With the Smart Parking Assist function, ZF meets the need for providing innovative driver assistance systems for mobility in the urban environment. The system combines several new approaches in chassis and driveline as well as networked electronic systems. Thus, ZF Smart Parking Assist determines suitable parking spaces and can park the all-electric ZF Advanced Urban Vehicle fully automatically with minimal moves. The technical prerequisite comes in the shape of an innovative front-axle concept, which facilitates steering angles of up to 75 degrees. In order to utilize this wheel deflection from standstill, the all-electric axle drive eTB (electric Twist Beam) mounted close to the wheel features a torque vectoring function, which assists the steering movements of the front axle. In total, 14 sensors detect parking spaces and precisely determine changes in the vehicle's position as it is parking. The electronic control unit coordinates all the systems involved so expertly that even the smallest perpendicular and parallel parking spaces can be negotiated. There are, however, no problems when getting in or out since the system can also be triggered from outside the vehicle – for instance, with a smartwatch or smartphone.
“Smart Parking Assist is one of the key features of the ZF Advanced Urban Vehicle and illustrates the many practical benefits innovative driver assistance systems offer,” says Dr. Harald Naunheimer, Head of Corporate Research and Development at ZF Friedrichshafen AG. The system not only provides assistance when determining suitable parking spaces; it can also park fully automatically. The driver can even trigger this process from outside the vehicle using a smart device. “Smart Parking Assist thus enhances individual comfort and driver benefits at the same time. It also creates – insofar as this kind of system is rolled out extensively – the opportunity to utilize the scarce parking space in large and mid-sized cities optimally and highly efficiently,” says Harald Naunheimer.
Innovative front-axle concept:
The hardware makes the difference
The Smart Parking Assist differs primarily from today's standard parking aids through the way in which all the systems interact seamlessly. This starts with the hardware: The agile front axle and its agile steering angle of up to 75 degrees create the basis for the sophisticated ZF parking aid. The innovative chassis concept substantially reduces the steering effort during parking, thus enabling the ZF Advanced Urban Vehicle to park in the tightest perpendicular and parallel parking spaces – and do so with minimal moves. In order to accommodate the system in the tight space of a subcompact car, structural changes also had to be made to the front-end on the passenger car prototype. The chassis concept replaces the standard McPherson suspension with two control arms, which are connected by a sickle-shaped wheel carrier. Special axle kinematics working together with the modified steering gear of the electric power steering system facilitate the high steering angle. Space also had to be created in the wheel arches for the wheels that can swivel out up to 75 degrees.
Torque vectoring: Support from the rear
This driver assistance function is supported by an all-electric rear-wheel drive, which enables torque vectoring – in other words distributing the drive force transversely to each individual wheel.
The starting point in this respect is the ZF concept of the electric Twist Beam (eTB), a semi-independent rear suspension featuring a compact drive unit mounted on the left and right wheel respectively. It consists of an electric motor and transmission in a lightweight aluminum housing and currently develops two times 40 kW. The drive torque can be distributed to each individual wheel via the two motors and so this torque vectoring supplements the steering movement of the front axle. Torque vectoring supports the modified front-axle kinematics and comes into its own particularly when turning around as well as moving into and out of parking spaces.
System networking – beyond the vehicle
System networking is another key component for Smart Parking Assist. The electronic control unit obtains its information from twelve ultrasound sensors around the vehicle as well as two infrared sensors close to the front axle. They collect the information necessary for determining and measuring suitable parking spaces. This streamlined sensor solution relies on the ability to drive by at walking pace. The parking aid depends entirely on its ability to determine the location and path as precisely as possible, and so ZF has also optimized the odometry – in other words, using each revolution of the wheels to measure the distance traveled.
The information is processed in a central control unit, which activates the necessary systems for the fully automatic parking function – such as the steering wheel angle of the electric power steering or the supporting torque vectoring of the driven wheels. Like many other functions in the Advanced Urban Vehicle, the control electronics provide the information and input options for the driver and occupants via a human machine interface (HMI). In this way, the driver can interact with the vehicle electronics from inside the vehicle via a tablet computer in the console. The HMI can also be extended beyond the confines of the vehicle. With the Smart Parking Assist such a feature is particularly useful since it makes it easier for occupants to get out of the vehicle before parking in tight perpendicular parking spaces in particular. Thus the vehicle's control electronics can be activated from outside using a smart device. The command to park can be given if the occupants have already left the vehicle, tight perpendicular parking spaces, such as near to walls or pillars, can thus be utilized more effectively.