Harshness Symptoms And Causes of Malfunction


By harshness, we mean a single-stroke impact such as one produced by striking an object with a hammer. Along with a loud noise, this impact is felt through the steering wheel, seats, and the floor. This kind of impact occurs when driving over a gap or a bump in the road.
1.Main causes
Envelopment characteristics of tires
Worn suspension components (bushings, shock absorbers, etc.)
2.Mechanics of noise and vibration development
(1)A longitudinal impact is applied to the tire, causing a sectional deformation, when the vehicle runs over a bump or a gap in the road.
(2)This impact is further transmitted to the suspension arms. The suspension bushings are therefore compressed, transmitting the abrupt noise or vibration to the vehicle body.
Tire characteristics, and the shape and spring constants of the suspension arm bushings have the most decisive influences in the development of harshness.
1.Tire characteristics
(1)Tires with low vibration-transmitting properties are able to absorb vibrations: Usually these are soft tires.
(2)A tire with good envelopment characteristics:
Since radial tires have stiff belts in their treads, their envelopment characteristics are inferior to those of bias tires.
The force of the impact created at the time the tire runs over a bump or a gap on the road is a combination of the tire’s vibration-transmitting and envelopment characteristics. For this reason, when a radial tire, which possesses inferior envelopment characteristics in comparison to bias tires, rolls over a gap or a bump in the road, it readily transmits the impact to the suspension at low vehicle speeds. But at higher speeds, the softer sidewalls of the radial tires are capable of absorbing such impacts. 2.Suspension arm bushings
The longitudinal slits in the suspension arm bushings are designed to soften the fore-and- aft impacts applied to the vehicle by allowing the bushings to flex. The inter-rings provide rigidity in the transverse direction.

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