chap88 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 88, the reader should be able to: • • • Prepare for ASE Suspension and Steering (A4) certification test content area “B” (Suspension System Diagnosis and Repair) Describe how suspension height sensors function Explain the use of the various sensors used for electronic suspension control Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 88, the reader should be able to: • • Discuss the steering wheel position sensor Explain how solenoids and actuators are used to control the suspension Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: actuator • air suspension • armature • AS • automatic level control (ALC) CCVRTMR • computer command ride (CCR) desiccant • driver select switch • EBCM • ECU • electromagnet handwheel position sensor • height sensor input • lateral accelerometer sensor • LED magneto-rheological (MR) • mode select switch • motor • MRRTD • output Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: output • perform ride mode • photocell • phototransistor • pulse width • pulse-width modulation real-time dampening (RTD) • RPO • RSS selectable ride (SR) • solenoid • solenoid controlled damper • stabilitrack • steering wheel position sensor touring ride mode vehicle stability enhancement system (VSES) VS sensor • yaw rate sensor Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Since the mid-1980s, many vehicle manufacturers have been introducing models with electronic suspension controls that provide a variable shock stiffness or spring rate The main advantage of electronic controls is that the suspension can react to different conditions Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONICALLY-CONTROLLED SUSPENSION Electronically-controlled suspension provides a firm suspension feel for fast cornering and quick acceleration and braking, with a soft ride for cruising Figure 88–1 An electronically controlled suspension system can help reduce body roll and other reactions better than most conventional suspension systems Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC CONTROLS AND SENSORS Sensors and switches provide input to the electronic control module (ECM), or computer Also referred to as the electronic control unit (ECU), the ECM is a small computer that receives input in the form of electrical signals from the sensors and switches and provides output electrical signals to the system actuators Figure 88–2 Input devices monitor conditions and provide information to the electronic control module, which processes the information and operates the actuators to control the movement of the suspension The electrical signal causes an actuator to perform some type of mechanical action Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Height Sensors A height sensor senses the vertical relationship between the suspension component and the body Its signal indicates to the ECM how high the frame or body is, or how compressed the suspension is A number of sensor designs are used to determine ride height, including a photocell sensor Figure 88–3 A typical electronic suspension height sensor, which bolts to the body and connects to the lower control arm through a control link and lever Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Four height sensors, one at each wheel, deliver an input signal to the ECM All use a control link, lever, slotted disc, and photo interrupters to transmit a signal Each photo interrupter consists of a light-emitting diode (LED) and a phototransistor, which reacts to the LED The LEDs and phototransistors are positioned opposite each other on each side of the slotted disc The ECM applies voltage to the LEDs, which causes them to illuminate Light from an LED shining on the phototransistor causes the transistor to generate a voltage signal Signals generated by the phototransistors are delivered to the ECM as an input that reflects ride height See Figure 88–4 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What Are Self-Leveling Shocks? - Part Inside the piston rod is the pump chamber containing an inlet and outlet valve When a load is placed in the rear of the vehicle, it compresses the suspension and the shock absorber When the vehicle starts to move, the internal pump is activated by the movement of the body Extension of the piston rod causes oil to be drawn through the inlet valve into the pump When the shock compresses, the oil is forced through the outlet valve into the high-pressure chamber The pressure in the oil reserve decreases as the pressure in the high pressure chamber increases The increasing pressure is applied to the piston rod, which raises the vehicle height When the vehicle’s normal height is reached, no oil is drawn into the chamber Because the shock is mechanical, the vehicle needs to be moving before the pump starts to work It requires about miles of driving for the shock to reach the normal ride height The vehicle also needs to be driven about miles after a load has been removed from the vehicle for it to return to normal ride height Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Inflator or Compressor Relay The suspension control module energizes the relay to activate the compressor motor, and adjusts the rear trim height The suspension control module controls the compressor relay for normal operation or for the accessory air inflator Figure 88–36 Schematic of the ALC system On RTD or RSS systems with a compressor, the scan tool may display DTCs associated with compressor relay operation On some applications, the scan tool can be used to command the relay to verify proper operation Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Compressor A positive-displacement air pump and can generate up to 150 lbs of pressure