How Automotive Suspension Systems Work

How Automotive Suspension Systems Work


today we’re going to be talking a little bit about automotive suspensions and how they work to smoothen the ride of your car now the purpose of the automotive suspension system is to number one support the weight of the vehicle number two maintain accurate tire contact with the ground so if vehicle remains controllable and number three to absorb any shock that you get through the road when you hit a bump now most modern vehicles come with an independent front suspension now what that means is if one wheel hits a bump it does not disturb the other wheel and as a result you end up with a more refined and undisturbed right now coil spring is used to support the majority of weight in the car as it has a really good characteristics for absorbing any bumps as you go up and down on the road however Springs aren’t very good at dissipating that energy and that’s why you have the shock absorber which is there to smoothen out the ride and make sure the tire maintains contact with the road now in modern passenger vehicles the two most popular suspensions are your McPherson strut and double wishbone style of suspension so this depiction here you can see the differences between the McPherson and a double wishbone front suspension setups over here we have the strut that is connected to the body with the bearing at the top here and then we’ve got the lower ball joint here which joins at the knuckle now the knuckle is connected to the wheel so essentially your steering axis goes from the upper bearing on the strut to the lower ball joint and it turns about this point here now in this vehicle is a McPherson strut suspension so we’ve got a coil spring here with a shock damper on the inside of it then down at the bottom here we have this ball joint where it pivots on which is attached to this lower control arm so I’m just going to demonstrate how this strut actually rotates when you turn the wheel you can see that it actually pivots on the lower ball joint down there now the lower ball joint attaches to this lower control arm or lower wishbone and that’s responsible for locating the steering axis loggia to Denis as well as laterally on the vehicle now the control arm is attached to the subframe through these bushings over here which we’re going to talk about later now if you can imagine your lower ball joint on the bottom and the strut mount at the top and you draw an imaginary line between the two you’ll notice that it’s slightly tilted backward that’s called the steering axis inclination and it’s done like that for stability now if you look closely you also notice from the front that the strut is slightly mounted this way I was a McPherson strut suspension navigates a corner what’s going to happen as this tire is going to move in an arc shape and basically gain negative camber as the strut compresses and that’s where we come to the main disadvantage of the McPherson strut front suspension because the camera angle will change with suspension travel the contact area of the tire will only be minimized to one side or the other side when you’re taking your hard corners and that’s why McPherson strut suspensions are not ideal for vehicles we’re handling is an important characteristic however the main advantage of the McPherson strut suspension is that it’s really cheap and simple that’s why a lot of manufacturers are moving towards this design now if we take a closer look at the free body diagram for your McPherson strut suspension for the individual components the majority of the force is going to act in a vertical motion on any type of suspension system and that’s just because it has to take the weight of the vehicle so if we’ve got the force coming from the wheel acting through the steering knuckle it’ll go directly through the spring and be supported by the body at the strut mount to the top here which is fairly strong as a result the lower ball joint does not take any vertical force and it’s only there to locate the spindle laterally now because the strut is taking all of the load of the wheel the ball joint at the bottom is merely a follower ball joint and it is not a loaded ball joint therefore it does not wear out nearly as fast now what ties the two independent suspensions to the body is this subframe where the control arms bolt up to up with the top here’s where their strut mounts to the body as well as the bolt for the damper now underneath the subframe there’s a couple of nineteen millimeter bolts that go into the unibody that I’m going to remove do with all the bolts free from the bottom the subframe is now free from the unibody and it’s just dangling by the struts no I can read it here we have a subframe with the front suspension completely removed from the vehicle over here we have the strut at the top here we have this bearing which allows the strut itself to rotate the strut joins to the steering knuckle through these two big 19 millimeter bolts now the knuckle itself is responsible for holding the brakes the wheel hub as well as the wheel itself to the suspension now I’m going to remove these strut bolts and what the strut bolts removed I can remove the strut itself from the steel this here is the stabilizer linkage is attached to the anti-roll bar and that goes over to the other side we’re gonna talk about that later and this here is where the ball joint connects to the steering knuckle it’s got this castle nut over here we have the brake caliper I’m just going to remove that leave the caliper bracket and then we’re left with the bare knuckle with the ball joint and of course the bearing on the inside now back up here at the control arm you can see how the control arm will flex up and down with the suspension it joins to the subframe with this bushing here as well as a bushing at the back here so I’ve got the