Device of suspender McPherson and its advantage and shortcomings
Any cyclist knows how inconvenient can be the vehicle which is not equipped with the system of mitigation of vertical fluctuations at journey of roughnesses of the road. As this two-wheeled the CU is given to force by means of muscular force, any notable weighting of design is unacceptable here.
Another matter – the car for which comfort level for drivers and passengers comes to the first roles. For this reason the suspender is indispensable Component practically all of types of vehicles, from the scooter to the large dump truck.
Shock and telescopic dampers of hydraulic type are suspender elements – the difficult design providing interaction between wheels to which fluctuations at contact piece to roadbed, and the car are transferred. It is considered that inventor of one of the most widespread options – McPherson suspensions – is somebody” Guido Fornaka, the engineer of the well-known company “Ford” who used this gear still in the twenties of last century. He has suggested to use the two-lever system assuming use of the top lever in combination with trunnion ball at which the depreciation block was located from above. However, such design was very far from perfect as limited maneuverability of the car. Much later Earl Stili Macpherson who is also the employee of Ford has adopted Fornak’s development and modernized it, having used the rotary hinge installed on mudguard. It has reduced the price of design, has simplified it, having allowed to equip with such suspender the most budget cars. The McPherson suspension has gone to series in the second half of the 40th years, after the end of World War II. The Ford models intended for the market of the Old World became the first cars equipped by such depreciation block – Conducts, the Zephyr and the Consul.
Over time the design of McPherson suspension was improved, but the principle of its functioning remained invariable. Advantages and shortcomings of suspender of McPherson there are several alternative options of creation of the gears providing smoothness of the course of the car Now. The McPherson suspension is one of the most widespread, but it is difficult to call it not having worthy competitors – despite existence big peppery obvious advantages, it has also not less obvious shortcomings. Let’s describe pluses and minuses of suspender like Macpherson, having begun with advantages: the gear of this type is rather technological that is successfully combined with rather low cost of production. Small amount component allows to assemble knot as a unit that significantly simplifies process of assembly of the car – on installation of suspender one technological operation which is carried out on separate or common assembly line is taken away; the compact sizes of design of Macpherson allow to install it even on the most tiny cars. At the same time, despite the small sizes, the suspender is able to sustain the big weight of the car (certainly, in terms of one half shaft, as a rule – lobby); the compactness wonderfully is combined with the big vertical course of the depreciation block, allowing to provide the optimum course in the wide borders of work of knot characteristic of daily operation. The last property – long distance between basic elements on height – allows to reduce significantly the level of the longitudinal and side forces operating on the car in the place of fastening of suspender to body; the small weight of the device – the additional plus affecting both wear of details running and on reduction of consumption of expensive fuel; the good resource at Macpherson allows at the correct operation of the vehicle throughout long time not to think that the knot will prematurely fail; optimum load distribution between all loaded suspender elements, and first of all between lower arm and joint ball, allows to unload and increase the term of trouble-free operation of other components of the running, including sylent block, barrel, etc.; thanks to the suspender functioning by the principle of McPherson there was possibility of longitudinal seating of the power unit in under hood space that also promises number of advantages; the excellent diagnose ability of the device – to you will not be required a lot of time and efforts to localize failure in this knot that reduces repair cost.
McPherson suspender on car Unfortunately, it is impossible to call such unit ideal in any way – the list of shortcomings of system Macpherson is not small too, as has caused limited scope of suspender. Let’s list them: change of kinematics of the car at significant fluctuations of elements of suspender concerning vehicle body. At hit in similar situation the normal camber which is positive changes on negative. Thereof such indicators as road ability and stability of the car worsen; Macpherson is feature of suspender the raised load of mudguards. The main blow at arrival of the car on obstacle is the share of mudguard. Therefore at production of the cars using this type of suspender, mudguards surely strengthen. Otherwise, if the car is exposed to intensive operation in the conditions of bad roads, the mudguard begins to collapse gradually and consistently; also the shock strut which at continuous exploitation on the roads which are not differing in high quality also collapses is subject to the same raised loadings. First of all fail lower the valve, then the turn of destruction of the basic platform comes. Repair of such breakages is unpleasant both in terms of finance, and because of high labor input; longitudinal rocking of the car is characteristic of suspender like McPherson. Especially it is noticeable in braking time when sharp pressing pedal of brake is resulted by car peck which the suspender is not able to compensate. Moreover, because of cross spatial arrangement of levers this peck can even amplify; surely to blank out vertical fluctuations, diameter of rod of rack is done rather big. At the same time friction forces increase that involves reduction in the rate of reaction of suspender to blanking out of vertical fluctuations; at last, it should be noted the increased noisiness of the device of this type in comparison with suspenders of other designs.
