- Email: [email protected]
ELECTRONIC REGULATION OF AN AUTOMATED CAR TYRES PRESSURE CONTROL SYSTEM
ELECTRONIC REGULATION OF AN AUTOMATED CAR TYRES PRESSURE CONTROL SYSTEM Germano Sandoni ∗,1 , Martin Ringdorfer ∗
MAGNA STEYR Fahrzeugtechnik, MSF/EEC Liebenauer Hauptstrasse 317, 8041 Graz, Austria Phone: +43 316 404 5612, Fax: +43 316 404 5955 E-mails: [email protected], [email protected] ∗
Abstract: Modern cars have a lot of features and electronic systems which support the driver in dangerous driving situations. Such systems are not only developed for keeping the cars under control, but they also try to improve the subjective feeling during driving and comfort. One of such systems has the task to measure and control the pressure of the tyres: Automated Tyres Pressure System (ATPS). The prototype system which is mentioned in this paper is able to check the pressure of the tyres and to adapt automatically the pressure of each tyre to the currently existing driving situation. The main principles concerning hardware structure, the particular software architecture and also some results, which have become important during the development of a first prototype car, are mentioned and described. Keywords: Control applications, System engineering, Automotive, Pressure measurements, Tyres, Dynamic behaviour, Valves, Prototyping, Prediction methods, Sensors.
1. INTRODUCTION Nowadays the automotive industry is one of the most exciting and challenging fields of development, where the electronic engineering takes place. A key role in the modern development of a vehicle is played by the design of electronic hardware and software. Also economical cars have mounted a lot of decentralized electronic control units, which have the task to keep factors like security, consumption, emission, performance and comfort under control. In this field it is very important to mention the electronic control of the driveline, vehicle dynamics e.g. global chassis controller, traction control, the antilock braking system, the steer by wire system and fault detection 1
Corresponding Author.
device, see (Bosch, 2000) and (Loomann, 2003). A revolutionary investment in safety and comfort, as well as vehicle stability, is the dynamic control of the tyres pressure during driving. Statistics show that every second technical reason for a car accident is due to the tyres: in fact a too low tyres pressure cause more rolling friction, the tyres become more noisy and the rubber get warm, see (Biermann, 2004). Even the best test driver has problem to control a car with a broken tyre. The automatic adaptation of the tyres pressure, depending on the currently existing driving situation, changes the whole vehicle dynamics and makes the car more reliable, e.g. if the tyres are damaged or have small leakages. In the next few years, the cars which have to be sold in the United States have to be equipped with systems which indicate a low tyres pressure, see (Normann N., 2000). Providing the driver an accurate infor-
514
mation about the pressure levels, it could create better security feeling. Most systems, which are state of the art, detect such a critical situation by the changing in the frequency spectrum of the rotating tyres, or they measure directly the pressure of each tyre, see (Bochmann H., 2005). In connection with this fact, it seems a logical further step, not only to indicate the driver that the pressure in one tyre is not correct, but also to control it. A revolutionary investigation is the electronicpneumatic regulation of the pressure of the tyres (ATPS). Existing tyres pressure measurement systems use pressure sensors, with battery inside, which are mounted on the valves of the wheels. By introducing a measurement cycle and a transmitting cycle the information of the currently measured pressure can be transmitted to a control unit, see (Technical, 2003). In special situations these concepts might cause problems because of lacks in the energy supplied by the battery inside the wheels, or because of issues in the transmission phase. Other systems use the changing in the radio frequency spectrum in combination with piezoelectric sensors for operating without batteries. These systems have the disadvantage that they can’t operate all the time. Therefore a prototype car has been equipped with a system which is independent of such tyres sensors, and has already the possibility to adapt the tyres pressure to the currently existing driving conditions. Especially in situations where the tyres have small leakages, the so called ATPS has the advantage that the driver is warned that the tyres loose air, but he has the possibility to drive to the next service station, see (Ringdorfer M., 2005). The main principle of the system, which is described in this paper, is to measure the pressure of the tyres with standard pressure sensors located in the ATPS on the car, and to adapt the tyres pressure if necessary. This includes the decreasing of the pressure if it is too high, by releasing air through the tyres rim, and it also includes the refilling of the tyres, if there are small leakages. 2. HARDWARE AND SOFTWARE CONFIGURATION 2.1 Electro-Pneumatic System Description As shown in Fig. 1, the hardware system consists of a rapid control prototype unit (MABX), a Power- and Communication-Interface (PCI) and an air-pneumatic unit, called Central Air Unit (CAU). In Fig. 3, it is possible to see a more detailed schematic of the air-pneumatic unit. All the valves in the CAU, are actuated by the rapid control prototype unit. These parts are installed in the boot bottom in a prototype car, in the space normally assigned to the reserve wheel (not anymore necessary). Each tyre is connected to the
Control Pipe HMI
Supply Pipe
Central Air PCI+MABX Unit
Fig. 1. Automated tyres pressure control system mounted in a prototype car. air unit by using two pneumatic pipes: one Control Pipe for actuating the valves in the tyres rim (V9 , . . . V12 ), the other Supply Pipe for delivering the air to the tyres. The pneumatic connections between pipes and rims in the tyres are describe in the (SSF GmbH Patent, 2003). The driver can instruct and supervise the ATPS via a Human Machine Interface (HMI) mounted in the cockpit, see Fig. 2. From the electrical point of view, the PCI
2.2 bar 25 ˚C
2.2 bar 25 ˚C
2.2 bar 25 ˚C
2.2 bar 25 ˚C
AUTOMATIC
Automatic
Front Axle Increase Pressure
Rear Axle Increase Pressure
Front Axle Decrease Pressure
Rear Axle Decrease Pressure
A M MANUAL
Manual
