pedal operation - Google Patents

Abstract

The automobile braking system has first wheel brakes (VL1,VR1) and second wheel brakes (VL2,VR2), for independent braking of the vehicle front wheels, supplied with the braking pressure via respective independent braking circuits, with a brake pressure modulator (14) controlled by signals from a sensor (6) detecting the brake pedal operation. The wheel brakes are adjusted so that the sum braking force corresponds to the depression of the brake pedal (5).

Description

The invention relates to a power brake system for a driving according to the preamble of claim 1.

DE 198 04 676 A1 describes a method for Avoiding squeaking conditions. That revealed there External braking system has four, one wheel each Wheel brake devices assigned to the vehicle, the contact pressure pressure of the brake pads of the wheel brake devices during a measurement technically recorded squeak condition to eliminate the squeak can be modulated.

Furthermore, a hydraulic brake system is known from US Pat. No. 3,799,300 known, which has a hydraulic brake booster, that for actuating a master brake cylinder by means of a Apply hydraulic auxiliary pressure to the motor / pump unit is cash. This auxiliary pressure is applied when the brake pedal is actuated directly via an output of the brake booster wheel brake devices of the front wheels supplied.

By means of the head Brake cylinders become more when the brake pedal is pressed Brake pressure devices on the front wheels with brake pressure strikes. The over the master brake cylinder or directly over the Brake boosters are applied to wheel brake devices hydraulically connected to each other via a brake circuit the. The braking system is designed such that the Brake pressure is the same in all wheel brake systems.

From DE 43 28 304 A1 a brake system for a  Vehicle known in which by means of a hydraulic pressure the pedal pressure exerted by the driver is measured, the sen Apply the value in a control unit to a pump the control signal is converted, and via the pump in one Brake pressure hydraulic circuit generates a brake pressure that a wheel brake device is supplied, which a brake exerts force on the wheel in question.

In order to avoid that in If the distance between the vehicle and the egg is too short a vehicle in front and / or an excessive difference speed there is a risk of a collision, the Braking system an automatic braking process can be initiated at which, depending on the relative distance, relative speed speed and absolute speed of the vehicle regardless of the brake pedal position exerted by the driver of the situation appropriate brake pressure is generated.

A brake system with hydraulic brake booster is also known from the publication DE 35 26 556 A1. The brake position includes a master cylinder to be operated by the brake pedal the one who communicates with a pedal travel simulator, whereby at actuation of the brake pedal hydraulic fluid from the pressure Chamber of the master cylinder displaced into the pedal travel simulator becomes. An actuating piston is moved in the pedal travel simulator, the pressure or the pressure change in the pedal travel simulator and underlies the control of an electric pump is that a pressure supply system with the required Chen applied brake pressure.

So even if the Power supply enough braking power is available in the event of a malfunction, the brake pressure is generated directly via the master cylinder generated by the pedal pressure exerted by the driver over the Master cylinder is passed directly to the hydraulic system.

In such a brake designed according to the prior art systems, the problem can arise that both with manual  Brake actuation as well as with automatic brake actuation in the area of the wheel brake ei acting on the wheel ne self-excited, quasi-stationary vibration (brake squeal) occurs, which leads to an unpleasant noise and above can also be mechanically transferred to the chassis where can result from loss of comfort. There is also especially with large braking systems, there is a risk that in the long run operation of the brake overheating with decreasing brake effect occurs.

The invention is based on the problem of an external power Brake system for a vehicle with high operational safety and to create high comfort. In particular, disruptive Ge noise and vibrations without impairing the possible braking effect be prevented when the brake is actuated.

This problem is solved according to the invention with the features of the patent Proverb 1 solved.

The novel power brake system has at least on the Ra the vehicle front axle each have a first and a second wheel brake device on. The second wheel brake device is with tels of a brake circuit independent of the first brake circuit strikes, the second wheel brake device basically un depending on the first wheel brake device via sensor signals can be set, resulting in an additional free degree of safety when operating the brake system.

