Category Archives: Steering

Citroen 2.0l HDi – Auxiliary belt issue

A 2008 Citroen 2.0L HDi had been fitted with a new Synchronous Belt Drive System (SBDS) kit. A few thousand miles later, the SBDS failed prematurely. The mechanic reported valve-to-piston contact and confirmed that the engine was extensively damaged. An element of mystery was provided by the fact that the drive belt from the Auxiliary Belt Drive System (ABDS) was no longer present.

Premature failure

A wide number of associated installation issues are known to contribute to the premature failure of an SBDS. These include incorrect tensioner set up; insufficient torque on the tensioner bolts; and subsequent failure of a water pump that was not installed at the same time as the timing belt kit.

Good workshop practices can be used to manage many of these issues however.

Workshop procedures

Appropriate installation procedures seemed to have been followed and a timing belt kit was fitted.

Investigation

A diagnosis is impossible without a comprehensive examination of the vehicle. Once the Gates inspector (pictured, above) arrived, an immediate attempt was made to establish the sequence of events that led to the failure of the SBDS.

Two things were immediately apparent:

1) The ABDS belt was missing completely

2) The water pump had not been changed

Let’s consider the second point first.

Replacement option

Although it was clear that this water pump hadn’t contributed to the engine damage and had remained fully operational, the inspector recommended water pump replacement at the scheduled change as it had completed the same duty cycle as the belt.

An undetected leak will lead to drive system failure so it is sensible to install a new water pump at the same time as the kit. This achieves a complete drive system overhaul and preserves drive system integrity. Moreover, if the water pump is sourced from the same supplier as the belt kit, a single investigation will be required in the event of any subsequent problems.

Missing belt

The missing ABDS belt drew attention to other factors that may contribute to premature drive system failure. These include misalignment and foreign substances (oil, water, debris) in the drive.

The garage confirmed that although a visual check of the ABDS was made at the time of the original job, none of the ABDS parts were replaced. The ABDS was examined and scoring was evident on the SBDS drive cover. This suggested belt chafing and this may have been a factor causing the belt to break.

Debris in the main drive system would compromise the timing belt. So what if the debris included fragments from the missing ABDS belt? The SBDS cover was removed and the sequence of events became clear. Fragments of the ABDS belt were wrapped around the crankshaft pulley. This had wound down into the drive, causing the pulley to fail and making valve-to-piston contact inevitable.

Overview

Although garages may be confident that good workshop practices have been observed, failure to replace the water pump at the same time as the belt kit undermines their case.

Although the water pump was not culpable in this case, strong evidence links them with premature SBDS failure, therefore Gates recommends replacement in every case.

Drive system maintenance issues raised at Gates training sessions

Despite the added expense to the job, most garages now accept the need to install timing belt kits, rather than just the belt. Current estimates indicate that at the scheduled change, Synchronous Belt Drive Systems (SBDS) kits are installed 90% of the time.

Gates has stepped up its campaign to include water pumps as well, by extending its PowerGrip Kit Plus Water Pump range. This has prompted mechanics attending recent Gates technical workshops to ask a few questions in relation to SBDS and Auxiliary Belt Drive Systems (ABDS) kits:

Q. There are a lot of components in the ABDS – how can I justify the cost of replacing them all when there’s only a problem with one of them?

A. .Wear to any one of these components can adversely affect the performance of others. The ABDS in the latest cars supply the drive for an alternator, the power steering pump, an A/C compressor and, sometimes, the water pump. Note the presence of the safety critical item – the power steering.

The ABDS itself usually includes a multi-ribbed belt, a tensioner, an idler, a torsional vibration damper (TVD) and an overunning alternator Pulley (OAP). The use of EPDM (the chemical abbreviation) to construct most belts makes it impossible to judge the wear to the belt from a visual check. Secondly, most mechanics now accept the need to replace the multiribbed belt, the tensioner and the idler at the same time.

