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The Mazda Speed Sensing Computerised 4-Wheel Steering System.
Three and a half decades ago, two young Mazda designers arrived at a far-sighted and well-calculated conclusion that was quite revolutionary for the time. In their technical presentation at the October 26, 1962 Japanese Automotive Engineers' Society Technical Conference, Dr Tadashi Okada and engineer Toshiaki summarised their arduous research concerning vehicle dynamics as follows.
1. The basic difference in the characteristics of oversteer and understeer lies in the magnitude of time delay and response.
2. a vehicle that is stable under high speed must possess understeer characteristics
3. the rear wheel tyre reflects heavily on the stability and
4. a major improvement on control and stability may be anticipated by means of the automatic rear wheel steering system.
The conclusions and formulations presented by these two engineers established the foundation for Mazda's present-day reputed suspension technology. Over years of dedicated research and development expertise, their original discoveries and theories have contributed to some of the most significant achievements within the recent history of automotive chassis engineering, incorporated by Mazda within its series production products. These developments include the twin trapezoidal link rear suspension, first employed in the original front-wheel drive Mazda 323 (1980) and the Mazda 626 (1982), and then perfected within the updated Mazda 626; the award winning Dynamic Tracking Suspension System of the second generation Mazda RX-7 (1985); and the elaborate E-link rear suspension of the new Mazda 929 (1987).
While various external forces and loads are exerted to the rear wheels of a vehicle as it combats the elements of the law of motion as defined by Sir Isaac Newton, these new suspension systems convert those forces into "4WS effects" which positively aid in vehicle stability and agility.
The Mazda designers' and engineers' ultimate goal was still a positive measure to generate forces for positive controls; a Four-Wheel Steering system.
In 1983, Mazda astonished the automotive world with the introduction of an engineering concept car, the MX-02, exhibited at the Tokyo Motor Show. This four-door Sedan, with generous passenger accommodation on an unusually long wheelbase, incorporated among its numerous advanced features a true 4WS system that aided high-speed stability as well as its low-speed manoeuvring. The degree of rear wheel steering was determined by the measurement of both front wheel steering angle and vehicle speed, by means of a central computer unit.
The MX-02 was followed by another exciting concept car; the MX-03, first exhibited at the Frankfurt Motor Show in September 1985. This sleek four seat futuristic coupe of the 1990s combined a refined electronically-controlled 4WS system with a continually varying torque-split, four-wheel drive system and a powerful three-rotary engine.
Mazda Electronically -Controlled Four-Wheel Steering System:
A Beneficial Technology
Mazda's electronically-controlled, vehicle-speed-sensing Four-Wheel Steering System (4WS) steers the rear wheels in a direction and to a degree most suited to a corresponding vehicle speed range. The system is mechanically and hydraulically actuated, producing greatly enhanced stability, and within certain parameters, agility.
The driver of a Mazda 4WS-equipped car derives five strategic benefits, over and above the conventional vehicle chassis.
1. Superior cornering stability
2. Improved steering responsiveness and precision
3. High-speed straightline stability
4. Notable improvement in rapid lane-changing manoeuvres
5. Smaller turning radius and tight-space manoeuvrability at low vehicle speed range
The most outstanding advantage of the Mazda 4WS is that it contributes to a notable reduction in driver fatigue over high-speed and extended travelling. This is achieved by optimally:
1. reducing the response delay to steering input and action and
2. eliminating the vehicle's excessive reaction to steering input
In essence, by providing the optimum solution to the phenomena researched by the two young Mazda engineers in the early sixties - by the method advocated by them - the 4WS system has emerged as a fully beneficial technology.
Strategic Construction
The Mazda 4WS consists of a rack-and-pinion front steering system that is hydraulically assisted by a twin-tandem pump main power source, with an overall steering ratio of 14.2:1. The rear wheel steering mechanism is also hydraulically assisted by the main pump and electronically controlled - according to the front steering angle and vehicle speed. The rear steering shaft extends from the rack bar of the front steering gear assembly to the rear steering-phase control unit.