According to the invention of the two wheel brake devices generated braking forces matched in such a way that the sum of the braking forces of both wheel brake devices is the same is like the setpoint corresponding to the brake pedal actuation.

This setting ensures that the resulting Braking force corresponds exactly to the value that the driver  is specified according to the pedal actuation.

At the same time it is possible in the wheel brake devices of different heights train brake forces, whereby defined pressure ranges in the Brake pressure curve can be avoided in which the Ge drive that there is a stationary or quasi-steady state forms and a self-excited vibration arises, the greatest is. The danger of brake squeal or the danger of Transmission of mechanical vibrations is largely reduced graces.

The fact that the first and second wheel brake device a ge apply common wheel of the vehicle, driving dynami influences due to the different levels of braking force te of both wheel brake devices are completely prevented. Since the resulting braking force level remains unchanged, ver the wheel in question keeps in view of the vehicle dynamics mic completely neutral.

In a first advantageous embodiment, both brake force a steady course, whereby the level of Braking forces differs. This spread of braking force can an intermediate print window can be left out at wel chem the risk of vibration in the wheel brake direction is particularly large.

According to a further advantageous embodiment, this changes Braking force level of the first and second wheel brake devices over time, with the braking forces out of phase with each other are, so that in total there is a constant, resulting Braking force results. Due to the changing course over time, which is characterized in particular as a harmonic, sinusoidal vibration steady states are formed, which prerequisite for the generation of undesirable vibrations are avoided. The braking forces of the two wheel brake devices can be used here  both at the same average level, but with each other out of phase, as well as different levels of through Take the cutting level, which in total is the desired one Corresponds to the setpoint. In any case, the deflection is Braking force of the first wheel brake device above or below it middle level out of phase with the braking force curve of the two th wheel brake device in order to sum up a constant setpoint To achieve braking force.

If the average level of the braking forces of the two wheel brakes equipment differs, i.e. a spread before lies at which the braking force level of the first wheel brake device tion below and that of the second wheel brake device is above the setpoint, the distance between the middle Braking force levels of both braking forces depending on predefined boundary conditions can be set.

These include in particular known brake pressure window, in which with unpleasant Ge noise developments can be expected and should therefore be avoided are, but also an increased heat dissipation, by the wheel brake device which has increased braking force is raised to a high temperature level, where due to the large temperature difference to the reverse temperature a disproportionately high heat dissipation in the Comparison to the wheel brake device that sets is at a lower average braking level.

However, it may also be appropriate for targeted purposes Influencing the driving dynamics of the vehicle one of the rest To set different braking force levels on the wheels len. Finally, it is also conceivable, in the event of a change in time brake force curves of the individual wheel brake devices not a phase-shifted wheel, but one at least to specify at least partially in-phase progression, so that the resulting braking force is not constant, but also  takes a time-varying course.

The wheel brake devices can also be used in electronic or me chatronic vehicle systems are integrated, for example in automatic braking systems, which depending on the situation automatic or independent of the brake pedal position trigger partially independent braking, or in anti Blocking systems or the like. By the interaction of the Power brake system according to the invention with additional driving Assistance systems can be an overall concept from the aspect maximum security can be realized.

The power brake system is advantageous as an electric hydraulic braking system designed in which each wheel brake device has a separate hydraulic circuit, wherein the brake pressure in each hydraulic circuit of one to generate electrically operated pump, which is about Control signals, which from the sensor signals to determine the Pedal actuation are derived is set. Such electro-hydraulic brake systems are characterized by high speeds reliability.

Further advantages and practical designs are the others Entities, the description of the figures and the drawings ent to take. Show it:

Fig. 1 is a brake system for a motor vehicle with a total of six independent brake circuits, of which an error occurs, two brake circuits can be actuated,

Fig. 2 shows a braking system for a motor vehicle with a total of eight independent brake circuits, of which two brake circuits are operable in the event error,

Fig. 3, a brake pressure path diagram with a Bremsdruckfen art that marks a pressure area which is from the individual wheel brake to avoid,

Fig. 4 corresponding to Fig. 3 time-dependent braking pressure variation in the individual to a wheel we kenden wheel brake,

Fig gen sinusförmi. 5 is a diagram showing an example of a phase-offset and time-varying braking pressure variation.

