SE509168C2 - Procedure for axle load dependent braking force distribution in a braking system in a vehicle - Google Patents

Abstract

The method involves using sensors (1,2,10,11) for detecting the rotational speed of the vehicle axles. The sensors emit a first rotational speed signal (V1) assigned to the first vehicle axle, and a second rotational speed signal (V2) assigned to the second axle. Brakes (3-6,12-15) are provided for decelerating the vehicle axles, which can be actuated depending on a first and second brake requirement signal (P1,P2). The method further involves using first and second coordination mechanisms (20,21) for generating the first and second brake signals (P1,P2). An auxiliary signal (M2) is provided as the second input signal for the second coordination mechanism (21), which is determined on the base of the first and second rotational speed signals (V1,V2).

Description

10 15 20 25 30 40 509 168 2 roadway and cornering. In the case of vehicles with more than two axles, the known method cannot be used other than if the vehicle is equipped with additional axle load sensors.

Against this background, the object of the invention is to develop a shaft load dependence distribution of braking force in the braking system of a vehicle intended for use, as in use of a single axle load sensor independent of the static axle loads enables an axle load dependent distribution of braking force on any number of axles in a vehicle in such a way that the vehicle can be braked to the maximum while maintaining stable behavior while driving.

The object is fulfilled in the case of the procedure with the invention stated in claim 1.

Preferred embodiments of the method are set out in the appended dependent claims. vein.

In the following, a distinction is made between the speed of the vehicle and the rotational speed of the individual axles or wheels of the vehicle. The speed of rotation may differ from the speed of the vehicle. hot, for example by spinning the vehicle's driving axle or due to locked wheels.

By rotational speed signal for a vehicle axle is meant in the following a signal which emitted by one or fl your sensing devices (sensors).

If the vehicle has a single sensor per axle, the sensor is usually arranged so that it knows the arithmetic mean of the rotational speeds of the individual wheels on respective shaft. In the case of the rear axle of a vehicle, the sensor is then placed, for example, at the output from the gearbox, ie. before the differential gear.

If an axle in a vehicle is equipped with several sensors, for example a pulse speed sensor at each wheel, hereinafter referred to by rotational speed signal as one of the rotational speed the signals for the individual wheels formed combined signal. The individual signals are transmitted together to the rotational speed signal of the wheel axle by arithmetic mean formation. The sensors can, for example, be formed in a known manner by electromagnetic pulse rotations. voice transmitters. These interact with gears that follow the rotation of the vehicle wheels and can be attached to any part of the vehicle's wheel suspension or to a braking device.

What has been said above also applies by analogy to the axle load signal, which represents it instantaneous axle load on an axle in the vehicle. The shaft load signal is formed by additional sensors.

It can be formed by a single sensor, which senses the shoulder load and is preferably arranged at the center of the shoulder. It can also be formed by separate wheel load sensors, which are arranged at the wheels on the axle. When using your wheel load sensors, the axle load signal is preferably as the arithmetic mean of the individual signals.

The invention has the advantage that the existing components of the vehicle's braking system can be used to determine the braking forces for the individual axles of the vehicle. It be- thus no extra components are needed, especially no extra axle load sensor. By using the combination of combining devices, which emit output signals in the form of input signals of brake command signals, which are applied to brake devices to provide brake forces on the vehicle axles, a signal generation and signal processing method is obtained which is much easy to adapt to different vehicle types.

By adding one of the signals to at least one combiner instead of the signal from an auxiliary axle load sensor is an auxiliary signal which is determined by means of the speed signals from the vehicle axles, the significant sensors can be used in a a simple and efficient way. Furthermore, in practice it can be very inaccurate and complicated 10 15 20 25 30 35 40 3 ii 509 168 the determination of the static shaft load is avoided by using the auxiliary signal. Therefore the invention can also be used in cases where short-term large variations occur in it static axle load, for example if the load of the vehicle is shifted due to an emergency braking.

According to a first preferred embodiment of the invention, the auxiliary signal is determined as a difference value AX between at least a first and a second rotational speed signal through subtraction. According to the simplest embodiment, the first rotational speed signal is subtracted. from the second rotational speed signal. It is also possible to form the difference AX from signals obtained from the rotational speed signals by signal processing, to example filtering.