The rear steering system is comprised of the input end of the rear steering shaft, vehicle speed sensors, a steering-phase control unit (determining direction and degree), a power cylinder and an output rod. A centering lock spring is incorporated, which locks the rear system in a neutral (straightforward) position in the event of hydraulic failure. Additionally, a solenoid valve that disengages hydraulic assist (thereby activating the centering lock spring) in case of an electrical failure is included.
The 4WS system varies the phase and ratio of the rear-wheel steering to the front wheels, according to the vehicle speed. It steers the rear wheels toward the opposite phase (direction) of the front wheel during speeds less than 35km/h (22mph) for a tighter turn and "neutralizes" them (to a straightforward direction, as in a conventional two-wheel steering principle) at 35km/h (22mph). Above that speed, the system steers toward the same phase-direction as the front wheels, thereby generating an increased cornering force for stability. The maximun steering angle of the rear wheels extends 5 degrees to either left or right, a measurement that Mazda has determined to be optimally effective and natural to human sensitivity.
Primary Components
1. Vehicle speed sensors Interpret speedometer shelf revolutions and send signal to the electronic computer unit. two sensors, one within the speedometer and the other at the transmission output, are used to crosscheck the other for accuracy and failsafe measures.
2. Steering phase control unit* Conveys to the power steering cylinder booster valve the direction and stroke of rear wheel steering by the combined movement of the control yoke angle and bevel gear revolutions.
3. Electric stepper motor Performs altering of the yoke angle and bevel gear phasing
4. Rear steering shaft Transmits front wheel steering angle by turning the small bevel gear in the steering phase control unit, which rotates the main bevel gear in the assembly.
5. Control valve Feeds hydraulic pressure to the steering actuator, according to the phase and stroke required for appropriate rear wheel steering.
6. Hydraulic power cylinder Operates the output rod by hydraulic pressure and steers the rear wheels. It locks the rear wheels in a "neutral" (straightforward) position with the centering lock spring, which is activated by a solenoid valve in case of failure to ensure a normal 2WS function for the vehicle.
7. Hydraulic pump. Provides hydraulic pressure to both the front and rear steering systems.
Details of Steering Phase Control Unit
The steering phase control unit alters the direction and degree of rear wheel steering. It consists of a stepper motor that controls the rear steering ratio, a control yoke, a swing arm, a main bevel gear engaged to the rear steering shaft via a small bevel gear, and a control rod connected to the control valve. It operates:
a. Opposite phase (direction) steering under 35km/h (22mph)
1. Control Yoke is at an angle activated by the stepper motor
2. Front wheels are steered to the right. The small bevel gear is rotated in direction X by the rotation of the rear steering shaft. The small bevel gear, in turn, rotates the main bevel gear.
3. Rotation of the main bevel gear causes movement of the control rod toward the control valve.
4. Input rod of the control valve is pushed to the right, according to the degree of the control rod's movement (determined by the disposition of the swing arm), which is positioned to move in an upward direction, to the right. The rear wheels are thus steered to the left, in an opposite direction to the front wheels.
5. As the angle of the control yoke is increased in direction A as vehicle speed decreases, the rear-to-front steering ratio proportionately increases and the vehicle's steering lock tightens.
b. Same phase (direction) over 35km/h (22mph)
The operation of this phase is the reverse of the opposite phase one, because the control yoke is angled toward "positive" in this vehicle speed range, as illustrated. The phasing of the swing arm, yoke rod and bevel gear steers the rear wheels toward the right-the same direction as the front wheels.
c. Neutral phase, at 35km/h (22mph) The control yoke's angle is horizontal (neutral). Thus, the input rod is not affected, even if the control rod is moved with the rotation of the bevel gear unit. As a result, the rear wheels are not steered in this mode.
Power Cylinder
The movement of the input rod of the control valve unit is transmitted to the power cylinder's spool. The spool's displacement to the sleeve causes a pressure difference between the right and left side chambers in the hydraulic power cylinder. The pressure difference overcomes the output shaft load and initiates sleeve movement. The sleeve-power rod assembly is moved in the direction of the input rod by a proportionate degree. The output rod transmits steering action to the tie rod on either end of the rear wheel steering control-mechanism unit, thereby steering the rear wheels.
