Otis Singleton
Electro-hydraulic systems are a combination of hydraulics and electrics, which have been used in the aeronautical sector for several years. In vehicles, electro-hydraulic systems are being used in braking and steering systems. Electro-hydraulic braking systems consist of a pump and various valves, allowing a control computer to stop the car. Electro-hydraulic steering systems (EHS) supply hydraulic pressure via a fully electronic and software-controlled electric motor, along with a high-performance and low-noise hydraulic gear pump (e-pump) unit.
Characteristics and Values of Electro-Hydraulic Functioning of a Vehicle System
| Characteristics | Values |
|---|---|
| Braking System | Reduces stopping distance and electric energy consumption |
| Optimizes software strategies and hardware redundancy | |
| Reduces vehicle operating costs | |
| Improves control precision | |
| Steering System | Supplies hydraulic pressure via a fully electronic and software-controlled electric motor |
| Reduces parasitic losses in steering systems | |
| Reduces installation costs | |
| Reduces noise pollution | |
| Power Management | High power density |
| Easy motion control | |
| High reliability and sturdiness | |
| Customizable solutions | |
| Excellent resistance to vibrations | |
| Absorbs impulsive loads | |
| Simple thermal exchange management |
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What You'll Learn
Electro-hydraulic braking systems
In an EHBS, the required brake pressure is generated by a hydraulic pump and accumulator assembly. The distribution of brake pressure around the car is controlled by a hydraulic unit, which receives pressurised fluid from the accumulator and motor. When the driver steps on the brake pedal, sensors monitor the pressure applied and the travel of the pedal. This information is interpreted by a brake electronic control unit (ECU), along with other inputs such as vehicle speed and steering angle, and control signals are generated for the hydraulic control unit. In response, pressurised brake fluid is discharged from the accumulator and travels through solenoid-operated valves in the hydraulic control unit to the individual brakes, slowing the car.
One advantage of EHBS is its ability to continue increasing braking pressure in emergency situations, even if the driver does not press the brake pedal hard enough or quickly enough. EHBS can also be implemented without legacy hydraulic systems and mechanical connections, allowing for redundancy and ensuring the vehicle can still brake even if some brake systems fail. This is achieved through redundant power supplies, sensors, and communication networks.
EHBS has been implemented in various vehicles, including Toyota and Lexus hybrid models, the R230 generation of Mercedes-Benz SL-Class, and the Alfa Romeo Giulia. However, EHBS has faced some challenges, such as failures and customer dissatisfaction with the feel and actuation of the brakes, as was the case with Mercedes-Benz's 'Sensotronic Brake Control' system.
Overall, EHBS offers advantages in terms of safety and functionality but has also faced some challenges in terms of customer acceptance and reliability.
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Hardware redundancy
In engineering, redundancy is the intentional duplication of critical components or functions of a system to increase reliability, often in the form of a backup or fail-safe. Hardware redundancy, such as dual or triple modular redundancy, is one of the two primary backup strategies for electro-hydraulic braking systems in autonomous vehicles. The other strategy involves optimizing software strategies in conjunction with other systems.
Electro-hydraulic systems combine the advantages of hydraulics with those of electric systems. Hydraulic systems are known for their high power density, easy motion control, reliability, sturdiness, and excellent resistance to vibrations. Integrating them with electric systems allows for simple thermal exchange management and the implementation of customized solutions.
In the context of electro-hydraulic braking systems, hardware redundancy among various actuators maximizes the vehicle's capabilities and results in cost savings. This is because, in the event of a failure, the redundant hardware components can take over and maintain the functionality of the system. For example, in an anti-lock braking system, when the system fails, a redundant control algorithm can achieve effective slip rate control under different driving road conditions, ensuring the safety of the vehicle.
Additionally, the electro-hydraulic management of these systems allows for important secondary functions. These include concentration, the ability to use a single power unit to power multiple actuators simultaneously, and splitting, the ability to subdivide actuators into lines, allowing for the insulation of a damaged or poorly functioning line.
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Software strategies
One of the primary goals of integrating software strategies with electro-hydraulic systems is to reduce traffic accidents, which are often caused by driver reaction time. By implementing software-controlled electronic components, vehicles can automate certain driving tasks, minimising human error. This automation involves controlling actuators such as the steering wheel, accelerator, and brake through a combination of electric and hydraulic mechanisms.
Electro-hydraulic braking systems, for instance, utilise a pump and valves to allow a control computer to stop the car. This system can work in conjunction with the original circuit to provide redundancy and ensure the car can be halted independently by either mechanism. Additionally, software strategies can optimise the performance of these braking systems, reducing stopping distances and electric energy consumption, leading to increased safety and reduced operating costs.
The diffusion of computerized control systems has led to the adoption of servo-hydraulic systems, where servo-valves act as the interface between the electronic and hydraulic components. This integration enables functions such as concentration, where a single power unit can simultaneously power multiple actuators, and splitting, which allows for the insulation of a damaged or malfunctioning line.