According to a preferred embodiment, the combining devices contain curve fields, which controls the combination of the input signals of the device into an output signal. The curve fields are preferred suitably adapted to the physical conditions of the associated vehicle axle on such way that the brake command signal generated as the output signal leads to the actual value of the the deceleration of the net at least approximately corresponds to the setpoint deceleration requested by the driver Z.

No other input signals are needed for this, for example one of the rotational speed signals determined actual value for the deceleration. As a result, both towing vehicles and trailers can be braked according to the ECE-13 series 9 directive using the braking systems of commercial vehicles. An appropriate method for determining the curve fields is described in, for example, DE-A-4 142 670.

One way of determining the auxiliary signal from the difference value AX is to honest system calculate an integral of the difference value and in a time-discrete system sum the individual difference values.

According to a preferred embodiment of the invention, the auxiliary signal changes automatically as soon as the difference value AX leaves an interval whose upper limit is determined by a first limit value and whose lower limit is determined by a second limit value. Otherwise, the help signal is kept constant. This avoids erroneous reactions when determining the auxiliary signal, to examples of disturbances in the rotational speed signals. The automatic increase in the signal when the first limit value is exceeded and the automatic decrease when it the second limit value can be exceeded according to a suitable mathematical function, preferably however, time-proportional to a fixed gradient.

According to a particularly preferred embodiment of the invention, the auxiliary signal is determined from the difference value AX in such a way that the auxiliary signal corresponds to the instantaneous axle load on the other vehicle axle, which is not equipped with a axle load sensor. Thus, they can the first and second combining devices have an almost identical design. Especially if one microprocessor executing a program is used to perform the procedure according to It will then be possible to design the combining devices as a repeater callable subprogram for the microprocessor, whereby data for the curve fields can be supplied the sub-program axis dependency as parameters. The embodiment further makes it possible to determine the total mass of the vehicle and, if necessary, display it on an indicator device, to example in the vehicle's cab.

In the following, "signal scaling" means a scaling of signals. As signal scaling, especially rotational speed scaling, is hereinafter referred to as the ratio of one of the emitted signal, in particular a rotational speed signal, and the actual physical value, especially for the rotational speed. Factors affecting the scaling of the rotational speed 10 15 20 25 30 40 509 168 4 are, for example, the tire dimensions, the gearbox gear ratio and, when using a pulse speed sensor and a gear as a sensor, the number of teeth.

The invention is particularly advantageous when the signal scaling of the rotational speed signals clays used to determine the difference value AX are equal or almost equal. According to a preferred embodiment of the invention is therefore used in the determination of the difference it AX a signal derived from at least one of the rotational speed signals which has the same signal scaling as the second rotational speed signal used to determine the difference value AX. Such a derived signal can, for example, be generated by one from the ABS system prior art device according to DE-A-4 114 047 for equalizing the effect of the tires.

The additional sensors used to generate the shaft load signal are formed according to a preferred embodiment of the invention of at least one force sensor. Thereby, the axle load the signal is processed easily and directly without conversion. If a single force sensor is used this is placed within the middle part of the vehicle axle to be sensed, and senses thus the weight of the vehicle axle. When using fl your power sensors, these are arranged at the wheels belonging to the axle and determines the weight present at each wheel, i.e. wheel load.

According to a preferred embodiment of the invention, additional sensors are used at least one road sensor, which determines the distance between the vehicle axle and the vehicle chassis.

In this case, chassis means any vehicle part whose distance to the vehicle axle can vary due to the effect of the vehicle's suspension. The instantaneous axle load is then determined from the road sensor signal or signals based on the fi alignment curve for the sensed vehicle axeln. If the invention is used in a vehicle with level control, the sensors as in this cases used to sense the level are advantageously also used in the determination of the axle load. ten. The vehicle then does not need to be equipped with additional components for the axle load determination.

A particularly preferred embodiment, which is particularly suitable for vehicles with pressure medium suspension and / or level control, have as additional sensors at least one pressure sensor, which senses the instantaneous pressure in the pressure medium suspension. This has the advantage that they additional sensors will be very cheap. By a pressure medium suspension or level control is preferably arranged on the rear axle of the vehicle, which carries the greater part of the payload. According to a preferred embodiment of the invention, the rear axle of the vehicle is used as first vehicle axle. Thereby, the sensors that are still needed for the pressure medium suspension can or the level control is also used to determine the axle load signal without the need for ligare components.

