MAE 442 Mechanical Engineering Department N.C. State University PERFORMANCE SHOCKS Adam Shifflett  Heath Spivey  Scott Tedrick

Shocks provide resistance by forcing incompressible hydraulic fluid through valves or a series of high quality valve washers in the piston as it moves up and down. Shock Overview

Shock Types Monotube/1 Way Damper 2 Way Adjustable Damper 3 Way Adjustable Damper Used in NASCAR Nextel Cup and Goodies Dash Series Most versatile and cost effective Offers most “tunability”, used for both low and fast shaft movements Pictures from

Best for racing and off-road applications Higher performance made to tighter tolerances Less Variance Dissipate heat faster Allow a larger bore size to be used in the same space More damping control Why use Monotube Shocks? Pictures from

The end cap provides containment for the rest of the assembly and maintains the volume of nitrogen used to fine tune the shock. The valve allows increased pressure to be applied into the reservoir and thus applies higher pressure to the fluid on the other side of the piston increasing the flow resistance throughout the shock, increasing damping. End Cap Reservoir Piston Nitrogen Valve Shock Parts Pictures from

The damper body provides a housing for the other components of the damper as well as providing a containment vessel for the fluid pressure that provides damping. The head valve piston provides tunable resistance to fluid flow via interchangeable valve washers. Shock Parts

Valve Stacks  Damping characteristics determined by compression and rebound valve stacks, which are made to flex under the force of fluid flowing through piston ports then to return to original shape  Insert thicker shims to increase damping  Individual shim thicknesses range from 0.004” – 0.020”  Each piston face has a standard 1° dished surface o Preloads valve shims flat against piston face Shock Parts Pictures from Penske 7000 Series Tech Manual

Rebound and Compression valve stacks Pictures from Penske 7000 Series Tech Manual

High speed rebound/compression Enters through piston orifices Travels through piston orifices Exits around deflected washer valve stacks Low speed rebound/compression Enters through piston orifices Travels through piston orifices Exits through piston orifices and shaft bleed hole without deflecting washer valve stacks Path of Fluid Travel Pictures from Penske 7000 Series Tech Manual

Poppet and jet assembly: Interchangeable jets  Provides broad range of adjustment for bleed past piston on rebound  Utilizes spring-loaded poppet valve to check flow o Better seal against flow o Quicker response time in direction changes Picture from Penske 7000 Series Tech Manual

The shaft provides a mount point for the various methods of resisting fluid flow and also accepts the various jet options. Open, compression, or rebound jet options can be installed by replacing the jet and associated hardware located near the valve stacks. Pictures from Penske 7000 Series Tech Manual

This schematic displays a full compression and rebound cycle Quadrant 1 - Beginning of compression stroke - fluid travels through low speed bleed bypass Quadrant 2 - Continuation of compression stroke - Fluid travels through compression valve stack Quadrant 3 - Beginning of rebound stroke - Fluid travels through low speed bleed bypass Quadrant 4 - Continuation of rebound stroke - Fluid travels through rebound valve stack Pictures from Penske 7000 Series Tech Manual

Low speed shaft bleed bypass flow path: At slow speeds, fluid travels through the slow speed shaft bleed bypass and is controlled by the jet/poppet assembly. Through interchangeable jets, low speed damping is fully adjustable. Picture from Penske 7000 Series Tech Manual

Eyelet Assembly High Angularity Spherical Joint Allows for wide range of motion encountered in racing and off- road applications Allows for easy interchangeability  Bleeder Valve Allows removal of air when filling with hydraulic oil Prevents bubble formation Prevents bounce Quicker resistance

Cost 7300 series shock from Roehrig Enders Suspension Inc. Cost: $790. Weight: 2.1 lbs

Shock Testing Two Types of Racing Shock Tests –Shock Dynamometer Used in all racing shops and in the team transporter for at track testing. –Vehicle Dynamics Rig Most teams rent out dynamics rigs for days at a time. Used to test many car components at once.

What is a Shock Dyno? Measures Force vs. Shaft Speed Pictures from

How a Shock Dyno Works Machine compresses and expands the damper at known speeds and measures the force produced. Electric Motor with a drive belt and pulleys spin a crank plate which is attached to the damper shaft. Works much like a piston and cylinder in an ICE. Bolt holes in Crank Plate allow for different stroke lengths. Different pulley diameters allow for different rotational speeds. The load cell measures the force generated by the damper. Pictures from

How a Shock Dyno Works Pictures from

How a Shock Dyno Works The damping force exerted on the compression stroke is known as the bump, while the damping force as the shock is expanding is known as the rebound. Most dampers give more force in rebound than compression. The damping forces are only recorded at maximum velocity which happens once during the compression stroke and once during expansion. Pictures from

Why do you need a Shock Dyno? To insure all 4 shocks on a car are responding in the same manner. To find problems before they find you, such as: –Contaminated oil –Bad seals –Warn parts Allows you to see the effects of external adjustments.

Why do you need a Shock Dyno? Shocks influence tire grip Determine how the car feels to the driver Adjusting shocks allow for a faster racecar Documentation and tests conducted on each shock allows for similar track set-ups Pictures from

Example Dynamometer Electro-Magnetic Actuator Plays back real time track data collected from the onboard data acquisition system. Fully computer controlled with damper analysis software. Up to 45hp Motor Output on a 220 Volt Power Supply. Price Tag - $68,000 Picture from

Vehicle Dynamics Rig Used for tuning vehicle suspensions Hydraulic actuators simulate: –Road excitation –Downforce –Cornering –Braking Loads Advantages: –Operates in a controlled environment –Cost considerably less than track testing Pictures from

Vehicle Dynamics Rig Comprised of 7 posts –4 hydraulic actuators provide road excitation –3 actuators mount to the car Font, Middle, Back –Scale pad under car shows normal force Test Methods –Track simulation examines body responses and contact patch loads at the tires. –Static tests measure ride rates, roll rates, and friction Pictures from

Low shaft speeds Dish of piston surface More dish = more preload = more low speed damping Overview of Adjustability Pictures from Penske 7000 Series Tech Manual

Bleed through jet  Less bleed = more low speed damping Overview of Adjustability Pictures from Penske 7000 Series Tech Manual

High Shaft Speeds  Thickness of shim stack  Thicker shims = more high speed damping Overview of Adjustability Pictures from Penske 7000 Series Tech Manual

References &cat=1&page=1http:// 5&cat=1&page=1

Special Thanks to: Brian Wilson N.C. State Alumni #2 Nextel Cup Team Engineer