Fig. 2. Human Machine Interface mounted in the prototype ’Air Vehicle’. provides the rapid control prototype unit information from the vehicle CAN and from an installed HMI. With this information and the status data coming from the CAU, the software algorithm calculates the necessary actuation sequences for controlling the tyres pressure. The Control Commands are send to the power interface of the rapid control prototype unit and forwarded to the air unit. The air unit, shown in Fig. 3, consists of: pressure sensors S1 , S2 and S3 , for measuring the pressure in the accumulator PS1 , and for measuring the pressures in the supply pipes PS2 and PS3 , valves for setting up the necessary tyres pressure levels V1 , . . . V12 , a compressor C1 , composed of a motor M1 and a pump P1 and an accumulator A1 for storing the compressed air. Additionally an air-dryer AD1 is present, which is used for
515
Front Tyre „Right“
Interface Input V9
V1
Control Logic PI
V10 V2
S2
Manual Mode Automatic Mode
V5 V7
Front Tyre „Left“
V8 C1
Rear Tyre „Right“
P1 V11
PI
A1
S1 V3
AD1 M
M1
Accumulator Pressure Control Loop
Tyres Pressure Control Loop
Vehicle Controller
PI
V12 V4
S3
V6
Rear Tyre „Left“
Interface Output
External Information Flow Internal Information Flow
Fig. 3. Proposed Pneumatic System: Central Air Unit(CAU). protecting the valves especially in wet and cold ambient conditions. 2.1.1. Tyres Pressure Increasing By controlling the valves V5 and V6 of the air unit, it is possible to deliver compressed air from the accumulator A1 to the front/rear supply pipes. Then it is possible to actuate additional valves which are placed in the rims V9 , . . . V12 , as shown with the dotted arrows in Fig. 3. The valves which are placed in the rims can only be controlled pneumatically with the outstreaming air coming from the electriccontrol valves V1 , . . . V4 . This has the advantage, that the connections between the rotating parts of the rims and the parts of the pipes, which are at standstill, is executed just with compressed air: this can guarantee a long system lifetime. 2.1.2. Tyres Pressure Decreasing The decreasing procedure is analog to the increasing procedure with the difference that, before opening the valves in the rims V9 , . . . V12 , the front/read pipe needs to be deflated at the ambient pressure. This can be done by opening the valve V7 , or if it is needed, to regenerate the air-dryer AD1 , by opening the valve V8 . 2.2 Software Architecture Concept The ATPS software architecture is shown in Fig. 4. It is divided in four main parts: one consists in the controlling of the accumulator supply pressure PS1 (Accumulator Pressure Control Loop), the other three parts have the task to control the valves in the air unit and as consequence the regulation of the valves in the rim V9 ,...V12 . To observe, that this two control functionality can’t be considered completely independent, because they are interacting, along the same pipe, during the refreshing of the air-dryer AD1 . This means, that a simultaneously increasing of the pressure in the accumulator is not possible while the pressure in the tyres are deflating with a regeneration
Reference Pressures Information / Command Flow
Fig. 4. Proposed Control Software Architecture. of the air-dryer. As shown in Fig. 4, a Vehicle Controller module has the task to calculate the tyres pressure references, which are needed for the currently existing driving situation. This target pressures are then passed at the Tyres Pressure Control Loop module that actuates the CAU. For overviewing the different SW parts, a module, so called Control Logic, has been introduced with the aim to enable the different control loops and to recognize eventual error conditions. Additional software parts were needed to make the ATPS working on the prototype car: a kind of communication interface between the HMI, the CAN and the CAU has been developed. 2.2.1. Accumulator Pressure Control Loop The control loop for the accumulator pressure has the task to keep the supply pressure PS1 within a certain range [PS1min , PS1max ]. A special control strategy based on the rotational speed nC1 of the compressor DC motor M1 has to be carried out. Following variables have been taken into consideration, see eq. (1): the currently existing accumulator pressure PS1 , the rate of changing of the pressure dPS1 /dt, the operating time of the compressor Ton , the compressor temperature o TC1 and the velocity of the car vv . This has the effect to reduce the noise and the vibrations produced by the compressor during the reload of the accumulator at low car speeds. nC1 = fn (PS1 ,
dPS1 o , Ton , TC1 , vv ) dt
(1)
As a further step, if there would be more than one compressor, the regulation of the rotational speed could be replaced by a sequential turning ”On” and ”Off” of the compressors. Not only the regulation of the steady state rotational speed nC1 is considered, also the minimization of the motor effort during the starting up of the compressor has been evaluated: in fact when M1 is starting, the valve V8 is opened for a short time, in order to avoid a full load start and to decrease the peak of current absorbed from the battery. Since the
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2.2.2. Tyres Pressure Control Loop Through the HMI the driver has the ability to choose between two different working modes: ”manual mode” and ”automatic mode”. By choosing the ”manual mode” the Control Logic allows the driver to adapt the tyres pressure from himself: e.g. in off-road conditions for maximizing the traction forces or for increasing the damping, it is necessary to reduce the tyres pressure. This can be done manually by pressing the two buttons Front/Rear Axle Increase/Decrease in the HMI, see Fig. 2. For giving at the ”operator” a feedback about his actions, the currently existing tyres pressure is displayed in a small screen in the cockpit. A SW-check avoids that the driver increases/decreases manually the tyres pressure outside at the safety admitted ranges. In ”automatic mode” the SW calculates the individual tyres pressure for providing best effort in terms of comfort, fuel consumption and traction. Depending on the currently driving situation (vehicle speed vv , vehicle acceleration/deceleration av , axles loads Mf , Mr , brake pedal Br , tyres temperatures Tio and road state St ) the admitted target pressures ranges [PRmini , PRmaxi ], i=1...4 are calculated by the Vehicle Controller module and passed at the Tyres Pressure Control Loop. [PRmini , PRmaxi ] =
experimental results of the system performance for a filling process
35 30 25 filling time tmi[sec]
air-dryer AD1 needs to be refreshed/regenerated during the deflating of the tyres, a special action has to be fulfilled, if the compressor is simultaneously working. Putting the priority on the refreshing phase, the pump P1 needs to be temporary turned off. In this case, the Control Logic stops the Accumulator Pressure Control Loop module in favor of the Tyres Pressure Control Loop.
