Abstract:
Setting or regulating a tire inflation pressure in one or more vehicle tires includes measuring and inflating in cycles. In each case, a seal is applied in at least one rotary transmitter. When the seal is applied, a tire filling pressure is changed and/or measured, and then the seal is removed again. The measuring and filling cycles can even be initiated while the vehicle is traveling. In intermediate time periods between the measuring or filling cycles, the seal is not applied. The measuring and filling cycles and the intermediate time periods are set as a function of ascertained current vehicle variables.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to setting or regulating a tire inflation pressure in vehicle tires. 
       BACKGROUND OF THE INVENTION 
       [0002]    EP 1051302B1 describes a tire inflation pressure-setting device and method of the general type under consideration. In agricultural vehicles, the tire inflation pressure can be checked and set by the vehicle itself. For this purpose, rotary signal transmitters, which permit compressed air transmission of the tire inflation pressure for the connected vehicle tire, are provided in the region of the wheel connections or rims. The tire inflation pressure can therefore be checked, and compressed air can be topped up or let out. The tire inflation pressure-setting device generally has a compressed air port for a compressed air supply, an electronic tire inflation pressure-control device and suitable valve devices, wherein compressed air is distributed from a compressed air supply via the valve devices to connecting lines to the rotary signal transmitters. Given a corresponding pneumatic actuation, the respective seal of the rotary signal transmitter can be applied, with the result that it seals when the vehicle tire is turning. Subsequently, in an inflation phase, compressed air can be topped up; and, subsequently, in a measuring phase, the current tire inflation pressure of the respective vehicle tire can be measured, for which purpose, for example, a central pressure sensor is provided. 
         [0003]    The seal of the rotary signal transmitter is heavily loaded during travel, since the rotating vehicle tire has to be connected to the compressed air system, which is fixed to the vehicle. This loading of the seals generally limits their operational capability and service life. 
       SUMMARY OF THE INVENTION 
       [0004]    Generally speaking, it is an object of the present invention to provide a system and a method for setting or regulating a tire inflation pressure in one or more vehicle tires, which permit reliable operation with low wear of the rotary signal transmitter seals. 
         [0005]    In accordance with inventive embodiments, setting or regulating the tire filling pressure includes measuring and inflating in cycles. In each case, a seal can be applied in one or more rotary signal transmitters. When the seal is applied, a tire filling pressure can be changed and/or measured, and then the seal is decoupled again. In intermediate time periods between the cycles, the seal is not applied. The measuring and filling cycles and the intermediate time periods can be set as a function of ascertained current vehicle variables. The measuring and inflating cycles are therefore no longer defined statistically in advance, for example according to predefined times. 
         [0006]    The current vehicle variables can comprise driving dynamics variables of the vehicle, such as the speed or the wheel rotational speeds, in particular the wheel rotational speed of the respective vehicle tire. The current vehicle variables can also comprise temperature values, in particular a brake temperature of the wheel brake, which is provided at the respective wheel of the vehicle tire, and furthermore an external temperature, in order to be able to determine cooling processes. 
         [0007]    Loading of the seals of the rotary signal transmitters can be estimated from basically available or determinable current vehicle variables. This loading can be determined by:
       the brake temperature, since the wheel brake is located in the direct vicinity of the rotary signal transmitter, and gives rise to considerable temperature increases. The wheel brakes are, as are the rotary signal transmitters, provided in the region of the wheel rims or wheel connections, with the result that a considerable flow of energy from the wheel brake to the rotary signal transmitter takes place. In this context it is recognized that the sealing material of the inserted seal of the rotary signal transmitter can be severely damaged at the high temperature loading.   the frictional power of the rotary signal transmitter, which, on the one hand, gives rise to temperature loading, and, on the other hand, to wear.   the speed and wheel rotational speeds, when the wheel rotational speed of the respective vehicle tire can be used to determine the frictional power of the rotary signal transmitter and also for the brake temperature of the wheel; the speed is relevant also for cooling processes.   the external temperature, in particular for cooling processes, and the time for the determination of durations; furthermore also the date and data relating to the distance lying ahead.       
 
         [0012]    The temperature of the seals is relevant; high temperatures at the seals bring about failure of the sealing material and/or damage thereto. The temperature-induced loading can be calculated or estimated from a model using the energy supply by transporting heat from the wheel brake and the frictional power of the seals and cooling processes by means of the ram air as a function of the speed. In this context, both the measuring and inflating cycles and the intermediate time periods between them can be taken into account. 
