Haldex’s latest and lightest air disc brake, ModulT, comes to trucks.

Haldex continues to work with customers to develop its air disc brake range. Most recently, Haldex has been working on the first two truck applications of what have previously been only trailer applications.

The first ModulT brake in the medium-duty range, the DBT22 MD, will launch into serial production in the middle of 2022. It will be used in trucks and buses by a Chinese truck manufacturer whose name has not been released. The brake offers a higher braking force than either model in the existing ‘light trailer’ or LT range: up to 25kNm braking force from a 35kg unit (which includes pads, though weights can vary depending on the carrier design).

Elsewhere, a special disc brake model has been made for a European truck: Daimler’s Unimog all-terrain vehicle. The limited chassis space in the small-frame 4x4 can’t easily accommodate a linear arrangement between brake actuator and brake. Instead, Haldex developed an adapter that rotates the pushrod at an angle relative to the brake, so the brake chamber can stand up nearly vertically above the chassis frame (although it can be installed in a number of other orientations if needed). The adapter incorporates a Y-shaped lever to alter the force direction. It rotates on an axis fitted with needle bearings to conserve 97% of the actuator’s mechanical efficiency. Brakes and adapter have been in production since 2019. This special use case is an example of Haldex’s willingness to customise its products to meet the needs of its customers.

Both truck brake designs are based on the latest GenII versions of the ModulT trailer disc brake. That GenII design, launched in 2018, offers 10% weight savings compared to the original ModulT versions launched in 2011, without sacrificing performance. Its reduced weight translates into greater load capacity and/or greater fuel efficiency. In the GenII design, both caliper and carrier are lighter, thanks to sophisticated software that allowed designers to optimise the size and shape of brake components.

The GenII trailer brakes’ model numbers indicate the wheel sizes (in inches) to be paired with; 19 for 19.5in and 22 for 22.5in wheels. The brake with least mass in the so-called ‘light trailer’ or LT range, is DBT19 LT. It offers design rated maximum braking force of 18kNm and weighs in at 29kg, including pads. Its bigger sibling, the 30kg GenII DBT22 LT, offers up to 20kNm braking for larger trailer wheels.

As far as operation goes, the ModulT works in the same way as all disc brakes. The brake actuator pushrod pushes the brake’s lever, whose pivoting action turns a threaded spindle; the spindle’s rotation amplifies that force and applies it to a tappet, which is connected to a thrust plate. That presses the inner brake pad against the disc. At the same time, contact between pad and disc generates a reaction force through the caliper, forcing it to slide laterally, engaging the outer pad against the other side of the disc (while applying the same pressure as the inner, to help maintain even pad wear).

One distinctive Haldex feature is its use of stainless steel for disc brake slide pins; the hard metal lasts a long time and provides a smooth, but lubrication-free, sliding function. Only Haldex brakes feature stainless steel slide pins.

Also, these GenII brakes show their ModulT heritage by sharing key design characteristics with GenI. A single monoblock cast caliper, rather than a two-piece split casting used in the previous ModulX brake design, saves weight. A single tappet (rather than two) reduces complexity, cost and weight. Two central slide pins (rather than four) further reduce weight.

A couple of design features help optimise operation. First, the dimensions and shape of the thrust plate, T-shaped and relatively wide, ensures an even pressure application to the brake pad, even with only a single tappet. Second, double roller bearings in the lever mechanism help reduce brake hysteresis.

Third, an integrated adjustment unit within the threaded spindle automatically compensates for pad wear. In addition, to further keep on top of wear, ModulT can be fitted with either pad wear indicators or pad wear sensors as options. Indicators consist of a special fitting attached to the brake pad retainer and special pads with metal elements embedded to a depth chosen to indicate maximum wear. When the pads wear down to that level, the metal elements contact the fitting on the brake pad retainer and send a signal that causes a dashboard warning light to illuminate. In contrast, the pad wear sensor offers continuous brake pad monitoring through a sensor fitted to the caliper, axle or another part where pad wear can be measured.

Speaking of brake pad wear, GenII has continued the tool-less brake pad replacement feature of ModulT GenI; all that technicians need to do is press and slide the retainer clip, remove the pad springs and swap out the pads. In fact, the GenII pad retainer has been redesigned to be even simpler to actuate.

As developments in its premium disc brakes demonstrate, Haldex continues to innovate to improve the value of its products for customers.

In short

New Unimog disc brake application demonstrates Haldex ability to customise products
Series production begins next year on ModulT brake for heavy duty trucks, for Chinese OEM
Latest generation disc brakes are 10% lighter than previous versions