per square inch (PSI) The compressor is found on the ALC, AS, RTD, and RSS systems A 12-volt permanent magnet motor drives the compressor The compressor supplies compressed air to the rear air shock absorbers or struts to raise the vehicle See Figure 88–37 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 88–37 Air compressor assembly can be located at various locations depending on the vehicle Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Air Dryer Within the compressor is an air dryer The air dryer is responsible for removing moisture from the compressor system Improper air dryer operation can cause a premature failure in the system if an air line restriction occurs due to excessive moisture build-up A dryer on the output side of the compressor contains silica gel desiccant, which removes moisture from the discharge air before it travels through the nylon air hoses to the air chamber of the rear shocks Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Exhaust Solenoid located on the compressor, relieves pressure in the system The ground-side switched exhaust solenoid has three main functions: It releases compressed air from the shock absorbers or air springs to lower the vehicle body It relieves compressor head pressure By exhausting air, it protects compressor start-up from high head pressure, which can possibly cause fuse failure The solenoid acts as a pressure relief valve, which limits overall system pressure See Figures 88–38 and 88–39 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 88–38 The exhaust solenoid is controlled by the rear integration module (RIM) The special functions on many scan tools can command the solenoid and verify its operation Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 88–39 Schematic showing the rear integration module (RIM) and how it controls the ALC compressor ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 MAGNETO-RHEOLOGICAL (MR) SUSPENSION MR fluid shocks use a working fluid inside the shock that can change viscosity rapidly depending on electric current sent to an electromagnetic coil in each device The fluid is called magnetorheological (MR) and is used in monotube-type shock absorbers This type of shock and suspension system is called the magnetorheological real-time damping (MRRTD) or chassis continuously variable real-time dampening magnetorheological suspension (CCVRTMR) See Figures 88–40 and 88–41 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 88–40 Vehicles that use magneto-rheological shock absorbers have a sensor located near each wheel, as shown on this C6 Corvette Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 88–41 The controller for the magneto-rheological suspension system on a C6 Corvette is located behind the right front wheel Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Under normal operating conditions, fluid flows easily through the shock and provides little dampening Figure 88–42 A cutaway of a magneto- rheological shock absorber displayed at the Corvette Museum in Bowling Green, Kentucky When a large or high-frequency bump is detected, a small electrical current is sent from the chassis controller to an electromagnetic coil in each shock and the iron particles in the fluid respond, aligning in fiberlike strands This causes the MR fluid to become thick, increasing firmness of the shock This type of shock is used to control squat during acceleration, brake dive and reduce body roll during cornering Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Can Computer-Controlled Shock Absorbers and Struts be Replaced with Conventional Units? Maybe If the vehicle was manufactured with or without electronic or variable shock absorbers, it may be possible to replace the originals with the standard replacement units The electrical connector must be disconnected, and this may cause the control system to store a diagnostic trouble code (DTC) and/or turn on a suspension fault warning light on the dash Some service technicians have used a resistor equal in resistance value of the solenoid or motor across the terminals of the wiring connector to keep the controller from setting a DTC All repairs to a suspension system should be done to restore the vehicle to like-new condition, so care should be exercised if replacing electronic shocks with non-electronic versions Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY General Motors uses seven types of electronic suspension under many different names Suspension height sensors and steering wheel (handwheel) position sensors are used in many systems A vehicle speed sensor signal is used to control the suspension at various speeds Many electronic suspension systems use a lateral accelerometer sensor, which signals the suspension computer when the vehicle is rapidly accelerating, braking, or cornering Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Solenoids and motors are used to control the suspension movement by moving valves in the shock absorbers or air springs An air pump and air shocks are used to raise the rear of the vehicle to compensate for a heavy load Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ... applications The sensor is typically located at the base of the steering column Always refer to service information for vehicle-specific information See Figure 88–8 and 88–9 Automotive Technology: ... River,NJ NJ07458 07458 Located at the top mount of the air spring variable shock assembly of each wheel, the suspension control actuator moves a control rod that regulates air pressure to the... suspension controls that provide a variable shock stiffness or spring rate The main advantage of electronic controls is that the suspension can react to different conditions Automotive Technology: Principles,