20 15 10 5 0 5 6 7 8
accumulator pressure PS1[bar]
9 10
1
2.5
2
1.5
3
3.5
4
actual tyres pressure Pi[bar]
Fig. 5. Experimental measurements of the actuation time as function fS of the accumulator pressure PS1 and the actual tyres pressure Pi .
Reference pressures Existing tyre pressures
Supervise tyre pressure
yes
OK
no Accumulator pressure
Estimate control times Choose actuation sequence
Send command to CAU
Command executed
yes
Existing tyres pressure
Supervise tyres pressure
f Ti (vv , av , Mf , Mr , Br , Tio , St )
This SW-Module, on the base of the difference between the measured pressures Pi and recommended target tyres pressure PRi = avg(PRmaxi , PRmini ) and also depending on the available accumulator pressure PS1 , estimates the actuating time ton/offi for each tyres, as shown in eq.(2). ton/offi = tRefi − tmi tRefi = fS (PRi , PS1 ) tm i = fS (Pi , PS1 ), i=1...4
Tyres pressure OK or timeout error
no
yes Command to CAU: „Finish control procedure“
(2)
Fig. 6. Control Sequence of the ”automatic mode” in the Tyres Pressure Control Loop.
In the first prototype the estimation of the controlling time ton/offi is based on experimental measurements on the car, as shown in Fig. 5. After estimating each time ton/offi , the Actuation Sequence for the tyres that has a longer time starts. It is also possible that front/rear pipes can be shared, and more than one tyre is controlled at the same time, therefore a proper actuation command is send to the CAU. In Fig. 6 the Control Sequence for the ”automatic mode” is summarized in a flow chart. To observe that in total are possible 19 different CAU Actuation Commands,
as summarized in Tab.1. If one pressure is too high PRi < Pi , the air which needs to be taken out of a tyre can be used for filling another tyres only if this is on the same axle. If the pressure of the accumulator PS1 is not too low, the outstreaming air is used to refresh the air-dryer AD1 , viceversa the accumulator is reloaded and in the same time the valve V7 , with the direct outlet, is opened. In Fig. 7 the Actuation Sequence which it is used for executing an Actuation Command in the CAU is shown. In both cases, that the actution command is coming from the ”manual mode”, or ”automatic
517
Command No
Command Description
NOP (0) IncFL (1) DecFL (2) IncFR (3) .. . AllDec (14) FaLock (15) RaLock (16) Pcalib (17) ChkSens (18)
No Op.: valves in default position Increase press. in the front left tyre Decrease press. in the front left tyre Increase press. in the front axle .. . Decrease press. in all tyres Equalize the front axle pressure Equalize the rear axle pressure Calibrate all pressures equal Check pressure sensors
Front tyre „right“ V9 V1
PI
V10 V2
Actuation command n
V8 C1 P1 V11
AD1
A1
PI
S1
M
V3
Tyre Pressure
PI
V12 V4
M1
S3
V6
Accumulator Pressure
Rear tyre „left“
Fig. 8. Front right tyre pressure measurement sequence.
Close control valves
Reduce pipe pressure
Select, determine and set up supply pipe pressure
Close supply valves
stable and will nearly be the same as the pressure in the tyre itself. For avoid that small amount of air of the tyres is lost, during the measurement process, the pipes are preloaded from the accumulator, before opening the valve in the rim. 3. MEASUREMENTS RESULTS
Set error-bit
yes Open control valves
10
20
accumulator pressure P
S1
↓
S2
5
10
Operation Command N0
←front supply pipe pressure P 0
Operation Command N →
S2
Fig. 7. Actuation Sequence for executing an Actuation Command in the CAU.
