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Advances in Automobile Engineering: Brake Assisted Differential Locking System
Abstract
“It takes 8,460 bolts to assemble an automobile, andone nut to scatter it all over the road.”
Some of the biggest advances in the field of automotive technology in the past 10 years have come in the area of safety.Spurred by the improvements in the microprocessor speed,miniaturization, and software development, the automobile continues to evolve.
In this new approach proposed, I am going to have an electronic and a pneumatic circuit to automatically control the traction of the vehicle.
During ordinary conditions, when the vehicle is driven down a straight road, or if the difference between speeds of the two(rear) wheels is below a specified limit, no signal will be generated by the electronic circuit. This helps the vehicle negotiate the turns with better traction control as differential action is unaltered. But if the difference between speeds is beyond a specified limit, the signal will be generated by the electronic circuit which will actuate the pneumatic circuit. This causes gradual braking on the faster wheel until it gains traction.Hence, the wheels will never lose traction.
This system ensures a reduction of more than 50% in the capital investment as compared to the already existing systems can tilt the scales in the favour of the manufacturing company and eventually the cost conscious consumer.
Key words: Differential locking, traction control, Limited slip differential, pneumatic braking.
I. INTRODUCTION
Are you really comfortable manoeuvring your vehicle through a muddy patch?
In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground .As long as the tyre grips the road,providing a resistance to turning, the drive train forces the vehicle forward.
Driveline torque is evenly distributed between the two rear drive axle shafts by the differential. When one tyre encounters a slippery spot on the road, it looses traction, resistance to rotation drops, and the wheel begins to spin. Because the resistance has dropped, the torque delivered to both the wheels changes. The wheel with good traction is no longer driven. If the vehicle is stationary in this condition, only the wheel over the slippery spot rotates. Hence the vehicle does not move. This situation places stress on differential gears. As the traction fewer wheels rotates at a very high speed, amount of heat generated increases rapidly, lube film breaks down, metal to metal contact occurs, and the parts are damaged. Now if the spinning wheel suddenly has traction, then the shock of the sudden traction can cause severe damage to the drive axle assembly.
So presently how do we overcome these difficulties?
To overcome these problems, differential manufacturers have developed the –Limited Slip Differential. In automotive applications, a limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity. The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate at twice its intended velocity – the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels. The clutch type LSD responds to drive shaft torque. The more drive shaft input torque present, the harder the clutches are pressed together and thus the more closely the drive wheels are coupled to each other.
Limitations of the Limited Slip Differential
a) Heat dissipation leads to lube film breakage, metalto-metal contact occurs.
b) If the friction lining of the energized clutch is damaged, the whole assembly has to be dissembled.
c) High quality lubrication required.
d) Due to presence of large number of mechanical components, reliability is less.
e) As the speed increases, noise of vehicle also increases.
f) Complicated and costly.
II. PROPOSED INNOVATION-BRAKE ASSISTED DIFFERENTIAL LOCKING
SYSTEM (BADLS)
In this new approach, there is an electronic and a pneumatic circuit to automatically control the traction of the vehicle. During the ordinary conditions, when the vehicle is driven down the straight road, or if the difference between the speeds of the two (rear) wheels is below a specified limit, no signal will be generated by the electronic circuit. This helps the vehicle negotiate the turns with better traction control, as the differential action is unaltered. But if the difference between the speeds is beyond a specified limit, the signal will be generated by the electronic circuit, which will actuate the pneumatic circuit. This causes gradual braking on the faster wheel until it gains traction. Hence, the wheels will never lose traction. The BADLS control module senses that a wheel is about to slip based on the input sensor data and in turn pulses the normally open inlet solenoid valve closed for that circuit.This allows fluid to enter the circuit. At the same time, the control module opens the normally closed solenoid valve for that circuit. This leads to the application of pneumatic pressure on the brake pads, leading to the artificial braking. Once the affected wheel returns to the same speed as the other wheel the control module returns both the valves to their respective normal positions releasing any residual pressure in the pneumatic circuit of the affected brake.