A preferred device for carrying out the procedure described above it contains in addition to the sensors already described, which generate rotational speed signals the axle load signal and the load deceleration signal Z, brakes and their associated forming the first and second braking devices together, and a control device.

The brakes can be formed in the usual way by drum or disc brakes, which are operated of each hiring device via a control rod system.

When applying the invention, an applicator device contains a pressure gauge medium-operated brake system, preferably an adjusting cylinder and a valve, which control the pressure the flow of the medium to and from the actuating cylinder. The valve may, for example, be designed to 10 15 20 25 30 35 40 5,509,168 operated with electrical signals. The electrical signals can be applied to the valve from the control device through an electrical wire. If the invention is utilized in an electrical brake system (EBS), it is advisable to provide interface means for the valve. These bodies can convert a brake command signal from the control device into an electrical control signal for the valve. Thereby, the hiring devices can be directly supplied to those who signals formed the brake command signals.

The control device is preferably an electronic unit and provided with a microprocessor. executing a program. Furthermore, the control device has signal receiving means, which converts the rotational speed signals, the setpoint deceleration signal Z and the shaft load signal to calculation values of a first kind and signaling means which converts values of a second kind to control signals, in particular brake command signals, for the hiring devices.

The signal receiving means may, for example, be formed by analog-to-digital converters. interface elements for receiving serial data or schmitt triggers. The signaling the means can be formed, for example, by digital-to-analog converters or switch transistors. In control the device's computing means, in particular a microprocessor, computes from the calculation values of the first kind the calculation values of the second kind.

The invention will now be explained in more detail with reference to one shown in the drawing working examples. In this case, fi g 1 schematically shows the essential parts of the invention a braking system in a vehicle and an associated control device, Fig. 2 is a block diagram of a part of the signal processing means in the control device, and fi g 3 the method according to ñnningen shown as fl fate diagram.

In fi g 1, 2 and 3, the same reference numerals for details and signals are used as correspond to each other.

In fi g 1, the connecting wires between the external mechanical, electrical or electromechanical components 1, 2, 3, 4, 7, 10, 11, 12, 13, 17 with signal names V2R, V2L, P2R, P2L, Z, V1R, V1L, PIR, P1L, P. These are independent of the physical representation of the signals logical signal channels. The direction of the signal i in the signal channels is indicated by arrows.

The signal channels shown in Fig. 1 are also shown in part in Fig. 2 with the same designations. Signal The cells are preferably formed by digital electrical signals. As signal channels are then used electrical wiring, which may, for example, be designed as a serial bus system. In this In this case, the different logic signal channels according to fi g 1 can also be physically represented as one single bus system, to which components 1, 2, 3, 4, 7, 10, 11, 12, 13, 17 are connected.

Fi g 1 shows an electrically controllable braking system (EBS), which as a mechanical component The front axle contains wheel brakes 5, 6 and the rear axle wheel brakes 14, 15. Furthermore, the rear axle of the vehicle fitted with an air spring bellows 16 as suspension and for leveling at varying loads. Compressed air can be supplied to or led away from the air spring bellows 16 through a compressed air system (not shown), which contains, for example, a supply of pressure medium and when the level of the vehicle is to be changed.

The wheel wells 5, 6, 14, 15 are each operated by their respective mounting device 3, 4, 12, 13.

The mounting devices 3, 4, 12, 13 operate the associated wheel brakes 5, 6, 14, 15 via mechanical rod devices. The mounting devices are supplied with brake command lerna PIR, P1L, P2R, P2L. The brake command signal is converted into a control force or 10 15 20 25 30 35 40 509 168 6 an operating override for the wheel brake in that the mounting device preferably has one electronic control device, which processes the brake command signal, a pressure medium connection and a valve connected thereto, which supplies the pressure medium to an actuating cylinder. Thereby the electronic control device controls the valve in such a way that the brake pressure on the wheel brake then corresponds to the brake command signal. The pressure medium connection of the mounting device are connected to a pressure medium system, not shown here, which may, for example, contain a compressor and a compressed air tank.