Owing to the listed shortcomings as we already noted, scope of suspenders of this kind is limited. Nevertheless, in category of passenger cars it is dominating on front axle irrespective of whether the drive gear is front or rear. Mass use Macpherson fell on the 70th years of last century when designers managed to raise significantly operational resource of shock struts which was the bottleneck of design before. The inventor of suspender was sure that it equally is suitable for application on both shafts. Attempts to establish it behind were made repeatedly. For the first time it has been shown on Lotus Elite, and to K. Chapman, the designer of the English car maker, it was necessary to make many changes to suspender thanks to what she has received his name. But, as practice has shown, Macpherson’s installation was behind inexpedient therefore there have decided to be limited to independent suspension with longitudinal springs.
The suspender device like McPherson suspender Design Macpherson if to compare it to the classical device of suppression of vertical fluctuations, simpler. The typical knot consists of the following elements: the lower arm connected to joint ball; wheel nave with brake plate; the telescopic shock strut established on basic cup; swivel member assembled with track rod and board; twisted spring; the tire-tread buffer of compression equipped with protective boot (plastic or rubber); the top cup with supporting bearer; the cross pull-rod providing stability of the car. Certainly, exactly such configuration is applied not always. There are many versions different from the classical scheme of suspender Macpherson. In particular, the cult carat of Porsche 911 was equipped with torsion bar instead of classical spring – the similar design had smaller height that for the underestimated Porsche silhouette was obvious plus. Approximately the same scheme was used on some French cars. And, say, on rather popular Mercedes-Benz W124 the spring costs separately from the telescopic damper. The similar design is used on the Fox platform on the basis of which a number of Ford models is made. Strictly speaking, the potential of Macpherson suspender is not exhausted therefore it is possible to expect, as in the future its design will be exposed to improvement. Considering simplicity and compactness of design, this type of suspender still the long time will remain predominating in the market of cars. Construction features Macpherson are that that the telescopic shock strut is mounted in motor compartment above to mudguard, and below to swivel member. Despite ruggedness of joint, the design has many degrees of freedom allowing to rotate to knot in certain directions and ranges
The suspender device the Suspender Macpherson consists also of joint ball which is mounted on the lever, and through which there passes the front half shaft with the rolling bearing. If to speak about telescopic rack, then it in independent spring suspension of this type performs several functions at once: defines vector of the movement of the gear in the vertical direction; blanks out such vertical fluctuations; acts as kingpin analog for front wheels. The suspender device Macpherson generally provides the following reaction to journey of roughnesses of the road: when the wheel gets to pole or on hump, it or falls, or, on the contrary, rises up. If the depreciation block was not, the car body would also move in the similar direction and as the failure or raising of wheel at the movement at speed has short-term character, the vector of the movement so immediately changes on opposite. Considering that at the car weight considerable, forces of inertia are incapable to react to rapidly changing situation, and because of the raised loading the gear of interface of wheels and body quickly would collapse. Let’s notice, we here do not even mention inconvenience for the driver and passengers – it is meant by default. In the presence of suspender loading from wheel is perceived by twisted spring which contracts/is straightened under the influence of the corresponding force. Along with it also the telescopic rack works, being respectively shortened or extended. At hit on obstacles of the big size the spring is deformed so that part of fluctuations is transferred to body. In the following time point the spring changes vector of the movement for opposite, seeking to restore the former form that affects also change of length of rack. This process in terms of physics – fluctuations which are blanked out thanks to the depreciation gear. The spring and the telescopic damper are more qualitative, the quicker there is attenuation of oscillating motion
Here it is necessary to mention the gear of fastening of suspender to car shaft as at turning movements of the car the main loading is the share of this to component. Experts call this knot the stretcher. It is peculiar basis which serves as the place of fastening of the steer, anti roll bar and bearing part of the lever. To body the stretcher fastens by means of sylent block. Lever bearing parts usually have rubber details thanks to which the vibration transferred to car body and also the noise published at operation of the gear of blanking out of fluctuations decreases. The lower cross arms fasten to the stretcher by means of rubber inserts, and on both sides. Such design feature promotes increase in ruggedness of design. From the lever underside to it the swivel member which is components the rotary gear fastens. It provides steering of car wheels at implementation of maneuvers. On swivel member the wheel nave is pressed, and the gear joins track rod by means of pivot connection. Because of the listed above shortcomings of PM it is not used by trucks, SUV s, frame cars, sports cars and racing cars.