However, they raise eyebrows about the simultaneous replacement of the TVD and the OAP. TVDs are crankshaft pulleys that contain a rubber-damping element. It helps improve the NVH (noise, vibration and harshness) characteristics of the drive. Designed to operate in high temperatures and absorb vibration, TVDs are subject to wear as the rubber can become loose and harden, crack or lose its elasticity with age.

The TVD has also been known to break free from the engine. What’s more, wear is not always obvious from an inspection, while its symptoms (increased vibration) are often misdiagnosed and attributed to the belt, idler or OAP. Note the reference to a misdiagnosis as replacing a worn tensioner to fix vibration issues may cure a symptom, but not necessarily the cause.

A worn TVD can also increase vibration, causing premature wear of the new tensioner. In this case the TVD, rather than the tensioner, may have been the cause. OAPs are the OE response to the expansion of on-board comfort and leisure accessories that draw extra electrical power.

The OAP allows the alternator to ‘freewheel’ or ‘overrun’ under deceleration, while dampening the vibrations generated; however, they can seize and lose their dampening ability. This would increase vibration and lead to premature belt failure.

However, there are different types of OAP and they’re not interchangeable. Supplying them from a kit is the easiest and most practical solution.

Q. If I’ve checked the water pump and it seems OK, why should it be changed now when it could run happily for another few years?

A. If the waterpump is the OE fitment, it was installed when the belt and tensioner(s) were new. So, the old water pump will now run off the new belt and metal parts you are about to install. If it fails a short time after the kit replacement, the cost of replacing the engine is at stake. Who pays?

The convincing argument that supports the case for change is that standard times for installing kits, as well as a new water pump, are usually the same as for the standard kit alone. If the customer has already paid for the labour, it makes sense to fit the new water pump, too, to add value for money. For that little extra, the SBDS has been completely overhauled.

So, all of the parts are new. If they are from the same kit, you can a) guarantee they are the correct parts and b) have the protection of a warranty from one supplier.

Summary

In both of these cases Gates believes that SBDS and ABDS kits provide the best solution because the result is a complete overhaul of the drive system. The added expense argument can be countered in both instances with the same riposte: ‘Which is more expensive – installing the kit or replacing the engine?’

EPS systems – a look at the future

In addition to offering a ‘green’ power-steering solution, EPS is a key building block for providing a number of vehicle safety features – both in terms of working together with other active systems, such as driver assist systems, or electronic stability control, and its ability to include new features to mitigate vehicle “error-states”.

This type of steering system allows vehicle manufacturers to differentiate their offer through a host of these features, which can be programmed within the EPS software – a number of which are being enabled by TRW.

EPS features

Frank Lubischer, Vice President, TRW Steering Engineering comments: “With the given mechanical and hydraulic constraints of traditional hydraulic steering systems, there are limits to what can be achieved – compromising the ability to implement functions and steer feel characteristics beyond conventional physical boundaries.

“One of the beauties of electric steering is that these functions are controlled through software – and can be programmed quickly to allow for the desired outcome. For example, the amount of power steering assist can easily be varied: full assist at slower speeds for tight turning maneuvers such as parking, or a stiffer, sportier response at high speeds such as highway driving, and these modes could be chosen by the driver.

“Likewise, the electric steering system can be programmed to intelligently respond to varying vehicle and environmental conditions – such as different tyre types, payloads or road surfaces.”

Using electronic control algorithms, the company works in close collaboration with its customers to develop and implement several advanced steering functions – a number of which are in production or due to go into production in the next two to three years.

These fall into two functions – driver assist and safety. Frank adds:” Electric steering plays a significant role in TRW’s Driver Assist Systems technology roadmap, as it represents the one system in the vehicle that has a permanent connection with the driver, continuously translates the driver’s directional commands, and directly provides feedback from the vehicle’s tyres to the driver’s hands.”

Staying safe

Safety functions are those that can detect and react to hazardous conditions, like slippery or icy road surfaces and torque feedback that infers a driver’s drowsiness or attention. When coupled with sensors, surrounding or approaching vehicles can be detected, enabling the system to warn drivers of dangerous conditions.