         [0013]    As a result, in a model for evaluating the current temperature of the seals of the rotary signal transmitters, heat-feeding-in processes can be taken into account by means of the measuring and inflating cycles themselves, that is, the frictional work of the seals and furthermore feeding in of heat by the respective wheel brake, as well as cooling processes by means of, for example, the conduction of heat in the wheel rim region, which, for example, can be estimated roughly in accordance with a model or else can be estimated from previous measurements or calibrations, and in particular cooling processes as a result of the ram air. 
         [0014]    The brake temperature can be measured by a brake temperature sensor. As an alternative, the brake temperature can be determined from a model using the braking times, braking powers (as a function of the speed or reduction in the kinetic energy of the vehicle as a result of the braking) by taking into account cooling processes. 
         [0015]    The relevant vehicle data can be made available via a vehicle-internal databus, in particular the CAN bus. Preferably, a tire inflation pressure-control device with an interface for the vehicle-internal databus is provided. As a result, in addition to the driving dynamic variables such as the speed and wheel rotational speeds, data relating to the time, date and external temperature can also be received. The brake temperature can, if appropriate, be received by an ABS control unit if the latter determines this value. 
         [0016]    By evaluating the brake temperature, which can be measured or estimated by means of a simulation computation, measuring and inflating cycles can therefore be entirely suppressed in the case of hot seals in order to protect the seal. For this purpose, it is possible to define a maximum brake temperature for the brake temperature above which no measuring and inflating cycles are initiated. As an alternative, it is possible to provide that when the maximum brake temperature is exceeded, relatively long intermediate time periods are defined, and short measuring phases are defined in the measuring and inflating cycles. 
         [0017]    Therefore, when travel starts with cold vehicle tires it is possible to set the pressure to, for example, 0.1 bar precisely (as a function of the external temperature), after which the tire inflation pressure is increased, which can be tolerated up to a maximum limit of, for example, +15%. Subsequently, in each case it is determined on an up-to-date basis when measuring and filling cycles are to be initiated. The temperature of the seals can then be estimated by means of a simulation calculation, and the application of the seals can be controlled as a function thereof. Furthermore, additional speed ranges can be defined. 
         [0018]    According to an embodiment of the present invention, the wear of the seal can also be estimated for this purpose, activation cycles can be counted, or the wear can be simulated taking into account the application pressure and the wheel rotational speed, since, given a relatively high application pressure in the rotary signal transmitter, the wear is higher, and the wear on the seal is also larger in the case of an increasing wheel rotational speed. As a result, a certain minimum service life of the seals can be targeted. 
         [0019]    Furthermore, it is possible to take into account that a vehicle tire can be repaired automatically again by sealing after its pressure has dropped, for example in the case of a leak. In this case, the system can be switched to an emergency inflation mode in which seals are applied for a relatively long time period. In this context, for example, relatively short measuring phases can be carried out in the measuring and inflating cycles in order to have available inflating phases that are as long as possible. The emergency inflating mode is advantageously activated only in the stationary state, i.e., at speed v=0. 
         [0020]    According to a further embodiment, it is possible to provide that in the intermediate time periods between the measuring and inflating cycles, in addition to or as an alternative to the internal simulation in the tire inflation pressure-control device, monitoring is carried out by the brake control device, for example an ABS control device or EBS control device. The brake control device can infer a reduction in the tire inflation pressure from the comparison of the wheel rotational speeds of the vehicle wheels; such tire pressure monitoring systems using wheel rotational speeds are known. They can therefore be carried out, in particular, in the intermediate time periods, wherein when a drop in the tire inflation pressure is detected the tire inflation pressure-control device of the tire inflation pressure system can subsequently be activated in order to initiate the measuring and inflating cycle. 
         [0021]    Alternatively or also additionally it is also possible to set the measuring and inflating cycles, and the intermediate time periods, as a function of the brake temperature instead of the determined seal temperature. 
         [0022]    Furthermore, a regulating or setting process can also be carried out to the effect that minimization of the rotational-speed-dependent wear of the seals is targeted. In this context, wear of the individual seals can be estimated as a function of the wheel rotational speed; therefore, measuring and inflating cycles are carried out at times with low wheel rotational speeds and therefore a low speed. 