Fail-Safe Measures
The system automatically counteracts possible causes of failure, both electronic and hydraulic. In either case, the centering lock spring housed in the steering system unit returns the output rods in the "neutral" straightforward position, essentially alternating the entire steering system to a conventional 2WS principle.
Specifically, if a hydraulic defect should render a reduction in pressure level (by a movement malfunction or a broken driving belt), the rear wheel steering mechanism is automatically locked in a neutral position, activating a low-level warning light.
In the event of an electrical failure, such would be detected by a self-diagnostic circuit integrated within the 4WS control unit, which stimulates a solenoid valve and then neutralizes hydraulic pressure and return lines, thereby alternating the system again to that of a 2WS principle. Henceforth, the warning light referencing the 4WS system within the main instrument display is activated, indicating a system failure.
車輛與動力工程學(xué)院畢業(yè)設(shè)計說明書
4座微型客貨兩用車設(shè)計（前懸架、轉(zhuǎn)向系設(shè)計）
摘 要
在這次畢業(yè)設(shè)計中，我主要負(fù)責(zé)轉(zhuǎn)向系統(tǒng)及前懸架系統(tǒng)的設(shè)計。經(jīng)過收集各類型的懸架的資料，實(shí)車觀測，老師的指導(dǎo)。在研究了各類型的獨(dú)立，非獨(dú)立懸架系統(tǒng)之后，總結(jié)了其各自特點(diǎn)，認(rèn)識到了各自優(yōu)劣，分析對比之后，最終確定本車懸架系統(tǒng)：麥弗遜前獨(dú)立懸架。
在前懸的設(shè)計中主要圍繞麥弗遜獨(dú)立懸架展開。前期的工作主要是收集相關(guān)資料，信息，在此過程中，其結(jié)構(gòu)是研究的重點(diǎn)。計算主要集中在了彈性元件—普通圓形螺旋彈簧的各個重要參數(shù)。如，彈簧剛度，中徑，彈簧鋼絲直徑等等。隨后對這些數(shù)據(jù)進(jìn)行了必要的校核。
最后對減振器和橫向穩(wěn)定器的結(jié)構(gòu)以及它們在整個懸架系統(tǒng)中的作用進(jìn)行了一些探討。
轉(zhuǎn)向系統(tǒng)設(shè)計內(nèi)容主要包括轉(zhuǎn)向系統(tǒng)形式的選擇、轉(zhuǎn)向器的選擇、轉(zhuǎn)向梯形的選擇及其布置。
我們所設(shè)計的車型是小排量車，鑒于我國路面質(zhì)量的逐步提高和作用于方向盤的作用力(144.865N-177.06N)不是很大，故在設(shè)計中考慮采用機(jī)械式轉(zhuǎn)向系統(tǒng)。
由于齒輪齒條式轉(zhuǎn)向器與其他的轉(zhuǎn)向器相比，雖然其逆效率很高，但其具有結(jié)構(gòu)簡單、緊湊、殼體采用鋁合金或者鎂合金壓鑄而成，轉(zhuǎn)向器質(zhì)量比較小、傳動效率高達(dá)90％以上，因此本設(shè)計選用齒輪齒條式轉(zhuǎn)向器。
由于我們設(shè)計的車前懸比較短，發(fā)動機(jī)占有的空間相對來說很大，且由于轉(zhuǎn)向系統(tǒng)轉(zhuǎn)向梯形最小傳動角和轉(zhuǎn)向器的安裝距離有很大的關(guān)系，綜合以上因素我采用后置式轉(zhuǎn)向梯形。
關(guān)鍵詞：獨(dú)立懸架，麥弗遜式，機(jī)械式轉(zhuǎn)向系，齒輪齒條式轉(zhuǎn)向器。
THE DESIGN OF THE FRONT SUSPENSION AND STEERING SYSTEM OF THE MINIATURE MOTORCAR TO CARRY PERSONS AND GOODS WITH 4 SEATS
ABSTRACT
In this graduation design, I am responsible for automobile's steering system and the front suspension system design of the miniature motorcar to carry persons and goods with 4 seats mainly..In weeks ,I work hard to get the more useful information to do my work better. With the helping of Mr Li and other teachers ,and observation on vehicle in laboratory .I got a conclusion : the front independent McPherson suspension is the best form for this automotive .