Fig. 1 SCHEMATIC CIRCIUT OF BADLS
WORKING:
Normal Braking System Artificial Braking System(BADLS)
When Slipping Take Place
Normal Braking Condition
When Speed Sensors Detect The Slipping Condition
Brake Control Valve Actuated
Microcontroller Actuates Normally Opened Solenoid Valve2
Microcontroller Actuates Normally Closed Solenoid Valve1 And Normally Opened Solenoid Valve2
Solenoid Valve1 Remains In
Default Normally Closed State
Artificial Braking Is Applied To The Required Wheel By Flowing In The Auxiliary Circut
Air Flows From Maste Cylinder Through The Main Circuit By Passing The Auxiliary Circut
空氣經(jīng)主電路從主汽缸流出繞過輔助電路
Fig. 2 WORKING OF THE BADLS CIRCUIT
Flowchart to explain working of the circuit shown in Fig 1 is given above in Fig 2. First flowchart shows working of normal breaking circuit and the latter shows the working when the badls circuit is working. During normal breaking condition solenoid valve 1 is in closed condition so air from master cylinder flows in main braking circuit bypassing the auxiliary circuit through solenoid valve 1 and thus normal breaking action is achieved. .In slipping condition microcontroller actuates normally closed solenoid valve and normally open solenoid valve 2 and thus artificial braking is applied to the required wheel.
A. The BADLS Control module
The system is provided a control system, at least two driven wheels, a differential for transmitting power from the engine to the driven wheels and permitting relative velocity between the driven wheels. The control system includes two wheel velocity sensor, a comparator circuit and a control circuit. The wheel velocity sensor is configured to detect the angular velocity of the two driven wheels and to generate a signal. The comparator circuit is coupled to the wheel velocity sensor and is configured to compare the signals of the sensors and to generate a slip signal representative of the degree of slip of the driven wheels. The control circuit is coupled to the comparator circuit and to the brake assisted differential locking mechanism and is configured to generate control signals when a predetermined degree of slip occurs and to apply the control signals to the differential locking mechanism to limit relative velocity between the driven wheels.
III. PROPOSED ARCHITECTURE FORBRAKE ASSISTED DIFFERENTIAL LOCKING SYSTEM
The control circuit shown below in Fig.3 is configured to receive signals representative of vehicle operating parameters (condition of slipping of wheels) and to generate control signals corresponding to the desired state of the brake assisted differential locking mechanism for limiting relative velocity between two driven wheels. Sensors are associated with the rear wheels. Control logic executed by the control circuit in a continuously cycled routine determines the desired state of the differential locking mechanism based upon the operating parameters.
Fig. 3 PROPOSED ARCHITECTURE OF SYSTEM
The control circuit applies an appropriate control signal to the differential locking mechanism causing engagement or disengagement in accordance with the desired state. Wheel velocity sensor are configured to detect the velocity of the two rear wheels and to generate a wheel velocity signal given as an input to the micro controller. A comparator circuit of the micro controller is coupled to the wheel velocity sensors generate a slip signal representative of the degree of slip of the driven wheel. A control circuit is coupled to the comparator circuit and to the differentia locking mechanism and configured to generate control signals when a predetermined degree of slip occurs and to apply the control signals to the differential locking mechanism to limit relative velocity between the driven wheels by applying artificial braking by actuating the solenoid valves. The control circuit is further configured to disengage the differential locking mechanism when the degree of slip decreases to a level below a predetermined threshold. Wheel velocity sensor is provided for each of the driven wheels, each of the wheel velocity sensors being configured to generate wheel velocity signals and to apply the wheel velocity signals to the comparator circuit, and wherein the control circuit is configured to generate control signals for limiting relative velocity between the driven wheels when slip of any driven wheel exceeds a predetermined threshold value.