1
Actuation command n+1
S3
t n+1
2
3
4
Send status message
In this section the measurements results of a prototype ATPS system are presented: in Fig. 9 the ”manual mode” procedure is shown. In this meaSystem Pressure P , P , P ; Tyre Pressure P , P , P , P [bar]
no
OK
V7
Rear tyre „right“
Table 1. CAU Actuation Commands. tn
V5
S2
Front tyre „left“
S1
mode”, this loop is always the same. As already mentioned, first the pipes are filled and then the valves in the rim are actuated. To observe that ↓ ↓ ↑ ↑ during the transition from a command n to the next command n + 1 the state PSfrag of the replacements system 0 0 0 1 2 3 4 5 6 7 8 9 10 is evaluated, and the pipes are inflate/disinflate t[s] only if necessary. For this reason 19*(19-1)=342 Fig. 9. Pressures behaviour during operating in possible cases, of transition from one command to ”manual mode”. the next, have been taken into consideration. surements, at t'0.5s, both buttons ”Front/Rear 2.2.3. Tyres Pressure Measurement Sequence Axle Increase Pressure” of the HMI are pressed, in For evaluating the right control action the tyres order to increase the pressures Pi in all four tyres. pressures must be measured. Every tyre is meaThe Actuation Command number 13 is executed, sured automatically with a certain sequence that at first by increasing the pressure in the supply fill up the correspondent supply pipe. In Fig. 8 pipes and then after reaching a certain threshold is shown the configuration of the valves for mea(dependent of the actual accumulator pressure suring the pressure in the front right tyre. The PS1 ), the valves in the rim are open and the filling pressure measurement of the tyres is executed procedure starts. After a few seconds (t ' 3.5s), with the pressure sensor S2 or S3 in the pipes. The the driver decides to increase the pressure only of pipes connections between the pressure sensors the tyres of the front axle (Actuation Command S2 , S3 and accumulator A1 needs to be closed. number 5). The pressure in the front pipe is kept The air which is taken out of the accumulator go while the pressure in the rear pipe is decreased, to actuate one of the valves in the rim V9 . After with refreshing of the air-dryer. At t'5.5s both a short time, the pressure in the supply pipes is buttons are pressed again: the pressures in the ←rear supply pipe pressure PS3 rear left tyre pressure P3
rear right tyre pressure P4
front right tyre pressure P2
front left tyre pressure P1
518
pipes are set up immediately, without any deflation, before that the filling procedures restart. In Fig. 10 and in Fig. 11 are shown the measurements for the ”automatic mode”. Depending on
rag replacements
40
reference pressure P
→
V
Rmax
Vehicle Velocity v [km/h]
Tyre Pressure P1, P2, P3, P4 , Reference Pressure PRmax, PRmin [bar]
4
rear right tyre pressure P4
2
↓
rear left tyre pressure P3 reference pressure P
20
↓
Rmin
↓
↑
front right tyre pressure P2
↑
front left tyre pressure P1
←vehicle velocity vV
0
0
5
4.1 Acknowledgements 10
15
20
25
0 30
t[s]
Fig. 10. Dynamic changing of the tyres pressure during driving in ”Automatic Mode”(starting from an initial condition where all pressures Pi are too low). the vehicle velocity vv and on the other variables, the ranges of reference pressures [PRmin, PRmax ] for all tyres are calculated. Starting from the rear left tyre, one after the others, the pressures are regulated within the optimal ranges. After few seconds, the correct pressures are reached and the passengers can enjoy the driving. In Fig. 11 are 100
←reference pressure PRmax front left tyre pressure P
1
↓
rear left tyre pressure P3
front right tyre pressure P2
↓
↓
2
50 ↑
rear right tyre pressure P4
↑
reference pressure PRmin
Vehicle Velocity vV[km/h]
Tyre Pressure P1, P2, P3, P4 , Reference Pressure PRmax, PRmin [bar]
4
rag replacements
←vehicle velocity vV
0
0
10
system not only the accurate measuring of the tyres pressure is possible, but also an automatic adjustment of the pressures corresponding to the currently existing driving situation. The shown system has been realized in a prototype car and the control software is becoming an utility patent. Further investigations in the systems concept, pneumatic technology and in the strategy of controlling might bring additional improvements in term of actuation speed and space occupied on board. This leads to the possibility of a real-time vehicle dynamics control, which could create new driving feelings, and make cars and trucks more save and comfortable.
20
30
40
50
0 60
t[s]
Fig. 11. Dynamic changing of the tyres pressure during driving in ”Automatic Mode”(starting from an initial condition where all pressures Pi are too high). shown the regulation results for the ”automatic mode” starting from an initial condition in which the pressure in all four tyres are too high, this could append e.g. when the temperature of the road change. 4. CONCLUSION A system for monitoring and controlling the tyres pressure of a car is presented. With the proposed
Hearty greetings at all the people that directly or indirectly support the construction of the prototype Audi A8 with ATPS. Particular thanks at the company Ventrex Automotive GmbH for the construction of the CAU, and at the company SSF GmbH for the mechanical implementation of the connection to pipe-rim. Without these partners the realization of the system would have been not possible. REFERENCES Bochmann, H., Kessler, R. and Schulze, G. (2005). Stand und aktuelle Entwicklungen bei Reifendruck-Kontrollsystemen. Automobiltechnische Zeitschrift (Jahrgang, Ed.), 107, Pages: 110 - 117, February, 2005. Biermann,J.-W.,Beckmann, T., Wech, L., Meier, R. (2004). Analyse des Reifenabrollger¨ auschs. Automobiltechnische Zeitschrift (Jahrgang, Ed.), 106, Pages: 950-956, June, 2004. Bosch, R. (2000). Kraftfahrtechnisches Handbuch (Vieweg-Verlag, Ed.), Pages: 708-768. Loomann (2003). Handbuch Kraftfahrzeugtechnik (Vieweg-Verlag, Ed.), Wiesbaden (Germany). Normann, N.(2000). Reifendruck-Kontrollsysteme f¨ ur alle Fahrzeugklassen. Automobiltechnische Zeitschrift, (Jahrgang, Ed.), 102, Pages: 950956. Ringdorfer, M. (2005). Regelung eines automatischen Reifendruckkontrollsystems (MAGNA STEYR Fahrzeugtechnik - FH Joanneum), Graz (Austria). SSF, Steyr-Daimler-Puch Spezialfahrzeug GmbH Patent: EP1141595B1 (2003). Anordnung mit konzentrisch zueinander angeordneten und relativ zueinander rotierbaren Bauteilen und Verwendung dieser Anordnung bei einer Reifenf¨ ullanlage, Wien (Austria). Technical Research Centre of Finland (2003). Intelligent Tyre Systems - State of the Art and Potential Technologies, Pages: 82-91.
