If you were to read ten reviews of any recent BMW model, chances are you would have caught at least seven of them raving about all that’s good of the test vehicle’s excellent/fantastic/impressive/insert-any-other-adjective 8-speed automatic transmission by ZF.
Transmission making is a very delicate business. It is an undertaking most car manufacturers choose to outsource and ZF is one of the world’s most renowned transmission suppliers boasting a portfolio of very distinguished clients across the automotive industry. But whilst transmissions are ZF’s best-known products, they are far from being the company’s biggest or most important.
ZF’s history started exactly 100 years ago with founding of Zahnradfabrik GmbH in Friedrichshafen as a spin-off company of Luftschiffbau Zeppelin GmbH working on gears and transmissions for various forms of transport. Within a few years, ZF grew to become a key transmission supplier in Germany’s then fledgling automotive industry before diversifying into steering systems.
In the years since, ZF has maintained a steady rate of growth and expansion, establishing new facilities in the USA and China to widen its production footprint whilst acquiring other companies such as the Lemforder Group in 1984 and Mannesmann Sachs AG in 2001 to further widen its scope of products to include chassis, powertrain, and suspension components.
Previously, ZF was also involved in a 50:50 joint venture with Robert Bosch GmbH that made power steering systems since 1999. The company has divested its interests in that particular venture, previously known as ZF Lenksysteme GmbH and now a fully-owned entity by Bosch henceforth known as Robert Bosch Automotive Steering GmbH.
The deal by no means signaled the end of ZF’s involvement in the steering business, however, as it merely paved the way for the company’s recently-completed acquisition of TRW Automotive, which sees it acquire TRW’s expertise and patents in steering systems along with its portfolio of braking and other safety-related products.
Following a merger agreement signed on 15 September last year, the transaction was officially completed precisely eight months later on 15 May 2015, with TRW to now operate as a fifth division of ZF’s corporate structure. Full integration of the two company’s operations will take between three and five years, but ZF is keen to emphasize that maintaining existing customer relationships will be high on the agenda and that the TRW brand name will be retained for the foreseeable future.
“With pro forma sales exceeding €30 billion and more than 130,000 employees, the combined company is a top three global automotive supplier,” said Stefan Sommer, ZF’s Chief Executive Officer, following the acquisition.
Engineers from the two now-merged companies have been quick to get to work in order to show what their combined expertise have to offer for their clients. Within just six weeks of working together, they were able to put together a fully-functioning concept vehicle incorporating various innovations already developed or under development by the companies since before the merger.
Called the Advanced Urban Vehicle, Sommer summed up the prototype’s importance in saying, “This study also marks to a certain extent a starting point from which concepts for future urban mobility can be derived very specifically – also with regard to the new competency areas opening up for ZF thanks to the acquisition of TRW.”
Notable innovations in the Advanced Urban Vehicle, include the ability to be remote-operated at low speeds and a front axle that can be steered up to 75 degrees. Propulsion of the car is supplied by two electric motors that are innovatively mounted into the trailing arm of the vehicle’s torsion beam rear suspension, a design which ZF refers to as the electric Twist Beam. It is theoretically possible to design a similar concept for vehicles with independent rear suspension as well, although ZF has yet to get off the drawing board on that one.
The Advanced Urban Vehicle was one of many items of interest shown to members of the global motoring press, including Autoworld.com.my, invited to attend ZF’s Global Press Event of 2015 held at the German ADAC Test Centre near Potsdam, Germany. At the event grounds, we were given the opportunity to try out a range of cars in varying stages of developments to experience the various technologies at ZF’s disposal.
[Editor’s Note (20/7/2015): The Advanced Urban Vehicle was previously called the Smart Urban Vehicle by ZF. This article was initially published identifying the vehicle with the latter designation. Following the official name change by the company, we have since updated the article to identify the vehicle based on its new official designation.]
8HP and 9HP automatic transmissions
As their names suggest, the 8HP and 9HP are 8- and 9-speed automatic transmissions respectively. We are, as stated earlier, very familiar with the 8HP thanks to its exploits with various BMW models; the 9HP is a much newer transmission and off the top of our head, we only know of the Range Rover Evoque currently using this transmission in Malaysia.
Despite their similar designation, these are very different transmissions. For starters, they are oriented differently in the vehicle – the 8HP is designed for longitudinal installation, whilst the 9HP is mounted transversely. At the event grounds, ZF made various vehicles, all production-spec, that operate these two transmissions available for our sampling.
The 8HP camp included, as you would expect, a couple of BMWs, a Maserati Ghibli, and, fascinatingly, an Iveco van. It’s not often one gets to drive a van that can claim to share its gearbox with BMW, but the familiar physical characteristics of the transmission, namely its smooth and seamless gear changes, are nigh on unmistakable, only quite obviously governed by different shift parameters to suit the van’s more robust duties.
For the 9HP, this writer chose to try out a European-spec Honda CR-V 1.6 i-DTEC AWD. The petrol-powered versions of the CR-V that we’re more familiar with utilize Honda’s in-house 5-speed automatic transmission. After setting off, it was quickly apparent that the infusion of mid-range torque of this model’s diesel engine and closer stacking of gear ratios made progress a lot more effortless to summon in the European CR-V compared its petrol counterparts we have back home.
Rear-Wheel Steer
Recent years have seen increasingly popular application of rear wheel steering as a tool to enhance handling characteristics of higher performance vehicles. BMW’s outgoing F01 7 Series was one of the earlier adopters of this particular form of rear wheel steering, which turns the rear wheels at minuscule angles either following or against the direction of the front wheels.