         [0023]    Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
         [0024]    The present invention accordingly comprises the features of construction, combination of elements, arrangement of parts, and the various steps and the relation of one or more of such steps with respect to each of the others, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The present invention is discussed in greater detail below with reference to the accompanying drawings, in which: 
           [0026]      FIG. 1  is a circuit diagram showing a vehicle equipped with a tire inflation pressure-setting system according to an embodiment of the present invention; 
           [0027]      FIG. 2  is an electropneumatic circuit diagram of a tire inflation pressure-setting system in a vehicle with dual rear tires in accordance with an embodiment of the present invention; and 
           [0028]      FIG. 3  is a timing diagram illustrating a sequence of measuring and inflating cycles according to an embodiment of the present invention. 
       
    
    
     LIST OF REFERENCE SYMBOLS 
       [0000]    
       
         
           
               1  Vehicle 
               2  Front tire 
               3  Rear tire 
               4  Tire inflation pressure-setting system 
               5  Central tire inflation pressure-modulation device 
               6  Tire inflation pressure-control device 
               7  Pneumatic connecting lines 
               8  Pneumatic devices 
               9  Rotary signal transmitter 
               10  CAN bus 
               12  Brake control device 
               14  Wheel brakes 
               15  Brake temperature sensors 
               17  Electropneumatic brake system 
               18  Rotational speed sensors (ABS sensors) 
               20  External temperature sensor 
               22  Measuring and inflating cycle 
               22   a  Inflating phase 
               22   b  Measuring phase 
               23  Intermediate time period 
               24  Seal 
               30  Pressure sensor 
               31  Interface 
               32  Compressed air supply 
             t Time signals 
             t 1  Starting time 
             t 2  End time 
             Δt 3  Time interval 
             T_A External temperature 
             T_Br Brake temperature 
             Tg Brake temperature limiting value 
             v Speed 
             vg Vehicle limiting speed 
             n Wheel rotational speed signals 
             p Tire inflation pressure 
             px Maximum limit of the tire inflation pressure 
           
         
       
     
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0065]    Referring now to  FIG. 1 , a vehicle  1 , in particular a utility vehicle, has vehicle tires  2 ,  3 , specifically two front tires  2  and two rear tires  3 . According to the embodiment shown in  FIG. 2  the rear tires can, for example, also be dual rear tires. 
         [0066]    The vehicle  1  has a tire inflation pressure-setting system  4  for setting the tire inflation pressure p in the vehicle tires  2 ,  3 . The tire inflation pressure-setting system  4  generally has a central tire inflation pressure-modulation device (TPC modulation device)  5  with a tire inflation pressure-control device  6  (TPC control device)  6 . Decentralized pneumatic devices  8  on the vehicle tires  2 ,  3  are connected via pneumatic connecting lines  7  to the central tire inflation pressure-modulation device  5 . The tire inflation pressure-modulation device  5  is generally connected to a compressed air supply  32 , shown by way of example in  FIG. 2 . 
         [0067]    The pneumatic devices  8  have rotary signal transmitters  9 , which permit inflation of the tires through the tire inflation pressure-modulation device  5  even during travel. For this purpose, a seal  24  of the respective rotary signal transmitter is applied pneumatically and brings about frictional contact with the respective vehicle tire  2  or  3  or the wheel. In the case of a two-channel design of the connecting lines  7 , the rotary signal transmitters  9  can be actuated directly, that is, the pneumatic devices  8  are formed entirely or essentially by the rotary signal transmitters  9 . In the case of single-channel actuation, pneumatic devices  8  generally have additional pneumatic circuits for actuating the rotary signal transmitters  9 . The connecting lines  7  permit a bidirectional compressed air line in order to measure the tire inflation pressure p in the vehicle tires  2 ,  3  by means of a pressure sensor  30 , which is provided in the tire inflation pressure-modulation device  5 . 
         [0068]    The rotary signal transmitters  9  are actuated pneumatically by means of the respective connecting line  7 , with the result that, at a starting time t 1 , the respective seal  24  is applied and therefore a compressed air connection is formed between the vehicle tire  2  or  3  and the respective pneumatic connecting line  7 , and therefore the tire inflation pressure-modulation device  5 , as a result of which a measuring and inflating cycle  22  is started, which, for example, first comprises an inflating phase  22   a  and subsequently a measuring phase  22   b , after which, at an end time t 2 , the seal  24  is opened again. 
