Power steering is a system that reduces the driver’s effort required for steering to turn the steering wheel. With the help of power steering, it easier for the vehicle to turn or maneuver. The power steering unit is located at the lower end of the steering column in place of the usual conventional steering gear. It is connected by two oil lines to the hydraulic pump mounted on the generator. The pump with a relief valve avoids excessive oil pressures.
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 91, the reader should be able to: • Prepare for ASE Suspension and Steering (A4) • • • certification test content area “A” (Steering Systems Diagnosis and Repairs) Discuss the components and operation of power steering pumps List the components of a typical powerrecirculating-ball-nut steering gear system Describe the operation of a power rack-andpinion steering system 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: BPP • cold climate fluid • EHPS • EPS • EVO flow control valve • force • integral reservoir • magnasteer pascal’s law • poppet valve steering gear • pressure • pressure-relief valve • PSCM • PSP remote reservoir • rotary control valve self-park • SPS • SSS • TFE • VES 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 Power-assisted steering hydraulically boosts the mechanical steering gear operation so the driver can turn the steering wheel with less effort for the same response Hydraulic power steering has been available since the 1950s, and many late-model systems are enhanced by electronic controls 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 POWER STEERING HYDRAULIC SYSTEMS Hydraulics is the study of liquids and their use to transmit force and motion through the use of fluid pressure Force is a push or pull acting on an object and is usually measured in pounds or Newtons Pressure is force applied to a specific area Pressure is usually measured in force per unit of area, such as pounds per square inch (PSI), or kilopascals (kPa) One PSI equals 6.895 kPa The Pascal is a unit of measure named after the French scientist Blaise Pascal (1623–1662) One of his discoveries, known as Pascal’s law, was that pressure on a confined fluid is transmitted equally in all directions and acts with equal force on equal areas See Figure 91–1 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 Hydraulic systems transmit force and motion through liquids because a liquid cannot be compressed Figure 91–1 Hydraulic fluid transmits the same force whether it passes through a single chamber or two chambers connected by a narrow passage No matter how much pressure is placed on a liquid, its volume remains the same This allows a liquid to transmit force much like a mechanical 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 Figure 91–2 A fluid applies a force equal to the applied force on a surface that is equal in size to the applying surface If the surface is half the size, then the fluid exerts half the force: if the surface is twice as large, the fluid exerts twice the force Because it assumes the shape of its container, a liquid can transfer force around obstacles or through pipes and passages of any shape As explained by Pascal’s Law, a liquid can also decrease or increase the force it transmits depending on the area of the output surface to which the force is applied 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 POWER STEERING PUMP AND RESERVOIR The power steering pump draws fluid from the reservoir, pressurizes it, and delivers it to the power steering system The fluid reservoir may be either integral to (built into) the pump or remotely mounted and connected to the pump by a hose The power steering fluid reservoir is usually made of either plastic or stamped metal, and it includes the fluid filler neck, cap, and dipstick An integral reservoir is part of the pump, and the pump itself operates submerged in power steering fluid See Figure 91–3 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 Once common, steering pumps with an integral reservoir have given way to those with a remote reservoir on current-production vehicles The remote reservoir allows for a smaller, more compact pump assembly better suited to a cramped engine compartment Figure 91–3 A typical integral power stering pump when the pump is mounted in the reservoir 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 A remote reservoir is a separate assembly from the pump and provides fluid to it through a suction hose Most power steering systems use an engine-driven hydraulic pump Power steering hydraulic pumps are usually belt driven from the front crankshaft pulley of the engine Figure 91–4 Typical remote reservoir Figure 91–5 Typical integral power steering pump assemblies 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