IV. SPECIFICATIONS FOR ELECTRONIC COMPONENTS
? MICRO CONTROLLER
? ANALOG TO DIGITAL CONVERTER
? SIGNAL CONDITIONER
1. Transistor
2. Diode
A.MICROCONTROLLER
USE IN BADLS: The microcontroller input is the speed of the two wheel speed sensors. The microcontroller obtains the difference in between the two speed sensor outputs and compares it with the maximum allowable variation. If the variation is beyond the stipulated value, it activates the solenoid valves, thus enabling the auxiliary circuit, avoiding any slipping of the wheels.
B.SOLENOID VALVE
USE IN BADLS: They act as ON/OFF switches and control flow of pressurized air into the Auxiliary Circuit.
TYPE: Spool Type
C.ANALOG TO DIGITAL CONVERTER
USE IN BADLS: the analog speed signal from the wheel speed sensors is converted into the digital format by the ADC which is supplied as the input to the microcontroller
D. AIR BRAKING SYSTEM
In the air brake's simplest form, called the straight air system, compressed air pushes on a piston in a cylinder. The piston is connected to a brake shoe, which can rub on the wheel, using the resulting friction to slow the train. The pressurized air comes from an air compressor and is circulated by a pneumatic line made up of pipes and hoses. In order to apply the braking force to the brake shoes, compressed air is used. An air brake system in general includes a compressor unit, air-reservoir tank, brake chamber and wheel mechanism.For maintaining adequate braking force at all times even whenthe engine is not running and air-reservoir tank is also necessary. To maintain air pressure, which is small air pump,is used.
The compressor takes air from the atmosphere through the filter and the compressor air is sent to the reservoir through the unloader valve, which gets lifted at a predetermined reservoir pressure and relieves the compressor load. From the reservoir the air goes to the various accessories and also to the brake chambers also called the diaphragm units at each wheel, through the brake valve. The control of brake valve is with the driver who can control the intensity of breaking according to the requirements. The unloader valve in the air breaking system serves to regulate the line pressure.
V.TESTING AND EVALUATION PARAMETERS
The system has been tested on a SAE BAJA test vehicle at the Automotive Research Association of India (ARAI), pune. This was done keeping in mind that this application would be really helpful for SAE BAJA teams who encounter conditions like slipping of wheels very often. Since vehicle slip is usually about 12-15% while turning, this microcontroller of the system has been designed to active at about 20% slip conditions and deactivates at about 5% slip. The system was tested successfully and the next step would be practical implementation in automobiles after some minor modification.The vehicle was jacked up on one wheel with the other wheel resting on ground surface .This was done to simulate the condition of maximum slipping. This condition will be present in actual conditions when vehicle is negotiating rocky terrain. The engine was started and accelerated. Due to one wheel being in air, the vehicle did not move forward and the jacked wheel rotated excessively. Now the solenoid was activated for the slipping wheel and artificial braking was provided. As a result the torque transmitting capacity of the wheels increases and consequently, the vehicle pulls over the rocks and gravel on the basis of the torque from the individual wheel.
VI.COST COMPARISION TABLE
As can be seen from the above table that this system ensures a reduction of more than 50% in the capital investment as compared to the already existing systems.
Table I. COMPARISON OF BADLS SYSTEM WITH EXISTING LSD SYSTEM IN THE MARKET
EXISTING SYSTEM
LIMITED SLIP DIFFERENTIAL(LSD)
l TRD LSD Rs.60000
l QUAIFE LSD Rs.70000
TOTAL-RS 65000 or $1625
PROPOSED SYSTEM
1. OPEN DIFFERENTIAL ：Rs.20000
2. ELECTRONIC CIRCUIT ：Rs.1000
3. SPEED SENSORS ：Rs.7500
4. CHECK VALVE ：Rs.1000
5. SOLENOID VALVE ：Rs.1000
TOTAL-RS 31000 or $750
VII.ADVANTAGES
a) Can be easily implemented in vehicles having pneumatic braking systems with slight modification.
b) As electronic circuitry is used, response time, control and reliability are better than the existing systems.
c) Low grade lubricants can be used as heat loss is reduced.
d) Last but not the least; the system is economical and simple.
