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Mathematical modeling of the mesh friction of a rack and pinion system has been carried out in order to predict the mesh friction of a steering gear. The three dimensional gear geometry and force diagram of a rack and pinion gear is represented in vector form. With proper boundary conditions applied to the equations, the mathematical model simulates the friction forces resulting from the mesh. An experimental apparatus was also built to measure mesh friction between a rack and pinion. A number of rack and pinion steering gears have been tested under several load conditions. Experimental results are then compared with the simulation results to verify the mathematical model.

This paper describes the operation of an advanced CMOS opto-ASIC used in a digital torque and angle sensor. Its purpose is to resolve the relative and absolute angular position of two bar-coded disks rotationally coupled by a stiff torsion bar. The resulting digital output of the sensor comprises two absolute angle measurements with up to 18-bit accuracy, and a torque measurement calculated from the difference of the two angular measurements. The measurement of torque and absolute angle in a single sensor eliminates the need for additional steering angle sensors for other vehicle dynamic systems such as dynamic stability control (DSC) or intelligent cruise control (ICC).

This paper describes the attributes, performance and development status of a high performance opto-electronic sensor intended for use in electric and electrohydraulic steering systems. This sensor can be used in both underhood and in-cabin environments and provides a measurement of torque, absolute angle and angular velocity to a steering controller. This device overcomes deficiencies of existing sensors that generally exhibit combinations of problems such as high cost, low stiffness, poor resolution, hysteresis, susceptibility to electromagnetic fields, drift from mechanical wear, overload or environmental extremes and other problems. It has been designed to eliminate the need for calibration during and after manufacture, and can be disassembled and reassembled without recalibration.

A power assisted rack and pinion steering gear is mathematically modelled, enabling the development of quantitative definitions for power steering ‘stiffness’ and ‘feel’. Both these quantities are defined as instantaneous derivatives, being a function of various valve parameters such as differential boost rate, effective pinion pitch radius, piston area, torsion bar stiffness, etc. The resulting stiffness and feel relations are plotted for two types of valve boost curve: a conventional tan-function-like boost curve and a linear boost curve. The latter is shown to yield proportional feel and stiffness in the cornering region of valve operation. The application of this theory to the performance evaluation of two families of speed sensitive valve systems is also addressed.

A roll-imprinting process is presented as a method of manufacturing valve rotors with high index-accuracy and uniquely featured metering edges. Such rotors enable a rotary valve to simulate the superior differential boost characteristics of the more expensive hydraulic reaction valves, particularly in respect of achieving a low differential boost rate in the on-centre region of valve operation, followed by a relative swift ‘turn-around’ to a region of linear boost increase over the remaining operating region of the valve. A slotting process is also presented which enables one-piece valve sleeves to be cheaply manufactured with a high degree of index accuracy.

The justification for variable-ratio rack and pinion steering is discussed in the context of the modern front-wheel-drive car. The rack tooth geometry associated with this new steering technology prompted the development of a rack forging process which enables the forming of the entire rack cross-section in a single blow. The die is essentially flashless and enables the simultaneous forming of the variable-ratio teeth and a ‘Y’ shaped rack section. The evolution of the ‘Y’ die design and associated processes is described in some detail, together with methods of gauging variable-ratio racks.