Wheel module for a vehicle with an electrically controlled braking system (EBS)

A wheel module for the control of the braking force on a wheel of a vehicle with an electrically controlled braking system (EBS), in which the need for data transfer to other wheel modules, or to a central module, if present, is reduced considerably. All magnitudes required for an ABS regulation of a wheel such as, for example, vehicle reference speed, are calculated directly in the wheel module according to the invention, so that these magnitudes need not be transmitted from a central module via a data bus.

BACKGROUND OF THE INVENTION
 The invention relates to a wheel module for a vehicle with an electrically
 controlled braking system (EBS) for controlling the braking force on at
 least one wheel of the vehicle, and more particularly a wheel module which
 transmits an adjusting signal, computed thereby on the basis of a brake
 value and wheel specific signals transmitted thereto, to an actuator
 installed on the wheel for the adjustment of the braking force.
 A wheel module of this type is disclosed, for example, in EP 0 467 112
 (U.S. Pat. No. 5,255,962, which is incorporated herein by reference).
 The known wheel module comprises part of an electrically controlled braking
 system which, in addition to the wheel modules, includes a central module
 and signal transmission devices, such as, for example, a brake signal
 transmitter. Such wheel module is assigned to a particular wheel of a
 vehicle. A signal representing the rotational speed of the wheel is
 produced by means of a speed sensor assigned to the wheel, and is
 transmitted to the wheel module assigned to the same wheel for evaluation.
 An electronic control system located in the wheel module, and including a
 microprocessor, calculates a speed signal based upon such evaluation, and
 transmits same via a data bus system. Several wheel modules, each of which
 emits a corresponding speed signal, are connected via the data bus system
 to the central module. The central module evaluates the speed signals
 received by the data bus system and, from this, calculates, for example, a
 vehicle reference speed which is required for an anti-lock brake system
 (ABS) regulation. This vehicle reference speed and, if applicable,
 additional calculation results required for an ABS regulation, are then
 sent back by the central module to the wheel modules, which then use the
 data for an ABS regulation on the wheels corresponding thereto.
 Consequently, relatively large amounts of data must be exchanged via the
 data bus system among the modules connected to it.
 It is therefore the object of the present invention to provide a wheel
 module and a braking system in which the need for data transfer is
 reduced.
 SUMMARY OF THE INVENTION
 In accordance with these and other objects of the invention, there is
 provided a wheel module for a vehicle equipped with an electrically
 controlled braking system (EBS) for controlling the braking force on a
 wheel of the vehicle. The wheel module receives a brake value
 representative of a desired target brake value for the wheel and transmits
 an adjusting signal to an actuator which is installed on the wheel for
 adjustment of the braking force. The wheel module includes a main
 regulating channel assigned to the wheel and at least one additional
 regulating channel, and in each of the regulating channels wheel-specific
 computing steps are carried out. A wheel-specific signal of the wheel and
 at least one additional wheel specific signal of an additional wheel is
 transmitted to the wheel module, and the adjusting signal, which is based
 upon the brake value and the wheel-specific signals, is computed in the
 main regulating channel by using computing results of the additional
 regulating channel or channels.
 The invention provides the advantage that the need for data transfer among
 the modules of the braking system is greatly reduced, inasmuch as the
 calculation results required for brake control with ABS regulation are
 derived directly and locally in a wheel module from the input signals for
 calculated results, such as, a vehicle reference speed, slip signals,
 acceleration signals, braking force reduction, stop and/or resumption
 signals, rather than at a central location, i.e. in a central module which
 then transmits the results via the data bus system to the wheel modules.
 Furthermore, since an ABS regulation, in particular, is very time
 sensitive, regulating quality can also be improved, since time delays,
 normally attendant data transmission between the central module and the
 wheel module, are avoided. The wheel module according to the invention
 provides the further advantage that the ABS regulating process can
 continue to be operational, without limitations, even following a failure
 of the central module. Thus, a process referred to as modified individual
 regulation, such as that disclosed, for example, in DE 28 51 107 C2 (U.S.
 Pat. No. 4,313,166, which is incorporated herein by reference), can be
 carried out on a steerable axle, even without a central module to
 attenuate yawing moment changes. Additional regulating principles, which
 are familiar to the skilled artisan, such as, for example, variable axle
 regulation or modified axle regulation, can be applied with or without a
 central module.