control arm removed from the vehicle and you’ll actually notice that there’s two bushings that are mounted perpendicular to each other now the rear bushing here is a softer bushing and that’s meant to absorb any vibrations that are not absorbed by the spring and it gives you a nice soft and comfortable ride now this bushing here is much stiffer it’s it’s closer in line with the wheel and that gives you good response in terms of handling now you’ll also notice that this bushing is directional there is a little arrow on it here and there’s two voids on this side that means it allows to only flex in one direction now your strut itself consists of the strut mount with the bearing at the top you have a bump stop at the top here in case this thing completely maxes out when we have the dust boot followed by the shock absorber itself where it mounts to the steering knuckle at the bottom now this here is called the anti-roll bar or your sway bar and what it does it connects the left side controller with the right side controller now because the control arms actually pivot up and down with the suspension when you take a corner the inside wheel will have a tendency to pick up while the outside wheel will have a tendency to go down and that can cause body roll which can be dangerous and that’s where the sway bar comes in it basically acts like a torsion beam where it connects the right side control arm with the left side control arm to even out the body roll so you can corner much flatter now in my Lexus we have a double wishbone front suspension which is a form of a multi-link suspension system now in this design you have the upper control arm here which attaches from the body to the steering knuckle and the steering knuckle leads all the way down towards the actual spindle you’ve got your lower ball joint down at the bottom here and that connects the lower control arm which goes to the body now the strut is actually encased in this coil over here and that’s mounted firm to the body it does not allow it to rotate now that will mount directly to the lower control arm over here instead of being mounted to the spindle as in the McPherson design so it does not need to rotate the lower controller notes of the body again using a ride and a handling bushing now if we compare that to the double wishbone suspension you’ve got this very big long steering knuckle here that goes from the lower ball joint all the way up to the upper ball joint here and it pivots between these two ball joints so it rotates like that notice when I turn your steering wheel how the knuckle rotates they you can see here and this is a rear-wheel drive vehicle so you’ve got the steering tire that connects in front of the lower ball joint and it’s called a front steer and then inside of here we have the little stabilizer link that goes to your sway bar to the other side and the main advantage of a double wishbone design is of course handling and with a double wishbone design with the body as your fourth linkage you essentially have a four bar mechanism and that’s great because it allows the wheel to stay perpendicular to the body as it navigates a corner or as it goes over a bump and that maintains good tire contact patch no matter where the wheel is situated now another advantage of this design is that it can be made adjustable where you can control the position of this upper control arms ball joint this way or this way or in and out to control your caster and camber angles now probably the main disadvantage of your double wishbone suspension is that you’re gonna see ball joints wearing out a lot faster than Anna McPherson design now the free body diagram for the double wishbone suspension is a little bit more complex because the spring now is attached through the lower control arm and the lower ball joint so as the result of force that goes through the wheel has to go through the steering knuckle through that lower ball joint and then out to the spring to be supported by the body the upper Bulger’s in this case does not take any vertical force and is just there to locate the spindle laterally in this case we’ve got a lower ball joint that is essentially a loaded ball joint because it has to support the weight of the vehicle whereas in a Macpherson design the lower ball joint is not loaded because the upper strut mount is was taking the majority of the force that comes through the wheels now the main disadvantage of the double wishbone design and the reason why I am Zahra way from this design I’m moving towards McPherson design is simply well simplicity and the reason for that is you can see there’s a lot more extra components in here they wear out a lot faster it’s a little bit more difficult to work on and as you know most people a favor fuel economy nowadays over driving dynamics so there’s no point in having this design on mass-market vehicles so here we have my Lexus which has a double wishbone front suspension driving along the road here you can see how all of the links move together we’ve got the strut that attaches to the lower control arm and then it goes through the lower ball joint to connect to the knuckle and you can see as we hit a bump here how the shock absorber absorbs that through the lower controller and here we have the McPherson strut suspension which is in my Toyota Camry you can see that the strut at the top there is mounted to the knuckle and directly takes the impact coming through the wheel and the lower ball joint is just following along and that’s pretty much the two main types of automotive suspension systems used in passenger vehicles now of course there’s a few other suspension designs we didn’t talk about such as your solid axle design your torsion beam design and your multi link design but that is it for now longitudinally as well as latitude latitude


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