VIII.LIMITATIONS
The overall efficiency depends on the combined efficiency of both the electronic as well as the pneumatic system.
IX.APPLICATIONS
The system can be successfully incorporated in vehicles having pneumatic/hydraulic braking system, with a view to provide improves traction. It can be put to use in especially All Terrain Vehicles (ATV) and vehicles operating in high altitude areas (vehicles for military application) where snow causes excessive loss of traction. This system ensures a reduction of more than 50% in the capital investment as compared to the already existing systems which ensures the cost effectiveness of the endeavour.
ACKNOWLEDGMENTS
The author is grateful to Prof. R.B.Patil, Head of Department,Army Institute of technology, India and Dr KC Vora at the Automotive Research Association of India, (ARAI) for their guidance and support.
REFERENCES
[1] Jack Erjavec, Automotive Technology- A systems approach (Delmar Thomson Learning, 2000)
[2] T.K. Garrett, K.Newton, W.Steeds, the Motor Vehicle (Butterworth Heinmann, 2001)
汽車工程的進步：微分鎖剎車輔助系統(tǒng)
摘要
“要組裝一輛汽車需要8460個螺栓，要把它全部撒在路上只需要一個螺母?！?
在過去十年里，汽車技術(shù)領(lǐng)域的一些最大進步已經(jīng)發(fā)展安全。由于微處理器速度的提高、小型化和軟件開發(fā)的刺激，汽車能夠繼續(xù)發(fā)展。
在提出的這種新方法中，我將用一個電子電路和一個氣壓回路來自動控制車輛的牽引。
在正常情況下，當(dāng)車輛沿著直線道路行駛，或者兩個(后)車輪的轉(zhuǎn)速差低于限制值時，電子電路將不產(chǎn)生信號。這有助于車輛以更好的牽引力控制系統(tǒng)判定轉(zhuǎn)向，因為微分動作是恒定的。但是，如果速度差超過指定限制時,電子電路將產(chǎn)生信號驅(qū)動氣壓回路，使?jié)u進制動發(fā)生在速度更快的車輪上，直到它獲得牽引力。因此，車輪將永遠不會失去牽引力。
和已經(jīng)存在的系統(tǒng)相比，這個系統(tǒng)能確保減少超過50%的資本投資，可以使效益天平傾向于制造公司，并最終傾向于具有成本意識的消費者。
關(guān)鍵詞：微分鎖；牽引力控制；防滑差速器；氣壓制動
1 介紹
當(dāng)你操縱你的車通過一塊泥濘的土地時，你真的感到舒適嗎？
