The history of steering technology within the ZF Group

1932

Zahnradfabrik Friedrichshafen Aktiengesellschaft breaks new ground in steering technology by acquiring a licence for building Ross steering systems.

In 1932, production of Ross steering systems begins in Friedrichshafen following the acquisition of a licence from Ross Gear & Tool Company Inc., USA. In Ross steering systems (often called one-finger steering systems) a fixed or roller-bearing-supported peg or finger meshes with the worm gear. The worm gear transmits the rotational movement of the steering wheel via the peg shaft to the drop arm, which moves laterally. A steering linkage attached to the drop arm transfers the steering movement to the front wheels.

ZF selects the Ross steering system because it is easy to manage, with no vibration and little play. It returns automatically and can be easily adjusted. Ten thousand units are sold in the first year of production alone.

In addition, ZF acquires a patent for a self-locking differential from Knaub in Nuremberg.

 

1937

On 15th June, ZF opens a new plant on Ziegelwiesenstraße (today’s Graf-von-Soden-Straße) in Schwäbisch Gmünd. Its 21 employees manufacture self-locking differentials and other components.

In the very same month the first differentials are delivered to Porsche for the VW Porsche Kübelwagen.

At the end of the year the Schwäbisch Gmünd plant has 142 employees.

 

1938

ZF opens a second plant in Schwäbisch Gmünd, called Schwäbische Zahnradwerke GmbH. However, construction is delayed because of the increasing military build-up, which has created a strong demand for raw materials and labour.

On 1st April, eleven apprentices begin their training at the factory to become mechanics, electricians and fitters.

 

1939

The ZF-Ross steering system model series is expanded and improved. Vehicles can now be equipped for steering axle loads of 500 to 6,500 kg.

 

1942

During World War II ZF moves its steering gear production facilities from Friedrichshafen to Schlettstadt (today Séléstat) in Alsace.

 

1945

The ZF branch plant and the Schwäbische Zahnradwerke GmbH plant in Schwäbisch Gmünd survive the war without major damage. Although American troops seize the plants on 20th April, ZF soon receives permission to resume operations. American maintenance personnel remain at Schwäbische Zahnradwerke GmbH.

The steering gear plant at Schlettstadt is moved back to Schwäbisch Gmünd, which rapidly becomes an important development centre for steering systems. The first 20 units are delivered to Ford already in November.

The plant now manufactures worm-and-roller steering systems (Goba system) in addition to ZF-Ross steering systems.

 

1948

Three years after being seized by the Americans, Schwäbische Zahnradwerke GmbH in Schießtal, Schwäbisch Gmünd, resumes production.

 

1950

Production launch of single-wheel steering systems for tractors from 12 to 40 hp. Here the two front wheels are steered by push rods moving in opposite directions. The main advantages are greater ground clearance and a smaller turning radius.

ZF now has some 1,500 employees in Schwäbisch Gmünd and manufactures 150,000 steering assemblies annually.

 

1951

On 28th February, property control is lifted, and on 18th June Schwäbische Zahnradwerke GmbH merges with the ZF branch plant.

 

1952

ZF delivers its 500,000th steering assembly since the end of the war, a model 782 ZF-Ross steering system for MAN’s 8.5-ton vehicle.

 

1953

ZF and the American Gemmer Manufacturing Company, based in Detroit, sign a licence agreement on 1st August. For the Schwäbisch Gmünd plant, which specialises in steering systems, this marks an important step towards large-scale production. The manufacture of mechanical and hydraulically assisted Gemmer steering systems begins. In the mechanical version, also called a worm-and-roller steering system, the rotation of the steering wheel is transmitted via the steering spindle to an hour-glass-shaped worm gear. Depending on the loading profile, a two- or three-tooth steering roller on the roller shaft meshes with the steering roller gear and actuates the drop arm.

Production of steering systems is concentrated in the Schießtal plant in Schwäbisch Gmünd. The other plant, on Graf-von-Soden-Straße, manufactures gearboxes.

Market launch of the ZF-Gemmer hydraulic power steering system in Europe. The first hydraulic power steering manufactured in Schwäbisch Gmünd is an integral unit. The steering gear housing comprises a complete mechanical Gemmer steering system along with the hydraulic servo unit, which has several valves and controls the oil pressure needed to operate the two working pistons. The pistons are connected via a pressure roller to the steering roller shaft and generate additional torque, reducing the steering effort by 70-80 percent. This system can be used for commercial vehicles with steering axle loads up to 12,000 kg. Paraxial or angled systems are available depending on how the system must be installed.

 

1954

ZF Schwäbisch Gmünd advances to become Europe’s largest manufacturer of steering systems.