The brake system shown in FIG. 1 for a motor vehicle consists of an actuation unit 2 , a hydraulic unit 3 and a wheel brake 4 , the units 2 and 3 and the brake 4 communicating with one another. The Betätigungsein unit 2 includes a brake pedal 5, a pedal travel of the brake pedal 5 receiving pedal travel sensor 6, a acted upon by the brake pedal 5 hydraulic cylinder 7 of the hydraulic from a primary circuit 8 and a secondary hydraulic circuit 9 comprises a brake fluid container 10 with the circles 8 and 9 of the hydraulic cylinder 7 is in communication and a pedal path simulator 11 which is hydraulically connected to the primary circuit 8 .

The hydraulic unit 3 consists of two hydraulic devices 12 , 13 which have the same basic structure. The first hydraulic device 12 has a pressure modulator 14 which, in the exemplary embodiment, comprises an electric motor / pump unit and which is controlled by control signals from the pedal travel sensor 6 and supplies a total of four brake circuits 15 a, b, 16 a, b with brake pressure. Each brake circuit in each case comprises a pressure line, via which the brake fluid can be supplied to the braking device of a wheel. The two brake circuits 15 a and 15 b supply wheel brake devices HL and HR on the wheels of the vehicle rear axle with the brake pressure, the two brake circuits 16 a and 16 b supply wheel brake devices VL1 and VR1 on the wheels of the vehicle front axle with the brake pressure. In the pressure lines of the two brake circuits 16 a, b operable valves 17 , 18 are arranged via electrical actuators via which the brake circuits 16 a, b alternatively can be connected either to the pressure modulator 14 or to pressure lines 22 , 23 , via which Brake pressure from the primary circuit 8 or secondary circuit 9 of the hydraulic cylinder 7 can be transmitted directly to the two wheel brake devices VL1, VR1. The valves 17 , 18 are expediently designed in such a way that a continuous connection to the hydraulic cylinder 7 is established in the de-energized state, so that in the de-energized state a brake pressure can be transmitted to the two brake circuits 16 a, b exclusively by mechanical actuation of the brake pedal 5 , which act on the wheel brake devices on the wheels of the front axle. In the energized state, however, the valves 17 , 18 are switched in such a way that the brake pressure generated in the pressure modulator 14 is transmitted to the brake circuits 16 a, b and the pressure connection to the hydraulic cylinder 7 is interrupted .

The second hydraulic device 13 of the hydraulic unit 3 is constructed comparable to the first hydraulic device 12 . Also in the second hydraulic device 13 , a pressure modulator 14 is provided, which applies two brake circuits 19 a, 19 b with brake pressure, the brake circuits 19 a, b supplying wheel brake devices VL2, VR2 to the wheels of the front axle, which, however, are independent of the Wheel brake devices VL1, VR1 of the brake circuits 16 a, b are formed, which are acted upon by the first hydraulic device 12 with brake pressure. Also in the brake circuits 19 a, b of the second Hydraulikeinrich device 13 electrically operable valves 20 , 21 are provided, via which the brake circuits 19 a, b alternatively either with the pressure modulator 14 or via pressure lines 24 , 25 with the brake circuits 16 a, b of the first hydraulic device 12 are to be connected, the valves 20 , 21 establishing a connection to the first two brake circuits 16 a, b in the de-energized state, in the energized state, however, severing the connection to the brake circuits 16 a, b and a connection with produce the pressure modulator 14 .

