POSSIBILITIES OF USING PNEUMATIC STABILIZATION OF VEHICLES MOŽNOSTI POUŽITIA PNEUMATICKÉHO STABILIZAČNÉHO SYSTÉMU

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1 ACTA FACULTATIS TECHNICAE XX ZVOLEN SLOVAKIA 2015 POSSIBILITIES OF USING PNEUMATIC STABILIZATION OF VEHICLES MOŽNOSTI POUŽITIA PNEUMATICKÉHO STABILIZAČNÉHO SYSTÉMU Jan HURTEČÁK 1 Viktor NOVÁK 1 Jaromír VOLF 1 1 Czech University of Life Sciences Prague, Department of Electrical Engineering and Automation, Faculty of Engineering, Kamýcká 129, , Prague 6, Czech Republic ABSTRAKT: Příspěvek popisuje zcela novou a původní možnost stabilizace motorových vozidel na vozovce, která využívá stlačený vzduch jako podporu konvenčním stabilizačním systémům. V článku jsou nejprve shrnuty stávající způsoby stabilizace motorových vozidel, trendy a vývoj v dané oblasti, výhody a nevýhody jednotlivých systémů. Dále je detailně popsána metoda pneumatické stabilizace, jednotlivé prvky systému a jejich funkce. Následně je stručně nastíněn postup výpočtu, jsou provedeny příslušné kalkulace působících sil, jež jsou slovně i graficky prezentovány a hodnoceny. Na základě vypočtených hodnot je závěrem diskutována efektivita celého pneumatického stabilizačního systému. Kľíčová slova: ABS, ESP, pneumatická stabilizace, trysky ABSTRACT: This paper describes a new and original pneumatic way of car stabilization, using compressed air as the support of the conventional stabilization systems. The article summarizes the presently used methods, trends and development in car stabilization and it points out their advantages and disadvantages. Then the paper describes the designed pneumatic system in detail. Thereafter, there is briefly quoted the calculation method of the pneumatic system, the acting forces are calculated and the results are subsequently presented and discussed. Finally, the overall efficiency of the system is analyzed. Key words: ABS, ESP, pneumatic stabilization, jets INTRODUCTION Modern cars, trucks and motorbikes as well are today equipped with a lot of active and passive safety components. Among the basic ones is the ABS Anti-Lock Braking System. It is used in personal cars and lorries and recently motorbikes, too. This anti-lock system was first introduced in 1978 by firms Bosch and Mercedes-Benz as extra equipment for additional charge at model S and since then it has been widely spread in all models of all car types (Kovanda, 2009). But there is still a danger of accidents due to increasing ACTA FACULTATIS TECHNICAE, XX, 2015 (2):

2 traffic and unexpected or unpredictable traffic or weather conditions. The car stabilization systems help the driver to keep the vehicle on a safe track, but the function of the conventional stabilization systems is restricted due the limited friction between the road and the tyre. In the article we present an original method of car stabilization using pressurized air based on the principle of action and reaction. PRESENT STATE OF CAR STABILIZATION Overview of the car stabilization systems The ABS has been gradually connected with other systems, which make the comfort better and increase the car safety and the safety of other transport participants as well. These other systems are especially: BAS (brake assistant) recognizes critical situations and by increasing the pressure it enables the full braking effect ASR (anti-slip regulation) prevents slip-spinning at acceleration and moving off by reducing the torque of the engine EMS reduces the rotary inertia until the powered wheels are at the full adhesion MSR (Motor-Schleppmoment-Regelung) prevents slip-spinning when braking using the engine ESP (Electronic Stability Program) prevents the car slipping by braking a selected wheel and thus eliminating understeering and oversteering Since these systems keep the vehicle in the required direction, they are very important and they surely help the car driver. But there are also situations when all these mostly preventive systems cannot help the car because the behaviour of driving people is sometimes unpredictable, and it is also influenced by other drivers who can affect the behaviour of the driver, thus his reaction is wrong. The weather can play an important role, too. There are situations, when on a very clean road without snow or ice after machinery clearing, there are some rest icy places for example on bridges. The new method of car stabilization could be useful in these situations and it could help the driver and solve a problematic situation more easily and it could even save peoples lives. The driver can get into these critical situations either by an inadequate speed in turning, or when there is an adhesion loss in turning, e.g. by change of the roadway surface or by both conditions together. The problem is that using only adhesion based systems the force that can be transferred between the tyre and the road is limited depending on the coefficient of friction. The purposed system uses the Newton s Law of Action and Reaction, and it is not limited due the friction with the road. Description of the individual ABS components and functions Presently used car stabilization systems work in connection with the ABS. From the pressure sensor of brake fluid the control unit is informed about the pressure in braking system. The sensors measure the pressure that is created by pressing the brake pedal. Then the ABS control unit compares these signals in both ways. The control unit is informed about the actual pressure in brake system by the pressure sensor of the brake fluid. If interference is necessary, the control unit uses then the actual value of the brake pressure to the calculation of side forces. 46 ACTA FACULTATIS TECHNICAE, XX, 2015 (2): 45 50