Furthermore, a rotational speed sensor 1, 2, 10, 11 is provided for each wheel. The same operates with a pole wheel (not shown) arranged on each wheel and supplies a control device 9 signal V1R, VLL, V2R, V2L, which represents the rotational speed of the wheel. The determination of the rotational speed of the vehicle wheels is otherwise described to a sufficient extent in connection with ABS system. Another input signal Z to the control device 9 is generated by a brake value sensor 7, which is mechanically connected to the vehicle's brake pedal 8. When the driver actuates the brake pedal 8, the brake value sensor 7 emits a signal Z, which corresponds to the deceleration of the vehicle requested by the driver.

A further sensor device 17 supplies the control device 9 with a signal P, which corresponds the pressure in the air bellows 16.

The control device 9 performs a number of different control and regulation functions in the vehicle. A functional tion is that on the basis of the deceleration Z requested by the driver and with the use of additional inputs V1R, VlL, V2R, V2L, P control the wheel brakes in such a way by means of of the output signals PIR, P11, P2R, P2L that the vehicle achieves the requested deceleration and maintains a stable behavior during this braking. For this purpose, the control device performs 9 different functions, which interact with each other and are superimposed on each other, to example to prevent locking at low friction values, to minimize wear on the brake pads and providing a axle load dependent distribution of the brake crate between the axles of the vehicle.

These functions are shown symbolically with blocks 9a, 9b, 9c in fi g 1. Each function 9a, 9b, 9c has access to all input signals to the control device to the extent required.

One of the above functions, namely to distribute the braking force on the vehicle axes as a function of the axle load are shown in more detail in fi g 2. In the function 9a according to fi g 2 gives the block 20 for the setpoint signal Z the brake command signal associated with the rear axle P1, from which the brake command signals P11, PIR for the individual rear axle actuator 12, 13 are formed. The combining function in the block 20 is stored therein in the form of a table with several columns. The output signal P1 then corresponds to a table value whose table rows are determined of the input signal Z and whose table columns are determined by the input signal M1. The input signal M1 to the block Is obtained by multiplying the signal P, which corresponds to the pressure in the air spring bellows 16, by a conversion factor K in block 18.

Block 21 generates analogously with block 20 the brake command signal P2 for the vehicle front axle. From the signal P2, the individual brake command signals P2L, P2R are generated for setting devices 3, 4. Block 21 retrieves in the same way as block 20 with lead of the input signals Z and M2 the corresponding output signal P2 from a split table. While the signal M1 taking into account the tolerances of the measurement roughly corresponds to the physical one the axle load on the rear axle, the signal M2 is generated in the blocks 19, 22 from the rotational speed signals from the individual wheels V1L, V1R, V2L, V2R and from the setpoint signal Z. The signal M2 10 15 20 25 30 35 40 7 509 168 therefore corresponds to the physical axle load signal for the front axle only during certain conditions. In doing so, the following conditions must be met: - I. The combination tables in blocks 20, 21 must allow a physically correct connection between added and given values.

- II. The signal M1 must correspond to the physically correct axle load on the rear axle.

- III. No other functions, which affect the determination of the brake command signals P1, P2, for example the ABS function 9b or the wear optimization function 9c, may be ma in the control device or be superimposed on the function 9a.

If the above conditions are met, which is normally the case when braking with high deceleration on a road surface with a high friction value, is generated in block 19 as a function of the input signals V1, V2, Z the output signal M2 as a physically correct axle load signal for the vehicle front axle.

Block 19 is preceded by a block 22 for converting the rotational speed signals V1L, VIR, V2L, V2R from the individual wheels to rotational speed signals V1, V2 for vehicle axles lama. The transformation takes place axially by forming the arithmetic mean value for those to an axis hearing the rotational speed signals. Use a single sensor for a vehicle axle the described conversion of the rotational speeds of this axis is omitted.

The operating steps to be performed in block 19 for processing the input signals and generate the output signal is shown in fi g 3 as a fl diagram. The sequence begins with block 23.