The company delivers its one-millionth steering system since the end of the war. This is the three-millionth since the start of production in 1932. The company now manufactures 400,000 units per year.

Acquisition of a licence from Eaton, UK, for the manufacture of ZF-Eaton high-pressure and low-pressure pumps. The key components of this positive-displacement pump are an internally toothed outer rotor and an externally toothed inner rotor. The inner rotor, which has one less tooth than the outer one, is the drive element. Its is shaped such that each tooth is in constant contact with the external rotor. From now on, these steering pumps are an important part of hydraulically operated steering systems.

 

1956

More than a million vehicles are built this year in the Federal Republic of Germany. ZF establishes itself as a major partner of the car manufacturers.

The ZF spindle-type power steering system, designed in-house, comes onto the market. This slim, but rugged steering gear combines the transfer mechanism, operating cylinder and control valve in a single unit. The rotational movement of the steering wheel is converted into axial movement of the piston by the trapezoidal thread on the threaded spindle. A connecting rod attached to the piston transmits the hydraulically assisted steering force to the cross shaft and drop arm. The slewing range of the drop arm can be restricted by means of an optional hydraulic steering limiter, thus protecting the mechanism.

This type of steering is available for off-road vehicles, commercial vehicles, construction machinery and agricultural vehicles with steering axle loads of roughly 2,500 to 15,000 kg.

 

1957

In Schwäbisch Gmünd the two-millionth steering system since 1945 is delivered.

Series production of worm-and-sector steering systems begins. In these systems the rotational movement of the steering spindle is transmitted to a worm gear which engages a worm sector on the steering shaft. The resulting swivel motion of the shaft is transmitted by the drop arm and steering linkage to the wheels.

Delivery of the first rack-and-pinion steering systems. This space-saving design dispenses with a steering linkage and reversing lever, which are prone to wear. The motion of the steering wheel is transmitted via the steering column to the drive pinion, which causes an axial movement of the steering rack. Tie rods attached to the rack transmit the steering force directly to the steering arms.

 

1958

Start of production for hydraulic power steering units based on the Saginaw design.

The development of ball-and-nut power steering systems begins. In this design, often referred to as a recirculating ball system, the gearbox contains a mechanical steering gear assembly, a working piston and a precisely controlled steering valve. When the steering wheel is moved, the worm gear turns in an endless ball chain, causing an axial motion of the piston. At the same time the sector shaft, which runs perpendicular to the length of the piston, is made to rotate. The drop arm mounted on the sector shaft thus moves the steering linkage leading to the steering arms that control the wheel angle. A rotary piston valve controls the pressure build-up according to the desired steering behaviour and assists the piston movement initiated mechanically by the steering wheel. A hydraulic steering limiter is optionally available.

 

1959

Inclusion of Ross power-assisted steering in the production range. This design was adopted from ATE.

 

1960

The company’s export share, which was one percent in 1950, rises to almost 23 percent. The first licence for mechanical steering units is granted to a company in Sweden; licences to other companies worldwide follow.

Production of steering units now comes to 550,000 per year.

 

1961

The Schwäbisch Gmünd plant manufactures its four-millionth steering unit.

 

1962

The 100,000th hydraulic power steering unit is delivered.

Start of production for recirculating ball power steering units for commercial vehicles.

 

1963

In Schwäbisch Gmünd series production of multidisk self-locking differentials is launched.

Development of a hydraulic power steering system (Ross design) called Servostat for volume production. In this design the steering force is transmitted to the wheels hydrostatically (via tubes, hoses). There is no mechanical connection between the steering wheel and steering linkage. The steering work is performed by one or more operating cylinders. Oil pressure is controlled by a valve or, in exceptional situations, by the hand-driven pump of the hydrostatic steering system.

The five-millionth steering unit (mechanical and hydraulic) is manufactured.

 

1964

Production of semi-integral hydraulic power steering units begins. Systems of this kind are used in commercial vehicles, which a require large steering force on account of their high steering axle loads and need more hydraulic work than can be efficiently supplied by the operating cylinder of an integral steering gearbox. Hydraulic assistance is supplied by operating cylinders connected via tubes with the control valve of the semi-integral hydraulic steering unit.

The vane pump, designed by ZF, is hugely successful. This product is an important accessory for hydraulic power steering units and steering assists. A rotating drive shaft and rotor press the radially movable vanes, which run in grooves, against the guide of the cam insert with the help of centrifugal force and oil pressure. Successive pairs of vanes form a total of ten cells separated by pressure plates. Each cell conveys the maximum volume of fluid twice in each rotation. The chambers, formed by suction and pressure, are arranged in such a way that the radial forces operating on the rotor cancel each other out. A pressure- and flow-limiting valve keeps the oil pressure at a set level and ensures maximum flow.