 Because the same control program can be provided in every wheel module, the
 invention provides the further advantage that development costs are
 relatively low, since only a single control program need be provided in a
 vehicle, regardless of the number of installed wheel modules.
 In an advantageous further development of the invention, the assignment of
 the wheel of a wheel module is effected by entering a wheel position
 parameter into an electronic control system provided in the wheel module.
 This provides the advantage that identical wheel modules can be produced,
 and, only at a relatively later point in time, for example, at the time of
 their installation in a vehicle, are their functions assigned in detail. A
 wheel assignment is necessary in order to carry out the ABS regulation on,
 for example, a steerable axle of a vehicle, according to a principle, such
 as, for example, a modified individual regulation as mentioned above,
 which is different from one applicable to a non-steerable axle of the
 vehicle and on which, for example, individual regulation is carried out.
 The wheel position parameter can be entered manually, for example, by
 operating a diagnostic device which transmits the appropriate data to the
 wheel modules. In an advantageous further development of the invention, a
 central module is provided in the braking system, and the central module
 assigns the wheel assignment automatically, for example, one time during
 the first installation of the braking system. For this purpose,
 information on the wheel assignment and the braking system are stored in
 the central module.
 In order to carry out certain regulating functions in which the speed of
 several wheels must be available, for example, modified individual
 regulation, it is necessary for certain wheel modules to transmit the
 speed signal calculated by their respectively assigned rotational speed
 sensors via the data bus system. In an advantageous further development of
 the invention, however, not all wheel modules transmit their respective
 speed signal. Rather, only those wheel modules whose speed signals are
 needed in other wheel modules transmit a speed signal. In this manner, the
 need for data transfer is kept at a low level. The electronic control
 system of a wheel module is able to recognize, advantageously through the
 wheel position parameter, whether the speed signal should be transmitted
 through the data bus system or not.
 In an advantageous further development of the invention, wheel modules
 which are installed on a third or additional vehicle axle, i.e. not on a
 steerable or on the driven axle, do not transmit any speed signal via the
 data bus system as a result of the determination of the wheel assignment.
 The brake system can thereby be expanded in a modular manner to a number
 of wheel modules that is, in principle, unlimited, as required by the
 vehicle, without significantly increasing the need for data transfer and
 without requiring special adaptation tasks.
 In accordance with an advantageous embodiment of the invention, a braking
 system is equipped with several wheel modules of the type described above,
 as well as with a central module. These modules are connected to each
 other via one or more data bus systems for the exchange of information
 among each other. The central module in such embodiment preferably serves
 for the execution of central brake control functions which are needed only
 once in the vehicle. In this regard, functions referred to as brake
 management functions are thus preferably assigned to the central module.
 This is understood, for example, to be an axle-load dependent braking
 force distribution function, a braking force distribution function
 promoting uniform wear of the brake linings or regulation of the vehicle
 deceleration. The central module can also carry out additional central
 functions such as, for example, an engine control as part of a drive slip
 regulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring now to the figures, and in particular FIG. 1, the internal
 structure of a wheel module, generally designated by the reference numeral
 1, is schematically depicted. For the sake of greater clarity, depiction
 of the various control elements comprising an electronic control system
 installed in the wheel module 1 is restricted to a microcomputer 28, a
 non-volatile memory device 23 and an output amplifier 35. Other additional
 control elements, such as level adapters, analog/digital converters,
 drivers, etc., which are normally provided in practice and which are
 therefore known to the person skilled in the art, are not shown in any
 detail.
 The microcomputer 28, which is advantageously a 16-bit microcomputer, such
 as, for example, a Motorola model 68010, is supplied with operating
 current via an electric cable 24. The microcomputer 28 is connected via a
 data bus system 7 to additional wheel modules and, if applicable, also to
 a central module. A CAN data bus is advantageously used as the data bus
 system 7.
 When necessary, the microcomputer 28 emits an adjusting signal via an
 output amplifier 35 to a valve arrangement 29. The valve arrangement 29 is
 provided in the form of a 3/3 way valve. A supply pressure P.sub.B, which
 the valve arrangement 29 receives via a pressure medium channel 25, can be
 put through thereby, on the output side thereof, as a function of the
 adjusting signal, to a brake cylinder 30 connected to the wheel module 1
 and serving for the mechanical actuation of a wheel brake connected to a
 wheel 31.