Steering angles applied to the rear wheels go no more than 2-3 degrees, with electronics deciding if the wheels should be steered following or against the direction of the front wheels. The system’s control logic is governed primarily by speed, with around 60kph being the typical switch-over point – above it, the rear wheels turn the same direct as the front for better lane-changing stability; below, they turn opposite direction for improved low-speed maneuverability around tight spaces.
At the event grounds, we were put behind the wheel of a BMW 5 Series (F10) prototype that had the mechanical components of the Integral Active Steer rear-wheel steering system, but without its control logic. In its place is a second steering wheel mounted on the passenger side that gives the front passenger direct control on the steering angles of the rear wheels.
With a ZF team on the driver’s side, participants were given the wheel on the passenger side. For this writer, the experience was initially unsettling, as the ZF driver charged his way around the test track without any apparent restraint on the throttle. All I had was the ability to direct the rear wheels – on a wide open patch, while he held his steering straight and I swirled mine, I was made to appreciate the considerable influence which the rear wheels were able to exert on the vehicle’s change of direction.
Brake-by-wire
Traditionally, the main controls of our vehicle connect to the system they operate via a series of mechanical linkages and even hydraulic pumps. In recent years, electronic control have assumed prominence – the accelerator cable has made way for drive-by-wire, the hydraulic power steering pump replaced by electric motor, and the hand brake cable substituted for an electronic switch and wire.
Most recently, we tested the Infiniti Q50 with the world’s first series-production steer-by-wire system in which the mechanical connection between steering and wheel are totally eliminated. Next up from ZF comes brake-by-wire, which we tested on a specially-modified BMW ActiveHybrid 5 that is, other from the modification to its brake actuation system, completely stock standard. Instead of direct linkage between the brake pedal and its master cylinder pump, the pedal now acts as a switch, which in turn relays signals to the braking system in order apply the amount of pressure which it believes the driver is calling for.
At standstill, stepping the brake pedal of the modified BMW test vehicle produced curious sensations – the pedal has a bouncy feel as a result of active springs that are used to simulate brake pedal feedback when the brakes are used on the move. Within the confines of our controlled test, the brake pedal felt natural enough when used, although we did not put it through very severe braking.
There is a mechanical failsafe mode that enables manual braking of the vehicle in the event the circuits fail, although it comes in the form of unassisted braking. It was quite a task to haul a two-tonne BMW 5 Series to a complete stop without any form of brake boosting, that’s for sure.
As driving enthusiasts, we don’t fully welcome the elimination of another mechanical linkage in the vehicle, although as observers of the automotive industry, we can understand it. By putting the braking system under complete electronic control, it eases application of autonomous driving systems that are already beginning to gain widespread use.
Composite Transverse Leaf Spring
We all know of leaf springs from their application in commercial vehicles, but the transverse leaf spring is quite a different piece of hardware altogether. One of the most famous users of the transverse leaf spring design is the Chevrolet Corvette and more recently, Volvo has adopted a similar set up for its all-new XC90.
The transverse leaf spring operates in conjunction with independent rear suspension. It is installed with its middle part fixed to the vehicle’s chassis whilst both its ends, each connected to one wheel, are allowed to bend freely. In this case, the leaf spring’s elasticity to bending substitutes the function of a coil spring in a typical suspension.
ZF is currently working on developing a new composite transverse leaf spring which we tested at the press event on a specially modified Volkswagen Golf 7. This is, of course, no indication that Volkswagen is working on implementing the transverse leaf spring in a future model; ZF personnel explained that the Golf was used as a test bed for this particular design simply because it is the segment’s benchmark car in the European market.
In our limited run with the car, all we could say is that the expertly calibrated chassis balance that we are familiar with in the Golf 7 did not appear adversely affected by this major alteration to its suspension layout. This in its own, is perhaps an adequate demonstration of the design’s triumph, as a more compact suspension design is able to deliver similar dynamic properties to a bulkier one. Space that was previously occupied by coil springs at both ends of the rear axle, can be appropriated for other purposes.
Autonomous Driving
Like it or not, autonomous driving is an inevitable part of our future and development in this field has grown to become something of an arms race between various parties, and ZF is right in the thick of it. At the press event, we were given demo runs albeit as passengers, on stretches of the famous German autobahn no less, in a pair of Opel Insignia demo vehicles specially outfitted with ZF’s autonomous driving systems.
Currently, European traffic law maintains a requirement for drivers to remain in control of the vehicle’s steering wheel at all times, meaning full implementation of autonomous driving, even if all the relevant technologies are ready for serious production, is not possible in that continent yet. The two prototype vehicles being tested by ZF had to receive special permission from German transport authorities before they were allowed on the road.
Individually, many of the relevant sensing and actuation components needed to make autonomous driving a reality are already available in the market. We can count autonomous emergency braking and active cruise control as being two already-common features under the autonomous driving umbrella, whilst active lane-keeping assist is another system gaining popularity.
The two Insignia prototypes demonstrated these technologies at work in unison in creating a car that is, under smooth highway conditions, able to effectively pilot itself with minimal driver intervention. For the most part, it was effectively no different from a vehicle equipped with active cruise control, but with the ability to track and follow its lane as the road curves.
Activating the indicators trigger autonomous lane changing – on the test vehicles, the driver was needed to keep an eye on the side mirrors for oncoming vehicles, but we foresee that in a series production vehicle, such a system will inevitably be linked with the car’s blind spot detection system, which will then trigger a failsafe to cancel the maneuver if an approaching vehicle is detected.
Keyword: ZF and TRW ready to forge ahead in common future