 

1965

ZF Schwäbisch Gmünd takes over Otto Meyle GmbH, a gear factory in Bietigheim. From now on, this is where all high-pressure pumps, low-pressure pumps and valves will be manufactured.

 

1966

ZF Schwäbisch Gmünd takes over Otto Meyle GmbH, a gear factory in Bietigheim. From now on, this is where all high-pressure pumps, low-pressure pumps and valves will be manufactured.

 

1967

ZF begins to recover from the economic slump. However, it must still lay off workers owing to a decline in sales.

1970

The ten-millionth steering unit is shipped from Schwäbisch Gmünd. For the first time, annual production exceeds the one-million mark.

 

1971

Delivery of the millionth hydraulic power steering unit.

New vehicle models make additional demands on hydraulically assisted steering systems. A short version of the recirculating ball power steering unit for commercial vehicles, manufactured in Schwäbisch Gmünd, offers one solution.
The main difference between this unit and its predecessor is that the steering valve is integrated in the working piston, which saves space.
Oil pressure is produced by a valve piston placed transversely in the working piston, using a flexural bar. This significantly reduces the fitting length.

 

1973

Rack-and-pinion power steering assemblies go into series production in Schwäbisch Gmünd. These systems extend the principle of mechanical rack-and-pinion power steering by adding hydraulic components. Hydraulic oil, regulated by the rotary piston valve, flows through tubes to two cylinders which are separated by a piston attached to the rack. The piston, which is located outside on a cylinder pipe, transmits the hydraulic steering force via the rack and tie rods directly to the steering arms.

 

1975

Since 1945, more than 500,000 locking differentials, 2 million power steering units and 2.5 million oil pumps have been manufactured in Schwäbisch Gmünd and Bietigheim.

 

1976

The worldwide recession is gradually overcome. The automotive industry begins to revive. More cars are being bought than ever. 

 

1977

The Bietigheim plant, which is devoted entirely to pump production, puts a transfer line into operation. On 30th September the one-millionth model 7672 pump leaves the factory.

Porsche’s large new 928 sports car features the responsive model 7840 rack-and-pinion power steering unit, made by ZF. It also has a ZF vane pump and a DL 275 self-locking differential.

 

1979

ZF ships its one-millionth power steering system for cars and its five-millionth oil pump.

Adam Opel AG names ZF Schwäbisch Gmünd Supplier of the Year 1978 for outstanding quality, cooperation and reliability as a supplier of production material.

Series production of model 7881 rack-and-pinion power steering units begins for the Audi 80.

 

1980

Construction of the one-millionth model 8052 car steering assembly.

The model 7810 rack-and-pinion power steering unit for cars, with variable ratio, inaugurates a new era. Its advantages include low-cost production and low space requirements. Steering is optimised by improved measurement methods.

 

1982

Presentation of speed-dependent ZF Servotronic power steering. This innovation, which goes beyond the familiar advantages of recirculating ball and rack-and-pinion power steering systems, features a steering valve with hydraulic feedback, permitting adjustment of a vehicle’s steering behaviour to the road speed. By changing the steering characteristics electronically, it allows one to park with minimal steering effort. With increasing speed, the vehicle is able to hold the road better and better.

A revolutionary technology is introduced at ZF: computer-aided design (CAD).

 

1984

ZF Steering Gear (India) Ltd. is officially opened in Pune, India. ZF has a 26 percent holding in this company, which produces hydraulic steering assemblies for the Indian automotive industry.

In late April, employees in Schwäbisch Gmünd assemble the one-millionth self-locking differential. This product group is now the company’s third-largest source of revenue.
 

1985

ZF Servocom, a recirculating ball power steering unit for commercial vehicles, goes into series production. It is compacter and lighter than its predecessor. The new Servocom series has smaller exterior dimensions, lower weight and better performance. The deflection of the drop arm is increased to 94°. Improvements in the rotary slide valve, ball circulation, gears and bearings provide a high degree of functionality and steering comfort.

ZF founds ZF Steerings in Penang together with partners from Malaysia. The company is responsible for manufacturing and selling ZF steering assemblies in South-East Asia.

 

1986

ZF Servotronic goes into production. Experts call this individually programmable steering assembly for passenger vehicles the “germ of a revolutionary steering system”. It permits effortless steering when a vehicle is standing still and provides a gradual increase in steering power when it picks up speed.

A modern test and measurement track for steering trials is dedicated in Schwäbisch Gmünd.
 