 In the case of different adjusting signals, the braking pressure in the
 brake cylinder 30 can be reduced or held to an existing value by operation
 of the valve arrangement 29. In the two latter instances, the brake
 cylinder 30 is not connected to the supply pressure P.sub.B. The braking
 pressure, which is present in the brake cylinder 30 and which represents
 the actual braking force, is converted, by means of a pressure sensor 33,
 into an electric signal which is transmitted to the microcomputer 28.
 In addition, a signal produced by means of a rotational speed sensor 32 is
 transmitted to the microcomputer 28 for evaluation via an electric cable
 34. The rotational speed sensor 32 is preferably an
 electromagnetically-acting rotational speed indicator which interacts with
 a pole wheel provided with a plurality of teeth, which is not shown in
 FIG. 1. The signal produced as a result of the rotation of the pole wheel
 comprises a sequence of voltage impulses, the time interval between which
 represents a measure of the rotational speed of the wheel 31. The
 microcomputer 28 computes a speed signal from the time intervals, while
 utilizing additional information which is stored in the wheel module, such
 as, for example, the circumference of the wheel 31.
 Signals of additional sensors, for example, a brake lining wear sensor, are
 transmitted to the microcomputer 28 via an electrical cable 22. The
 microcomputer 28 is furthermore able to read data from a non-volatile
 memory device 23, for example, an EEPROM, via the cable 22, or write data
 into same. Information, such as, for example, the wheel position parameter
 and the circumference of the wheel 31, can be stored in the memory device
 23.
 The microcomputer 28 receives a brake value from the data bus system 7,
 which indicates the target braking force to be imposed on the wheel 31.
 The brake value is transmitted either directly by a brake signal
 transmitter connected to the brake pedal, or by a central module connected
 to the brake signal transmitter. The wheel module is responsible for
 converting this brake value into a corresponding braking force, or a
 braking pressure in the brake cylinder 30, so that the vehicle is braked
 as indicated by the brake pedal actuation.
 In the event that an initiation of a locking of the wheel 31 is detected,
 the braking pressure is reduced in a known manner, in variance from the
 brake value which would normally be set within the framework of an ABS
 regulating process, or is modulated through continuous adaptation in such
 manner that the slip of the wheel 31 is adjusted to a constant value of
 approximately 20%, through evaluation of the signal supplied by the
 rotational speed sensor 32. Within the framework of the ABS regulating
 process, additional speed signals of other wheel modules, in addition to
 the speed signal produced by the rotational speed sensor 32, are taken
 into account in the microcomputer 28.
 The wheel module 1 can also be integrated structurally into the brake
 cylinder 30, resulting in a very compact structure and simplified
 assembly.
 In another advantageous embodiment, several brake cylinders which are
 assigned to the wheels of a wheel or axle group of the vehicle, and which
 should be subjected to the same braking pressure, can be connected to the
 wheel module instead of just one brake cylinder. In such instance, the
 wheel module would be adapted for connection with one or several
 additional rotational speed sensors which would serve to sense the
 rotational speed of the other wheels of the wheel or axle group.
 Turning now to FIG. 2, a sequence of individual program steps of an ABS
 regulating process, executed in the microcomputer 28, is shown as an
 example. The ABS regulating process consists in principle of identical
 program steps 101, 102, 103, 104, 105, 201, 202, 203, 204, 205, 301, 302,
 303, 304, 305, 401, 402, 403, 404, 405, associated with the respective
 wheels, and also, of common program steps 10, 11 applicable to several or
 all wheels. The identical program steps associated with the wheels are
 also referred to as regulating channels.
 In the example of FIG. 2, four regulating channels are represented.
 Regulating channel 1 consists of the program steps 101, 102, 103, 104,
 105, regulating channel 2 consists of the program steps 201, 202, 203,
 204, 205, regulating channel 3 consists of the program steps 301, 302,
 303, 304, 305 and regulating channel 4 consists of the program steps 40,
 402, 403, 404, 405. Depending upon the application, it is also possible to
 provide a different number of regulating channels, for example, two or
 three regulating channels.
 Each regulating channel is provided, in principle, for the processing of an
 input signal of a rotational speed sensor and for emitting an adjusting
 signal for a valve arrangement. The ABS regulating process represented in
 FIG. 2 could therefore be used in a suitable control device for the ABS
 regulation of four wheels of a vehicle, thereby operating in the manner of
 a four-channel ABS system.