         [0069]    The tire inflation pressure-control device  6  has an interface  31  at a vehicle-internal CAN bus  10  via which it is connected to further control devices of the vehicle  1 , in particular a brake control device  12 , which can be, for example, an ABS and/or EBS control device and advantageously controls an electro-pneumatic brake system  17 . The brake system  17  has wheel brakes  14 , which have, if appropriate, brake temperature sensors  15 , which output measuring signals of the brake temperature T_Br to the brake control device  12 . The measuring signals of the brake temperature T_Br of the individual wheel brakes  14  are passed onto the tire inflation pressure-control device  6  via, for example, CAN bus  10 . 
         [0070]    The brake system  17  has, at the individual wheels of the front and rear tires  2 ,  3 , rotational speed sensors (ABS sensors)  18 , which output corresponding wheel rotational speed signals n to the brake control device  12 . The wheel rotational speed signals n of the individual front and rear tires  2 ,  3  are also correspondingly transmitted via the CAN bus  10  to the tire inflation pressure-control device  6 . Furthermore, the tire inflation pressure-control device  6  receives, via the CAN bus  10 , signals relating to the external temperature T_A, which, can, for example, individually measure values of an external temperature sensor  20  of the vehicle  1 , and a speed signal v. The tire inflation pressure-control device  6  also has an internal clock or receives the corresponding time signals t with indications about the time and date via the CAN bus  10 . 
         [0071]    The tire inflation pressure-control device  6  therefore determines the starting times t 1  for initiating the measuring and inflating cycles  22  and the end times t 2  for ending the measuring and inflating cycles  22 , from these signals or measurement values, that is, the wheel speeds n, the time signals t, the signals relating to the external temperature T_A, the speed v and advantageously—if present—the measurement signals of the brake temperature T_Br of the individual vehicle tires, i.e., the front tires  2  and rear tires  3 .  FIG. 3  shows the time profile as a time arrow. The time interval Δt 3  between the measuring and inflating cycles and the time length t 2 −t 1  of the measuring and inflating cycles  22  is determined by the tire inflation pressure-control device  6 . 
         [0072]    In this context, the tire inflation pressure-control device  6  or a simulation or computing device connected thereto carries out a simulation calculation for estimating the brake temperature T_Br of the individual wheel brakes  14 . The objective is to suppress entirely or largely measuring and inflating cycles  22  in the case of hot wheel brakes  14 . As a result, for example, the determined brake temperature T_Br can be compared with an (upper) brake temperature limiting value Tg, with the result that, in the case of T_Br&gt;Tg, no measuring and inflating cycle  22  is initiated, in order to protect the seals  24  of the rotary signal transmitters  9 , or the number and frequency of the measuring and inflating cycles  22  is reduced. Furthermore, the measuring phase  22   b  can be reduced. 
         [0073]    At the start of travel, on the one hand the brake temperature T_Br and also the cooling of the wheel brakes  14  after activation can be estimated by means of the determined external temperature T_A, additionally, for example, by means of the time signal t. As a result, the state of the vehicle tires at the start of travel, that is, the cold tire temperature, can be determined or estimated. For example, in a first measuring and inflating cycle  22 , the tire inflation pressure p can therefore be set to 0.1 bar precisely, also independently of the external temperature T_A. After the start of travel, the tire inflation pressure p increases, which is tolerated, for example, up to a maximum limit of px=1.15, that is, an increase of 15 percent. 
         [0074]    Measuring and inflating cycles  22  can basically be initially set periodically, for example according to time or also according to kilometers traveled. In this context, this classification according to measuring and inflating cycles  22  and intermediate time periods  23  is initially aimed at by the tire inflation pressure-control device  6 ; by measuring the brake temperature T_Br it is determined in this way whether the brake temperature limiting value Tg is, under certain circumstance, exceeded, with the result that in this case a measuring and inflating cycle  22  is not initiated but rather postponed. 
         [0075]    Furthermore, the measuring and inflating cycles  22  can be set already from the onset, or else as a function of ambient conditions, to specific speed ranges, for example v&lt;vg, with vg as the vehicle limiting speed or wheel rotational speed limiting values, since at relatively high wheel rotational speeds n the loading on the seals is correspondingly greater. In this context, it is possible to provide, for example, that when the brake temperature limiting value Tg is exceeded and/or the vehicle limiting speed vg is exceeded, a measuring and inflating cycle  22  is initiated in each case after relatively long time periods for safety reasons—despite the high brake temperature T_Br or high speed v—wherein these time periods are then set, for example, to be significantly longer than the time interval Δt 3  of the normal intermediate time periods  23 . 