3 Next part of the ABS represents sensors of vehicle acceleration. The accelerometers give a considerable proportion of information about the car s behavior. They are used not only for measurement of eccentric or inertial forces, but also for determination of the subject position, its declination or vibrations, too. The sensor of the longitudinal vehicle acceleration is assembled to a four-wheel drive car only. On cars with drive of only one axletree the system calculates the longitudinal vehicle acceleration from the brake pressure sensor signals, from the wheels revolutions sensors and from the information of the engine control unit. The sensor of the side acceleration informs about side forces applied on the car. This information is important for calculations of the forces that have to be overcome for staying up the car in the intended way. The sensor read stay if the car doesn t revolve around the vertical axis. The micro mechanic system with the double tuning fork from silicon monocrystal placed on the sensor desk is the basic part of the sensor of the rotary speed. The double tuning fork is created by exciting tuning fork and specific tuning fork. The sensor of the steer angle is the next part of the car stabilization. This sensor sends a partly signal about the steer angle and a partly signal about the speed of the steeringwheel turn. Both signals are first evaluated in the control unit and they are then sent to the control unit of electromechanical servo control. Two absolute magnetic angle sensors are used in the control unit Bosch. These absolute sensors unlike incremental sensors give the information about the steer angle in the full angles range in every time (Cerha, 2010), (Kovanda, 2010). All these car stabilization types use information about the car behavior and about the upon a car acting forces to keep the car in the intended trajectory by separate wheels braking, by the engine torque changing, or by its redistribution to the separate axletree, respectively on the separate wheel. PNEUMATIC STABILIZATION OF CAR Description and operation of the pneumatic stabilization system The cohesive security system pneumatic car stabilization can be a new trend in development and some system upgrade to above-mentioned conventional antiskid systems. It bases on the Newton s Law of Action and Reaction. Very pressurized air volume will grab in the critical moment form jets which are placed in car s body corners next to wheels (Direct Industry, 2013), (JS Humidifires, 2013). A schematic design of the system s components is represented in Fig. 1. Fig. 2 shows the positioning of the jets in the front view on the car. The necessary components with respective numbers relating to the figures are following: Compressed-air reservoir (1) Compressed-air tubes to jets (3) Independent jets in the car s body corners (4) Quick vents operating the jets Compressor (2) Connection to the ESP control unit ACTA FACULTATIS TECHNICAE, XX, 2015 (2):

4 Fig. 1. Schematic design of the pneumatic stabilization system Fig. 2. Front view on the car with air jets The compressed air reservoir is placed in car s center of gravity. The compressed air is supplied by the air compressor, which is placed in the front part of the car. The compressed air is distributed by the pressure tubes to the jets. The jets are operated by very quick air valves and they are placed in the car s corners. This way the speedy air emission from the jets is guaranteed. The compressor will preferentially use electrical energy obtained by car braking or by riding from a hill, alternatively the right moment of the compressor run may be defined by means of GPS navigation data of the car. It this case it is also possible to use energy recuperation. In the future, the pneumatic security system may be linked to still developing ITS services, so that the driver can be warned by pilot light about the impeding danger in advance and the system can be prepared for the relevant action, e.g. about a dangerous icy part of the road on a bridge. 48 ACTA FACULTATIS TECHNICAE, XX, 2015 (2): 45 50