在干燥條件下，當(dāng)有足夠的牽引力時，車輪的扭矩量被發(fā)動機和傳動裝置所限制；在低牽引力的情況下，例如在冰上開車時，扭矩量小于或等于最大值，不會導(dǎo)致車輪在這些情況下打滑。所以，即使一輛車可以產(chǎn)生更多的扭矩，仍然需要有足夠的牽引力將扭矩傳遞到地面。只要輪胎抓住路面，提供一個轉(zhuǎn)動阻力,傳動系就能驅(qū)動車輛前進。
動力傳輸線上的扭矩由微分裝置均勻分配到兩個后輪傳動軸之間。當(dāng)一個輪胎在路上遇到滑移點時，它會失去牽引力，旋轉(zhuǎn)阻力下降，同時車輪開始旋轉(zhuǎn)。因為阻力已經(jīng)下降，傳遞給兩車輪的扭矩就會改變。有足夠牽引力的車輪將不再被驅(qū)動。如果在這種情況下車輛是靜止的，那么只有在滑移點上的車輪能旋轉(zhuǎn)。因此，車輛不能移動。這種情況強調(diào)了差速齒輪的重要性。隨著牽引力變少，車輪以一個非常高的速度旋轉(zhuǎn)，熱量迅速增加，潤滑油膜分解，金屬與金屬表面直接接觸，造成接觸部分損壞?，F(xiàn)在，如果旋轉(zhuǎn)的車輪突然獲得牽引力，那么這種牽引力帶來的沖擊會在組成上對傳動軸造成嚴重損壞。
所以，目前我們?nèi)绾慰朔@些困難呢？
為了克服這些問題，差速器制造商開發(fā)了防滑差速器。在汽車應(yīng)用中,防滑差速器(LSD)是差速齒輪裝置的一種調(diào)整或派生類型，它允許輸出軸存在轉(zhuǎn)速差，但不允許速度差值增加并超出預(yù)設(shè)量。在一輛汽車中,這樣的防滑差速器有時被用來代替標(biāo)準差速器，他們能以更大的復(fù)雜性為代價，傳達特定的動態(tài)優(yōu)勢。通過考慮在一個車輪完全沒有接觸地面的標(biāo)準（或者“開放”)微分的情況下，防滑差速器的主要優(yōu)勢就被發(fā)現(xiàn)了。在這種情況下，接觸的車輪保持靜止，不接觸的車輪以兩倍預(yù)期的速度旋轉(zhuǎn)。在兩個車輪上傳遞的扭矩相等，但不會超過移動車輛所需的閾值扭矩，因此，車輛將保持靜止。在典型道路上的日常使用中，這種情況并不太可能發(fā)生，因此正常的微分就足夠了。但是，對于更高要求的使用，例如駕駛越野，或者高性能車輛，這種情況是不可取的，但是LSD可以解決這個問題。通過限制一對驅(qū)動輪的速度差，只需在至少一個車輪上獲得些許摩擦，就可以傳遞有效的扭矩。離合器類型的LSD對驅(qū)動軸扭矩作出反應(yīng)，驅(qū)動軸輸入扭矩越多，離合器壓合越困難，驅(qū)動輪被相互連接地更緊密。
防滑差速器的劣勢
a)散熱導(dǎo)致潤滑油膜破損，金屬和金屬間的接觸發(fā)生。
b)如果離合器的摩擦片被損壞，整個組成必須被分解。
c)要求高質(zhì)量的潤滑。
d)由于存在大量的機械部件，可靠性變得更少。
e)隨著速度的增加，汽車的噪音也會增加。
f)復(fù)雜并且昂貴。
2 提出創(chuàng)新—微分鎖剎車輔助系統(tǒng)(BADLS)
在這種新方法中，有一個電子電路和一個氣壓回路來自動控制車輛的牽引。在正常情況下，當(dāng)車輛沿著直線道路行駛，或者兩個(后)車輪的轉(zhuǎn)速差低于指定值時，電子電路將不產(chǎn)生信號。這有助于車輛以更好的牽引力控制系統(tǒng)判定轉(zhuǎn)向，因為微分動作是恒定的。但是，如果速度差超過指定限制時,電子電路將產(chǎn)生信號驅(qū)動氣壓回路，使?jié)u進制動發(fā)生在速度更快的車輪上，直到它獲得牽引力。因此，車輪將永遠不會失去牽引力。微分鎖剎車輔助系統(tǒng)(BADLS)的控制模塊在輸入傳感器的數(shù)據(jù)基礎(chǔ)之上，捕捉到車輪將要發(fā)生滑移的信號，反過來脈沖給該電路的常開進氣電磁閥使其關(guān)閉，這允許液體進入回路。與此同時，控制模塊打開回路的常閉電磁閥，使氣壓壓力作用于剎車片，引起手動制動。一旦受影響的車輪速度和其他車輪速度相同，控制模塊就讓兩個閥門回到他們各自的正常位置，在氣壓回路中釋放剩余壓力。