The brake system 1 works as follows: when the driver presses the brake pedal 5, the pedal movement is usually measured by the pedal travel sensor 6 and the pressure modulator 14 signals both the first hydraulic device 12 and the second hydraulic device 13 of the hydraulic unit 3 when the brake system is functioning fed. In the pressure modulator 14 of the two hydraulic devices 12 , 13 , according to the transmitted signal value by actuating the electric motor / pump unit of the pressure modulator 14, a pedal pressure assigned to the brake pressure is generated, which circles 15 a, b, 16 a, b in the assigned brake and 19a, b. The valves 17 , 18 and 20 , 21 in the brake circuits 16 a, b and 19a, b are in the energized state in the position shown in FIG. 1, in which the brake circuits 16 a, b, 19a, b directly with Brake pressure of the associated pressure modulators 14 who supplied the. The brake pressure is the hydraulically actuated wheel brake devices HL, HR (brake circuits 15 a, 15 b), VL1, VR2 (brake circuits 16 a, 16 b) of the first hydraulic device 12 and the wheel brake devices VL2, VR2 (brake circuits 19 a, b) second hydraulic device 13 supplied. A braking force for decelerating the vehicle is generated in the wheel brake devices in accordance with the supplied brake pressure.

The brake pedal 5 is coupled to an actuating cylinder 26 , which sets the volume in the primary circuit 8 of the hydraulic cylinder 7 , this volume change also having an effect on a piston located between the primary circuit 8 and the secondary circuit 9 on the secondary circuit 9 . The primary circuit 8 communicates with the pedal travel simulator 11 via the pressure line 22 , so that when the brake pedal 5 is depressed, brake fluid flows from the primary circuit 8 of the hydraulic cylinder 7 via the pressure line 22 into a receiving space of the pedal travel simulator 11 . The receiving space of the pedal travel simulator 11 is spring-loaded, so that an elastic behavior of the brake pedal 5 arises.

The two hydraulic devices 12 , 13 are in an archic relationship to one another here, which guarantees that the braking force can be maintained as far as possible in the event of a fault. The first braking device 12 takes on the superordinate role of a master hydraulic device, the second braking device 13 takes on the subordinate role of a slave hydraulic device.

If the second brake device 13 fails, the valves 20 , 21 in the brake circuits 19 a, b return to their de-energized closed state, in which the brake circuits 19 a, b via the pressure lines 24 , 25 with the two brake circuits 16 a, b ver connected, so that the brake pressure of the brake circuits 16 a, b is also transmitted to the brake circuits 19 a, b and thus it is ensured that the two wheel brake devices on a front wheel VL1, VL2 or VR1, VR2 with sufficient brake pressure be charged.

If the superordinate first hydraulic device 12 fails, the valves 17 , 18 of the brake circuits 16 a, b return to their normally closed state, in which the brake circuits 16 a, b via the pressure lines 22 , 23 with the circuits 8 , 9 of the Hydraulic cylinder 7 communicate, so that the brake circuits 16 a, b are immediately acted upon by the brake pressure generated mechanically via the Bremspe dal 5 . If the case has not also detected the second hydraulic device 13 , the valves 20 , 21 of the brake circuits 19 a, b are further in the open position shown, in which a connection between the pressure modulator 14 of the second hydraulic device 13 and the two brake circuits 19 a, b exists. If only the first hydraulic device 12 fails, the front axle brake circuits of this hydraulic device are mechanically supplied with brake pressure via the brake pedal 5 , the second hydraulic device 13 , on the other hand, is still subjected to brake pressure via the pressure module 14 .

If both hydraulic devices 12 , 13 of the hydraulic unit 3 fail, all the valves 17 , 18 of the first hydraulic unit 12 and the valves 20 , 21 of the second hydraulic unit 13 are in the de-energized closed state. In this case, the brake circuits 19 a, b of the second hydraulic device 13 are connected to the brake circuits 16 a, b of the first hydraulic device 12 and communicate via the brake circuits 16 a, b with the hydraulic cylinder 7 , so that the brake circuits 19 a, b of the second hydraulic device 13 via the pressure lines 24 , 25 in the same way as the brake circuits 16 a, b of the first hydraulic device 12 are mechanically supplied with brake pressure via the brake pedal 5 .