1987

Since 1945, ZF has manufactured almost 30 million steering assemblies for vehicles of all kinds.

ZF Servocom, a dual-circuit steering system, is introduced to meet increased safety requirements and provide emergency steering characteristics for commercial vehicles.

 

1988

The DAF 95 is named Truck of the Year. DAF is one of ZF’s oldest and best customers. The new 95 series is equipped with ZF power steering units and ZF gearboxes.

 

1989

ZF Schwäbisch Gmünd and ZF Friedrichshafen receive the coveted Q1 Award from Ford, USA, in recognition of high quality.

The Société de Fabrication de Directions is founded in Thionville, France. It is part of the Schwäbisch Gmünd steering technology area and manufactures steering valves for customers like Peugeot and Renault.

The new BMW 850i, which features ZF recirculating ball power steering and Servotronic as an option, draws particular attention.

 

1990

For the first time, the Schwäbisch Gmünd plant manufactures more than two million power steering systems in a single year.

In Oakwood, Georgia (USA), ZF teams up with the Japanese company Unisia to establish ZF Unisia Autoparts Inc. (ZUA). The plant manufactures steering pumps.

 

1993

A new steering system plant is dedicated in the Gügling industrial estate, Schwäbisch Gmünd. The plant serves as a model for restructuring and introducing a new manufacturing philosophy.

 

1994

Founding of a joint venture with Shanghai Automotive Industry Corporation (SAIC), China, for manufacturing mechanical and hydraulic steering systems.

Start of large-scale steering valve production.

 

1995

The compact power steering system (K steering system) goes into production. With its compact design and weight optimisation, it is especially suitable for vehicles with critical installation conditions. Extensive application of chipless manufacturing technologies permits eco-friendly production.

1996

ZF Shanghai Steering Co. Ltd. opens a new plant in Jiading, China. ZF has a 51 percent share of the joint venture.

In Schwäbisch Gmünd the 50 millionth steering assembly is shipped since the start of production in 1945.

The newly developed CP 1 lightweight pump, a very compact unit, is manufactured at various locations worldwide.

 

1997

Servocomtronic, a recirculating ball power steering unit for commercial vehicles, goes on the market. It provides the same operating convenience as the Servotronic passenger car steering system. When a vehicle is stationary or moving at low speeds, the electronically controlled unit requires only minimal steering effort. At higher speeds the steering effort increases and the driver can steer with great precision thanks to the excellent road contact.

 

1998

Servocom RAS (Rear Axle Steering), a hydrostatic steering system for a non-driven rear axle controlled by a recirculating ball power steering unit, is manufactured in Schwäbisch Gmünd.

The RAS system consists of a conventional ZF Servocom system plus two special working cylinders and a hydraulic pressure reservoir. The system, which does not require a heavy, space-filling linkage, makes it possible to steer the non-driven rear axle of a commercial vehicle in curves and to stabilise it in straight-line driving.

 

1999

ZF Friedrichshafen AG and Robert Bosch GmbH found a 50:50 joint venture for the development and production of steering systems. ZF contributes its expertise in steering technology and steering columns, and Bosch contributes electronics know-how. The new company is called ZF Lenksysteme GmbH and is based in Schwäbisch Gmünd.

 

2000

On 27th June, ZF Steerings (Malaysia) celebrates the production of its two-millionth steering assembly.

 

2001

ZF Lenksysteme GmbH opens a new factory for commercial vehicle steering systems in St. Thomas, Ontario, Canada, with the name ZF Heavy Duty Steering Inc.

On 11th January, the two-millionth Servocom comes off the belt in Schwäbisch Gmünd.

Production of the electrohydraulic power steering system (EHPS) is launched in Schwäbisch Gmünd. The heart of the system is an electrically driven steering pump called the power pack. It runs on the vehicle power system and can provide energy savings of up to 75%, depending on the collective load and power control strategy. By attaching the power pack directly to the rack-and-pinion power steering system or compact power steering system, one can deliver this system just in time to the vehicle manufacturer’s assembly line as a fully functional, tested system module.

 

2002

ZF Lenksysteme launches volume production of ZF Servolectric power steering assemblies in a steering column version for compact cars and a dual-pinion version for separate installation of the sensor unit and drive unit. The customers include BMW and the VW Group. Thanks to its electric drive, this rack-and-pinion steering system saves up to 0.3 litres of fuel per 100 km compared to hydraulic power steering. The reason is that it draws power only when steering assistance is required. A modern electronic control unit, which registers a wide range of parameters, allows the power assistance to be matched to any vehicle model. The servo unit is fitted on the steering column. Dual-pinion and paraxial versions follow.