A branch block 24 asks if there is a braking request from the driver or if the vehicle is being braked. If no braking is in progress (Z = 0) is calculated the scaling factor S in a calculation block 27 for which the ratio between the rotational speeds rear axle V1 and front axle V2. In this case, the sequence ends with block 34.

On the other hand, if the vehicle is braked (Z in 0), the sequence from the branch block 24 goes on calculation block 25. In this a corrected rotational speed signal VZKORR is formed for the front axle as the product of the scaling factor S and the rotational speed signal of the front axle V2. Using the conjugated rotational speed signal VZKORR prevents this errors occur in the process due to different rotational speed scaling between the front axle and rear axle, for example due to different tire dimensions. In the following calculation, therefore, the difference signal AX is calculated from the difference between the corrected one the rotational speed signal VZKORR and the rotational speed signal V1 of the rear axle.

In the branch blocks 28, 29 it is examined whether the difference signal AX is above an upper one limit value AXMAX or below a lower limit value AXMIN. About the upper limit AXMAX is exceeded, the sequence continues with branch branch 30. If the lower limit if AXMIN is undershot, the sequence continues with branch branch 31. Otherwise, it ends the sequence with block 34.

The upper limit value AXMAX and the lower limit value AXMIN are vehicle specific and can be determined, for example, by testing. Suitable values are, for example, AXMIN = 0.4 km / h and AXMAX = 0.4 km / h.

In the branch block 30 it is examined whether the signal M2 has already exceeded the associated one the limit value M2MAX. Also in this case, the sequence ends with block 34. Otherwise, the sequence is branched to the calculation block 33, in which the signal M2 is raised by one step AM. Where- after, the sequence ends with block 34.

Claims (13)