In the brake system 1 shown in Fig. 2, the same construction parts are provided with the same reference numerals as in the embodiment of FIG. 1. Also, the brake system of Fig. 2 has ei ne hydraulic unit 3 with two hydraulic devices 12, 13, but unlike the embodiment of FIG. 1, the second hydraulic device 13, both the two front axle brake circuits 19 a, 19 b and two rear axle Brake circuits 27 a, b are subjected to brake pressure via the assigned pressure modulator 14 . The front axle brake circuits 19 a, b supply the wheel brake devices VL2, VR2 on the wheels of the front axle with brake pressure, the rear axle brake circuit 27 supply additional wheel brake devices HL2, HR2 on the wheels of the rear axle with brake pressure. A total of eight brake circuits 15 a, b, 16 a, b, 19 a, b, 27 a, b are seen in the brake system 1 according to FIG. 2, two wheel brake devices VL1 and VL2, VR1 on each wheel of the vehicle and VR2, HL1 and HL2 as well as HR1 and HR2 act.

The first hydraulic device 12 and the second Hydraulikein device 13 are in an equal ranking, the one devices are constructed in the same way and work fully independently of each other. The front axle brake circuits 16 a, b of the first hydraulic device 12 are supplied in the event of a fault when the valves 17 , 18 are closed via the pressure line 22 with brake pressure generated mechanically via the brake pedal 5 from the primary circuit 8 , whereas the front axle brake circuits 19 a, b second hydraulic device 13 in the event of a fault when the valves 20 , 21 are closed via the pressure line 23 from the brake pressure generated mechanically in the secondary circuit 9 via the brake pedal 5 . In the event of a hydraulic device failure, the functionality of the second hydraulic device remains.

In FIGS. 3 to 5 show different operating modes of two acting on a common wheel wheel braking devices is are provided.

Fig. 3 shows a diagram with the brake pressure p as a function of the pedal travel s, wherein a linear relationship has been assumed in the exemplary embodiment. In order to prevent unpleasant squeaking noises, mechanically noticeable brake vibrations which impair driving comfort and, if necessary, to improve the heat dissipation from the brakes, the brake pressure / pedal travel characteristic curve has a pressure window 28 which identifies a particularly endangered brake pressure range, in which one of the brake probes is more likely the aforementioned unpleasant side effects when braking. To prevent these side effects it is provided that in case that the predefined by the driver pedal s _is a braking pressure corresponding to within the print window 28, corresponding brake pressure _to p value p by superposition of individual brake pressures ₁ wherein s _is the actual pedal stroke and p ₂ of the first and the second brake circuit is reached from the cooperative wheel brake devices. The two Bremsein devices each generate different brake pressures p ₁ and p ₂ , which are each seen separately from the pressure window 28 and, in total _, correspond to the desired brake pressure setpoint p Soll. The brake pressure p _soll can be represented as the arithmetic mean of the brake pressures p ₁ and p ₂ that are actually generated by the two wheel brake devices. The distance of the actually exerted pressure value p ₁ or p ₂ from the area of the pressure window 28 to be avoided may depend on the position of the desired pressure value within the pressure window 28 and additional boundary conditions, in particular with regard to heat dissipation and particularly vibration-sensitive areas.

Fig. 4 shows an example of the time-dependent variation of the brake pressure p shown for a constant braking pressure command value P _desired and for the actual brake pressures p ₁ and p ₂ of the two wheel brake to sammenwirkenden. In the embodiment of Fig. 4, the actual brake pressures p _1, p ₂ of Radbremsein directions constant in time.

In FIG. 5 another example of a time-dependent manner is detected braking pressure variation is of the two actual brake pressures p ₁ and p ₂ of the two wheel brake shown. The level of the brake pressure setpoint p set _{to be set} is achieved by adding the actual brake pressure profiles p ₁ , p ₂ , the actual brake pressure profiles p ₁ , p ₂ not being constant over time, but rather being variable in the exemplary embodiment shown in FIG. 5. In order to achieve a constant result of the brake pressure level p _should , the two actual brake pressure profiles are 180 ° out of phase, but otherwise identical. In the exemplary embodiment according to FIG. 5, both actual brake pressures p ₁ , p _{2 run} sinusoidally and each swing about an intermediate pressure p _{1, m} or p _{2, m} ; Frequency and amplitude are the same at both brake pressures.