All focus on elastic part .Because elastic is the most important part in them .And I have got some important data for my design work . If I can’t get those data ,I could not do my work in the following days .I get many data ,but for front independent McPherson suspension the main thing is about spring , such as spring rate ,middle diameter ,spring wire diameter and so on .spring rate is the most important data for my independent suspension ,it do many influence about suspension.
In the last I discussion shock absorber and anti-roll-bar a little,and involve the basic of them and the important usefully in modern car’s suspension.
Because the motortcar we design is a kind of small output volume, seeing that the gradual improvement of the road surface quality of our country and effort of acting on the steering wheel are not very large, so I choose the manual steering system.
Compared with others steering gear, though the negative efficiency of the rack and pinion steering gear is high, but it have of simple structure, compactness, shell adopt aluminum alloy or magnesium alloy die casting, the weight of the rack and pinion steering system is much smaller than others, transmission efficiency is up to more than 90%, so in this design I choose the rack and pinion steering system.
Because the front overhang of the car is very short and the engine occupied comparatively very big space, what is more, the minimum transmission angle of the Ackerman steering has a very close relation with installation distance of the steering gear, so I choose fit the Ackerman steering in the back of the car conceding all those factor above.
KEY WORDS : independent suspension,MacPherson，the manual steering system, the rack and pinion steering gear
目 錄
第一章 前言．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．1
第二章 汽車轉(zhuǎn)向系設(shè)計．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．3
§2.1 概述．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．3
§2.2 轉(zhuǎn)向系的設(shè)計要求．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．7
第三章 轉(zhuǎn)向器、轉(zhuǎn)向傳動操縱機(jī)構(gòu)、轉(zhuǎn)向傳動機(jī)構(gòu)．．．．．．．．．9
§3.1 轉(zhuǎn)向器．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．9
§3.2 轉(zhuǎn)向操縱機(jī)構(gòu)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．9
§3.3 轉(zhuǎn)向傳動機(jī)構(gòu)和布置．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．10
第四章 轉(zhuǎn)向系有關(guān)的計算及校核．．．．．．．．．．．．．．．．．．．．．．．．11
§4.1 轉(zhuǎn)向系主要性能參數(shù)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．11
§4.2 轉(zhuǎn)向器有關(guān)參數(shù)的設(shè)計計算及校核．．．．．．．．．．．．．．．．14
§4.3 轉(zhuǎn)向傳動機(jī)構(gòu)的設(shè)計計算與強(qiáng)度校核．．．．．．．．．．．．．．15
第五章 懸架結(jié)構(gòu)方案分析．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．19
§5.1 懸架的功用．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．19
§5.2 懸架系統(tǒng)的組成．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．19
§5.3 懸架的類型及其特點(diǎn)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．21
第六章 前懸架的設(shè)計計算．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．25
§6.1 彈簧形式的選擇．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．25
§6.2 彈簧參數(shù)的計算．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．25
§6.3 彈簧的校驗(yàn)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．27
第七章 減震器的結(jié)構(gòu)原理及其功用．．．．．．．．．．．．．．．．．．．．．．28
§7.1 減震器的作用．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．28
§7.2 減震器的結(jié)構(gòu)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．29
§7.3 減震器的工作原理．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．29
§7.4 減振器主要尺寸的確定．．．．．．．．．．．．．．．．．．．．．．．．．．．．29
第八章 橫向穩(wěn)定器的作用．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．32
第九章 結(jié)論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．34
參考文獻(xiàn)．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．35
致謝．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．． 36
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