11-09-2017, 12:15 PM
Power steering systems complement the torque the driver applies to the steering wheel. Traditional power steering systems are hydraulic systems, but power assisted steering (EPS) is becoming much more common. EPS eliminates many HPS components such as pump, hoses, fluid, drive belt and pulley. For this reason, electric steering systems tend to be smaller and lighter than hydraulic systems.
EPS systems have variable power assistance, which provides more assistance at lower vehicle speeds and less assistance at higher speeds. They do not require any significant power to operate when no steering assistance is required. For this reason, they are more energy efficient than hydraulic systems.
How does the system work:
• The electronic control unit EPS (ECU) calculates the required power depending on the torque applied to the steering wheel by the driver, the steering position and the speed of the vehicle.
• The EPS motor rotates a steering gear with an applied force that reduces the required driver torque.
There are four forms of EPS based on the position of the auxiliary motor. The type of column support (C-EPS), type of pinion support (P-EPS), type of direct drive (D-EPS) and type of support frame (R-EPS). The C-EPS type has a power assistance unit, a torque sensor and a controller all connected to the steering column. In the P-EPS system, the power assistance unit is connected to the pinion shaft of the steering mechanism. This type of system works well on small cars. The D-EPS system has low inertia and friction because the steering mechanism and the assistance unit are a single unit. The R-EPS type has the assistance unit connected to the steering mechanism. R-EPS systems can be used in medium to full-size vehicles due to their relatively low inertia from high reduction gear ratios.
Unlike a hydraulic power steering system that continuously drives a hydraulic pump, the efficiency advantage of an EPS system is that it feeds the EPS engine only when needed. This results in lower vehicle fuel consumption compared to the same vehicle with an HPS system. These systems can be adjusted simply by modifying the software controlling the ECU. This provides a unique and cost-effective opportunity to adjust the "feel" of the steering to fit the class of the automotive model. An additional advantage of EPS is its ability to compensate for unilateral forces such as a flat tire. It is also capable of steering in emergency maneuvers along with electronic stability control.
In current systems, there is always a mechanical connection between the steering wheel and steering gear. For safety reasons, it is important that a failure in electronics never result in a situation where the engine prevents the driver from driving the vehicle. The EPS systems incorporate safety mechanisms that de-energize the engine if a problem with the ECU is detected.
The next step in the electronic direction is to eliminate the mechanical link to the steering wheel and convert it into a purely electronically controlled direction, which is known as a wire direction. This works by transmitting digital signals to one or more remote electric motors instead of a rack and pinion assembly, which in turn controls the vehicle. While it has been used in electric forklifts and some tractors, as well as a handful of concept cars, the 2014 Infinity Q50 was the first commercial vehicle to implement cable ox. Although there is normally no direct mechanical linkage, the Q50 has a mechanical backing. In the event that a problem is detected with the electronic controls, a clutch commits to restore the mechanical control of the driver. As with throttle control systems, cable governance is likely to become the standard once electronic controls prove to be safer and more reliable than today's hybrid systems.
EPS systems have variable power assistance, which provides more assistance at lower vehicle speeds and less assistance at higher speeds. They do not require any significant power to operate when no steering assistance is required. For this reason, they are more energy efficient than hydraulic systems.
How does the system work:
• The electronic control unit EPS (ECU) calculates the required power depending on the torque applied to the steering wheel by the driver, the steering position and the speed of the vehicle.
• The EPS motor rotates a steering gear with an applied force that reduces the required driver torque.
There are four forms of EPS based on the position of the auxiliary motor. The type of column support (C-EPS), type of pinion support (P-EPS), type of direct drive (D-EPS) and type of support frame (R-EPS). The C-EPS type has a power assistance unit, a torque sensor and a controller all connected to the steering column. In the P-EPS system, the power assistance unit is connected to the pinion shaft of the steering mechanism. This type of system works well on small cars. The D-EPS system has low inertia and friction because the steering mechanism and the assistance unit are a single unit. The R-EPS type has the assistance unit connected to the steering mechanism. R-EPS systems can be used in medium to full-size vehicles due to their relatively low inertia from high reduction gear ratios.
Unlike a hydraulic power steering system that continuously drives a hydraulic pump, the efficiency advantage of an EPS system is that it feeds the EPS engine only when needed. This results in lower vehicle fuel consumption compared to the same vehicle with an HPS system. These systems can be adjusted simply by modifying the software controlling the ECU. This provides a unique and cost-effective opportunity to adjust the "feel" of the steering to fit the class of the automotive model. An additional advantage of EPS is its ability to compensate for unilateral forces such as a flat tire. It is also capable of steering in emergency maneuvers along with electronic stability control.
In current systems, there is always a mechanical connection between the steering wheel and steering gear. For safety reasons, it is important that a failure in electronics never result in a situation where the engine prevents the driver from driving the vehicle. The EPS systems incorporate safety mechanisms that de-energize the engine if a problem with the ECU is detected.
The next step in the electronic direction is to eliminate the mechanical link to the steering wheel and convert it into a purely electronically controlled direction, which is known as a wire direction. This works by transmitting digital signals to one or more remote electric motors instead of a rack and pinion assembly, which in turn controls the vehicle. While it has been used in electric forklifts and some tractors, as well as a handful of concept cars, the 2014 Infinity Q50 was the first commercial vehicle to implement cable ox. Although there is normally no direct mechanical linkage, the Q50 has a mechanical backing. In the event that a problem is detected with the electronic controls, a clutch commits to restore the mechanical control of the driver. As with throttle control systems, cable governance is likely to become the standard once electronic controls prove to be safer and more reliable than today's hybrid systems.