Up to not old time incompatible with this suspender cars with hydro pneumatic suspender as here just there was deficiency of the place for seating of the depreciation block were among, but now this problem is successfully solved. The provided description of design of suspender Macpherson will be incomplete if not to tell about such shortcoming as constantly positive shoulder of running in. It means that the shaft of turning movement is always located from the inside of wheel (more true – points of its contact piece to roadbed). It leads to deterioration in road-holding ability of the CU, increasing the efforts spent at turning movement of steering wheel. ZF Lemförder from Germany modified classical design of McPherson that has allowed to solve also this problem. In particular, in the scheme of suspender two additional hinges have been introduced thanks to what function of the rotary gear and guide managed. Such patent gear has received the name Revo-Knuckle. It has allowed to reduce friction of gears, to reduce indignation level from the available backlashes and to improve high-speed road-holding ability.
The principle of functioning Having studied design of front suspension Macpherson, it is possible to start consideration of the principle of work of this knot that will allow to understand what it is necessary to be afraid at non-compliance with service regulations of the car of. You already know that at journey of roughnesses of the road the wheel of the car is displaced up or down concerning body that leads to compression of spring and shock strut. At the same time the most part of shock influence is the share of spring. Being the inertial gear, she is fully not capable to extinguish moment of inertia, and then she is come to the rescue by telescopic rack which basic purpose – to extinguish surplus of energy of blow. To some extent the car wheel at head-on crash is affected also by longitudinal force, forcing it to move forward or back. That it did not occur, in design of suspender there are levers installed under certain corner (there are options with one lever of the And-shaped form). As after journey of roughness there is the return process (the wheel moves in opposite direction), the spring seeks to return to home position. Usually on restoration several iterations are required, at the same time each of front wheels “works” independently of each other. There can be such phenomenon as onboard rolling of the vehicle – there is enough that the vector of the movement of both wheels has turned out in anti phase that for bad roads – everyday occurrence. This lack of independent suspensions like Macpherson is compensated by existence of the anti roll bar. It is that link which connects both suspenders in whole. Physically cross stabilizer is the usual torsion bar interfering twisting forces. It also blanks out lateral vibrations of the car.
Such is in general principle of work of suspender Macpherson. Proceeding from it, it is possible to understand why it is so demanded on front-wheel passenger cars of the middle and small class why it seldom is established on rear axle. Let’s provide the small list of modern models on which McPherson suspender “works”: Hyundai Creta; Audi 80; Mitsubishi Lancer; VAZ 2109; Ford Focus; Chevrolet Aveo; Nissan Maxima; Volkswagen Passat; Skoda Octavia; Kia Soul; Toyota Camry. We are sure that among our readers for certain there will be owners of cars of the listed models. But number of design features does not allow to use this unit on the following vehicles: on racing/sports cars. The reason – bad kinematic characteristics that for this class of cars unacceptably owing to specifics of their use; lorries of easy class. Here use Macpherson is inapplicable because of too high loading falling on mudguard in the place of fastening of shock strut; SUVs which are intended for operation under trying conditions. The same reason – loads of the place of fastening of rack which lead to premature collapse of mudguards; frame cars for which top mounting of rack demands application of special brackets of the big size. Such design not only makes heavier the car, but also does its service inconvenient; car with suspender of hydropneumatic type. Such cars are available in assortment of many companies, especially for the French. Here the reason is banal – the bulky design of knot which is not leaving the place for Macpherson. But French designers from Citroën managed to solve this problem. Unlike multilever, the suspender Macpherson is almost ideal for the cars of passenger class which are operated mainly in city conditions and only occasionally used for trips in cross-country conditions. Look narrowly at the car – it is possible that on its front axle
Macpherson’s gear is used.