Furthermore, software-controlled electro-hydraulic steering systems (EHS) offer several advantages over conventional hydraulic power steering. EHS systems supply hydraulic pressure through a fully electronic and software-controlled electric motor paired with a hydraulic gear pump. This setup does not draw power from the engine, reducing parasitic losses, and provides power savings through pressure-on-demand and variable speed control, resulting in reduced energy consumption. Additionally, EHS systems can be designed for low noise, making them ideal for urban environments with noise pollution requirements.
Overall, software strategies are essential in harnessing the potential of electro-hydraulic systems in vehicles, enhancing safety, efficiency, and performance while reducing operating costs.
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Electronic parking brake systems
An electronic parking brake (EPB), also known as an e-brake or electric parking brake, is a mechanism used to secure a parked vehicle in place. Unlike traditional hand-operated parking brakes, which use a mechanical lever and cables to engage the braking system, electronic parking brakes utilise electrical and electronic components to control the application and release of the parking brake.
The traditional handbrake lever tensions a cable when pulled up. This cable then squeezes the car's rear brake pads or shoes onto the brake discs or drums, holding the car firmly in place. The principle remains the same for all types of handbrakes: locking the rear wheels to prevent the vehicle from moving. Electronic handbrakes, or electronic parking brakes, work in a similar fashion but use electric motors to achieve the locking effect. When the button is pressed, motors on the rear brakes press the pads onto the discs. The whirring noise of the motors can often be heard.
Electronic parking brakes are activated by pressing or pulling a button or switch on the dashboard or console. When activated, an electronic control unit (ECU) signals an actuator motor to set the parking brake, eliminating any physical effort by the driver. Automakers are using two types of EPBs in late-model vehicles. The first is a "cable and puller" system, a hybrid of new and old technology. It replaces the small pedal or handbrake in the passenger cabin with an electric actuator that puts tension on the cable. Instead of a long thick cable running from the cabin to the rear wheels, a small electric wire is used to trigger the actuator. The second type is a caliper-integrated system, where a small electric motor (servo) is placed at each brake caliper to lock each wheel individually. This system gives automakers more flexibility as they don't have to worry about cables running through the chassis.
Electronic parking brakes offer several benefits over traditional handbrakes. They can automatically adjust for pad wear, ensuring consistent and reliable braking performance. They also often offer additional safety and convenience features such as hill-hold assist and automatic brake hold. Furthermore, they save space in the car's centre console and improve the vehicle's styling. However, they are more complex than manual handbrakes, making DIY fixes nearly impossible and increasing repair costs. Additionally, since they rely on electronic power, they can remain locked if the car's battery dies, preventing a push-start.
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Vehicle automation
Vehicular automation is the use of technology to assist or replace the operator of a vehicle. Vehicles that can be automated include cars, trucks, aircraft, rockets, military vehicles, and boats. Assisted vehicles are semi-autonomous, while fully autonomous vehicles can travel without a human operator.
The automation of vehicles is enabled by advanced driver-assistance systems (ADAS) of varying capacity. Related technology includes advanced software, maps, vehicle changes, and support outside the vehicle. Automation can be especially complex for road travel due to the unpredictability of the driving environment, including diverse road designs, driving conditions, traffic, obstacles, and geographical/cultural differences.
The Society of Automotive Engineers (SAE) classifies road vehicle autonomy into six levels, ranging from fully manual to fully autonomous:
- Driver assistance: The vehicle controls steering or speed autonomously in specific circumstances.
- Partial automation: The vehicle controls both steering and speed autonomously in specific circumstances.
- Conditional automation: The vehicle controls both steering and speed under normal environmental conditions, but the driver must be ready to take control in other circumstances.
- High automation: The vehicle travels autonomously under normal environmental conditions and does not require driver oversight.
- Full automation: The vehicle can complete travel autonomously in any environmental conditions.
- Level 0: Vehicles without adaptive cruise control.
While fully automated vehicles are not yet available to consumers, many vehicles on the road today have driver assistance technologies that help to save lives and prevent injuries. These technologies can warn drivers of potential crashes, or even take action to avoid them. The advantages of automation include improved safety, reduced human error, and economic benefits.
Electro-hydraulic systems have been used to automate certain vehicle functions, such as braking. These systems combine the advantages of hydraulics with the benefits of electric solutions. Electro-hydraulic braking systems can improve safety and reduce vehicle operating costs.
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Frequently asked questions
Electro-hydraulic systems combine the advantages of pure hydraulics with the benefits of electric solutions. The electric part of the system manages information and transmission, while the hydraulic part is responsible for power conversion and transmission.
Electro-hydraulic systems offer high power density, easy motion control, high reliability, and sturdiness. They can also implement customized solutions and are highly resistant to vibrations. Additionally, they provide simple thermal exchange management and reduce vehicle operating costs.
Electro-hydraulic systems have been used in braking systems for autonomous vehicles, where they can improve safety and reduce stopping distance. They are also used in steering systems, providing hydraulic pressure through a fully electronic and software-controlled electric motor, resulting in reduced energy consumption and lower noise levels.