 In contrast with a four-channel ABS, the electronic control system provided
 in the wheel module 1 is adapted for connection with only one rotational
 speed sensor 32 and one valve arrangement 29. For this reason, the signal
 of the rotational speed sensor 32 is transmitted for evaluation to only
 one of the regulating channels, which shall be referred to hereinafter as
 the main regulating channel. The other regulating channels, hereinafter
 referred to as additional regulating channels, obtain their speed
 information from the data bus system 7. A logical switch 106, 206, 306,
 406, which can be adjusted by means of programming of the wheel module
 within the framework of wheel assignment, is provided in each regulating
 channel for the selection of the data source for speed information.
 In the same manner, a logical selection switch 12 is provided for the
 transmission of the adjusting signals computed by the four regulating
 channels, the selection switch 12 being programmable in the same manner,
 and preferably programmed in such manner that the adjusting signal is
 transmitted by the main regulating channel to the valve arrangement 29.
 In the example of FIG. 2, the regulating channel 1 is defined, per wheel
 assignment of the wheel module, as the main regulating channel. The
 regulating channel 1 is provided for an ABS regulation of a wheel located
 on a steerable front axle of a vehicle, as is the regulating channel 2.
 Several program steps of an ABS regulation, which are known in detail to a
 person schooled in the art, are executed between the input of the speed
 signals into the regulating channels and the output of the adjusting
 signal. Examples of the program steps, as shown, are:
 Calculation of the speed signal 101, 201, 301, 401,
 Calculation of wheel reference speed 102, 202, 302, 402,
 Calculation of vehicle reference speed 10,
 Calculation of wheel slip 103, 203, 303, 403,
 Calculation of deceleration/acceleration 104, 204, 304, 404,
 Modified individual regulation 11, and
 Calculation of adjusting signal 105, 205, 305, 405.
 The program steps 101, 201, 301, 401 are provided for a conversion of the
 signals emitted by the rotational speed sensor 32, for example, the
 sequence of impulses with variable time interval, into the speed signal
 which can be processed by the subsequent program steps. In the example of
 the present embodiment, the signal of the rotational speed sensor 32 is
 processed in program step 101. The regulating channels 2, 3 and 4 receive
 their speed information from the data bus system 7, as mentioned above. In
 addition to being used in the regulating channel 1, the speed signal
 computed in the program step 101 is furthermore emitted on the data bus
 system 7 (not shown). As seen in FIG. 2, wheel-specific reference speed
 for each regulating channel is calculated (program steps 102, 202, 302,
 402), referred to as the wheel reference speed. In a subsequent common
 program step 10, a common vehicle reference speed is computed as a first
 intermediate result of the computation from all the previously calculated
 wheel reference speeds.
 With the help of the common vehicle reference speed, a wheel slip for each
 wheel is then calculated in each regulating channel (program steps 103,
 203, 303, 403). In addition, the momentary deceleration or acceleration is
 also calculated for each wheel in each regulating channel (program steps
 104, 204, 304, 404).
 In a following program step 11, an additional intermediate result is
 calculated for the regulating channels 1 and 2, such intermediate result
 causing an attenuation of the yawing moment on the front axle upon the
 final calculation of the adjusting signal for the valve arrangement, in a
 manner in accordance with the previously mentioned modified individual
 regulation.
 By using this additional intermediate result, a respective adjusting signal
 is then calculated in the individual regulating channels 1 and 2.
 An individual regulation is carried out for the regulating channels 3 and 4
 assign to the rear wheels of a vehicle in the example of the embodiment of
 FIG. 2, i.e. no intermediate result is calculated for a modified
 individual adjustment. For this reason, a respective adjusting signal is
 calculated without calculating additional intermediate results in the
 regulating channels 3 and 4.
 If, for example, a variable axle regulation were to be applied to the rear
 wheels, a program step common to the regulating channels 3 and 4, and
 similar to the program step 11, would be provided between the program
 steps 304, 404 and 305, 405, in which computation steps would then be
 executed for the previously-mentioned variable axle regulation.
 In accordance with the above-described program structure, the main
 regulating channel which ultimately produces the adjusting signal for the
 valve arrangement 29 is supplied with an especially frequently updated and
 therefore very recent speed information due to the direct tie to the
 signal from the rotational speed sensor 32 assigned to the wheel module.