         [0076]    When the sealing is applied during travel, that is, v&gt;0, the seals  24  of the rotary signal transmitters  9  are heated by the frictional power, and are furthermore subjected to direct frictional wear. The temperature can be estimated by a simulation calculation of the tire inflation pressure-control device  6 , with the result that the times for the application of the seals  24  in the measuring and inflating cycles  22  can be controlled in this way. 
         [0077]    Furthermore, braking processes also bring about an increase in the temperature of the seals  24 , since the wheel brakes  14  are mounted in the wheel connecting region or region of the rims, and therefore in the direct vicinity of the rotary signal transmitters  9 ; there is direct conduction of heat to the seals  24 . 
         [0078]    As a result in this context, further designs or embodiments are possible. For example, the measuring and inflating cycles  22  can be counted and used to simulate the wear of the seals  24  under different conditions. The measuring cycle frequency, that is, the number of measuring and inflating cycles  22  or the proportion of the time length t 2 −t 1  of the total time, can be set, with the result that a specific minimum service life of the seals  24  is achieved. 
         [0079]    If it is determined that the tire inflation pressure p in a front tire  2  or rear tire  3  has dropped severely, for example after a leak, which can be repaired again by a sealant, the system can be switched to an emergency inflating mode. In this emergency inflating mode, the seals are applied for a longer time period than the time length t 2 −t 1  in order to bring about re-inflation. Correspondingly, the measuring phases  22   b  in the measuring and inflating cycles  22  are set correspondingly lower, in order to be able to fill in as much air again in the shortest possible time. This mode can advantageously be activated only in the stationary state, that is, when v=0. 
         [0080]    If the brake control device  12  has tire inflation pressure monitoring by evaluation of the wheel rotational speeds n, which monitoring compares the wheel rotational speeds n of an axle, i.e., of the two front wheels  2  or of the two rear wheels  3  and detects a relatively low tire inflation pressure p from wheel rotational speeds n, which are relatively high, over the medium term or long term, since the radius of the wheel of the respective vehicle tire  2  or  3  is smaller, an interface can be provided between the functions of the brake control device  12  and the tire inflation pressure-control device  6 . The latter can be configured such that the brake control device  12  performs the monitoring of the respective vehicle tires  2 ,  3  in the intermediate time periods  23 , in which measurement does not take place, and an estimation of the tire inflation pressure p, which has not been determined, is enabled by comparing the wheel rotational speeds n. In brief measuring and inflating cycles  22  it is possible to perform recalibration in each case, that is, to carry out adjustment to the actual measured values. 
         [0081]    It is possible, for example, to stipulate a vehicle limiting speed vg of 60 km/h for normal driving mode, with the result that measuring and inflating cycles  22  are carried out only at speeds v&lt;vg=60 km/h. However, if v&gt;vg is present over a relatively long time period, it is also possible, for example, for a certain number of measuring and inflating cycles to be permitted up to, for example, an upper vehicle limiting speed vg2=90 km/h if the measured or determined brake temperature T_Br and external temperature T_A do not exceed a defined threshold. If, on the other hand, a sufficiently frequent change in the speed level is detected, inflating and measuring cycles  22  are carried out only below vg=60 km/h. 
         [0082]    Furthermore, the inflating and measuring cycles  22  can be counted according to the number or even total duration for use in simulating the wear of the seal under various conditions. It is possible, for example, to control the measuring cycle frequency predicatively, with the result that a specific minimum service life of the seals  24  is reached. For example, a maximum seal application duration per 1000 km can be predefined on the basis of a service life, which is measured in test bench trials and the aimed-at total distance to be traveled by the vehicle. Depending on the driving profile and ambient conditions, a varying cycle frequency can therefore be achieved over the service life. 
         [0083]    Furthermore, an emergency inflation mode can be provided in which, when a leak is detected that can be automatically repaired again by a sealant, the system is switched to an “emergency inflation mode”. In this emergency inflation mode, the seals are applied over a relatively long time period, wherein this mode can advantageously be set only in the stationary state when v=0. In such an emergency mode, as described above, only a few measuring phases  22   b  in the measuring and inflating cycles  22  can be effected, in order to be able to use as much time as possible for feeding in air again. 
         [0084]    It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
         [0085]    It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall there-between.