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MAGNA STEYR Fahrzeugtechnik, MSF/EEC Liebenauer Hauptstrasse 317, 8041 Graz, Austria Phone: +43 316 404 5612, Fax: +43 316 404 5955 E-mails: [email protected], [email protected] ∗
Abstract: Modern cars have a lot of features and electronic systems which support the driver in dangerous driving situations. Such systems are not only developed for keeping the cars under control, but they also try to improve the subjective feeling during driving and comfort. One of such systems has the task to measure and control the pressure of the tyres: Automated Tyres Pressure System (ATPS). The prototype system which is mentioned in this paper is able to check the pressure of the tyres and to adapt automatically the pressure of each tyre to the currently existing driving situation. The main principles concerning hardware structure, the particular software architecture and also some results, which have become important during the development of a first prototype car, are mentioned and described. Keywords: Control applications, System engineering, Automotive, Pressure measurements, Tyres, Dynamic behaviour, Valves, Prototyping, Prediction methods, Sensors.
1. INTRODUCTION Nowadays the automotive industry is one of the most exciting and challenging fields of development, where the electronic engineering takes place. A key role in the modern development of a vehicle is played by the design of electronic hardware and software. Also economical cars have mounted a lot of decentralized electronic control units, which have the task to keep factors like security, consumption, emission, performance and comfort under control. In this field it is very important to mention the electronic control of the driveline, vehicle dynamics e.g. global chassis controller, traction control, the antilock braking system, the steer by wire system and fault detection 1
Corresponding Author.
device, see (Bosch, 2000) and (Loomann, 2003). A revolutionary investment in safety and comfort, as well as vehicle stability, is the dynamic control of the tyres pressure during driving. Statistics show that every second technical reason for a car accident is due to the tyres: in fact a too low tyres pressure cause more rolling friction, the tyres become more noisy and the rubber get warm, see (Biermann, 2004). Even the best test driver has problem to control a car with a broken tyre. The automatic adaptation of the tyres pressure, depending on the currently existing driving situation, changes the whole vehicle dynamics and makes the car more reliable, e.g. if the tyres are damaged or have small leakages. In the next few years, the cars which have to be sold in the United States have to be equipped with systems which indicate a low tyres pressure, see (Normann N., 2000). Providing the driver an accurate infor-
514
mation about the pressure levels, it could create better security feeling. Most systems, which are state of the art, detect such a critical situation by the changing in the frequency spectrum of the rotating tyres, or they measure directly the pressure of each tyre, see (Bochmann H., 2005). In connection with this fact, it seems a logical further step, not only to indicate the driver that the pressure in one tyre is not correct, but also to control it. A revolutionary investigation is the electronicpneumatic regulation of the pressure of the tyres (ATPS). Existing tyres pressure measurement systems use pressure sensors, with battery inside, which are mounted on the valves of the wheels. By introducing a measurement cycle and a transmitting cycle the information of the currently measured pressure can be transmitted to a control unit, see (Technical, 2003). In special situations these concepts might cause problems because of lacks in the energy supplied by the battery inside the wheels, or because of issues in the transmission phase. Other systems use the changing in the radio frequency spectrum in combination with piezoelectric sensors for operating without batteries. These systems have the disadvantage that they can’t operate all the time. Therefore a prototype car has been equipped with a system which is independent of such tyres sensors, and has already the possibility to adapt the tyres pressure to the currently existing driving conditions. Especially in situations where the tyres have small leakages, the so called ATPS has the advantage that the driver is warned that the tyres loose air, but he has the possibility to drive to the next service station, see (Ringdorfer M., 2005). The main principle of the system, which is described in this paper, is to measure the pressure of the tyres with standard pressure sensors located in the ATPS on the car, and to adapt the tyres pressure if necessary. This includes the decreasing of the pressure if it is too high, by releasing air through the tyres rim, and it also includes the refilling of the tyres, if there are small leakages. 2. HARDWARE AND SOFTWARE CONFIGURATION 2.1 Electro-Pneumatic System Description As shown in Fig. 1, the hardware system consists of a rapid control prototype unit (MABX), a Power- and Communication-Interface (PCI) and an air-pneumatic unit, called Central Air Unit (CAU). In Fig. 3, it is possible to see a more detailed schematic of the air-pneumatic unit. All the valves in the CAU, are actuated by the rapid control prototype unit. These parts are installed in the boot bottom in a prototype car, in the space normally assigned to the reserve wheel (not anymore necessary). Each tyre is connected to the
Control Pipe HMI
Supply Pipe
Central Air PCI+MABX Unit
Fig. 1. Automated tyres pressure control system mounted in a prototype car. air unit by using two pneumatic pipes: one Control Pipe for actuating the valves in the tyres rim (V9 , . . . V12 ), the other Supply Pipe for delivering the air to the tyres. The pneumatic connections between pipes and rims in the tyres are describe in the (SSF GmbH Patent, 2003). The driver can instruct and supervise the ATPS via a Human Machine Interface (HMI) mounted in the cockpit, see Fig. 2. From the electrical point of view, the PCI
2.2 bar 25 ˚C
2.2 bar 25 ˚C
2.2 bar 25 ˚C
2.2 bar 25 ˚C
AUTOMATIC
Automatic
Front Axle Increase Pressure
Rear Axle Increase Pressure
Front Axle Decrease Pressure
Rear Axle Decrease Pressure
A M MANUAL
Manual
