How Does BMW Power Steering Work?

Power steering is one of the key advancements in automotive technology that has given drivers more control over their vehicles. It only became common for the average car in the 1950s and 60s, and before that people had to control the steering wheel all on their own. Fortunately, today’s cars are much easier to handle. 

As a brand that prides itself on precision and control, BMW has been a global leader in developing power steering technology for decades. Look under the hood and check out how BMW’s advanced power steering systems work.

Hydraulic Power Steering

The most common type of power steering system is the hydraulic variety. You can find this system in most BMWs made before 2000, especially the classic models from the 60s through the 80s. If you’re interested in bimmers from this era, you’ll be happy to learn that power steering wasn’t so complicated back then.

Hydraulic power steering (HPS) relies on pressure generated by a power steering pump to assist the driver’s steering motion. The power steering pump is connected to the engine, which sends pressurized hydraulic fluid to steering gear to make the wheel easier to turn.

Here are the other key parts of an HPS:

  • Power Steering Fluid: Power steering fluid is the hydraulic liquid that provides lubrication and pressure to ensure smooth steering operation. It’s located in a reservoir next to the engine, which must store an adequate supply to keep the HPS functional.
  • Steering Gear: The steering gear consists of a rack and pinion assembly, which converts the spinning motion of the steering wheel into a lateral movement in the car’s axle, causing the wheels to turn. 
  • Steering Rack: The steering rack horizontally connects the steering wheel to the steering gear, converting the steering force applied by the driver to the turning wheels through the rack and pinion assembly.
  • Steering Column: The steering column vertically connects the steering wheel to the steering gear, allowing the wheel to transfer its torque to the gear during a turn.
  • Power Steering Hoses and Hydraulic Lines – The Power steering hoses and hydraulic lines move the pressurized power steering fluid from the pump to the steering gear. They are designed to handle extremely high pressure and keep the fluid flowing in any conditions.

If your BMW starts to make wider turns than usual and you notice that the steering wheel is harder to control, there is likely a problem with the power steering. This problem is known as “understeering” because the wheel fails to complete the turn despite the driver making the correct maneuver.

You are technically still capable of driving with dysfunctional power steering. You will notice a clunkier and heavier feel to the steering wheel, but it’s still possible to control the vehicle on your own. However, it is not safe to rely on HPS without power steering fluid. You need to replace this fluid roughly every 80,000 miles or two years depending on how often you drive.

Electric Power Steering

Electric Power Steering (EPS) is the newer type of steering system with most of the same parts, but with one key difference. Instead of relying on pressure from hydraulic fluid, an EPS utilizes an electric motor to assist with the driver’s steering input. This motor is connected to the steering column and can account for the vehicle’s speed and the overall driving conditions.

BMW first started using EPS in the Z4 E85 and E86 coupes from 2002 to 2008 and has adopted the technology for nearly all of its new releases ever since. 

Here are the other unique components of an EPS along with the electric motor:

  • Steering Column Torque Sensor – This sensor detects the amount of torque or rotational force that the driver applies to the steering wheel. This information goes to the power steering controller.
  • Power Steering Controller: The power steering controller is located in the vehicle’s electronic control unit (ECU) and is the brains of the operation. It receives input from the sensors in the motor and the steering column torque sensor and estimates the exact force the motor must exert to assist with the turn. 
  • Vehicle Speed Sensor – This sensor tracks the speed of the vehicle and gives the power steering controller constant input, allowing it to change the level of assistance based on the speed and driving conditions.

EPS has several benefits over HPS. Since the electric motor only consumes power when the driver requires assistance, it’s more fuel-efficient than HPS. The torque sensor also allows for greater steering response flexibility based on the driver’s preferences, the vehicle’s design or the road’s conditions.

Lastly, drivers can pair EPS with other electronic vehicle systems, including driver assist and stability control systems. These combinations lead to improved vehicle performance and much safer driving.

Know Your BMW’s Power Steering

If you own a newer BMW model, you need to learn the ins and outs of your car’s electric power steering system. Those who own classic bimmers should focus on learning about hydraulic power steering. In either case, you need to know your BMW’s power steering components to ensure a consistent driving experience.

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