 

2003

After four years of use in urban buses, the electronically controlled rear axle steering system ZF Servocom RAS-EC is installed in HGVs as well. This system is especially suitable for commercial vehicles with a large wheelbase and several rear axles. The electronic control unit allows the steering angle on the steerable rear axle to be adjusted according to any desired driving parameters. A motor-driven pump supplies hydraulic oil to the separate circuit. A proportional valve connected with the electronic control unit initiates the turning movement. This valve supplies pressure to a hydraulic operating cylinder in order to generate the necessary steering force.

In October 2003, the fifth Golf generation takes a leading place on the world market thanks to its technical superiority and matchless appearance. The dual-pinion version of the ZF Servolectric power steering system contributes to this success.

Volume production of Active Steering starts with the BMW 5 series. This system is based on the ZF Servotronic 2 with its many convenience features. The special feature of the ZF Active Steering system is the superimposed transmission integrated between the steering valve and the substructure, with two input shafts and two output shafts. This unit transmits the torque from the steering wheel via the steering column and steering valve to the drive pinion, and it also transmits the additional motor angle (superimposed angle) generated by the electric motor.

This means that a steering angle can be generated by the driver and electric motor independently via the superimposed transmission. Through networking with other vehicle systems it is possible to implement both kinematic steering assistance functions and stability functions.

 

2004

The Schwäbisch Gmünd plant manufactures its three-millionth Servocom.

In less than three years the plant also puts out its one-millionth Servolectric power steering system.

Premiere of the ZF Servotwin at the IAA for commercial vehicles. In this innovative concept an electric steering unit is added to a ZF Servocom system, which provides the main steering assist. Besides permitting greater steering precision and improved steering comfort, the system represents the first implementation of driver assistance functions in commercial vehicles. In design it is a dual-circuit steering system with separate power supplies as required by law.

The ZF Servoline also makes its debut at the IAA for commercial vehicles. This linear steering concept for HGVs and buses features a mechanical rack-and-pinion steering with steering valve arranged in parallel with a hydraulic cylinder. The specific advantages of this setup: short overall length, low weight, a system that can be standardised for all steering axle loads, possible configuration with a rigid axle and independent wheel suspension, use in high weight categories as a single-circuit design.

Active Steering wins the Innovation Award of the German Business Association.

 

2005

The two-millionth Servolectric power steering system is shipped.

More than 80 million steering assemblies have left the Schwäbisch Gmünd plant since production began in 1945.

ZF Lenksysteme is marked out as one of the best suppliers to the VW Group.

 

2006

First-ever presentation of ZF Servoactive at the IAA. This system, which is based on the Servocom, adds a superimposed gear with an electric motor and a Servocomtronic steering valve. A planetary gear adds or subtracts a controllable motor angle to the driver’s steering angle. The sum of these two angles is then applied to the steering gear that determines the wheel angle. By controlling this angle it is possible to actively intervene in the steering behaviour and driving dynamics of the vehicle. In addition, by means of the steering valve the hydraulic steering assistance can be varied as a function of driving speed and steering angle. Through networking with other systems a wide range of driver-independent and driver-supporting interventions are possible.

Volume production of the Varioserv adjustment pump starts in Berlin.

 

2007

Following its introduction in the BMW 5 series in 2003 and later in the 3 series, Active Steering now penetrates the SUV segment. After its rollout in the USA in late 2006, the new BMW X5 is launched on the German market in 2007. Its innovative Active Steering system is an important convenience and safety feature.

The ZF Group celebrates 75 years of steering technology.
 

2009

ZF Lenksysteme presents a new version of the Servolectric power steering system at the IAA. Here the servo unit is mounted on the steering column, saving a great deal of space. The company thus demonstrates its ability to equip both large and small cars with electric power steering.

With its experience from the manufacture of ten million electric power steering systems since their introduction in Germany in 2002, ZF now opens a factory in the USA. This is its first foreign production facility. In Florence, Kentucky, it manufactures dual-pinion Servolectric systems along with other products.

 

2011

At the 60th International Motorpresse Colloquium held by Robert Bosch GmbH from 7th to 9th June, ZF Lenksysteme convincingly demonstrates that its Servolectric power steering system can be used in the entire range of passenger cars, from subcompact cars to light commercial vehicles.

ZF Lenksysteme enters two new segments of the automobile market by winning a German and an Indian customer. For the subcompact segment it offers an electric steering system with a servo unit mounted on the steering column, and for vehicles with high steering axle loads it offers a version with the servo unit mounted parallel to the steering rack.

 

 

 

 

 

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