Fig. 2. Human Machine Interface mounted in the prototype ’Air Vehicle’. provides the rapid control prototype unit information from the vehicle CAN and from an installed HMI. With this information and the status data coming from the CAU, the software algorithm calculates the necessary actuation sequences for controlling the tyres pressure. The Control Commands are send to the power interface of the rapid control prototype unit and forwarded to the air unit. The air unit, shown in Fig. 3, consists of: pressure sensors S1 , S2 and S3 , for measuring the pressure in the accumulator PS1 , and for measuring the pressures in the supply pipes PS2 and PS3 , valves for setting up the necessary tyres pressure levels V1 , . . . V12 , a compressor C1 , composed of a motor M1 and a pump P1 and an accumulator A1 for storing the compressed air. Additionally an air-dryer AD1 is present, which is used for
515
Front Tyre „Right“
Interface Input V9
V1
Control Logic PI
V10 V2
S2
Manual Mode Automatic Mode
V5 V7
Front Tyre „Left“
V8 C1
Rear Tyre „Right“
P1 V11
PI
A1
S1 V3
AD1 M
M1
Accumulator Pressure Control Loop
Tyres Pressure Control Loop
Vehicle Controller
PI
V12 V4
S3
V6
Rear Tyre „Left“
Interface Output
External Information Flow Internal Information Flow
Fig. 3. Proposed Pneumatic System: Central Air Unit(CAU). protecting the valves especially in wet and cold ambient conditions. 2.1.1. Tyres Pressure Increasing By controlling the valves V5 and V6 of the air unit, it is possible to deliver compressed air from the accumulator A1 to the front/rear supply pipes. Then it is possible to actuate additional valves which are placed in the rims V9 , . . . V12 , as shown with the dotted arrows in Fig. 3. The valves which are placed in the rims can only be controlled pneumatically with the outstreaming air coming from the electriccontrol valves V1 , . . . V4 . This has the advantage, that the connections between the rotating parts of the rims and the parts of the pipes, which are at standstill, is executed just with compressed air: this can guarantee a long system lifetime. 2.1.2. Tyres Pressure Decreasing The decreasing procedure is analog to the increasing procedure with the difference that, before opening the valves in the rims V9 , . . . V12 , the front/read pipe needs to be deflated at the ambient pressure. This can be done by opening the valve V7 , or if it is needed, to regenerate the air-dryer AD1 , by opening the valve V8 . 2.2 Software Architecture Concept The ATPS software architecture is shown in Fig. 4. It is divided in four main parts: one consists in the controlling of the accumulator supply pressure PS1 (Accumulator Pressure Control Loop), the other three parts have the task to control the valves in the air unit and as consequence the regulation of the valves in the rim V9 ,...V12 . To observe, that this two control functionality can’t be considered completely independent, because they are interacting, along the same pipe, during the refreshing of the air-dryer AD1 . This means, that a simultaneously increasing of the pressure in the accumulator is not possible while the pressure in the tyres are deflating with a regeneration
Reference Pressures Information / Command Flow
Fig. 4. Proposed Control Software Architecture. of the air-dryer. As shown in Fig. 4, a Vehicle Controller module has the task to calculate the tyres pressure references, which are needed for the currently existing driving situation. This target pressures are then passed at the Tyres Pressure Control Loop module that actuates the CAU. For overviewing the different SW parts, a module, so called Control Logic, has been introduced with the aim to enable the different control loops and to recognize eventual error conditions. Additional software parts were needed to make the ATPS working on the prototype car: a kind of communication interface between the HMI, the CAN and the CAU has been developed. 2.2.1. Accumulator Pressure Control Loop The control loop for the accumulator pressure has the task to keep the supply pressure PS1 within a certain range [PS1min , PS1max ]. A special control strategy based on the rotational speed nC1 of the compressor DC motor M1 has to be carried out. Following variables have been taken into consideration, see eq. (1): the currently existing accumulator pressure PS1 , the rate of changing of the pressure dPS1 /dt, the operating time of the compressor Ton , the compressor temperature o TC1 and the velocity of the car vv . This has the effect to reduce the noise and the vibrations produced by the compressor during the reload of the accumulator at low car speeds. nC1 = fn (PS1 ,
dPS1 o , Ton , TC1 , vv ) dt
(1)
As a further step, if there would be more than one compressor, the regulation of the rotational speed could be replaced by a sequential turning ”On” and ”Off” of the compressors. Not only the regulation of the steady state rotational speed nC1 is considered, also the minimization of the motor effort during the starting up of the compressor has been evaluated: in fact when M1 is starting, the valve V8 is opened for a short time, in order to avoid a full load start and to decrease the peak of current absorbed from the battery. Since the
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2.2.2. Tyres Pressure Control Loop Through the HMI the driver has the ability to choose between two different working modes: ”manual mode” and ”automatic mode”. By choosing the ”manual mode” the Control Logic allows the driver to adapt the tyres pressure from himself: e.g. in off-road conditions for maximizing the traction forces or for increasing the damping, it is necessary to reduce the tyres pressure. This can be done manually by pressing the two buttons Front/Rear Axle Increase/Decrease in the HMI, see Fig. 2. For giving at the ”operator” a feedback about his actions, the currently existing tyres pressure is displayed in a small screen in the cockpit. A SW-check avoids that the driver increases/decreases manually the tyres pressure outside at the safety admitted ranges. In ”automatic mode” the SW calculates the individual tyres pressure for providing best effort in terms of comfort, fuel consumption and traction. Depending on the currently driving situation (vehicle speed vv , vehicle acceleration/deceleration av , axles loads Mf , Mr , brake pedal Br , tyres temperatures Tio and road state St ) the admitted target pressures ranges [PRmini , PRmaxi ], i=1...4 are calculated by the Vehicle Controller module and passed at the Tyres Pressure Control Loop. [PRmini , PRmaxi ] =
experimental results of the system performance for a filling process
35 30 25 filling time tmi[sec]
air-dryer AD1 needs to be refreshed/regenerated during the deflating of the tyres, a special action has to be fulfilled, if the compressor is simultaneously working. Putting the priority on the refreshing phase, the pump P1 needs to be temporary turned off. In this case, the Control Logic stops the Accumulator Pressure Control Loop module in favor of the Tyres Pressure Control Loop.