5 Calculation of the pneumatic stabilization system and calculated results In the calculation of the designed system we based on aerodynamics, namely on the equation of state of gases. The outflow speed of the air ejecting from the jets has been calculated and subsequently the forces that acts on the car has been determined. The calculation of the outflow speed of the air includes the change of volume, temperature and pressure in the adiabatic expansion of the ejecting air. All calculations were performed using the software Mathlab. The control calculations were implemented for the jet with the output diameter 3,5 cm and the narrowest diameter 1,5 cm, compressed-air reservoir with pressure values of 10 MPa, 15,5 MPa and 20 MPa, volume of the reservoir 0,05 m 3, car mass kg, speed of the car 80 km.h -1 and the radius of turn 50 m. Fig. 3 shows the results of the calculations for individual pressures and temperatures. The graph shows the dependency of the sum of compensation forces generated by the jets on the start pressure and temperature conditions. For the initial condition of 15,5 MPa, the pressure in the reservoir decreased to the final value of 3,5 MPa in 3,2 s. The centrifugal force acting on the sample car has the value of 9,88 kn. The sum of acting forces generated by the jets reached the value of 6,28 kn for the starting pressure 15,5 MPa and the temperature 323 K, which represents approximately 64 % of the centrifugal force. The option with the reservoir pressure of 10 MPa resulted in compensation force of 3,86 kn (39 % of the centrifugal force) and the option with the reservoir pressure of 20 MPa gave the compensation force up to 8,30 kn, which represents even 84 % of the centrifugal force. The dependency of the compensating force on the reservoir pressure is not linear; a reduction of pressure by 36 % leads to reduction of compensating force by 61 %, respectively an increase of pressure by 29 % results in increase of force by 32 %, compared with the 15,5 MPa pressure option K 423 K 523 K (Mpa) 15,5 (Mpa) 20 (Mpa) Fig. 3. The dependency of the compensation force on the pressure and the temperature ACTA FACULTATIS TECHNICAE, XX, 2015 (2):

6 The calculated results give utilizable values for a real time compensation of the centrifugal forces. The calculations confirm that the designed pneumatic stabilization system can be effectively utilized and it can help the ESP in a critical situation, primarily in very low friction conditions on an icy surface, where the transferred force by the common adhesive stabilization systems is insufficient. CONCLUSION The aim of the article was to present an entirely new car stabilization system pneumatic stabilization using compressed air. The layout and function of the individual system components was described. Based on the preformed calculations, the overall capability of the system to produce an adequate compensating force for the sample car has been proved. The compensating forces from the jets reached up to 84 % of the centrifugal force in a sample turn. The pneumatic system has proved its ability to contribute to stabilization of the vehicle in an adhesion-loss situation. There are possible some further improvements of the system, e.g. use of higher pressures that are more potent or drying of the ingested air by the compressor to avoid possible freezing of the air humidity. The device might be mainly placed at the bottom of the car so that it would not occupy other usable space; it might be easily incorporated into present ESP system. In case of mass production even the price might decrease considerably and the costs would be compensated by a major safety gain. REFERENCES [1] CERHA, J Hydraulické a pneumatické mechnismy I. Liberec: Technická univerzita v Liberci, ISBN [2] KOVANDA, J., RŮŽIČKA, T., KEPKA, M Bonding of Structural Parts of Vehicle Bodies and Aspects of Passive Safety. In: Transactions on Transport Sciences, ISSN: X, 2009, vol. 2, no. 2, pp [3] KOVANDA, J Driver Car Interaction & Interface. Praha: Ústav Informatiky AV ČR, p. ISBN [4] DIRECT INDUSTRY. Air Eliminator. [online]. [cit ]. < com/prod/mankenberg-gmbh/air-eliminators html>. [5] JS HUMIDIFIERS. Jet Spray The World s Leading Air & Water Atomising Humidifier. [online]. [cit ]. < Contact adress: Ing. Jan Hurtečák, MBA 50 ACTA FACULTATIS TECHNICAE, XX, 2015 (2): 45 50