It can in principle be any time-dependent curves for the actual brake pressures p ₁ and are given p ₂ as long as the addition of the two brake pressures p _1, p _2, the constant, the aktuel len pedal position corresponding total braking pressure p _{is intended} results.

An advantage of the invention is that the failure of one Wheel brake device by the second wheel brake device, the cooperates with the first wheel brake device, completely can be compensated so that braking force failures and insta difficult driving conditions can be avoided.

When using a split four-piston fixed calliper or Two-piston floating saddle, each with two pistons or one Pistons are assigned to a wheel brake device and each egg Pistons can be applied to a separate brake circuit cher size used, but with different brake pressure ken are applied. This can cause toppling moments be balanced and at the same time lower part costs Realized using the same components as well as comfort advantages become.

The above-described versions relating to the brake pressure apply in a corresponding manner to that of the wheel brake device lines generated braking forces on the wheels of the vehicle be transmitted.

Claims (14)

1. power brake system for a vehicle, in particular brake system with electro-hydraulic brake booster, with a plurality of braking force-generating wheel brake devices that can be controlled by a respective assigned modulator ( 14 ) as a function of signals from a sensor for detecting an actuation of the brake pedal ( 5 ) are characterized by
that a first (VL1; VR1) and a second wheel brake device (VL2; VR2) are provided at least on the wheels of the vehicle front axle, the wheel brake devices being able to be acted upon by brake pressure via an associated brake circuit, and the brake circuits, at least in the case of trouble-free functioning Brake system are fluidically separated,
and that the first (VL1; VR1) and the second wheel brake device (VL2; VR2) can be set such that the sum of the braking force of the first wheel brake device (VL1; VR1) and the braking force of the second wheel brake device (VL2; VR2) corresponds to a desired value corresponding to the actuation of the brake pedal ( 5 ). 2. Brake system according to claim 1, characterized, that the time course of the braking forces of the first and the second wheel brake device is steady.   3. Brake system according to claim 1 or 2, characterized, that the braking forces of the first and second wheel brakes are direction a time-changing and phase-shifted Ver have run. 4. Brake system according to claim 3, characterized, that the braking forces of the first and second wheel brakes are direction has a phase-shifted sinusoidal curve sen. 5. Braking system according to claim 2, characterized, that the braking forces of the first and second wheel brakes are direction have a constant value. 6. Brake system according to one of claims 1 to 5, characterized, that the average distance of the braking forces from the setpoint in Ab of predeterminable boundary conditions is adjustable. 7. Braking system according to claim 6, characterized in that the individual values of the braking forces of the two Radbremsein directions lie outside a predefinable braking force window ( 28 ), in which noise can occur on the wheel brake. 8. Brake system according to claim 6 or 7, characterized, that the mean values of the braking forces of the two wheel brakes are directions is adjustable in such a way that the heat emission is optimized by the wheel brake devices to the environment. 9. Brake system according to one of claims 6 to 8, characterized, that if a wheel brake device fails, the remaining wheel brake device ent to generate braking force speaking is increased. 10. Brake system according to one of claims 1 to 9, characterized in that each rear wheel of two wheel brake devices (HL1, 2; HR1, 2) is acted upon ( Fig. 2). 11. Brake system according to one of claims 1 to 10, characterized, that at least one wheel brake device actuates a hydraulically includes brake circuit, the brake pressure of a steu erable pump can be generated and acts on a brake caliper. 12. Brake system according to claim 11, characterized, that all wheel brake devices acting on a wheel are hydraulically trained.   13. Brake system according to one of claims 1 to 12, characterized in that a manual hydraulic actuation unit ( 2 ) is hen hen, which is to be activated via the brake pedal ( 5 ) in the event of a failure of the power brake system ( 1 ). 14. Brake system according to one of claims 1 to 11 or 13, characterized, that at least one wheel brake device actuates electromechanically is applicable.