20 15 10 5 0 5 6 7 8
accumulator pressure PS1[bar]
9 10
1
2.5
2
1.5
3
3.5
4
actual tyres pressure Pi[bar]
Fig. 5. Experimental measurements of the actuation time as function fS of the accumulator pressure PS1 and the actual tyres pressure Pi .
Reference pressures Existing tyre pressures
Supervise tyre pressure
yes
OK
no Accumulator pressure
Estimate control times Choose actuation sequence
Send command to CAU
Command executed
yes
Existing tyres pressure
Supervise tyres pressure
f Ti (vv , av , Mf , Mr , Br , Tio , St )
This SW-Module, on the base of the difference between the measured pressures Pi and recommended target tyres pressure PRi = avg(PRmaxi , PRmini ) and also depending on the available accumulator pressure PS1 , estimates the actuating time ton/offi for each tyres, as shown in eq.(2). ton/offi = tRefi − tmi tRefi = fS (PRi , PS1 ) tm i = fS (Pi , PS1 ), i=1...4
Tyres pressure OK or timeout error
no
yes Command to CAU: „Finish control procedure“
(2)
Fig. 6. Control Sequence of the ”automatic mode” in the Tyres Pressure Control Loop.
In the first prototype the estimation of the controlling time ton/offi is based on experimental measurements on the car, as shown in Fig. 5. After estimating each time ton/offi , the Actuation Sequence for the tyres that has a longer time starts. It is also possible that front/rear pipes can be shared, and more than one tyre is controlled at the same time, therefore a proper actuation command is send to the CAU. In Fig. 6 the Control Sequence for the ”automatic mode” is summarized in a flow chart. To observe that in total are possible 19 different CAU Actuation Commands,
as summarized in Tab.1. If one pressure is too high PRi < Pi , the air which needs to be taken out of a tyre can be used for filling another tyres only if this is on the same axle. If the pressure of the accumulator PS1 is not too low, the outstreaming air is used to refresh the air-dryer AD1 , viceversa the accumulator is reloaded and in the same time the valve V7 , with the direct outlet, is opened. In Fig. 7 the Actuation Sequence which it is used for executing an Actuation Command in the CAU is shown. In both cases, that the actution command is coming from the ”manual mode”, or ”automatic
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Command No
Command Description
NOP (0) IncFL (1) DecFL (2) IncFR (3) .. . AllDec (14) FaLock (15) RaLock (16) Pcalib (17) ChkSens (18)
No Op.: valves in default position Increase press. in the front left tyre Decrease press. in the front left tyre Increase press. in the front axle .. . Decrease press. in all tyres Equalize the front axle pressure Equalize the rear axle pressure Calibrate all pressures equal Check pressure sensors
Front tyre „right“ V9 V1
PI
V10 V2
Actuation command n
V8 C1 P1 V11
AD1
A1
PI
S1
M
V3
Tyre Pressure
PI
V12 V4
M1
S3
V6
Accumulator Pressure
Rear tyre „left“
Fig. 8. Front right tyre pressure measurement sequence.
Close control valves
Reduce pipe pressure
Select, determine and set up supply pipe pressure
Close supply valves
stable and will nearly be the same as the pressure in the tyre itself. For avoid that small amount of air of the tyres is lost, during the measurement process, the pipes are preloaded from the accumulator, before opening the valve in the rim. 3. MEASUREMENTS RESULTS
Set error-bit
yes Open control valves
10
20
accumulator pressure P
S1
↓
S2
5
10
Operation Command N0
←front supply pipe pressure P 0
Operation Command N →
S2
Fig. 7. Actuation Sequence for executing an Actuation Command in the CAU.