10 15 20 25 30 35 40 509 168 8 If the sequence is due to the lower limit value AXMIN being branched off from block 29 to the branch block 31, it is examined in this if the signal M2 has already fallen below the associated lower limit value M2MIN. If so, the sequence ends with block 34. Otherwise, the signal M2 is reduced by step AM in calculation block 32, after which the procedure ends with block 34. The upper limit value M2MAX and the lower limit value M2MIN depend on the vehicle type. Suitable practical limit values may, for example, be the maximum permissible axle load for M2MAX and the unladen axle load according to the vehicle's M2MIN registration certificate. The step AM may also be determined by testing. A suitable value when performing the sequence according to fi g 3 with a time interval of 5 ms is AM = 10 kg. The steps in calculation blocks 32 and 33 can also have different values for AM1 and AM2. Before the sequence according to fi g 3 is performed for the first time, the signal M2 is set to an initial value. The lower limit value M2MIN is preferably used as the initial value. The setting of the initial value is not shown in fi g 3, but is preferably made immediately after switching on the control device 9. Patent claim A method of axle load-dependent braking force distribution in a braking system of a vehicle, having the following features: - a) the vehicle has at least a first and a second wheel axle, - b) the rotational speeds of the wheel axles are sensed by sensors (1, 2, 10, 11), emitting a rotational speed signal (V1) associated with the first wheel axle and a rotational speed signal associated with the second wheel axle (V2), - c) the wheel axles are braked by means of braking devices (3, 4, 5, 6, 12, 13, 14, 15) , which is operated as a function of a first brake command signal (P1) belonging to the first wheel axle and a second brake command signal (P2) belonging to the second wheel axle, - d) the first brake command signal (P1) is generated by a first combining device (20) and the second brake command signal (P2) is generated by a second combining device (21), - e) each combining device (20, 21) determines the respective output brake command signal based on a first and at least a second input signal, - f ) as the first input signal to the first and the second combining device (20, 21) a setpoint deceleration signal (Z) is supplied, which is emitted by a braking value sensor (7) as a function of the driver's brake pedal operation and represents the requested deceleration of the vehicle, - g) which second input signal to the first combining device (20) is supplied with an axle load signal (M1) emitted by additional sensors (17, 18), which represents the instantaneous axle load on the first wheel axle, characterized by the following features: - h) as a second input signal to the second combining device (21) an auxiliary signal (M2) is applied, which is determined on the basis of the first and second rotational speed signals (V1, V2). Method according to claim 1, characterized in that the auxiliary signal (M2) is determined on the basis of a difference value (AX), which is determined from the difference between the second rotational speed signal (V2) or one derived therefrom. signal and the first rotational speed signal (V1) or a signal derived therefrom. Method according to claim 1 or 2, characterized in that the combining devices (20, 21) determine the required brake command signals (P1, P2) for each axle from a curve field belonging to each axle in such a way that the scarring of the vehicle becomes at least approximately equal to that of the driver requested the setpoint deceleration (Z). Method according to Claim 2 or 3, characterized in that the auxiliary signal (M2) is automatically increased if the difference value (AX) exceeds a first limit value (AXMAX), that the auxiliary signal (M2) is automatically reduced if the difference value (AX) falls below a second limit value (AXMIN) and that the auxiliary signal (M2) is otherwise kept constant. Method according to one of the preceding claims, characterized in that the auxiliary signal (M2) represents the instantaneous axle load of the other vehicle axle. Method according to one of Claims 2 to 5, characterized in that at least one of the signals used to determine the difference value (AX) is a signal (VZKORR) derived from at least one of the rotational speed signals (V1, V2). and that the signals (V1, VZKORR) used to determine the difference value (AX) have the same signal scaling, in particular the same rotational speed scaling. Method according to claim 6, characterized in that a correction value (S) is determined from the rotational speed signals (V1, V2) during unbraked travel with the vehicle and that the derived signal (V2KORR) is determined from the correction value (S) and one of the rotational speed signals ( , V2) during braking of the vehicle. Method according to one of the preceding claims, characterized in that the first wheel axle is the rear axle of the vehicle. Method according to one of the preceding claims, characterized in that the further sensors (17, 18) are designed as at least one force sensor. Method according to one of Claims 1 to 8, characterized in that the further sensors (17, 18) are designed as at least one sensor, which senses the distance between the wheel axle and the vehicle chassis and determines the axle load from the sensor signal or signals, and the suspension wheel's suspension curve. Method according to one of Claims 1 to 8, characterized in that the shaft provided with the further sensors (17, 18) has a pressure medium suspension and that the further sensors are designed as at least one pressure sensor (17) which senses the instantaneous the pressure in the pressure medium spring or springs Method according to one of the preceding claims, characterized by the following features: - a) the vehicle has an additional wheel axle, - b) the rotational speed of the additional wheel axle is sensed by means of sensors which emit an additional rotational speed signal associated with the additional wheel axle, - c) the the additional wheel axle is braked by an additional brake device, which is operated on the basis of an additional brake command signal belonging to the additional wheel axle, - d) the additional brake command signal is generated by means of an additional combining device - e) in the additional combining device the output additional brake command signal is determined based on the setpoint deceleration signal (Z) and an additional auxiliary signal, which is determined on the basis of the rotational speed signals from the first and the additional wheel axle. Device for carrying out the method according to one of the preceding claims for axle load-dependent braking force distribution, a braking system in a vehicle, with the following features: - a) the vehicle has at least a first and a second wheel axle, - b) the rotational speeds of the wheel axles are sensed by sensors (1, 2 , 10, 11), which emits a first rotational speed signal (V1) belonging to the first wheel axle and a second rotational speed signal (V2) belonging to the second wheel axle to at least one control device (9), - c) the wheel axles are braked by brakes (5 , 6, 14, 15), which are operated by the control device (9) via at least one first attachment device (3, 4) belonging to the first vehicle axle and at least one second attachment device (12, 13) belonging to the second vehicle axle, - d) a brake value sensor (7), which is activated by the driver operating the brake pedal, supplies the control device (9) with a setpoint deceleration signal (Z), which represents the requested deceleration of the vehicle, - e) a sensor (17) which said acting on the first wheel axle supplies the control device (9) with a signal (P) representing the instantaneous axle load on the first wheel axle, - f) the control device (9) has signal receiving elements which convert the rotational speed signals (V1, V2), the setpoint signal (Z) and the signal (P) representing the instantaneous axle load on the first wheel axle to the first value of the ramming values, - g) the control device (9) has signal emitting means which converts calculation values of a second kind into operating signals for the first and the second mounting device ( 3, 4, 12, 13), - h) the control device (9) contains calculation devices, in particular a microprocessor executing a program, for calculating the calculation values of the second type from the calculation values of the first type.