Brake Pedal—制動踏板
Check Valve—檢測閥門
Master Cylinder—主缸
Brake Wheel—制 動 輪
圖1.BADLS電路示意圖
工作過程：
正常制動系統(tǒng) 手動制動過程（BADLS）
當(dāng)滑移發(fā)生
正常剎車情況
當(dāng)車速傳感器檢測到滑移狀態(tài)
驅(qū)動制動控制閥
微控制器驅(qū)動常開電磁閥2
微控制器啟動常閉電磁閥1和常開電磁閥2
電磁閥1保持默認的常閉狀態(tài)
手動制動經(jīng)空氣流入被應(yīng)用于需要的車輪
空氣經(jīng)主電路從主汽缸流出繞過輔助電路
上面給出了解釋
圖2.BADLS電路的工作過程
上面給出了解釋圖1所示電路工作過程的流程圖。在圖2中，第一張流程圖展示了正常制動電路的工作過程，而后者展示了BADLS電路工作時的工作過程。在正常制動狀態(tài)下，電磁閥1處于關(guān)閉狀態(tài)，所以主缸的空氣流入主制動電路，通過電磁閥1繞過輔助電路，從而獲得正常的剎車行動。在滑動狀態(tài)下，微控制器啟動常閉電磁閥和常開電磁閥2，使手動制動應(yīng)用于需要的車輪。
2.1 BADLS控制模塊
該系統(tǒng)有一個控制系統(tǒng)、至少兩個驅(qū)動輪、一個差速器，用來將來自發(fā)動機的動能傳遞到驅(qū)動輪，并允許驅(qū)動輪間存在相對速度差。該控制系統(tǒng)包括兩個車速傳感器，一個比較器電路和一個控制電路。車速傳感器被用于檢測兩個驅(qū)動輪的角速度并生成速度信號。比較器電路被連接到車速傳感器，用于比較傳感器的信號并生成一個代表驅(qū)動輪滑移程度的滑移信號?？刂齐娐繁贿B接到比較器電路和微分鎖制動機構(gòu)，并用于當(dāng)一個預(yù)先確定的滑移量發(fā)生時，生成一個控制信號，將控制信號應(yīng)用于微分鎖機構(gòu)來限制驅(qū)動車輪之間的相對速度。
3 微分鎖剎車輔助系統(tǒng)的體系結(jié)構(gòu)
下面圖3所示的控制電路被用于接收代表車輛操作參數(shù)(車輪滑動的狀況)的信號，以及生成對應(yīng)于所需的用于限制兩個驅(qū)動輪間相對速度的微分鎖剎車輔助機構(gòu)狀態(tài)的控制信號。傳感器與后輪相連接，由一個不斷循環(huán)程序中的控制電路執(zhí)行的控制邏輯決定了基于操作參數(shù)的微分鎖機構(gòu)所需的狀態(tài)。
Analog to Digital Covert—模數(shù)轉(zhuǎn)換器
Reference Vol Regulator—參數(shù)調(diào)節(jié)器
Micro controller——微 控 制 器
Output Drivers——輸 出 驅(qū) 動
Solenoid valve——電 磁 閥
Wheel Sensor——車 輪 傳 感 器
圖3.提出的系統(tǒng)的體系結(jié)構(gòu)
控制電路將一個適當(dāng)?shù)目刂菩盘枒?yīng)用于微分鎖機構(gòu)，引起根據(jù)所需的狀態(tài)接觸或分離。車速傳感器被用于檢測兩后輪的速度并生成一個輸入到微控制器的車速信號。微控制器的比較器電路被連接到車速傳感器，生成一個代表驅(qū)動輪滑移程度的滑移信號?？刂齐娐繁贿B接到比較器電路和微分鎖機構(gòu)并被用于當(dāng)一個預(yù)先確定的滑移量發(fā)生時，生成一個控制信號并將控制信號應(yīng)用于微分鎖機