1
Actuation command n+1
S3
t n+1
2
3
4
Send status message
In this section the measurements results of a prototype ATPS system are presented: in Fig. 9 the ”manual mode” procedure is shown. In this meaSystem Pressure P , P , P ; Tyre Pressure P , P , P , P [bar]
no
OK
V7
Rear tyre „right“
Table 1. CAU Actuation Commands. tn
V5
S2
Front tyre „left“
S1
mode”, this loop is always the same. As already mentioned, first the pipes are filled and then the valves in the rim are actuated. To observe that ↓ ↓ ↑ ↑ during the transition from a command n to the next command n + 1 the state PSfrag of the replacements system 0 0 0 1 2 3 4 5 6 7 8 9 10 is evaluated, and the pipes are inflate/disinflate t[s] only if necessary. For this reason 19*(19-1)=342 Fig. 9. Pressures behaviour during operating in possible cases, of transition from one command to ”manual mode”. the next, have been taken into consideration. surements, at t'0.5s, both buttons ”Front/Rear 2.2.3. Tyres Pressure Measurement Sequence Axle Increase Pressure” of the HMI are pressed, in For evaluating the right control action the tyres order to increase the pressures Pi in all four tyres. pressures must be measured. Every tyre is meaThe Actuation Command number 13 is executed, sured automatically with a certain sequence that at first by increasing the pressure in the supply fill up the correspondent supply pipe. In Fig. 8 pipes and then after reaching a certain threshold is shown the configuration of the valves for mea(dependent of the actual accumulator pressure suring the pressure in the front right tyre. The PS1 ), the valves in the rim are open and the filling pressure measurement of the tyres is executed procedure starts. After a few seconds (t ' 3.5s), with the pressure sensor S2 or S3 in the pipes. The the driver decides to increase the pressure only of pipes connections between the pressure sensors the tyres of the front axle (Actuation Command S2 , S3 and accumulator A1 needs to be closed. number 5). The pressure in the front pipe is kept The air which is taken out of the accumulator go while the pressure in the rear pipe is decreased, to actuate one of the valves in the rim V9 . After with refreshing of the air-dryer. At t'5.5s both a short time, the pressure in the supply pipes is buttons are pressed again: the pressures in the ←rear supply pipe pressure PS3 rear left tyre pressure P3
rear right tyre pressure P4
front right tyre pressure P2
front left tyre pressure P1
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pipes are set up immediately, without any deflation, before that the filling procedures restart. In Fig. 10 and in Fig. 11 are shown the measurements for the ”automatic mode”. Depending on
rag replacements
40
reference pressure P
→
V
Rmax
Vehicle Velocity v [km/h]
Tyre Pressure P1, P2, P3, P4 , Reference Pressure PRmax, PRmin [bar]
4
rear right tyre pressure P4
2
↓
rear left tyre pressure P3 reference pressure P
20
↓
Rmin
↓
↑
front right tyre pressure P2
↑
front left tyre pressure P1
←vehicle velocity vV
0
0
5
4.1 Acknowledgements 10
15
20
25
0 30
t[s]
Fig. 10. Dynamic changing of the tyres pressure during driving in ”Automatic Mode”(starting from an initial condition where all pressures Pi are too low). the vehicle velocity vv and on the other variables, the ranges of reference pressures [PRmin, PRmax ] for all tyres are calculated. Starting from the rear left tyre, one after the others, the pressures are regulated within the optimal ranges. After few seconds, the correct pressures are reached and the passengers can enjoy the driving. In Fig. 11 are 100
←reference pressure PRmax front left tyre pressure P
1
↓
rear left tyre pressure P3
front right tyre pressure P2
↓
↓
2
50 ↑
rear right tyre pressure P4
↑
reference pressure PRmin
Vehicle Velocity vV[km/h]
Tyre Pressure P1, P2, P3, P4 , Reference Pressure PRmax, PRmin [bar]
4
rag replacements
←vehicle velocity vV
0
0
10
system not only the accurate measuring of the tyres pressure is possible, but also an automatic adjustment of the pressures corresponding to the currently existing driving situation. The shown system has been realized in a prototype car and the control software is becoming an utility patent. Further investigations in the systems concept, pneumatic technology and in the strategy of controlling might bring additional improvements in term of actuation speed and space occupied on board. This leads to the possibility of a real-time vehicle dynamics control, which could create new driving feelings, and make cars and trucks more save and comfortable.
20
30
40
50
0 60
t[s]
Fig. 11. Dynamic changing of the tyres pressure during driving in ”Automatic Mode”(starting from an initial condition where all pressures Pi are too high). shown the regulation results for the ”automatic mode” starting from an initial condition in which the pressure in all four tyres are too high, this could append e.g. when the temperature of the road change. 4. CONCLUSION A system for monitoring and controlling the tyres pressure of a car is presented. With the proposed
Hearty greetings at all the people that directly or indirectly support the construction of the prototype Audi A8 with ATPS. Particular thanks at the company Ventrex Automotive GmbH for the construction of the CAU, and at the company SSF GmbH for the mechanical implementation of the connection to pipe-rim. Without these partners the realization of the system would have been not possible. REFERENCES Bochmann, H., Kessler, R. and Schulze, G. (2005). Stand und aktuelle Entwicklungen bei Reifendruck-Kontrollsystemen. Automobiltechnische Zeitschrift (Jahrgang, Ed.), 107, Pages: 110 - 117, February, 2005. Biermann,J.-W.,Beckmann, T., Wech, L., Meier, R. (2004). Analyse des Reifenabrollger¨ auschs. Automobiltechnische Zeitschrift (Jahrgang, Ed.), 106, Pages: 950-956, June, 2004. Bosch, R. (2000). Kraftfahrtechnisches Handbuch (Vieweg-Verlag, Ed.), Pages: 708-768. Loomann (2003). Handbuch Kraftfahrzeugtechnik (Vieweg-Verlag, Ed.), Wiesbaden (Germany). Normann, N.(2000). Reifendruck-Kontrollsysteme f¨ ur alle Fahrzeugklassen. Automobiltechnische Zeitschrift, (Jahrgang, Ed.), 102, Pages: 950956. Ringdorfer, M. (2005). Regelung eines automatischen Reifendruckkontrollsystems (MAGNA STEYR Fahrzeugtechnik - FH Joanneum), Graz (Austria). SSF, Steyr-Daimler-Puch Spezialfahrzeug GmbH Patent: EP1141595B1 (2003). Anordnung mit konzentrisch zueinander angeordneten und relativ zueinander rotierbaren Bauteilen und Verwendung dieser Anordnung bei einer Reifenf¨ ullanlage, Wien (Austria). Technical Research Centre of Finland (2003). Intelligent Tyre Systems - State of the Art and Potential Technologies, Pages: 82-91.
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