 The additional regulating channels receive their speed information from
 the data bus system 7, as a rule, with a lower updating frequency. As a
 result, regulation of a high quality can be achieved on the wheel with
 dynamic processes, especially with regard to the ABS regulation.
 In accordance with the embodiment described with reference to FIG. 2, the
 wheel position parameter comprises information on the setting of the
 logical switch 106, 206, 306, 406, 12. The number of the main regulating
 channel can, for example, also be used as a wheel position parameter, i.e.
 in the present example, the wheel position parameter would then have to be
 set to value 1. The adjustment of the logical switch 106, 206, 306, 406,
 12 would then be derived by the microcomputer 28 from this value.
 Instead of the above-described program structure with four regulating
 channels, a different number of regulating channels could also be used.
 Referring now to FIG. 3, an arrangement of wheel modules 1, 2, 3, 4, 5, 6
 and a central module 8 which serves to control the braking system of a
 three-axle vehicle, for example, with a front axle and two rear axles, is
 depicted. The wheel modules 1, 2, 3, 4, 5, 6 are connected among each
 other, and to the central module 8, via the data bus system 7. All the
 wheel modules 1, 2, 3, 4, 5, 6 are of the same type, i.e. they include the
 structure as described in FIG. 1, and the program structure according to
 FIG. 2. The central module 8 is connected to a brake signal transmitter 9
 which emits a signal representing the brake actuation carried out by the
 driver. This signal is processed in the central module 8. The processing
 result is transmitted via the data bus system 7 to the wheel modules 1, 2,
 3, 4, 5, 6 as a target brake value. Among other things, the central module
 executes central, vehicle-wide brake control functions during this
 processing such as, for example, axle load-dependent braking force
 distribution. For this purpose, the signals of additional sensors, for
 example, information from the wheel modules, are available to the central
 module 8 (not shown).
 The central module 8 preferably transmits information concerning the wheel
 assignment of a wheel module to each of the wheel modules during a
 first-time start-up of the braking system or of the vehicle. This
 information is then stored in a wheel module in the non-volatile memory
 device 23 and, from then on, is constantly available.
 The central module 8 and the brake signal transmitter 9 can also be
 combined in one component.
 As mentioned previously, it is also possible to carry out electrical
 control of the braking system without using the central module 8, by using
 only wheel modules 1, 2, 3, 4, 5, 6. In such case, the brake signal
 transmitter 9 would be connected directly to the data bus system 7 via a
 suitable interface arrangement. The brake value emitted by the brake
 signal transmitter would then represent the driver's braking intention.
 The determination of the wheel assignment of the wheel modules would be
 carried out by using a diagnostics device connected preferably to the data
 bus system 7 at the first start-up of the braking system. The diagnostics
 device would then be removed upon completion of the assignment procedure.
 In the arrangement shown in FIG. 3, the wheel modules 1, 2 are assigned to
 the steerable front axle of a vehicle. The wheel modules 3, 4 are assigned
 to a rear axle, for example, the drive axle of the vehicle. The wheel
 position parameters in the wheel modules 1, 2, 3, 4 are adjusted in such
 manner that the adjustment signal is transmitted to the regulating channel
 of the valve arrangement 29, a regulating channel number of which is the
 same as the numbering of the corresponding wheel module according to FIG.
 3. In other words, the regulating channel 1 is defined as the main
 regulating channel in wheel module 1, regulating channel 2 is the main
 regulating channel in wheel module 2, etc.
 The wheel modules 5, 6 are assigned to an additional rear axle of the
 vehicle. The wheel assignment of these wheel modules 5, 6 has been
 effected in the same manner as for the wheel modules 3, 4, which are also
 assigned to a rear axle. Consequently, the regulating channel 3 has been
 determined to be the main regulating channel in the wheel module 5 while
 the regulating channel 4 was determined to be the main regulating channel
 in wheel module 6. If additional wheel modules are used, they would be
 given a similar wheel assignment as a function of the type of wheel axle
 to which they are assigned.
 Having described preferred embodiments of the invention with reference to
 the accompanying drawing, it is to be understood that the invention is not
 limited to those precise embodiments, and that various changes and
 modifications may be effected therein by one skilled in the art without
 departing from the scope or spirit of the invention as defined in the
 appended claims.