Frank continues: “Electric steering safety enhancements are achievable through integration with other systems. For example, Driver Steer Recommendation functionality can be delivered through the integration of EPS and ESC to help correct situations, such as oversteer in hard cornering or when encountering a slippery surface on one side of the vehicle and dry pavement on the other. Tests have shown up to an 8% reduction in stopping distance.

“When combined with driver assist technologies, such as camera-based systems, electric power steering can help assist the driver in staying in the intended lane by providing a torque through the steering wheel that guides the driver back toward the centre of the lane. A full lane guide system can actively assist in keeping the vehicle in the centre of the lane.”

What are driver assist functions?

TRW’s driver assist functions can help the driver in unpleasant, but necessary, steering tasks, such as when mitigating road and environmental conditions, as well as to support parking manoeuvres. These include:

Pull drift compensation (PDC)

This can detect if the vehicle is drifting to one side (through a suspension error or from a side wind or cambered road), and will make automatic adjustments, eliminating the need for constant steering wheel corrections.

Active disturbance and road shake compensation

This helps reduce vibration in the steering wheel, caused by uneven road conditions and imbalanced torque at the wheels.

Torque steer compensation

To correct the tendency in some front-wheel-drive vehicles to pull to one side under the influence of high-engine torque.

Semi-automatic parking

When linked to proximity sensors, EPS can ‘automate’ the sometimes challenging task of parallel parking. Sensor information along with algorithms are used to calculate the best parking trajectory and EPS provides the assistance to steer the vehicle.

Driver steer recommendation

Provides an interface to the braking system in order to request an additional driver torque overlay to the steering system. Usually, the braking tuning is a compromise: the shorter the stopping distance, the more unstable the vehicle becomes. With Driver Steer Recommendation, the braking system can be tuned to minimise the stopping distance and simultaneously request a steering torque to stabilise the vehicle.

“ESP saves lives.”

Gerhard Steiger, President of the Bosch Chassis Systems Control Division, charts the development of a now integral part of a vehicle’s safety system.

The end of 2015 will see an EU adoption of the electronic stability program (ESP) as a universal standard. As of November 1st last year, newly registered passenger cars and light commercial vehicles with a gross vehicle weight of up to 3.5 tonnes have to be equipped with the ESP anti-skid system. The regulation will then take effect for all other vehicles one year later.

In 2011, ESP prevented more than 33,000 accidents involving injury and saved more than 1,000 lives in the EU member states (of which there were 25 at the time), even though the system was only installed in an estimated 40% of vehicles. An accident research study by Bosch confirms its effectiveness. After the seat belt, ESP is the most important vehicle safety system; even more so than the airbag. Bosch has manufactured 100 million ESP systems since series production began in 1995.

How does it work?
Swerving on dry, wet, muddy, or slippery roads often results in severe traffic accidents. Using smart sensors 25 times per second, ESP compares whether the car is actually moving in the direction in which the driver is steering it. If the measured values do not match, the anti-skid system intervenes and first reduces engine torque. If that is not sufficient, it additionally brakes individual wheels, generating the counterforce needed to keep a vehicle on course.

ESP is the logical next step in the further development of the ABS antilock braking system, created by Bosch in 1978. Today, it is much more than a mere anti-skid system. A number of value-added functions now account for most of its performance, including the ability of ESP to prevent a vehicle from rolling backwards during hill starts. It is also able to stabilise swerving trailers and to reduce the rollover risk of sports utility and light commercial vehicles.

Driving assistance
The electronic stability program also plays a key role when it comes to many driver assistance systems and automated driving, which is why its development is always ongoing. With its customised solutions, Bosch supports the worldwide efforts of manufacturers and governments to make active safety systems standard equipment in every vehicle.

PREVENTION
Since being launched in 1995, ESP has prevented 190,000 accidents and saved more than 6,000 lives across Europe.

NO SKIDDING
According to independent studies, up to 80% of skidding accidents on the road could be prevented if all vehicles were equipped with an anti-skid system.

WATCH IT
Want to see how ESP works with your own eyes? View the animated video: